Application of Solar Technology to Today's Energy Needsñvol. I

Application of Solar Technology to Today's Energy Needs—Vol. I

June 1978

NTIS order #PB-283770 Library of Congress Catalog Card Number 78-600060

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402, Stock No. 052-003-00539-5 ———-—

FOREWORD

This report reviews a range of solar energy systems designed to produce thermal and electrical energy directly from sunlight with units small enough to be located on or near the buildings they are designed to serve. It examines the state-of-the-art of the technology, identifies the circumstances under which such systems could be economicalIy attractive, and discusses the problems encountered in integrating these devices into existing energy generation and delivery systems. The study also assesses the impact that widespread use of decentralized solar energy equipment could have on the United States — its energy supplies, its ability to achieve foreign policy objectives, its physical environment, its levels and patterns of employment, and the functioning of society as a whole. It is apparent from the study that development of a large market for such equipment would have a profound impact on the way an industrial society evolves.

The analysis conducted for this report found that with aggressive Federal support, there are realistic circumstances in which small-scale energy systems could compete favorably with conventional energy sources in many residential, commercial, and industrial applications by the end of the next decade. Given the limited number of choices available for meeting our future energy needs, the options made available by this technology deserve serious consideration

RUSSELL W. PETERSON Director Off ice of Technology Assessment

. /// OTA Solar Advisory Panel

Jerry Grey, Chairman Private Consultant

William W. Caudill Paul Maycock Caudill, Rowlett & Scott Texas Instruments’

John J. Gunther Marjorie Meinei United Conference of Mayors University of Arizona Larry T. Papay Klaus P. Heiss Southern California Edison Co. ECON, Inc. Paul Rappaport Morton Hoppenfeld RCA-David Sarnoff Research Center** University of New Mexico Floyd E. Smith Charles Luttman International Association of The Ralph M. Parsons Company Machinists

James MacKenzie Ephraim M. Sparrow Massachusetts Audubon Society University of Minnesota

OTA Energy Advisory Committee

Milton Katz, Chairman Director, International Legal Studies, Harvard Law School

Thomas C. Ayers George E. Mueller President and Chairman of the Board President and Chairman of the Board Commonwealth Edison Company System Development Corporation

Kenneth E. Boulding Gerard Piel Professor of Economics Publisher, Scientific American Institute of Behavioral Science University of Colorado John F. Redmond, Retired Eugene G. Fubini Shell Oil Company Fubini Consultants, Ltd. John C. Sawhill Levi (J.M.) Leathers President Executive Vice President New York University Dow Chemical USA

Wassily Leontief Chauncey Starr Department of Economics EIectric Power Research New York University Institute

*Resigned after accepting posltlon with U S Department of Energy. * * Resigned after accepting position as Director of the Solar Energy Research I nstltute

iv OTA Solar Energy Project Staff

Lionel S. Johns, Energy Program Manager Henry Kelly, Project Leader David Claridge John Furber John Bell

OTA Energy Staff Consultants Richard Rowberg Timothy Adams Lynda Brothers Linda Ashworth Marvin Ott Richard Bourbon Dorothy Richroath Allen Brailey Linda Parker Jack Burby Lisa Jacobson Peter Ceperley Joanne Seder Thomas Erwin Radmilia L. Bartok Crayson Heffner Rosaleen Sutton Sam iker Ann Cline Kelly Renal Larson TechnicaI Assistance Robert Morse Oak Ridge National Laboratories Corbyn Rooks Sandia Laboratories Edward Sproles Lawrence Livermore Laboratory Donald Veraska Department of Energy Don Watt Division of Solar Energy Mary Zalar

Contractors

American Institute of Architects Cotton & Wareham Research Corporation Jet Propulsion Laboratory Environmental Law Institute University of Oklahoma, Science& Thermo Electron Corporation Public Policy Program

OTA Publications Staff

John C. Holmes, Publishing Officer Kathie S. Boss Joanne Heming Acknowledgment

This report would not be possible in its present form without the careful review and information supplied by hundreds of individuals and companies in the many fields and specialties covered by this report.

vi Contents

Chapter Page

Overview ...... 3

1. Introduction ...... 11

Il. Overview of Onsite Solar Technology and Summary of Economic Analysis...... 21

Ill. FederaI Policy for Promoting and Regulating Onsite Solar Energy . . . . 59

Iv. Onsite Electric-Power Generation ...... 115

v. The Relationship Between Onsite Generation and Conventional Public Utilities. ,..,...... 139

AppendixV-1.–Analytical Methods ...... 161

VI. Legal Aspects of Onsite Solar Facilities...... 175

VIl. The lmpac of Solar Energy on U.S. Foreign Policy, Labor, and Environmental Quality ...... 199

Vlll. Collectors ...... 245 Appendix Vlll-A.–Techniques Used to ComputetheOutput of Representative Collector Designs ...... 303

lx. EnergyConversion With Heat Engines ...... 329

x. Energy Conversion With Photovoltaics .,...., ...... 393

xl. Energy Storage ...... 429

Appendix XI-A.–A Technique for Estimating the Allowable Cost of Storage Devices...... 487 Appendix Xl-B. —Analysis of Performance ...... 488 Appendix Xl-C. —Costs of Designs Chosen for Analysis ...... 496

xl 1. Heating and Cooling Equipment ...... 507

NOTE: This volume summarizes the analysis of system performance and costs, discusses policy, major impacts and constraints on solar markets, and reviews direct solar technology. Volume II discusses the analytical methods used and provides details on each system analyzed.

vii OVERVIEW OVERVIEW

Page Results of the Economic Analysis...... 3 Onsite Solar Technology ...... 5 Major Impacts ...... 6 What Can the Federal Government Do?...... 7 Overview

This assessment reviews the potential of a family of solar energy equipment called “onsite” energy systems because they are designed to be located on or near the buildings or groups of buildings which they provide with heat or electricity. The technologies examined produce useful energy directly from sunlight; equipment making indirect use of solar energy, such as wind machines or devices using biological materials as a fuel, is not examined. The technical feasibility of most direct, onsite solar energy systems has been experimentally established. While onsite solar energy systems are competitive with conventional energy sources in a limited number of applications today, widespread use will require demonstrating that projected cost reductions can be achieved. By the mid-1980’s, the range of costs which can be reasonably forecast for energy from onsite energy devices will overlap the range of costs forecast for energy from conventional sources for a variety of residential, commercial, and industrial applications. An uncertainty inherent in such comparisons is the price society will be willing to pay for the social and environmental benefits of onsite solar energy.

If energy can be produced from onsite riers, provide financial incentives, and sup- solar energy systems at competitive prices, port an aggressive research, development the increasing centralization which has char- and demonstration program, however, it is acterized the equipment and institutions unlikely that onsite equipment will be able associated with energy industries for the to contribute significantly to U.S. energy past 30 years could be dramatically altered; supplies by the year 2000. With such sup- basic patterns of energy consumption and port, it is possible that onsite solar devices production could be changed; energy-pro- could be made competitive in markets rep- ducing equipment could be owned by many resenting over 40 percent of U.S. energy de- types of organizations and even individual mand by the mid-1980s, although the output homeowners. Given the increasing fraction of solar equipment installed by this date is of U.S. industrial assets which are being in- unlikely to be able to meet more than a vested in energy industries, tendencies small fraction of this potential market. Exist- toward centralization of many aspects of ing Federal programs controlling fuel prices society couId also be affected. and subsidizing nonsolar energy sources have created a situation where, without The onsite solar energy industry is in most compensating subsidies, solar energy is cases a straightforward extension of existing uniquely disadvantaged. Federal support of heating, cooling, and air-conditioning in- solar energy has concentrated dispropor- dustries. It could clearly develop without tionate attention to central electric gener- Federal participation. Unless a concerted ef- ating systems instead of exploiting the fort is made to identify the special problems special opportunities provided by onsite of onsite technology, remove reguIatory bar- equipment

RESULTS OF THE ECONOMIC ANALYSIS

1 Solar systems designed to provide do- of the United States today if compar- mestic hot water (3,5 percent of U.S. isons are based on the average monthly energy demand) are competitive with payments made for energy during the electric hot water systems in most parts life of the system. Solar space-heating 3 4 ● Solar Technology to Today’s Energy Needs

for new residential and commercial tions on a life-cycle cost basis; in other buildings (1 7.8 percent of U.S. energy de- cases, however, 100-percent solar sys- mand) is somewhat less advanced but is, tems were twice as expensive. or should soon be, marginally competitive with heat pump and electric resist- 7 Providing backup electricity to onsite ance space heating in many areas of the solar energy systems may, in some cases, country. cost electric utilities more per unit of energy delivered than the average utility 2. On the same basis, solar space-heating cost. Solar energy systems are not and hot water systems may be competi- unique in this respect, however, since tive with oil or gas delivered to typical many conventional buildings impose de- residential or commercial customers by mands on electric utilities which ad- the mid-1980’s. The solar energy equip- versely affect utility costs. When the real ment should be competitive with heating incremental cost of producing electricity systems using synthetic oil and gas. for each type of building is computed, the total cost of operating solar energy 3. Solar energy from systems which provide systems backed up with conventional 100 percent of the heating and hot water electric utilities is, in many cases, com- required by large buildings or groups of parable to the cost of operating conven- houses may not cost significantly more tional all-electric buildings. Most solar than energy from systems designed to heating systems are equipped with ener- meet 50 to 70 percent of these demands. gy storage devices which, at a modest additional expense, can be used to re- 4. Cost reductions and improvements in the duce or possibly eliminate most adverse performance of solar cells (photovolta- effects on electric utilities attribut able ics), small engines powered from solar to solar demand patterns. sources, and solar collectors possible by the mid-1 980’s may result in onsite solar 8 Existing rate structures and available energy systems capable of producing metering equipment may not be ade- electricity for residential and commer- quate to produce an acceptable pattern cial buildings for $0.04 to $0.10/kWh — a of charging and discharging onsite stor- price which would probably be competi- age equipment. As a result, onsite stor- tive with electricity delivered to these age equipment may not be able to elimi- customers from conventional utilities. nate al I adverse affects of solar equip- 5. Full exploration of the potential for ment on electric utilities. It is extremely energy conservation and the use of sim- expensive to leave costly generating ple “passive” solar space-conditioning equipment idle; large electric-generating techniques should clearly precede any systems may therefore not be the most attempt to use more complex solar ener- attractive way to provide backup power gy equipment. to onsite solar energy systems, partic- uIarly if the onsite devices generate elec- 6. It will be possible to construct onsite tricity as well as thermal energy and low- energy systems capable of supplying all cost electric storage is not available. The electrical and thermal energy needs of a best technique for providing backup building from direct solar energy sys- power requires a careful understanding tems, but it wilI usualIy be less expensive of the relative costs of onsite and cen- to rely on some other form of energy as a tralized storage equipment, energy dis- backup if this alternative is available. In tribution costs, and the costs of main- some of the cases examined, the 100- taining standby generating capacity. percent solar systems did not cost signif- These costs vary greatly around the icantly more than smaller solar install a- country. Overview ● 5

9. By the mid-1980’s, solar systems de- only the initial purchase price), the rate signed to provide agricuItural or indus- at which an infrastructure for manufac- trial process heat at temperatures below turing, installing, and supporting such 5500 F (2 to 7 percent of present U.S. systems develops, the removal of regula- energy demand) will not be competitive tory barriers, and the incentives which with direct combustion of coal in large are avaiIable. industries but may be an attractive alter- 11. The small size of onsite solar equipment native in situations where the direct use does not preclude utility ownership, of coal is expensive or restricted because although there may be regulatory prob- of environmental regulations, lack of ac- lems associated with such an arrange- cess to coal supplies, or other factors. ment. Utilities can provide market ag- 10. The fact that onsite solar energy systems gregation and financing for systems are calculated to be competitive on the where building owners are unable to basis of monthly costs does not mean raise capital. Utilities wilI uniquely com- that these devices will rapidly penetrate pare the cost of energy from new solar the market. The fraction of U.S. energy equipment with the cost of energy from supplies which onsite systems wit I supply new conventional plants — energy which will depend on the extent to which cus- typically is more expensive than the tomers make purchases on the basis of average cost of energy delivered to util- operating costs (instead of comparing ity customers.

ONSITE SOLAR TECHNOLOGY

1. Onsite technology is not characterized by 3 Development of simple collectors– both a single dominant design concept but stationary systems and devices which rather by an enormous variety of com- move, tracking the Sun — is of central im- peting approaches. Systems must be tail- portance. While a wide range of applica- ored to specific climates and applications can probably be found for colIectors tions. The equipment works best when the which cost $7 to $12 per square foot, de- building or industrial process which it velopment of collectors costing $4 to $7 serves is designed to make the most effi- per square foot would greatly increase the cient use of the solar resource. number of potential near-term uses for solar energy equipment. The optical and 2. There are no clear economies of scale in mechanical problems confronted in de- solar collectors, solar cells, or in many types of engines compatible with solar veloping such devices will more probably be overcome with patience and clever energy, although there are economies of designs than with fundamental research scale in many kinds of energy storage breakthroughs. equipment. Small, distributed energy systems can readily “cogenerate” heat and 4 The potential of low-cost thermal storage electricity and have several advantages has not been adequately explored. This not easily expressed in conventional eco- shouId make possible solar heating sys- nomic terms: relative ease of using low- tems requiring no backup energy. Devel- temperature heat, short construction opment of a chemical reaction capable of times which permit rapid adjustment to storing solar energy efficiently and eco- changing energy demand; relatively small nomicalIy in chemical form would greatly investments in each installation; and effi- expand the potential uses of solar energy. cient land use (since collectors can be Neither approach has been given ade- located on rooftops). quate priority. 6 . Solar Technology to Today’s Energy Needs

5. The cost of solar cells can be reduced by oped which amounts to a system for plac- mass producing current silicon cell ing bets on a broad spectrum of schemes. designs, developing thin films of amor- 6. There is a large overlap between technol- phous silicon material, cadmium sulfide, ogy developed for onsite solar energy or other materials with acceptable effi- systems and technology developed to im- ciencies, or by designing low-cost optical prove the efficiency of using conven- systems to focus Iight on high-efficiency tional energy sources — particularly in cells. Solar engines can be designed to energy storage and engine design. operate at 1300 to 2000 F using machines that are essentially refrigerators running 7. No major technical problems should be backward, at intermediate temperatures encountered in connecting solar thermal (using standard steam engines and ad- or solar electric systems to electric utility vanced designs), and at high temperatures grids. Utilities should be able to purchase (1,400 0 F) using Stirling engines and other excess electricity generated in onsite units machines with potentially high efficien- for 25 to 100 percent of the price they cies. A funding strategy must be devel- charge for electricity.

MAJOR IMPACTS

1. Onsite solar energy services can be easily intensive energy sources, however, are not integrated into the existing construction welI understood. and heating, ventilating, and air-conditioning industries. The equipment can be 4. Solar energy systems produce far less ag- manufactured, installed, maintained, fi- gregate air and water pollution during nanced, and insured by the organizations their manufacture and operating Iifetimes and individuals now performing the same than energy systems based on fossil fuels. services for conventional heating and Solar equipment may be a particularly at- cooling and industrial equipment. tractive energy source in areas where increases in emissions are prohibited. The 2. If small solar energy systems prove eco- major environmental problem of solar nomically attractive, the concept of the equipment is the use of land. However, “natural monopoly” of existing utilities this impact on land use can be minimized wouId need to be reviewed. by carefully integrating solar collectors into building designs, but densely popu- 3. The widespread use of onsite equipment lated urban and suburban communities would increase the number of jobs re- may have regions where shade from trees quired to generate energy. Jobs would be or buildings make the use of onsite solar created because imported oil would be energy unattractive. replaced with energy from domestically produced solar equipment and because 5. Widespread use of solar energy world- solar energy is more labor intensive than wide could greatly reduce tensions asso- energy from conventional sources. The ciated with world competition over dimin- new jobs would be primarily in construc- ishing sources of fossil fuels without en- tion trades, metals, and chemicals. They couraging the use of technologies which would tend to be located where such jobs increase the risk of nuclear weapons pro- now exist and should provide a relatively liferation. Growth of a solar industry stable source of employment, The long- wouId reduce imports and encourage in- term implications of a shift to labor- vestments in the U.S. economy, WHAT CAN THE FEDERAL GOVERNMENT DO?

1 The most straightforward, but politically rapidIy, ReguIations preventing nonutility

the most dIfficuIt, approach to stimu- ownership of onsite generating equip- lating markets for onsite solar energy ment, and interfering with utiIity owner- wouId be to remove prlce controls and im- ship of onsite energy equipment need to plicit subsidies granted to conventional be reviewed and updated. energy sources, and aIlow energy prices to 5 A variety of Federal subsidy programs rise to the cost of energy from new pro- already exist which can be modified to en- d u c t Ion f a c i I i t i es courage the use of solar energy systems 2 The marketing of solar equipment could The use of solar equipment on Federal in- be seriously disrupted if incompetent or stalIations can stimulate sales and reduce unethical dealers give the technology a costs, reputation for poor performance Per- formance standards and uniform testing 6 A significant amount of basic research procedures must be developed rapidly to and advanced development work remains prevent abuses It is necessary, however, to be done. Promising areas of research that these standards be continually up- were noted in the previous discussion of dated to keep pace with a rapidly moving onsite technology technology and to insure that the regula- 7, The U.S. program in onsite solar energy tions do not inadvertently discriminate couId be improved through closer coop- against new concepts eration with foreign programs. Many 3 Investment tax credits, low-interest loans, types of onsite solar energy are likely to exempt ions from property tax, and accel- be economically attractive abroad before erated depreciation aIlowances on solar they enter commercial markets in the equipment can significantly reduce the United States. It is unlikely that other na- cost of solar energy perceived by prospec- tions will move rapidly to integrate solar

tive buyers No one program will work energy options into their energy planning equally well to provide incentives for all unless the United States makes a major systems to a I I types of owners, SimiIar commitment to use of solar energy. kinds of incentives applied to manufac- 8. Perhaps the most important step which turers could be used to reduce the price can be taken with respect to onsite solar of solar equipment. energy is to insure that the advantages of

4 Regulations governing the rates at which the onsite approaches are seriously con-

energy is sold to and purchased from on- sidered in constructing overalI U.S, energy site energy systems need to be developed planning, Chapter I INTRODUCTION Chapter l.— INTRODUCTION

Page Page Onsite Solar Technology ...... 15 Federal Policy ...... 24 Techniques for Assessing Onsite Standards ...... 25 Technology ...... 15 Other Specialized Legal and Regulatory integration of Onsite Facilities With Problems ...... 25 Other Energy Sources...... 15 Comparison With Current Policy...... 26 Research and Development ...... 17 Economics ...... 18 PossibIe lmpacts of Onsite Solar Energy...... 22 LIST OF TABLES U.S. Security and World Trade ...... 22 Labor ...... 22 Table No. Page Utility Participation...... 23 l. The Potential of Onsite Solar Energy Environment and Land Use ...... 23 Equipment ...... 19 Chapter I Introduction

Small solar energy units attached to or located near individual buildings, industries, or groups of buildings (called “onsite” energy systems throughout this work) must be considered potentially important additions to the limited number of opportunities for meeting the world’s demand for energy both in the next few decades and into the indefinite future. This study examines a set of these technologies characterized by the fact that they convert the Sun’s energy directly into useful thermal and electric energy; the study does not examine wind power, systems using biological materials as fuels, or other concepts for using the Sun’s energy indirectly. The major barrier to the widespread use of onsite solar energy is its cost. Developments in research can lead to reduced costs and improved performance, but the fundamental feasibility of the technology is well established. Onsite solar devices are technicality capable of meeting virtually all residential, commercial, and industrial energy requirements; they can provide heating and air-conditioning, hot water for residences, heating for industrial and agricuItural processes, and mechanical and electrical power. The energy supplied by these systems is expensive by today’s standards. The extent to which this continues to be a barrier depends in part on the success of numerous programs designed to reduce the cost of solar equipment. It will also depend heavily on changes in the price of conventional energy. The market for new types of energy producing and consuming devices is likely to change rapidly in the next two decades as energy costs increase and become a major concern. In many ways it is easier to make confident predictions about the future costs of solar energy—which depend for the most part on predictable manufacturing techniques —than it is to estimate the cost of fuels whose price may depend on monopoly price manipulation, international competition over diminishing energy supplies, the stringency of federally imposed environmental controls, and other problems which are difficult to anticipate.

The issue of costs is treated in much more and care as other options for meeting energy detail in later sections of this report, but the needs in the future. only fair way to summarize the results of the analysis is to note that the range of possible The analysis indicated, for example, that costs of solar energy overlaps the range of solar systems for providing domestic hot possible costs of energy from conventional water and building heat are marginally com- sources in a large number of cases. It is petitive with electric heating in many parts simply not possible to make dogmatic state- of the Nation today, These systems may be ments about the conclusions. The signifi- competitive with oiI and gas (where it is cance of the fact that solar and nonsolar available) in many parts of the country costs overlap, however, should not be under- with; n a decade if solar prices fall and the estimated since this overlap means that it price of oil and gas rises at rates which ap- may be necessary to choose future energy pear in reasonable forecasts. Solar equip- options on the basis of criteria other than ment should be able to compete with syn- the estimates of future costs (the cost anal- thetic fuels. Electricity from solar sources is ysis being indecisive). At a minimum it im- now only attractive in remote areas where plies that the solar energy alternative should alternate energy sources are very expensive. be supported with at least as much attention There are sound reasons to speculate, how- 11 12 ● Solar Technology to Today’s Energy Needs

ever, that the price of solar electricity may to build per unit of output, more efficient, fall by a factor of 15 or more by the mid- and able to use a greater variety of fuels. 1980’s and reach a price where solar electric Siting problems (for large plants) tended to devices could be installed to provide sup- be minimized by the ability to choose a few plemental electricity to houses and commer- remote locations. Conventionally fueled on- cial buildings. site facilities were often abandoned because their owners were concerned about the cost Inflation resulting from increases in ener- of maintaining equipment and the chance gy prices may have the effect of offsetting that a system failure would be expensive. ln- some of the cost reductions expected from vestments in onsite equipment were usually new designs. It is entirely possible, however, not as attractive as investments in areas that even the price of solar equipment now more directly related to the business and a in mass production will rise more slowly feeling emerged that energy generation was than the price of conventional energy. Proc- best left to the expertise of utilities. As a esses used to manufacture the components result, most design improvements in the past of solar devices are Iikely to make more effi- few decades have occurred in the technol- cient use of energy if energy prices rise since ogy of larger generating equipment, and the there is clearly considerable room for im- bulk of Federal research activity in energy proving the energy efficiency of American has been conducted in large systems. industry. The design of solar devices can also be changed to minimize the use of com- There are, however, reasons to suppose ponents whose costs are linked most closely that the unique nature of onsite solar energy to energy costs. Frames for solar collectors, equipment may offset some of the advan- for example, can be made from steel, alumi- tages which impelled centralization: num, concrete, plastic, wood, and many ● The basic solar resource is distributed. other materials. Ultimately, of course, it Solar units on individual buildings would be possible to manufacture solar could in some cases reduce transmis- equipment using solar energy. sion and distribution costs and losses. Integrating the equipment with a build- A number of the advantages of solar ing roof or with a parking facility can energy equipment are not comfortably ex- minimize the land required for solar pressed in the strict economic terms dis- equipment. cussed above. For example, widespread use ● Location of equipment onsite greatly of onsite solar equipment could have a fa- increases design opportunities and vorable impact on American labor — by cre- makes it easier to match the energy ating attractive new jobs, on international equipment designs to specific onsite stability — by easing the competition for energy demands; in particular, it is conventional energy sources without in- easier to use the thermal output of the creasing opportunities for proliferation of collectors. A great deal of overlap ex- nuclear weapons, and on the environment — ists between techniques and devices be- by replacing polluting energy sources. ing developed for onsite solar systems (These advantages are discussed at some and equipment used for energy conser- length in chapter `Vii.) The use of solar vation. The solar designs are usually energy during the next two decades wilI de- most successful when integrated into a pend largely on the value which society at- coherent plan for matching energy re- taches to these advantages. sources to the end use. Widespread use of onsite solar equipment ● Smaller equipment can be built more [or indeed of onsite energy equipment of quickly than larger facilities, thereby any kind) would reverse a 40-year trend reducing interest and inflation during toward centralization of energy sources. construction. This equipment can be The larger plants tended to be less expensive added in relatively modest increments. Ch I Introduction 13

● Onsite systems can also match reliabil- Another singular feature of the small solar ity to local needs. A highly sophis- devices is that, in comparison to larger ener- ticated industry, for example, may not gy equipment, they are relatively unsophis- be able to tolerate power failures last- ticated and would probably be manufac- ing a few hours per year while some tured, financed, insured, and maintained by areas in developing countries may be the people and institutions now performing very pleased with systems which may the same kinds of services for conventional not provide power for a few days each heating and cooling systems or industrial year—particularly if there are signifi- equipment. cant savings associated with accepting this level of reliability. Centralized A fourth distinction between using solar systems force all customers to accept energy and energy derived from conven- the highest level of reliability demand- tional fossil fuels is that the cost of solar ed by any customer. energy typically depends on temperature and on when the energy is needed. Solar In evaluating the advantages and prob- energy is best suited for meeting energy Iems of onsite solar equipment, it is impor- demands during daylight hours. Fossil fuels tant to recognize that solar equipment dif- typically burn at temperatures near 2,000 ‘C, fers from conventional systems in several whether this high temperature is needed or significant ways: not. There is no great penalty associated with operating an industrial process at high In the first place, the systems which are temperatures up to this threshold. While examined in this study do not really repre- solar energy can provide high temperatures sent a single technology, but rather an enor- (indeed, one of the first sophisticated uses mous range of technologies, A great variety of direct solar energy was a facility for high- of equipment components have been devel- temperature metallurgy), fluids at such tem- oped (many of which are reviewed in later peratures are expensive to collect, transport, sections of this study) and these compo- and store. The implications of having energy nents can be combined in many different costs depend on temperature and time have ways to meet specific energy requirements never been seriously evaluated. It is an issue in specific climates. which may be of increasing concern regard- A second unique characteristic of onsite less of whether solar energy is used, since systems is the number of arrangements there are many ways of recovering relatively which can be made for owning and operat- low-temperature energy from commercial ing onsite equipment, The small scale of the and industrial processes. If an economy devices makes it possible for individuals or began to reflect this new set of costs, the institutions other than utilities and major oil relative values of energy-intensive materials companies to invest in equipment capable and sources could change significantly. It of generating useful energy. This does not may be necessary to reevaluate the tech- necessarily mean that investor-owned util- niques used for each industrial process to ities will not play a useful role in the devel- make maximum use of the solar resource. opment of the technology; there are cases (Development of a successful thermo- where there may be advantages associated chemical or photochemical reaction which with utility ownership and maintenance of can use solar collectors to produce chemi- onsite equipment. It is also possible that cals capable of being transported, stored, municipal utilities, nonregulated companies and later reacted to produce high tempera- selling or renting onsite equipment, or even tures would do much to eliminate the penal- neighborhood cooperatives will play a role ty paid for high-temperature solar energy.) in owning and managing the equipment, Each of these possibilities raises different While the cost of solar energy may de- legal and regulatory issues. pend on temperature, it may not depend on 14 ● Solar Technology to Today’s Energy Needs

the size of the system employed. Economies vide a major fraction of the energy used in of scale in solar equipment are very difficult the United States, For example, the com- to establish, particularly if it is possible to bined output of all solar heating and hot connect several small generating and con- water systems used in the United States dur- suming facilities with a common electrical ing 1977 displaced about 1 billion kilowatt or thermal distribution system. hours of thermal energy and this is less than 1/200 of 1 percent of total U.S. energy re- Solar collectors are generally modular quirements in 1977. The peak electrical out- and typically the only economies of scale in put of all solar electric systems was about coIIector arrays resuIt from price reductions 1,500 kilowatts. Starting from this small obtained through large single purchases. base, solar sales would need to increase by This also applies to solar cells used to gener- about 50 percent per year for 20 years to ate electricity since even the largest solar achieve an output equivalent to 10 percent cell systems consist of arrays of small, in- of U.S. energy requirements. Achieving this dividual generating units. Large heat engines level of output would require an investment are typically less expensive per unit of out- of more than $500 biIIion. put than small systems of identical design, but the cost of these engines is typically a While the growth rates and the in- small part of the overall cost of the solar vestments required to increase use of onsite energy system; the cost of these systems is equipment seem ambitious, and would usually dominated by the price paid for col- clearly require an enormous growth in the lectors. It may also be possible to produce infrastructure of manufacturers, installers, small heat engines which are as efficient as and salesmen needed to make, market, fi- larger engines. The cost per unit of output nance, and service the solar equipment, it could be comparable to that of large en- must be recognized that any technology gines if mass-production techniques are which will supply a large fraction of U.S. used. Many types of storage systems, how- energy needs by the turn of the century will ever, do show significant economies of scale require an enormous growth rate and invest- at least up to a size where they are capable ment; yet some new technology must be of storing enough energy for several hun- available during this period as the world dred typical residences. Much more work reaches the physical Iimits of low-cost sup- needs to be done to determine the best size plies of oil and gas. The transition cannot be and placement of storage devices of all a painless one since all of the new energy kinds. sources are Iikely to be more expensive than All onsite solar facilities will face the dif- current energy. The major remaining ques- ficulties which have led to the steady de- tion is whether we will be able to take ad- cline in conventional onsite generating facii- vantage of the warning which the geologists ities: poorly engineered designs, inability of have given us, reflect on the options avail- organizations other than utilities to raise able, explore their potential, and prepare a capital for investments with relatively long strategy for a graceful transition to energy payback times, uncertainties about mainte- sources we can live with, or, whether energy nance costs, and numerous other concerns. policy will be guided by inadvertence, Given the uncertainties inherent in an anal- chance, and reactions to sudden crises and ysis of this type, it was simply not possible shortages. to establish that there either clearly were or The remainder of this study is devoted to were not economic advantages for small defining the circumstances in which onsite solar systems. solar technologies, with their rather curious Even if onsite solar energy systems could set of characteristics, could play a signifi- be unambiguously shown to be a preferred cant role in supplying energy. It examines energy source, it is clear that they would the technical opportunities now available have a long way to go before they could pro- and under development; reviews the current Ch. I Introduction ● 15

and potential future cost of integrated sys- of the environment, on the American labor tems based on these technologies operating force, and on the achievement of major U.S. in several representative cities in the United foreign policy objectives; and finally, it at- States; explores the legal and regulatory tempts to define the role and responsibility problems encountered by operators of small of the Federal Government in reguIating and generating equipment units; tries to explain promoting the technology. Some of the ma- the impact which widespread use of onsite jor results of this analysis are outlined in the solar technology might have on the quality present chapter.

ONSITE SOLAR TECHNOLOGY

Adequately assessing the opportunities is particularly true when the costs of onsite presented by onsite technology is enor- systems are compared with the cost of cen- mously difficult because there is such a di- tralized generating facilities; an accurate versity of approaches, many of which have estimate of the cost of energy from a central never been adequately investigated. The unit should include an analysis of all losses number of options is increased by the fact in transmission and inefficiencies encoun- that, by its nature, onsite equipment is tered when the energy from the central facil- tailored to specific applications in specific ity is converted to useful energy at the site. climates, since the equipment is much more In the analysis presented in this report, sys- efficient if care is taken to integrate the on- tems have been compared on the basis of site equipment into the building or indus- their ability to meet all of the energy re- trial apparatus to which it provides energy. quirements of a single family house, an apartment building, and other defined pat- The number of technical alternatives in terns of energy consumption. Computer onsite solar equipment is astonishingly analysis has been used to evaluate the per- great, in part because research in these formance of equipment operating in Albu- areas is on a scale where a smalI firm or in- querque, N. Mex., Boston, Mass., Fort Worth, dividual inventors can develop useful con- Tex., and Omaha, Nebr. The performance of cepts. Concepts have been developed by a system component cannot be fairly eval- groups ranging from backyard inventors to uated without examining its performance as well-funded Government and industrial lab- a part of an integrated system. The utility of oratories. More than 200 firms are now a collector design, for example, cannot be manufacturing solar coIIectors, and com- assessed without understanding how it will petition will probably eliminate many of the perform when connected to thermal storage products on the market, This fact presents a devices and subjected to the winds, tem- particularly difficult problem for Federal perature changes, cloud patterns, and fluc- planners attempting to develop a coherent tuating energy demands that characterize research program. actual installations.

TECHNIQUES FOR ASSESSING ONSITE TECHNOLOGY INTEGRATION OF ONSITE FACILITIES WITH OTHER ENERGY SOURCES It is important to compare competing technologies on the basis of their ability to Carrying the logic of this thesis one step perform a specific set of tasks in a specific further, it can be seen that it is also neces- location – generalizations and simple “mea- sary to review the performance of onsite sures of merit” can be very misleading. This energy equipment as an element of a system 16 ● Solar Technology to Today’s Energy Needs

capable of providing all of the energy re- trical grids should present major problems. quirements of a region. Because most onsite Relatively inexpensive devices are on the devices will be connected with conventional market which will disconnect onsite equip- energy sources which provide backup pow- ment from utility Iines so that Iinemen can er, the performance characteristics of the perform repairs safely, and meters are avail- onsite devices can affect costs of energy de- able which can monitor the production of livered to all parts of the community. This is thermal energy and the purchase and sale of particularly true if electricity is used to pro- energy from onsite systems. Moreover, on- vide backup power since the cost of electric site equipment should not create insur- power increases significantly if it is required mountable load management problems for to meet irregular demands; it is very costly utilities, even if a relatively large number of to maintain generating equipment which their customers use onsite devices. will only be used during cloudy periods. The relatively low cost of onsite thermal The question of providing backup power energy storage creates a situation where it to solar energy systems is intimately con- may be preferable to store electrical energy

nected with the problem of determining generated in central electric-generating fa- whether energy generated from onsite solar cilities during the night (when electric equipment should be stored, or whether it demands are low) in onsite thermal storage should be transmitted to other consumers when this energy is to be used for heating. who may have a need for the excess onsite The storage tanks typically associated with energy. Analysis conducted for this study in- solar heating systems provide an ideal op- dicates that it is usually preferable to allow portunity for this kind of storage but con- the onsite unit to sell energy to a commun- ventional buildings can be equipped with ity-wide electric distribution grid than to storage facilities which are charged only store the excess electricity in onsite battery with electricity from conventional sources. equipment (although this result could be When a careful analysis is made of all of the reversed if very low-cost batteries are devel- costs incurred in meeting the energy needs oped). In general, if energy transmission is of typical buildings (including both onsite relatively inexpensive, it is preferable to costs and the real costs undertaken to pro- connect as many customers and producers vide backup power) it appears that costs of together as possible. The value of the excess both solar and conventional buildings are energy sold from onsite generating equip- reduced when energy used for heating (or ment depends on the nature of the conven- backup heating for the solar system) is tional generating equipment in the region, stored onsite during periods when demands the local climate, and a number of other fac- on the electric utilities are low. The costs of tors. The analysis indicates that electric conventional systems were reduced more companies shouId be able to purchase ex- than the costs of the solar systems, however, cess electricity generated by residential and and solar heating systems compared less fa- commercial onsite solar facilities for 25 to vorably with conventional systems when 100 percent of the price at which they sell these methods were used. There were, how- energy. Determining a just rate for pur- ever, a number of cases where the solar chases and sales can be extremely complex equipment still was economicalIy prefer- and in some States, legal and regulatory able. problems may have to be overcome to It is important to recognize that while the achieve a just relationship. Presently few relatively uneven loads imposed by pro- utilities are willing to purchase energy from viding backup power to solar energy equip- onsite generating systems. (These issues are ment can have an adverse effect on overall discussed in detail in chapters V and VI.) utility costs, many other kinds of energy- None of the technical problems asso- consuming devices also impose very uneven ciated with connections to existing elec- loads on a utility. Insulating a building, for Ch. I Introduction ● 17

example, tends not to decrease the peak expensive generating equipment, may cre- electrical demand significantly during the ate a situation where it is preferable to pro- summer (the period when most utility peaks vide backup entirely from natural or even are highest), but does decrease demands synthetic oil or gas. In several cases exam- during the winter, resulting in increased ined, it was less expensive to provide back- utility costs. Similarly, electric heat pumps up from these chemical sources than from impose much more uneven loads than base- electricity even if it was assumed that the board resistance heating. (In fact, when all chemical systems’ fuels increased rapidly in costs are evaluated, heat pumps may be price. more expensive to operate than electric resistance heating systems which purchase electricity only at night. ) RESEARCH AND DEVELOPMENT

In evaluating costs, it was assumed that in a surprising number of cases, onsite the electric utility used a set of central solar technologies are not economically at- generating systems which were optimally tractive because of the high costs of such chosen to meet each type of demand, This is mundane processes as instalIing and align- the only valid way to compare costs over the ing collectors and bending metal in fabricat- long term, It is tautological that equipment ing facilities. If these costs cannot be re- designed to minimize costs for a conven- duced with some ingenious procedures, it is tional load pattern will be less efficient if it difficult to imagine a research breakthrough is used to meet a different load pattern (e. g., which would radically reduce the cost of loads which include a large amount of solar solar energy derived from such systems. If backup demands). Admittedly, regulatory these costs can be reduced, a number of at- delays and the mortmain of existing plants tractive devices are possible with existing and equipment will always prevent utilities technology. What is needed is perhaps more from optimizing their facilities to new load the genius of the man who invented the zip- patterns over the short term. per than the genius of an Einstein.

There are circumstances where it may be There are a number of areas where re- preferable to transmit thermal energy rather search and development seem particularly than to store it onsite since there are very important. significant economies of scale in thermal ● storage. The analysis in this study discov- Determining the best way to design a ered several areas where 100 percent of the building structure to maximize natural heating and hot water requirements of in- heating and cooling, dividual houses could be met by solar ener- ● Developing simple collectors from ex- gy if a number of homes were connected to tremely low-cost materials (e. g., cheap, a large central storage tank. Distributing durable plastic films), energy in thermal form instead of electrical ● Developing techniques for reducing the form was also found to be attractive in a cost of manufacturing simple tracking number of conventional solar energy systems designed to meet all of the energy and concentrating collectors, needs of a large community. I n these cases, ● Developing economical techniques for the thermal energy was very inexpensive storing large amounts of energy in hot because it was a byproduct of generating water or rocks in order to meet all of electricity and the bulk of the cost of the the annual thermal demands of energy was the cost of delivery. buildings,

The difficulties encountered in providing ● Improving techniques and materials for backup power from electric utilities to on- laying insulated pipes for thermal site solar facilities, characterized by large, distribution systems, 18 ● Solar Technology to Today’s Energy Needs

● Developing chemical reactions which I ing at very high temperatures (e. g., can be used to store or transfer thermal 1,4000 to 2,0000 F), energy, ● Developing low-cost materials for solar cells, and • Developing advanced electrochemical storage devices, ● Developing dyes for a simple concentrating collector. ● Designing an inexpensive and reliable It is also vitally important that a strong heat engine capable of working at program in basic research accompany these relatively low temperatures (e. g., below applied development projects. Research in 2500 F), sol id state physics, surface chemistry, metal- Iurgy, thermochemical and photochemical ● Designing an inexpensive, reliable, reactions and heat transfer is of particular high-efficiency engine capable of work- interest.

ECONOMICS

Table l-l indicates the size of different hot water in the mid-1980’s, if consumers are energy markets in the United States, sum- convinced that oil prices will increase to $23 marizes the potential of direct solar energy to $35 per barrel by the year 2000, or that in each market, and estimates when solar gas prices will reach an equivalent level. equipment could begin to enter this market. Fuel prices would probably rise at least as rapidly as this if a major fraction of U.S. liq- Direct onsite solar energy equipment is uid fuels were derived from synthetic likely to make its first major impact by pro- sources by the year 2000. viding supplemental heat and hot water for residential and commercial buildings. This is Most of the solar heating and hot water not an insignificant market since demand systems installed today are not capable of for energy in this category represented meeting all of the heating requirements of about 20 percent of all energy consumed in the buildings they serve; a conventional fur- the United States in 1975. There is already a nace or baseboard heaters must be used dur- growing market for solar hot water systems ing periods of prolonged cloudiness. This in regions with plentiful sunlight and high limits the fraction of the energy consumed electric rates where natural gas is not avail- for building heat which solar devices can able for new buildings. A market for solar replace. It is possible, however, to construct heating systems is also developing in these solar systems providing 100 percent of a areas. If it was assumed that electric rates building’s heating demands by using a suffi- increased 45 percent by the year 2000, solar ciently large storage facility. The analysis heating and hot water systems with plausi- conducted for this study indicated that ble near-term costs showed lower life-cycle within 3 to 5 years it should be possible to costs than heat-pump systems in houses in construct systems capable of supplying all three of the four cities examined in this of the heating and hot water requirements study. The solar system was competitive in of large buildings at prices which would be all four cities when a 20-percent investment competitive with conventional electric heat- tax credit was given to the solar system. ing in three of the four cities examined. The systems would be competitive in all four Solar energy was found to become an at- cities if a 20-percent investment tax credit tractive alternative to oil and gas heating of was granted to the solar equipment. Ch. I Introduction ● 19

Table I-1.—The Potential of Onsite Solar Energy Equipment

Percentage of total U.S. energy demand Potential of onslte solar Demand type in 1975 energy equipment

1. RESIDENTIAL AND COMMERCIAL (36) a. Hot water 3.5 Competitive now with electric hot water heating on life-cycle cost basis and with oil and gas if year 2000 prices expected to reach$15-20/bbl equivalent. b. Space-heating 17.8 Combined hot water and heating systems marginally competitive with resistance heating and heat pumps now or in the near future, competitive with oil and gas if solar prices drop, or, if year 2000 prices expected to reach $23-35/bbl equivalent. Many ‘‘passive” approaches clearly attractive. c. Electricity for lighting and other 9.0 Possibly competitive by mid- to late-1980’s if electric miscellaneous demands rates increase by 50 percent by the year 2000. Competitive in remote areas today. d. Air-conditioning 4.3 Some systems available, but economically attractive systems unlikely until early or mid-1980’s. e. Gas cooking and other 1.2 Cooking conveniently available from direct solar miscellaneous uses sources only through electricity.

Il. TRANSPORTATION (26) No major role probable for direct, solar energy. Some market possible for electric vehicles charged from onsite electric systems or vehicles using chemical energy generated on site.

Ill. INDUSTRY (38) a. Electric motor drives, 8.7 Penetration of this market unlikely until 1990’s unless electrolytics, & misc. research progresses faster than expected. Solar electrical demands cogeneration systems may be attractive in some areas by the mid-1980’s. b. Process heat at temperatures 2.0 (7.0)’ Possibly competitive with oil and gas by 1980’s if prices below 2120 F are expected to increase to $14-16/bbl equivalent by the year 2000. Competition with direct combustion of coal unlikely in large plants unless conversion to coal is very expensive. c. Process heat at temperatures 5.3 (6.5)* Possibly competitive in 1980’s with oil and gas if of 2120 to 5500 F prices reach $19-25/bbl equivalent by 1985 and $30-40/bbl by 2000.

d. Process heat at temperatures 18.6 (12.4)* ● Probably competitive only when onsite solar energy for greater than 550° F electric motor drives is competitive. e. Chemical feedstocks 3.3 No market for direct solar energy.

“If heat used to raise the temperature of materials from 600 F IS Included . . Nearly 90 percent of the process heat used at these temperatures IS consumed In blast fUrnaCe% steel mills! stone, 91a5S, and clay processing, and petroleum reflnlng SOURCES. Total energy requirements for Industry, transportation, restdentlal, and commercial consumers obtained from U S Department of the Interior (Bureau of Mines) News Release March 14, 1977 Details for residential and commercial consumption patterns obtained from J R Jackson and W S Johnson, Cornnrercla/ Errergy Use A Dlsaggregat{on by Fue/, Bui/dlrrg Type, and End Use, Oak R[dge National Laboratory (ORNLICON-14) February 1978, page 9 E Hlrst and J Carney, Resldent~a/ Energy Use to the Year 2000 Conservation and Econorrr(cs, Oak Ridge Nat!onal Laboratory (ORNUCON 13) September 1977, page 9 Details of Industrial energy consumption based on D S Freeman, (ed ) A Tlrne fo Choose, Balllnger, Cambridge, Mass , 1974, p 456 InterTechnology Corporation, Ana/ysls of /he Econornlc Potentfa/ of .So/ar T/rerrna/ Energy fo Pfovlde /ndusfrla/ Process F/eaf (ERDA COO/2829.1}, p 53 (This survey Included Institutions using 59 percent of U S Industrial process heat ) 20 ● solar Technology to Today’s Energy Needs

Electricity used in residences and com- There are, however, several major obsta- mercial facilities for lighting, television sets, cles to solar use in industry and agriculture. dishwashers, and other appliances is ex- Consumers in these categories can use a va- pected to represent about 9 percent of the riety of different conventional fuels (many primary energy consumed in the United can burn coal directly) and pay much less States in 1985. Residences and commercial for electricity than residential and commer- buildings pay the highest rates for electricity cial customers. Moreover, they typically ex- since these rates must include charges for pect payback times on the order of 1 to 3 the costly equipment needed to distribute years for investments in new plant equip- the electricity to a large number of small ment. The cost of industrial solar heat can consumers. It is likely, therefore, that de- also be somewhat higher than solar heat vices for generating electricity from sunlight provided for homes and residences if it is ne- will find their first large markets in this sec- cessary to install collectors in fields where tor. (Solar electric devices will find substan- land, footings, and other aspects of site tial markets in remote military outposts, sig- preparation must be charged to the solar nalling devices, and other installations equipment and where piping heat to the fac- before the large residential market can be tory can be expensive. Smaller installations approached. The market for systems in can be supported by building roofs and heat remote areas could, however, amount to is generated close to the site where the several hundred millions of dollars of an- energy is used. nual sales, particularly if markets in nonin- dustrial countries can be captured.) Within Analysis of the cost of providing electric- 10 to 15 years it may be possible to develop ity and process heat to a large three-shift in- onsite solar devices capable of producing dustry from different kinds of energy equip- electricity for $0.04 to $0.10/khVh, rates ment which began operating in 1985 indi- which may be competitive with the cost of cated that direct solar heat for low-tempera- electricity delivered to residential and com- ture applications would be competitive with mercial customers from new utility gener- oil if it was assumed that oil prices increase ating plants. to $15 to $20 per barrel by the year 2000 and if the solar equipment is financed by a pri- There is also a potentially large market vate utility. Solar heat at temperatures in for direct solar energy equipment in industry the range of 3500 F was competitive only if and agriculture. Table l-l indicates that 2 to it was assumed that oil prices reach $19 to 7 percent of U.S. energy is consumed in $25 per barrel by 1985, and are $30 to $40 these sectors at temperatures below the per barrel by 2000. Competition with natural boiling point of water, and 7 to 13 percent is gas and coal was possible for systems start- consumed at temperatures below 3500 F. ing in 1985 only if it was assumed that the Solar equipment is now available which can prices of these fuels increase by a factor of easily provide fluids or direct heating at nearly three (from 1976 levels) by the year these temperatures. In many ways, in- 2000 (e.g., coal costing $60 per ton). While dustrial and agricultural markets are more such price increases are possible for natural attractive than the residential and commer- gas, it seems unlikely that coal prices will in- cial markets since the residential and com- crease at this rate. It is also possible that mercial customers are much more diverse solar heat at temperatures below 5000 to and will probably require a more complex 6000 F will be competitive with heat derived and expensive infrastructure for sales and from synthetic hydrocarbons made from installation. The larger customers are also coal. likely to be confronted with gas curtail- ments during the next decade and will be in While most solar heating systems for large the process of selecting a replacement for industrial or agricultural facilities may not natural gas. be fully competitive with conventional fuels Ch. I Introduction ● 21

before the mid-1980’s, it will almost certain- site direct solar energy. There may be some ly be possible to find industries whose speci- circumstances where electric vehicles could fic problems are well suited to the use of be charged from solar-generated electricity. solar energy in the near future. There may Development of a thermochemical reaction welI be a large near-term market for grain which yields a portable chemical with a drying systems in less-developed countries, high-energy density would also make “di- for example. Near-term markets for solar rect” solar transportation a possibility. It is equipment in the industrial sector could unlikely that the direct solar sources wouId also result from existing environmental be preferred to synthetic fuels from biolog- legislation; solar energy may prove to be an ical or other sources. attractive way to expand industrial capacity Considerable caution must be exercised in while minimizing increases in emissions. interpreting statements about the “competi- Solar cogeneration devices using solar tiveness” of solar energy systems. First, the cells or Stirling engines may be attractive in benefits of solar equipment can only be roughly the same circumstances that found realized if the prospective owners compare solar hot water competitive, although the solar and alternative systems on the basis of solar systems were less attractive when com- life-cycle costing. Life-cycle costs will, in pared with cogeneration systems using con- turn, depend on the type of owner since ventional fuels. It seemed unlikely that solar each wilI have a different tax status, sources electric systems which did not cogenerate of capital, and economic expectations. would be able to compete with the low cost Solar devices may be owned by the residents of electricity delivered to industrial facil- of the building, a private corporation, or a ities from conventional sources until at least municipal or privately owned utility. Each the mid-1 990’s, although unexpected prog- will make different estimates of the advan- ress in research could well accelerate the tages of the solar investment. Whether pro- rate at which the solar electric systems spective solar customers will actually em- become competitive. ploy such a procedure is difficult to anticipate and will depend to some extent on the Solar energy used for direct heat in blast skill with which the solar equipment is sold. furnaces, glass plants, and other facilities re- It is difficult to establish a fair basis for quiring heat at very high temperatures (uses representing 12 to 19 percent of U.S. energy computing the cost of nonsolar equipment consumption) are unlikely to be competitive since the performance of nonsolar equip- before solar electric systems. Development ment is Iikely to improve as the price of con- of an efficient thermochemical process, ventional energy increases. There is also which could be conducted in a solar collec- great variation in the cost of energy around tor and reversed in a special burner at high the country; regional differences in energy temperature when heat is needed, would prices are greater than differences in the greatly improve the prospects for using amount of sunlight avaiIable. direct solar energy in high-temperature ap- it must be recognized that if onsite solar plications. energy is to make a major impact on the U.S. energy economy by the turn of the century, Direct solar energy is unlikely to be used it will be necessary to find ways of instalIing as a substitute for any of the chemical solar equipment on existing buildings. This feedstocks which now consume about 3 per- process can be difficult: such installations cent of U.S. energy. Biomass would clearly are likely to be more expensive than devices seem to be the preferred solar source for attached to new structures, although there is feed stocks. at present no reliable information about the Similarly, transportation, which consumes additional costs which could be expected. It about 25 percent of U.S. energy, is unlikely is Iikely that the percentage increase in costs to provide a major near-term market for on- would be smalIer in larger buiIdings, 22 ● Solar Technology to Today’s Energy Needs

There may well be situations where it is come from onsite systems. Building orienta- not possible to retrofit an existing structure tion may present difficulties in some cases with solar equipment. Densely populated ur- but a roof must have a particularly poor ban areas and heavily treed suburbs present orientation or roof shape to present a major particularly difficult problems, and solar problem for a solar installation. energy used at these sites is unlikely to

POSSIBLE IMPACTS OF ONSITE SOLAR ENERGY

Since onsite solar equipment would un- I n spite of the development of indigenous doubtedly be designed, manufactured, fi- solar industries abroad, foreign markets for nanced, installed, and operated by the same solar energy devices may provide an excel- organizations currently associated with the lent opportunity for U. S. exports, Since construction of buildings and industrial many nations will find it desirable and possi- facilities, the impact on American society as ble to manufacture solar equipment locally, a whole will probably be very minimal. Sev- the sale of licenses, patents, and turn-key eral areas, where impacts would probably plants may dominate exports. The interna- be greatest, have been identified and tional utilization and impact of solar ener- studied in some detail. gy, however, may depend critically on U.S. initiatives over the next few years. I n most areas, U.S. research is the most advanced in U.S. SECURITY AND WORLD TRADE the world, so many nations will look to the United States for guidance in this field. A Extensive worldwide development of so- U.S. commitment to solar power would en- lar energy systems would, in time, relieve courage foreign commercialization of the some of the strain imposed on international technology, if only by giving it prestige. stability by competition for energy resources, reducing economic difficulties LABOR faced by oil-importing nations. It could provide a reliable source of power not depend- Onsite solar technology appears to be ent upon imports, and the necessary tech- more labor-intensive than contemporary nology would be accessible without a need techniques for supplying energy, thus, in the for large numbers of highly trained engi- short term, the introduction of solar energy neers or foreign technicians to operate devices will create jobs in trades now suffer- them. It should be possible for many coun- ing from serious unemployment. Jobs would tries to manufacture solar equipment using also be created by replacing imported oil existing industrial and construction skills and gas with solar energy derived from do- and facilities. Solar energy will be econom- mestically produced equipment. Jobs would icalIy attractive i n most other countries be- be created in the following areas: fore it is competitive in the United States ● Manufacturing of components (solar where energy is relatively plentiful and inex- collectors, heat engines, photovoltaic pensive. The development of indigenous devices, storage batteries, controls, energy sources abroad should also reduce etc.), pressures to accelerate the development of nuclear power, thereby reducing opportu- ● Installation of systems (plumbing, nities for the proliferation of the technology sheet-metal work, steamfitting, electri- and materials required to make nuclear cal work, carpentry, excavation, and weapons. grading), and Ch. I Introduction ● 23

● Maintenance of installed systems (in- ● Utilities alone can compare the cost of cluding routine adjustments and repairs energy from new onsite equipment with for small systems and full-time opera- the cost of energy from new central fa- tors for larger units). cilities — al I other owners wilI compare onsite costs with the lower, average The work created in these areas will be cost of energy from all central gener- distributed widely across the country, allow- ating faciIities; ing most workers to find jobs in areas close ● Utilities can offer the equivalent of 100 to their homes, and the jobs created should percent financing for new generating be relatively safe. One effect of emphasiz- plants (onsite or otherwise) and are able ing onsite solar energy, for example, would to raise capital for investments with be to create more new construction jobs long-term paybacks–something which than new coal-mining jobs. It is also in- few other institutions can do; and teresting to notice that nearly a third of the employment associated with a conventional ● Utilities already have maintenance electric utiIity involves transmission and crews and billing services, which could distribution of energy and billing and other be expanded to cover the operation of services — services which would probably onsite generating equipment. not be affected in any way by a shift to on- A number of these advantages could be real- site power. There would be no need for ized without utiIity ownership of onsite sys- laborers to live in remote or temporary con- tems if care is taken in the design of utility struction sites. Work on solar equipment rates. shouId require onIy simple retraining programs for most construction trades. There Municipal utilities may be able to play an may, however, be shortages both of engi- important role in regional planning for on- neers and architects qualified to design site solar energy systems and their access to solar equipment, and of operators trained in relatively low-cost capital may make muni- the maintenance of some of the larger and cipal financing of solar energy projects at- more sophisticated solar devices that have tractive. been proposed. The long-term applications for employ- ENVIRONMENT AND LAND USE ment of solar and other new energy technologies cannot be reliably assessed with contemporary economic methods. Long-term While solar energy equipment is not com- labor impacts will depend on forecasts of pletely free of adverse environmental ef- future growth rates, both in the economy fects, providing energy from sunlight will and in U.S. energy consumption — subjects have a much smaller environmental impact about which there is great confusion and than conventional sources providing equiva- disagreement. Ient amounts of energy. Solar energy may provide an opportunity to expand population and increase indus- UTILITY PARTICIPATION trial capacity in areas where such growth may be constrained by the Clean Air Act. Large-scale conversion to the direct combus- Utility participation in onsite generating tion of coal wiII make it difficuIt to maintain facilities offers several advantages: current levels of air quality unless solar ● The utiiity is i n the best position to op- energy, or some other nonpolluting energy timize the size and placement of all source, is introduced to reduce the demand generating, storage, and transmission for energy from fossil sources. The use of equipment in the region; solar energy can also reduce the net releases 24 ● Solar Technology to Today’s Energy Needs

of carbon dioxide. The significance of this equal the extra emissions associated with depends on the extent to which greatly in- the manufacture of the solar device in 3 to 9

creased CO2 releases could adversely affect months. In addition to these primary effects, world climates— and this is not well under- a number of the specific storage and energy stood now. conversion systems discussed in later sections of this report could have adverse en- The primary environmental effect of util- vironmental effects because of noise, minor izing onsite solar energy will be reduction of emissions (associated primarily with manu- the potential adverse environmental effects facturing components), and use of toxic associated with other energy sources. The chemicals. negative environmental effects of solar energy devices stem primarily from two The land-use impact of onsite solar equip- sources: (1) land-use requirements, which ment can be less serious than the problems could compete with other, more attractive associated with isolated solar equipment, uses of land near populated areas, and (2) since in most cases the onsite equipment emissions associated with the mining and can be integrated into buildings or local manufacture of the materials used to manu- landscapes and extensive transmission facil- facture solar equipment (e. g., manufactured ities are not required. If additional surface steel, glass, aluminum, etc. ) In most of the area is required, however, lack of suitable cases examined, however, the reduction in land close to populated areas could place emissions attributable to operating a solar major constraints on the use of onsite solar facility instead of a conventional one can equipment.

FEDERAL POLICY

One of the attractive features of onsite There is little doubt that without Federal solar equipment is that it may be the only assistance, solar markets wilI grow relatively new energy source that can be developed, fi- slowly. Legislation can greatly accelerate nanced, and installed without Federal assist- the rate at which this market grows if this is ance of any kind; it is simply an extension of judged to be a desirable objective. existing construction industries. Federal energy policy will, however, affect the rate The following types of policies can be ef- at which onsite solar energy enters the mar- fective. ket, regardless of whether an attempt is made to develop a specific policy for solar 1. Direct incentives to potential custom- energy. Federal poticies have made the mar- ers (chiefly tax incentives, loan subsi- ket in which solar technologies compete an dies, and allowances of accelerated de- artificial one. Energy prices are influenced preciation). by a bewildering array of regulations, sub- 2. Assistance to manufacturers (including sidies, and controls which, in several in- incentives for purchase of manufactur- stances, have had the inadvertent effect of ing equipment, research and develop- reducing the attractiveness of solar equipment grants, and Federal purchases) ment. Examples include the policy of main- and assistance for testing laboratories taining residential energy rates at artificially certifying the performance of onsite low levels, decisions to support larger types equipment. of energy equipment with preferential tax credits, and disproportionate amounts of 3 Support of basic research and develop- research funding given to larger energy ment programs in fields related to on- equipment. site solar energy. —.—

Ch. I Introduction ● 25

4 Legislation which might eliminate some stimulated by the subsidy, thus producing barriers to usage of onsite solar systems increased tax revenues. This analysis of (this would include freeing onsite costs does not attempt to attach a monetary equipment from regulation as a public value to the health benefits of reduced air utility and assisting States in designing polIution and other social benefits local procedures for protecting the Federal support of small solar energy sys- “sun rights” of owners of solar equip- tems has been consistently hampered by the ment). small staff available to DOE’s Division of 5. Encouragement of the use of solar ener- Solar Energy Small staffs make it difficult gy in other countries through foreign to manage a large number of innovative assistance grants, joint research pro- projects. grams, and other techniques.

6. Programs to support education and training in fields related to solar energy. STANDARDS Tax credits, low interest loans, acceler- A difficulty encountered with any new ated depreciation alIowances, and exemp- technology, and particularly one involving tion from property tax can be powerful tools as many small and inexperienced manufac- in reducing the perceived cost of solar turers as in the current solar energy industry, energy. A 20-percent investment tax credit, is that it is necessary that standard testing for example, could reduce the effective cost procedures be developed rapidly, and in of solar energy in residential applications by step with the development of each type of 15 to 30 percent; the combination of a 20- technology. It is also necessary, however, percent investment tax credit; 5-year depre- that these standards be reviewed constantly ciation alIowance, and an exemption from so that new and different design approaches property tax, could lower the perceived cost are not inadvertently ruled unacceptable. of solar energy by 50 to 80 percent. A pro- Small firms are frequently in such a weak gram making 3-percent loans available to financial position that it is difficult for them homeowners would be equivalent to an in- to offer acceptable guarantees. A reputa- vestment tax credit of about 34 percent. tion for failed installations could be a These subsidies would have the effect of in- serious barrier to the rapid expansion of the creasing sales, resulting therefore in a solar industry, decrease in the cost of individual components if they stimulate mass production. Standards have been slow to develop and inspectors frequently do not know what to Tax credits reduce Federal revenues but look for in novel systems. the net cost of the credits to the Govern- ment is difficult to calculate, The Federal subsidy per unit of energy produced by subsidized solar equipment is roughly equal to OTHER SPECIALIZED LEGAL AND the difference between the costs (with or REGULATORY PROBLEMS without incentives) of a unit of solar energy perceived by equipment owners. That is, if a Onsite solar facilities are currently con- policy has the net effect of reducing the trolled by laws and regulations written with customer’s perceived costs by $0.01/kWh, entirely different energy systems in mind. the Government will lose approximately Although that is the case, this study finds $0.01/kWh in tax revenues for each kWh surprisingly few barriers to large-scale in- generated by the solar system receiving the stalIation and operation of onsite solar facil- subsidy. The Government’s costs, however, ities. The legal barriers which do exist can, in will be compensated to some extent by the most cases, be removed with routine regula- fact that solar-related businesses would be tory review. Resistance to changes in zoning 26 ● Solar Technology to Today’s Energy Needs

or building codes, for example, generally COMPARISON WITH CURRENT POLICY arise when an interested party will be adversely affected; it is not Iikely, however, This report does not make prescriptive that builders, owners, labor unions, or pub- recommendations, but presents three points lic officials will perceive onsite solar gener- of view which give rise to a range of specific ation as a threat. poticies affecting onsite solar power generation. The discussion (which appears in chap- Some concern has been expressed about ter I I I of this report) is intended to illustrate the fact that owners of solar facilities have the policy alternatives available and to no legal grounds for objecting to construc- assess their relative effectiveness. This anal- tion projects which would have the effect of ysis found several broad approaches to be shading their collectors. While this may pre- potentially effective which do not play a sig- sent a serious problem, the skillful applica- nificant role in current Federal programs. As tion of existing legislation, local covenants, a consequence, the emphasis of this report zoning authorities, and buiIding code regu- differs in several significant respects from lations will probably provide as much pro- Administration policy. tection as it is reasonable to expect. The 1. The policies examined here would analysis conducted for this study found no place greater emphasis on accelerating need for Federal action in this area. a wide variety of onsite solar energy systems (including solar electric sys- The regulatory problems which may pre- tems) during the next decade; the ex- sent the greatest problems for onsite solar isting program appears to stress heating energy devices, and the ones which it may and cooling systems, relegating most be most difficult to resolve, involve the laws other applications of solar power to and rulings governing public investor-owned longer-term research programs and gas and electric utilities. If it becomes possi- placing major emphasis on the develop- ble to generate energy at competitive prices ment of large, centralized electric-gen- using onsite solar energy equipment, the erating systems. “natural monopoly” of utility generation of 2. The policies examined here place a high electricity, which forms the basis of most priority on bringing life-cycle costing utility law, would be called into question; techniques to the attention of consu- the only real “natural monopoly” may be mers, investors, and other groups in a equipment for transmitting and distribution position to make decisions about ener- of energy. gy equipment.

3. In contrast to the Administration’s plan, Problems in this area fall primarily into which concentrates exclusively on con- three categories: 1 ) establishing just rates for sumer incentives, the policies examined power sold as backup power for onsite solar here will include a number of tech- instalIations and just rates for utility pur- niques for providing direct assistance chases from onsite faciIities, 2) resolving the to equipment manufacturers. regulatory problems faced when an individual or institution other than a utility at- 4. Policies examined here place major em- tempts to sell electricity or thermal energy phasis on the problem of ensuring an (utilities are given a monopoly on such sales equitable relationship between onsite in many regions), and 3) resolving the regula- solar equipment and existing utilities, tory problems confronted when existing util- with particular emphasis on establish- ities attempt to own and operate onsite ing reasonable rates both for the pur- energy equipment. Resolving these issues re- chase of backup power from the utility quires a clear concensus about the proper and for the sale of power generated by role of utiIities in onsite equipment. onsite equipment to utilities. More at- Ch. I Introduction ● 27

tention is paid to providing backup diverse set of institutions will be very dif- from natural gas and chemical fuels ferent from the programs designed to devel- rather than electricity and more atten- op new central generating plants which will tion is paid to the opportunities for clearly be designed for use and operation by distributing thermal energy. utiIities.

5. Policies here emphasize the encourage- What will be needed is an unprecedented ment of foreign sales of onsite gener- amount of bureaucratic flexibility, imagina- ating equipment, licenses, and patents tion, and care in determining where Federal and of providing assistance to nations intervention can help and where the best attempting to acquire a reliable, in- policy is restraint. digenous source of power. There will be no way to avoid taking risks. The bulk of this report attempts to provide Onsite solar energy has unique features as the basis for comparing the risks associated an energy source, so Federal policy must with onsite solar energy equipment with the have unique features to encourage its devel- risks which must be taken in supporting opment. Unfortunately, precedents for Fed- other energy sources. If nothing else, the eral programs, which have succeeded in en- study indicates that the potential of onsite couraging the development of a commercial solar energy systems cannot be easily dis- product, are almost impossible to find; prod- missed and that it is dangerous to be dog- ucts developed and promoted by agricul- matic about the subject at this early stage. tural extension services are perhaps the only There is enough uncertainty about the fu- clear exception. BadIy managed Federal in- ture of the world’s energy supplies, and tervention in the market can do more harm enough problems have developed with con- than good. At a minimum, it must be recog- ventional solutions, that it is necessary to be nized that developing and promoting a di- a little humble about the extent to which verse set of technologies to be manufac- fundamental questions about supplying and tured, installed, financed, and owned by a consuming energy are understood. Chapter II OVERVIEW OF ONSITE SOLAR Technology AND SUMMARY OF ECONOMIC ANALYSIS Chapter II.--OVERVIEW OF ONSITE SOLAR TECHNOLOGY AND SUMMARY OF ECONOMIC ANALYSIS

Page Table No. Page - Introduction em. ... .,*, *...... ** 31 5 Levelized Monthly Energy Costs Per Unit in a 196-Unit High Rise Apartment...... 35 Methodology 8 - 9 ...... 32 6. Levelized Monthly Energy Costs for Solar Summary of System Costs for Heating and Hot Water Systems ...... 41 conventional Buiidings ● . . . . ● ...... ● ..34 7. Solar Heating and Hot Water Systems for Technology Overview ● .*,**...,.....**.,,.. 36 Single Family Houses Compared With Passive Solar Energy Systems ...... 36 Conventional Systems Based on Oil Active Solar Systems ...... 36 and Gas...... 42 . Summary of Cost Comparisons...... 40 8. Levelized Monthly Energy Costs for Solar Solar Heating and Hot Water ...... 40 Air-Conditioning and Heating ...... 43 9. Fiat-Plate Photovoitaic Systems on Solar Air-Conditioning . . . ● * ● . . ● ...... 43 Solar Electric Systems Using Photovoitaics .43 Houses With Extra insulation and Storm Solar Electric Systems Using Heat Engines.. 48 Windows ...... 44 . Community Energy Systems ...... 46 10. Flat= Plate Photovoltaic Systems Mounted Industrial Systems ...... 50 on the Roof and Over the Parking Lot of a 196-Unit High Rise Apartment ...... 45 11. Photovoitaic Concentrator Systems on High Rise Apartments ...... 46 12. Heat-Engine Systems ...... 47 LIST OF TABLES 13. Buildings in the Community of 30,000.....46 14. Levelized Monthly Energy Costs Per Unit Table No. Page for a Community in Albuquerque, N. Mex.. ..49 1. Assumed Residential Fossil Fuel 15. Levelized Monthly Energy Costs Per Unit Prices In the Year 2000 ...... 33 for a Community in Omaha, Nebr...... 50 2. Typical Assumed Nonsolar Electricity Rates 16. Assumed Conventional Energy Costs for in the Year 2000 ...... 33 Large industrial Users, 1976 Dollars ...... 51 3. Levelized Monthly Energy Costs for Single 17. industrial Direct Heat Systems Levelized Family Houses Not Using Solar Energy ....35 Monthly Cost ...... 52. 4. Levelized Monthly Energy Costs for Single 18 industrial Cogeneration Systems Levelized Family Houses With Extra insulation ...... 35 Monthty Cost ...... 54 . Chapter II Overview of Onsite Solar Technology and Summary of Economic Analysis

INTRODUCTION

This study examines the cost and performance of a cross-section of onsite solar energy systems designed to meet all or part of the energy requirements of five different categories of energy customers: —A two-story, single family, detached house with approximately 1,700 square feet of Iiving area.

—A 10-story, 196-unit, high rise apartment building. —A shopping mall with approximately 300,000 square feet of commercial space. —A residential community consisting of a mixture of single family houses, townhouses, low rise and high rise apartments, and commercial facilities. —A series of industrial installations requiring differing amounts of process heat and electricity.

The systems were examined in four U.S. – Electricity (from solar cells or heat cities— Albuquerque, Boston, Ft. Worth, and engines); and Omaha– chosen to represent a range of different climatic conditions (both in terms of — Electricity and thermal energy (using the availability of the solar resource and the total energy or cogeneration systems). heating and cooling demands). The cities also represent a spectrum of different elec- It was not possible to review the per- tricity and fossil fuel costs; this was impor- formance of all possible systems for onsite tant since the cost of energy from conven- systems designed to meet onsite energy tional sources around the country tended to needs with direct solar energy, and it was show greater variation than the amount of not possible to optimize the performance of available sunlight. The results presented in the systems selected. The analysis presented this chapter are Iimited to an analysis of the here is intended only to establish the cred- costs of hypothetical systems operating in ibility of different proposals and to make Albuquerque and Omaha. broad comparisons between competing concepts. The technologies chosen for analysis include devices which supply: This chapter only summarizes the results – Hot water for domestic or industrial of the anaIysis; a much more compIete use; assessment of the technologies represented is reported in chapters VII l-Xl I of this – High-temperature fluids for industrial- volume. Volume I I presents a much more process heat; detailed review of the assumptions made in – Hot water and space-heating; the study, the methodology employed, and reports the results of analysis of a much — Hot water, space-heating, and air-con- larger number of cases than can be sum- ditioning; marized here. .31 32 ● S0lar Technology to Today’s Energy Needs

METHODOLOGY

WhiIe the cost of different energy sources taken in the four cities in 1962 (1963 for can be compared in a number of different Boston). ways, the comparisons presented here were all made by computing the average monthly An accurate estimate of Iifecycle bill paid by the ultimate consumer of the costs cannot be made by simply adding energy. This consumer might be the owner up all of the outlays made during the of a single family house, a tenant in a high 30-year interval chosen for comparison. rise apartment, or an individual purchasing A dollar spent in the 30th year will not a product or service from a commercial or be as important to the owner of the sys- manufacturing facility. These calculations tem as a dollar spent during the first were made as follows: year of the system’s operation —since, in principle, the payment required in 1. Systems were compared on the basis of the 30th year could be met in the first their ability to meet the same set of year of operation by investing an final or “end-use” demands for energy. amount much smaller than a dolIar in In the case of a single family house, for an account earning compound interest. example, this means providing energy Cost comparisons were therefore made for domestic hot water, space-condi- by comparing the “present value” of all tioning, and electricity for motors and expenditures, where present value is de- other miscelIaneous uses. If the solar fined to be the amount which, if in- energy equipment was unable to meet vested at interest in the first year of a the demand (or was not designed to system’s operation, would be able to meet some of the demands), these ener- meet all cash requirements for energy gy needs were met by using electricity (including the initial cost of the system). or fossil fuels from conventional Since each owner will have access to sources. The biIIing for this conven- different types of investments, a dif- tional energy was made on the basis of ferent effective interest rate must be actual rates currently charged in the used to compute the present value of region. outlays for each owner.

2 All comparisons were made on the 3. It was assumed that consumers com- basis of “life-cycle” costing methods. pare costs on the basis of the “present This required an estimate of all outlays value” of their energy-related payments for operating and maintaining equip- and expect to earn a 10-percent return ment, electricity and fuels purchased, (after taxes) on all investments. Pay- taxes, and major replacements over a ments consumers made were estimated selected 30-year period (1 985-201 5), as by computing the charges which would well as an estimate of the initial cost of be levied assuming the utilities or apart- the system. Estimates of the electricity ment building owners earned the same and fuel required by the different sys- rate of return on their energy invest- tem designs were obtained by using a ments that they earn on other types of computer model capable of calculating investments. the energy needed by each building type for each hour of the year (des- Using this method of comparing con- cribed in detail in volume I I). When sumer costs, of course, does not imply solar devices were used, the computer that consumers will actually select model also provided hourly estimates energy equipment on the basis of such of the amount of solar energy available. a sophisticated financial analysis. Pur- The analysis was based on weather data chasing decisions are Iikely to be heav- Ch. II Overview of Onsite Solar Technology 33

iIy infIuenced by first costs, the custom- operating during the next few decades. The er’s estimate of a system’s reliability price of electricity, oil, and gas from con- and convenience, and the skill with ventional sources may change rapidly dur- which the item is marketed. No attempt ing the next few years, and the performance was made, therefore, to anticipate ac- of equipment designed to consume energy tual consumer behavior. The present from these sources may change dramatical- value technique is, however, the most ly as a result. Estimates of the future price of accurate technique available for eval- oil, gas, and electricity vary greatly. And no uating the real cost of energy, and it estimate is certain because of such im- could be used to market energy-related ponderable as the rate of future oil discov- equipment in the future. The major eries here and abroad, the stringency of en- uncertainty in the method is the choice vironmental controls, and political deci- of the consumer’s expected return on sions made by international energy sup- investments, pliers. Given the uncertainties about such a critical variable, it was necessary to com- 4. All systems for meeting the fixed set of pare costs using several different forecasts. end uses were compared as integrated The three forecasts used for most of the systems. This meant, for example, that comparisons in this paper are summarized the performance of solar collectors and in tables I l-l and 11-2. They include assump- the heating and cooling demands of tions that: energy required to meet the heating and cooling needs of buildings were –The cost of electricity and fossil fuels computed on an hourly basis assuming will increase at the pace of general in- that the buildings were operating in a flation (5. s percent in this analysis). realistic set of climatic conditions. (This is called “projection (1 ).”)

While computing the cost of many types of solar energy systems is treacherous be- Table n-2.-Typical Assumed Nonsolar cause of differing estimates of the cost and Electricity Rates in the Year 2000 (1976 $/kWh ) performance of solar equipment which may e become available in the next decade, it also is extremely difficult to establish the cost of Projec- Projec- Projec- tion (1)* tion (2) tion (3) conventional energy systems which may be Albuquerque SF ...... 0244 .0354 .0802 HR/SC ...... 0207 .0300 .0680 Table 11-1.—Assumed Residential Fossil Fuel Boston Prices in the Year 2000 SF ...... 0440 .0638 .1445 (1976 $/kWhJ HR/SC ...... 0557 .0808 .1830 Ft. Worth SF ...... 0269 ,0390 Projec- Projec- Projec- .0884 HR/SC ...... 0294 .0426 .0966 tion (l)* tion (2) tion (3) Natural gas Omaha Albuquerque...... 0.0050 0.011 0.016 SF ...... 0248 .0360 .0815 Boston. ... , ...... 0.011 0.024 0.036 HR/SC ...... 0217 .0315 .0713 Ft. Worth...... 0.0050 0.011 0.016 Omaha...... 0.0037 0.0082 0.012 .Actual 1976 rates. NOTES These average values are representative of the more elaborate #2 Heating oil electric rates! rUCl ure aClual!y used In the computer mode) The model used actual utdlty rates In the region Includlng de. Albuquerque...... 0.010 0.014 0.033 mand charges and decllnlng block rates when these features ap- Boston...... 0.010 0.015 0.034 plied In the region Ft. Worth...... N,A. N.A. N.A. SF = prices charged for single family houses using electric Omaha...... 0.0096 0.013 0.031 heating HR/SC = average rates charged for h(gh rwe apartments and shopping centers Demand charges are Included, based on the . Actual 1976 rates N A = not available estimated peak demands of the bu( Idtngs In each city NOTE A fuel prfce of $001/kWh corresponds to an average monthly fuel An electricity price of $0 02/kWh corresponds to an average elec- b(ll of about $40/month for a single family house In Albuquerque trlc bill of about $70/month for an all electrlc house In Albuquer- using fuel for hot water and heat!ng que 34 . Solar Technology to Today’s Energy Needs

– Energy prices wilI rise at rates predicted —Energy prices will increase by a factor by a Brookhaven National Laboratory of 3.4 by the year 2000. Under this as- (BNL) study. Electricity prices are ex- sumption, the price of oil and gas in pected to rise by about 41 percent (in most cities would be roughly equal to constant dollars) by the year 2000 (to the price of synthetic fuels. Electricity roughly the current marginal cost of rates would increase to $0.07 to $0.10/- electricity from new plants) and gas kWh in all cities examined except prices to increase by 123 percent during Boston, where the price wouId be some- the same interval. (This is called “pro- what higher. * jection (2).”)

SUMMARY OF SYSTEM COSTS FOR CONVENTIONAL BUILDINGS

The increases in energy prices already ex- what above those now made in the cities in- perienced, and anticipation of further involved, since the levelized costs shown re- creases, have accelerated the development flect inflation occurring during the period of efficient energy-consuming equipment. I n when the system is operating. almost all of the cases examined, invest- Table II-3 shows the Ievelized monthly ments in these energy-conserving devices energy payments for houses equipped with were more profitable than investments in several different kinds of gas furnaces, elec- solar energy equipment, and it is always tric heaters, and heat pumps now on the preferable to make a careful assessment of market. The table also indicates the pay- options for conserving energy before design- ments which would result if the performing solar equipment for a building. Careful ance of the equipment is improved. Oil and control of energy consumption will, of gas furnace efficiencies can be increased course, reduce the cost of the solar equip- with careful design of the burners and by ment required to meet the remaining load. reducing flue temperatures. Hot-water heat- The cost of providing energy to single ers can be made more efficient by adding in- family homes in Albuquerque and Omaha sulation. The table shows that investments which use different kinds of energy equip- in these improvements are attractive, even if ment are compared in tables I I-3 and I I-4. In the price of energy remains at 1976 levels all cases, the costs were computed for the (projection (1 )). years 1985-2015. (Most of the original equip- While the heat-pump systems are less ex- ment is replaced during this period, some of pensive to operate than electric-resistance it twice; all of these replacement costs are systems, the benefits of the energy-saving, evaluated in the analysis. ) The numbers heat-pump systems are smaller than ex- shown in the tables are the “levelized pres- pected when a careful life-cycle cost analy- ent value” of monthly energy bills. This sis is used. This is because the heat pumps “levelized” payment is defined to be the are more expensive to purchase initialIy and monthly payment which, if made regularly the expensive compressor elements of heat for 30 years, would result in the same pre- pumps typicaliy are replaced every 8 to 10 sent value, from the customer’s perspective, years. (Analysis in chapter V shows that the as the actual expenditures. The actual ex- comparisons are even less favorable to heat penditures will, of course, vary from year to pumps when the real cost of providing year. The average monthly payments were power to baseboard and heat-pump systems displayed because most consumers find esti- from conventional electric utilities is com- mates of monthly energy payments easier to grasp intuitively. It should be noticed, how- ‘All energy prices cited here and elsewhere In the ever, that the average payments are some report are given In 1976 dol Iars Ch. II Overview of Onsite Solar Technology 35

Table II-3.—Levelized Monthly Energy Costs for Table II-4.—Levelized Monthly Energy Costs for Single Family Houses Not Using Solar Energy* Single Family Houses With Extra Insulation*

Energy projection* ● ● Energy price project ion ● ●

Standard houses* ● (1) (2) (3) (1) (2) (3) With Gas furnace, gas hot 116 173 287 20-percent water, central electric a/c 125 180 302 ITC on energy con- Gas furnace and hot 111 160 265 servation water with improved 121 169 284 equipment efficiency, central elec- Gas furnace, gas hot A 106 153 254 tric a/c water, central electric a/c O 111 154 261 Gas heat, hot water, 122 187 295 Oil furnace and hot A 153 195 380 127 188 297 gas absorption a/c water, central electric O 163 208 402 Oil furnace and hot 179 230 458 a/c water, central electric 204 263 522 Baseboard-resistance A 149 198 399 a/c heat, electric hot o 159 211 423 Oil furnace and hot 163 208 406 water, window a/c 186 237 461 water with improved Heat pump and A 142 183 350 efficiency, central elec. electric hot water 0 161 208 399 tric a/c Gas heat pump and on- A 113 146 173 Baseboard-resistance 177 238 490 site electric generator O 106 133 157 heat, electric hot 206 277 570 (using waste heat) water, window a/c Electric heat pump and 156 203 395 “System operates from 1985-2015 6-inch fiberglass Insulation !n walls, 12 electric hot water 190 249 490 Inches [n celling, storm windows, and doors . ● See table 11-1 Improved electric heat A 146-162 187-203353-367 A = Albuquerque O . Omaha ITC = Investment tax credtt. pump, electric hot water O 173 223 424 ——. used to operate the heat pump compressor “System operates from 1985.2015 is also used to generate electricity. Waste +‘3 !iz.inch.fiberglass Insulation (n walls, 6 lnCheS In Celllng “‘ “See table 11-1 heat from the engine’s cooling system is A = Albuquerque O = Omaha used to supply hot water and supplement puted – the tables reflect electric rates now the heating system. The cost of operating charged in the regions. ) The performance of such a system is expected to be very close to heat pumps can be increased by developing the cost of operating an all-electric house. better compressors, using multiple compres- Table 1 I-5 compares the Ievelized monthly sors, and with other techniques. These improvements can make the heat pump sys- Table II-5.—Levelized Monthly Energy Costs Per Unit in a 196-Unit High Rise Apartment* tems more attractive if the cost of the improvements is low, A 50-percent improve- Energy price projection* ● ment i n heat pump performance is eco- (1) (2) (3) With nomic if it increases heat pump cost by 20 20-percent ITC on percent, but may not be if the cost increase energy con- is 80 percent. servation equipment Table I I-4 indicates the Ievelized monthly Gas heat, gas hot A 51 71 129 costs which result from adding extra insula- water, central electric a/c O 57 76 129 tion and storm windows and doors to the houses examined in table 11-3. It can be seen that this investment is attractive even if energy prices do not increase in real terms. Table I I-4 also shows the costs which could be expected from a system that provides all energy needs, including electricity, by burning natural gas. This is a “total- energy” system using a gas-fired heat pump .System operates from 1985-2015 “ “See table 11-1 to provide heating and cooling; the engine A = Albuquerque O . Omaha ITC = Investment tax credit 36 ● Solar Technology to Today’s Energy Needs

costs borne by the tenants of a high rise tem, which provides all needed heating, apartment, assuming that all energy equip- cooling, hot water, and electricity. Heat is ment was financed with the rest of the build- received from the engine by placing a boiler ing. It is assumed that capital costs are simp- in the exhaust of the diesel. Some of this ly included in the building rent. The ad- thermal energy is used to operate a low- vanced system shown in this case assumes temperature heat engine when electric the use of a diesel engine, total-energy sys- demands are high.

TECHNOLOGY OVERVIEW

PASSIVE SOLAR ENERGY SYSTEMS shutters which can be adjusted to reflect outside heat or preserve heat in the building The techniques just described for conserv- interior as needed. Carefully designed in- ing energy in buildings can be supplemented terior ventilation can amplify the heating by carefully designing buildings to: (1) max- and cooling available from such systems. imize the amount of solar energy absorbed These systems may well be able to pro- during winter and (2) minimize the heat ab- vide space-conditioning at a price com- sorbed and maximize natural convective parable with or lower than the price of solar cooling during the summer. Such tech- energy from the active systems examined in niques, which have come to be called “pas- greater detail in the remainder of this sive” solar systems, are principally skillful chapter. It is often difficult, however, to architecture and landscaping; many of the determine the real incremental cost of pas- most attractive techniques were in wide- sive solar equipment. (For example, how spread use in building designs before low- does one account for the fact that the addi- cost energy sources created a situation tion of a greenhouse may make a building a where buildings were designed without at- more pleasant place to Iive?) While passive tention to energy consumption. systems are usually extremely simple, and the principle of operation easily understood, Energy requirements can be reduced by analysis of their performance is only begin- paying careful attention to the orientation of a building on its lot, the location of trees, ning. This study did not attempt to perform a detailed examination of these systems. the use of awnings or overhangs which permit sunlight to enter a room during the winter but shade the window during the ACTIVE SOLAR SYSTEMS summer cool ing season, and other basic architectural features. Window size and A Survey of Components location are particularly important. Large Active solar systems require components south-facing windows can provide over sO which are distinct from the basic building percent of the heating requirements of a structure. The systems consist of three basic room, even in climates with severe winters. elements: Some passive buildings have covered the southern face of the house with a green- 1 A solar collector exposed directly to house. The performance of such systems the Sun which converts light into a can be improved by using thick walls and heated fluid or, in the case of solar floors to store heat in the building’s interior cells, converts light directly into elec- and by using movable insulation, such as tricity. Ch. II Overview of Onsite Solar Technology ● 37

2. An energy-storage system which stores tors that follow or track the Sun during the excess energy available during sunny day. Nontracking or flat-plate collectors periods for use when direct sunlight is have no mirror surfaces or moving parts and not avaiIable. thus have the advantage of simplicity and reliability. They can be integrated into most 3. An energy-conversion system which architectural styles without being obtrusive. converts the heated fluids into mechan- Flat-plate systems can capture “diffuse” ical energy or electricity through a gen- sunlight (light reflected from the ground or erator using a turbine or piston engine. the clouds), which most focusing collector Not all solar systems will use storage or systems cannot do. energy-conversion equipment. Concentrating collectors that track the Sun can generate much higher temperatures than flat-plate collectors and therefore are SOLAR COLLECTORS more valuable for systems that use heat The design of attractive, reliable, low-cost engines or for some types of industrial proc- collector systems is critical to the future of esses. They also can provide somewhat solar energy since the bulk of the cost of more output than flat plates. Few tracking solar systems usually is attributable to the collectors are now on the market, and most collectors and they are often highly visible. are relatively expensive. The potential for The collectors must cover areas large savings in production costs is large because enough to collect the solar energy required, they can use thin reflecting surfaces or and these areas can be substantial since, at plastic lenses over most of the area covered. its peak, sunlight provides only about 1 kilo- Whether the cost of maintaining the equip- watt (kW) per square meter. The actual out- ment required to keep them pointed toward put of a square meter of collector, however, the Sun offsets the increased output is not is much less than 1 kW. A typical photovol- now known and cannot be determined with- taic coIIector can convert only about 10 per- out operating experience. Collector alter- cent of the incident sunlight energy into natives are discussed in greater detail in electricity, and the average intensity of chapter VII I. sunlight (averaged over all hours of the year – day and night) is typically about one- fifth of the peak solar intensity. As a result, SOLAR ELECTRIC SYSTEMS about 50 square meters (540 square feet) of EIectricity can be generated directly from these collectors (connected to an appro- sunlight in two ways: (1) by heating fluids to priate storage device) are needed to provide operate heat engines (such as steam tur- a continuous kilowatt of solar electricity. (A bines) that turn electric generators; and (2) continuous kilowatt wouId keep ten 100- by using photovoltaic cells (solar cells) that watt light bulbs burning. ) Providing this con- are solid-state devices made from the same tinuous kilowatt, therefore, means that so basic materials as transistors. Both ap- square meters of some kind of material must proaches can be used to produce electricity be supported and made secure against ad- alone or to provide both electricity and heat verse weather. Thermal collectors, used to in a “total energy” or “cogeneration” provide hot water for heating or other pur- system. poses, typically are 2 to 4 times as efficient as the photovoltaic systems just described Heat Engines and require a proportionally smalIer area to Heat engines operate by taking a high- provide a continuous kilowatt of thermal temperature fluid (which may be steam or a output. heated gas) and converting some of the Two types of collectors are now on the fluid’s energy into mechanical power or market: nontracking collectors and collec- electricity, cooling the fluid in the process. 38 . Solar Technology to Today’s Energy Needs

The fluid which emerges from the engines tend to be bulky and expensive in small can still be quite hot, however, and can be sizes. used for space-heating or other applications. A number of heat-engine designs also are A number of heat engine designs even- available which are able to operate at the tually may be used in solar installations, but opposite extreme of temperatures. Brayton- the small engines now on the market which cycle devices, similar to the gas turbines are compatible with solar energy applica- used in aircraft engines, may be practical if tions are quite expensive. Small gas and collectors can be developed which are capa- diesel engines cannot be easily used in solar ble of producing temperatures of 1,4000 For systems since they require heat applied in- more at reasonable cost. Such systems will side a cylinder; most engines designed for require the use of heliostat fields or other solar applications must be able to operate two-axis collectors. Relatively little work has from heat applied to some external surface been done on small, high-efficiency, Bray- (e.g., to the boiler of a steam turbine). ton-cycle devices, however, although several concepts are being pursued in connec- Technology is available, however, for tion with research on gas-powered heat designing engines capable of operating from pumps. many different kinds of solar-heated fluids. The most straightforward approach is to use Small engines based on the Stirling or the a solar coIIector to produce steam (typically Ericsson cycle may eventually prove to be at temperatures between 4000 and 1,0000 F) the most attractive devices if high tempera- and use this steam in standard steam tur- tures are available. These engines may be bines or piston engines. The engineering of able to achieve efficiencies as high as 50 to large steam turbines (100 megawatt and 60 percent at relatively modest cost, but larger) is very advanced, and efficiencies much more development work is required above 40 percent are possible with high- before reliable systems will appear on the temperature steam. Much less work has market, It is unlikely that any engines based been done on smaller steam engines in re- on these two cycles will be available com- cent years, however, and designs tend to be mercially for several years, and they will be somewhat archaic. quite expensive unless mass produced. The use of steam, of course, means that a In addition to the systems just described, high-performance tracking-collector system a large variety of devices capable of con- must be used, and a storage device must be verting thermal energy to electrical and me- developed which is capable of holding high- chanical power are in early stages of devel- temperature thermal energy. It is possible to opment. Chapter IX discusses engine cycles use much simpler collectors and storage de- in greater detail. vices with engines designed to operate at lower temperatures. Water is not a desirable Photovoltaic Systems working fluid at temperatures below 4000 F (and may not be desirable at temperatures Photovoltaic devices, similar to the “solar below about 8000 F). Engines analogous to cells” used to provide power for spacecraft, steam engines have been designed which are can convert sunlight directly into electricity able to operate from fluids at temperatures with no moving parts. As a resuIt, they can as low as 1300 to 1800 F. These engines use be extremely reliable and quiet. The cells freons (similar to the fluid used in refrigera- are not as efficient as the best heat engines, tors) or other organic fluids instead of water. but they can compete in efficiency with The low-temperature systems can be ex- heat engines at lower temperatures (i. e., tremely reliable (they are essentially refrig- 4000 to 5000 F or lower). The main disadvan- erators working backwards), but their effi- tage of the photovoltaic technology at pres- ciency is low (less than 10 percent if fIuids of ent is its extremely high cost. While inexpen- 1500 F are used), and contemporary devices sive heat engines may cost as Iittle as $100 Ch. II Overview of Onsite Solar Technology . 39

to $200 per kilowatt, photovoltaic systems which can be manufactured at low currently selI for approximately $11,000 per cost. One feature of the concentrating kilowatt. (The photovoltaic systems can pro- systems is that it may be economically vide this peak output only in bright sun- attractive to cool the cells with a fluid light, ) Current Federal research programs and use the heated flu id for space-heat- have as their goal a cost for photovoltaic ar- ing or other processes, thereby taking rays of $2,000 per kilowatt by 1982 and $500 maximum advantage of the investment per kilowatt by 1986 (in 1975 dolIars). Photo- in the coIIector. voltaic systems are discussed in detail in 4. Using properly designed sheets of plas- chapter X, tic or glass imbedded with a fluorescent There are four basic approaches to dye to concentrate sunlight reaching achieving a cost reduction for solar celIs: the face of the sheet on the thin edge of the sheet. (Anyone holding a sheet or 1. Reducing the cost of manufacturing sil- rod of clear plastic may have noticed icon celIs, which are the most common how the edge or end sometimes seems photovoltaic devices This requires de- to glow. ) The use of such a concen- veloping mass-production techniques trator would eliminate the need to to replace the inefficient processes now develop a low-cost focusing and track- used to fabricate cell arrays, and it will ing system, but there would be a need require developing inexpensive tech- to find a low-cost dye with the proper niques for producing and slicing silicon optical properties capable of surviving crystals. Silicon is an attractive mater- bright sunlight for many years. ial because it is plentiful and nontoxic.

2. Developing cells based on “thin films” During the last few years, a number of of materials, such as cadmium sulfide techniques have been proposed for using or amorphous siIicon, which can be ap- photochemistry to generate hydrogen and plied directly to glass or other sup- other chemicals directly in solar collectors porting material at very low cost. The with chemical reactors driven by sunlight, main difficulty with the present thin The chemicals produced could then be film cells is their relatively low efficien- stored or burned much like natural gas. cies. Low efficiencies mean that rela- Several preliminary tests have demonstrated tively large areas are required, and the the feasibility of the approach, although the cost of supporting these large areas of efficiency of current processes is quite low, cells may exceed the cost of the cells themselves Competitive thin film cells ENERGY STORAGE AND BACKUP probably will require efficiencies greater than 10 percent. The real cost of solar energy technology cannot be evaluated without considering 3. Using concentrating collectors to focus the cost of energy supplied when direct sun- sunlight on photovoltaic cells, thereby light is not available. The optimum process reducing the area of celIs required for a for maintaining energy availability depends given energy output. A number of cell on the relationsip between onsite users and designs are being developed which are existing utilities and on the eventual cost able to operate in a wide range of solar and performance of various storage technol- intensities. Some of these designs are ogies. Three basic approaches are possible variants of siIicon designs, whiIe others for providing energy in an onsite solar sys- are based on galIium arsenide or other tem during periods when direct solar energy materials, The use of concentrating col- is not avaiIable: lectors replaces the problem of reducing cell costs with the mechanical prob- – Energy can be generated by using fuel lem of designing a focusing collector at an onsite faciIity. 40 . Solar Technology to Today’s Energy Needs

— Electricity can be purchased from elec- ergy during the summer for use during the tric utilities for backup (and possibly winter. sold to utilities when the output of onsite devices exceeds local demand). High-temperature thermal storage is more expensive. Some types of oil can be used to — Energy can be stored in onsite storage store energy at temperatures up to about devices. 6000 F for $2 to $5 per kilowatt-hour. Stor- There are several approaches to storing age at higher temperatures (1 ,4000 to 1,6000 energy at a given site: fluids produced by F) costs $3o to $5o per kilowatt-hour. thermal colIectors can be stored directly, for Electric storage is another option. The example, and electricity generated by onsite only electricity storage systems now com- systems can be stored in batteries or other monly used by electric utilities employ hy- electrical storage systems. It may be desir- droelectric facilities, in which water is able to transmit thermal energy, electricity, pumped into an elevated reservoir when de- or chemicals generated in onsite devices to mand is low and released to generate elec- central or regional storage faciIities. tricity when demand is high. Other storage The lowest cost systems now available for techniques in various stages of development storing thermal energy at low temperatures include advanced batteries, flywheels, (below 2500 F) are simple hot water tanks or magnetic storage rings, and compressed air bins of heated rocks. These systems are so in underground caverns. The only electric- inexpensive that it will be difficult to find storage systems which are Iikely to be com- competitive alternatives, Present storage patible with onsite solar systems in the near costs in such devices range from $0.50 to $5 future will use some kind of battery. per kilowatt-hour of capacity of the device. The choice between storing energy and Some advanced concepts for storing large providing backup energy from some other amounts of low-temperature energy in un- source is very sensitive to the cost of storage derground caverns, aquifers, or porous rock and fuels. I n many cases, it is more attrac- could reduce this cost to $0.10 per kilowatt- tive to burn even an expensive fuel for a few hour or less, The somewhat lower efficiency hundred hours during the year than it is to of these large storage systems partially off- provide all backup requirements from onsite sets the advantage offered by their low ini- storage. Storage equipment is examined in tial cost. detail in chapter Xl, and the cost of different The price advantage of low-temperature kinds of backup is discussed in detail in storage may make it desirable to store en- chapter V.

SUMMARY OF COST COMPARISONS

SOLAR HEATING AND HOT WATER charged for energy from nonsolar energy sources. Moving from city to city, it is impor- Although installations in four cities were tant to notice there is greater variation in examined in detail, this chapter presents the price of electricity than in the amount of only the results from Omaha and Albuquer- sunlight available. Because of this, solar que. Omaha was the least favorable loca- energy is nearly as competitive in Boston tion for solar energy systems of any of the (where there is relatively little sunshine but cities examined in the study because it where energy prices are high) as in Albuquer- receives only average amounts of sunlight que where the reverse is true. and utility electricity and natural gas prices there are relatively low. Albuquerque Solar energy systems designed to provide receives nearly 40 percent more sunlight, domestic hot water and space-heating re- but, like Omaha, is below average in rates quire little more than a simple flat-plate col- Ch. II Overview of Onsite Solar Technology . 41

Iector and a tank for storing the heated by solar energy. (Notice that this is not the water. Since it is often not desirable to run fraction of the heating or hot water load met tapwater through a collector, a “heat ex- with solar energy, but the fraction of all changer” is typicalIy used to transfer ther- energy consumed for heating, hot water, mal energy from the collectors to the water lighting, etc.) When electricity is displaced, circulated to the house. Heat can be provid- the primary energy consumed to produce ed to the building interior by running the electricity from fossil fuels is computed. solar-heated water through radiators or by It is clear that solar hot water systems circulating the water through coils and compare favorably with conventional elec- blowing air over these coils and subsequent- tric systems in both cities, even in cases ly through standard ductwork. where no increase in the real cost of energy Table II-6 shows the Ievelized monthly is assumed, Solar space-heating systems are costs for solar systems designed to provide marginally competitive with the conven- building heating and hot water in Albuquer- tional heat-pump systems only if electricity que and Omaha. (The cost range reflects dif- prices rise as forecast by the Brook haven ferent estimates of the future price of flat- National Laboratory (BNL); they look ex- plate colIectors; the higher costs correspond tremely attractive if prices rise faster than approximately to the price of some equip- the BNL estimate. The solar devices would, ment which should soon be on the market of course, appear more attractive in the case for new installations. Retrofits will probably of BNL price forecasts if investment tax be more expensive ) credits or other incentives are enacted.

The table also shows the percentage of Houses connected together with a ther- the building’s total energy requirements met mal-piping system to a central “seasonal-

Table II-6.—Levelized Monthly Energy Costs for Solar Heating and Hot Water Systems*

Energy price projection ● ● (2) With 20- (3) With 20- percent ITC percent ITC on solar on solar Percent (1) (2) equipment equipment solar Single family houses House with electric heat pump and 156 203 203 395 0 electric hot water (shown for ref- 190 249 249 490 0 erence) Solar hot water 141-147 176-182 174-179 316-321 28 184-191 234-241 232-237 437-442 17 Solar heat and hot water 158-187 184-213 177-201 284-309 48 201-227 245-271 237-260 416-438 29 Solar heat and hot water (300 houses 165-214 184-234 171-211 249-290 65 connected to central ‘‘seasonal” 215-299 237-321 217-285 307-375 76 thermal storage tank)

High rise apartments (cost per unit) All-electric conventional systems 83-84 112-113 112-113 229-232 0 (shown for reference) 83-87 109-113 109-113 215-223 0 Solar hot water (all-electric backup) 84-87 110-114 109-112 218-220 19 85-89 109-113 107-110 203-206 13 Solar heat and hot water (all-electric 87-95 113-120 109-115 212-218 31 backup) 91-104 111-123 105-114 186-196 26 Solar heat and hot water with 57-85 69-97 66-84 116-134 53 seasonal thermal storage 92-127 103-137 90-114 134-157 61

.System operates 1985-2015 . “See table 11.1 A = Albuquerque O = Omaha ITC = Investment tax credit

28-842 0 - 4 42 . Solar Technology to Today’s Energy Needs

storage” facility can be provided with 100 tional building design was chosen for anal- percent of their heat and hot water demands ysis so that the costs estimated would apply at prices not significantly higher than for to a wider range of new and existing struc- isolated solar systems on individual resi- tures. dences. In fact, the seasonal system is less expensive in cases where energy prices are The table also shows the cost of systems expected to increase sharply. capable of providing 100 percent of the heating and hot water needs of the high rise Table I I-6 also indicates the costs of sev- building. In this case, there was no need to eral heating and hot water systems designed connect several buiIdings to a common stor- for use in a high rise apartment. The roof age tank, since the tank for storing thermal area available on the building was not suffi- energy for the apartment was large enough cient to support al I of the collectors re- to achieve the required economies of scale. quired by the heating system examined; it The tank used in the analysis was assumed was necessary to erect racks over the park- to be a commercial steel or concrete tank ing lot for the building to provide the addi- buried under the parking lot. (There is more tional collector area required. Use of these than enough room for such a tank under the racks, of course, added to the cost of the parking lot assumed for the building. ) solar-heating system. It would be possible to design a high rise building with much more Table I I-7 compares the cost of solar- area for collectors, thereby reducing the heating systems backed up with oil and gas cost of solar energy. However, a conven- with the cost of conventionI energy sys-

Table n-7.-Solar Heating and Hot Water Systems for Single Family Houses Compared With Conventional Systems Based on Oil and Gas*

Energy price projection ● ● (2) With 20- (3) With 20- percent ITC percent ITC on solar on solar Percent (1) (2) equipment equipment solar Natural gas used as a backup Albuquerque— Conventional gas system ...... 116 173 173 287 Solar hot water system ...... 121-127 167-173 165-170 268-273 Solar heating and hot water system . . . . 143-172 172-201 164-188 251-276 Omaha— Conventional gas system ...... 125 180 180 302 Solar hot water system ...... 135-142 185-191 182-188 298-303 Solar heating and hot water system . . . . 165-191 207-233 199-221 308-330

Heating oil used as a backup Albuquerque— Conventional oil heat ...... 179 230 230 458 0 Solar hot water system ...... 168-173 210-216 207-212 392-396 18 Solar heating and hot water system (45m 2) ...... 165-194 193-222 185-209 302-326 45 Omaha— Conventional oil heat ...... 204 263 263 522 Solar hot water system ...... 202-209 254-261 252-257 480-486 Solar heating and hot water system (40m 2) ...... 219-244 262-288 255-277 444-466 26

“System operates 1985-2015. ● ● See table II-1. ITC = Investment tax credit. NOTE: In all cases, solar systems are backed up with the fuel used by the conventional system used as a reference Ch. II Overview of Onsite Solar Technology ● 43

terns using these fuels. In Albuquerque, the what difficult to interpret. Solar heating and solar devices will be competitive with both cooling systems backed up with gas com- oil and gas, if prices rise along the BNL pare favorably with conventional all-electric forecasts, and will be attractive in both systems, if BNL price projections are assum- cities, if prices rise more rapidly. An increase ed. The solar systems compare favorably in gas prices which exceeds the price in- with the all-gas conventional systems only if creases forecast by BN L is clearly possible. a rapid increase in gas prices is assumed. An investment tax credit for the solar systems, SOLAR AIR-CONDITIONING however, could eliminate the cost differences in some locations. Three types of solar cooling were simu- lated with the computer model: SOLAR ELECTRIC SYSTEMS 1. A solar-heated fluid can be used to USING PHOTOVOLTAICS replace the burner in an absorption air- conditioner simiIar to conventional air- A simple photovoltaic system can consist conditioners operated by burning of an array of cells connected with an “in- natural gas. verter” capable of converting the direct current produced by the cells into the 60-cycle 2. Solar-heated fluids can be used to alternating current which is compatible with operate a heat engine connected to the electricity provided by electric utilities. (It is compressor of a standard air-condition- possible to use direct current for most lighting unit ing, electric stoves, electric heating, and 3. Photovoltaic devices can generate elec- other purposes with Iittle or no modification tricity which operates a conventional in the equipment –but a building would electric air-conditioner. need special wiring and switching to use direct current, and this possibility will not be Typically, the first two types of solar- examined in detail. ) Onsite storage can be cooling systems require fluids at tempera- provided using batteries, but it is usually tures of 1800 to 3000 F and, as a result, re- preferable to sell excess electricity to the quire higher performance collectors than electric utility rather than storing it onsite, solar heating and hot water systems. Utility storage tends to be less expensive, Table II-8 compares the cost of several and excess onsite energy is typically avail- different conventional and solar approaches able during periods when there is a large de- to air-conditioning. The results are some- mand for utility electricity and the excess

Table II-8.—Levelized Monthly Energy Costs for Solar Air-Conditioning and Heating*

Energy price projection ● ● (2) With 20- (3) With 20- (1) (2) percent ITC percent ITC on solar on solar Percent equipment equipment solar Single family houses

“System operates 1985-2015 “ ‘See table II-1 A = Albuquerque O = Omaha ITC = Investment tax credit 44 ● Solar Technology to Today’s Energy Needs

onsite electricity is particularly valuable to the cell arrays, and that the roof needs no the utiIity. special reinforcement for mounting the arrays. (The General Electric Company has As noted previously, a number of difficult proposed using a photovoltaic array as a legal, regulatory, and rate-setting problems shingle and argues that the devices should will need to be overcome before onsite sys- be given a credit as a roofing material, but tems can be connected to utility grids in no such assumption is used in the calcula- most areas. (There should be no prohibitive tion presented in the table. ) It is assumed technical problems. ) For the purposes of this that backup electricity is purchased at ac- chapter, it is assumed that electric utilities tual commercial rates (including demand purchase power from single family resi- charges) and that utiIities are wilIing to pur- dences at exactly half the rate charged by chase electricity in excess of onsite de- the utility for power and that utilities buy mands at a rate equal to 50 percent of the power from high rise apartment systems at a price charged for electricity, rate equal to 0.4 times the price the apartments pay for electricity. The analysis indicates that cells which Table I I-9 examines a number of flat-plate meet Department of Energy cost goals photovoltaic devices which can be used on ($0.50 per peak watt) will be able to com- the roof of a single family house. It is as- pete with conventional systems, if electric- sumed that a weathertight roof exists under ity prices increase slightly faster than the

Table ll-9.— Flat-Plate Photovoltaic Systems on Houses With Extra Insulation and Storm Windows*

Energy price projection ● ● (2) With 20- (3) With 20- (1) (2) percent ITC percent ITC on solar on solar equipment equipment

Air-cooled silicon arrays ($0.50/watt) A 170 197 187 294 0 196 231 221 364 Air-cooled silicon arrays ($0.50/watt) A 190 215 202 303 and 20 kWh onsite batteries o 217 251 239 378 Air-cooled silicon arrays ($0.50/watt), A 157 177 164 182 and heat-engine backup o 161 178 165 182 (no electric connection) 29 32 38 37 46 37 90 75 100 80

“System operates 19852015 “ “See table II 1 tUse Improved heat pumps A = Albuquerque O . Omaha ITC = Investment tax credit Ch. II Overview of Onsite Solar Technology . 45

projection (2) forecast and some kind of in- Table I I-10 illustrates the cost of fIat-plate vestment tax credit is given to the solar systems used for apartment buildings. The system; the solar systems would almost cer- cost of the electricity from these systems is tainly be competitive with the marginal cost somewhat higher than in the houses since of electricity produced from new plants. special racks need to be constructed for supporting the arrays over parking lots. This The development of 10-percent efficient places an added penalty on low-efficiency thin-film arrays costing as little as $0.10 per systems requiring large collector areas. The peak watt would result in systems able to advantage of using the cells as a building produce electricity at prices somewhat less material, avoiding the cost of supports, is than the silicon systems. The savings are par- clearly apparent by examining the next-to- tially offset by the added cost incurred in Iast example shown in the table. In this in- supporting and mounting the relatively large stance, it is assumed that cells are used to arrays of thin-fiIm celIs. cover the southern wall of the apartments. Development of an efficient fluorescent No credit is given for the weatherproofing dye concentrator system would lead to very achieved by the arrays, but the cost of significant savings, and systems based on mounting and installing the cells is not such designs would be able to provide a charged as a solar-system cost. It can be large fraction of the total energy require- seen that this application is attractive even ments of buildings with arrays covering the though the cells are not mounted at an angle southern roof. Such devices, of course, must which would maximize their output. The be considered extremely speculative at pres- building chosen for analysis again is not ent. well-suited to such applications, since its southern wall can only accommodate cells One of the cases examined in table II-9 capable of providing 5 to 6 percent of the assumes that the house has no connection total energy needs of the building. to the electric utility grid. It has all of its backup power supplied by a gas-fired heat Table 11-11 compares the cost of energy pump and generator. This system will be from a variety of different photovoltaic sys- competitive with the all-electric systems, tems mounted on concentrating, tracking ar- even if gas prices increase significantly fast- rays. It is assumed that the installed cost of er than electricity prices. two-axis tracking devices is approximately

Table 11-10.—Flat-Plate Photovoltaic Systems Mounted on the Roof and

Over the Parking Lot of a 196-Unit High Rise Apartment ● 46 ● Solar Technology to Today’s Energy Needs

Table II.11 .—Photovoltaic Concentrator Systems on High Rise Apartments*

Energy price projection ● ● (2)With 20- (3)With 20- percent lTC percent lTC (1) (2) on solar on solar Percent equipment,, equipment,, solar All-electric system (shown for 83-84 112-113 112-113 229-232 0 reference) 83-87 109-113 109-113 215-223 0 One-axis tracking unit with silicon 164 188 164 261 63 cells (near term) 154 170 147 213 41 Two-axis tracking unit with silicon 120 114 214 37 cells, cogeneration (near term) 125 113 178 42 Two-axis tracking unit with GaAs 85 100 153 cells (low cost) 99 104 108 Two-axis tracking unit with 40- 103 123 113 192 100 percent efficient cell 106 112 92 117 86 Two-axis tracking unit with 40- 81 92 78 79 percent efficient cell, diesel total- 76 87 75 72 energy system for backup Two-axis tracking unit with GaAs A 114 114 92 92 100 cells, 100-percent solar system with o 218 218 176 176 100 seasonal electric storage (low-cost iron-REDOX batteries) and no backup

● System operates 1985-2015. ● ● See table 11-1. A = Albuquerque O = Omaha ITC = Investment tax credit.

$16/ft.2 The cogeneration systems are some- price which may be possible, if the advanc- what more attractive than the flat-plate ed iron-REDOX battery is developed. systems, even though the collectors are It must also be recognized that the eco- more expensive, because a much higher net nomics of the 100-percent solar system prob- efficiency is achieved from the collectors ably could be improved considerably, if (both thermal and electrical energy is pro- more care were taken to optimize the sys- duced). In cogeneration applications, the tem —by examining the detailed tradeoffs very high efficiency celIs do not show major between collector sizes and the size of ther- advantages over the lower efficiency de- mal and electrical storage devices installed. vices — they produce the wrong ratio of elec- Finally, the 100-percent solar systems re- tric to thermal output for the building quire collector areas too large to fit on a chosen for study and excess electricity is typical high rise parking lot. sold at a low rate.

Systems capable of providing electricity SOLAR ELECTRIC SYSTEMS and 100 percent of the heating and hot USING HEAT ENGINES water requirements of the building compare favorably with conventional systems in sev- Solar electric systems using heat engines eral cases. The system designed to provide tend to be somewhat more complex than 100 percent of the building’s energy needs photovoltaic systems and impose a more from the solar equipment is competitive on- difficult set of design decisions. The highly if electricity prices increase relatively temperature fluids produced by the collec- rapidly. The 100-percent solar systems tor systems can be stored for later use in the shown here must be considered rather spec- engine, the engines can have one or more ulative, however, since it has been assumed stages, heat can be extracted from the that electric storage costs only $11/kWh – a engine at different temperatures to meet .

Ch. II Overview of Onsite Solar Technology ● 47

direct heating requirements, and this rela- axis tracking system capable of producing tively low-temperature energy can be stored hot oil at 4000 F. Table II-12 indicates that separately. The electricity produced by the such a system could be attractive only if engine generator can be stored in batteries electricity prices rise relatively rapidly. or other onsite storage faciIities. Hydrocar- Several more ambitious systems were ex- bon fuels can be burned to operate the amined for use with high rise apartments engine when solar heat is not available. and other building types. An organic Ran- Since it seemed unlikely that single family kine-cycle system capable of meeting 100 homes would be equipped with high-tem- percent of the energy requirements of the perature collectors or large tracking dishes, building appears attractive only if thermal- the only heat-engine system examined for energy storage is very low in cost (less than these buildings involved the use of a one- $0.10/kWh) and electricity prices rise rapid-

Table ll-12.—Heat-Engine Systems*

Energy price projection* ● (2) With 20- (3)With 20- percent ITC percent ITC (1) (2) on solar on solar Percent equipment equipment solar Systems designed for use on a well-insulated family house House with gas heat, hot water, and 163 163 260 absorption air-conditioner (shown for 158 158 254 reference) One-axis tracking system with 218 203 235 organic Rankine engine, low- temperature thermal storage only (Albuquerque) One-axis tracking system with high- A 203 185 203 temperature thermal storage o 276 251 280 Systems designed for use on a 196- unit high rise apartment All-electric system (shown for 112-113 112-113 229-232 reference) 109-113 109”113 215-223 Low-temperature organic Rankine 130-179 102-141 102-141 engine with seasonal thermal storage 205-220 149-177 149-177 (flat-plate or pond collectors), 100- percent solar

o 129

Stirling engine system on two-axis 77 tracking collectors (32-percent effi- 107 cient engine), fuel backup Stirling engine system on two-axis 67 tracking collector (47-percent effi- 92 cient engine), fuel backup Stirling engine seasonal storage 140 (high-temperature storage, 47- 217 percent efficient engine)

“System operates 1985-2015. “ “See table 11-1. A = Albuquerque O = Omaha ITC = Investment tax credit. 48 ● Solar Technology to Today’s Energy Needs

Iy. The Stirling engine systems probably are energy needs of the community in Albuquer- the most speculative heat-engine cycles que if high performance engines were used. shown here, but are potentially the most at- Lower performance devices and less sunny tractive. Their performance is roughly anal- regions would require significantly more ogous to the high-performance photovoltaic area than is available from the roofs and systems shown in the previous table. parking facilities, and roads and special areas would have to be set aside for collector fields. It would be possible to greatly COMMUNITY ENERGY SYSTEMS decrease the energy demand in the community if a concerted energy conservation program were implemented. The next cases examined involve systems designed to meet the energy requirements of As in the previous cases, the different sys- a residential community of 30,000 persons. tems are compared on the basis of the The community examined is roughly charges made to the energy consumers in square — about a mile on a side. The distri- the community. Three “conventional” com- bution of building types found in the communities were selected for reference: (1) a munity is summarized in table I 1-13. This community with a mixture of heating and table also indicates that about 0.5 km2 of cooling systems roughly in proportion to the area is available for solar collectors on mixture actually occurring in the area being southern-facing roofs and parking facilities. examined; (2) a community in which all 2 Another 0.25 km would be available if all buildings are assumed to use electric resist- roadways in the community could be cov- ance heating and electric air-conditioning; ered with collectors. This combined area and (3) a community in which al I single fami- would be nearly enough to provide all of the ly houses, townhouses, and low rise apartments use heat pumps. The costs of providing energy to the com- Table 11-13.—Buildings in the munity from a number of different solar- Community of 30,000 and conventional-energy systems are com- Typical Area pared in tables 11-14 and I i-l 5. Results are area available shown assuming that the systems are owned available on roofs and operated by either a municipal utility Number on south- and park- (which is able to finance the project from Of ern roofs ing lots buildings (m’) (mz) tax-exempt bonds) or a privately owned elec- Single family detached tric utility. residences...... 1,864 81,600 81,600 8-unit townhouses . . . . . 232 75,800 150,000 Two conventional cogeneration systems 36-unit low rise apart- are examined: ments. , ...... 72 48,500 103,400 196-unit high rise apart- 1. A diesel-engine system burning gas and ments. , ...... 20 20,000 103,000 using an organic Rankine system oper- Shopping center...... 1 28,800 63,000 Total roof and parking ating from the heat in the diesel ex- lot area...... 2,189 254,700 501,000 haust to increase the performance of Total road surface. . . . 250,000 the electric generation when electricity Total available surface 751,000 demands are high.

Ground area required for 100-percent solar system 2 A steam cycle burning coal in which in Albuquerque hot water is extracted for use in absorp- Area needed (m2) tion air-conditioners and district heat- Parabolic dishes/Stirling engines. 800,000-1,000,000 ing. Photovoltaic concentrator system (two-axis tracking) ...... 1,400,000-1,800,000 In both cases, energy is distributed Pond collectors/ORCS engine. . . . 1,900,000-2,500,000 throughout the community in two ways — as Ch. II Overview of Onsite Solar Technology 49

Table ll-14.— Levelized Monthly Energy Costs Per Unit for a Community in Albuquerque, N. Mex. (Municipal and Private Utility Ownership)

Energy prices increase to level shown by year 2000 (Gas prices in $/MMBtu; electricity in $/kWh) Gas: $3.18 Gas: $4.77 – Gas: $1.46 Elec: $0.0388 Elec: $0.0884 Percent Elec: $0.0271 Gas: $3.18 20-percent 20-percent solar (No increase) Elec: $0.0388 solar ITC solar ITC 1977 mixture of buildings...... 0 90 126 126 226 All-electric resistance heat ...... 0 130 174 174 357 Heat pumps in most buildings ...... 0 125 165 165 325 Diesel/ORCS (gas backup)...... 54.0 127 (160) 140 (173) 132 (164) 93 (225) Coal steam cogeneration...... 41.7 125 (165) 136 (175) 126 (164) 57 (195) Solar steam cogeneration ...... 70.1 150 (203) 156 (208) 143 (192) 58 (208) Solar steam total energy with fossil superheat (coal backup)...... 66.4 144 (193) 150 (199) 37 (184) 55 (202) Solar Stirling (high efficiency, gas backup) ...... 91.4 146 (196) 149 (198) 37 (184) 148 (195) Solar Stirling (low efficiency, gas backup) ...... 90.4 157 (207) 159 (210) 47 (195) 160 (207) 100-percent solar, low-temperature ORCS(60 o-170 o,200 o F)...... 100.0 207 (278) 207 (278) 89 (256) 189 (256) 100-percent solar, low-temperature ORCS (90o-180 o,200 oF) ...... 100.0 252 (338) 252 (338) 230 (311) 230 (311) 100-percent solar, silicon concentrator. 100.0 188 (255) 188 (255) 171 (235) 171 (235) 100-percent solar heating, cooling, and hot water, flat-plate collectors ...... 67.0 157 (213) 166 (222) 153 (205) 191 (244) 100-percent solar heating, cooling, and hot water, flat-plate collectors ...... 67.0 128 (172) 138 (181) 127 (168) 165 (207)

100-percent t solar hot water and heat- pond collectors...... 54.7 140 (175) 155 (191) 147 (181) 210 (244) 100-percent solar hot water and heat- pond collectors...... 54.7 127 (158) 143 (173) 135 (165) 199 (228)

( ) = Private utlllty ownership. ITC = Investment tax credit.

electricity and as thermal energy. Hot and 2. A system which uses solar heaters to cold fluids are sent to each building for boil water and a coal boiler to increase space-conditioning. the temperature of the steam to the “superheated” level, which results In The tables also show the costs of a num- the most efficient steam cycle. ber of solar systems analogous to those previously discussed for use in individual build- No easy interpretation of the results is ings. Two systems not previously discussed possible. It is apparent that most of the solar are systems do not become attractive on a 1 A system based on a heliostat field and strictly economic basis unless the most a central receiver which can provide gloomy forecast of the price of conven- high-temperature steam to a standard tional energy is accepted. with a tax credit steam turbine; and or with municipal utiIity financing, however, 50 ● Solar Technology to Today’s Energy Needs

Table 11-15.—Levelized Monthly Energy Costs Per Unit for a Community in Omaha, Nebr. (Municipal and Private Utility Ownership)

Energy prices increase to level shown by year 2000 (Gas prices in $/MMBtu; electricity in $/kWh) Gas: $2.39 Gas: $3.59 Gas: $1.10 Elec: $0.0329 Elec: $0.0748 Percent Elec: $0.0229 Gas: $2.39 20-percent 20-percent solar (No increase) Elec: $0.0329 solar ITC solar ITC 1977 mixture of buildings...... 0 98 133 133 236 All-electric resistance heat ...... 0 131 174 174 351 Heat pumps widely used ...... 0 130 169 169 326 Central oil heat, electric a/c, grid elec . . 34.9 127 (152) 149 (174) 144 (168) 237 (261) Diesel/ORCS (gas backup)...... 55.8 134 (170) 147 (183) 138 (173) 197 (232) Coal steam cogeneration...... 45.5 139 (183) 150 (194) 139 (181) 173 (215) Solar steam cogeneration ...... 67.7 188 (253) 195 (260) 178 (240) 198 (260) Solar steam cogeneration (fossil superheat) ...... 65.1 177 (238) 184 (245) 169 (227) 191 (248) Solar Stirling (high efficiency, gas backup) ...... 87.5 197 (264) 200 (268) 184 (248) 200 (264) Solar Stirling (low efficiency, gas backup) ...... 85.8 208 (276) 212 (280) 195 (260) 214 (278) 100-percent solar, low-temperature ORCS(60°-170°,200° F)...... 100.0 280 (371) 280 (371) 257 (343) 257 (343) 100-percent solar, low-temperature ORCS(90°-180°,200°F)...... 100.0 371 (495) 371 (495) 339 (456) 339 (456) 100-percent solar, siIicon concentrator with minimum collector area...... 100.0 339 (460) 339 (460) 308 (423) 308 (423) 100-percent solar, siIicon concentrator with extra collector, less battery. . . . . 100.0 296 (403) 296 (403) 268 (370) 268 (370) 100-percent solar hot water and heat- pond collectors...... 60.1 174 (221) 188 (236) 177 (222) 237 (282)

( ) = Private utlllty ownership ITC = Investment tax credit.

a number of very large solar systems are the optimum size and density of a solar able to compete with conventional utility community, costs in Albuquerque and are surprisingly close to the cost of the conventional cogeneration systems, As expected, the solar systems are somewhat less attractive in INDUSTRIAL SYSTEMS Omaha, where the solar energy resource is smalIer, The finaI series of tables examines solar Since the thermal distribution system devices used to provide energy for a large in- adds considerably to the cost of all of the dustrial plant. It is assumed that the pIant community cogeneration systems examined, requires a constant input of 150 MW of ther- it is possible that the community chosen for mal energy and 30 MW of electric energy analysis is too large for an optimum solar throughout the year. The analysis assumes community system. Much more analysis that the factory works on three shifts, but would be required, however, to determine the solar equipment would be more attrac- Ch. II Overview of Onsite Solar Technology ● .51 —.. — ———.——-.——.—.— .—

Table 11-16.—Assumed Conventional Energy Costs for Large Industrial Users, 1976 Dollars

1976 rates, Year 2000 rates, Year 2000 rates, year 2000 rates, energy cost, energy cost, projection (1) project ion (2) projection (3)

Electricity ($/kWhe ...... A .01526 .02190 .0499 0 .01704 .02445 .0557

Natural gas—mils/kWht and ($/bbl oil equiv.) ...... A 2.696 (4.60) 5.869 (10.02) 8.811 (15.04) o 2.365 (4.04) 5.149 (8.79) 7.729 (13.19)

Residual Fuel Oil No. 6—mils/kWht and ($/bbl) ...... A 6.335 (10.81) 8.856 (15.12) 20.703 (35.34) o 5.474 (9.34) 8.025 (13.70) 17.889 (30.53)

Coal —mils/kWht and ($/ton)...... A 2.80 (20) 4.42 (31.55) 9.15 (65.36) — A = Albuquerque O . Omaha

tive if it were assumed that the factory was Three different techniques for financing not operated during the night. industrial equipment were examined:

In general, it is more difficult for solar 1. Financing from a conventional indus- energy systems to compete with the price of try, assuming that 75 percent of the fuels conventionally used by industry. (In- cost was corporate equity on which a dustrial fuel prices are summarized in table 20-percent return after taxes is ex- 11-16. ) Industries can use a wider variety of pected, and 25 percent financed with fuels than residential and commercial cus- bonds; tomers, and electricity is delivered to industry at “bulk rates” which are usually con- 2. Financing from a privately owned util- siderably lower than residential and com- ity; and mercial electric rates The low industrial 3. Financing from a municipal utility (or rates are due principally to the fact that no from low-interest bonds available from distribution system is required, billing serv- some other source). ices are simplified, and large industrial loads tend to be more regular than commercial and residential loads. A variety of different direct solar devices can be used to generate hot water for food The use of solar energy in the industrial processing, textiles, washing, and other and agricultural sectors also is hindered by industrial and agricultural applications. The the high cost of capital used for typical in- cost of operating these systems is compared vestments in industrial equipment. I n many with the cost of conventional industrial cases, industries need to finance a large equipment in table 11-17. It can be seen that fraction of their new plant investments with the least expensive devices are the solar equity and expect high rates of return on the ponds, which may cost as little as $30/m2. investments, Payback times of 1 to 3 years Energy from conventional flat-plate collec- frequently are expected. Widespread indus- tors in industrial applications costs more trial use of cogeneration facilities based on than energy from roof-mounted collectors, conventional fuels also makes it more dif- since field-mounted systems require founda- ficult for solar energy to compete with con- tions, mounting racks, and expensive piping ventional alternatives. networks, 52 ● Solar Technology to Today's Energy Needs Ch. 11 Overview of Onsite Solar Technology ● 53

The table indicates that the pond systems solar energy provided at these temperatures should be able to produce hot water in Albu- costs about twice as much as the solar ener- querque at prices competitive with oil, even gy provided by pond collectors at tempera- if oil prices do not increase. Solar heat in the tures below 2120 F. Table I 1-17 also in- less-favored Omaha climate would start to dicates the cost of solar energy produced at be competitive in 1985 only if oil prices are 3500 F (177 “C). It can be seen that state- expected to increase to $14 to $16 per barrel ments made about the competitiveness of by the year 2000. Virtually all of the solar direct solar hot water production can be ap- hot water systems would be competitive by plied to heat produced at this higher tem- 1985, if the price of oil is assumed to in- perature, if it is assumed that fuel prices increase to $30 to $35 per barrel by the year crease about twice as fast as assumed in the 2000. Municipal utility financing, or some previous statements. Since even the low- other form of subsidized financing, would cost tracking collectors examined cost more make it much easier for industrial solar- per pound than many types of manufac- energy systems to compete. tured products, it may well be possible to reduce solar costs below those shown here. If solar hot water systems are to compete with natural gas by 1985, it must be assumed The cost of several different solar cogen- that industrial gas prices will rise by more eration systems is shown in table I 1-18. Solar than a factor of three by the year 2000 (i. e., cogeneration systems, using small heat to the equivalent of $14 to $16/barrel of oil engines or photovoltaic devices, may be or more). Solar units should be able to com- competitive with conventional fossil sys- pete with the heat generated by burning hy- tems in roughly the same conditions that drocarbons made synthetically from coal, solar hot-water systems were shown to be but would not be able to compete with di- competitive. Presumably, this is because the rect combustion of coal by 1985— unless the cogeneration systems are able to provide price of coal increased to more than $60 per relatively expensive electricity and more ton by the year 2000, a price increase which useful energy per unit of collector area. seems unIikely at present. Three types of solar systems were exam- It must be emphasized that there were ined: few applications where solar energy was competitive with conventional fuels, if the 1. A two-axis tracking system using a thin solar equipment was financed with conven- plastic lens focusing light on a silicon tional industrial-plant financing. The solar photovoltaic cell (waste heat is as- equipment was considered “competitive” if sumed to be collected from each cell at the Ievelized price, assuming private-utility 1800 F and piped to a central storage financing, was equivalent to the Ievelized reservoir). price of energy from conventional sources, 2 A two-axis tracking frame covered with Low- interest “municipal” utility financing an array of mirrors focusing on a Stirl- lowers the fuel cost at which the solar ing engine (waste heat at 3500 F is col- systems become competitive. lected with a piping system).

About 5 percent of U.S. energy is con- 3 A steam system using a field of mirrors sumed by agricultural and industrial proc- (heliostats) focusing light on a central esses at temperatures between 5500 and tower (in this case, the waste heat at 2120 F (6.5 percent, if preheat energy is 3500 F is available at the tower site). counted. ) Relatively simple one-axis tracking CoIIectors can be used to provide proc- One difficulty encountered in reviewing ess heat at temperatures as high as 5500 F the future value of solar-generated heat for (288 ‘C) Collectors for this purpose were industry is that as energy prices increase, in- assumed to cost $80 to $1 40/m 2 [not industries undoubtedly will find many places cluding installation) and, as a result, the where low-temperature heat can be recov- Solar Technology to Today’s Energy Needs

40 Ch. 11 Overview of Onsite Solar Technology ● 55 — ered from existing manufacturing processes than $20 to $25/barrel before solar com- at relatively low cost, possibly narrowing the pared favorably market for solar equipment Conventional cogeneration also will become increasingly It can be seen, therefore, that while a mar- attractive as fuel costs rise. Solar cogenera- ket for solar heat and electricity for industry tion systems were able to compete with con- may develop by the mid- to late-l 980’s, the ventional cogeneration systems used in in- major near-term use of solar energy in these dustry In sunny regions only if It was assum- applications is likely to occur in situations ed that oil prices increase to more than $1 6/- where conventional fuels are not readily barrel by the year 2000 (the more expensive avaiIable or inconvenient to use, or where systems required prices near $30/bbl to com- increased use of these fuels is forbidden by pete) In less-favored climates, it was neces- national standards for air and water quality, sary to assume that oil prices rose to more Chapter Ill FEDERAL POLICY FOR PROMOTING AND REGULATING ONSITE SOLAR ENERGY Chapter llI- FEDERAL POLICY FOR PROMOTING AND REGULATING ONSITE SOLAR ENERGY

Page Table No, Page A Surveyof Policy Options ...... 61 2. The Effective Cost of Solar Energy in Policies That Would Increase the Cost Residential Buildings in Omaha, Nebr., of Conventional Energy Sources...... 61 [¢/kWh]WithaHigh Level of Policies That Would Reduce the Net Cost Incentives ...... 75 of Producing and/or Purchasing Solar 3. Property Tax Rates unselected U.S. Equipment ...... 61 Cities ...... 78 Research and Development Support...... 63 4. Authorizing Appropriations for the Legal and Regulatory Considerations...... 63 Energy Research and Development Policies That Would Establish Foreign Administration, U.S. House of Repre- Assistance Programs Involving Solar sentatives, 95th Congress, Conference Technology ...... 64 Report No.95-671 ...... 109

Programs in Education and Public 5< Authorizing Appropriations for the information...... 65 Energy Research and Development Policy Options From Three Perspectives . . . . . 65 Administration, U.S. House of Repre- Perspective...... 65 sentatives, 95th Congress, Conference Perpsective B...... 67 Report No.95-671 ...... 110 Perspective C, ...... 73 issues ...... 74 Issue I. Federal Tax Laws...... 74 lssue 2. Financing Onsite Solar...... 80 issue 3. Solar lnstallations on Federal Buildings ...... 90 LIST OF FIGURES lssue 4. Use of Existing Grant Programs . . . 96 lssue 5. Proprietary lnterests vs. Public Figure No. Page Dissemination of lnformation ...... 98 I. Effective Capital Costs as a Function of Issue 6. Competition...... 99 Investment Tax Credit...... 76 Issue 7. Consumer Protection ...... 100 2. Effective Capital Costs as a Function Issue 8. Demonstration Programs ...... 101 of Depreciation Schedules...... 77 Issue 9.CoordinationofFederal R&D...... 103 3. Effective Capital Costs With and lssue l0. Priority Given to Decentralized Without Property Taxes ...... 79 Soar...... 104 4. The Effect of Loan-To-Value Ratios lssue ll. Priorities in Solar RD&D ...... 105 on Overall Capital Costs...... 82 lssue 12. DOE Solar Funding ...... 109 5. The Effect of interest Rates on Issue 13. SERi ...... 110 Coverall Capital Costs ...... 83 lssue 14. Staffing Limitations ...... 111 6. Lender Perceptions of Likely impact of lncentive Options on Loan Decisions ...... 85 7. The Effective Cost of Capital to the LIST OF TABLES Government as a Functionof the

Discount Rate Used in Decisionmaking- . . . . 92 TableNo. Page 8. The Effect of Federal Discount Rate l. The Effective Cost of Solar Energy in on the Perceived Cost of Federal Omaha, Nebr., for 20 Percent investments in Three Types of Solar lnvestment Tax Credit [¢/kWh] ...... 72 Installations...... 93 Chapter Ill Federal Policy for Promoting and Regulating Onsite Solar Energy

One of the attractive features of onsite solar energy is that it can be developed and marketed with very little special assistance from Federal or State governments. A small solar industry already exists and the analysis of this paper suggests that a market for unsubsidized equipment may expand rapidly. Solar energy systems are easily compatible with existing institutions: They can be produced by any of a large number of existing industries; financed in conventional ways; built and operated with existing labor skills. Moreover, they will not have a major negative environmental impact. As a result, their introduction will not need to be controlled by an elaborate set of new regulations, legislation, or regulatory agencies— modest adjustments of existing regulations governing conventional heating and cooling equipment should suffice i n most cases. The solar industry may not be able to have a major impact on U.S. energy supplies, however, without coherent and sustained support from Federal and State governments.

Since onsite solar technology will appar- The fact that these policies have the ef- ently develop without Federal incentives, it fect of reducing the cost of fossil and might be tempting to conclude that the best nuclear energy relative to solar energy may policy for the Government to adopt would be largely inadvertent. They have, however, be no policy at all Existing Federal energy produced a situation where a decision to policy, however, will affect onsite solar make no change in policy translates into a energy equipment whether or not an at- decision to continue disincentives to onsite tempt is made to develop a specific policy solar energy. for it. The energy market in which solar tech- Without Federal assistance, the fledgling nology must compete is highly artificial solar industry is likely to grow slowly. Typ- because of the layers of Federal regulations, ically, several decades are required before controls, and subsidies which have accumu- major innovation moves out of a laboratory lated over the years; energy legislation and becomes a commercially marketable adopted during the next few years is likely product. In the case of solar products, there to increase the complexity of these regula- are a number of reasons for delay, Con- tions rather than eliminate them. In many sumer concerns about the reliability of the ways, current policies acting as disincen- technology, about the resale value of tives for on site solar equipment include: buildings with the equipment attached, and about the possible rapid obsolescence of – Policies which maintain the price of novel equipment must be allayed. Investors residential fuels at artificialIy low lev- and financial institutions must be convinced els; that a market of sufficient size exists to justify the investments required for mass – Policies which permit tax advantages to production. Installers, architects, code of- mining and drilling operations and larg- ficials, and equipment designers must feel er utiIity-owned generating faciIities that they have reliable and accurate in- but which do not provide equivalent formation about the costs and performance subsidies to onsite equipment. of the equipment and about techniques for – Policies which subsidize research on evaluating competing designs before they centralized generating facilities with- can seriously consider the options offered out giving serious support to onsite by a novel technology, Insurance companies equipment. must be convinced that risks are acceptable.

59 60 ● Solar Technology to Today’s Energy Needs

As a burgeoning technology, solar energy since different observers will have different faces a uniquely difficult marketing prob- perceptions about the future costs, availa- lem because it requires a large initial invest- bility, and acceptability of different energy ment; that is, the bulk of the money spent sources; moreover, different observers will for solar energy goes for purchasing the attach different values to the environmental equipment rather than paying monthly fuel and social benefits which solar energy can bills. Thus, the attractiveness of solar equip- offer. While there may be disagreement ment is generally only apparent if “life cycle about the desirability of action, however, costing” techniques are used, but such there is little doubt that Federal legislation techniques are currently seldom employed can accelerate the rate at which solar equip- by consumers. ment enters the market, if this is judged to No matter how modest the objectives, be a desirable objective. developing coherent and useful legislation By way of caution, however, it must be re- for onsite solar technology presents a chal- membered that the Government has almost lenging problem. Unlike the Federal pro- no history of intervening in the development grams to develop nuclear fission or fusion of commercial products. While it has a well- reactors where a relatively small number of established role in supporting basic research organizations manufacture or purchase the and in regulating the impact of new technol- facilities, development of an adequate ogies which have become established, it has policy for stimulating onsite solar equip- rarely set about to nurse a specific technol- ment will require the Government to assess ogy out of the research laboratory and into the needs and preferences of large numbers the marketplace. The one noteworthy exam- of groups and individuals, each with its own ple of Federal success in this area is the agri- interests. Units will be built, owned, and cultural extension program which has, on a operated by individuals and organizations continuous basis, transformed university- with skills and expectations that cover a born concepts into routine farming prac- wide range. And, because solar technology tices, Another possible example is the Feder- must be tailored for specific climates, al program to develop a commercial nuclear buildings, and energy requirements, incen- power program, although many in the indus- tives must apply to a large variety of dif- try seem to feel that Federal participation in ferent system concepts. the program has been at best a mixed bless- One of the greatest challenges in designing. ing an effective Federal program in this area Most of the products which have reached will be to insure that the programs deal fair- the commercial market because of Federal ly with the diverse group of individuals and development funding have been serendipi- organizations that may be affected by the tous “spinoffs” from projects sponsored by policy. It will be necessary, for example, to the -Department of Defense or by the Na- find a way to deal equitably with innova- tional Aeronautics and Space Administra- tions originating from organizations which tion. In these cases, the commercialization differ greatly in size. Similarly, it will be process was not a goal of the Federal sup- necessary to insure that policies designed to port program, but rather resulted because affect consumers provide incentives which the Federal contract enabled the company are accessible to persons with low incomes. to develop equipment and expertise needed (It does little good to provide a low-interest to meet a commercial application. Some loan or a tax credit to an organization or in- outstanding examples are the transistor individual unable to provide the downpay - dustry developed by Texas Instruments and ment for a solar device. ) other companies as a result of space and There will, of course, be disagreement defense requirements and the Boeing 707 jet about the types of legislation needed in aircraft which grew out of that company’s regard to onsite solar energy generation design of the military KC-1 35. ,> Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy ● 61

It is important to recognize that there are almost certainly have been designed very dangers associated with overzealous Feder- differently if the Government had had an al participation in the development of com- adequate grasp of the real problems faced mercial products. A poorly designed pro- by builders. gram can interfere with the normal development of business relationships, promote inferior products, encourage the wrong enter- Successfully administering a program for prises to enter the field, and otherwise the commercialization of solar technology, distort the development of normal markets. with its complex matrix of problems and op- It is certainly possible to find examples portunities, will severely tax Federal bu- where Federal efforts to alter existing reaucracies accustomed to dealing with market structures have failed. The “opera- small numbers of well-structured projects. tion breakthrough” program, an attempt to An effective program will require imagina- reshape the home building industry in the tion, flexibility, and a willingness to try new image of the aerospace companies, wouId ideas and live with some mistakes.

A SURVEY OF POLICY OPTIONS

Before turning to a more detailed discus- on foreign-exchange resulting from oil im- sion of the different kinds of incentives ports, and national security risks. available, it may be useful to review the A policy of increasing the cost of conven- kinds of policy options which have been pro- tional energy would clearly not be without posed for promoting and regulating solar problems. Such a policy would create infla- energy, and the Iikely effects of each: tionary pressures and the burden would be borne most heavily by people with low in- POLICIES THAT WOULD INCREASE comes unless some compensating mechanism of repayments can be found. Continu- THE COST OF CONVENTIONAL ing our present course of increasing oil im- ENERGY SOURCES ports, with the attendant balance of payments deficits problems which such policies One of the simplest and most powerful create, can also be inflationary. It is unclear ways to provide incentives to solar equip- how long Federal policy will be able to ment wouId be to increase the cost of con- maintain U.S. fuel prices at their current ventional fuels. This could be done by (a) levels while world prices increase rapidly. removing implicit subsidies, (b) freeing There is reason to believe that it would be prices from controls, or (c) taxing the energy preferable to encourage a gradual increase sources directly. This technique would re- rather than to find prices growing explosive- quire virtually no net Federal expenses and ly during a short interval. would require the least Federal involvement in decisions made by the free market. In- creasing the cost of conventional energy POLICIES THAT WOULD REDUCE THE sources could be justified solely on the basis NET COST OF PRODUCING AND/OR of the need to conserve those resources PURCHASING SOLAR EQUIPMENT which are being rapidly depleted under the current price structure. It could also be Policies designed to accomplish this ob- justified as an attempt to have prices in- jective fall into four basic categories: clude such external costs as environmental damage, social disruption, the indirect drain 1. Providing financial incentives to poten- 62 ● Solar Technology to Today’s Energy Needs

tial owners to encourage them to pur- tising and demonstrating their utility chase solar equipment, thereby (see Issue 3). creating an expanded market and justi- 3. Providing direct incentives to manufac- fying mass production. Techniques for turers of solar equipment in one or accomplishing this include: more of the following ways:

–Giving income tax credits and allow- — Loan guarantees and loan subsidies. ing accelerated depreciation techniques (see Issue 1). * –Tax relief similar to that discussed for equipment purchases (i.e., invest- – Removing barriers to obtaining ment tax credits, or accelerated de- financing for solar equipment (see preciation allowances). Issue 2). –Cost-sharing through direct grants –Encouraging States and municipal- (see Issue 4). ities to exempt solar equipment from property taxes and sales taxes (per- — Encouragement of exports (partic- haps by providing Federal payments uIarly to developing countries). to States in compensation for lost Incentives to manufacturers could be ex- revenues, see Issue 1). tremely useful today, since solar equipment — Permitting tax exemptions for in- is developing rapidly. Manufacturers are come derived from loans for solar understandably reluctant to invest in pro- equipment. duction equipment that they feel may soon become obsolete. This reluctance could be — Enhancing consumer confidence in reduced considerably if they were permitted equipment by developing a system of to “write-of f” manufacturing equipment unified performance standards by over a relatively short period through ac- certifying (and perhaps subsidizing) celerated depreciation allowances. Another testing laboratories (see Issue 7), and problem for firms attempting to market a by ensuring proper training for build- new concept, availability of financing, can ing inspectors. be particularly troublesome for small com- These incentives could have a significant panies lacking established relationships with effect on the perceived cost of solar equip- lending institutions. ment. One potential problem, however, is Designing an effective policy for assisting that although tax incentives would minimize manufacturers of solar equipment will re- Government interference in the free market, quire overcoming a difficult problem. It is they could so reduce the risks of purchasing desirable to ensure that the results of feder- novel equipment that an opportunity would ally sponsored development programs are be opened for fraud through the marketing widely disseminated and utilized. If the of unreliable systems. This prospect could company performing the research is unable be diminished by requiring that all who wish to maintain any proprietary interest in the to qualify for incentives must purchase only product developed, however, it may be re- equipment that meets minimum Federal luctant to invest in production (see Issue 5). standards. A balance must be found between the desire for a free market and a It will be necessary to ensure that no or- need for Government oversight. ganization gains monopoly control over cru- 2. Using Federal purchases of solar de- cial areas of the solar industry and to ensure vices to stimulate the market by adver- that small businesses are fairly treated (see Issue 6). *These numbers refer to the next section of the 4. Providing assistance in developing report, which is organized around several crucial issues and provides a more complete discussion of equipment standards and a testing cap- these topics ability in private testing la boratories.. Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy ● 63

This assistance would be valuable smalI energy generating equipment are fre- because it could help to alleviate concerns quently archaic, and sometimes confusing, about performance and reliability which In some cases, they can present serious bar- have been a major barrier to sales. riers to the use of onsite equipment:

– In some States the owner of an apartment building or shopping center would RESEARCH AND DEVELOPMENT SUPPORT apparently be unable to sell solar-derived energy to clients or customers without filing as a public utility. The Federal support for basic research and de- procedural complexity of operating as velopment of small solar energy equipment a utility wouId almost certainly prevent can clearly accelerate the rate at which new the installation of onsite equipment. types of solar devices reach the market. The investment required to develop most of the — Laws establishing the right of utilities to onsite equipment considered in this assess- own and operate energy generating ment may be consistently smaller than that equipment located in buildings not needed to develop operational systems us- owned by utilities are frequently un- ing synthetic fuels, fusion, or advanced fis- c I ear. sion reactors. As a result, it should be possi- —There is no well-established procedure ble to explore a wider range of small, onsite for ensuring that utilities will provide technologies than if the same amount of backup power for onsite equipment at funds were invested in developing technol- rates which would be fair to all parties, ogy for larger, more centralized equipment. and there are no procedures governing This means that investments can be made in the rates at which utilities should pur- promising, but high-risk projects without chase energy from onsite generating committing large amounts of Federal capi- systems during periods when such facil- tal. ities are generating more energy than is On the other hand, if the Federal Govern- needed onsite. The analysis of the legal ment does not provide the relatively modest aspects of onsite energy equipment funding required for development of onsite which appears in chapter VI of this re- solar equipment, the effect will amount to a port indicates that these utility-related disincentive; that is, the current dispropor- problems are the principal legal and tionate Federal research emphasis on non- reguIatory issues Iikely to require im- solar technologies would place solar equip- mediate attention. ment at a disadvantage in relation to subsidized energy supplies Policy alternatives for dealing with these issues fall into two categories: LEGAL AND REGULATORY 1. Policies designed to clarify the rights of CONSIDERATIONS owners of onsite energy equipment Al- ternatives include:

Policies Governing the Relationship — Exemption of onsite equipment from Between Utilities and Onsite regulation by public utility law (some Generating Equipment definition will be required to distln- guish “onsite” equipment from conventional utility equipment), The vast majority of all energy consumed in the United States is generated and sold by — Establishment of the right of owners electric and gas utilities utilizing large, cen- of onsite energy equipment to pur- tralized equipment. As a result, State laws chase power from existing utilities at and regulations governing the operation of fair rates. 64 ● Solar Technology to Today’s Energy Needs

— Establishment of the right of owners and industrial parks to formulate cove- of onsite energy equipment to sell nants which will protect the sunrights energy to electric utilities at fair rates of al I property owners,

2. Policies designed to encourage utility –The Federal Government could sub- ownership of onsite equipment, to per- sidize training programs for local plan- m it flexibility in joint ownership proj- ners and zoning officials which would ects, and to clarify the difficulties help them to use local regulations more which might arise if a utility owned or effectively to protect sun rights. operated equipment located in build- — The Federal Government could encour- ings not owned by the utility. age States to confirm the rights of in- The techniques available for implement- dividual property owners to negotiate ing these utility policies depend critically on easements guaranteeing Iight and air, whether a statement of Federal jurisdiction as has already been done in Colorado, in this area, such as the one contained in the and help prepare standard forms and proposed National Energy Act of 1977, be- recording procedures, comes law. If Congress finds that “the —A requirement to assess solar energy generation, transmission, and sale of elec- impacts could be added to the Iist of tric energy and the transportation and sale factors which must be considered in of natural gas affect interstate commerce, evaluating federally sponsored or regu- and that adequate and reliable supplies of lated building projects, State govern- electric energy and natural gas are neces- ments could be encouraged to follow sary for the general welfare and national suit. security,”1 the options discussed above can be directly implemented by Federal legislation requiring State utility commissions to POLICIES THAT WOULD ESTABLISH impose the reguIations and procedures rec- FOREIGN ASSISTANCE PROGRAMS ommended. Otherwise, the Federal Govern- INVOLVING SOLAR TECHNOLOGY ment’s power would be Iimited to persua- sion, encouragement, and perhaps the provi- These foreign assistance programs would sion of analytical support and guidelines for have the objective of relieving stress on the recommended policies. world fuel markets by helping to provide the means to use locally available energy. Such programs could also stimulate an overseas Sunrights market for onsite solar equipment devel- Another area which requires some atten- oped and possibly manufactured in the tion is the issue of “sunlights. ” Although United States. Options for Federal policy in- there are presently no Federal laws designed clude: to protect the right of an owner of solar – Ensuring that onsite solar energy tech- equipment to have adequate access to sun- nologies be included in programs for light, the analysis prepared for this study has foreign economic assistance whenever indicated that probably none will be need- appropriate, ed. The Federal Government could, however, facilitate efforts along these Iines be- —Subsidizing the training of foreign na- ing made by State and local regulatory tions in the skills needed to design, bodies. Options include the following: manufacture, and instalI solar equipment. — States could be encouraged to require new subdivisions, commercial malls, —Augmenting the funds available to international lending institutions for ‘ Proposed National ~ nergy Act of 1977, SectIon 501 loans related to solar energy equip- (a) ment. Ch. Ill Federal Policy for Promoting and Regulating Technology ● 65

–Providing a continuing international — Federal assistance for midcareer train- flow of information about products, ing in the problems of designing energy- technical developments, analytical efficient buildings and industrial sys- work, and other progress made in solar tems for architects, engineering con- equipment. sultants, and other relevant groups. This could be done under the auspices —Tailoring the U.S. research program to of existing trade associations. maximize its usefulness internationally whenever this is possible. (For example, —A program subsidizing labor union if a choice between a complex and a training programs designed to develop simple approach is difficult. The deci- additional skills needed to install and sion may be tilted in the direction of operate on site energy equipment. developing a simple system, if international needs are considered. ) Another problem is the fact that most potential customers for onsite equipment wilI not consider it as a serious alternative PROGRAMS IN EDUCATION AND when making purchasing decisions simply PUBLIC IN FORMATION because they are unfamiliar with the approach. This could be remedied to some ex- One of the barriers to the introduction of tent with programs designed to bring life cy- onsite equipment is the shortage of archi- cle costing to the attention of prospective tects, builders, system designers, instalIers, buyers (possibly through the auspices of and operators familiar with the practical lending institutions). It might also be useful problems and advantages of the equipment. to conduct brief training programs for pro- This could be remedied in a variety of ways: fessionals in a position to affect the deci- –A program offering federally funded sions made by their organizations about fellowships and scholarships in engi- building designs and the purchase of energy- neering and architectural programs. related equipment,

POLICY OPTIONS FROM THREE PERSPECTIVES

Selection of a specific set of policies from the next several decades, by gas, coal, and the catalog of options just discussed is not nuclear sources — and without dramatic cost an easy process since such decisions must increases, a dangerously high proportion of be made without the comfort of confident imports, or unacceptable environmental forecasts about the long-term costs of solar risks. Adherents of this position believe that or any other energy technology. Moreover, these sources will last until their use is political judgments must be made about the superseded by a new technology — fusion ultimate value of the potential benefits of being the most commonly mentioned. It is solar equipment which cannot be evaluated assumed that this new technology will pro- in conventional economic terms. The fol- vide energy at prices very close (in constant lowing section discusses three different per- dollars) to those charged for electricity to- spectives on these issues, and presents day. In this view, solar energy would play groups of specific policies which might be only a minimal role; indeed, its only func- chosen to meet each objective. tion would be to serve as a kind of insurance against the failure of fusion to develop into PERSPECTIVE A a usable technology.

It is sometimes argued that the Nation’s From this perspective, it is logical that energy requirements can be met, at least for Federal policies concerning solar energy 66 ● Solar Technology to Today’s Energy Needs

should be limited to: (a) those designed to Programs to Provide Information About Solar eliminate obstacles to development and use Equipment and Education Programs for of the technology, and (b) those providing Designers and Installers for basic research. Such research would be 1. Require that any energy audits con- of a comparatively low priority and could ducted of Federal buildings, and any not be expected to have an impact on the standards established for Federal pur- commercial energy market for many years. chase and rental, include an analysis of The resources committed to the effort the potential contribution of solar ener- would be relatively modest. gy equipment for heating, cooling, and In more specific terms, the following cogeneration. policies would appear to be consistent with 2 Require similar energy audits of all Perspective A. housing and building projects which receive any Federal assistance or which POLICY OPTIONS FOR PERSPECTIVE A are under the jurisdiction of Federal Incentives for Owners of Buildings agencies (this would include public housing, housing repossessed under de- 1. Amend the National Housing Act to faults in FHA, Veterans Administration make it clear that Federal Housing Ad- (VA), and FmHA loan guarantee and in- ministration (F HA) insurance can be surance program s,) given to solar energy projects under Title I (for retrofit of solar devices and 3. Provide midcareer training for public for mobile homes) and under 203b (for officials in a position to make judg- new construction). ments about buiIding designs and ener- 2 Amend the Federal Home Loan Mort- gy-related equipment for Federal buildings. Such training wouId famiIiarize gage Corporation Act (FHLMCA) so that them with solar technologies, design the Federal National Mortgage Associa- alternatives, and techniques for evalu- tion will be empowered to provide a ating their economic merit. secondary market for mortgages and loans covering onsite solar energy 4. Subsidize midcareer training programs equipment. for architects, engineers, and interested builders. 3 Amend the National Housing Act to permit Federal Housing Administration 5 Establish a university fellowhsip and Title I funds to be used as second mort- scholarship program which would pro- gages associated with Farmers Home vide training in areas of science and Administration (FmHA) loan guaran- engineering relevant to solar energy tees. development programs.

4 Provide funds to ensure that techniques 6 Develop standards for emerging solar for measuring the performance of col- equipment and certify testing labora- lector and storage systems are devel- tories. oped by the National Bureau of Stand- ards or its designers and that these techniques are rapidly communicated to Research and Development private testing laboratories. From this perspective, the most profitable 5. Require that all collectors and onsite strategy would be to fund a number of basic storage systems sold be accompanied research projects, looking for ways to dra- by literature clearly showing the equip- maticalIy reduce costs or improve the per- ment’s standardized performance char- formance of solar equipment. An orderly acteristics as measured by reputable procedure would be developed to test the laboratories. many advanced concepts which have been Ch. Ill Federal Policy for Promoting and Regulating Onsite Solar Energy ● 67

proposed before making any decision about Incentives to Stimulate Market large-scale demonstrations. 1. All owners would be given an investment tax credit of 20 percent on quali- Analysis of Policy Options Above fying solar equipment (including heat- 1. Effectiveness. – These policy opt ions ing, cooling, process heat, heat pumps have limited objectives. They would and other applications requiring me- remove obvious impediments to wider chanical drives, and electric genera- use of solar technology, but they would tion). After a 5-year experiment with not greatly accelerate the rate at which these incentives, depreciation sched- solar equipment enters the market. ules would revert to standard and tax Commercial markets could well over- credits would be reduced to 10 percent. take federalIy sponsored efforts. Homeowners and owners of residential apartment buildings, however, would 2. Cost.– Since most of the elements of retain the right to use credits and this policy are regulatory in nature, the depreciation schedules permitted for proposals would cost very little. The industry. Refunds would be made if the only direct expense involved would be credits exceeded tax Iiability. for energy analyses of buildings (investments which should be cost-effective) 2. An easy-to-use computer program and training programs. would be subsidized to evaluate the effectiveness of a variety of solar hot water, space-heating, cooling, and elec- PERSPECTIVE B tric generating systems which may be used on typical building types. The pro- A second view holds that the future price gram would be adjusted for each cli- and availability of all nonsolar fuel sources matic region and would need to be up- is very uncertain and that solar-based tech- dated annually to maintain current in- nology holds real promise of playing a major formation about costs and perform- role in supplying energy in the near future. ance. Such a program could be devel- Those who accept this view also believe that oped by the American Society of Heat- the real price of fossil fuels could increase ing, Refrigerating, and Air-Conditioning by as much as as a factor of 2 or 3 and elec- Engineers (ASH RAE) or some other pro- tricity prices increase by as much as 50 per- fessional society with Department of cent over the next two to three decades and Energy (DOE) support. It should be flex- that the price levels for energy produced by ible enough to reflect local climatic such planned nonsolar technologies as fu- conditions and building costs, and to sion may be high enough to make solar tech- assess the potential of the equipment nology competitive. when used on a number of typical building types. It should provide prac- Thus, they feel that solar technology tical information about anticipated ini- should be treated on an equal basis with all tial and life-cycle costs, which should other promising new energy sources. This be based on a predetermined consumer perspective would require additional Feder- discount rate (perhaps 10 percent for al action as outlined below. homeowner-owned units and higher for commercial systems). Life-cycle costing would be based on an assumed rate of POLICY OPTIONS FOR increase in conventional energy costs PERSPECTIVE B to be established by DOE. The program should be accessible on a time-sharing All of the Policies Discussed Under basis via computer terminal and tele- Perspective A (except as modified below) phone from as many regions as possi- 68 ● Solar Technology to Today’s Energy Needs

grams to determine what funds appro- ble. It should be made simple to under- priated in these areas can be used to stand, easy to operate, and inexpensive subsidize the purchase of solar equip- to run. ment (see Issue 4 for details): 3. The National Housing Act, the Service- –The community development block man’s Readjustment Act, and the acts grants. establishing the Federal National Mort- gage Association (FNMA), the Federal – Housing rehabiIitation programs Home Loan Bank Board, and the Farm- (Section 21 3). ers Home Administration could be grants (Section 302). amended to require that all applica- – Homeowner tions for guarantee, or mortgage in- — Homeowners incentive demonstra- surance, and all mortgages eligible for tion programs (Title IV). repurchase by FNMA or the FHLMA be accompanied by a document showing — Housing finance interest subsidies. that the building has been reviewed for – Funds allocated by the Energy Con- energy efficiency under an approved servation and Production Act for re- procedure which includes assessment newable technologies. of the potential of solar equipment. –Grants administered for energy con- The Federal analysis program described servation by the Administration on above could be used for this purpose. Aging (HE W). This would permit both the prospective borrower and lender to review the cur- —Grants administered for energy con- rent and future costs of supplying ener- servation by the Social Services Ad- gy for the building and to give both par- ministration. ties an opportunity to analyze the value — FmHA grants for improving rural of solar equipment in reducing these homes so that they can meet code re- costs. It would, in effect, be equivalent quirements. to legislation requiring that the efficiency of consumer products be clearly – Grants made under the Public Works shown whenever the items are sold. and Economic Development Act.

4. All Federal buildings, including defense –Any other grant programs which the installations in the United States and Administration feels might be used to abroad, and all buildings operated un- purchase solar equipment. der Federal auspices (e.g., public housing, repossessed housing) wouId be re- Incentives for Manufacturers viewed to establish the cost effectiveness of solar equipment. Funds 1. Allow qualifying manufacturers of so- would be provided for retrofit installa- Iar equipment a 20-percent tax credit tions wherever cost-effectiveness was and 3-year depreciation allowances on established. The Administration should machinery used in producing solar be instructed to determine the circum- energy equipment. These incentives stances under which existing appropri- would apply to equipment purchased ations to subsidize operating costs of during the next 5 years. federally owned buildings and build- 2 Require the administration to conduct ings operated with Federal subsidies a study that would evaluate the desir- could be diverted to capitalize solar abiIity of a variety of alternative cost- equipment under current legislation sharing programs which would be effec- and regulations. tive in subsidizing manufacturers’ rele- 5. The Adminstration should be required vant research in solar energy, which to examine the following grant pro- could be made available to the public Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy ● 69

in some form, and yet at the same time ACTIVE SPACE-HEATING SYSTEMS protect the patentabiIity of devices de- AND SOLAR WATER HEATING veloped in part with private funds. A number of advanced collector designs 3. Measure cost sharing in terms of the (used both for heating and air-conditioning) fraction of a company’s total assets remain in preliminary stages of develop- which it is willing to make available for ment. Devices include improved plastics for Federal cost sharing (instead of requir- inexpensive colIectors, air-inflated collec- ing smalI companies to compete direct- tors, nontracking concentrators, tubular col- ly with larger concerns in total dollars lectors with and without simple concen- available for cost sharing). trators, simple booster devices, one-axis tracking devices using mirrors or lenses, and 4 Subsidize the development of a com- a variety of other systems. puter model which would facilitate the analysis of the detailed performance of SOLAR COOLING a variety of different onsite solar devices attached to realistic building Solar cooling is not a commercial technol- and industrial loads. Ensure that the ogy but a number of different concepts are widest possible group of system design- ready, or nearly ready for demonstration. ers and engineers have access to the These include advanced absorption, adsorp- program, (An attempt should be made tion, and Rankine cycle devices and inte- to ensure that existing work in this area grated total energy systems with fossil fuel is not duplicated. The Canadian Gov- used as a backup. ernment, for example, has apparently developed a similar program for use by AGRICULTURAL AND INDUSTRIAL Canadian designers). PROCESS HEATING

Research, Development, and A number of commercial products are Demonstration (RD&D) available in the lower and intermediate temperature ranges. A balanced program of research, develop- Demonstrations in this area shouId in- ment, and demonstration should be devel- clude: oped and carefulIy integrated with the requirements of the industries which will — Drying for agricultural products; manufacture, install, and support the equip- — Desalinization; ment developed. The program should in- cIude the folIowing areas: – Process water for washing, textiles, paper, food processing, and other IOW- PASSIVE HEATING AND COOLING temperature applications; and

Work needs to be done to design and — Irrigation pumping, make instrumented tests of buildings matched to a large variety of climatic condi- Research work would include the devel- tions Other research topics in this area opment of inexpensive collectors for low which would benefit from additional work (150° to 250° F) temperature, intermediate include: temperature (250° to 500°F) and high temperature (greater than 5000 F) applications. ● Computer simulations of passive building designs. THERMAL STORAGE ● Studies of retrofit potential of passive buildings, A variety of techniques have the theo- ● Demonstration of passive facilities for retical potential for providing large amounts livestock, storage, and other nonresi- of thermal storage at very low cost. Devel- dential application opment of such technologies would remove 70 ● Solar Technology to Today’s Energy Needs

many of the problems faced in providing –Advanced research on amorphous backup power for solar energy devices. It silicon, thin film materials (e. g., CdS, III- should be possible, for example, to build IV heterojunctions, organic substances systems capable of providing 100 percent of and dyes), amorphous silicon, poly- the heating and hot water requirements of crystalline silicon, concentrator cells apartment buildings or clusters of houses us- (GAA1As, multifunction cells, high effi- ing large tanks of water (with earth pro- ciency silicon thermophotovoltaic de- viding the principal insulation), ponds, vices, interdigitated back contact cells, trenches full of hot rock, aquifer storage of vertical multifunction cells, etc.). Basic hot water, storage in in-situ rock, and other research on semiconductor properties techniques. Research in more advanced of interesting materials. thermal storage systems (multiple tank, salt –Systems analysis and engineering of gradient, phase change, organic and in- control systems for practical applica- organic chemical reaction devices, etc. ) is tion, installation problems, mounting also needed and much work remains in- racks, cleaning, cogeneration studies complete. and designs, heat exchange designs, SOLAR THERMAL ELECTRIC plumbing, etc.

work needs to be done on development –Silicon solar array technology (pilot of collectors, integration of solar devices plant for polysilicon production, full- with end-use equipment, improved heat- scale demonstration of advanced crys- transfer systems, receivers, heat engines, tal growing and slicing machinery, subs i- and many other components which would dizing design of large-scale fabrication increase design flexibiIity and reduce costs. and production facilities, advanced encapsulation, etc), Development of low-temperature Ran- kine engines, high-temperature Stirling and —Concentrator development (unique Brayton cycle engines, and improved small problems associated with cell attach- steam cycle systems is needed. Research in ment, cogeneration, heat rejection) for advanced materials (particularly ceramics) a range of concentrators including: dye would be useful for both colIector and en- concentrators, lens, and mirror systems. gine designs. Work on systems integration needs to be DISSEMINATION OF RESULTS done to identify promising concepts in a Ensure that results of Federal RD&D pro- broad range of potential applications of grams exploring technology for heat en- smalI and intermediate size. gines, thermal and electric storage, collector Research on electric storage systems is a designs, and other subsystems which can be critical factor. Work is needed on a number used in onsite solar energy equipment are of advanced Iead-acid, high-temperature, widely disseminated to the diverse com- aqueous, and REDOX batteries, as welI as in munity of institutions and individuals work- mechanical storage concepts such as fly- ing on onsite solar equipment. wheels, underground pumped hydro, and others. Thermochemical storage systems DEMONSTRATION AND RESEARCH STRATEGY could greatly reduce the cost of storing and Develop and propose a program for the transporting solar energy for use in thermo- demonstration of a comprehensive spec- electric systems and in direct high-tempera- trum of onsite solar energy systems. This ture process applications. would include (but not be limited to) the PHOTOVOLTAICS following:

Areas where research would be useful in- — A detailed plan for the demonstration cIude: of the range of solar thermaI and solar Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy ● 71

electric facilities from existing simple Underwrite the testing of solar equipment

hot-water and heating systems to larger, developed by small companies, such testing more complex, and perhaps more ex- to be conducted in Federal or private lab- perimental devices oratories. —A systematic program for developing Foreign Assistance and demonstrating a large number of subsystem technologies which are ap- 1. Ensure that programs developing priori- plicable to small onsite units but which ties for Government-supported re- could be enlarged or aggregated for search and federally sponsored studies larger systems. For example, concen- include an assessment of the potential trating collectors developed for onsite for overseas sales. applications could provide valuable in- 2 Encourage the development of skills formation on designs that would be use- related to solar energy in developing ful in larger facilities Smaller demon- nations by providing fellowships as a strations would permit a greater variety part of an economic assistance proof technologies to be tried. gram, – A strategy for identifying intermediate 3 Encourage and expand joint research and long-term markets for onsite solar ventures with other governments and energy systems. The plan shouId exam- international organizations engaged in ine a variety of potentiaI applications, solar energy research. the significance of regional variations in climate, energy prices, and other fac- 4 Augment U.S. contributions to interna- tors. tional lending institutions with the objective of encouraging onsite solar A fixed sum should be set aside with the energy facilities in developing nations. single purpose of funding innovative small- scale energy technologies that show prom- 5 Provide foreign aid in the form of tech- ise These monies would be distributed as nical assistance for demonstrating on- direct prizes or grants to all types of inven- site solar systems in less-developed tors in typical amounts of $50,000 to countries $100,000 The selection of these projects 6 Any proposal for foreign economic should be performed by panels of qualified assistance involving energy must con- experts drawn from a broad cross-section of sider onsite solar equipment on an equi- equipment developers and designers, in- table basis. Training should be provided cIuding, among others, Independent inven- for United Nations, Agency for lnterna- tors, manufacturing firm researchers, univer- tion Development, and Peace Corps of- sity engineering and science staffs, con- ficials planning such programs. Outside suIting engineers, and personnel from Gov- experts in this area should be utilized to ernment laboratories Application pro- facilitate a review of proposals. cedures should be as simple as possible to encourage broad participation; the program Policies Affecting Public Utilities should be widely advertised; and winners shouId be announced with fanfare, Assuming that involvement in regulation of public utiIities by the Federal Govern- Develop a system to subsidize proposals ment has been established as a legitlmate made by smaII organization. This might in- activity under the “interstate commerce cIude a procedure by which brief submls- cIause‘‘ of the Constitution, the folIowing sions from quaIifylng small businesses policies could be established by Federal wouId be screened for InitiaI technical mer- Iegislation. it. SmaII grants might then be awarded to assist them in developing the proposaI. 1. No organization which generates less 72 ● Solar Technology to Today’s Energy Needs

than 5 MW of thermal or electric ener- 4. Any studies conducted by utilities to gy will be regulated as a public utility determine fair pricing policies for sell- unless this status is desired by the ing electricity and for purchasing elec- organ i z at ion, In the latter instance, tricity from industrial “cogenerators” conventional reguIatory procedures must be expanded to include an anal- wouId apply. The nonregulated organi- ysis of the costs of supplying backup zation wouId be permitted to generate power to a variety of types of onsite and sell energy to all consumers in its solar electric generating faciIities. immediate area, without Iimitations on’ the prices charged or income earned. A Effectiveness study should be commissioned to determine if this size threshold should be in- It is always somewhat perilous to forecast creased. the impact of any program for providing tax subsidies since consumer behavior can be 2. No organization which generates less unpredictable. Table I I l-l indicates the ef- than 5 MW of thermal or electric ener- fect of a 20-percent tax credit on the per- gy shall be required to obtain a cer- ceived cost of solar energy provided by a tificate of convenience and necessity variety of different types of solar equip- from local utility regulatory commis- ment, assuming that consumers utilize a life sions in order to construct a plant cycIe costing technique to determine aver- (unless it has asked to be regulated age energy costs. It can be seen that the tax under existing utiIity statutes). credit would have the effect of reducing the 3. The Administration should be in- cost of solar energy by 0.5¢ to 3¢/kWh. The structed to examine the Sherman and more the solar system costs, the greater the Clayton Antitrust Acts and the Public tax credit and the greater the effective Fed- Utility Holding Company Act to deter- eral subsidy. The table also shows the cost mine whether they prevent utilities of the subsidies to the Government as a re- from owning onsite energy equipment. suIt of loss of tax revenues. The direct costs If they do so, amendments should be shown, however, significantly overestimate proposed which would remove such the net cost of the subsidies because extra barriers. tax revenues will result from production in-

Table 111-1 .—The Effective Cost of Solar Energy in Omaha, Nebr., for 20 Percent Investment Tax Credit [¢/kWh] — — 20 percent Direct No Investment Federal

Incentives Tax credit subsidy ● — Solar hot water ...... 2,0- 4.2 1.4-3.3 0.6-0.9 Solar heating and hot water...... 3.0- 7.7 2.0-6.6 1.0- 1.1 Heating and hot water with seasonal storage . 3.8- 6.9 2.5-4.7 1.3-2.2 Solar heating hot water and cooling ...... 6.0 4.0 2.0 Solar Photovoltaic electricity...... 3.8-11.8 2.8-9.1 1.0-2.7 —..

‘This IS the effective cost of the subsidy to the Government rellting from the tax revenues because of the tax credits It IS calculated assuming that the Government applles a 10 Percent discount rate to future costs (See text )

Assumptions 1985 startup of equipment The price ranges reflect the cost differences expected in the variety of resldential equipment see Volume II Chapter IV Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy Ž 73

creases by businesses manufacturing and in- 1. All of the policies discussed under stalling solar equipment, and from increased Perspective A and B except as strength- sales in supporting industries, such as the ened below. manufacture of glass and primary metals. 2. All owners would be given an invest- This revenue would at least partially offset ment tax credit of 20 percent on qual- the direct revenues lost because of the ifying solar equipment (including heat- credits I t a dolIar is spent on solar equip- ing, cooling, process heat, mechanical ment manufactured in the United States drive, and electric generating devices) rather than on imported oil, the U.S. gross and would be permitted to depreciate national product (GNP) could be increased solar equipment over a 5-year interval, by $2 to $5 Since the average Federal tax These incentives would continue until revenue per dolIar of GNP is about 20 per- Congress determined that they were no cent, an incentive which encouraged a dol- longer required to ensure the competi- lar Investment in solar equipment could tiveness of solar equipment. yield as much as $().40 to $1.00 in added Fed- eral tax revenue Since this revenue would 3, The income from all loans made for be obtained close to the time when the sub- solar equipment would be exempt from sidy was granted, its “present value” to the Federal taxation. Government would be high. 4. All manufacturers of solar equipment Reducing the price of solar equipment would be given an investment tax credit also would be expected to expand sales and of 20 percent on qualifying manufac- thereby encourage the introduction of mass turing equipment over a period of 5 product ion equipment in technologies years. These incentives would continue where such equipment can be used effec- until Congress determined that they tively. were no longer required to ensure the competitiveness of solar equipment.

PERSPECTIVE C 5. Federal purchases of onsite solar energy equipment would be required for ex- A third perspective is an extension of the isting and new Federal buiIdings con- view just discussed (Perspective B). It constructed with Federal support, in all tends that the cost of energy could soon cases when it could be shown that the climb rapidly because of increasing com- technology would be cost-effective petition for limited supplies. In this view, the based on a low discount rate (e. g., 3 per- virtues of solar energy — notably its benign cent) and a high assumed increase in impact on the environment, its desirable im- the cost of conventional energy, pact on labor, its impact on reducing com- 6. petition on world energy supplies, its ability FHA minimum property standards would be required to include onsite to avoid monopoly ownership of energy solar equipment whenever an analysis sources, and its potential for reducing the demonstrated that risks of climatic change and nuclear prolif- the equipment would be cost-effective on the basis of eratlon — merit an aggressive promotional approved analytical techniques dis- program, even if the technology is not ex- cussed previously. pected to become fulIy competitive in con- (As a possible ventional economic terms. variant of this approach there might be a provision for subsidized interest rates to cover the incremental cost of solar POLICY OPTIONS FOR equipment. ) PERSPECTIVE C 7. Utilities would be required to inform all An example of the policies which would residential and small industrial and be added under this perspective include: commercial customers of the savings 74 . Solar Technology to Today’s Energy NeedS

they might realize by instalIing a varie- Research and Development ty of different types of onsite solar The development of solar energy equip- equipment. The utilities also would be ment under this approach would be ag- required to provide installers and finan- gressively pursued as a major national cing for any projects selected by the priority. The basic categories of projects owners of the buildings. The utility receiving support would be the same as would be reimbursed with charges add- those discussed under Perspective B, but ed to the owner’s bilI over a 10-year funding would be given to a broad range of period. (This is similar to the program projects, marketing programs would be ac- for insulating buildings proposed in the celerated, and emphasis placed on both National Energy Plan. ) near-term and long-term approaches Part of 8. The price of electricity would be raised the price of an accelerated program, judged to a rate which reflects the marginal to be acceptable because of the priority cost of providing electricity from the given the undertaking, would be an increase most recent plant placed online. And in funds wasted on designs which are even- the price of oil would be raised to tually overtaken by better approaches. Pro- refIect the cost of adding additional oil ponents of this point of view argue that if supplies. The funds generated by the the United States were willing to make a taxes required to do this would be redis- multi bill ion dolIar commitment to a project tributed in the manner proposed by the to put man on the moon, a commitment of National Energy Plan. similar size would be justified to develop safe and reliable solar energy equipment. 9 It would be determined that the development of low-cost solar coIIection, Analysis conversion, and storage equipment is a major national priority. An aggressive The incentives discussed in this perspec- research and marketing program with tive will, as expected, have a greater effect ambitious goals for cost reductions and in reducing the cost of solar energy per- installed capacity would be funded at a ceived by solar equipment owners, and will rate which would reflect the urgency of cost the Government more to implement. the priority given Table I I I-2 indicates the impact of a group of policies which consist of: 10, A separate section of the Small Busi- ness Administration would be established solely to guarantee loans made – A 20-percent investment tax credit, for manufacturing equipment used to produce solar equipment. –A 5-year depreciation allowed for all solar equipment, and 11. Environmental legislation would be strictly enforced, conventional power- – Exemption from property taxes plants held to strict safety standards, and proposals for nuclear waste dis- It can be seen that these credits reduce posal be subjected to exhaustive ex- the effective cost of residential solar energy aminations. by 1.5¢ to 6¢/kWh

ISSUES

ISSUE 1 How much would such policies cost the taxpayers? What changes in the Federal tax laws would be the most effective in encourag- The tax laws can provide powerful incen- ing private investment in solar equipment? tives for the use of solar equipment without Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy ● 75

Table ill-2.—The Effective Cost of Solar Energy in Residential Buildings in Omaha, Nebr., [¢/kWh] With a High Level of Incentives

Direct No Federal Incentives Incentives* subsidy**

Solar hot water ...... 2.0- 4.2 0.8-2.0 1.6-2.2 Solar heating and hot water...... 3.0- 7.7 1.1-4.1 1.9-3,6 Solar heating and hot water with seasonal storage. . . Solar heating and hot water with seasonal storage. . . 3.8- 6.9 1.3-2.9 2.5-4.0 Solar heating, cooling, and hot water ...... 6.0 2.2 3.8 Solar photovoltaic electricity...... 3.8-11.8 1.2-5.7 2.6-6.1 ——.

. Fd Incenl[ves consist of a 20 percent Investmen! tax credit, an allowed 5 year deprec[at[on schedule, and exemption from property tax

“” This IS the effective cost of the subs!dy to the Government resultlng from the tax revenues because of the tax credits It IS calculated assuming that the Government applies a 10 percent discount rate to future costs (See caveat In text )

Assu mptlr)ns 1985 startup of eqwpment See volume II for detads of systems analyzed

the need for major Federal intervention in 2. Accelerated depreciation allowances. the operations of the free market. Several Accelerated depreciation allowances alternatives are possible: wouId be of greatest interest to corporations, utilities, and individuals in 1. A direct income tax credit. Such credits high tax brackets. No individual is pres- wouId allow the taxpayer to subtract a ently permitted to depreciate equip- fixed fraction of the initial installed ment in his own home, although equip- cost of soIar equipment from his in- ment installed in the home by a com- come tax Since these credits are deduc- pany which sells energy could depre- tions from taxes rather than from in- ciate the equipment. come, they wouId apply equalIy to al I applicants provisions must also be The effect of different types of deprecia- made so this program is fair to low in- tion schedules is illustrated in figure I I I-2, come famiIies who are not now re- Several observations can be made immedi- quired to fiIe tax returns and to famiIies ate y: whose tax credits exceed the taxes they 1. Permitting a homeowner to depreciate owe The effect of different types of tax the capital he invested in solar equip- credits is iIIustrated in figure III-1. ment over a period of 3 to 5 years Under existing laws, tax credits are would reduce his effective capital permitted for some commercial and in- charges by about one-third Since in- dustriaI equiprment, but not for invest- stitutional owners of energy-generating ments in buildings, Nor are they allow- equipment are permitted to depreciate ed for heatlng, cooling, or other energy- their equipment, the current tax policy generating equipment i nstaIled in forbidding homeowners to do this has buildings However, a company that in- the effect, if not the intention, of staII such equipment in a buiIding it discriminating against the ownership of does not own — and then selIs the ener- such equipment by the homeowner. gy produced –- wouId probably qualify (This incentive would be of greatest for a tax credit under present laws benefit to owners in high tax brackets ) 76 ● Solar Technology to Today’s Energy Needs

Figure Ill-1 .— Effective Capital Costs as a Function of Investment Tax Credit

0.20

0,15

0.10

0.05

SOURCE: Office of Technology \Assessment 0.00 0 100/0 Figure lII-2.– Effective Capital Costs as a Function of Depreciation Schedules

0.20

0.15

0.05

SOURCE: Oftice of Technology Assessment

0.00 0 5 10 15 20 30 No Depreciation Depreciation Period (Years)

NOTES ( 1 ) The ~ffer tlve Interest rate paid on raplfal ‘ shown here Is the ratio between the ( apital related component of Ihe prlre percel~ ed by the consumer and the - total n I I J Ins tallerj P OSt Of the en~ rqy eq u I pme n t I n quest on Cap\ la I re Iated f. x penses I n I Iude return on debt return on equ I ty (u n less 1 he equ I pment Is I J w n~d by the homeowner) la XPS ( w t h al I [~w an ces for d epr~~ iat Ion and (~t h er w rl tc offs) and Insurance (2 I Th~ t>asf, II n e assumpl I I ns and fh r? Ie[ h n Iq ues used fc f,~]m pute th c data sh, w n {In t h IS f q u re are dI sc ussed I n detal I I n the r hap fer on Analy I I ral Methods ‘‘ 78 . Solar Technology to Today’s Energy Needs

2. Commercial, industrial, and utility own- Some problems may arise concerning the ers can also be strongly influenced by property taxes paid by utilities and other altering policies on deductions for de- organizations if they own solar equipment. preciation. In the cases shown in figure Because in many cases these organizations III-2, real estate investors, who expect a pay taxes at much higher rates than those 10-percent return on their capital after paid by individuals, there would be a disin- taxes can reduce their capital-related centive to invest in solar equipment. costs by over one-third if they are per- Whether this is desirable must be decided. mitted to depreciate equipment rapid- Another decision is whether to exempt com- ly. The effect is even greater for an in- panies which manufacture solar equipment dustrial owner expecting a 20-percent from property taxes. There might also be rate of return. some confusion about charging the property taxes in a case where a utility or other PROPERTY TAXES private concern places equipment on a house or building and charges the building Property taxes can add as much as 10 to owner for the energy produced. 25 percent to the cost of solar energy. The taxes, of course, are imposed entirely by Property taxes are not imposed by the States and municipalities and vary greatly Federal Government and therefore cannot around the country (see table 11 1-3). I n some be removed with Federal legislation. It may urban areas in the northeast, for example, be possible to use Federal programs to en- taxes are so high that an investment in on- courage local governments to remove prop- site solar equipment would be prohibitively erty taxes, perhaps by agreeing to compen- expensive for many individuals and com- sate them in some way for lost revenues at- panies. Figure I I I-3 illustrates the substantial tributable to solar property tax exemptions effect of removing a “typical” property tax or to penalize States which do not reduce since, in most cases, the tax increases the ef- property taxes by withholding Federal solar fective investment cost by nearly 10 per- subsidies. The National Energy Plan pro- cent. posed by the Administration states that it

Table III-3. —Property Tax Rates in Selected U.S. Cities

Residential Property Tax Rates in Selected Large Cities: 1974

Effective Tax Effective Tax Rate per $100 Rate per $100 City Rank Rate City Rank Rate

Boston...... 1 $5.94 New York City ...... 16 $2.18 Buffalo ...... 2 4.31 San Francisco ...... 17 2.13 ,– OTA Milwaukee ...... 3 3.63 Cleveland ...... 18 1 88 Baseline Los Angeles ...... 4 3.43 Seattle...... 19 1.82 assumption San Antonio ., ...... 5 3.43 St. Louis ...... 20 1.80 $200 Indianapolis ...... 6 3.29 Memphis ...... 21 1 77 Baltimore ...... 7 3,24 Denver ...... 22 1,71

Pittsburgh ...... 8 2.82 Jacksonville ...... 23 1. 69 Philadelphia...... 9 2.80 New Orleans ., ...... 24 1,69 Chicago...... 10 2.75 Kansas City ...... 25 1,57 Detroit ...... 11 2.73 Phoenix...... 26 1.55 Dallas ...... 12 2.60 Washington, D.C...... 27 1.54 Houston ., ...... , . . . . 13 2.38 Nashville ...... 28 1 39 Atlanta ...... 14 2.24 Cincinnati ...... 29 1.31 San Diego. ., ...... 15 2.23 Columbus ...... 30 1.17

SOURCE: Government of the Dwtrict of Columbia, Department of Finance and Revenue, Tax Bj}rdens (n Wash InrItnn DC Corn pared wlfh Ma/or Stafe and Loca/ Tax Burdens in the Naf/on’s Thirty Largest C/t(es 1974. Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy ● 79

Figure lll-3.— Effective Capital Costs With and Without Property Taxes

0.20

0.15

0,05

0.00

NOTES ( 1 I The ‘e ffertlve !nterest rate paid on raplfal’ shown here IS the rat(r) bet ~ eon th(> “a~~i!al related -omponf>nt {~f thf prl L e ~er elved by the consumer and the total n I t al Ins fal led , r,st (of I he energy {,q u p men t I n quest Ion Ca ~, tal r(,lat~,l P x pen SPS n{- I u~e return [~n debt return on equ I ty (U nlf?ss lh~ eq [J I preen t Is ow n~d by the n om~c w n Pr) !a k Ps (w It h al I o wancps for deprc - !at l~)rl and r)th ~r t+ rl tP o ffs J and I ns u ran~e (2) Thf bas~>ll nf assumpt JrJS and th~ tf hn q ues use(j t ) Jnl FJ u Ie !h r, dala sh j N rI , !n 1 h IS f q u re dre d ISr USSL ‘~ I n deta I I n I he I ha~j te r on Anal y t I al M~t hods

SOURCE Off Ice of Technology Assessment 80 . Solar Technology to Today’s Energy Needs

would be desirable for the States to exempt SUMMARY solar devices from property taxes, and The short answer to the first question is: several have already done so.23 probably, at least for a while. Banks and other Iending institutions are understand- SALES TAXES ably reluctant to invest in mortgages for Sales taxes also lie beyond the Federal residential buildings that plan to use costly sphere, but they, too, can present an impedi- new energy equipment with unproven mar- ment to the installation of solar equipment. ket value, since they might not be able to Here again, the rates for sales taxes vary recover the value of such loans i n a fore- from State to State. In Connecticut it is 7 closure sale. They are similarly reluctant to percent, in Nebraska it is 2.5 percent, in New provide funding for commercial and in- Hampshire there is none.4 Removing the tax dustrial equipment if the owner cannot con- from sales of solar equipment would be of vince them that the system wilI produce a some benefit in reducing initial costs. How- favorable cash flow during the period of the ever, an exemption would not have as great loan. Present statistics about the market- an effect as the property tax exemption ability and performance of most types of which must be paid each year. solar energy equipment are inadequate to support actuarialIy sound decisions, and The Cost of Tax Incentives to the Government few prospective lenders appear to have seen what little information is now available. The cost to the Government of changes in Although solar devices with proven charac- tax policy can be computed from the data in teristics can be expected to gain gradual ac- figures II l-l and II I-2 if it assumed that the ceptance in the lending industry, the ques- Government and the private investor use the tion of whether the Government can or same discount rate (see volume 11, chapter should accelerate this process has not been l). This is done by finding the difference be- resolved. tween the “effective cost of capital” which would apply with and without the change in The Government has successfully used policy. For example, if the effective interest loan guarantee and mortgage insurance pro- rate paid on capital applied to a real-estate grams in the past to induce private lending investor is 10.6 percent without a tax credit institutions to provide funds for projects and 8.6 percent with a 20-percent credit, the deemed socially desirable; Federal Housing average annual loss of revenues to the Gov- Administration (FHA) and Veterans Adminis- ernment during the Iife of the equipment is tration (VA) have made loans available to simply 2 percent of the initial cost. prospective homebuyers for decades. The Government is also in a position to alter current banking practices through the great variety of regulatory and secondary mort- ISSUE 2 gage institutions which operate under Feder- al charter, The potential for using these Will difficulties in obtaining loans hinder the organizations to stimulate loans for solar installation of onsite solar-energy equip- programs is discussed below, ment? If so, can Federal authority to regulate the mortgage reduce such problems? THE PROBLEM

In the absence of adequate information on the reliability, lifetimes, and marketabil- ‘The National Energy Plan, p 76 ity of soIar equipment, many banks are re- ‘National Bureau of Standards, Survey of State luctant to include solar devices in the value Legislation In Solar Energy ‘The World Almanac and Book of Facts 1977, of mortgages made on residential buildings. Newspaper Enterprise Association, I nc , Cleveland & In a recent survey by Regional and Urban New York, p 105 Planning Implementation, Inc. (R UP I), 63 Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy ● 81

percent of the lending institutions inter- investment i n a home. Since the borrower is viewed Indicated that they would “exclude equally committed to carrying the energy the excess cost (of solar equipment) from costs of his home, there has been specula- the appraised value of the house” for loan- tion that the PIT I formula may be expanded making purposes, and an additional 22 per- to include energy costs (although this is not cent indicated that they would lower the now a common practice). loan-to-value ratio of the loan. 5 The average Lack of information about home energy loan actualIy issued by the institutions inter- consumption and the value of solar equip- viewed covered 55 percent of the vaIue of ment makes it difficult for institutions to the solar devices. ’ (However, the institutions evaluate energy costs, even if they have a felt that it solar devices were deemed to be desire to do so. Only 9 percent of the lenders an actuarialIy sound investment, they would interviewed in the RUPI study had seen esti- lend funds for the devices at the same rates mates of solar energy savings, only 4 percent they charged for other types of buiIding had seen cost benefit analysis for solar loans. ) Most of the solar loans were issued equipment, and only 9 percent had seen an for expensive custom-built homes, and in installed solar device or plans for an opera- many cases the owners or builders had an tional system. 9 established relationship with the lender. 7

This reluctance to issue loans for solar THE EFFECT OF MORTGAGE devices is accentuated both by the fact that POLICY ON SOLAR COSTS most banks are simply unaware of the in- The availability of financing can present a format ion gathered about solar equipment, major barrier to rapid introduction of solar and by the tact that very few lending institu- equipment. The effects of loan-to-value ra- tions take energy costs into account when tios on overall capital costs are shown in determining the abiIity of a prospective bor- figure III-4 and the effect of changing in- rower to meet mortgage payments. terest rates is shown in figure I I I-5. The Most Iending institutions do not include results require some interpretation: an applicant’s projected energy biIIs in an — From the perspective of a present value assessment of his abiIity to meet mortgage anaIysis, the fraction borrowed has payments But this practice is changing. relatively little effect on the capital Forty percent of the lending institutions in- costs perceived by the homeowner, terviewed in the RUPI study indicated that given the assumption that the owner since 1973 energy considerations had in- uses a 10-percent discount rate to fluenced lending decisions “a great deal” or evaluate future costs. This is because had become “critical” in lending decisions, the discount rate chosen in the calcula- and 50 percent stated that the importance tion is close to the interest rate charged of energy in these decisions would increase.8 for the loan. The fraction borrowed can Most banks rely primarily on the principal, have a much greater effect than figure interest, taxes, and insurance (PIT I) evalua- 1 I I-4 indicates, however, since the re- tion technique, which compares a prospec- quirement for a large downpayment tive borrower’s income before taxes to the can be a prohibitive barrier. PIT I costs which he must bear to support his –The fraction borrowed strongly affects the prices which must be charged by in- ‘Keglonal and Urban Pldnning Implementation Inc (R UP I), Home Mortgage Lend/ng and So/ar Energy, dustrial firms and, to a lesser extent, the February 1977, p 13 (Prepared for the Divlslon of prices charged by the hypothetical real Energy, Bulldlng Technology and Standards, Otflce of estate investor. This is simply due to the POIIC Y Development and Research, HUD ) fact that the investors expect a much ‘Ib{d , p 99 ‘I bld 8RUPI, p 52 ‘RUPI, p 61 82 ● Solar Technology to Today’s Energy Needs

Figure ill-4.—The Effect of Loan-To-Value Ratios on Overall Capital Costs

0.40

0,35

0.30

0.25

0.20

0.15

0.10

0.05

SOURCE: Office of Technology Assessment

0.00 0 .25 .5 .75 1 Fraction Borrowed

P.U. = .142 M.U. = .095

NOTE The baseline assumptions and the techniques used to compute the data shown on this figure are discussed In detail In the chapter on “Analytical Methods “ Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy ● 83 —

Figure ill-5.—The Effect of Interest Rates on Overall Capital Costs

0,20

0.15

0,05

SOURCE: Office of Technology Assessment

0.00 0 2 4 6 8 10 12 14 16 18 20

Interest Rate on Loan (O/. ) 84 ● Solar Technology to Today’s Energy Needs

higher return on their capital than the grams from the revenue-raising func- interest rates assumed for the loan. tion of the Internal Revenue Service.

— Interpretation of the effect of interest 2. The benefits of a subsidized loan may rates on loans is straightforward. The be easier for a prospective buyer to un- policy issue raised here is one of finding derstand and its impact is more im- a way to persuade lending institutions mediate. It is apparent that consumers to risk investments in solar equipment. of solar energy equipment must be per- suaded to make purchases on the basis Figure I I I-6 shows the results of a recent that their net monthly payments for survey of the reaction of a number of lend- energy will be lower if they install solar ing institutions to a number of proposed energy equipment. It is easier to make policies. It is apparent that the lenders are comparisons between conventional and not interested in tax incentives which assist solar billing when loan incentives are potential owners. They are much more in- provided. terested in performance certification of the devices and in Federal insurance and sec- A tax rebate requires owners to tie up ondary markets for mortgages. their own capital while waiting for a re- fund. This wait can create real financial Many existing Federal programs insure or difficulty and the delayed gratification subsidize loans to promote objectives can have a psychological impact reduc- deemed socially desirable. These programs ing the attractiveness of the incentive. are discussed in the following section. How-. ever, one difficulty with a policy that cre- 3. It may be easier for low-income ates such distortions in the loan market is families to take advantage of a loan that the implicit subsidies are extremely dif- program which requires a relatively ficult to calculate, Encouraging the use of small downpayment, for example, than capital in one area necessarily removes the a program which requires negotiating capital from other applications; thus, it is loans from conventional sources. It is never clear who, if anyone, suffers as a interesting to notice that loan incen- resuIt. tives may be more attractive to low- income homeowners than to home- Another option for encouraging lending owners with large incomes. Families in institutions to make financing available to high-income tax brackets pay a lower potential owners of solar equipment would effective interest rate since interest is be to find some way of requiring lending in- deductible, and would therefore not stitutions to include estimates of the bor- benefit as greatly from an incentive rower’s ability to cover utility costs in the which lowered the interest rates and process of estimating the borrower’s ability hence their deduction. to pay back the loan. This type of analysis might often benefit solar equipment owners. 4. If it is possible to place the loan as a Several techniques for doing this are dis- part of a mortgage package used to cussed. finance an entire building or house, it may be possible to reduce the cost of A SOLAR LOAN PROGRAM administering the program and apprais- ing the solar equipment. If tax programs A program which made loans more attrac- are used, the IRS must presumably find tive to potential solar customers would have a way to make independent audits of several generic advantages over tax incen- the projects. tives: Loan programs, of course, are not without 1, They avoid complicating the tax laws. problems. They can be complex and costly Recent tax reforms have attempted to to administer, particularly if it is necessary separate Government incentives pro- to establish a separate bureaucracy to over- Ch. Ill Federal Policy for Promoting and Regulating Onsite Solar Energy . 85

Figure lll-6.— Lender Perceptions of Likely Impact of Incentive Options on Loan Decisions

Percentage of Lenders Indicating Incentive Would Have “Substantial Impact” or Be “sufficient To Make Loan”

Type of Incentive Program

1. “Conversion” Insurance

2. Certification of Solar Energy Systems

3. Top Part of the Risk Insurance

4. Secondary Market Eliglbility (FHLMC, FNMA)

5. GNMA Purchase with Lender Servicing

6. FHA/VA Eliglbility with Higher Mortgage Limits

7. Value Protect Ion Insurance

8. Local Property Tax Exemption for Added Cost

9. (For Multi-Family) Accelerated Deprectation

10. Subsidized Interest Rates

11, Income Tax Credit for 1st Costs (or Investment Credit)

12. “Public ” 2nd Mortgage Loan for Extra Solar Costs

13. Linked to Special Feature— (e.g., Variable Interest Rate, Balloon, etc.)

SOURCE RUPI CIp .[1 86 ● Solar Technology to Today’s Energy Needs

see the operation of the program. Lending lating the U.S. financial community. These institutions constantly complain about the fall into the following categories: amount of paperwork required by Federal 1. Direct Federal loans and programs regulatory authorities and this paperwork which subsidize the interest paid to pri- can contribute significantly to the cost of a vate lending institutions; loan. Since the costs of paperwork are nearly Independent of the size of the loan, loan 2. Programs which “guarantee” loans with subsidies may not be an detractive tech- a contract in which the Government nique for encouraging the installation of agrees to purchase a mortgage offered solar equipment costing less than $1,000 to by a private investment company if the $1,500. In these cases, it is much more likely borrower defaults (typically the debtor that the purchaser will be able to make a is then still Iiable to the Government for single payment for the equipment and a the outstanding funds and must either direct grant or tax credit would be easier to sell the property or permit the Govern- administer. ment to sell it for him);

There has also been some concern about 3. Loan “insurance” programs, in which loan support programs which commit the the Government charges the borrower a Government to administering programs over smalI annual fee and agrees to reim- a term of many years. burse the lender in the event of a de- fault; The significance of all of the problems 4. Federally cited here depend on the details of how the chartered but privately loan program is administered. Concern owned “secondary mortgage” institutions, which purchase mortgages from about long-term Federal commitments can primary lenders in order to free the be reduced, for example, by simply having funds of these lenders for further mort- the Government make a single payment to a lending institution which would administer gages; the Federal National Mortgage Association can borrow funds directly the loan, to cover the difference between from the Federal Treasury; and the return received from a subsidized and a commercial loan. 5. Regulatory institutions which oversee the operations of banks, savings and If the Government uses an 8-percent dis- loan institutions, and other lending count rate (roughly the current cost of long- organizations, term Government bonds) a 3-percent loan covering 95 percent of the cost of a solar Each of these programs and organizations system owned by an individual homeowner could retard the installation of solar equipment or, if Federal leverage is applied, ac- has roughly the same effect on average monthly costs as an investment tax credit of celerate it. 34 percent. If the system is owned by the Direct Federal Loan Guarantees for Buildings owners of an apartment building, the loan would be equivalent to a credit of about 62 Most direct Federal loans are issued to percent. The Government cost associated projects designed to serve low-income with the loan program for homeowners groups–urban housing projects, hospitals, would be about the same as that for an in- homes for the aging–although some funds vestment tax credit of 29 percent (assuming are available for experimental communities no loan placement fee). and new energy equipment. Any direct loans for solar equipment will have to compete with their use for urgent social programs. It EXISTING FEDERAL LOAN PROGRAMS may make sense to increase funding in these The Federal Government has a great vari- direct-loan programs to reduce dependence ety of programs for subsidizing and regu- on long-term Federal support for operating Ch. Ill Federal Policy for Promoting and Regulating Onsite Solar Energy . 87 — costs (see discussion in the previous issue), necessary for this program; the money is left The major direct-loan programs are: over from the FmHA’s Section 502 home- construction loan program. But the conser- Programs Administered by the Department vation guidelines do not permit structural of Housing and Urban Development (HUD).– work, thus precluding solar installations. No 1) Public Housing: The Housing Act of 1937 legislation would be necessary to change (section 5) permits the Federal Government the regulations; it could be done adminis- to directly finance housing for low-income tratively within the Agriculture Department families and the elderly through federally guaranteed municipal bonds. Additional The second large program is the Rural funds are allocated each year to allow Electrification Administration (REA) loan “modern i z at ion” of existing structures program to electric cooperatives. There are These programs do not have specific goals two parts to this program — a direct loan au- for energy conservation, although the prop- thority of $75 million to $900 million (in FY erties must meet certain minimum HUD 76) to cooperatives for electric distribution standards. Energy conservation features and transmission faciIities. This program couId be included in these standards. would appear to have no solar applications. However, a second REA program would. It is (2) Housing for the Elderly and the Hand- an open-ended REA loan-guarantee pro- icapped: Section 202 of the Housing Act of gram, again to co-ops, for construction of 1959 provides loans for nonprofit sponsors electric generating faciIities. of new or substantialIy rehabiIitated rental housing for the elderly or the handicapped. These loans, at prevailing interest rates, The program also has no standards specif- are made by a commercial bank or, more icalIy designed for energy conservation. The commonly, through the Federal Financing projects constructed under this section, Bank within the Treasury Department. In however, tend to be initiated by experienced calendar 1976, such REA-guaranteed loans and sophisticated managers, contractors, totaled $3.7 bill ion, and architects, who are more likely to be at- There are no restrictions, either under the tracted to novel energy systems than are the law or under REA regulations, as to what builders of public housing projects, which type of electric generating facility may be have been plagued by cost overruns, de- made with the REA-guaranteed loans. Thus, faults, and tenant problems, a solar electric generating plant could quali- Programs Administered by the U.S. Depart- fy for such a loan – at least so far as REA is ment of Agriculture (USDA). — The Depart- concerned — assuming that the lending in- ment of Agriculture has two large Federal stitution and the local electric cooperative loan programs for low- and moderate-in- conclude that the solar installation would come rural families that could have applica- be cost-effective. tions for solar technology. The two largest impediments to using this The first is a new conservation program large Federal program to foster the solar under the Farmers Home Administration market would seem to be (a) the need for a (FmHA), a $500 million to $1 billion project backup system (a small diesel generator announced on February 28, 1977. Under this could suffice) and (b) the problem of con- program, customers of electric cooperatives vincing banks and co-op officials that a can receive 8 percent loans, repayable solar generating facility would be practical through their monthly electric bills, for such (when it is possible to make such a case). conservation measures as weatherization, REA officials stress that their agency’s mis- storm window and door instalIation, and in- sion is not to experiment with new or novel stalIation of attic cans, to a maximum ex- technologies, but to provide electricity to penditure of $1,500 a family. No new Feder- rural customers at the cheapest possible al appropriations or authorizations were rates. 88 . Solar Technology to Today’s Energy Needs

Programs Administered by the Small Business medical practice facilities, The insurance Administration (SBA).– The SBA has funds program collects premiums from borrowers available for subsidizing loans to qualifying and provides a fund to reimburse lenders in smalI businesses. These funds might be use- the case of defaults. The value of interest ful to firms manufacturing or installing solar rates allowed for FHA-insured loans varies equipment, since such firms tend to be quite and has recently been below the rate smalI. charged by the private mortgage insurance companies. In 1977, home-purchase loans Loan Guarantees financed under Section 203b charged 8- percent interest; home-improvement loans Veterans Administration (VA).– The Serv- under Title I charged 12 percent. iceman’s Readjustment Act of 1944 allows the VA to guarantee loans to qualifying FHA’s direct participation in the mort- veterans for residential buildings with one to gage market is diminishing. It now insures four units. The program guarantees about only about 17 percent of the loans made on 350,000 units a year, The loans can be made 1- to 4-unit nonfarm residential buildings. for any amount and cover 100 percent of the The program is still extremely influential, value of the property. There are no energy- however, if only because of the standards it conservation requirements, although the VA sets for residential structures. All older will only insure property which meets “mini- homes purchased with FHA insurance must mum property standards” established by the be appraised by the FHA and receive a “Cer- FHA. tificate of Reasonable Value, ” which forms Federal Energy Administration (FEA).–The the basis of the loan amount. New homes Energy Conservation and Production Act can be insured only if they meet FHA’s provides loan guarantees for a wide range of “minimum property standards, ” As noted conservation and solar energy equipment. earlier, these standards form the basis for Regulations governing the application of the many other Federal loan programs. They are funds were still being drafted in mid-1977. also widely used by private lending institutions as the standards of value. Builders HUD Loan Guarantee Programs.–Amend- designing low-cost housing have, in many ments to the Housing Act of 1968 authorize cases, chosen to meet these standards, HUD to make loan guarantees for privately since housing quality that did not measure developed new towns and for a variety of up to them would have reduced the avail a- community facilities. To date, the program bility of financing for potential buyers. has extended guarantees to 13 new towns, some of which have projects for solar heat- The FHA standards reflect both the qual- ing and cooling funded under the ERDA/- ity of the construction and its marketability. HUD solar heating and cooling demonstra- No firm policy has been established for tion program. solar-energy devices, although a 1974 amendment to the FHA law permits the use Mortgage Insurance of FHA loans for solar equipment (The amendment may have been unnecessary, as The Housing Act of 1934 established the FHA loans were used during the 1930’s to Federal Housing Administration (FHA) and purchase solar water heaters in Florida. ) the FHA Insurance Fund to allow families with low and moderate incomes to obtain Current FHA solar standards of perform- mortgages at reasonable rates, The program ance quality employ the National Bureau of has since expanded to include apartments, Standards “ Interim Performance Criteria” cooperatives, nursing homes, and group for solar devices. ” The major difficulty,

[) ‘ F’ubl IC Ldw 94-385, Title IV, section D “RUPI, p 133 ‘ ‘Title IV of the Hou\lng Act of 1968, amended as 1‘FHA document FPMC-FHA, dated February 19, Title VII of the Housing Act of 1970 1976 Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy . 89

however, will not be the quality of the 2 Section 111 clarifies the definitions for equipment but whether it wiII contribute to energy-conserving equipment and solar- the resale value of the house. FHA is par- energy devices. ticularly sensitive on this point, since it 3 Section 112 provides an opportunity to deals primarily with low- and middle-income use Title I funds for experimental families to whom initial housing costs are energy equipment but at higher interest important, A recent FHA publication noted rates than those conventionIIy that in inspecting property with solar charged for home improvements, Ac- devices, “[the] field office must also deter- tual rates would be determined by a mine that a ready market exists for the pro- study conducted by the Secretary of perty with the increased cost of the solar HUD. equipment."14 An applicant faiIing to obtain FHA certification for a solar device has the Federally Chartered Secondary. Mortgage Institutions right to a hearing before the local FHA office The results are difficult to predict and Many of the mortgages issued for residen- wi II doubtlessly depend on the officials’ tial buildings in the United States are not familiarity with costs and benefits of solar held by the primary lending institution for equipment. Failing to obtain a direct FHA the full mortgage period. Instead, they are loan, the applicant has the option of utiliz- sold to organizations which are more in- ing a H U D “ Experimental Housing Program terested in holding notes over a long period (Section 233). ” and which use the primary lenders as agents to acquire them. Selling mortgages to a HUD’s experimental housing program is secondary-mortgage institution frees the designed to provide an incentive for the con- assets of the primary lender, who is then struction of innovative or unconventional able to use these funds to issue further mort- housing systems that do not meet the con- gages. The Federal Government sponsors servative standards of the FH A certification two of the largest purchasers of secondary processes. The program’s larger purpose is loans: the Federal National Mortgage Asso- to develop familiarity with experimental ciation (called “Fannie Mae” by generations designs that will provide the basis for alter- of brokers unable to pronounce FNMA), and ing the FHA standards.15 Unfortunately, in- the Federal Home Loan Mortgage Corpora- fluence of experimental programs on tradi- tion (alias “Freddie Mac”). tional housing has not been notable thus far, Primary lenders are critically interested in Loans for home improvement and mobile ensuring that their loans will be repurchased homes insured under Title I do not require a by these organizations. If the secondary- preinspection, although FHA audits projects mortgage institutions are negatively inafter loans are granted. Up to $7,500 can be clined toward solar equipment, this could obtained without security. affect the willingness of primary lenders to The proposed National Energy Act would approve loans involving such equipment. amend the act establishing these loan guar- According to the RUPI study cited earlier, antee programs in three ways: both FHLMC and FNMA have indicated that “until solar systems achieve some degree of 1. Section 110 would add public utilities market acceptance, they may conclude that to the types of institutions which can incremental first costs should be largely, place loans for energy-conservation perhaps even entirely, excluded from the equipment insurable by FHA. mortgageable value for the purpose of their programs,’” The manager of FNMA apprai-

sals was quoted as saying that if “people 14 FPMC-FHA 76-8 150rvjlle Lee, D/rector of HUD’s SectIon 233 pro- “Title 12 (Banks and Banking, subchapter I I 1, gram$, private communlcatlon, 1977 171 6a) 90 Ž Solar Technology to Today’s Energy Needs

wish to experiment they should do so with funds, entirely by subscription, from the in- their own money, not someone else’s."17 stitutions it services. The FHLMC’s regulations place more risk on the primary lenders. On the other hand, the quasi-public na- For example, the FHLMC can require the ture of these organizations makes them sus- primary lender to take back a repurchased ceptible to public-policy guidance. loan if irregularities are discovered. The Federal National Mortgage Associa- The proposed National Energy Act would tion was established by Congress in 1934 to amend the charters of both the FHLMC and “provide supplementary assistance to the FNMA, to make it clear that funds can be secondary market for home mortgages by used for loans for “energy-conserving im- providing a degree of liquidity for mortgage provements to residential real estate.”20 investments, thereby improving the distribu- Solar devices are not explicity mentioned, tion of investment capital available for but their inclusion may have been intended. home mortgage financing” and to provide special assistance for special purposes. It Regulatory Authority purchased about $7 billion in loans in 1974.18 It raises funds by private subscrip- Nearly 97 percent of all loans granted in tion, but has “backstop” authority to bor- the United States are issued by lending or- row directly from the Federal Treasury. Five ganizations subject to some kind of Federal of its 15 board members are appointed di- regulation. Savings and loan associations, rectly by the President of the United States, for example, are tightly controlled by the Fannie Mae can purchase loans guaranteed Federal Home Loan Bank Board. The Feder- by FHA or other institutions [section al Deposit Insurance Corporation regulates 1717(b.1 )] at full value. It can also purchase mutual savings and commercial banks. Nei- conventional uninsured loans, subject to re- ther appear to have a specific policy for en- strictions on the loan-to-value ratio and couraging or discouraging energy-related other limitations [section 1717(b.2)]. About loans. 85 percent of its loans are purchased from mortgage bankers. ISSUE 3 The FNMA tends to place great reliance on the judgment of primary lenders, and as a Can purchases of solar equipment for Feder- result, its lending policies tend to be deter- al buildings be used to stimulate the solar in- mined by the values of the mortgage bank- dustry? ing industry. A major program for installing solar The Federal Home Loan Mortgage Cor- equipment on Federal buildings could be poration operates under the auspices of the one of the Government’s most powerful Federal Home Loan Bank Board (FHLBB) tools for encouraging the development of and primarily serves savings and loan in- mass production of solar equipment by pri- stitutions. The Corporation purchased ap- vate industry. proximately $1.5 billion in loans in 1974. The members of the board of the FHLMC are Consider the following: appointed by the FHLBB, who in turn are ap- ● The Federal Government owns or leases pointed by the President. The Corporation approximately 446,000 buildings in the acts under regulations established in the United States, with a combined floor Federal Home Loan Bank Act, It raises area of nearly 3 billion square feet and was spending almost $1.7 bill ion an- ‘ ‘Barrett, Flnanclng the Solar Home, NSF Grant nually by mid-1977 to heat and cool APR 75-18360 (j une 1976), p 141 ‘a Barrett, op cit., p 139 them. (That figure was expected to “Barrett, Financing the Solar Home, NSF Grant APR 75-18360 (June 1976), p 139 ‘OTltle 1, sections113 and 114 Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy Ž 91

reach $1 9 billion by the end of 1977, There is a considerable amount of and about $3.5 billion by 1985, ) If 10 disagreement among analysts on this point percent of the present heating/cooling Some argue that the Government should costs were capitalized — used for debt make decisions with the same expectations payments for the purchase of solar of return as private investors This view was equipment — the Government could formalized in a ruling by OMB, which held purchase nearly 100 million square feet that the Government should only invest In of solar coIIectors annualIy. * equipment which wouId resuIt in a 10-percent return on investment since this rate ● The Federal Government subsidizes “represents an estimate of the average rate operating expenses, including heating of return on private investment before taxes and cooling costs, of a large number of and after infIation.”21 Others argue, how- projects built with Federal assistance. ever, that the free market does not neces- The Department of Housing and Urban sarily accurately assess the social costs of Development alone paid more than investments and that the Federal Govern- $575 in 1977 to subsidize the million ment shouId therefore use investment cri- operating and energy bilIs of the nearly teria which better reflect social costs. Even 1 million units of public housing ad- if this basic principle is accepted, however, ministered by subsidized local housing it becomes extremely difficuIt to determine authorities If 10 percent of this were what economic expectations are proper In- capitalized, the Government could sup- vestments must be assigned values based on port the purchase of nearly 30 million concerns about the environment, social square feet of colIectors annualIy. costs, benefits to labor, benefits to national Ž It wouId be difficuIt for the Govern- security, the stability of resource supplies, ment to encourage private concerns to and other criteria difficult to evaluate in instalI solar equipment if it is not using conventional economic terms solar equipment on its own buildings. When the Government makes an invest- In spite of the enormous potential, Feder- ment that pays less than the return which al programs for purchase of solar equipment could be realized if invested in the free have been proceeding quite slowly, largely market, society is losing some of the value because of concern about the cost effec- of that capital. This of course means that tiveness of solar devices. This concern is society is subsidizing the investment In often magnified by the inability of program some way. The exact amount of this subsidy, administrators to accurately evaluate the however, can be as difficult to quantify as costs of solar techniques, I n some cases, re- the value society might realize from the in- quired formulas for determining the worth vestment. of a Federal investment (i. e., fixed Iimits on Nonetheless, several discount rates can building costs, and present value computa- be used to evaluate Federal equipment pur- tions with high discount rates) have in- chases: hibited these programs. ● 10 percent rate of return after taxes and The opportunity to use Federal buildings before inflation: this technique would for experimental energy equipment raises result in Federal investments in solar three difficult but important questions: equipment which neither lead nor lag 1. What should the Government use as a investments made by private industry. “discount rate” to evaluate alternative in- ● Use of a rate of return equal to the rate vestments? of the growth of the U.S. GNP: this

“George P Shultz, “Discount Rates to Be Used In ‘Assuming $20 per square foot for an Installed sys- Evaluating Time-Dlstrlbuted Costs and Benefits, ” tem OMB Circular A-94, Mar 27, 1972 91 Ž Solar Technology to Today’s Energy Needs

would encourage Federal purchases of stimuIus to Federal purchase of the solar equipment and ensure that funds equipment. (Zero percent discount extracted from the economy by the rate. ) Government were not affecting overall economic growth. (This would imply a The effect of applying different Federal real discount rate of 2 to 5 percent. ) discount rates to prospective Federal in- ● Require only that the Federal Govern- vestments is iIlustrated in figure III-7; the an- ment recapture its initial investment ticipated effects of three separate discount without earning a return on the funds: rates on Federal decisions to purchase ener- this would obviously be a stronger gy equipment are shown in figure I I 1-8.

Figure ill-7.—The Effective Cost of Capital to the Government as a Function of the Discount Rate Used in Decisionmaking

(Assumptions methodology used in preparing this figure are discussed in detail in volume 11, chapter 1)

020

9 SOURCE Of f(c e of Technology Assessment

15 Ch. Ill Federal Policy for Promoting and Regulating Onsite Solar Energy ● 93

Figure Ill-8.—The Effect of Federal Discount Rate on the Perceived Cost of Federal Investments in Three Types of Solar Installations

(in $/month/unit in a 196 unit high rise apartment)

2 12J s[jldr hratl n q a no h I t w a tc r systf-m uses 4100 m of flat @df(, r olle[ tors w h I h 2 r~sl 196 $Imz Installed (near term prII es) and 1 2 mtlllon k ~ h I(}v. temperatu rf t h c r{Tl al SII ~ raqe ~ s{a> Jn al I n u ndf, rq ro u nc Ian ks 2 2 (31 s Id r ,.{{. tr # 1 b C,(, S 2500 m ~f t ~ o ax Is t rdr k mq I f~lle tf~rs w I f h GaAs phO!u vol Idl( . el Is The c olleI t{]rs f OS! 102 $ ‘m I n stall e[~ In- IU d !ng I R IS (an [I 1 I rr~ I \ 1 I es! nla te (Jf fu I(J re pr! I.es I 10000 k w h fjf low Ie m pc>ra tLJ re thermal st( I rdqf> no batlerles are used - 2 (4) solar CIICI trl #2 uses 4263 m of one ax Is t rar k I n 9 ~ [ III(J 1 Jr \ w,! h s II I Jn ~h{ I(J Y olt al I el Is The -7,11 [~1 tci rs I ost 300 $fm2 I n c I L d n q t he - f]st o I the 15000 $1 ~~cak k w ) the sysl e m has 17000 k w h of low tern pera! u r{, t h ermal sto ragf all d n J bat t (rles

assumes 1976 start u [J ~ ost an\ ~, ler ! r I r prj PS n reas I n q al~~nq BN L f( J re n a~fs

\ assumes that electrlc prtces Increase by a factor of 5 over 60 = years (In constant dollars) m

2. If it is determined that the Government been given time to develop along traditional should subsidize the market in novel en- lines, In extreme cases, mistakes might ac- ergy equipment, how should it select tually result in slowing the rate at which equipment? solar equipment enters the market if the Federal stimulus results in accelerating the If it is assumed that the Government will instalIation of less desirable devices,

purchase equipment which cannot be justi- thereby diminishing interest in promising fied in traditional economic terms, values alternatives. At a minimum, any Federal pro- other than those used by the free market curement program must be carefulIy inte- must be applied This is a perilous under- grated with an overall plan to promote a taking since it runs the risk that the bureauc- market for solar equipment as discussed in racy wilI select equipment which would not the section reviewing overalI policy alter- have been chosen by the market if it had natives. 94 ● Solar Technology to Today’s Energy Needs

3. What future fuel prices should the Gov- annually without subsidy if the current price 23 ernment assume when evaluating the of cells dropped by about 50 percent. cost-effectiveness of solar technologies DOD is also testing the applicability of solar for specific applications? power in several new DOD construction projects and indications are that the results, THE POTENTIAL OF INDIVIDUAL AGENCIES if promising, will be phased quickly into other DOD construction and modernization Department of Defense (DOD) projects. The Department of Defense operates Veterans Administration (VA) 380,000 buildings with a total fIoor space of 2.5 billion square feet. ” This includes Several solar projects have been proposed 260,000 units of family housing in the United in the VA’s 5-year plan: States. It recognizes that energy costs are ● Retrofit of the San Diego VA Hospital becoming a major burden and a program is for solar heating and cooling. now underway to install a variety of solar- equipment designs on several typical DOD ● A solar-assisted heat pump for a new building types. Some of the projects are VA hospital to be built in Palo Alto, funded by DOE; some are funded internally. Cal if. The projects include: ● Solar hot water systems for three new –Shopping centers at Kirkland and Ran- hospitals under construction. dolph Air Force Bases (heat and cool). ● 20 other projects were in the design –Administration building at Fort Hood stage for FY 77; 40 more were i n the pre- (heat and cool). liminary design stage for FY 78,

— High-temperature water from concen- The VA’s 171 hospitals are built, operated, trating collectors at Fort Carson, Colo. and maintained by the VA itself, rather than by the General Services Administration —132 residential units on 16 Air Force, (GSA), which is responsible for acquisition Navy, and Army bases (heat). and maintenance of the VA’s non hospital fa- –Three Army Reserve centers (heat and cilities (these are discussed under the GSA cool). program). Fuel expenditures for the 171 VA hospitals amounted to $23.5 million in FY — 50,000 square feet of classroom at Fort 75. Huachuca, Ariz. VA officials have informally indicated –Air Force Academy housing (heat and that the agency’s hospital system could ac- cool, funded by USAF). commodate 120 solar installations, at a cost – Refrigeration at the Navy regional med- of some $32 million. They estimate that retical center at Orlando, Fla. rofit would save $1.6 miIlion annualIy in fuel costs and that this saving could be diverted According to a study conducted for DOD into a principal/interest debt repayment by the BDM Corporation, solar photovoltaic fund for the solar equipment. ” To accom- cells can compete with many generating de- plish this, the VA’s 5-year Energy Plan would vices now used to provide electricity to have to be revised. But apparently no legis- remote sites, (Standard DOD techniques lation nor additional funding would be re- were used to measure cost-effectiveness. ) quired. The study estimated that DOD could purchase over $100 million of silicon solar cells 2 “’DOD Photovoltalc Energy Conversion Systems Market Inventory and Analyses, ” Prepared for DOD and FEA, spring 1977 “ERDA-76-6, pp 71, 75. 24 Clark Granninger, VA, 1977 Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy ● 95

U.S. Postal Service (USPS) ● RegionaI GSA adminstrators are soon to make recommendations for solar en- An FEA-sponsored study found that USPS ergy projects for one or two GSA build- “owns or operates approximately 75 million ings in each region of the country, square feet of floor space in 36,000 buildings. ” Of this floor space, approximately 80 GSA’s ability to install solar equipment is percent is concentrated in 750 buildings. ” limited by the fact that in recent years it has The USPS has two solar demonstrations often chosen to lease buildings rather than underway: a new post office building under to purchase them. construction in Ridley Park, Pa., and a retrofit project in Boulder, Colo A study is being Health, Education, and Welfare (HEW) made of the possibility of designing solar The Department of Health, Education equipment for a standardized buiIding de- and Welfare is charged with demonstrating sign which the USPS could use in many parts solar heating and cooling in Federal and of the country. private hospitals and other health-care facilities as part of DOE commercial demon- The USPS leases more than 80 percent of stration program. An interagency agreement its buildings from the private sector, and the between DOE and HEW authorized HEW to agency has the legislative authority and ad- solicit proposals for such projects, it calls ministrative flexibility to work any kind of for an “open” solicitation; that is, solar con- variation on utility payment responsibility tractors are to be invited to make proposals At present, however, it has no positive pro- for heating and cooling demonstrations at gram for promoting the use of solar power in certain health care facilities Five or six proj- its leasing program. The agency has not de- ects are anticipated under the proposal, and veloped a comparative cost analysis system, about $1 million in DOE funds is involved. but USPS officials feel that regional USPS personnel are professionally competent, as In addition, DOE has funded a $300,000 welI as definitely inclined, to solicit solar as project for a solar installation at an Indian part of its leasing program if encouraged to health-care facility in New Mexico and a 26 do SO. project at a Public Health Service hospital,

General Services Administration (GSA) BUILDINGS OPERATED FULLY, OR IN PART, UNDER REGULATIONS ESTABLISHED BY The General Services Administration has THE FEDERAL GOVERNMENT jurisdiction over all Federal office space, with the exception of post offices, DOD The Federal Government, in addition to facilities, VA hospitals, and certain other the buildings it owns or leases, supervises specialized faciIities It has installed solar the operation of many buildlngs that receive equipment on only two Federal buildings — Federal loans or operating subsidies The one In Saginaw, Mich , the other in Man- Government could use Its leverage to en- chester, N.H. Planned projects include: courage the use of solar-energy equipment on such projects. In the case of buiIdings . Heating and cooling faciIities i n a new which receive operating subsidles partialIy Border Patrol building at Marfa, Tex. attributable to energy costs, the Govern- Ž Heating and cooling facilities at ment might directly benefit from diverting Federal office buildings in Denver, annual subsidy funds to programs designed Colo , and Carbondale, III, to capitalize solar devices.

● Solar heating and cooling faciIities at a The largest number of federalIy spon- Forest Service buiIding in Arizona sored residential units have been con-

‘‘Sola r Energy Government flu I Id Ings Project, hl I TR E (-orpor,it Ion, p 4 “Carl Conner, ERDA, priv.ite c omrnunl( .it Ion, 1977 96 ● Solar Technology to Today‘s Energy Needs

structed under public housing programs. ating funds for solar equipment, since HUD Over 1 million units of low-cost housing officials are skeptical that solar devices have been constructed with federally sub- could be economically attractive on their sidized municipal bonds since 1937. Projects projects without additional Federal subsi- covered under Section 8 of the Housing Act dies. aIso receive annual payments to ensure that tenants are charged no more than 15 to 25 Acquired Housing percent of their annual income for rent, In addition to public housing, the Federal Unfortunately, current accounting pro- Government acquires a substantial number cedures make it difficuIt to determine the of residential units because of foreclosures fraction of annual subsidies attributable to on VA, FHA, and FmHA loans (HUD current- energy costs. HUD officials estimate that ly owns approximately 90,000 such units). energy costs currently account for 20 to 30 The current policy is simply to dispose of percent of the subsidy payments. this property as rapidly as possible without making modifications to the structures. It Public Housing might be desirable, however, to require that The Public Housing Program has funds for the Federal Government provide certain of modernizing existing structures (the approx- these houses with energy-conserving equip- imately $20 mill ion available in FY 77 was ment before they are resold. capitalized by local developers into about $200 million in project funding). Energy con- ISSUE 4 servation is considered a major objective of recent modernization investments. How- Could any existing Federal grant program be ever, HUD has no program-wide conserva- used to subsidize the purchase of solar- ener- tion goals. There are no real incentives for gy equipment? local housing officials to invest in conserva- Yes; many of them could, Some direct- tion equipment, largely for the following grant programs already have energy conser- reasons: vation as an explicit objective; others, –There is a general feeling that the Fed- though initially designed for other purposes, eral Government wiII have to continue couId be used to administer funds for solar to subsidize energy costs, and local of- insta I I at ions, ficials therefore apply all available Taken together, funding for such pro- funds to other modernization projects. grams totaled over a billion dollars in FY 77 –There is much less glamour in retrofit- and thus could be used to provide substan- ting older establishments with conser- tial subsidies for solar equipment—even if vation equipment than in overseeing only a small fraction of the funds could be innovative new projects. The effec- justified for this purpose. However, it will be tiveness of area personnel tends to be difficult to divert funds from many existing judged on the basis of their perform- programs because they are already over- ance on newer projects. subscribed for their primary purposes; in these cases, solar equipment would have to Until late 1974, HUD’s legal staff had be paid for through additional funding. To ruled that operating subsidies for public have solar grant money administered housing could not be used to capitalize in- through existing programs would have the vestments in energy-conservation equip- advantage of avoiding the addition of still ment. A more recent ruling changed that another separate program to what is already opinion, and there are now judged to be no a bewiIdering array. legal barriers to using operating funds for solar and other energy equipment. However, If an attempt were to be made to coor- there has been Iittle attempt to use oper- dinate these diverse and frequently overlap- Ch. III Federal Policy for Promoting and Regulating Onsite Solar Energy ● 97

ping programs in the interests of acceler- effectiveness of incentives for encouraging ating the commercialization of solar energy, homeowners to install energy-conservation it would probably be desirable to use the or solar energy devices, Two hundred mil- services of the Federal Regional Councils in Iion dollars were authorized for the program each of the 10 Federal regions nationwide. in FY 77. Councils are headquartered in Atlanta, Bos- Housing Finance Interest Subsidies are pro- ton, Chicago, Dallas, Denver, Kansas City, vided under the 1974 Housing and Commu- New York, Philadelphia, San Francisco, and nity Development Act. This Act allows HUD Seattle These councils can use personnel to make grants to State housing finance from several different agencies to coor- agencies that use the money to cover in- dinate programs across jurisdictional lines terest payments on bonds sold for rehabil- and which receive funding from several dif- itating housing. Buildings must be examined ferent sources. by HUD before such grants are made. They must meet HUD’s minimum property stand- FEDERAL GRANT PROGRAMS ards. (See Issue 2 for a discussion of the im- It will not be possible to summarize all pact of these HUD standards.) Federal grant programs which could be used to subsidize solar energy systems. A few of Programs Administered by the Department the programs which seem most immediately of Energy relevant are: The Energy Conservation and Production Act (P. L. 94-385) established a 3-year program in Programs Administered by HUD which $200 m i I I ion would be given to people Community Development Block Grants are with low incomes for the purpose of insu- provided under the Housing and Community lating and “weatherizing” their residences. Development Act for a variety of urban re- The funds are to be administered at the newal and community improvement activi- local level by community action agencies ties which may include the rehabilitation of Standards for allowable improvements will housing. About $250 million was spent dur- be established by the National Bureau of ing FY 76 to secure loans totaIing about $500 Standards. miIIion Energy conservation was not a major priority of these programs since most of Programs Administered by the Department of Health, the funds were needed simply to make Education, and We/fare buildings habitable. The Administration on Aging oversees a pro- Housing Rehabilitation Programs are funded gram which gives emergency relief to elderly under Section 312 of the same Act. Their persons finding themselves unable to meet purpose is to rehabilitate housing and to en- rising fuel bilIs. Grants also are made to sure that housing meets the requirements of State agencies which provide direct assist- local building codes. Use of these funds for ance in insulating and weatherizing resi- conservation is improbable because the pro- dences.27 The program is very modest; its gram’s success tends to be measured by the budget is approximately $1.5 million. number of units completed. Solar installa- The Social Services Administration provides tions would reduce this number. up to $500 for winterization to families qual- Homeowner Grants are provided by Sec- ifying for Aid to Families with Dependent tion 302 of the Housing and Community De- Children. ” The program requires the recip- velopment Act to assist persons needing ients to match the amount of the Federal funds for housing repairs. grant Homeowners Incentive Demonstration Pro- grams, authorized under the FEA extension ‘701der Americans Act, Title I I I act (Title IV), are designed to evaluate the ‘“Socla! SecurltY Act, SectIon 403 98 ● Solar Technology to Today’s Energy Needs

Programs Administered by the U.S. ture, the Product Dissemination Program of Department of Agriculture HUD, the Comprehensive Employment and The Farmers Home Administration may Training Act administered by the Depart- make loans or grants in amounts up to ment of Labor, the Community Services Ad- ministration, and Action. Some of these pro- $5,000 to low-income rural residents for the purpose of improving their homes to meet grams are bringing energy conservation Into local code standards. z’ The funds can also their activities through various means. be used to purchase insulation. Its appli- These include grants for weatherization, cabiIity to solar equipment is uncertain. providing labor for performing this weatherization, and information services on reduc- Programs Administered by the U.S. Department ing energy costs to homeowners. of Commerce These programs appear to have the flex- The Economic Development Administration ibility to incorporate solar energy in their ac- is authorized by both the Public Works and tivities. As such, their contact with a large Economic Development Act of 1965 and by portion of the American population could the Public Works and Capital Development serve to accelerate the penetration of solar and Investment Act to make grants to com- energy. A similar course is being proposed munities with the central objective of stimu- with regard to the Energy Extension Service lating employment in regions with severe now being developed by DOE. unemployment problems. Annual expenditures are typically in the order of $200 milIion, although a special “one-shot” infu- sion of $2 billion was granted in 1976 be- ISSUE 5 cause of severe unemployment problems. When private companies are subsidized with It may be easier to use this program for Federal funds to develop equipment for the solar and conservation investments than any commercial market, how can a balance be other Federal grant program. This is because struck between the company’s need to retain money used for these purposes would not a useful proprietary interest in the technol- have to compete with other, critical uses of ogies developed and the Nation’s right to the Federal grant funds (e. g., housing rehabi- have complete disclosure of the results of litation). The object of the program is to federally sponsored research? stimulate employment and, as shown elsewhere in this paper, solar energy is a labor- There is no easy answer to this question. intensive industry which requires skills in But it raises what is likely to be a central job areas currently suffering serious unem- problem for all federally sponsored efforts ployment. Funds from the CD I program, to develop small, commercially viable ener- however, are typically used for “public gy technology. works” projects which have high visibility. On the one hand, the public has a clear interest in ensuring the widest possible dissem- FEDERAL INFORMATION PROGRAMS ination of research and development work In addition to the major grant programs conducted under Federal auspices. This is described above, a series of activities which particularly important with onsite solar provide grants and/or technical services ex- equipment because many of the manufac- ist within the various Federal agencies. turers are small, having neither large re- These include such things as the Extension search staffs nor easy access to information Service of the U.S. Department of Agricul- about a rapidly changing technology.

On the other hand, a company which is not permitted to retain any proprietary in- ‘9 Housing Act of 1949, Sect Ion 504 formation concerning the equipment it de- Ch. Ill Federal Policy for Promoting and Regulating Onsite Solar Energy ● 99

velops with Federal funds may conclude ISSUE 6 that it has no commercial interest in the development. Without patent protection Should the Federal Solar Program include a and without any advantage of advanced major effort to encourage competitiveness in design knowledge, the company may deter- solar energy and promote small solar busi- mine that it cannot risk manufacturing the ness? equipment. The company would undoubted- The relatively small investments associ- ly enjoy some competitive advantage as a ated with onsite solar energy devices have result of its research, if only because of the made it possible for many smalI businesses experience and ideas it obtained. The Feder- to enter the market. Indeed, much of the inal grant would have placed the firm on the novative work now being done in the area edge of the “state-of-the-art” in at least one has emerged from firms with very limited area of technology— a position that would assets. This unique feature of the onsite leave the company in a uniquely favorable solar energy field presents a difficult choice position to make further progress with its for the policy maker. A program for support- own funds. Most of the commercial technol- ing small, relatively simple technologies will ogies which have “spun off” from research have many more firms to choose from than sponsored by the Department of Defense a program for developing large energy tech- and by NASA have resulted from such situa- nologies, which require large capital in- tions. Even in situations where the complete vestments in individual projects. Supporting results of research work were published, the some of the small solar energy firms offers companies involved retained valuable ex- an opportunity to explore a rich variety of perience in the practical difficulties asso- concepts without a massive investment in ciated with manufacturing and design which any one approach, as well as a better op- might be difficult or impossible to publish. portunity to foster competition in the ener- (A machinist who d is covers that a driII works gy market. Apart from any such pragmatic best if you spit on it before making a critical advantages, promoting small business has hole, for example, may hold the key to a always been considered a desirable objec- problem which would require another com- tive in and of itself; the small, independent pany months to resolve. ) competitive firm is still a cherished ideal of the American economic system.

At present, the Government does not have On the other hand, small firms are likely much flexibility in adjusting its policies in to have Iimited marketing experience, no na- this area Only NASA is now able to grant ex- tionwide representatives and contacts, and clusive Iicense protection to products devel- limited research funds. Some may be ineffi- oped with FederaI support. Several innova- ciently managed and others have Iimited ex- tive approaches have been proposed, how- perience with the difficulties associated ever, and DOE is funding the development with taking a good engineering concept, de- of a new heat-engine design in an experi- veloping a marketable product, construct- mental arrangement with the Sunstrand Cor- ing equipment for mass production of com- poration. In this program, the Government is parable products, and developing sales and acting very much Iike a private source of advertising policy. The policy options of- “venture capita l,” giving partial develop- fered in this paper do not resolve this dilem- ment funding and retaining a partial interest ma; they give encouragement to small enter- in the resuIt prises but do not include requirements which ensure that small enterprises get a specified share of Federal funding. A major effort should be made to explore alternative approaches to Federal support The Small Business Administration (SBA) for commercial products, and to determine has played a very limited role in promoting their utllitv and jiustice to the taxpayer. smalI solar energy businesses, although it 700 ● Solar Technology to Today’s Energy Needs

has begun to investigate the field as the which sells collectors as well as gas appli- result of congressional prodding. SBA will ances.30 The advantages and difficulties of participate in DOE’s program to finance utility participation in ownership of onsite selected energy-related inventions. solar energy equipment is discussed in some detail in chapters V and VI. It will be ex- A separate but related issue concerns Fed- tremely difficult for any organization to eral policy on restraint of trade. It is appar- monopolize the solar industry because of ent that solar energy systems, particularly the inherent diversity of approaches; there onsite devices, will increase competition in will probably always be intense competition the energy supply industry. A substantial between different designs. Probably the fraction of the cost of smaller solar systems most serious danger to competitiveness in (particularly and virtually the entire cost of the solar industry is the Federal Government passive solar systems) results from onsite itself. The potential for competition be- construction work which would be per- tween different organizations and different formed by local building contractors. The engineering concepts could be distorted if building industry is one of the most com- Federal funding is unwisely allocated. petitive industries in the country, The diversity of approaches, the fact that different climates will call for different systems, and ISSUE 7 the relatively small investments required to manufacture many simple types of solar de- What sort of consumer protection is required vices will almost certainly maintain the in solar energy products? competitive nature of the solar manufacturing industry. There will, of course, be items The central problem, not surprisingly, is which can only be produced economically the novelty of the equipment. Homeowners, in very large quantities. Production of sit i- builders, architects, and the financial in- con solar cells, for example, probably must dustry share these fears: take place in facilities capable of producing 1, Will the system work as advertised? 5 to 50 MWe annually if low cell costs are to be achieved. 2. How long will it last? 3. Will operational costs be prohibitive? The Federal Trade Commission is monitor- ing the solar industry to insure that existing 4. Will a solar unit hurt the resale value oil companies and utilities do not dominate of property on which it is installed? the field to the point of restraint of competi- 5. Will the technology change so rapidly tion in the area. Both utilities and major oil that the equipment now available will companies are entering the solar industry. A soon be obsolete? majority of the photovoltaic devices manufactured in the United States for example, These anxieties are intensified because: (a) are produced in subsidiaries of major oil there are no standard techniques for pre- companies. Both the Electric Power Re- senting performance data on the variety of search Institute and American Gas Associa- different systems for sale, and (b) many sys- tion have sponsored projects in solar energy tems are offered by small organizations and a number of utilities have undertaken without substantial assets or wide experi- projects on their own. (For example, the ence in manufacturing. Indeed, many of the Southern California Gas Company has been firms now producing solar collectors, for ex- involved in a large-scale program for dem- ample, are Iikely to vanish during the next 10 onstrating solar hot water in California since years, leaving their customers with equip- 1973. ) The Pennsylvania Gas and Water Company acts as a manufacturer’s represen- ‘“j H Williams, “Solar Energy and the Gas Utility, ” tative for solar collectors, and Gasco Inc. of February 1977 (Dlstrlbuted by the American Gas Honolulu has a direct merchandise arm Association ) Ch. III Federal Policy for Promoting and Regu/ating Onsite So/ar Energy ● 101

ment no one else is qualified to repair. That The Government could also help by re- part of the problem will get even worse, be- quiring that all systems sold bear perform- cause potential buyers will be faced with an ance ratings conducted under procedures ever-widening array of equipment and ad- prescribed by Federal law. vertising c Iaims. Another major problem has been the To be sure, any new technology under- shortage of building inspectors trained to goes such growing pains. And in due course recognize mistakes made in installing solar certain manufacturers will establish reputa- equipment. InstalIation costs often repre- tions for high-quality products and for back- sent a significant fraction of the total cost of ing their systems with attractive mainte- a solar system, and a large fraction of the nance contracts. Unfortunately, it could problems encountered with solar equipment take years for this to happen — and in the is attributable to improper installation. Fed- meantime some unscrupulous dealers are eral support of training programs for inspec- likely to enter the field. tors could provide useful assistance in this area. Can the Government help to remove most of these concerns? It will be extremely dif- However, none of these approaches can ficult the way things look now — the Govern- eliminate the basic fear which surrounds a ment itself is uncertain about the best novel technology. The most powerful influ- technical approaches to support, and it ence on the public’s reaction to onsite shouId not be dogmatic anyway. However, equipment will be the behavior of the solar standards have been established for the industry itself. Because of its strong self- equipment the Government buys, and this interest in policing itself, the industry may could provide some guidance for prospec- welI be the best source of advice for ways in tive purchasers. A process for developing which the Government might assist in build- standards for solar heating and solar hot ing consumer confidence water equipment has been underway for some time, and plans are being made to certify a national testing laboratory which can ISSUE 8 assure that tests are properly administered. Progress on both fronts, however, has been What are the objectives of the solar demon- frustratingly slow Great care is needed to stration program, and what criteria should be make sure that such standards do not in- applied to the systems demonstrated? advertently eliminate novel approaches. There has been considerable confusion in both areas. On the one hand, demonstration At a minimum, it will be necessary to projects are presumably not a part of a re- develop mechanisms to ensure that stand- search program since the systems demon- ards are updated to take account systema- strated are presumably commercialIy avail- tically of advances in solar technology. It able. On the other hand, there is little point will not be an easy matter to work out stan- i n demonstrating that commerciaI systems dards for another reason: each subtechnol- work if a market for them already exists or i n ogy will require its own set of standards, demonstrating that they are too expensive if which must be arranged in such a way that there is no market. The program could be they are applicable to a variety of buiIding used to reduce costs only if the program pur- sites Some such work has already been chased so many units of a given type [halt done The National Bureau of Standards has manufacturers could justify installing mass- developed interim standards for solar heat- production equipment, This course seems ing and hot-water systems, and NASA-Lewis undesirable, however, since funds used for has developed preliminary standards for the this purpose could probably be better used photoelectrlc systems which wiII be pur- to support tax incentives and loan assist- chased for electric generation. ance. 102 . Solar Technology to Today’s Energy Needs

Passively heated and cooled buildings are to the attention of the local population and perhaps a unique case, however. A large providing an example of a real, functioning number of concepts are possible, and it is unit which can be visited by interested frequently difficult to predict how designs building contractors, potential investors, wilI work or how much they add to construc- and other interested parties, tion cost without field demonstrations. A large number of demonstrations is needed THE EXISTING MARKETING PLAN since it is necessary to carefuIIy tailor de- There is a great deal of confusion in the signs to each climate (perhaps to each mi- current program about which technologies croclimate). Another possible objective of should be demonstrated, when they should the program is to provide information about be demonstrated, and the size of the ap- the lifetime, reliability, operating costs, and plications which should be chosen for dem- unexpected problems associated with instal- onstrations. The lack of a coordinated plan lations operated by inexperienced owners. has resulted in the following: While information in this area is needed, the use of expensive demonstration programs to 1. A consistent underemphasis on retrofit gather it must be justified carefully. At a applications when the retrofit market is minimum, the demonstration programs much larger than the market for new should be integrated with an effort to obtain construction. data in these areas using laboratory testing 2. Underemphasis on combining solar and equipment. An effort should be made to conservation demonstrations, Passive publish the results of instrumented analysis solar buildings have received little at- of the demonstration units in many different tention as a result. climatic regions as soon as possible and to communicate this information to building 3. Lack of planning to extend demonstra- designers in the area. tion into electric generation and cogeneration equipment and into industrial Information gathered about the cost of and commercial markets. the units purchased in connection with the demonstration program must be treated A lack of a systematic approach to these with great caution and cost data prepared technologies has resulted in many a situa- with considerable care. It is important, for tion where systems intermediate between example, to separate costs incurred in the residential and large utility applications demonstration unit which would not have have been given much too little attention. been incurred if the device were built with- Part of this distortion, of course, is inherent out Federal support (the cost of instrumenta- in the unevenness of congressional support tion, for example, must be separated from for different kinds of programs. other costs). Interpretation of cost data is Commercial and industrial facilities and difficult since, if the demonstration program multifamily residential units are attractive is choosing its sites properly, the demonstra- initial markets for solar equipment for a tion solar device will be among the first of number of reasons: its kind in the region. It is to be expected that installers charge more for installing the 1. It should be easier to retrofit solar demonstration units than they would charge equipment on commercial buildings once such installations become routine. than on residential buildings since run- Mistakes encountered in the first-of-a-kind ning pipes from collectors to the heat- installation can be avoided as experience is ing and cooling equipment would dis- gained. rupt a proportionately smaller part of the building. Perhaps the most useful function of the demonstration program is simply one of 2 The owners of commercial buildings propaganda: bringing solar energy systems tend to be more sophisticated at anal- Ch, /// Feclera/ Po/icy for Promoting and Regulating Onsite Solar Energy ● 103

yzing life-cycle costing than owners of ly investing heavily in designs for such single family residences. systems out of internal funds — as well as using solar celIs to power spacecraft), the De- 3. Systems on commercial buildings may partment of Agriculture (which is develop- have greater visibility than systems in ing solar heating for barns and other farm residential neighborhoods, and busi- buildings, along with equipment for agricul- nesses would frequently advertise their tural process heat, irrigation pumps, etc.), use of solar energy. and the National Bureau of Standards 4 Cooling technology and some heat en- (which is developing standards and testing gine technology which is not ready for procedures for solar equipment following in- residential demonstrations is now avail- itial work by NASA). The Department of the able for commercial demonstration. Interior and many other agencies have smaller programs, most of them for the in- 5. Single commercial systems would have stallation of a solar hot water or heating a much greater impact on fuel con- system at one of the agency’s buiIdings. sumption than an individual residence, and would be easier to manage with a Still other Federal agencies are in a posi- smalI staff than numerous installations tion to implement regulations affecting on different types of residences. solar energy systems. For example, the Fed- eral Energy Regulatory Commissin(FERC) in DOE (formerly the Federal Power Com- ISSUE 9 mission) is helping to develop design requirements for solar electric commercializa- Which Federal agencies are conducting solar tion projects. The Veterans Administration research programs, and how well are these is examining the feasibility of allowing VA programs coordinated? loans to be used for solar equipment and is planning to use solar equipment at some of Those agencies with major responsibilities its hospitals. The section of HUD charged in solar energy are DOE (which has been giv- with administering FHA loans is examining en responsibiIity for al I solar research pro- the possibility of changing minimum proper- grams and is developing programs to accel- ty standards to permit funding of solar erate the commercialization of solar tech- equipment. The Council on Environmental nologies which are ready for market) and Quality is conducting an independent study HUD (which is managing the residential of solar heating and cooling for single fami- heating and cooling demonstration pro- ly houses, The list could be extended. grams). I n addition to these major activities, To some extent, of course, duplication be- however, there are solar programs in the De- tween agencies in solar research and devel- partment of Health, Education, and Wel- opment produces healthy competition. It fare, the National Science Foundation can prevent the development of a monolith- (which retains a small solar-energy staff ic approach to solar-technology research even though the bulk of research has been which could lock out innovative concepts. transferred to DOE), the National Oceanic and Atmospheric Administration [which col- On the whole, officials interviewed agree lects such climatic data as sunlight inten- that duplication exists, But they argue that sities and wind-speeds for use in the evalua- most work is complementary and that it is tion of solar technology), the Defense De- coordinated with administration-wide solar partment (which is going to install a variety policy. They contend that each agency of solar devices on military property, in- should carry out its unique responsibility in cluding electric systems for remote facil- this area. Some say that funding solar devel- ities], NASA (which has great institutional in- opment through a number of agencies prob- terest in the development of an orbiting ably results in a larger total solar budget solar photovoltaic system — and is reported- because it is easier for each of two depart- 104 ● Solar Technology to Today’s Energy Needs

ments to get a $2-million solar project than tems for nonutil ty appl cations, the bulk of it is for one department to get a single $4- DOE’s solar electric research program is di- mill ion project. rected at technologies designed exclusively for large, central generating facilities This There are, however, areas where confu- strategy has several difficuIties: sion in management could create difficulties: 1. There is no clear indication that large solar electric plants are more efficient — Plans to change FHA and VA loans are or produce less costly energy than proceeding without any clear guidance smalIer, onsite faciIities from DOE, which has a clear mandate to commercialize solar energy technol- 2 The large-scale projects being exam- ogy. ined are very unlikely to make a con- – In the meantime, HUD has proceeded tribution to commercial energy sup- to fulfill its mandate in the demonstra- plies before the 1990’s; smaller devices tion of residential units and is develop- may have greater potential for making ing technical expertise and manage- contributions in the near future ment experience in demonstrating nov- 3 The very large solar electric system be- el solar technologies ing contemplated will require simul- –There have been some misunderstand- taneous development of several novel ings between NOAA and DOE over types of technologies (collectors, re- which agency’s funds should be used to ceivers, storage devices, etc. ) These maintain installations for developing a systems will be required to operate on a data base on insolation, wind speed, large scale in the proposed multi-mega- and ocean temperatures. watt systems. It may be better to test — Total energy studies are proceeding in and evaluate components on a smaller HUD and the National Bureau of Stand- scale, or to develop components which ards, as well as in DOE Coordination could be used on a variety of systems of between these programs could be im- different sizes. proved 4, Concentration on large systems re- — Research in advanced heat engine tech- quires that difficult choices be made nology relevant to solar energy is being between many competing approaches funded by DOD, NBS, the Department before any of the alternatives have of Transportation, and NASA, as well as been adequately tested. Funding small- by DOE In some cases duplication has er projects would permit greater num- occurred. Coordination could be im- bers of concepts to be tested at much proved, lower risk. – Heavy NASA support of orbiting photo- DOE officials recognize that there are voltaic systems, not well coordinated numerous total energy concepts and pro- with DOE, could greatly distort the posals for generating electricity for special- overalI photovoltaic development pro- ized agricultural and industrial applications, gram. where available technology could be used in ISSUE 10 an expanded demonstration program, But they also note that additional funding would Does the present Federal program for devel- require additional staffing, which remains as oping solar electric generating equipment the Office of Solar & Geothermal Energy overemphasize large, central station ap- Program’s largest problem. The solar pro- proaches at the expense of smaller, onsite gram does project a number of experimental approaches? projects, which could include agricultural In spite of recent changes that have up- process heat, small community applica- graded research on electric generating sys- tions, agricultural and industrial centers, Ch. /// Federal Policy for Promoting and Regulating Onsite Solar Energy ● 105

and several other projects in thermal elec- HEAT ENGINES tric generation. At least one project of each An enormous range of technical possibil- type of total energy could be built to re- ities for heat engines is relevant to solar ap- search problems and demonstrate potential. plications. While heat engines currently Programs to develop heat engines and stor- available can be used in near-term solar age apparatus compatible with onsite elec- energy designs, few of the engines have tric equipment also appear to be supported been designed especially for solar applica- at much lower levels than is warranted by tions — modifications of engines produced the equipment’s potential. for some other application will be used. Ad- ditionally, most near-term applications of ISSUE 11 solar energy will utiIize smalIer heat engines than those typically used in utility opera- What kinds of research need increased em- tions, and the technology for small heat phasis in the Federal solar program? engines which can operate from an external heat source is frequently not as advanced as COLLECTORS the technology used for large central power- Supporting the development of advanced plants, in many cases, the only small heat collector design presents special difficulties engines available are based on European since there are a large number of devices be- designs. ing developed independent of Federal fund- The development of improved heat en- ing and the number of possible designs is ex- gines would unquestionably lower the cost tremely large. The development of reliable, of solar energy for applications requiring a inexpensive coIlectors is, however, probably high ratio of electrical to thermal energy the single most important technical problem New devices which could make efficient use faced by the solar community. of low-temperature solar heat sources could reduce the complexity of solar colIectors re- Federal support has concentrated in four quired for power generation. More efficient areas: 1 ) improving the design of flat-plate heat engines can reduce total system costs colIectors used in connection with the heat- by reducing the size of the collector field in and coollng demonstration program; 2) g needed to provide a given amount of elec- developing heliostats for the central re- trical or mechanical energy since collector ceiver demonstration projects; 3) developing costs tend to dominate overall system costs. and testing materials for use in collectors Development of a high-performance Stir- (e.g. , low-cost plastics for covers and receiv- ling, Ericsson, or closed-cycle Brayton ers), and 4) developing a series of distributed device would open many attractive options coIIector designs in connection with the to- for solar electric generation. Development tal energy program While the last program has been effectlve in testing a variety of col- of improved cogenerating systems would improve the overalI utilization of the solar lectors, an even greater variety must remain withiout serious Federal support. For exam- energy received in applications where there is a requirement for thermal energy, ple, relatively Iittle attention has been paid Most federally supported work on ad- to the development of Inexpensive pond col- vanced heat engines, however, is relevant lector and simple, Iightweight two-axis con- only for large central powerplants and the centrators for use with smalI heat engines funds available for engines designed for and photovoitaic devices designed for use in high-intensity sunlight One major difficulty solar, transportation, and industrial applica - with many federally sponsored designs has tions are very Iimited, been the temptation to “over-engineer” de- Background on Federal Programs vices rather than to emphasize techniques for simplicity, low material requirements, Most other work on advanced heat en- and low cost. gines in DOE is being funded by the Office 106 ● Solar Technology to Today’s Energy Needs

of Conservation. Projects are funded in 2. About $12 million will be spent on new three categories: heat engines during FY 78 by the “heat utilization” section of the Office of Con- 1. Heat engine research in the Division of 34 31 servation. Projects funded in this area Transportation Energy Conservation. will include support for two high-tem- Development of new heat engines for au- perature expanders which might be tomobiles and other road vehicles is being used for combined cycles, support for coordinated with major U.S. automobile designs which will increase the pump- manufacturers who apparently are unwilling ing efficiency of engines .35 Research on to fund development of advanced engines small devices will include the develop- without Federal prompting. ment of efficient steam turbine systems in the 2 to 6 MW range and studies of Three projects are of particular interest Stirling engine applications. The Stir- for solar applications: ling work will include studies of designs ● A program is underway to develop an suitable for solar applications as well as efficient Brayton-cycle (gas turbine) en- designs compatible with total 500 to gine. In the past years, tests have accu- 2,000 horsepower energy systems in res- mulated the equivalent of over 150,000 idences and industry. It is hoped that a road-miles on some designs. Work is Stirling device for utility applications also underway to develop ceramic en- could be produced commercially by gine components capable of withstand- 1982. 36 Work on Stirling engines is also ing very high temperatures (2,500” F). underway in DOE’s Office of Nuclear The government will purchase seven Energy Programs, DOD, NASA, and the GeneraI Motors Brayton engines during National Bureau of Standards, but con- FY 78 for $500,000. The engines will be servation and solar applications offi- used for road tests. cials claim there is Iittle duplication. 37 ● The Government is also contributing to the Ford/Philips program to develop a 3. Work is also being supported which will Stirling engine for road vehicles. This examine engines for topping or bottom- work will include continuing tests on ing cycles for utilities and for industrial the current 170 hp design and develop- processes. Therm ionic devices for high- ment of a smalIer (80 to 100 hp) design. temperature topping is being supported Work next year will include completing with the objective of actualIy operating engine performance and emission tests a device in a boiler by 1980.38 Three dif- and improvements on the difficult ferent designs for organic Rankine cy- “heater” heat exchanger which has cle devices are being supported for use plagued the Philips design. DOE is con- with medium-temperature waste heat tributing about $1.6 million to this proj- streams. Work on low-temperature sys- ect in a cost-sharing program during FY tems is beginning, although its exact 78.33 structure seems somewhat vague. ● Development of an organic Rankine de- Work on advanced heat engine designs is vice to increase the efficiency of a also being supported by the Fossil and truck diesel engine is also being sup- Nuclear Energy Office of DOE. These de- ported. This combined-cycle design would replace the truck’s muffler with a boiler for the organic fluid, “ERDA Budget Estimates (Amended FY 78), p 80 “lbtd., p 82 “John Beldlng, Research and Technology Dlvislon, “ ERDA Budget Estimates (Amended FY 78), Book 1, Office of Conservation, DOE, private communica- p 57 tion, 1977 “lbld , p 96 ‘7 George Pezdlrtz, Off Ice of Conservation, private ‘) Division of Transportation, Office of Conserva- communication, 1977 tion, DOE “ERDA Budget, p 86 Ch. /// Federal Policy for Promoting and Regulating Onsite Solar Energy Ž 107

signs are, almost without exception, ap- istry of photovoltaic devices. Serious work plicable only to large central power applica- in the area of developing materials for ter- tions. The fossil energy coal program has re- restrial solar celIs has been underway for quested $25.5 million in FY 78 budget au- only about 5 years. Work on the crystallog- thority to develop advanced power systems raphy, electrical, and optical properties of including combined cycle and Brayton cycle silicon and other photovoltaic materials devices. 39 The Nuclear Research and Appli- could be extremely useful. The properties of cations Office of DOE is financing two amorphous materials, which may have ap- studies into Stirling engines, one totaling plications in photovoltaic devices, are still almost $5 m i II ion to develop a Stirling iso- largely unknown, tope power system, contracted with General Electric, and the other with Mechanical The variety of cell designs which have Technologies, Inc., totaling more than $1.5 been proposed for use in inexpensive flat ar- m i I I ion. rays and in various types of concentrators is discussed in detail in chapter X. Many ad- In addition, Nuclear Research and Appli- vanced cell concepts are receiving minimal cations is funding a $2-million-a-year study Federal support. by Garrett Air Research, Inc., of Phoenix to develop a 1.3 kilowatt Brayton isotope Finally, a number of fundamental ques- power system, as well as a similarly financed tions about the most effective use of pho- study by Sunstrand Corp to develop an or- tovoltaic equipment must be resolved. De- ganic Rankine device, also for a 1.3 kilowatt tailed system design work will need to be system. Both are due to be demonstrated done on the following topics: during 1978; Nuclear Research and Appli- – Mounting and support (e. g., should low- cations officials say the choice will then be cost celIs be used as a buiIding mater- made between the two systems 40 ial ?).

PHOTOVOLTAICS –What kind of cell cooling should be used ? A well-designed photovoltaic program must maintain a carefuI balance between — How should the systems best be inte- basic research, development improvements grated into existing utility systems? to current manufacturing processes, and en- Should onsite or utility storage be used? gineering work on practical system designs. Should the system sell as well as buy This is a difficult task since the field is from an electric utility? Should an elec- changing very rapidly It would be tempting tric backup or onsite generator burning to delay major decisions in the area until fossil fuel be used when solar resources research work has sorted itself out, but it are not avaiIable? should be possible to design a balanced pro- — How often should the devices be gram, supporting production and demon- cleaned ? stration work in areas where prospects of success seem particuIarly high whiIe contin- In the near term, it will be necessary to uing to give support to advanced concepts. design practical and reliable systems (At a minimum, there seems to be no point for remote (often unattended) installa- in waiting for “research breakthrough” from tions arty of these devices without supporting a vigorous research program, ) STORAGE

There is room for a considerable amount The present DOE storage program IS dom- of research on the bas]c physics and chem- i nated by two objectives 1 ) develop I ng very large storage systems capable of operating

‘ 9 Fos511 E nerg}, E KDA ~u~get, P 45 i n electric u t I I i ties to ‘‘level” the loads met ‘“Robert Morrow, NRA, 1977 by these utilities, and 2) the development of 108 ● So/ar Technology to Today’s Energy Needs

batteries for electric vehicles. Relatively at a cost of less than $30 per kWh of storage little work is being conducted expressly for capacity. This program is also supporting solar energy or for other onsite applications. research to develop inexpensive and effi- There is, for example, presently no tech- cient inverters for turning d.c. into a.c. nique for adequately evaluating the com- power; such systems are needed to make ef- plex issues of load management, transmis- ficient use of batteries. Again, the primary sion, and economies of scale for an inte- objective is the development of technology grated energy system. for utility load leveling.

Simple systems for storing relatively low- The electric vehicle storage program in temperature thermal energy or chilled liq- the Division of Energy Storage Systems is u ids in tanks, ponds, and aquifers — systems examining a number of advanced batteries which appear very promising in the analysis which have low cost and low weight, and conducted in this report — have received which last 4 years. I n normal use the tech- relatively Iittle support or interest, An enor- nology which DOE apparently feels has mous amount of fundamental work in ther- most promise in this area is the Iithium/iron mochemical storage systems remains to be sulfide battery, although different pairs of done, and a number of known reactions reactors are being sought. Three firms fabri- have been characterized well enough to cated such devices and delivered them to merit accelerated engineering development DOE for testing in FY 7841 DOE’s utility bat- work, A number of simple systems for stor- tery program has the objective of producing ing high-temperature energy in latent and batteries capable of 75-percent efficiency specific sensible and latent heat have never and 10-year Iifetimes in normal utility ap- received serious engineering design work. A plications. Work on a large battery storage number of other advanced storage systems test facility in New Jersey financed jointly (batteries, flywheels, and other devices) with the EIectric Power Research Institute couId also profit from greater attention. began in FY 77.42 The first batteries in this realistic utility environment will be lead acid batteries, but advanced batteries (prob- Background on Federal Storage Programs ably zinc-chloride and sodium-sulphur bat- In the Division of Energy Storage Systems teries) will be tested in the next phase. of DOE, a program has been developed to Lithium/iron sulfide devices may be in- investigate a variety of thermal and chem- stalled by FY 81. DOE is officialIy optimistic ical storage techniques. The m a i n objective about the potential of these batteries and of these studies is to examine the feasibility believes that the goal of $30 per kWh of of storing heat or electricity in order to level capacity can be achieved. the loads of major utilities, although the Solar technology could also make prof- technologies developed will probably be itable use of the variety of advanced energy directly applicable to solar energy systetms storage techniques being considered in the for which the storage requirements are simi- Division of Energy Storage Systems. Hydro- lar. Research will be required, however, to gen production and storage, underground adapt such systems to solar applications. pumped hydroelectric storage, underground Adaptation may be particularly difficult for compressed air storage, flywheels, and mag- onsite systems which may have storage re- netic storage are all receiving at least some quirements many times smaller than the attention in the current program. Many of smallest utiIity units tested under this pro- the secondary objectives of the energy stor- gram. age program are also directly relevant to The storage program has an objective of solar technologies. For example, the pro- developing batteries with an overall efficiency of 75 percent, and a 10-year installed 4’ERDA Conservation Budget FY 78, revised p 22ff lifetime (approximately 2,500 deep cycles), “lbld Ch. /// Fecfera/ Po/icy for Promoting and Regulating Onsite Solar Energy ● 109

gram to increase the efficiency of building tions of the potential energy contribution of space-conditioning and the use of industrial each solar application in the year 2000. No process heat through the judicious use of clear correlation is apparent. EIectricity gen- thermal storage techniques has clear rele- erated by solar systems, for example, is ex- vance to solar programs. Major field tests of pected to represent only about 34 percent of seasonal and load-leveling storage for build- the total contribution of solar equipment in ings are being conducted with the objective the year 2000 but is receiving 64 percent of of improving the efficiency of conventional the funding, while industrial process heat is heating and cooling systems by 10 percent, expected to provide 52 percent of the ener- and a major portion of the FY 77 funds for gy generated by solar equipment while re- thermal storage were used to start work on ceiving only 4 percent of the funding. seasonal storage and structural materials DOE has given solar electric power “high- with thermal storage properties for use in est priority” in its planning because of its buildings. potential as an “inexhaustible resource” and, it is claimed, it will “be given priority comparable to fusion and the breeder reac- ISSUE 12 tors.”43 Solar thermal systems, however, are Should funding levels in DOE programs cor- relegated to a lower priority and character- relate to relative estimated contribution of ized only as technologies which should be different technologies? pursued only to “provide an energy ‘margin’ in the event of an R&D failure in other areas.”44 Tables I II-4 and I II-5 compare the percentage of DOE solar funding given to three 4‘E RDA-76 major solar energy applications with projec- ‘“l bid

Table ill-4.—Authorizing Appropriations for the Energy Research and Development Administration, U.S. House of Representatives, 95th Congress {1st Session], Conference Report No. 95-671 —. . ——.

Demand sector

cultural pro-

SOURCES H qh demand esf I Imat{ from ERDA 48 Vol 1 UB 11 Low demand estimate based orI a 1000 demand srenarl{~ constrw-ted by !he Inst Itute for Energy Analysls FY78 Budqet Au!hor!ty from U S House of Representat, +cs Con ferr, n ‘e Report Au Iborlr ng Appropraiiuns f ,r the Energy Research and Deve 10 D m~n I Ad m I n [strat on October 6 1977 p 61 E R DA solar ;}r[ ~C u 1 (n g ua Is t, I Ier le(~ and re ported n S Ild r En< rq y A IJ: I I,- at c ns — A Com parat!. e A nalys(s to t h e year 2020 Summary Rep)d Draft J u Iy 1977 prepared by the M I t re Corporation Me !rek D IV IS !on 110 ● Solar Technology to Today’s Energy Needs

Table 111.5.—Authorizing Appropriations for the Energy Research and Development Administration, U.S. House of Representatives, 95th Congress [1st session], Conference Report No. 95-671

Operating Capital Plant Total expenses equipment

Heating and cooling of buildings ...... 94.4 2.0 96.4 Agricultural and industrial process ... , . 10.3 0 10,3 Solar electric ...... 210.7 5.4 41 216.1

Heating & coolng ...... 94.4 2.0 0 96.4 Agricultural and industrial process . . . . . 10.3 0 0 10.3 Solar thermal ...... 61.1 3.0 41.0 105.1 Photovoltaics...... 76.2 0.3 0 76,5 Wind ...... 35.3 1.4 0 36.5 Ocean thermal ...... 2.8 0 0 2,8 Satellite power systems ...... 2.8 0 0 2.8

TOTAL SOLAR ELECTRIC ...... 210.7 5.4 41 256.9 Biomass ...... 20.5 0.5 0 21.0

It is difficult to evaluate those arguments to expedite the long-term development of since a comprehensive plan for integrating solar energy, ” and “. that the Nation Federal and industrial investments in solar undertake an intensive research, develop- research has not been developed, and there ment, and demonstration program” in solar is no clear technique for determining when energy, As a consequence, Congress de- the time has arrived for Federal research clared that it was the policy of the Federal support to be phased out and other types of Government to “pursue a vigorous and vi- nontechnical support initiated. I n addition, able program of research of solar ener- there has never been a comprehensive exam- gy .; and provide for the development and ination by DOE of either the economies and demonstration of practicable means to em- diseconomies of scale in solar technology or ploy solar energy on a commercial scale. ” the relative merits of direct-thermal, elec- To enable the Nation to fulfill this policy, tric, and combined electric and thermal Congress established, in the same Act, the operations. Solar Energy Research Institute (SE RI) to “perform such research, development, and related functions” as determined by the ISSUE 13 DOE, “or to be otherwise in furtherance of the purpose and objectives of this Act. ” In The Solar Energy Research Institute, in its other words, it was the intent of Congress present operating relationship with DOE, that SE RI, while providing support to DOE, may not be sufficiently independent of DOE should also be able to provide independent to effectively meet its responsibilities in reaching the objectives set forth by Con- direction and assessment of the Nation’s effort to develop solar energy. This was re- gress in the Solar Energy Research, Develop- iterated at oversight hearings held a year ment, and Demonstration Act of 1974. after the passage of the Act. There it was In the Solar Energy Research, Develop- stated that Congress intended that SERI be ment, and Demonstration Act of 1974, Con- “highly visible” and be an institute symbolic gress found that “it is in the Nation’s interest of the “national wiII and the national effort” Ch. Ill Federa/ Policy for Promoting and Regulating Onsite Solar Energy Ž 111

toward solar energy, It is clear, therefore, to adequately manage the rapidly changing that the Congress did not want SERI to be and growing solar program. The FY 76 solar completely dominated by any other organi- budget, for example, was $116 million, but zation responsible for portions of the Federal only 46 staff professional positions were solar energy program. allowed. This amounted to just over $2.5 mill ion per professional. The problem be- Since the startup of SERI nearly 1 year came even worse in FY 77, with a budget of ago, however, it appears this intent is not be- $290 million to be spent by 54 profession- ing met. I n particular, the present method of als — amounting to nearly $5.5 million per funding SERI is to enact a “tax” on other professional. The management of such large programs under the Assistant Secretary of amounts of funding is particularly difficult Research and Technology. No separate line in solar energy technologies, where the item for SE RI appears in the budget; this typical contract is much smaller than the severely Iimits the abiIity of Congress to average contract grant made by other sec- directly evaluate the effectiveness of SERI tions of DOE. through the budget process. Furthermore, it is not clear whether SERI can report directly The staffing shortage can create two to Congress without DOE approval and types of problems: c Iearance. 1. It makes it difficult for DOE to react to SERI must maintain an ability to fairly a large number of innovative ideas and assess and, if necessary, criticize the direc- increases the temptation to spend tion DOE takes on developing solar energy, funds in a small number of major and if it is to fulfill the original intent of the Act. predictable projects rather than in a A clear congressional reaffirmation of larger number of smaller projects some SERI’s responsibility and mission and sepa- of which may have a higher risk. rate funding status within the DOE budget, wouId contribute significantly to SERI's in- 2. It necessitates transfer of the detailed dependence In addition, it may be desirable management responsibility to organi- to establish a more direct Iink between Con- gress and SERI to emphasize the intent of zations outside the DOE’s Solar Energy Division. Congress that SERI be a “visible” and “symbolic” institute of the Federal policy toward The problem associated with short staff- development of solar energy and not simply ing have been aggravated by demands another group to carry out current DOE placed on staff by the continuing, extensive polIcy public and congressional interest in solar en- ISSUE 14 ergy which is flooding DOE with inquiries, Much of this difficulty has been relieved Staffing Limitations under a grant to Franklin Institute, which A per~lstent shortage of protesslonal staff has set up a toll-free number (800-523-2929) h.~s be(~n .I major con~triiint on DOE’s ability to answer inquiries about solar energy. Chapter IV ONSITE ELECTRIC-POWER GENERATION Chapter IV.—ONSITE ELECTRIC-POWER GENERATION

Page Table No. Page Background ...... 115 . 5. Engine Requirements for Systems Designed Capital Costs ...... 118 . to Provide ReliabilityEquivalent to Utility Generating Plants ...... 118 Power Reliability...... 131 Storage Devices...... 119 6. Reliability of Onsite Equipment ...... 132 SolarCollectors ...... 123 OtherAspectsofCapitalCost Comparisons 124 LIST OF FIGURES Waste-HeatUtilization ...... 125 Figure No. Page OperatingCosts ...... ● ..*...... *.**.. 129 Reliability .*.*...... 129 1. Trend in Self-Generation ...... 115 Siting Problems...... 133. 2. Data From Steamplant Surveys, 1965-77...120 MiscellaneousOperatingProbiems ...... 134 3. Steamplant Survey Results Showing Average Unavailability Versus Size for Plants Completed During the Survey Period...... 122 4. Historic and Projected Load Factors LIST OF TABLES of Utility Generating Facilities ...... 125 TableNo. Page 5. Components of a District Heating 1. 1985 Generation Costs as a Function of System in Sweden ...... 128 PlantSize...... 118 6. Annual Operating Costs Versus Equivalent 2. lmpacts of Energy Storage on Electric Full-Power Hours of Operation for PowerSystems...... ,123 Baseload Plants ...... 131 3. Load Factors forTypical Buildings ...... 126 7. Space Requirements of Typical Com- 4. OperatingCosts of VariousSystems ...... 130 bined-Cycle Plants...... 135 Chapter IV Onsite Electric-Power Generation

BACKGROUND

While most electricity generated in the United States originates in large, centralized facilities owned and operated by electric utilities, the number of onsite generating plants has declined steadily and the average size of utility generating plants has steadily increased. Figure IV-1 shows, for example, that onsite generating equipment represented nearly 30 percent of all U.S. generating capacity in 1920 but only 4.2 percent in 1973. ’ The percentage of electricity generated in plants with a capacity greater than 500 MW, however, increased from 40 percent in 1965 to 56 percent in 1974.2 Since many of the benefits and problems of onsite solar equipment are shared by on site generating devices of all types, an examination of the potential market for the solar equipment must determine whether any of the economic and institutional circumstances which produced the trend toward centralization might change during the next two decades. There are two reasons for undertaking an examination of this rather fundamental issue. The most obvious is that the ways in which energy is produced and consumed around the world will need to change dramatically during the next three decades, if only because reserves of inexpensive oil and natural gas will vanish during this period. These changes will require a reevaluation of alI conventional assumptions about energy. Secondly, the prospects for onsite generation may be improved by newly developed technologies—especially solar energy equipment. The solar resource is inherently distributed and economies of scale are often difficult to identify.

There are a number of explanations for the trend toward centralization: ● Larger equipment tended to be less expensive per unit of installed capacity ● Larger plants tended to be more efficient in their use of fuel and had lower maintenance costs per unit output, since a relatively small number of trained operators could reliably maintain large generating plants. ● Larger plants could be installed in remote locations, simplifying siting problems and ensuring that pollutants would be released at a distance from populated areas.

● In recent years, a major advantage of large plants was their ability to use coal instead of oil and gas as a fuel. The delivery of coal to a large plant, using a dedicated rail facility, could significantly reduce the effective cost of coal fuel. 115 116 ● Solar Technology to Today’s Energy Needs

● Onsite facilities were frequently unable One of the major objectives of this study to compete with “promotional” rates is to determine whether there are or will be charged during the periods when util- circumstances under which the advantages ities were enjoying declining marginal of onsite energy equipment, particularly costs. Under those circumstances, all solar energy equipment, can outweigh this utiIity customers benefited from in- rather impressive set of traditional reasons creased sales, since average rates for avoiding onsite equipment. It is in- declined as utility sales expanded. teresting to observe that many nations which have experienced higher fossil fuel ● Many companies were reluctant to in- prices than the United States make far vest in onsite equipment because they greater use of onsite electric power. For ex- were unable to finance a large fraction ample, 29 percent of the electricity gener- of the equipment with their own equity, ated in West Germany is produce d by onsite They were forced to turn instead to industrial plants. 3 debt financing, which had the effect of increasing company vulnerability dur- Onsite equipment can offer a number of ing periods of economic hardship, This advantages: meant that greater returns were expected of onsite generating equipment ● Location of equipment “onsite" greatly than were expected of investments in increases the design opportunities and product-oriented areas. makes it easier to match energy equipment to specific onsite energy de- ● There was a fear that a failure of onsite mands. In particular, it should make it equipment could have disastrous ef- easier to use the thermal output of fects on the operation of a business, solar collectors and the heat rejected and a feeling that the headaches of by electric generating systems which is electricity production should be left to typically discarded (often at some en- the utilities, whose primary business vironmental cost) and wasted by cen- was energy. tral generating facilities. There is a con- ● Electric utilities have frequently op- siderable amount of overlap between posed the installation of onsite gener- equipment being developed for energy ating facilities by industry and have conservation and onsite generating de- often been reluctant to own such equip- vices, and onsite designs are usually ment themselves. most successful when integrated into a ● Many onsite facilities have been poorly coherent plan encompassing both ener- designed and have received inexpert gy demand and supply. maintenance, and reports of failures ● The basic solar energy resource is avail- have frightened prospective investors. able onsite whether it is captured or ● Onsite generating equipment has tend- not. Integrating the equipment into the ed to be of somewhat archaic design. wails or roof of a building or into the landscape around a building can re- ● Federal and industrial research has con- duce the land which must be uniquely centrated almost exclusively on the assigned to solar energy. Onsite genera- development of improvements in large tion of energy can reduce the cost of centralized equipment rather than in transporting energy and reduce the systems optimally designed for onsite losses and environmental problems generation. ● Onsite equipment in some installations has created problems of noise and local 3 R Sukhula, et al (Thermo-Electron Corp ), A pollution, and some owners have en- Study of Inplant Electric Power Generation in the countered difficulties in expanding gen- Chemical, Petroleum Refining, and Paper and Pulp in- erating faciIities. dustries, june 1976, pp 1-4 Ch. IV Onsite E/ectric-Power Generation ● 117

associated with transmission. (The ex- energy systems, which result from econ- tent of these savings can be difficult to omies of scale in individual devices, from compute, and this topic is treated with the advantages resulting from the fact that greater care in chapter V.) the large systems meet a demand relatively free of the sharp demand peaks which char- Ž Onsite equipment can reduce invest- acterize individual energy customers. The ment risks, because it can be con- smooth demand results from combining structed rapidly and additional units many customers into a single diverse load, can be installed quickly to meet unex- and this advantage could be enjoyed by pected changes in demand. small generating centers able to buy and selI energy from a large energy transmission and ● Onsite equipment can be made as effi- distribution system. cient as centralized equipment, even if no attempt is made to use thermal energy exhausted by generating de- Since the primary objective of improving vices, If this heat is applied usefully, an energy system is to reduce the net price overall efficiencies as high as 85 per- paid for energy by all consumers, it is cent are possible. necessary to try to show how each component will affect the overall price of meet- ● High-efficiency energy use, possible ing real fluctuating demands for energy with combined electric and thermal throughout the year. This clearly is not a generation, can result in a reduction of simple undertaking, particularly since so polluting emissions produced by onsite many changes can be expected in the way devices burning conventional fuels. energy will be generated and used during the next few decades. Many new technol- Ž Onsite equipment can be manufac- ogies wilI undoubtedly emerge in gener- tured, installed, and maintained with- ating, storage equipment of all sizes, and in out major changes in the way energy- the technology of energy transport. related equipment has been handled in the past. It would not require novel approaches to financing, new types of businesses, major new categories of Energy can be transmitted in electrical, labor skills, or major participation by thermal, or chemical form, for example, and the Government. stored as mechanical, thermal, or chemical potential energy Energy can be generated In addition, there may be social, strategic, at a central facility and sent for storage in or political reasons for trying to reverse the onsite units (it is common in Europe, for ex- trend toward increasing centralization of ample, to store electricity which wilI be used energy production in the United States for space heating in the form of heated which have no direct connection with the bricks), and energy generated locally could economic merits of the case. Some of these be sent to a central facility for storage issues are discussed in chapter VI 1.

In assessing the relative merits of large optimizing the combination of onslte and and small equipment, it is necessary to central energy devices will be difficult be- judge both as a part of an integrated energy cause of the many variables and uncertain- system. Reviewing the performance of units ties, but the outcome of this analysis can operating in isolation can be very mislead- profoundly affect perceptions about the ing. relative value of different types of equipment and it can affect the designs chosen In particular, it is necessary to distinguish for onsite systems These issues are treated between the advantages enjoyed by large in more detaiI in the next chapter 118 ● Solar Technology to Today’s Energy Needs

CAPITAL COSTS

The only satisfactory technique for com- can be misleading; it is important to comparing the cost of onsite and centralized pare the costs and performance of devices power generation is to undertake the de- selected to perform optimally at the size tailed comparison of life-cycle costs of in- range selected. tegrated systems which is undertaken in detail in volume 11. It is interesting to notice, GENERATING PLANTS however, that there frequently is no clear correlation between the size and the unit Table IV-I indicates that the initial costs cost of generating and storage components. of onsite generating equipment may actual- Comparisons between different sizes of ly be less than the cost of larger pIants per equipment based on the same basic design unit of generating capacity.

Table IV-1 .—1985 Generation Costs as a Function of Plant Size (1975 dollars) Ch. IV Onsite Electric-Power Generation ● 119

Review of Electrical Wor/d’s Steam Sta- value of storage is a strong function of the tion Cost Surveys for the past 22 years’ cost of transporting energy and the strategy showed that, from 1965 to 1975, there was of its use Many types of storage are con- no significant decline in capital costs of structed from moduIar units and do not steam plants of all types as their size in- show strong economies of scale. creased. Figure IV-2 shows costs per unit of In most cases, low-temperature thermal generating capacity as a function of plant energy can be stored much less expensively size for steam plants completed from 1965 in large systems than in smalI storage tanks, to 1977 Only the 1977 survey gives any in- This is because the ratio of the surface area clination of economies of scale, and the required for a vessel containing a heated limited number of plants in that summary fluid to the volume of the fluid stored de- compared to previous surveys makes it very creases as the volume increases. A low ratio difficult to conclude that economies Of means that less material will be required for scale may again be valid. the storage vessel and that the area over Another trend determined in this review is which heat can be lost to the environment that unavailability frequently increases as per unit of energy stored is reduced. size increases, resulting in higher effective In some very large systems, no insulation capital costs (figure IV-3). It should be noted wilI be required other than dry earth. The ad- that the stations reviewed in these surveys vantage of large-scale storage of hot water are new, and the availability problems may would be increased significantly if tech- result in part from breaking in the new niques for storing hot water in aquifers can plants be developed. Taking advantage of this op- While small units manufactured in small portunity requires a piping network capable numbers may be substantially more expen- of delivering fIuids to the central point. sive per unit output than large systems, the Systems for storing energy at high cost of small systems can be substantially temperatures (e.g., above 300 OC/5720 F) typ- reduced using mass production techniques ically consist of a large number of relatively unsuitable for larger devices. Moreover, in- small modules, and large devices do not vestments in large generating faciIities are show economies of scale. In many cases, the so substantial that very conservative design storage must be located close to the site practices must be used. SmalIer systems per- where the energy will eventually be used. mit greater experimentation, and, in many For example, electricity can be “stored” in cases, innovations can be introduced into bricks, heated to high temperature, which the market more rapidly, Conservative de- are used to provide space heating for build- sign practices, however, play a large role in ings during periods when electric rates are determining which device will be selected high. Such devices must be located in the for mass production buildings they serve.

No clear pattern of cost emerges for STORAGE DEVICES devices capable of storing energy at intermediate temperatures. It is difficult to generalize about the Most of the techniques which have been economies of scale of storage since the proposed for storing electricity in mechanical form (in hydroelectric facilities, for ex- ‘ Ioth through 19th Steam Stat Ion Cost Survey, ample) are only feasible in relatively large E/ectrfca/ World, Oct 7, 1957, p 115, Oct 5, 1959, p units, although it may be possible to use the 71, Oct 2, 1961, p 69, oct 7, 1963, p 75, Oct 18, 1965, p 103, Oct 16, 1967, p 99, NOV 3, 1969, p 41, numerous small dams which already exist Nov 1, 1971, p 39, NOV 1, 1973, p 39, NOV 15, 1975, around the country for small amounts of p 51 storage. Battery systems now available for

Ch. IV Onsite .E/ectric-Power Generation ● 121

I 122 ● Solar Technology to Today’s Energy Needs Ch. IV Onsite Electric-Power Generation ● 723

storing large amounts of electricity for util- SOLAR COLLECTORS ities are more economical in relatively large units (several megawatt hours), although Since most types of solar collectors con- economies of scale disappear long before sist of arrays of individual devices with in- capacities equivalent to those of large dividual areas less than 30 square meters hydroelectric storage facilities are reached. (m’), there is no clear economy of scale for most types of coIIector arrays. An optimum In the future, however, it may be possible size for a heliostat central receiver system to develop low-cost batteries for which will probably be established as the costs of there is no particular advantage in designing these systems are better understood, but it is units larger than a few hundred kilowatt not clear whether a large penalty will have hours. This cannot be said for most other to be paid if the system is not at the opti- types of chemical storage systems. Large- mum size. Similarly, a system which requires scale storage of hydrogen or other gasses, piping to connect a series of distributed for example, can probably be best accom- thermal collectors will probably have an op- plished in large underground chambers. timum size since these plumbing costs will The economies of scale of storage devices become large for large systems. is discussed in detail in chapter Xl.

Onsite or regional storage facilities also Pond collectors and several other special- offer a number of other advantages which ized collector designs may also show some 2 are not directly reflected in initial costs of economies of scale up to 2,000 to 3,000 m , the systems. Table IV-2 summarizes the but again, the penalty for building a smaller benefits of centralized and decentralized system may not be large. Much more must energy storage devices identified in an ex- be known about the economics of collector am i nation of alternative techniques for stor- devices before confident statements can be ing electricity for utiIity use. made in this area.

Table lV-2.— Impacts of Energy Storage on Electric Power Systems Impacts Economic benefits*

Central Improved baseload capacity factor Low-cost charging energy energy Conservation of oil, natural gas Reduced fuel costs storage Reduction of spinning reserve capital cost credit ($20-40/kvv) Higher reliability/reduced reserve margin Capital cost credit (to be determined) More efficient load folowing Capital cost credit (to be determined) Dispersed All of the above, plus: All of the above, plus: energy 1. Deferral of new transmission and Capital cost credit ($50-100/kW) storage distribution lines 2. Deferral of substation reinforcement Capita l cost credit ($30-60/kW) 3. Misc. (transmission and distribution Capital cost credit ($10-20/kW) loss, volt-ampere reactive control, short circuit) 4. Increased security of supply/reduced Capital cost credit (to be determined) reserve 5. Rapid installation (factory built) Reduced interest during construction 6. Modular/incremental capacity growth High capacity factor of storage

“Probable ranges; actual benefits dapaod on specific condhons in incfrvidual power systems. SOURCE: F. R. Kalhammer, /rnpacrs of Energy Efficiency on E/ecfrk Power Systems, American Nuclear Society Meeting, San Francisco, November 1975. 124 ● Solar Technology to Today’s Energy Needs

OTHER ASPECTS OF large plants which require many years to CAPITAL COST COMPARISONS construct depend heavily on the accuracy of demand predictions covering periods of a The cost of equipment purchased for a decade or more. Utilities can react to unex- Iargeplant will always reflect the advantage pectedly low demand by delaying or defer- of discounts resulting from large purchases. ring plant construction, but this process can These savings occur because the manufac- be costly–with the cost depending on the turer’s marketing costs and other overhead amount of capital invested before the defer- costs are lower for large sales than for a ral. Forecasting mistakes can mean plants in number of small purchases. Larger systems operation which are badly underutilized, yet may also benefit because there is no need to inaccuracies are inevitable given uncertain- perform detailed engineering for each in- ty about the future of energy supplies, costs, stallation, as may be the case for some on- and demands. site energy systems. In the period 1973-75, demand did not rise Taking advantage of the ability to best in- as rapidly as expected. Demand has fallen tegrate an onsite generating system with the far below the predictions and, as a result, climate and demand pattern at each site many utilities had far more capacity avail- could, however, add to the engineering cost. able than they could profitably employ. The Contractor overhead charges tend to be disastrous effect of inaccurate predictions slightly higher for smaller systems. General- on the growth of electrical demand made izations are difficult, however, since it may during this period was reflected in the be possible to develop standardized designs decline in load factors and a rise in gross for small systems. peak margins (see figure IV-4). Both features Ease of rapid construction of small gener- indicate a serious underutilization of in- ating and storage facilities reduces the installed capacity, Utility commissions interest paid during construction —charges creased rates to permit these companies to remain solvent (although in many cases the which represent about 18 percent of the cost utilities argued that these rulings still of new electric-generating plants capable of 5 preclude profitable operations). generating 1,000 MWe. Rapid construction also means that the effects of infIation are Load factors for small systems (defined to easier to assess. Inflation occurring during be the peak output potential of the gener- the construction of a 1,000 MWe generating ating system divided by the annual average plant which wouId come online in 1983 is ex- output) vary widely because of the erratic pected to represent about 30 percent of the nature of onsite energy demands. While 6 total value of the plant. many large industries operate at virtually Short construction times can also provide full capacity throughout the day (and thus much greater flexibiIity in meeting new have relatively constant electric and ther- demands. mal demands), small industrial plants, commercial buildings, and residences can have This advantage is particularly significant very uneven demands. when rapid fluctuations in the growth of demand make predictions difficult. Plants The irregular demands lead to relatively which require only a month to construct re- poor utilization of the generating equip- quire predictions to be accurate only a ment. The problem usually diminishes as the month into the future. Moreover, a mistake size of the total demand increases since in forecasting is far less costly if the invest- large loads typically are an aggregation of a ment is limited. The economic benefits of number of small loads. Unless the small loads all change in unison, peak individual 5 L$ ASH- 1.? JO Revised demands will not all occur at the same time ‘ Ibid and the ratio of peak to average demand Ch. IV Onsite E/ectric-Power Generation ● 125

Figure lV-4.— Historic and Projected Load Factors of Utility Generating Facilities

Gross peak margin = ( installed capacity) - (peak demand) (peak demand) I I I I I L

SOURCE 26th Annual Electrical Industry Forecast, ’ E/eclr/cal Wor/d, September 15, 1975, p 46 wilI be less (This can be seen by noticing ways higher than onsite load factors, It is im- that the load factors shown in table IV-3 in- portant to notice that this advantage is at- crease with the size of the buiIdings served. ) tributable to the size of the grid intercon- Since the improvement is greatest when the nection and not to the size of individual largest possible number of loads are con- generating facilities. nected, utility load factors are almost al-

WASTE-HEAT UTILIZATION

One major advantage of onsite genera- ating facilities. From 60 to 80 percent of the tion of electric power is that an opportunity energy consumed by conventional gener- is provided for making use of thermaI ener- ating equipment is lost into the atmosphere gy usually wasted by central electric-gener- or nearby bodies of water, causing thermal 126 ● Solar Technology to Today’s Energy Needs

28.1 21.9

20.1 16.3

25.9 23.5

18.9 16,9

23.$

26.5

25.5

35.1

36.2

22 22 22 67 67 67

NOTE: The characteristics assumed for the buildings and heating and cooling equipment used by the buildings are described in detail tn chapter IV of volume IL In computing the ioad factors for industry, it was assumed that the facility operated at 70 percent of peek capacity during active shifts and tttat the Dlant was shut entirely for 2 weeks d“uring the year.

pollution in areas close to these plants. Ap- because the end requirement is generally for proximately 17 percent of the energy con- a much lower grade of heat than the fuel uti- sumed in the United States in 1972 was lized is capable of providing. The heat ex- wasted in this way and estimates show that hausted by e Iectric-generation prime this fraction will rise to 25 percent by 1985, movers can be used for many commercial when the United States is expected to be and industrial applications to produce an more heaviIy dependent on electricity. 7 overall efficiency of energy use in the range At the same time, enormous amounts of of 70 to 85 percent. The implementation of steam are generated for space conditioning this technology could both reduce demands for fuel and the demand for new capital in and industrial processes. These applications the electric utility industry. (Both com- are inefficient uses of the fuel consumed modities are in short supply. ) It has been 7 ERDA-48, Vol 1, appendix B estimated that if large-scale industries gen- Ch. IV Onsite E/ectric-Power Generation . 127

erated al I of their own electric-power re- rate of return to an investor, I n both cases, quirements by 1985 and served their proc- the issue depends crucially on the balance ess-heat requirements with waste heat, between thermal and electrical loads. where possible, the Nation would save 1,45 Quads* per year 8 Total energy is not commonly used in residential applications because of the large Systems which make use of this “waste daily and seasonal variation in thermal heat” are conventionally called “total ener- loads, In spring and fall, for example, there gy” or ‘‘ cogeneration” systems. A typical is a far smaller demand for thermal energy system is shown in figure IV-5. Equipment than during the winter and summer months. for total energy plants has been available In the high-rise apartment studied in this for many years, but use of such systems has assessment, for example, the ratio between declined In 1972, only about 0.2 to O 3 per- energy required for electricity and the cent of the U. S electric- generating capacity energy required for heating and hot water g made use of waste heat. This decline has varied from 0.21 in January, when the resulted both from an overalI reduction in heating load was maximum, to 1.5 during onsite power and from the fact that electric the spring and fall, when the primary re- sales have been more profitable than steam quirement for thermal energy was hot water. 10 saIes The use of large, remotely located, Only about 5 percent of the 550 total energy electric-generating plants has, of course, plants operating in the United States in 1972 made thermal distribution unfeasible in were installed in residences. The Depart- many cases. Total energy systems are still ment of Housing and Urban Development widely used in Europe and the Soviet Union. (HUD) is, however, conducting a large field experiment (MI US) with a total energy There is an enormous demand for thermal system serving a mixture of residential struc- energy in forms which are available from tures and commercial facilities. total-energy systems In 1973, for example, nearly 14 percent of the energy consumed in Total energy or cogeneration systems are the United States went into space heating, Iikely to be relatively more attractive in sites and 23 percent into industrial process where there is a consistent demand for heat. heat. 11 Buildings such as laundries, hospitals, and the food, paper, refining, and chemical in- Analysis of the economic attractiveness dustries are prime candidates. Most of the of both solar and nonsolar total-energy large factories can be expected to operate systems depends on whether the overaII cost on a three-shift schedule, permitting max- savings (e.g. , the amount by which the sav- imum utilization of the generating facilities, ings i n electricity or fossil-fuel costs exceed Many of the industries described use elec- the cost of owning and operating heat- tricity in ratios amenable to cogeneration recovery units) will result in an acceptable and can use steam at temperatures which can be conveniently supplied with cogenera - tion systems. The precise demands of buildings and industries of various types are “ Energy I ndu~trlal Center Studv, op cit , pp 6, 7 discussed in greater detail in the section on ‘ P R A( henb~ck and J B Cobel, $~te ArM/ysIs for “model building and industrial loads. ” the Application of Total Energy .$}~tern~ to Housing DPLe)opmentj, pre>ented dt the 7th I nter$oclety E ner- Some care should be exercised in using gy Convention E nglneerlng conference, San EIIego, the ratios which are developed for contem- ~al[t , Sept 25-29, 1972, p 5 porary buildings and industries, since the ‘“ Energy Industrial Center Study, op clt , p 21 thermal and electrical demands could ) 1 M H Ross and R H Wllllarns, A $se~~~ng the Po- change dramaticalIy as the resuIt of conser- tential for Fuel Conservation, The I n$tltute for Publ IC Po] I( y Alternatives, State Unlverjlty of New York, vation techniques and new technologies. Al bdny, N Y , July 1, 1975, p 19 Widespread use of electric automobiles, for 128 ● Solar Technology to Today’s Energy Needs

Figure lV-5.—Components of a District Heating System in Sweden

Fossil boiler 4 Units in individual homes or 2 Waste heat mains I , solar heater

(4) Consumer service (5) Large substation unit for private house in a school

SOURCES Figures (1) (2), (4). and (5) from “Dlstr{cl Heating” Teknlska Verken I Llnkop[ng AB [Sweden) Figure (3) from Margen, P H (Manager Energy Technology Dlvislon, AB Atomenergl, Studsvlk R&D center, Sweden), ‘“The Future Trend for Dlstr{ct Heating, ” page 68, presenteci at the Swedish Symposium on Combined Dlstrlct Heating and Power Generation Feb 2528, 1974 Ch. IV Onsite Electric-Power Generation ● 129

example, wouId increase the ratio of electric and heat recovery units could reduce ther- to thermal demand in residential buildings, mal demands,

OPERATING COSTS

Concerns about operating costs have Daimler-Benz reports up to 20,000 hours of been a major barrier to onsite equipment in engine life for its 10 kW engine.13 Operating the past, and badly designed systems have cost wilI depend strongly on the installation, been plagued by expensive maintenance. the skill of the operators, and the system Reliable data about the cost of operating design. In most cases, it will be extremely smalI systems designed for continuous-pow- difficult to predict operating costs until er output are extremely difficult to obtain some experience has been obtained with the because of the smalI number of installations particular application. in most of this size range. A summary of in- There is considerable variation in oper- formation from a variety of sources is shown ating costs of larger powerplants (see figure in table IV-4. IV-6), and it is difficult to choose a single number for comparative purposes. This is The greatest variation in the data occurs particularly true for nuclear plants, where in the small size ranges, where some of the experiences vary greatly and statistics on numbers are based on estimates made by long-term operating costs are cliff i cult to ob- designers, some represent attempts to oper- tain. It is interesting to note, however, that ate systems designed for “backup power” over half of the operating expenses of coal- operation in a continuous operation mode, fired plants are due to the cost of operating and some are averages of widely varying the boilers. Presumably, these costs would operating experience. For example, the mili- be eliminated in a solar system that did not tary standard for generator sets shows an rely on fossil backup, although the cost of engine Iife of 2,500 hours for 15 kW units maintaining the collectors would probably and 4,000 hours for 100 to 200 kW units. 2 compensate for this savings.

RELIABILITY

Concerns about reliability have been a not sufficiently reliable. Achieving high major impediment to onsite power genera- reliability with redundancy is, of course, ex- tion. Onsite installations can, in principle, pensive (see table IV-5). It is possible, be made as reliable as utility power—or however, that a simple, mass-produced heat more reliable if enough redundant units are engine could be designed to operate with purchased or great care is taken in design the reliability of a household refrigerator and manufacture. In fact, redundant onsite (which is a simple heat engine operating in power systems are occasionalIy used to pro- reverse). Designers working on a variety of vide realiable power when utility power is different onsite systems feel that this is not

“ Mllltary Standard, E Iectrlc Power Engine Cener- ator set, Family Characterlstlc Data Sheets, M/l- Std- ‘ ‘ Mercede~-Benz Diesel and Gas Turbine Catalog, 633 A(MO), Oct 8, 1965 (Data provided OTA by the Vol 36 (Data provided to OTA by the Aero$pace Cor- Aerospace Corporation ) poration ) 130 ● Solar Technology to Todav’$ Energy Needs

Table IV-4. —Operating Costs of Various Systems

operating and maintenance Design type cost (c/kWh) reference

A. Small systems (5-50 kW) —gas turbine 1.25 1 — diesel engine 0.4-2.4 2 — Stirling engine 0.74 3 —free-piston Ericsson 0.10 4 — air-conditioners 2-4 5

B. Intermediate systems (50-1,000 kWe) —gas turbine 0.1-0.3 6 —gas turbine 0.25-0.4 7 —diesel engine 0.23 8 —diesel engine 0.27-0.55 9 —diesel engine 0.4 10 — gas engine 0.2-0.4 11 C. Larger systems (1 MW and larger) — large diesel plants 0.33 14 — new coal-fired turbines 0.12 13 — new nuclear plants 0.3 13

Notes for Table IV-4.

1. International Harvester, Sofar Oivrsion, private communication, Marti 1976. 2. wm2,~-10.~hwm&~w~auis (astimatebasedcm combination ofdatafrom Allis Chalmers, Oatroit Oiesel, and Dalmler-Benz) assummg 30 percent of mlt!al cost ($400/kW) IS revested m each overhaul, 3. A% Program Review; ‘Qwrtparafive Assessment of Orbital and Terrestrial Central Power Systems”’ (Interim report), March 1976, p. 31. (Assumes a 15.year hfe and 1 man-how every 3 months.) 4. Est!mate by Glen Benson of Energy Research and Generation Corp., private communlcatlon, November 1976. (Assumes 1 mart-hour per year for,mamtenance.) 5. wonmaintenancecontractson2-tonairconditionerswf'tich areassumecf tooperateatpeak load--2 .000hoursperyear. Su&I contracts are sofd by Seam for $60-$120/year (depending on the age of the system). It is assumed that an aw- condi!tonlng cycle, operating m reverse as a heat engine, IS 17.percent efflctent, 6. MIUS T~nofogy Evaluation: “Prime Movers ORNL-HUO-MIIJS.1 l,”’ April 1974, p. 14. 7. Internahonal Harvester, Solar DivisIort, private commumcatlon, May 1976. 8. LXesel Engmeermg Handbook, 1966( inflated by 6 percent for 10 years) 9. “MIUS Prime Movers,” OP. CII., p. 21. IO, Assumes 30 percent of capital cost (assumed to be $300/kW) IS Invested for each 30,000 hours of operation.

Il. “MlUS,” Op. Clf., P. 14. 12. ‘

(6) insurance (Fuel cost excluded)

●

Table IV-5. — Engine Requirements for Systems Designed to Provide Reliability Equivalent to Utility Power Reliability

(Approximately 5 hours of outage per year, including failures in generating, transmission, and distribution equipment) Fraction of Number of peak load which Reliability engines in can be met required of Relative system by each engine each engine cost’ 132 Ž Solar Technology to Today’s Energy Needs

ample, have a “mean time between failures” operation and on the revolutions-per-minute of about 500 hours, 4 Diesels and gas tur- (r/rein) of the device. Low r/rein systems bines, in the range of 50 kW to 1 MWe, how- which are designed for continuous opera- ever, average 1.2 years between failures.15 16 tion can typically require one relatively in- Gas turbines typically operate 20,000 hours expensive overhaul, costing about 10 per- (2.3 years) without overhauls, even in in- cent of the initial investment each 10,000 stalIations where they must operate unat- operating hours, and a major overhaul cost- tended, and 40,000 hours between failures ing 20 percent of the investment each 20,000 have been experienced on some systems. ” operating hours. Almost all reliable data prototype Stirling engines have operated deals with systems larger than 50 to 200 kWe 10,000 hours without failures in bench test- and Iittle data exists for very smalI systems. ing.18 Free piston Ericsson-cycle devices, if designed properly, should be able to operate Standards for reliability cannot be meas- with very high reliability because of their in- ured in any systematic way. Requirements herent simplicity, the small number of mov- will differ from customer to customer. Some ing parts, and the fact that no seals around industries, for example, would face cata- rotating shafts are required. The reliability strophic losses if they lost power for an ex- of diesel equipment depends on whether the tended period (say several hours), while system has been designed for continuous residential customers might not be willing to pay a premium for extremely high reliability. ‘ 4 M/US Technology .E valuation: Prime Mo~ers, One of the disadvantages of providing OR NL-HUD-MIUS-ll, April 1974, pp 57-60 power from a centralized utility grid is that “ Ibid all customers must pay for a high system “ M Gamze “A Critical Look at Total Energy reliability whether they need it or not. On- Systems and Equipment, ” Proceedings, the 7th Annual site generation would permit much greater I ECEC Conference, San Diego, Callf , Sept 25-29, flexibility in this regard. 1972, p 1266 17 Robin Mac Kay, “Generating Power at High Eftl- clency, ” Power, June 1975, p. 87 Utilities currently try to maintain enough ‘“ R C Ullrich (North American Philips Corpora- capacity to ensure that failure of the gener- tion), private communlcatlon, October 1976 ating plant will curtail power for no more Ch. IV Onsite Electric-Power Generation ● 133

than 2.4 hours per year. (This is a typical of customers requiring backup would not working figure, but standards vary. Southern have a major impact on utility operation, California Edison Company, for example, and that a large number of customers with uses a standard of 1 hour in 20 years )19 It small backup requirements wouId not pose has been argued, however, that this standard a problem since failures would be distrib- for generating reliability is too high, and uted at random, Some correlation with that the last few hundredths of a percent of peak-demand periods could be expected reliabiIity are enormously expensive, 20 par- (Solar outages due to variations in sunlight ticularly since the transmission and distribu- wouId, of course, be correlated, but failure tion system is usually less reliable than the of equipment should be similar to other generating plant The effect may not apply types of onsite failures, ) A small number of to all utilities, however, and optimal expan- very large users wouId, however, pose a sion plans may welI result in maintaining serious problem if they depended on util- very high reliabilities in some instances. ities for complete backup. I n such cases, provision would have to be made for drastic Analysis of the requirements of different reduction of onsite demands whenever the types of customers in this regard is almost onsite generating equipment failed. The nonexistent It is difficuIt to anticipate how presence of electric storage, either onsite or much different customers wouId be wiIling in the utility grid, could do much to alleviate to pay for reliability If they were given a the problems of unanticipated equipment choice The costs of providing high-relia- failure bility service could be reduced, for example, if the customers were wi I I Ing to accept low- I t seems, therefore, that onsite equipment er reliabilities during predictable periods — can provide any desired level of reliability If such as during peak-demand hours — or dur- a premium is paid, if the utility is used to ing maintenance cycles provide backup power, or if the optimistic expectations of system designers are real- The requirement for providing high ized, Existing equipment can provide a very reliabiIity with onsite equipment can be re- high level of reliability without redundancy, laxed considerably if the utility grid can be although the exacting standards of utility used to provide complete ‘‘backup’ when power cannot be matched, The seriousness failures occur or when systems are disassem- of this f a i I u re wou Id have to be judged o n a bled for routine maintenance The impact of case-by-case basis, Unfortunately, there is providing this backup power on utility costs little operational experience for most promis a complex issue and cannot be treated in ising onsite equipment, and basic long-term detail in this paper concerns are unlikely to be finalIy resolved before an adequate base of experience with It is clear, however, that a small number these systems has been developed 134 ● Solar Technology to Today’s Energy Needs

variety of local and nationally based groups mental impact of equipment and emis- have legal standing orders to contest siting sions traceable to electric generation plants and rulings. wou Id be small,

Most small plants would be required to go It could be plausibly argued, in most through many of the procedural steps re- cases, that the impacts of alternatives quired of the larger plants, and less effort to onsite generating facilities would be may be required to justify the installation of more severe than those imposed by the a single large plant in a remote area than to on site design. justify several small facilities in areas where Onsite facilities would not require a local protest would be Iikely to develop. On major dislocation of populations, no the other hand, the onsite generating equip- construction camps would be required, ment might face far fewer objections than no new roads or new waterways would the large sites for a variety of reasons: be necessary, etc.

● Each plant would be relatively small, Large solar-electric systems, which re- and the impact on the local environ- quire large amounts of land in a single area ment would usualIy be sIight. for collectors, could also face serious siting ● I n the case of cogenerat ion and total problems. Smaller onsite solar systems, energy systems, energy would be re- which could be integrated into the buildings quired onsite for heating and industrial or immediate region being served with solar applications, even if no electricity were energy, wouId undoubtedly face far fewer generated onsite, and thus the incre- objections,

MISCELLANEOUS OPERATING PROBLEMS

A major constraint to onsite power gener- find and they command high salaries. Sev- ation has been the reluctance of owners and eral steam-system owners have indicated managers of companies other than utiIities fear about their vulnerability to losing a to accept the burden of owning and oper- chief engineer with unique experience. ating complex electrical generating facilities; there has been great apprehension Equipment has also been a problem; the about maintenance costs, reliabilities, per- market for onsite equipment is so small that little new design work has been done, Ex- sonnel requirements, and other technical uncertainties. isting onsite generating instalIations are nearly all “one-of-a-kind” designs; they are Operators of most commercially avail- often installed by engineers who do not able generating equipment require extensive have much experience in the area, and they training, and in many jurisdictions, local frequently use equipment in ways not origi- codes set specific standards. For example, nally contemplated by the manufacturer. As the District of Columbia requires operators a result, performance has often been disap- of high-pressure steam systems, capable of point ing.22 generating more than 55 kW of thermal power (equivalent to about 15 kW of electric power) to hold a “second-class steam 21 “Operation and Maintenance of Boilers and engineer’s Iicense. ” Obtaining such a license E nglnes and Licensing of Steam E nglneers, ” District of requires 3 years of experience with steam- Co/urnbIa Register, Washington, D C plants having pressures greater than 15 psi “ Maurice G Gamze, “A Critical Look at Total and passing a special examination.21 Energy Systems and Equipment, ” Proceedings, the i’th Annual IECEC Conference, San Diego, Callf , Sept Thus, qualified operators are difficult to 25-29, 1972, p 1266 devices eliminates one of the major impediments to conventional onsite equipment — their use of relatively expensive Iiq- uid and gaseous fuels Table IV-1 indicated that fuel costs dominate the cost of providing power from smalI generating equipment even at current fuel prices I n many cases, however, it may be attractive to try to provide backup for a solar-powered facility by burning a fuel during periods when solar energy sources are not available. It may be possible to develop boilers for small devices compatible with coal, waste products, and other “biomass” fuels The development of fluidized-bed boilers of various sizes may be particularly attractive for such an application. The development of such systems would, of course, also increase the attractiveness of onsite generating devices operating entirely from energy sources other than direct solar energy Figure IV-7. —Space Requirements of Typical Combined-Cycle Plants Chapter V THE RELATIONSHIP BETWEEN ONSITE GENERATION AND CONVENTIONAL PUBLIC UTILITIES Chapter V.–THE RELATIONSHIP BETWEEN ONSITE GENERATION AND CONVENTIONAL PUBLIC UTILITIES

Page Table No. Page Background ...... 139 7. Ratio of Price Utilities Can Pay for Solar Energy Generated Onsite to the Electric Transmission and Distribution ...... 141 Price Charged by Utilities for Electricity. ..155 Thermal Transmission and Distribution ...... 143 8. The Fractional Difference Between the Utility Costs Required To Provide Backup Power to Sale off PowerGenerated Onsite ...... 144 the Systems Shown and the Costs of Metering ....., ...... 144 Providing Power to a High Rise Apartment Safety ...... 144 Equipped With Central Electric Air-Condi- Quality of Power Fed Back to Utilities .. ...145 tioning, Electric Hot Water, and Baseboard Local Distribution Capacity ...... 145 Resistance Heating...... 156 Economic Dispatch...... 145 9. The lmpact of Offpeak Storage on Utility Control ...... 146 costs ...... 157 Time-of-Day Pricing...... 146 IO. Levelized MonthlyCosts for a Single Family Storage Strategy ...... 147 House Showing the Effect of Marginal Load Management...... 147 Costing and BuyingofOffpeak Power ....158 Offpeak Electricity ...... 148 11. Leveiized MonthlyCosts of Several Kinds of Energy Equipment in a Single Famiiy De- Ownership ...... 148 tached Residence in Albuquerque, N. Mex.160 Utility Attitudes ...... 150 A-1. Average Characteristics of PrivatelyOwned Utilities in 1974 ...... 163 The Cost of Providing Backup Power From an A-2. Numbers of Buildings in “Typical’’Utility Electric Utility ...... 151 Modeled WhichUseHeating and Cooling Backup PowerWithEnergy SourcesOtherThan and HotWaterEquipment ...... 163 Electricity ...... 159 A-3. industrial Load Profile Used...... 164 A-4. Characteristics of Equipment Used in the AppendixV-A.– Analytical Methods...... 161 Utility Model...... 170 A-5. Assumptions About the Nonconventional Systems Used in the Utility lmpact Analysis ...... 170

LIST OF TABLES LIST OF FIGURES Table No. Page l. A Comparison of the Cost of Transmitting and Distributing Energy in Electrical, Chemical andThermal Form ...... 140 Figure No. Page 2. Construction Expenses of Electric l.improvement in the Pattern of Electricity Companies ...... 142 . Consumption in England’s Southwestern 3. District Heating Systems ...... 143 Electricity Board Resulting From a Shift 4. The Capital lntensityof Major U.S. to Time-of-Day Electricity Rates ...... 146 Industries ...... 149 . A-1. A Typical Load-Duration Curve for an 5. The Fractional Difference Between the Electric Utility ...... 162 Utility Costs[¢/kWh] Required to Provide A-2, Ratio of PeakDemands to Average Backup Power to the Systems Shown and Demands as a Functionofthe Standard the Costs to ProvidePower to a Residence Deviation of ’’Wake-Up’’Times ...... 165 EquippedWith an Electric Heat Pump . . . . 153 A-3. Hourly ’’Miscellaneous” Electric Load 6. Levelized MonthlyCosts for a Well-lnsu- Profile for Single Family House With lated Single Family HouseShowing the DifferentTypes of Diversity ...... 166 Effect of Marginal Costing for Backup A-4. inverted Load-Duration Curve of a Power ...... 154. Typical Electric Load...... 168 Chapter V The Relationship Between Onsite Generation and Conventional Public Utilities

BACKGROUND

The value of onsite energy systems cannot be addressed by examining their performance as isolated systems. While it is possible to construct onsite solar devices capable of operating with no connection to other power sources, it is seldom economically attractive to do so when other sources of power are available. It is tautological that designing an optimum approach for providing energy in a given region requires that all equipment for installing and consuming energy be considered as components of a single integrated energy system designed to meet a fixed set of energy demands: maintaining building in- teriors at comfortable temperatures, providing lighting, supplying heat for industrial processes, etc. Any attempt to simplify the problem by considering the capabilities of components in isolation must result in a less efficient outcome. Moreover, it is likely that without taking this synthetic perspective, some critical aspect of the overalI system will be neglected.

Performing this kind of analysis is difficult because of the complex and highly interdependent energy systems which have emerged over the past few decades, the variety of equipment which is currently in use, and the bewildering variety of devices now u rider test and development. This chapter provides a perspective on some of the major issues confronted in integrating onsite systems into larger systems for supplying energy and provides the basis for making realistic estimates of the cost of operating onsite equipment.

The design of an optimum energy network which includes onsite solar facilities requires choices in the following areas. ●

. How much of the backup energy shouId be supplied from energy storage equip- ● ment, and how much backup energy should be supplied from convention I energy sources? (This usually transIates into determining the opt i m u m size for onsite storage equipment )

● 140 ● Solar Technology to Today’s Energy Needs

If it is possible to transmit energy inexpen- have to be large enough to meet the peak sively, overall energy costs can usually be demand of the building or industrial process reduced by connecting together as many which it is designed to serve. The load fac- energy consumers as possible. If onsite gen- tors of individual buildings are usually very erating systems are not connected, each unattractive (see table V-1 ). Onsite load fac- generating unit (solar plus backup) would

Table V-1 .—A Comparison of the Cost of Transmitting and Distributing Energy in Electrical, Chemical, and Thermal Form

Capital cost $92/kW (4)--

NOTES: 12ASSumeS end.use efficiency Of 65 Percent I 13tLResidential Energy Use to the Year 2(toO: Conservation and 1 A ~apltal ,ecoveV factor Of O . I 5 is used to calculate annual caPital Economics,” Oak Ridge National Lab, Report ORNIJCON.13, Oak Ridge, Term., Sept. 1977, charges. 141nyestor.owned electric utilities spent S2.8 bdlion on COn StrlJCtiOfl Of 2Assumes a capacity of 2,500 MW Ior one 765 kv line. distribution facilities for 21,700 kW of new capacity in 1975. 3Utility construction expenditures of $1,7 billion in 1975 for 3,762 ad. (Statlshcal Yearbook of the E/ectr/caf Ut///fy /rrdustry for 7975.) ditional miles or S461,000 per mile average. (Statistlca/ Yearbook of 151nvestor.owned utilities spent approximately $1.59 billion in 1975 for ffre Electrlc Utl//ty Industry for 1975, Edison Electric Institute, New distribution O & M costs for 1.5x10’2 kWh. (Statistlca/ Yearbook of York, N.Y , Oct. 1975.) the E/ectr/ca/ Utl/lty Industry Iof 7975.) 4 The 1970 Natlona/ Power Survey, Federal power Commission, 16 Calculated from the average cost of S400 per customer (Private Washington, D. C., p. 1.13.8, Dec. 1971. communication—American Gas Association) with an average hot 51nvestor.owned electric utilities spent approximately $851J million on water and space heating requirement of 36.4x10] kWh (121 MCF) per transmission O & M costs in 1975 for 1.5x10’Z kWh. (S fahstlca/ Year. year and an assumed load factor of 0.4. book of the E/ectrlc Utjllty /ndustry for 1975). 17AII natural gas utilities spent S1.1 billion on distribution 0 & M In 6Assume$ an end.use efficiency of 100 percent 1976 for 14.8 TCF (AGA Gas Facfs),

7Nat,ona/ Gas Survey, u,S Federal Power COmmisS.iOn, VOI. 1, P. 34. 18 See volume Il. 1975. 19 f1Evaluation of the Feasibility for Widespread Introduction Of COal in. 8AII natural gas companies spent $53 I million in 1976 for 1,845 miles to the Resldenttal and Commercial Sectors. ” Exxon Research and of new transmission pipeline or $287,000 per mile average. (7976 Gas Engineering Co., Linden, N. J., Vol. 11, p. 6.11, Apr. 1977. These two Facts, American Gas Association, Arlington, Va., 1977). studies give a construction cost of about S14 milllon for the size

9Four percent of total natural gas consumed was used for PiPeilne system in question, which requires a peak capacity of 70,000 kW, as fuel In 1976 This is equally allocated to transmission and distribu. shown by reference in note 20. tion. (AGA Gas Facts). 20 Annua\ o & M costs are calculated by assuming they are 3 Percent IONatlona/ Gas Survey, U.S. Federal Power Commission, VOI. Ill, P. 129, of capital costs, which is the average of the percentages for gas and 1973. electric systems. 11 All natural gas Utllilles spent $1 1 billton in 1976 on o & M for 21 The cost of energy lost in transmission was estimated usln9 transmission for 148 trillion cubic feet (TCF). 0.04c/kWh for electricity y and 1.5c/kWh for thermal energy, Ch. V The Relationship Between Onsite Generation and Conventional Public Utilities ● 141

tors can be as low as 15 percent, while typi- ty is large enough, collectors need only have cal utiIity load factors are 50 to 60 percent. an annual output large enough to provide Moreover, each onsite facility would have for heating and hot water requirements and to provide enough redundant equipment to storage losses. Such systems may require achieve acceptable levels of reliability. If an less collector area per building unit than interconnection is avaiIable, however, it is conventional solar heating and hot water necessary only that the combined output of systems using relatively small amounts of all generating units in the system be able to storage. meet the aggregate peak demand of the region. The aggregate peak will be lower than While connecting energy generating and the sum of the individual peak demands consuming devices into a single energy net- since individual peaks will occur at different work can lead to significant savings, the times (this is usualIy called “diversity” in the transmission and distribution systems re- demand). The advantage of the connection quired can be extremely expensive. The is magnified by the fact that most gener- costs of several types of energy transport ating devices operate less efficiently when systems are summarized in table V-1. Com- operated to meet an uneven demand. Inter- parisons of this type can be somewhat mis- connections also permit greater freedom in leading because costs will vary greatly from selecting generating and storage equipment site to site, but the table at least allows a (onsite and centralized facilities can be crude ranking of alternatives. It indicates, selected as they are appropriate), and it is for example, that transporting energy in easier to optimize the efficiency of the total chemical form is by far the least expensive system throughout the year by controlling approach. It is interesting to notice, how- the performance of each system in the net- ever, that distributing energy in the form of work in response to the total load. hot water over distances of 1 to 2 miles is on- The problem of uneven loads is a par- ly about 30 percent more expensive than ticularly difficult one in the case of electric transmitting electrical energy over typical utiIities since generating and storage equip- distances from generating facilities to con- ment tends to be extremely expensive, al- sumers, I n this comparison, no attempt was though chemical and thermal transport sys- made to share the cost of the trench dug for tems can also benefit from balanced loads. the hot water pipe with potable water, It may prove feasible, for example, to pipe sewer, telephone, or other Iines which could hot water generated in collectors located on be placed in the excavation, The electric a number of separate buildings to a central distribution costs would have been signifi- thermal storage facility, If this storage facili- cantly higher if buried cables were used.

ELECTRIC TRANSMISSION AND DISTRIBUTION

Electric transmission and distribution is transmission, and distribution equipment an expensive undertaking. Over half of the has fallen because of the rapid increase in

capital invested by electric utilities in the the cost of generating plants [see table V-2),

United States is invested in a massive net- Each dollar now invested in generating work of transmission and distribution equip- equipment is accompanied by a 16-cent in- ment. In recent years, the ratio between vestment in transmission equipment and a capital investment in electric generating, 23-cent investment in distribution systems, The high cost of the electric transmission IStat/st/cs of Pr/\ate/y Owned E/ectr/c Ut///eses in the and distribution system is due in part to the Un/ted States, Federal Power Commlsslon, 1974, p 40 fact that the lines have relatively low load 142 ● Solar Technology to Today’s Energy Needs

Table V-2.—Construction Expenses of Electric Companies

1965 1967 1969 1971 1973 1975 1977

Total Investment (billions of dollars) ...... 4.03 6.12 8.29 11.89 14.91 15.09 19.50 Production equipment (%). . . . . 32.3 41.7 46.1 56.3 58.9 65,1 68.3 Transmission equipment ...... 23.3 21.5 18.7 15.2 13.7 11.5 10.7 Distribution equipment...... 39.4 32.3 29.2 23.3 22.6 18.7 15.7 Other ...... 5.0 4.4 4.0 5.1 4.8 4.7 5.03

SOURCE. EBASCO 1977 Business and Economic Charts (Ebasco Services, Inc., New York, NY. )

factors. Hot water and steam distribution The cost of maintaining transmission systems used for heating buildings typically equipment can also be substantial. In 1974, have load factors of 33 percent (see table the cost of operating and maintaining the v-1 ). network of electric transmission and distribution lines owned by privately owned util- The electric transmission and distribution ities in the United States exceeded the cost lines now in place are typically 90-percent of operating and maintaining the generating efficient, but it is hoped that improved facilities (fuel costs excepted). ’ Annual technology will lead to overall efficiencies maintenance costs for a smalI hot water dis- of 92.5 percent by the year 2000.2 The im- tribution system can amount to about 3 per- proved efficiency, however, will most likely cent of the initial capital cost of the equip- add to the capital cost of the systems. Gas 6 ment. Maintaining steam systems may pipelines are typically 90-percent efficient, prove to be significantly more expensive. the losses being due primarily to the fact that gas is withdrawn to run pumps in the In addition to direct costs, transmission pipeline. 3 No comparable information is Iines can have serious environmental conse- available on the efficiency of hot water and quences. It is estimated that over 3 million steam transport systems. Losses are a strong acres wilI be required for new transmission function of the ground and fluid tempera- lines by 1990. ’ Much of this construction tures, the distances traveled, and the aver- will occur in scenic areas where opposition age size of the pipelines. Some recent steam is likely. In addition, it is possible that the distribution systems, however, have experi- large electric fields produced by high volt- enced losses on the order of 15 to 20 percent age transmission lines may be harmful. The and have created serious difficulties for the question is being investigated and the re- systems relying on them.4 sults are inconclusive at this time.

‘Statistics of Privately Owned Electric Utilities in the United States, op. cit , pp. 35, 39,40, 42,43. ‘W. R. Mixon, et al., Technology Assessment of ‘ERDA-48, Volume i, pp. B-10 and B-n, 1975. Modular Integrated Ut;//ty Systems, Oak Ridge Na- ‘American Gas Association. tional Laboratory, ORNL/HUD/MIUS-25, pp 3-189 and ‘American Public Power Association, private com- 3-190. munication, November 1977 7Thermo-E Iectron Corporation. Ch. V The Relationship Between Onsite Generation and Convention/ Pub/ic Uti/ities ● 143

Table V-3.—District Heating Systems

District Heating Systems in the United States

44 city systems New York

Total steam sold (millions of pounds). ., ...... 84,246 32,702 Total steam delivered to system (millions of pounds) ...... 96,672 38,469 Annual system load factor . . . ., . . ., ., ...... 33% 37‘A Number of customers (in thousands) ...... 14,903 2,514 Length of distribution system (in miles) ...... 573 100 Installed air-conditioning (tons) ...... , ...... 666,051 569,945

Note New York City has the largest American system, selling nearly 10 billion kWh per year The load Is 30 percent residences. 45 percent office bulldings, 11 percent industrles and 13 percent institutions.

SOURCE Offlcial Proceeding, 80th Annual Meetlng of the International District Heating Asscciation, June 1969, pp. 22-30, quoted on p 24 of ORNL-HUD-19, Ibid

District Heating Abroad

Sweden Denmark W. Germany U.S.S.R. (1973) (1973) (1973) (1971 )

Energy sold for district heat (millions of kWh) ...... 12 14 38 1,100,000 Units connected ...... 600,000 30% of dwellings 83,000 75%

SOURCES I G C Dryden, The Eff/c/enf Use of Energy, IPC Science and Technology Press, 1975, p 359 Quoted In Teploengetika, Vol 18, No 12, 1971, pp 2-5 W Hausz, and C. F Meyer, Energy Conservation Is the Heat Storage Well the Key?” Puh/Ic Uf,/,tfes Fortn,ghfl} APrIl 24 1975

THERMAL TRANSMISSION AND DISTRIBUTION

Most hot water and process steam is con- high-pressure, steam-generating facilities re- sumed close to where it is generated, but a quiring expensive water purification sys- number of cities have systems for distribut- tems. Table V-3 estimates the capacities of ing steam to residences and industries. I n district heating in the United States and the United States, many older systems have abroad. On the other hand, district heating been abandoned, and few new systems are has been used much more extensively in being built. The Modular Integrated Utilities Europe. For example, 30 percent of the resi- System (MI US) in Jersey City, N. J., is one of dences in Denmark are connected to district the few recent exceptions to this trend. The heating systems. Sweden estimates that 70 abandonment of steam distribution is due percent of its multifamily units and 20 per- mostly to the overalI decline of onsite gener- cent of its single family homes will be con- ation. This tendency is reinforced by the nected to district heating systems by 1980. fact that many older steam-distribution sys- West Germany plans to provide district heat tems were not designed to return water to to 25 to 30 percent of its dwellings by 1980,8 the generating plant, as the turbines operated on untreated water. This procedure be- 81 G C Dryden (ed ), The Eff/c;ent Use of Energy, IPC came impractical with the addition of large, Science and Technology Press, 1975, p 358. 144 ● So/ar Technology to Today’s Energy Needs

The feasibility of using district heating ble of serving a community of 30,000 people systems depends much on the density of in a mixture of apartments and single family dwelling units. A study conducted in con- units indicates that the cost per unit for this nection with the MIUS project estimated dispersed system would be nearly three that a garden apartment complex in the times as great, The ability of a system to Philadelphia area (60 buildings with 12 amortize these costs depends on the cost of apartment units per building) would cost the energy supplied and the yearly energy about $410 per unit for heated water dis- demand of each building. A rule-of-thumb tribution and $330 per unit for chilled applied until recently in West Germany was water, 9 A MIUS system was actually in- that a “break-even” housing density was one 2 stalled in Jersey City, NJ., for approximately which required 44 MWt/km for existing ur- 10 2 this amount. A preliminary estimate of the ban areas and 28 MWt/km for new devel- cost of a large district heating system capa- opments. Recent increases in fuel prices, however, have led them to consider areas 9G Samuels, et al , M/US Systems Ana/ysis, /n/t/a/ 2 with demands as low as 14 MWt/km . The Cornpar/sons of Modular Sized /rrtegratecf Ufi/;ty Sys- tems and Corrverrt;ona/ Systems, Oak Ridge National garden apartments in the MIUS study had a 2 Laboratory ORNL/HUD/MIUS-J une 6, 1976, p 144 demand of approximately 30 MWt/km . IOPaul R Achenbach and John B Coble, Site Ana/- ys;s for the App/;cat;on of Total Energy Systems to Hous/ng Developments. 1‘1 G.C Dryden, op clt , p 251

SALE OF POWER GENERATED ONSITE

METERING The metering problems of onsite electric generating systems depend on the nature of No major technical barriers need to be the customer’s relationship with the local overcome in designing meters for onsite utility, If the utility is wilIing to purchase energy equipment, but new types of meters energy at the same price as it sells energy to may have to be developed for this purpose. onsite users (or if it owns the generating If a utility owns onsite equipment with ther- equipment itself), it may not be necessary to mal output, some technique must be found change metering systems — because conven- for billing customers for the energy pro- tional meters can subtract from the net duced by the onsite device. One utility has energy account when energy is being sold suggested that the simplest technique would and add to the account when energy is pur- be to bill a customer on the basis of actual chased. This practice is currently permitted capital and maintenance costs, although in several New England States on an ex- meters capable of measuring the energy perimental basis. ” In cases where energy is generated by solar thermal systems of sold at a different price from that pur- various sizes are available.12 13 An electric chased, dual meters will be required —with utiIity in Florida is using such Btu meters on one ratchet to read sales to the customer solar hot water heaters installed under its and one ratchet to read purchases from the auspices. 4 customer,

1‘Phi Iadelphla E Iectric Company In an interview re- SAFETY ported In the General E Iectrlc study Conceptual De sign and Systems Analysis of Photovolta;c Power Sys- There could be risks associated with the tems. installation of onsite electric-generating 1‘For example, the E Iectron Advancement Corpora- tion sells meters measuring 1400 to 1500 F water at flow rates of 30 to 100 gpm at a price of $400 to $500 (price list Feb 9, 1977) “Ben Wolf, Gemini Company, private communlca- “So/ar Energy Digest, January 1977, p 9. tlon, Apr 27, 1977. Ch. V The Re/atlonship Between Onsite Generation and Convention/ Public Utilities ● 145

equipment which would not automatically utiIity systems, and quality of power has not disconnect from utility lines when repairs been an issue 20 are being made or when a utility Iine breaks in a storm or accident. As one utility put it, LOCAL DISTRIBUTION CAPACITY this “poses no problem for trained utility crewmen who treat al I Iines as hot unless One potential technical difficulty, iden- locally grounded The major problem can tified in the General Electric study, is the arise through exposure of laymen and chil- possibility that onsite units which feed elec- dren to potentially hot lines before repair tricity back into the power distribution grld crews arrive on the scene “ 16 This problem would exceed the capacity of the Iines and can be eliminated if the onsite generating transformers serving the area It is unlikely equipment is automatically taken off the that onsite units would produce excess line whenever the power fails. This is a power for sale at a rate high enough to ex- standard feature in at least one design of ceed the peak purchases of the onsite cus- smalI power-conditioning equipment now tomer. There could be some problems in on the market. 17 The utilities Interviewed in older communities, where distribution sys- the General Electric study indicated that tems were installed without considering the any type of onsite equipment which did not possibility that a substantial number of res- incorporate such a feature could be fitted idences might be equipped with al l-electric with a device al lowing the utlIity to sever systems. A typical distribution system, how- the connection with the utility distribution ever, should be able to accommodate the network through telemetry. Such units were output of residential photovoltaic systems estimated to cost about $100.18 (The same without major changes in transformers or units could also be used for interruptible Iines.21 service and for load management ) It would be necessary for the utility to approve the ECONOMIC DISPATCH onsite equipment connected to its grid in order to ensure that adequate safety fea- Electric utilities now control the schedul- tures of this type were installed ing of their generators via computer. This optimizes the efficiency of their entire system on a minute-to-minute basis throughout QUALITY OF POWER FED the day As long as a relatively small number BACK TO UTILITIES of a utiIity’s customers are using solar equipment which can generate electricity, no There shouId be no difficulty in construct- large-scale shift is necessary in current ing equipment capable of providing power economic dispatch practices. 22 The net load to utilities which meets utility standards of to the utility would fIuctuate throughout the 19 voltage regulation and frequency control. day, but current equipment and manage- One manufacturer of small inverter systems ment schemes are adequate to handle the has sold 65 units which are integrated into relatively large fluctuations that already occur with daily cycles, local weather variations, and industrial energy consumption. The utilities interviewed by the General “Paclflc Gas and t Iectrlc Company Interview pub- Electric Company indicated that special lished In General E Iectrlc’s photovoltalc study cited dispatch strategies would not be required, previously ‘ ‘Alan W Wilkerson (President of Gem[nl Com- even if onsite generating devices were in- pany), Synchronous /n~ers/on Techrr/ques for Utiliza- stalled by 10 to 30 percent of their cus- tion of Waste Energy, 1976 tomers. ‘‘Conceptual Des/gn and S ysterns Ana/ys/s of Photo- \o/ta/c S ysterns, General E Iectrlc Corporation, Sche- ‘OGemlnl Company, op clt nectady, N Y , Mar 19, 1977, pp 5-9 “General Electrlc conceptual design study, pp 5-3 “General Electrlc Company, op clt , pp 5-4 “General E Iectrlc conceptual design study 146 ● Solar Technology to Today’s Energy Needs

The Dow Chemical Company’s examina- much energy for a utility’s needs, the onsite tion of industrial cogeneration was “unable devices could simply be disconnected from to identify any problems or potential prob- the load. (The cost of this could be included lems of transient stability attributable to in the $100 per unit cited for interruptible dispersed industrial generation. The effect services meters. ) It is also possible that of dispersed generation close to load cen- economic dispatch of electric utiIities could ters is to improve system integration and improve if a number of onsite generating stability problems.”23 However, if dispatch- facilities were equipped with sufficient on- ing or system stability became a problem, site storage of a fossil backup system. Dis- the difficulty could be resolved by using the patch is not a problem for systems relying interruptible service devices discussed earli- on chemical fuels for backup. er. When onsite users were producing too

CONTROL

TIME-OF-DAY PRICING rate was imposed. Before the rate was introduced, very little electricity was con- Some of the advantages of connecting en- sumed during the night and an enormous in- ergy generating and consuming devices with a common energy transport system cannot Figure V-1 .— Improvement in the Pattern of be realized if control over the equipment is Electricity Consumption in England’s South Western Electricity Board Resulting From a not exercised by a central authority capable Shift to Time-of-Day Electricity Rates of optimizing the performance of the integrated system. This control can be exercised directly by a utility if it owns all of the storage and generating equipment in a system, but it can be exercised indirectly by such approaches as time-of-day pricing. For example, with time-of-day pricing, the costs of nonoptimum performance of equipment not owned by the utiIity wouId be communicated to the owners of this equipment through higher prices for energy consumed for backup power and lower rates for any energy sold to the utiIity. The electric rates now in effect in most parts of the United States, however, do not have the effect of enforcing optimum al locations between onsite and centralized generating equipment. --- 1972/73 CONSTANT DAILY LOAD LINE I n fact, many of the current rates tend to discourage onsite generation in spite of potential cost savings. (This problem is treated in chapter VI Legal and Regulatory Issues. )

Figure V-1 illustrates the dramatic change O 3 6 9 12 15 18 21 24 in electricity consumption in Great Britain HOURS which occurred after a time-of-day electric Winter-average Weekday Load Curve

SOURCE ‘ ‘The Dow Chernlcal (lompdny, et al , Energy /n- Ash bury, J G and A. Kouvalls, E/ectrlc Storage Heaflng The Ex- dustr/a/ Center Study. NSF Grant #OE P 7+2042, June perience in Eng/and and Wa/es and Jn fhe Federa/ Repub/lc of Gemrdr?y Arqonne Nallonal Laboratory, Energy and En 1975, p 70 \ fro n men ta( Systpms DIVIS ron A N LJES 50 1976 P 14 Ch. V The Relationship Between Onsite Generation and Conventional Public Utilities . 147

crease occurred in the morning when elec- if control is exercised over devices which tric heaters and other equipment were consume energy as well as over energy stor- turned on. After the variable rate was intro- age and generating equipment. Clearly, en- duced, many consumers purchased onsite ergy consumers will want to exercise as thermal storage devices which could be much discretion as possible over the amount charged during the night and used to heat of energy they use and when they use the buildings during the day. The result was a energy, but they also may be willing to much more uniform pattern of energy con- change their consuming habits to some ex- sumption. tent if they are required to pay large premiums for energy consumed during periods when energy is relatively expensive to pro- STORAGE STRATEGY duce. Consumers may be willing to post- pone or defer the use of appliances such as Onsite solar electric devices integrated in- to electric utility grids provide a good exam- dishwashers, disposals, clothes washers and ple of some of the difficulties which can dryers, and other equipment when electrici- arise from local control over storage equip- ty is expensive. ment, A solar electric system which is not The utility can exercise control through connected to a utility grid would charge its the use of “interruptible service” equipment batteries during the day and discharge its when onsite equipment includes onsite stor- batteries during the night. This is precisely age, Such devices wouId permit the utiIity to the wrong strategy of operation from the turn off water heaters and other appliances perspective of the electric utility since stor- with storage capabilities during periods of age devices owned by the utility would be peak demand. Equipment of this type has charged during the night, when demands are been installed for relatively large-scale test- low, and discharged during the day when de- ing by the Detroit Edison Co. If this equip- mands are greatest. ment could ensure that onsite generating There will be some overlap between the equipment (whether thermal or electric) pur- two operating strategies since both types of chases backup power only during off peak storage wouId be discharging near sunset periods, the cost of backup energy to the on- and during cloudy days, but it is clear that site customer might be reduced — perhaps to the storage equipment would be used to the point where energy could be bought and best effect if it were controlled by the util- sold at the same rate. An experiment was re- ity. The advantage of using the solar electric cently conducted in Vermont in which these devices to meet utility electric demands di- appliances were automatically turned off rectly during the day (instead of sending it to when utility rates were high. The customers be stored) is arnplified by the fact that stor- were able to switch them back on again, but age devices are typically only about 75-per- in most cases were wilIing to wait untiI rates 24 cent efficient This logic would apply even if fell. Well-insulated water heaters and a very large fraction of the utility’s energy freezers are able to operate effectively even were derived from solar sources, although in if their supplies of electricity are automat- this case the strategy of operating individual ically shut off during the day when electricity prices are high. Several cities in German storage systems would closely parallel the y operation of utiIity storage. (A quantitative have utilities which are able to exercise evaIuation of this issue appears i n the finaI elaborate control over energy-consuming section of this chapter, ) equipment The central load-management

“J G Ashbury and A Kouvalls, E/ectr/c Storage LOAD MANAGEMENT Heating The Experience in Eng/and and \l’a/es and In the Federal ~epub/Jc of Cermany, Argonne Ndtlona i The performance of isolated and inter- Laboratory, Energy and Environmental Systems DIv I- connected energy systems can be improved $Ion, ANL F S-50, 1976, p 20 148 ● Solar Technology to Today’s Energy Needs

computer can control both the generating in effect, they subsidize the price of elec- equipment and electricity-consuming de- tricity during the night by charging daytime vices. The computer sends a signal down the customers for all other utility costs. These electric wires which automatically shuts off costs are capital charges on generating industrial equipment, refrigerators, water plants and transmission and distribution sys- heaters, and other equipment where energy tems, the costs of maintaining the transmis- use can be deferred during peak periods. 25 sion and distribution lines, and all other overhead costs — including the added cost As was the case with the control over of maintaining dual meters for daytime and storage, however, the strategy of deferring nighttime rates. demand for energy will depend strongly on how the solar devices are connected with It is also important to recognize that there other energy equipment. If the solar device is not an unlimited supply of “off peak” operates in isolation, an attempt should be power available in a given utility. There are made to shift all demands for energy to many possible uses for the power available periods when the sun is shining, If an elec- at night, in addition to storing heat for tric utility is used for backup power, how- buildings. The power can be used to charge ever, it will usually be preferable to shift the batteries for electric vehicles and in other in- demands which would require backup pow- dustrial procedures which can be deferred er to the late evening. to use night rates. The utilities may find that they require the “off peak” nighttime energy OFFPEAK ELECTRICITY themselves to charge their own storage devices, if utiIity storage must be used as a re- It is sometimes argued that electric util- placement for the oil- and gas-fired genera- ities will be able to sell “off peak” electricity tors now used to meet utility peaks. (The at a rate which covers only the cost of oper- National Energy Plan places major emphasis ating a large “baseload” plant and the rel- on eliminating utility use of oil and gas. ) atively inexpensive fuels which can be used And utilities must also make some use of in these plants. Such rates are possible, but off peak periods to maintain their equip- they must be considered promotional since, ment. OWNERSHIP

The complex rates required to encourage ing overall utility costs. (This could, of design of onsite equipment best suited for course, also be done by a company the energy network of which it is a part, owning only transmission and distribu- would, of course, be obviated if utilities tion equipment, ) owned the onsite systems outright. While there clearly are disadvantages associated Utilities compare the cost of energy with expanding the monopoly position of derived from new solar equipment to utilities, there are a number of reasons for the cost of generating energy from new believing that utility ownership of onsite electric-generating equipment or the solar equipment may be attractive in many marginal cost of gas from new sources, circumstances: while all other solar owners must com-

● UtiIities are uniquely able to optimize pare solar costs to the lower imbedded the mix of generating and storage costs of energy which determine com- equipment in their service area and to mercial rates. develop control strategies for minimiz- Utilities are probably better able to “J [; Ashbury, op [-It , p 20 raise large amounts of capital for long- Ch. V The Relationship Between Onsite Generation and Convention/ Public Uti/ities ● 149

term energy investments than any other the future of the energy industry, and type of organization. As the statistics in difficulties in obtaining rate changes table V-4 indicate, electric utilities re- from utility commissions have, how- quire several times more capital per ever, made it progressively more dif- dollar of sales than typical industrial ficult for utilities to raise capital in re- firms (although the capital intensity has cent years, declined rapidly in recent years be- Utility capital tends to be less expen- cause of the rapid increase in fuel sive than capital required by more spec- costs) At the end of 1974, electric util- ulative industries. A typical utility can ities owned approximately $150 billion raise 50 percent of its capital from in plants and equipment— nearly 20 debt–while most manufacturers rely percent of all business plant equipment on debt for only 10 to 15 percent of new in the United States.26 investment capital, the remainder of the capital being purchased at higher Table V-4. —The Capital Intensity of Major U.S. Industries rates from investors, 27 Utility capital [Dollars of plant to secure $1.00 of revenue] costs may, however, be higher than those experienced by homeowners and can be higher than the cost of capital $ available for financing typical residen- Investor-owned electric companies: tial and commercial buildings. A home (1965) . ., . . ., . ., ... ., .. .4.51 (1970) ., ., ., . . ., ., ., ... ., .. .,4.39 owner earning a tax-free return of 10 (1975) ., ., ., ., ., ., ...... 3.20 percent on capital invested in solar (1977) (est. ) . , ., . . . 2.96 energy equipment may be well satis- Bell Telephone System (1971 ) . ., ...... 2.95 fied. This advantage is moot, of course, 10 major railroads (1971) ., . ., ...... ,2.48 Gas transmission companies (1971 ) ...... 2.43 if the individual is unable to raise any Gas distribution companies (1971 ) ...... 1.62 capital for the project at al 1. 10 major integrated oil companies (1971) ., .. ..,1.25 500 diversified industrial companies (1971) .. ...0.87 Utilities are already in the business of 50 major retailers (1971) ...... 0.43 selling energy and have the required infrastructure for billing, marketing, and SOURCES Naf~ona/ Gas Survey U S Federal Power Commjsslon repairing equipment, Some potential Ebasco Services Incorporated (New York, N Y ), 1977 Bus{ness and Economic Charts p 28 owners of onsite devices have been wary of investing in equiprnent which might lead them to unfamiIiar mainte- An ability to raise capital for long- nance problems or the hiring of special- term investments is particularly critical ized personnel, for solar energy devices since solar energy is very capital-intensive and typi- Utility ownership or marketing of solar calIy requires a number of years to re- equipment and a willingness to stand turn the initial investment. Utilities, behind the equipment once installed therefore, may be uniquely able to pro- could increase consumer confidence in vide initial capital for solar devices in the equipment. situations where individuals (particular- There is some ambiguity, however, about ly individuals in lower income groups) whether utility ownership of smalI solar en- and organizations may find the capital ergy equipment would be permitted by Fed- requirements prohibitive. Reverses in eral antitrust statutes. The legal issues of the stock market, uncertainties about

“Federal Power Comm[ss[on, National Power Sur- vey, Flnanc/ai Outlook for the Electric Power Industry. “Paul j Garfield and W F LoveJoy, Public Utility Report and Recommendations of the Technical Ad- Economics, Prentice Hall, Inc , Englewood Cllffs, N J , visory Comm/ttee on Finance, December 1974, P 50 1964, p 25 150 ● Solar Technology to Today’s Energy Needs

ownership are discussed in greater detail in On the other hand, most of the utility chapter V 1, Legal and Regulatory Issues. companies surveyed for a General EIectric study referred to earlier said they were reluctant to enter the business of selling ther- UTILITY ATTITUDES mal energy systems. Some indicated that it would require too much diversification; There is no industrywide position either others cited problems with metering and on the issue of onsite generation or on the other technical difficuIties. question of utility ownership of such facilities, Industry attitudes vary company by A study conducted for the Federal Energy company, and the diversity of attitudes is Administration found mixed opinions due, at least in part, to the fact that many among utilities on expanding capacity by utility companies simply have not taken a using conventional onsite generating equip- close look at the issue. ment, primarily cogeneration systems in fac- Natural gas utilities have expressed the tories and other generators of process greatest recent interest in onsite solar facil- heat. Examples include: ities since supplies of gas are diminishing ● A west-south-central utility which sells and the companies are looking for new ener- both steam and electricity. gy sources to replace natural gas in the future. Southern California Gas Co., for ex- ● A Pacific coast utility, which has in- ample, has tested solar-assisted gas heating stalled turbines at a paper mill, returns for apartment buildings as one means of low-temperature steam to the mill and conserving supplies and extending the Iife of pays $0,01 per kWh for the electricity the company’s resources .28 Interest is not generated. confined to gas companies. A recent survey ● A Vermont utility actively searching for found nearly 100 electric utilities which cogeneration opportunities. were initiating projects in solar heating and ● cooling. 29 30 The EIectric Power Research In- A Texas utility which stated flatly that stitute has an extensive program in solar they were “not in the business of selling energy equipment.31 At least one electric steam, ” and which turned down several utility has entered into an agreement with a opportunities. local installer of solar hot water heaters, and Although utility attitudes may be chang- a gas utility has proposed changes in regula- ing, there have been scattered complaints tions that would permit it to operate as a 32 33 that utilities have tried to thwart private combined gas and solar utility. companies intending to instalI onsite generating equipment. The Dow Chemical Co. reports that onsite industrial cogeneration

‘aAlan Hlrshberg, Pub//c Po/icy for So/ar Heating “has been consistently discouraged by long- and Cooling, October 1976, p 37 standing policies on the part of most pri- “Solar Energy Intelligence Report, Feb. 14, 1977, p vately owned electric utilities that have dis- 31 couraged in every way possible the genera- ‘“E Iectrlc Power Research Institute, Survey of E/ec- tion of electricity by any other type of or- tric Utility So/ar Prolects, Palo Alto, Callf , ER 321 -SR, 1977 ganization. Relevant here are rate schedules J‘ E Iectrlc Power Research I nstltute, E/ectric Power Research Institute: So/ar Energy Program, fall of 1976, E PRI RP 549, 1976 “E S Davis, Comrnercia/izing Solar Energy: The Case for Gas Uti//ty Ownership, mlmeo, Jet Propulsion 34 Dow Chemical Co , et al , Energy /ndustria/ Center Laboratory report, California Institute of Technology, Study, June 1975, p 23 June 1976 jSThermo E Iectron Corp., A Study of /rip/ant ~lectr;c “General Electrlc Corporation, conceptual design Power Generation in the Chernica/, Petro/eum Refin- study. ing, and Paper and Pti/p /ndustries, June 1976 Ch. V The Relationship Between Onslte Generation and Conventional Public Utilities . 151

that favor large industrial users (whether if no power is used) that make it uneconoml- justified or not by “cost of service”), and cal to use the utility as a standby source heavy demand charges (charges levied even backing up industrial power generation “‘b

THE COST OF PROVIDING BACKUP POWER FROM AN ELECTRIC UTILITY

There is no easy way to compute the cost The details of the technique used to com- of providing backup power to an onsite sys- pute utility costs, and detailed assumptions tem from a conventional electric utility made about the costs of equipment and since electric utility costs are very sensitive fuels experienced by each utlIity, are de- to the cost of equipment and fuels in the scribed in detail in appendix A of this area being served and to the times when chapter, but the basic method IS straight- electric backup power is demanded. A sim- forward: ple technique for computing these costs is 1. A “baseline” utility was constructed by presented here to illustrate some of the ma- combining the electric demands of a jor trends, to exhibit several different ways number of buildings and industrial of looking at the major trends, and to exhibit processes using a mixture of energy- several different ways of looking at the issue consuming equipment which was typ- of rates. It must be emphasized from the on- ical for the city under examination. The set that the method cannot be taken to be a cost of providing electricity for the precise calculation of the costs of electric combined utility load was then com- utiIities actualIy operating in the regions puted, assuming that the utility was op- covered. The results are so sensitive to local timized to meet the demands. (Both the conditions that each utiIity must make its cost of energy attributable only to the own analysis of the costs. The following generating units, the so-called “busbar analysis shows that utiIity costs are extreme costs, ” and the cost of energy delivered Iy sensitive to four variables: to customers were computed).

2 The cost of meeting a new set of elec- ● The regional cost of equipment, the tric demands resulting from adding a available financing, and the local cost specified number of solar and nonsolar of fuels; buildings to the utility was computed, assuming that the utility was optimized ● Local climatic conditions [for example, to meet the new demand pattern. solar backup costs are lower if peak 3 The effective cost of providing backup heating and cooling periods are cor- power for different types of buildings related with periods of clear skies); could then be computed by examining the incremental costs and the incre- ● The type of solar equipment installed mental utility costs which resulted (collector area, storage capacity, etc.); when the new buiIdings were added, and Since it was assumed that all of the equipment in the utility was new, and the costs Ž The number of buiIdings in a utiIity computed are all essentialIy marginal costs, service area equipped with solar energy the actual utility costs in the region would devices (a relatively small number of be lower because some fraction of the ener- solar facilities will contribute to load

diversity, but a large number will re- “DOW Chemical Co , et al , Energy /ndustr/a/ Center verse this resuIt). Study, June 1975, p 23 152 Ž Solar Technology to Today’s Energy Needs

gy would be generated from less-expensive, An examination of table V-5 reveals sev- older plants. There are a number of other ar- eral features: tificial ities in the technique: Ž Electricity for conventional houses us- ● The choice of an “optimum” set of util- ing gas for everything other than fans ity equipment does not use a detailed and miscellaneous electric loads costs analysis of overall system reliability the utility approximately the same and maintenance schedules— it instead amount as electricity for a heat-pump simply assumes that the utility will pur- house. chase 20 percent more in each gener- ● Electricity costs are lower for houses ating capacity than the peak required in , using electric resistance heat (presum- that category to meet the load; ably because they use more electricity ● Utilities will seldom be able to deploy during periods of mild winter weather equipment which is optimally suited to when utility demands are relatively load patterns because of regulatory de- low) and are higher for houses using gas lays, an inability to precisely predict de- heat and electric air-conditioning. (All mands, and the need to use older equip- of the utilities examined have peaks in ment; and the summer, and these peaks are increased by the added air-conditioning. ● I t was assumed that none of the utilities But the added equipment is underuti- evaluated owned storage equipment. In lized since the new houses do not use the future, utility storage devices may much electricity during the winter. ) play a major role in replacing the oil- and gas-burning devices now used to ● The houses using solar energy for heat- meet real demands. The impact of storing and hot water and a heat-pump age on the cost of backup power for backup cost the utility more per kWh solar systems will need to be carefully than the conventional houses using examined. One would expect that low- baseboard heat, but less than the cost storage would minimize the nega- houses using gas heat. tive impacts of solar equipment. The photovoltaic houses cost some what more than the houses equipped This technique has been used to compute only with solar heating and hot water, the cost of providing electric power to a but in no case is the utility cost sig- number of different single family houses, nificantly larger than the cost of pro- and the results are summarized in table V-5. viding backup power for a heat-pump This table compares the cost per kWh of house– in several instances, the utility providing electricity to the building de- costs are lower in the solar cases. The scribed to the cost per kWh of providing relatively favorable appearance of electricity to a similar building using an these solar systems results in part from electric heat pump. AlI comparisons are be- the fact that some of the utility air-con- tween delivered costs. Greater detail on the ditioning peaks can be reduced by the utility costs and the capacity of equipment solar devices. (About 50 percent of the installed is presented in volume I I.) For ex- total building energy requirement is ample, the table indicates that the electrici- provided by the photovoltaic devices, ty required by a single family house using and about 30 percent of the total ener- gas for heating, water heating, and air- gy requirement of the house is provided conditioning in Albuquerque, N. Mex., costs by the heating and hot water systems.) the utility 2 percent more than the electricity used to provide power for a conventional ● Utility costs per kWh of backup power single family house in the same city using a delivered are increased slightly if sales heat pump and electric hot water. to the utility are permitted. Ch. V The Relationship Between Onsite Generation and Convention/ Public Utilities ● 153

Table V-5.—The Fractional Difference Between the Utility Costs [¢/kWh] Required to Provide Backup Power to the Systems Shown and the Costs to Provide Power to a Residence Equipped With an Electric Heat Pump [see note for explanation]

Albuquerque Boston Fort Worth Omaha

1. Single family house with gas heat, hot water, and alr-conditioning” . . 0.02 -0.09 -0.15 0.03

2 Single family house with gas heat and hot water, and central electric air-conditioning ● ...... 0.26 0.28 0.15 0.32

3. Single family house with baseboard heat, electric hot water, and window air-conditioning” ...... – 0.14 -0.14 -0.15 -0.10

4. Single family house with solar heat and hot water backed up with a heat pump and electric hot water* 0.01 -0.13 0.06 -0.07

5. Single family house with extra insulation, electric hot water, and heat pump with: ● ● a. Photovoltaic system with no battery and no sale to the utility ...... -0.06 -0.27 ‘0.02 -0.07 b. Photovoltaic system with no battery and sales to utility permitted, ...... 0.07 -0.23 0.03 -0.01

C. Photovoltaic system with battery and no sales to utility. . . . . -0.30 -0.27 0.01 -0.05

“ Compared with single family house with electric hot water and heat Pump. “’ Compared with single family house with extra insulation, electrlc not water, and heat pump, NOTE: let Cr = Incremental utlllty costs resulting from adding 1,000 reference houses with heat pumps. let Kr = the Incremental number of kWh generated when 1,000 reference houses with heat pumps are added to the utility let Ct and Kt be the equivalent quantities resulting from adding 1,000 houses with a different kind of energy equi Prnent Then the fractional change JJlustrated above Is given as follows: F = Ct/Kt - Cr/Kr

Cr/Kr

Table V-6 indicates the Ievelized monthly was assumed to be the marginal cost of pro- costs which would be experienced by con- viding backup — giving credit to the value of sumers if they were charged electric rates electricity sold to the utility— it was as- reflecting the marginal cost of providing sumed that electricity is bought and sold at energy to several types of energy systems. the same price. ) Levelized costs assuming a moderate rate of increase in electric prices are shown for Except for Boston, the two techniques for comparison. In these cases, it is assumed computing Ievelized energy costs produce that an electric utility will purchase elec- similar estimates of Ievelized energy tricity from the onsite generating facility for charges. (It is Iikely that the techniques used 50 percent of the price at which it sells elec- to compute the marginal costs of electricity tricity. (In the cases when the electric price are overly optimistic about the costs of new

28-842 () - 11 154 Ž Solar Technology to Today’s Energy Needs

Table V-6.—Levelized Monthly Costs for a Well-Insulated Single Family House Showing the Effect of Marginal Costing for Backup Power

Electricity rates assumed to Electricity rates reflect marginal increase by BNL forecast utility rates (see appendix for methodology) No credits 20% ITC on No credits 20% ITC on given solar equipment given solar equipment I. ALBUQUERQUE

—no solar...... 183 183 204 204 —59 m2 silicon photovoltaics, no batteries, no sales to the the utility ...... 213(255) 202(246) 21 4(257) 204(248) —59 m2 silicon photovoltaics, no batteries, sales to utility permitted ...... 197(240) 187(231 ) 190(232) 179(223) —59 m2 silicon photovoltaics, no batteries, sales to utility permitted ...... 216(267) 204(257) 194(245) 181 (234) Il. BOSTON

—no solar...... , . . . 300 300 215 215 —59 m2 silicon photovoltaics, no batteries, no sales to the Utility ...... 319(362) 308(353) 215(259) 204(249) —59 m2 silicon photovoltaics, no batteries, sales to utility permitted ...... 305(348) 294(339) 200(244) 189(234) —59 m2 silicon photovoltaics, no batteries, sales to utility permitted ., ...... 324(376) 311 (365) 227(279) 21 3(267) Ill. FORT WORTH

—no solar...... 190 190 191 191 —59 m2 silicon photovoltaics, no batteries, no sales to the utility ...... 228(272) 216(262) 227(272) 216(262) —59 m2 silicon photovoltaics, no batteries, sales to utility permitted ...... 218(263) 207(253) 212(257) 201 (247) —59 m2 silicon photovoltaics, no batteries, sales to utility permitted ...... 240(293) 226(281 ) 242(295) 228(283) IV. OMAHA —no solar...... , ...... 211 211 219 219 —59 m2 silicon photovoltaics, no batteries, no sales to the utility ...... , . . . . 241 (284) 230(275) 238(282) 228(273 —59 m2 silicon photovoltaics, no batteries, sales to utility permitted ...... 231 (275) 220(265) 223(267) 21 2(258 —59 m2 silicon photovoltaics, no batteries, sales to utility permitted ...... 253(305) 239(294) 250(303) 237(291 )

NOTES: (1) All houses use heat pumps for space conditioning and electric resistance hot water heaters (2) Parenthesis ( ~ indicates utility ownership. (3) ITC = Investment Tax Credit Ch. V The Relationship Between Onsite Generation and Convention/ Public Uti/ities Ž 155

equipment in that region. ) More important- can be done simply by computing the dif- ly, however, the ranking of the Ievelized ference in utility costs which results when a costs of the four systems appears not to de- group of solar buildings is permitted to sell pend on whether marginal costs or average energy and dividing this cost by the total costs are used to make estimates. amount of kWh sold. The results are presented in table V-7 as a ratio between the value of the electricity available for pur- The same methods can be used to esti- chase and the average cost of electricity mate the price a utility should be able to generated by the utility. Since all costs in pay for electricity produced by an onsite the utility used in this analysis are effective- device which exceeds onsite demands. This ly “marginal costs,” the onsite devices are

Table V-7.—Ratio of Price Utilities Can Pay for Solar Energy Generated Onsite to the Price Charged by Utilities for Electricity

Albuquerque Boston Fort Worth Omaha

Purchase Purchase Purchase Purchase Purchase Purchase Purchase Purchase base reference base reference base reference base reference

1. Single family house with no onsite batteries ...... 0.67 0.65 0.62 0.55 0.31 0.28 0.57 0.59

2. Single family house with onsite batteries ...... 0.40 0.39 1.09 0.98 0.29 0.26 0.64 0.66

3. Single family house with extra insulation and no onsite batteries ...... 0.64 0.62 0.58 0.49 0.66 0.64 0.50 0.50

4. High rise apartment with no onsite batteries ...... 0.64 0.66 0.51 0.48 0.29 0.29 0.42 0.44

5. High rise apartment with onsite batteries ...... 0.41 0.43 0.38 0.36 0.29 0.28 0.36 0.38

Let x n (utlllty cost supplylng buildlng not selling electricity minus utility costs for building selling excess electricity to the utility)

Let y = (kWh generated by utility In supplying buildlng not selling electricity minus utility costs in supplying building selling excess electrlclty)

Let z n (added utility cost incurred in supplying building with no solar equipment) divided by (added kWh required to supply the bulldlng)

Let w = (total utlllty costs) dlvlded by (total kWh produced by the utility)—no additional buildings

Purchase = Xly Purchase = Xly Base w Reference x

All utlltty costs are dellvered costs 156 . Solar Technology to Today’s Energy Needs

not given credit for the difference between storage devices in a number of different the imbedded average utility costs used to types of buildings is shown in tables V-9 and determine selling prices and the fact that V-10. Chilled water can also be produced new solar systems will displace relatively ex- during the night and stored in tanks to pensive “new” generating facilities. reduce cooling loads during the day. The use of “off peak cooling” has the additional ad- Table V-8 shows information for high rise vantage of allowing the chilling equipment apartment buildings which is equivalent to to operate at night when it is more efficient. the data for single family houses shown in In computing the load pattern, it was as- table V-7. It can be seen that the solar de- sumed that the storage devices are charged vices are less attractive to the utility in these between midnight and 5 a.m. and that the cases, in part because the reference case amount stored is equal to the amount of chosen for the high rise building uses elec- backup energy for heating, hot water, and tric baseboard heating—which produces a cooling which would have been required for more even load than the heat pumps used the previous day with no off peak storage. for the single family reference case. As noted earlier in this chapter, the costs An examination of tables V-9 and V-10 of providing electricity can be reduced if on- shows that the savings to the utility can be site storage is available at each building site considerable if off peak storage is used on- which permits the buiIding to purchase ener- site. In the case of off peak storage of cool- gy during periods when the demand on the ing, utility costs per kWh attributable to the utility is relatively low. Solar equipment, of house are reduced by nearly 50 percent. In course, is typically already equipped with a all cases, the reduction in costs is lower if thermal storage device, and these devices solar equipment is installed, but in many in- can be converted to allow the system to pur- stances the difference is not very large. Typ- chase energy only during off peak periods ically, the utility cost per kWh to provide with a relatively simple change in their con- backup power for the solar houses with off- trol systems. The result of installing off peak peak storage is about 10 percent greater

Table V-8.—The Fractional Difference Between the Utility Costs Required To Provide Backup to the Systems Shown and the Costs of Providing Power to a High Rise Apartment Equipped With Central Electric Air-Conditioning, Electric Hot Water, and Baseboard Resistance Heating [see notes on previous table for explanation of how these fractional changes are computed]

Building equipment Albuquerque Boston Fort Worth Omaha

1. Gas heat, gas hot water, and gas air-conditioning...... 0 -0.11 -0.12 -0.05

2. Gas heat, gas hot water, electric air- conditioning...... 0.02 0.32 0.21 0.26

3. Electric hot water, electric baseboard heat, central electric air-conditioning, and a photovoltaic system: a. No batteries onsite, no sales to grid . . . . . 0.27 -0.01 0.21 0.03 b. No batteries onsite, sales to grid allowed . 0.31 -0.02 0.23 0.09 c. Batteries onsite, no sales to grid ...... 0.28 -0.02 0.22 0.08 d. Batteries used onsite, sales to grid allowed ...... 0.31 -0.02 0.22 0.08 Ch. V The Relationship Between Onsite Generation and Conventional Public Utilities ● 157

Table V-9.—The Impact of Off peak Storage on Utility Costs [fractional increase or decrease in backup costs per kWh–see notes]

Albuquerque Boston Fort Worth Omaha

Nonsolar houses

● Off peak storage for heat and hot water ...... -0.37 -0.38 -0.29 -0.34

● Off peak storage for heat, hot water, and cooling ...... -0.47 -0.45 -0.48 -0.44

Houses with solar heating and hot water . No off peak storage ...... 0.03 -0.11 0.12 -0.06 Ž Off peak storage for heating and hot water . . . -0.11 -0.24 0.003 -0.21 . Off peak storage of heating, hot water, and cooling ...... -0.30 -0.35 -0.32 -0.36

Notes The t‘ reference house’ is a single family house using electric resistance heating and hot water and window air-conditioners

All solar houses generate only heating and hot water from solar energy.

added u tI I It y costs resu It I ng from the add It ton of 1,000 reference houses Let Cr =

added kWh resu It I ng from the add It Ion of 1,000 reference houses K r = % = added u tI I Ity costs resu It Ing from the addlt Ion of 1,000 test houses (type noted In left column above) K = added u tI I Ity costs resu It I ng from the add!t Ion of 1,000 test houses

The fractional change ratto shown above IS calculated as follows: (Ct/Kt) - (Cr/Kr) F= (Cr/Kr)

than the utility cost per kWh attributable to dinary heating systems. Another difficulty conventional houses with off peak storage. with storage of off peak electricity in the form of thermal energy to be used for space heating is that, in the climates examined in It is apparent that the solar systems have this study, the use of off peak storage Ied to more difficulty competing with convention- a significant increase in the electricity con- al electric heating systems if the conven- sumed by each building—which would re- tional devices use off peak storage and are duce the economic advantage to the build- able to buy electricity during off peak peri- ing owner of using off peak storage. It must ods at reduced rates. There are, however, also be recognized that the costs shown in still a number of cases in the examples the tables implicity assume that an ideal shown where solar devices are able to com- “marginal rate” is charged in which the util- pete. Off peak storage equipment, while not ity is able to charge each customer precisely as expensive as solar devices, can still be the real incremental cost incurred by the costly: they require the installation of heat- utility in supplying that customer. In this ing (or chilIing) equipment which is larger in sense, the costs represent a “best case” for capacity than conventional equipment by off peak power. The rates also do not in- the ratio of 24 hours to the number of hours clude additional charges which might result used to charge storage; with existing tech- from additional metering and bilIing. The re- nology, heat pumps cannot be used to sults may indicate, however, that in the charge off peak heat storage and resistance long-run conventional electric utilities may heating must be used; and the devices re- prove to be poor choices for providing back- quire more sophisticated controls than or- up power to onsite solar instalIations. 158 Ž Solar Technology to Today’s Energy Needs

Table V-10.—Levelized Monthly Costs for a Single Family House Showing the Effect of Marginal Costing and Buying of Off peak Power

Electricity rates assumed Electricity rates reflect to increase by BNL forecast marginal utility rates (see appendix for methodology)

200% ITC on 20% ITC on No solar & off peak No solar & off peak credits equipment credits equipment

i. Albuquerque

—No solar or off peak buying: . Electric resistance heat. . . . 239 239 241 241 ● Heat pump heat ...... 204 204 229 229 —Solar only: ● Low cost coils . . , ...... 185(21 1 ) 179(205) 183(209) 177(203 Ž High cost ...... 205(240) 196(232) 203(238) 194(230) —Offpeak heating, & hot water only ...... N/A N/A 185(205) 181 (201 ) —Offpeak heating, cooling & hot water only...... N 1A N/A 198(232) 189(225) —Solar & off peak heating & hot water ● Low Cost coils ...... N/A N/A 177(207) 169(200) ● High cost coils ...... N/A N/A 197(236) 186(227)

—Solar & off peak heating, cooling & hot water ● Low Cost coils ...... N/A N/A 194(242) 181 (231 ) ● High cost CO iIS...... N/A N/A 214(272) 198(258)

Il. Omaha —No solar or off peak buying: ● Electric resistance heat. . . . 278 278 278 278 ● Heat pump heat ...... 250 250 268 268

—Solar only ● Low Cost coils ...... 252(282) 244(276) 234(265) 227(259) Ž High cost COiIS ...... 278(320) 267(31 1 ) 261 (303) 250(294)

—Offpeak heating & hot water only ...... N/A N/A 219(241 ) 21 4(237)

—Offpeak heating, cooling & hot water only...... N/A N/A 237(278) 227(270)

—Solar & off peak heating & hot water ● Low COSt Coils ...... N/A N/A 221 (258) 211 (250) . High cost colts...... N/A N/A 247(296) 234(284)

—Solar & off peak heating cooling & hot water ● Low Cost Coils ...... N/A N/A 244(303) 228(289) Ž High cost coILs...... N/A N/A 270(341 ) 250(324)

NOTE: Solar systems are thermal only; Housea are SF-3 Ch. V The Relationship Between Onsite Generation and Convention/ Public Utilities Ž 159

Table V-1 O also shows that when contem- ing and the utility peak occurred in the porary rate schedules are used, it costs less winter (both utilities examined have summer to heat a single family house with a heat peaks). The heat-pump systems would be pump than with electric resistance base- more attractive, if their performance were board heat. The difference in costs narrows improved or a technique could be devel- considerably, however, if marginal costs are oped for storing off peak energy for use dur- charged. The resistance system actually is ing periods when the heat-pump capacity is less expensive if off peak storage is used in inadequate to meet the load; in current sys- connection with the resistance heating. The tems, straight resistance heating is used in disadvantages of heat-pump systems would such situations. Clearly, more analysis is re- be magnified if a large number of customers quired in this area. in the regions examined used electric heat-

BACKUP POWER WITH ENERGY SOURCES OTHER THAN ELECTRICITY

It was noted earlier that the cost of pro- electric heating and hot water in many parts viding backup for solar equipment from rel- of the country in the relatively near future. atively expensive electric-generating equip- Table V-11 indicates some comparisons ment may be so great that it would be pref- between gas and electric backup. In the gas erable to provide backup by using seasonal cases, it is assumed that the system is not storage systems or relying on gas I n fact, it connected to an electric grid. Backup is pro- has been suggested that electric utilities, vided by a small, 32-percent efficient engine with their high capital costs, are uniquely burning natural gas to power a heat pump unsuited to providing backup for solar Electricity for lighting and other uses is pro- equipment. 37 Analysis presented in volume vided from a generator attached to the heat- II shows that for large buildings (and for pump engine The table indicates that the single famiIy structures which can pipe ther- gas backup alternative may be attractive mal energy to a central storage site), solar even if gas prices increase drasticalIy over heating and hot water systems capable of the next few decades This possibility may providing 100 percent of local requirements make it interesting to consider the possi- may become economicalIy competitive with bility of granting preferential allocation of gas to facilities using gas to backup solar facilities and permitting new gas hookups in 1‘J oseph C Ashbury and Ronald 0 A!LJel Ier, “solar Energy and E Iectrlc Ut I I It le~ Shou Id They be Inter- regions where such hookups are now per- tdceci?” \c/ence, 1954127, p 445 (1977] mitted if the gas is used as a solar backup 760 ● Solar Technology to Today’s Energy Needs

Table V-n .—Levelized Monthly Costs of Several Kinds of Energy Equipment in a Single Family Detached Residence in Albuquerque, N. Mex. (dollars per month)

Gas price in 2000 (¢/kWh) ...... 0.005 0.011 0.015 0.03 Percent of total Electric price in 2000 energy usage (¢/kWh) ...... 3 4.5 10 — supplied by Incentive ... , ., ...... none none 20% 20% solar energy tax credit tax credit

1. Heat pump, electric hot water ...... 156 203 395 — o

2. Solar heat and hot water, electric heat pump backup —High...... 187(223) 213(250) 309(354) — 28 —Low ...... 158(1 83) 184(210) 284(315) — 28

3. Extra insulation, 59 m2 photovoltaics at $500 kW, electric heat pump backup —No batteries ...... 169(207) 196(233) 294(338) — 52 —20 kWh batteries at $70/kWh ...... 190(228) 215(253) 303(349) — 45

4. Gas heat and hot water, central electric air-conditioning , ...... 116 173 287 500 0

5. Solar heat and hot water backup, electric air-conditioning —High...... 172(21 O) 201 (239) 276(323) 422(469) 41 —Low ...... 1 43(1 70) 172(1 99) 251 (284) 379(430) 41

6. Extra insulation, 50 m2 photovoltaics at $500/kW, gasfired heat pump/generator backup...... 157(1 96) 177(21 5) 182(230) 203(277) 50

7. Solar heat with central seasonal storage, homes connected with hot water piping, electric air- conditioning in each house —High...... 21 4(292) 233(31 1 ) 290(383) — 65 —Low ...... 164(21 2) 184(231 ) 249(306) — 65

Notes: All costs In 1976 dollars ( ) = utlllty ownership Appendix V-A Analytical Methods

BACKGROUND

Electric utility load pat ems can be most The amount of electricity sold would con- conveniently summarized in what is known sequently be reduced, but costs would not as a “load-duration curve. ” The curve for a be reduced proportionately because a large hypothetical utility is shown in figure V-A-1. fraction of utility costs are independent of It shows the number of hours per year the the amount of electricity generated. In this demand for electricity is greater than or case, a utility will have proportionately equal to alI demands from zero to the an- more peaking plants with relatively small nual peak For example, the figure shows capital costs, Unfortunately, such plants are that the power company in question had a less efficient than large plants in both their maximum load of 100 MWe and a minimum fuel consumption and operating and main- load of 25,0 MWe (i. e , the company pro- tenance expenses. Curve 3 indicates a sit- duced at least 250 MWe for all 8,760 hours uation where the solar equipment installed of the year). The company met a load which does not require supplementary power dur- was greater than or equal to 50 MWe for at ing the utiIity’s peak demand hours, I n this least 3,504 hours during the year Loads will case, more efficient generating facilities increase with each new year as a result of (baseload plants and cycling plants) would population growth and increases in the elec- be used to produce a greater fraction of the tricity consumed by each person. The in- total utility load, resulting in a lower cost for crease in per capita consumption is a result each kiIowatt-hour generated. of a shift to electric heating and other elec- In order to quantify both the extent of the tric appliances. impact and whether it is adverse or benefi- If solar equipment is installed in a signifi- cial, it is necessary to construct a “typical” cant fraction of the buildings served by a utiIity. From this, several Ioad-duration utiIity, the load pattern which it must meet curves for the utility’s operation can be con- could be significantly affected. Figure V-A-1 structed for 1985, involving a variety of illustrates two extreme possibilities. We scenarios both with and without solar equip- assume that curve 1 indicates the load-dur- ment. These hypothetical load-duration ation curve which a utiIity could expect if curves can then be used to determine the no solar equipment were installed. If solar kinds of equipment utilities will have to in- equipment requiring supplementary power stalI to meet the demand of their customers, during a utility’s peak demand hours and and the Ioadfactors for each piece of gen- not during off peak hours was installed, a erating equipment. In turn, electricity costs load-duration curve having roughly the and the utility’s fossil-fuel requirements can shape of curve 2 would resuIt. be estimated for each scenario,

CHARACTERISTICS OF A “TYPICAL” UTILITY

The model utility examined is as close as lowing sections briefly outline the physical possible to a “typical” utility which matches and financial structure of the utility at the the national average for privately owned end of 1975. electric utilities wherever possible. The fol- 162 ● Solar Technology to Today’s Energy Needs

Figure V-A-1 .—A Typical Load-Duration Curve for an Electric Utility

Curve #1 — —

Curve #2 — — — –

Curve #3 - — - —

I I I I I I I I

20 40 60 80 100

(1 752) (3504) (5256) (7058) (8760) Percent of time indicated load is exceeded (Hours)

Source: OTA. Appendix V-A

CHARACTER ISTICS OF THE MODEL UTILITIES Table V-A-1 .—Average Characteristics of

The hourly loads used to evaluate the cost of generation are constructed by combining the hourly electrical loads which apply to individual buiIding types The method for determining the hourly electric demands of individual buildings is explalned in Volume I I, The number of customers i n a typical private U. S. utility IS shown in table V-A-I. The number of buildings of each type used to construct the model utility used here for analysis is shown in table V-A-2.

Table V-A-2.—Numbers of Buildings in “Typical” Utility Modeled Which Use Heating and Cooling and Hot Water Equipment* —.. — .———— ———. Albuquerque Boston Fort Worth Omaha Single family detached houses Baseboard resistance heating...... 10,470 8,080 11,790 7,719 Central electric air-conditioning ...... 35,450 29,823 44,130 48,200 Window air-conditioning ...... 8,163 5,040 11,790 7,719 Electric hot water ...... 15,840 18,080 16,970 17,970 Total single family houses...... 55,920 55,920 55,920 55,920

Townhouses Baseboard resistance heating...... 648 1,429 2,010 1,350 Central electric air-conditioning ...... 4,132 3,464 4,950 5,610 Window air-conditioning ...... 424 895 2,010 1,350 Electric hot water ...... 1,043 1,211 1,120 1,208 Total townhouses ...... 6,960 6,960 6,960 6,960

Low rise apartments Baseboard resistance heating...... 201 444 624 419 Central electric air-conditioning ...... 1,282 1,075 1,536 1,741 Window air-conditioning ...... 132 278 624 419 Electric hot water ...... 324 376 348 375 Total low rise apartments...... 2,160 2,160 2,160 2,160

High rise apartments Fancoil resistance heating ...... 28 62 87 58 Baseboard electric heating ...... 28 62 87 58 Central electric chiller ...... 196 188 30 300 Window air-conditioning ...... 196 188 30 300 Electric hot water ...... 90 104 97 104 Total high rise apartments...... 600 600 600 600

Shopping centers Central electric chiller ...... 30 0 30 30 Electric resistance heating ...... 15 0 15 15 Total shopping centers...... 30 0 30 30 ● All figures are number of buildings not units—the townhouses have 8 units each, the low rise apartments 36 units each, and the high rise apartments 196 units each. NOTE: Detailed assumptions about the buildings modeled can be found In volume 11, chapter I Ar?a/y?ica/ Methods. 164 ● Solar Technology to Today’s Energy Needs

Commercial demands are approximated affected by approximately the same by simply using 30 shopping centers. A more weather at approximately the same detailed model would require many more time. (This is a conservative assump- load types–schools, hospitals, etc. indus- tion. Most utilities cover areas suffi- trial demand was approximated as a weekly ciently large enough to expect some load which is not weather dependent. Hour- weather diversity. Tielines can be used ly industrial loads used in the utility model between widely spaced utilities to even are shown in table V-A-3. They were chosen out weather loads. ) after examining a number of actual utility 2 It was assumed that the hourly varia- industrial loads. There are great variations in tion of “miscellaneous electric loads” these loads around the country, and the and domestic hot water loads was the data used can only show one “typical” pat- same for each building of a similar tern. Weekend loads were assumed to be 40 type. When they were added, however, percent of the weekday loads. The total it was assumed that each sequence yearly industrial load served by the utility is started at a different time. The spread 2.532 X 109 kWh. in “start times” was assumed to be the spread during which people wake up in Table V-A”3.—lndustrial Load Profile Used the morning, eat, and go to work which, in turn, was assumed to be the same as Hour Weekday Weekend the spread of traffic during rush-hour peaks in major cities (i. e., a normal distribution with a standard deviation of approximately 1 hour).

This technique is expressed quantitatively in the expression below:

where f(t) is the hourly load profiIe of an in-

dividual house, fN(t) is the hourly load profile of an aggregate of N such individual houses if N is large and if “wake-up times” are distributed in a Gaussoan distribution with a standard deviation of ó hours. The results of this smoothing for a variety of different values of the standard deviation are shown in figures V-A-2 and V-A-3.

LOAD DIVERSITY SIZING GENERATING EQUIPMENT

The load diversity factor used in forming The generating equipment installed by an aggregated utility load was determined the utility depends on the load-duration as follows: curve (which characterizes customer de- 1. It was assumed that heating and air- mands), costs of purchasing and operating conditioning loads had no diversity, alternative types of generating equipment, since all buildings in the area would be kinds of financing available to the utility, Appendix V-A ● 165

Figure V-A-2.— Ratio of Peak Demands to Average Demands as a Function of the Standard Deviation of “Wake-Up” Times

Standard deviation of “wake-up” times (hours)

Source: OTA 166 . Solar Technology to Today’s Energy Needs

I I I Appendix V-A ● 167 —

and current and projected fuel costs. As fuel price increases), and k3 is a multiplier selecting the best mix of generating equip- leveling the presumed inflation of operating ment is a complex task, a greatly simplified costs. approximation of the techniques actually The annual cost of operating a given employed by utiIIties IS used, The selection piece of generating equipment can then be of the appropriate mIX of such plants for written as follows:* meeting any Ioad-duration curve is dominated by the fact that: (1 ) larger plants have relatively high efficiencies and high initial costs and, as a result, are profitable only if operated for a large fraction of the year; and (2) smaller gas turbines and internal combustion systems are relatively inexpensive to purchase, but have relatively high-cost fuel consumption and are thus best used in situations where they operate only a few hours each day Larger plants, therefore, are used to meet the “baseload” requirements of the utility (the loads which will be constant throughout the year), with the smalIer plants used for intermediate and “peaking” purposes when the demand is greater than the baseload plant capacity

Storage can be used to meet some demands during peak periods If the utility has facilities for storing energy. Peaking plants would then be used only when storage output capabiIities were exhausted The heuristic arguments given above can be quantified quite easily if a few simplifying approximations are made The basic parameter used to evaluate a utility system is the total “levelized” annual cost of pro- (4) ducing electricity (which is called CT in the following discussion). This cost is the sum of the cost of capital invested in equipment and the average annual fuel, operating, and maintenance costs, Following the notation developed in the discussion of economic and financial analysis found in volume 11, chapter 1, the Ievelized annual cost of a piece of equipment is given as follows:

Cost = k1 x (Initial equipment cost)

+ k2 x (amount of fuel used annually) (2)

+ k3 x (annual operating cost)

Here k, is the effective cost of capital, k2 is a “levelized” fuel cost (which may differ from current fuel costs because of projected * Index 168 ● Solar Technology to Today’s Energy Needs

ward improvement to the current model The utility’s total operating costs can then would be to assume that the operating costs be approximated by examining the load-dur- were of a form X + YT, but the current ation curve. Figure V-A-4 (which is an in- method was chosen for simplicity. Another verted load-duration curve) illustrates the approximation which has been made is that sequence in which loads are met by generat- the efficiency is independent of the oper- ing plants. T(D) is the number of hours per ating strategy.

Figure V-A-4.— Inverted Load-Duration Curve of a Typical Electric Load

T(D)

Base load

T.= 8760 hours

■ Intermediate

Source: OTA. Demand (kW) Appendix V-A ● 169

year when the utility’s load exceeds D kil- The second problem can only be elimi- owatts. When there is no storage, the ap- nated with a detailed examination of the ac- proximate cost is given by: tual sequence with which plants are turned on and off. However, this is beyond the scope of this study. Choosing appropriate average values for operating costs and efficiencies should produce results which are sufficiently close to those of a detailed model, and serve the purpose of looking for major impacts of different load patterns. The optimum set of equipment to meet the loads is then determined by minimizing this function with respect to D, and D,. This Transmission and Distribution Costs minimum occurs when: In addition to generating costs, the utility will have expenses associated with transmission and distribution. These wilI vary great- (7) ly, since they are a function of the spacing of the utility’s generating facilities and the location of its customers. In this simple model, it is assumed that the transmission The optimum size of the plants is then and distribution costs are in direct propor- given by: tion to the utility’s peak generating capaci- (capacity of baseload plants) = D 1 ty. While generating plants represent ap- (capacity of intermediate plants) = D – D 2 1 proximately 44 percent of the total value of (capacity of peaking plants) = P–D 2 electric utility plants and equipment, ap- The approximate cost of generation for proximately 60 percent of the new capital the year is then given by using these quan- invested by the electric utilities in recent tities in equation [1 ). years has been invested in generating equipment and this trend is expected to continue Provision for Reserve Margin (see table V-2 in the main text). ’ 2 It is therefore assumed that for each dollar invested in Two major approximations have been generating capacity the utility invests $0.67 made in obtaining costs in this way: (1) no in transmission, distribution, and other provision is made for maintenance cycles, equipment. the need to maintain reserve capacity for unanticipated failures, and the need to I n addition, the cost of maintaining trans- maintain some capacity as spinning reserve, mission and distribution facilities is assum- and (2) no provision is made for the costs ed to be proportional to the total investment associated with starting or shutting off a in such facilities. Maintenance of transmis- plant and the inefficiencies of running at sion and distribution equipment in 1974 cost partial loads. privately owned electric utilities in the United States approximately 3.3 percent for The first difficulty is handled by simply in- every dollar invested in such equipment.3 It creasing the assumed capacity of each type of plant by 20 percent. If the analysis shows that an optimum size for baseload plants is ‘Statistics of Private/y Owned E/ectrlc Utllltles In the D , it will be assumed that the utility actual- 1 United States, 1974, Federal Power Commlsslon, p xx I ly installs baseload capacity equal to 226th Annual E Iectrlcal Industry Forecast, E/ectr/ca/ (1.2)D . In actual utilities, these reserve 1 World, September 15, 1975, p 49 margins are computed by carefully analyz- ‘Statistics of Pr/vate/ y Owned Electrlc Ut///tles In the ing the reliability and maintenance sched- United States, 1974, Federal Power Commission, pp uIes of each plant in the system, xxx VI, xxx vii, arrd xx I

2 fi-H 42 ( ) - 12 170 . So/ar Technology to Today’s Energy Needs

is therefore assumed that the annual trans- The costs of generating facilities fuel mission and distribution operating expenses costs and operating costs actualIy used in are 0.033 x (the investment in transmission the analysis are summarized in table V-A-4. and distribution equipment) = 0.022 x in- Some of the characteristics of the solar ener- vestment in generating equipment). gy equipment examined are summarized in table V-A-5.

Table V-A-4.—Characteristics of Equipment Used in the Utility Model

1. Generation costs Capital costs* Cycle Levelized fuel Variable $/kW efficiency cost ($/kWh) O&M ($/kWh) Albuquerque Nuclear ...... 796 0.328 0.0056 0.00072 Coal ...... 691 0.338 0.00682 0.00147 Combined cycle ...... 292 0.42 0.020 0.0012 Boston Nuclear ...... 845 0.328 0.0056 0.00072 Coal ...... 713 0.347 0.00760 0.00189 Combined cycle ...... 292 0.42 0.020 0.0012 Fort Worth Nuclear ...... 748 0.328 0.0056 0.00072 Coal ...... 725 0.327 0.00456 0.00214 Combined cycle ...... 292 0.42 0.020 0.0012 Omaha Nuclear ...... 769 0.328 0.0056 0.00072 Coal ...... 668 0.338 0.00626 0.00148 Combined Cycle ...... 292 0.42 0.020 0.012 Il. Transmission and distribution costs O&M—O.022 of investment in generating capacity Capital charges— 0.67 of generating capacity costs Efficiency of T&D—O.91 Ill. Other costs Cost of capital —O.15 Overhead–0.021 $/kWhr 20% excess generating capacity installed “Capital costs include an allowance for “fixed operating costs” computed by dividing the fixed operating costs per year by the Ievelized fixed charge rate. SOURCE: Technical Assessment Guide, EPRI, August 1977. Statistics ot Private/y Owned E/ectric Uti/ities, 1974, Federal Power Commission.

Table V-A-5.—Assumptions About the Nonconventional Systems Used in the Utility Impact Analysis

1. Albuquerque

Single family house –SF-2 —IF-2 Flat-plate collector—30m2 Flat-plate collector—59m2 Thermal output Photovoltaic output Low-temperature storage—200 kWh Battery storage—20 kWh

–SF-2 East-west axis tracking collector—92m2 –SF-3 Photovoltaic and thermal output Flat-plate collector—30m2 Low-temperature storage—200 kWh Thermal output Battery storage—23 kWh Low-temperature storage—200 kWh Appendix V-A ● 171

Table V-A-5.—Continued –SF-3 High rise apartment buildings Off peak purchase of electricity y –HR-2 Flat-plate CoIlector—30m2 East-west axis tracking collector— Thermal output 4,263m2 Low-temperature storage—232 kWh Photovoltaic and thermal output High rise apartment buildings Low-temperature storage— 1,700 kWh Battery storage— 170 kWh —HR-2 East-west axis tracking CoIlector— Iv. Omaha 2 4,263m Single family houses Photovoltaic and thermal output –SF-2 Low-temperature storage— 17,000 kWh 2 Flat-plate collector—40m Battery storage– 170 kWh Thermal output Low-temperature storage—200 kWh Il. Boston –SF-2 East-west axis tracking collector—92m2 Single family houses Photovoltaic and thermal output —SF-2 Low-temperature storage– 12 kWh Flat-plate collector—45m2 –IF-2 2 Thermal output Flat-Plate collector—59m Low-temperature storage—200 kWh Thermal Output Low-temperature storage—200 kWh –SF-2 –SF-3 East-west axis tracking collector—92rn2 Off peak purchase of electricity y Photovoltaic and thermal output Low-temperature storage—31 3 kWh Low-temperature storage—200 kWh –SF-3 Battery storage— 12 kWh Off peak purchase of electricity 2 —IF-2 Flat-plate collector—40m Flat-plate Collector—59m2 Low-temperature storage—293 kWh Photovoltaic output High rise apartment buildings Battery storage—20 kWh —HR-2 High rise apartment buildings East-west axis tracking collector— 4,263m2 —HR-2 Photovoltaic and thermal output East-west axis tracking collector— Low-temperature storage— 1,700 kWh 4,263m2 Batteries— 170 kWh Photovoltaic and thermal output —HR-2 Low-temperature storage— 17,000 kWh (seasonal storage) Battery storage— 170 kWh Flat-plate collector—4,100m2 Thermal output Low-temperature storage— Ill. Fort Worth 1,200,000 kWh

Single family houses NOTE: SF-2 single family house with heat pump and —SF-2 electric hot water. 2 IF-2 well-insulated single family house with Flat-plate collector —40m heat pump and electric hot water. Thermal output HR-2 high rise apartment buildings with central Low-temperature storage—200 kWh electric chiller, for coil resistance heating, central electric hot water. —SF-2 SF-3 single fmaily houses with window alr- East-west axis tracking collector—92m2 conditioners, baseboard resistance heating, Photovoltaic and thermal output and electric hot water. Low-temperature storage—200 kWh SF-3 off peak heating and hot water (with or Battery storage— 12 kWh without solar), window alr-condit ioners, electric resistance furnace, and electric hot water. –IF-2 SF-3 off peak heating, coollng, and hot water 2 Flat-plate collector—59m (with or without solar), central electric Photovoltaic output chiller, electric resistance furnace, and Battery storage—20 kWh electric hot water. Chapter VI LEGAL AND REGULATORY ASPECTS OF ONSITE SOLAR FACILITIES Chapter Vl.– LEGAL AND REGULATORY ASPECTS OF ONSITE SOLAR FACILITIES

Page Page Introduction ...... 175 . What Position Have Building Officials Solar Rights: Protecting Access Taken on Solar Facilities? ...... 182 State Standards...... 183 to Sunlight ...... 176. State Certification...... 183 Introduction...... , .. ...176 Existing Laws: Adequate Sunright OnsiteSolarFacilities and Public Utilities. ...184 Protection?...... ,.176 NewDevelopment...... 176 Introduction...... 184 Zoning ...... 176 Utilities: DoRates or Service RestrictiveCovenants. , ...... 176 Practices DiscriminateAgainst Express Easements...... 177 OnsiteSolarUsers?...... 184 Land-UsePlanning ...... 177 Conventional RateStructure ...... 184 TransferableDevelopment Rights...... 178 Selling Energy to a Utility...... 186 Existing Developments...... 178 RegulationsCovering Discrimination ....187 Should the Federal Government Enact AreOnsiteSolarSystemsSubject to Regu- National SolarAccessLaws?...... 178 lation as PubiicUtilities? ...... 190 Status of State Legislation ...... 179 Ownership ...... 191 Electricity, Steam, or Heat? ...... 192 Building Codes and SolarSystems ...... 180 Can a UtilityOwnanOnsite Solar Facility? .192 Introduction...... 180 Municipal Utilities...... 194 Do the Model Building Codes Cost-Sharing Issues ...... 194 CoverSolarSystems?...... 181 What RightsWill Utilities Have to What Solar System Standards Aquifers and OtherGeological Forma- Are Needed? ...... 182 tions Used for Thermal Storage? ...... 195 Chapter VI Legal and Regulatory Aspects of Onsite Solar Facilities

INTRODUCTION

Onsite solar facilities are controlled by laws and regulations often written with entirely different energy systems in mind. That being the case, this study finds surprisingly few barriers to large-scale installation and operation of onsite solar facilities. Existing legal barriers are almost entirely inadvertent. These barriers can delay the introduction of solar equipment, but in most cases they can probably be removed with routine regulatory action. Resistance to changes in zoning or building codes, for example, generally arises when an interested party will be adversely affected. It is not likely that builders, owners, labor unions, or public officials will perceive onsite solar generation as a threat. The exceptions to this generally optimistic conclusion are the laws and regulations governing public utilities. Most statutes and regulations governing energy generating equipment assume that energy would be supplied primarily by large regulated utility companies which would enjoy a “natural monopoly” in a given region. If small facilities become economically competitive, however, the only natural monopoly may be systems for transmitting and distributing energy. It is important to notice that most of the regulatory issues raised in connection with small solar energy devices also apply to con- ventionalIy powered on site cogenerating equipment. Application of existing utility regulations to onsite energy systems is frequently ambiguous, sometimes contradictory, and occasionally inadvertently discriminatory. Problems can arise if utilities attempt to own and operate onsite equipment, and if organizations other than utilities attempt to generate solar energy for sale. Regulations governing the rates charged by utiIities for backup power and the price at which they will be willing to purchase onsite power generated in excess of onsite needs can have an enormous effect on the cost of solar energy computed by nonutility owners of solar equipment. Existing rate structures, however, have been designed without attention to the problems of solar equipment and the analytical basis for determining equitable rates is only beginning to be established. Although regulated natural gas prices were designed to benefit gas consumers, the policy tends to reduce the attractiveness of solar energy devices. How these ambiguities are resolved can have profound effect on the future of the solar energy industry. Regulations can affect the designs chosen and patterns of ownership, and they can serve to retard, stifle, or stimulate the development of the industry. It is clearly an area where doing nothing could translate into a policy of restraining the growth of the solar industry. 176 Ž So/ar Technology to Today’s Energy Needs

SOLAR RIGHTS: PROTECTING ACCESS TO SUNLIGHT

INTRODUCTION which land may be used, control building heights and orientation, and govern lot An investment in a solar installation must sizes, yard requirements, the appearance of be considered insecure unless the owner can buildings, property, and secondary struc- be assured that the collectors will not be tures. shadowed by new construction or vegetation during the useful life of the equipment. If maximum use of solar collectors is Protecting this access to sunlight can be dif- desirable, it may prove useful to adopt man- ficult, since no property owner in the United datory minimum or uniform height regula- States has an absolute legal right to sun- tions similar to rules that now limit building shine.1 If procedures to ensure some such heights. ’ Since zoning laws generally allow protection cannot be developed, concern underdevelopment, problems are foresee- about “sun rights” could present a major able. For example, if a property owner in an barrier to the use of solar energy, It may not area zoned for 16-story development builds be easy to provide such protection in dense- only a 4-story building, shading problems ly populated areas or in areas graced with could ensue. Perhaps economic incentives large trees, In some cases–particularly old- wiII make such cases rare. er residential neighborhoods — it may be impossible to ensure access to sunlight for all RESTRICTIVE COVENANTS buildings. A considerable amount of protec- The numerous local building covenants tion can be provided, however, with imag- and architectural review boards provide inative use of existing laws, zoning ordi- another opportunity for protecting sun rights nances, and covenants; it seems unlikely in a community but may also present prob- that additional Federal legislation would be lems for solar equipment. These covenants able to contribute usefully to the resolution are private legal devices which are typically of these problems. in the form of reciprocal promises in each deed of a subdivided tract. They can be EXISTING LAWS: ADEQUATE used to provide detailed guidance about the SUN RIGHT PROTECTION? kinds of architecture and the building New Development materials which will be permitted in the region covered. Since many early solar col- Imaginative work is needed to determine lectors are likely to be ungainly (if not how best to use existing laws. Although local outright ugly), it is possible that the use of governments are able to help protect sun- solar devices will receive unfavorable treat- rights, under existing statutes this power ment by local organizations reviewing com- usually is not used to help solar equipment pliance with the building covenants. The owners. problem is Iikely to become much more dif- ZONING ficult if tracking collectors begin to enter The power to zone can literally shape a the market in significant numbers. The unat- community from broad outline to minute tractive appearance of the inexpensive solar water heaters in Israel has apparently detail, The zoning authority power is broad enough to enable States and municipalities presented a major problem for manufac- to assure solar access in new subdivisions, turers in that country, and there are isolated shopping malls, industrial parks, and small community developments, Existing zoning * Such a law may guarantee each structure reguIations may direct the purpose for enough sunlight for a hot water heater or other roof collectors, but would obviously not meet the needs of ‘ Fountainb/eau Hotel Corp. v Forty-five Twenty- vertical solar collectors (includlng windows) that are flve, /nc,, 114 So. 2d 357,181 Fla Supp 74 (1959) part of a structure’s wal Is Ch. VI legal Aspects of Onsite Solar Facilities ● 177

instances of local opposition to rooftop any compensation to be paid to any party in- solar systems in the United States. It r-nay be volved. The legislation should also assure useful to anticipate the problem and the recording of express solar easements develop regulations which would permit along with other land records. solar facilities in which some care has been Colorado has already enacted such legis- taken to minimize pipe-farms on rooftops lation, and Florida, Maryland, and Arizona while permitting enough flexibility in design are considering nearly identical bills. to ensure efficient performance of the equipment. Clearly, there will have to be The advantages of express easements are: some compromise between performance they cost governments almost nothing; they and aesthetics. allow highly motivated individuals to act on their own; they may offer more protection The advantages of using restrictive cov- than zoning laws, which can be changed; enants as a means of protecting sunrights and they are adaptable to specific needs of are threefold: (1) covenants can be used to different property owners. thwart impending interference of solar access (usualIy by injunction) before construc- Disadvantages are their transfer with the tion begins, thus assuring a continuous sup- sale of land cannot be forced, their cost is ply of sunlight; (2) they cost the Government uncertain, enforcement through the courts nothing; and (3) State or local governments could be costly, and the would-be owner of could encourage or require their use in new a solar structure must bear the entire cost of developments. an easement.

EXPRESS EASEMENTS LAND-USE PLANNING Express easements provide another pri- Commonly used techniques that could vate legal device to protect access to sun- promote solar utilization in new develop- light in both new and existing developments. ments include comprehensive city or county An easement confers the right to use (not plans, energy impact statements, and flexi- possess) specified parts of another’s prop- ble zoning techniques. erty for a special purpose. A property owner, concerned about shading, could bargain Many States use comprehensive plans to with a neighbor for an unimpeded path of guide long-range policy in local zoning. sunlight over the neighbor’s land. Ease- Some State courts require that local zoning ments, which may also be leased, are bind- agree with a comprehensive plan. At least ing on subsequent owners of both parcels in two States have considered including solar many States, but in others new legislation energy elements in their comprehensive may be necessary to assure continuity of ac- plans. cess to sunlight. Something of value is tradi- Nine States require that environmental tionally given in exchange for land (although impact statements discuss the effects of some courts don’t require it), and the agree- projects on energy consumption — two re- ment must be in writing to be enforceable. quire analysis of measures to conserve ener- if a State views easements for light and air gy resources,2 The developers of large tracts as benefiting a person (i. e., “in gross”) rather of land must usually file impact statements than a parcel of land, the State may not en- under State laws, and this procedure might force the agreements against subsequent be used to assure consideration of solar owners, although a subsequent owner prob- energy utilization. Colorado has considered ably could, To attain enforcement, a State can enact a short, simple statute stating that such easements must include the vertical ‘ Corbln Crews Harwood, Us/rig Land to Sa\e Ener- and horizontal angles over adjoining prop- gy (Carnbrldge, Mass Balllnger Publlshlng Co , for- erty; terms and conditions of the grant; and thcoming) 178 ● Solar Technology to Today’s Energy Needs

such a bill.3 The same Colorado bill would The Los Angeles Department of City Plan- require that subdivision regulations include ning concludes that its code may be ade- standards and technical procedures for solar quate to protect solar access in developed use. as welI as new neigborhoods,4 Transition neighborhoods, where new commercial de- Flexible zoning techniques include velopment is allowed alongside older resi- planned unit developments (PUDs) and dential sections, will be one of the most bonus or incentive zoning. Only a few States difficult areas in which to protect solar ac- specifically authorize PUDs, but some com- cess. If a newly zoned commercial area is munities use this technique without State south of an older residential neighborhood, authorization. This concept relaxes zoning the taller buildings may cause shading prob- requirements and allows builders to offer lems. Los Angeles zoning regulations deal layout, building design, and uses as a single with this by Iimiting new structures in such package. areas to six and three stories, “stepping To obtain approval of their plans, devel- down” heights gradually to avoid sharp con- opers could be required to indicate where trasts between old and new development. 5 shadows would exist and to justify designs that would create shadows. Bonus or incen- Existing Developments tive zoning offers governmental rewards in Assuring the protection of sunrights in exchange for a developer’s inclusion of neighborhoods can be a difficult problem. design elements otherwise not directly re- Many existing buildings in older commercial quired by zoning. areas probably could not be adapted to use solar energy unless basically rebuilt, which Transferable Development Rights means the demand for solar access in these A much-discussed but little-used ap- areas may be small. Clearly, it would be proach to land-use planning called trans- desirable to consider solar access when an ferable development rights (TDR) is unique- entire area is to be redeveloped, or even ly suited to protecting solar access. when individual permits for remodeling are issued, Under the TDR concept, rights for development conferred on lots by zoning codes Probably the strongest available tech- are transferable and can be sold independ- nique for protecting sunrights in existing ently of the land. Property owners could sell developments is the purchase of solar ease- development rights that they could not exer- ments. It may be possible (for a price) for a cise because of solar restrictions. For exam- prospective solar owner to purchase an ple, the owner of a commercial property easement that will require his southern that adjoins a neighborhood of single family neighbor to cut trees to provide access to homes might sell the right to build a tall sunlight. building to the owner of a lot where a tall building would not cast shadows on solar SHOULD THE FEDERAL GOVERNMENT equipment. Under this concept, a municipal- ENACT NATIONAL SOLAR ACCESS LAWS? ity can be a buyer-of-last-resort for development rights in cases where it is necessary to The Federal power to regulate commerce protect access to sunlight for solar collec- and provide for “the common defense” is tors The main advantage of the TDR concept is that it permits a municipaIity to 4 police solar access rights and avoid uncon- Charles S Rozzellee, Property Owners’ R/ghts to SurJ//ght, Los Angeles Department of City Planning, stitutional taking of property without com- City Pldn Case No .26110 (1976), see p 14 pen sat ion. 5 I bid , p 12 An admlnlstratlve problem could arise If the city were flooded with applications for ‘ (010 H B 1166(197’6) these special zones Ch, V/ Legal Aspects of Onsite Solar Faci/ities ● 179

apparently broad enough to allow Congress Solar access criteria could be added to the to adopt policies protecting the use of solar Department of Housing and Urban Develop- energy if it so desired. b It is probably not ment’s (HUD) Section 701 Community De- necessary (and may even be unwise), how- velopment program, which provides financ- ever, for the Federal Government to inter- ing for land-use planning.8 The overall aim vene in protection of individual access to of this program is compatible with the en- solar energy couragement of solar-access planning, since it is designed to encourage “a more rational Solar rights laws will have to be adapted utiIization of land and other natural re- to local conditions, no matter where sources and the better arrangement of resi- drafted The variables that must be con- dential, commercial, industrial, recreation- sidered in access laws include topography, al, and other needed activity centers, ” latitude, availability of alternative energy sources, long-term regional growth plans, impacts of past and present zoning laws, STATUS OF STATE LEGISLATION and even the relationship of streets to sunlight patterns. A variety of legislation has been proposed on the State level. A bill in Massachusetts It is possible, however, that State or (Senate No. 269, 1977) uses the building per- Federal encouragement will be needed to mit system to protect sunrights. Under this motivate local governments to incorporate proposed law, those wishing to erect active- solar access into their statutes. One expert or passive-type solar energy units would estimated that only 5,000 of 60,000 jurisdic- have to reasonably locate and angle their tions with power over land use exercised equipment to minimize the possibility of zoning powers in 1974 7 future interference with it, To get a building While preemption seems unnecessary, an permit, the equipment also would have to appropriate Federal role might be a national be reasonably sized relative to the structure. policy set by Congress. For example, the ex- The remaining problem of vegetation in ad- istence of solar access laws could be a fac- joining property would have to be solved by tor in choosing locations for federally express easement. In land zoned for devel- owned, funded, or operated structures. opments for four stories, the municipal plan-

‘ \t Ickard \ I l/burn, )1 7 U S 111 (1 942), a person trla 1, recreat Iond 1, and other needed a( t I\ Ity center$ “ grow I ng wheat on hl~ own land tor home use — a non- com m erc I d I dct I v I t} — w a $ tou nd to have enough ef - The regulations accompanying the 701 progralm (Ti- tec t on Interstate commerce to come under the Con- tle 24, part 600 — Comprehen~lve Plannlng As$lstance) gress’ power halve been dmended to emphd~l~e energy concern~ 7 Peter Welt, The Future oi the City N’ew Dlrcc- Se( tlon 60072 now state~ that In $ele( tlng prlorlttes, tjons (n Urban P/annln~ (New ‘r’ork Wa tson-Gupttl I edch reclplent shou Id con~ tder Public atlon~, Whitney Library ot Design, 1974), p 149 (,2) Prolectlons of land use needs and land resource

development Includlng energ} tac I I ltl~s sltl ng “ Crlterid \pPc I tIC J I Iy referring to solar ac( es< needs cou Id be ~ dded to H U D’~ Se{ t Ion 701 Cornmunlty De- vel opmen t prog rd m, w hlch provides financing for (7) The conservdtlon of energy through land use land-u~e plannlng that meets certain ( rlteria Sect Ion ~trdtegles des Igned to reduce energy consu mp 701(C) ot tire Flous[ng Act ot 1954 (ds dmended by the tion and the development of pol I{ IPS designed to tiouf~ng dnci Commurllty Development Act of 1974) tac I ! Itate the re{ oier~ ot energy re$ourc e$ I n d

\ays that tu nd 5 w I I I on I y be ava I I a b I e t o ap p I I c d nt ~ manner ( ompdt Ible with environmental I protec w ho have on go I ng co m prehen $ Ive p I d n n i ng p roces~es t [on that Inc I ude both a housl ng element and a I and use “ Energy tacll Itle> sltlng needs” could be Interpreted

e I e me n t The o~era I I a I m of t h Is program I \ corn pat I- to lncl ucle “talc I I ltle~” a~ ~ma I I as an drrdy ot ~old r c ol- ble with the encou rdgement of \ol ar-ac ce~~ pl ann I ng, Iectors on the roof of a ~lngle it ructure, but a more ex-

‘5 I n cc It hopes to en( ou rage ‘‘a more rat Iona I ut I I I zd - pl I c It ~tatutory conslderdt Ion of Jol a r energy needj I \ t Ion ot land and other natural resources, and the bet- rea I Iy needed te r a r rd ngement of res I den t I d 1, com m e rc I a 1, I nd u j- 42 u s c 5301 (c) (5) 180 . Solar Technology to Today’s Energy Needs

ning agency and the municipal governing the legislation give property owners a clear- body would have to approve a proposed er view of their rights than a vague protec- solar structure. Before a nonsolar structure tion of “sunlight necessary for the operation could receive a building permit under this of solar equipment. ” legislation, the records would have to show that there was no interference with an ap- The tiny town of Kiowa, Colo., has en- proved solar collector. acted a law declaring shadows on collectors to be public nuisances. This nuisance ap- A Minnesota bill suggests a very different proach could present several kinds of prob- legal approach (Minnesota H.R. 2064, 1976). lems: no certainty of protection would exist It would simply grant solar easements to any before a collector was installed, tangled collector owner. Anyone erecting an object complexity of the nuisance law, and costly shading the system would have to pay the Iawsuits would be required to settle dis- solar homeowner three times the actual cost putes. of implementing an alternative energy system. Although the penalty section is in- Law journal articles suggest applying triguing, this bill has many problems, in- ., -.&-- laws used in the West — the prior ap- cluding vagueness and unfairness based on propr iation doctrine — to solar access, and the first-come, first-served basis of the law. rev iv i ng the old English doctrine of ancient Colorado legislation would forbid proper- lights 10 11 No State has, to date, followed ty owners from allowing their trees and either of these suggestions, both of which shrubs to grow enough to shade solar collec- would require extensive litigation, provide tors between 9 a.m. and 3 p.m. ’ But it is an no compensation to the injured solar users, attempt to deal with the serious problem of and were not drafted specifically for solar vegetation, and the specific times listed in applications.

BUILDING CODES AND SOLAR SYSTEMS

INTRODUCTION fragmentation of the solar market, delays, additional expenses, and uncertainty to the Building codes, specifically applicable to builder or owner in the permit application hot water and space heating, air-condi- and process. There are, as a result, com- tioning, and electrical equipment, seldom pelIing reasons for enacting mechanisms for contain provisions covering onsite solar inspecting solar equipment similar to those systems. Code problems do not appear to in effect for other heating, cooling, and have been a major barrier thus far, but it is generating equipment installed in resi- clearly possible that uncertainty on the part dences or commercial buildings. of code officials resulting from a lack of information about solar devices and a shortage of standards and certification pro- The Federal Government, in a HUD dem- cedures for solar systems could result in onstration program, developed standards

the Energy Research and Development Admin[stra- ‘ Colorado S B 38 (1976) tlon, and IS an early effort In this direction It is available from E L I (1 346 Connecticut Ave , N W , ‘0 Mary D White, “The Allocation of Sunllght So- lar Rights and the Prior Appropriation Doctrine, ” Suite 620, Washington, D C 20036) for $750 University of Colorado Law Review 47 (1976) See the 1‘ Lawrence Kressel, “Harrsorr v Sa/is/ran Properrles, extensive review In the E nvlronmental Law Institute’s /rrc,, Preservation of View– Limltatlons as to Height (E Ll) Legal Barriers to Us/rig Solar Energy for Hearing of Improvements and Architectural Control In Uni- and Cooling f?ui/dings, which was contracted for by form Long Term Lease, ’’fnv. Law5(1974) 183 Ch. VI Legal Aspects of Onsite Solar Facilities ● 181

that could be used as models for incorpora- standards, which identify materials and tion in building codes. Certification that equipment that may be used in construc- solar systems meet those standards could be tion, or performance standards, which set delegated to approved testing agencies, standards that materials must meet. Specifi- thereby expediting the building permit proc- cation standards are easier to administer, ess for solar users. but are inflexible. Performance standards are more flexible, but require more trained personnel, time, and money to administer. DO THE MODEL BUILDING CODES COVER SOLAR SYSTEMS? Building codes regulate nearly everything that is constructed or built on land, with few The three most widely used model build- exceptions. Before granting permits for con- ing codes are: struction, remodeling, or repairs, buiIding ● The Basic Building Code of the Building officials decide whether plans conform to officials and Code Administrators code requirements. If a plan proposes use of (BOCA), found mostly in the East and materials and methods that are specifically Midwest; covered by a building code, approval is routine. If a plan calls for innovative materials ● The Uniform Building Code of the Inter- or techniques, however, a building official national Conference of Building Of- has the discretion to require testing of ma- ficials (ICBO), found mostly in the terials and submission of evidence that the West; and resulting structure will not be inferior to a ● The Standard Building Code of the traditionalIy built structure. Southern Building Codes Conference (SBCC), found mostly in the South. Most building officials display wide latitude in approving or rejecting materials, According to a 1970 survey of local equipment, and methods not specifically building departments, 63 percent of the 919 provided for in the codes. If alternative cities that had building codes of any kind materials or techniques are to be used, 1 used one of these three model codes. 2 building officials must be satisfied that the The most widely used standards for elec- resulting structure will be at least equal in trical wiring and equipment are those of the strength, fire resistance, safety, quality, and National Electrical Code of the National effectiveness to structures assembled with Fire Protection Association. Although no materials and techniques specified in the exact figures are available, it appears that code. I n such case-by-case showings, ap- these electrical equipment standards are plicants may be required to pay for testing even more widely used than any of the three at facilities chosen by the building officials, major model building codes. The electrical using methods approved under the codes or standards are adopted by reference in the chosen by them. BOCA code (Section 1500.3), but not by the For most kinds of construction materials other two model codes. and equipment, nationalIy recognized Building codes define terms, set standards standards, test methods, and testing agen- for materials and equipment, describe how cies are specified in the codes. Two ex- materials and equipment may and may not amples are the Underwriters Laboratories, be put together, and provide for enforce- Inc., for electrical equipment, and the Amer- ment through permits and inspections. ican Gas Association, for gas equipment, For Standards generally are either specification solar energy systems such nationalIy recognized standards, test methods, and listing agencies do not exist. ‘‘ Charles G Field and Steven R Rlvkln, The EluI/ding Code Burden, Lexington, Mass D C Heath Under al I three model codes, heating, ven- and Co , Lexington Books, 1975, p 43 tilating, and cooling appliances must be ap- 182 ● Solar Technology to Today’s Energy Needs

proved by building officials or carry the standards were written. The primary require- label of an approved testing agency or lab- ment for new standards is for solar collec- oratory. A “heating appliance” is presently tors, including photovoltaic and focusing defined in all codes as a device that gen- devices. erates heat from sol id, Iiquid, or gaseous Problems could result from novel usage fuels, or with electricity, Solar sources are of equipment and materials presently cov- not mentioned, nor are they included in the ered in the codes, involving risks of leakage definitions of ventilating or cooling ap- or explosion from excessive temperatures, pliances. In addition, there is no agency to high pressures, corrosion, and other compo- certify compliance and attach labels to nent failures. Standards should address solar equipment, nor is there a nationally these and other risks, including human con- recognized set of standards on which to tact with hot surfaces or broken glass, con- base compliance. Solar heating systems are tamination of drinking water with toxic therefore at a potential disadvantage as coolants if plumbing is not properly in- compared to conventional systems, which stalled, and damage to collectors from high can be approved for instalIation with a sim- wind or heavy snowfalIs, ple showing of a label. These risks would be relatively low in sys- Other possible impediments to the use of tems designed for low-temperature uses, solar facilities include code requirements such as heating buiIdings or drying grain, for maintaining rather high minimum build- but could be higher in some proposed solar ing temperatures in cold weather, and for- electric systems. Building codes must be mulas for determining window sizes. Limita- amended in ways that apply different stand- tions on awning and roof overhangs may in- ards for material and equipment according terfere with some passive solar designs. to the use of the solar energy facility. Standards for prefabricated assemblies may result in costly tests to demonstrate weather resistance. WHAT POSITION HAVE BUILDING OFFICIALS TAKEN ON More potential problems include limita- SOLAR FACILITIES? tions on residential building heights that may preclude roof collectors, chimney and Few builders have reported difficulties in plumbing clearances, application of new obtaining building permits to construct solar standards to remodeling of old buildings, facilities. The major problem with codes and implied prohibitions against using solar may prove to be an overly lax inspection colIectors as integral parts of a structure’s resulting from untrained inspectors rather roof or walIs, than codes so strictly written that they interfere with sound solar engineering. Build- WHAT SOLAR SYSTEM STANDARDS ing codes expert Steven Rivkin has said that, ARE NEEDED? “Rather than serving as a retardant, existing building codes have no bearing at all on the The only unique component of solar development of solar systems.’’13It is possi- heating, cooling, and generating systems is ble that building officials will continue to the collector. Once heat is collected, or look with favor on solar energy systems, and electricity is generated, it is transported, not rigidly enforce codes. stored, and utilized by the same type of equipment used in conventional systems. As solar energy systems gain in populari- Standards for pipes, ducts, valves, storage ty, some kind of additional code require- tanks, controls, wiring, storage batteries, and other components already exist, even ‘ ‘ AlA Research Corporation, Early Use of Solar though their use in a solar energy system lnergy In Buildings, 2 Vols , Washington, D C , August was probably not contemplated when the 1976, 211-32 Ch. VI Legal Aspects of Onsite So/ar Facilities ● 183

ments will need to be developed. Without for solar equipment would function within specific coverage in model building codes, Congress’ power to regulate interstate com- however, local interpretations of plans or re- merce, quirements for costly testing could fragment Certification is another matter. Federal ef- a potential market, result in higher costs of forts to certify solar appliances under its solar devices built to meet the strictest HUD standards met with some criticism, and standards found anywhere, and delay build- the Federal Government has traditionall ing and construction of solar systems. y been reluctant to favor one commercial All appliances face this problem at some product over another. However, because time, and the solution has been nationally some approved testing agency must be recognized standards and testing proce- designated as the solar industry grows, the dures for the various models of equipment Federal Government might provide seed and materials Applying the same procedure money for expanding an existing testing to solar equipment would put solar energy agency or creating a new one. systems on the same footing as other heating and electric systems State Standards

Most building codes are enforced at the States can write their own solar equip- local level, often with guidance from State ment standards, with variations based on laws but seldom with intervention at the State and local conditions, provided that Federal level. As has been noted, where they do not unreasonably burden interstate codes are in effect, the majority of com- commerce, One approach would be to munities adopt and adapt the model build- adopt standards similar to those already ing codes. The first step toward assuring ac- drafted by the Federal Government under ceptance of onsite solar facilities as stand- the HUD program, on an interim basis, until ard equipment is to draft a model set of private-sector standards have been ap- standards for inclusion in the major building proved. A recently enacted Minnesota law codes. The second is to designate a testing takes this approach, It requires a State agen- agency to certify performance of solar ener- cy to promulgate standards for solar heating gy systems. and cooling systems based on current interim Federal criteria. 14 The law also re- The effort to develop national standards quires State administrative agencies to up- couId be coordinated by the Federal Gov- date State standards as new Federal stand- ernment There is precedent for this, in- ards are adopted or as new technology dic- cluding an ERDA contract with the National tates. Conference of States on Building Codes and Standards to develop a model code for ener- State Certification gy conservation in buildings. States will want to assess the suitability of The Federal Government has already de- solar equipment as to safety, health, struc- veloped standards for commercial and resi- tural strength, and adaptability to State or dential solar facilities as part of a solar heat- local building codes. The Florida Solar Ener- ing and cooling demonstration program ad- gy Center in Cape Canaveral already is test- ministered by HUD. These standards, or ing and certifying the thermal performance some variation of them, are avaiIable for in- of colIectors sold in that State As an interim corporation in building codes. measure, State certification can provide local building officials with guidelines until A final Federal role in amending the codes a national testing and certification program would be to encourage State adoption of standards for solar equipment Federal legislation mandating, encouraging, or providing incentives for State regulations or standards ‘4 Mlnn Stat ~116 H 127 (1976) 184 . Solar Technology to Today’s Energy Needs

can be put in place. Some States may wish ficials to approve solar equipment that to go beyond furnishing guidelines, and can meets State standards and is certified by write laws that require local building of- State agencies.

ONSITE SOLAR FACILITIES AND PUBLIC UTILITIES

INTRODUCTION rates or service policies that unfairly discriminate against solar customers requiring State laws and regulations governing the utility power as backup. relationships between public and private utility companies and the owners of onsite The answer appears to be that current generating equipment are complex, and fre- laws will permit discriminatory rates for quently ambiguous, largely because these solar customers if the utility can prove that problems have seldom been addressed by the cost of providing service to solar cus- regulatory commissions. I n the small num- tomers exceeds the cost of providing service ber of cases where utilities and industries ex- to other customers. Although it cannot ar- change electrical power or process heat, bitrarily set prices or refuse service in an contracts have generally been written in effort to eliminate competition from solar ways benefiting both parties so that no devices, the burden of proving such discrim- lawsuits have been brought forcing the ination may falI on the solar customer. courts to rule on ambiguities in the law. Difficulties are likely to occur only when an electric utility is involved since gas util- The following discussion examines the ities would, in general, not be adversely af- statutes and regulations that now govern fected by a need to provide backup service relationships between public utilities and to onsite facilities. Calculating a rate for onsite generators of solar energy, and out- both the purchase and sale of electric ener- lines areas where ambiguities exist. It is an gy to a utility is an extremely complex prob- attempt to highlight areas where major regu- lem. The technical and economic bases for latory problems may exist. such rates are discussed in detail in chapter State regulation through State public util- V. The present chapter focuses exclusively ity commissions is the primary issue. Federal on the legal and regulatory mechanism for power authority has been limited to regula- setting rates. tion of wholesale rates of interstate sales of Conventional Rate Structure electricity, and siting of hydroelectric facilities, and is of less concern in the follow- The price a consumer pays for electricity ing analysis. The onsite solar systems, by the seldom directly reflects the cost of produc- very definition of “onsite,” are seldom in- ing it. I n the absence of widespread time-of- volved in interstate, wholesale sales, day metering, billings usually are based on although power sold to a utility grid may formulas that allocate peak costs of energy reach interstate commerce. and total monthly consumption according to the historical demand patterns of different categories of customers. UTILITIES: DO RATES OR SERVICE PRACTICES DISCRIMINATE The most common residential electric AGAINST ONSITE SOLAR USERS? rate is the “declining block rate, ” under which customers are charged a fixed fee for Perhaps the most crucial question in utili- monthly service, with declining rates for ty regulation is whether utilities may adopt each incremental block of energy consumed Ch. VI Legal Aspects of Onsite So/ar Facilities ● 185

beyond the amount covered by the fixed spot measurements of demand made with- fee. For example, the formula might call for out advance notice. a charge of $3 for the first kilowatt hour The impact of such demand rates on cus- (kWh), $004 per kWh for the next 100 kWh, tomers with onsite facilities can be very and $0.03 per kWh for the next 200. (Ex- great. In some cases, a demand charge amples of actual rate scheduIes in several could be so high that a purchase of energy cities are Iisted in volume I I.) The declining at high rates, when onsite equipment failed block rate was introduced when marginal or when cloudy weather persisted, could costs for electric utilities were declining and negate any savings attributable to the onsite utiIities were encouraging customers to use equipment for an entire year. The justice of 15 more electricity. Another frequent prac- such charges is a difficult issue to resolve, tice, designed to increase sales of electrici- Providing power to backup random failures ty, is to reduce rates if a house or commer- of onsite equipment among a large number cial buiIding is “al I electric. ” of small customers can clearly be managed Utilities justify using these rates in today’s without a large increase in a utility’s gen- market by arguing that all-electric cus- erating capacity. Relatively high backup tomers are more Iikely to use electricity dur- charges might be justified, however, if all of ing the night for heating and cooling than these customers abruptly demanded backup are other types of residential customers, power during a prolonged stretch of adverse who use electricity for Iighting and other weather. purposes during peak hours. ’6 The wisdom Still another rate structure is designed to of continuing a promotional rate schedule provide standby service to customers who in a period of declining energy reserves, do not use electricity under normal circum- however, has been seriously questioned in stances, although these rates would not many quarters. President Carter’s proposed apply to solar customers under the current National Energy Plan would have flatly pro- definition of “standby power.’” 7 If the def- hibited declining block rates. inition were changed to cover onsite facility Declining block rates can discourage the owners, however, the high minimum month- use of onsite solar power because a large ly charge associated with standby rates part of a customer’s utility bill is based on would not be advantageous to customers the first few kwh delivered, power which with onsite solar faciIities, would probably not be replaced with solar Some utilities have considered applying energy. demand charges to residential customers to Larger utility customers are frequently cover some of the market losses that would charged on the basis of their peak demand be inevitable with widespread installation of during some specified period. Such rates are onsite solar generators. One such proposal designed to achieve a more direct relation- by the Public Service Co., a Colorado utility, ship between consumption and the net gen- was fiercely opposed by solar custom- 18 19 erating capacity that must be installed to ers, who calculated that under such a meet the customer’s requirements, Tech- niques for determining peak demand vary 17 See, for example, Southern Calltornla Edison’s greatly. Some utilities charge according to rate schedule #5 (standby rates) the peak demand during the previous 6 mon- 18 Testimony of james H Ranntger, Manager of ths, some take the lesser of monthly peak Rates of Regu/atlon for the Publ IC Service Company of demands, and some percentage of annual Colorado Colorado Public Utllltles Commission ln- demand, and others charge on the basis of vestlgatlon and Suspension Docket No 935, Sept 25-26, 1975 15 See Berl In, Cicchettl, and G Illen, Perspective on 19 Testimony of Dr Ernst Ha bict, Jr , and Dr Wil- Power, chapters 1-3 Ilam Vlckery for the Environmental Defense Fund, “ Letter Insert In monthly bill from Potomac Elec- Colorado Public Utlllties Commission Investigation trlc Power Company, January 1977 (Op Clt )

2 d-H 42 { ) - 13 186 Ž Solar Technology to Today’s Energy Needs

rate structure a solar heating system that re- less expensive than additional units of stor- duced energy requirements by 70 percent age or collector area. 25 The National Energy would reduce electricity bilIs by only 35 per- PIan proposes that utility companies be “recent.20 The Colorado Utility Commission ini- quired” to offer interruptible rates to all tially granted the utility’s request for the customers. 26 rate change, but reversed the decision following a rehearing and ruled that the Selling Energy to a Utility issue was sufficiently complex to be addressed in a generic rate hearing. ” 22 As of today, few utilities are willing to purchase power from customers, although Lifeline rates have been adopted in a few special arrangements have been made with 27 States. ” Under this system, the charge is low several large industrial customers. I n some for the first units of energy. The goal is to cases, the price the utility pays for surplus ease the burden on low-income consum- power reflects only the cost of the fuel the 24 ers. This rate may incidentally benefit utility would burn to generate an equivalent solar users whose needs for supplemental amount of energy. I n other cases, the price sources of energy are small enough to fall reflects both fuel costs and the cost of within the “Iifeline” amount. equipment the utility would have to install A final type of utility pricing is interrupti- to generate the power. However, there are ble rates, This traditionally has been avail- so few arrangements for sale of surplus able only to industries willing to accept the power that clear patterns are difficult to risk of service interruptions in return for identify. lower costs, Some studies have pointed out Southern California Edison Co., for exam- that a solar user willing to accept the risk of ple, recently proposed a rate schedule under going without utility service on infrequent which it wouId buy energy from large in- occasions could save the utility substantial dustrial customers at “the lowest cost of amounts in capital requirements, justifying energy provided by any generating equip- a lower rate. I f the peak occurred onIy rare- ment in the BonnevilIe Power District.”28 ly, this alternative might be considerably This is about 3 mills per kwh, a rate that reflects a minimum energy displacement fee. However, in the same proposal the utility offered to purchase energy from a Iimited ‘[) Gary MIIIs, “Demand for Electrlc Rates A New number of residential and smalI commercial Problem and Challenge for Solar Heating, ” ASH RAE facilities at a rate that is essentially identical journal, january 1977, p 42 to the rate the utility charges residential I’ In the matter of proposed Increased rates and customers. 29 charges contained In tariff revlslons filed by Publlc Service Company of Colorado, Declslon No 87460 The Gemini Co., which sells devices to (Colo. Pub Utll Comm’n , Oct 21, 1975) connect onsite wind generators and other “ Home Builders Ass ‘n of Metropolitan Denver v equipment to utility distribution Iines, iden- Pub/Ic Serk Ice Co of Co/oracfo, Decision No 89573 (Colo Pub Utll Comm’n , Oct 26, 1976) ‘5 Feldman and Anderson, Uti/ity Pr/cing, p 120

11 E g , Miller-Warren Energy Lifeline Act, 1975, Cal “ National Energy Act, SectIon 513 Stats ch 1010 For other examples, see Energy Users “ Thermo E Iectron Corporation, A Study of /rip/ant Report (f3NA), Dec 16, 1976, p A-25 Power Generation in the Chernica/ Petroleum Refining ‘4 See “Llfellne Rates – Are They Useful?”, Energy and Paper and Pulp Industries, june 1976, U S Dept of Conservation Project Report, No 4 (January 1976), p Commerce, NTIS PB-255-659 13 (ECP Report IS a publication of the Environmental “ Southern California Edison rate schedule Law Institute, Washington, D C ) Some authorities changes proposed In a letter to the Cal Ifornla Publlc question whether the Ilfellne concept IS an effective Utilltles Commission, Feb 2, 1977 method to ald lower Income groups since these persons often consume relatively high amounts of ‘9 Southern California Edison, op cit., Experimental energy Schedule DC and AC Ch. VI Legal Aspects of Onsite So/ar Facilities ● 187

tifies widely varying patterns of proposed viding backup power to an onsite solar facil- surplus-power prices. Some New England ity is to accurately compute the marginal utiIities are wiIIing to buy electricity at their utility costs incurred in providing such own sales price because fuel represents a backup. large fraction of their overall costs. Utilities The parallel question involving a deter- with low baseload fuel costs have been mination of the rate which the utilities can more reluctant to buy surplus power. 30 be expected to pay for excess onsite power Regulations Covering Discrimination offered for sale is equally difficult; several very sensitive issues must be resolved. For The rates just described were, except for example, how shouId the costs of transmis- Colorado, not designed to discriminate sion lines be allocated between the price of against solar equipment, although their im- utility sales and the price charged by onsite pact is not diminished by the lack of an in- generators? Should the utility be expected tent to discriminate. to purchase energy at rates reflecting the One of the major purposes for public reg- marginal cost of providing the same amount ulation of electric utilities is the prevention of energy from new utility equipment or of unreasonable discrimination or undue simply for the average cost of utility power preferences. 31 Nearly every State has a generated. It will usually not be possible for statute prohibiting conduct that favors one utilities to pay a rate high enough to meet class of customer while harming another. typical industrial revenue requirements on Typical statutes proscribe policies that are capital invested in new energy projects. It is “unreasonable,” “unjust,” “undue,” or “un- possible, however, that special rates could lawful.’’” Discrimination is a question of be established which would permit utility fact to be determined on a case-by-case purchases at required rates, and it also is basis by the State utility commission, and it possible that, if a utility could sign a con- is very difficult to predict precisely how any tract with a firm guaranteeing purchases given discriminatory practice will be ana- over 10 to 20 years, the firm could accept a lyzed, smaller rate of return on funds invested in As the previous chapter showed, deter- the generating equipment. A simple tech- mining fair rates for electric utility power is nique for determining the amount which an an extremely difficult process. Uneven solar electric utiIity can pay for energy purchased demands on the utility can result in relative- was discussed in the previous chapter. ly poor utilization of expensive generating I n general, the cases and State utility deci- and transmission equipment, but it must be sions suggest that utilities have substantial recognized that demands imposed by many freedom to treat different classes of custom- nonsolar customers are also very irregular; ers differently.33 Two general principles the only fair measure of the cost of pro-

3‘ See, e g , Re Paclflc Cas & E Iec Co , 9 P U R 3d 97 1’] Ben W/o If, Gernl nl Corporation, private communl- (Cal publ Util Comm’n 1955), Re promotional Ac- cat Ion, Apr 17, 1977 tlvltles by Gas and Electrlc Companies, 68 P U R 3d 163 (N Y Pub Serv Comm ‘n 1967), Re Promotional ‘) To e[ onoml$ts, “price dlscrlmlnatlon” IS value Practices of E Iectrlc and Gas Utllltles, 65 P U R 3d 40s neutra I and In( Iudes any case where the same prod- (Corm Pub Utll Comm’n 1966), lle City Ice & Fuel uct IS sold ~t more than one price For purposes of this Co , 260 App DIV 537, 23 N Y S 2d 376 (1940) But dlscusslon, “dlscrlmlnatlon” is used [n its more gener- utll Ity comm Isslons have not been reluctant to strike a I 5en$e to refer to any dlstlnctlon [n favor of or down promotional practices they found to be of little against a person The economists’ deflnltlon pinpoints value to the utll Ity or the bulk of Its customers Re the I~~ue nicely what 15 the relevant “product” or Southwest Gas Corp , 61 P U R 3d 467 (Cal Pub Utll servl( e? The way the product IS defined WI]] deter- Comm’n 1965), Re Carollna Power & Light Co., 52 mine a talr price P U R 3d 469 (N C Utll Comm’n 1964); Re Portland ‘2 Priest, Prlnclp/es of Public Uti/ity Regulation, General Elec Co , 67 P U R 3d 417 (Ore Pub Util 1 2/36-88 Comm’n 1967) 188 ● Solar Technology to Today’s Energy Needs

emerge: (1) preferential treatment is more with most issues in public utility regulation, acceptable if it produces indirect benefits to the duty-to-serve requirement is interpreted all customers; and (2) utilities may treat cus- on a case-by-case basis with “reasonable- tomers differently if there is a reasonable ness” and the “public interest” as the economic basis for doing so, that is, costs to touchstones. the utility are clearly different. For exam- A public utility cannot refuse to provide ple, discrimination in favor of solar users backup power to onsite facilities unless it that would reduce rates for all customers by can demonstrate a compelling case that reducing the utility’s costs would be accept- backup service would cause substantial able. harm to the utility’s existing customers. It seems clear that public utilities may Refusal to provide service would violate not discriminate either against or in favor of on- only Federal antitrust laws, but also the utili- site solar users if the discrimination either ty’s common law and statutory duty to pro- benefits all customers or is based upon a vide utility service, Of course, the duty to reasonable economic basis. Discrimination provide adequate service has some limits; could be either as service practices (e. g., utilities may be excused from providing specific times at which backup power could service when prevented by acts of God, be used) or as rate practices (e.g., higher labor disputes, and shortages of fuel sup- rates for less energy use). ply. ” In some cases, utilities have been excused from providing service where to do so A public utility is subject to State regula- would be unusually expensive, although tion in addition to antidiscrimination laws, there is substantial precedent to the con- by virtue of being a public utility. Fun- 40 trary." damental to the concept of a public utility is its dedication of property to serve the public These laws would not, however, prevent without discrimination. AImost every State adoption of a policy which would discrim- has a statutory provision requiring utilities inate against new utility customers who did to “furnish adequate and safe service,”35 not use solar equipment. Existing statutes “provide such service, instrumentalities, and appear to permit a regulation which would facilities as shall be safe and adequate and prevent a utility from providing new service in all respects just and reasonable,”36 or to a customer not using solar energy equip- “furnish reasonably adequate service and ment. f abilities.”]’ Some States have taken measures to re- A public utility “may not pick and strict gas to certain customers or to elimi- choose, serving only the portions of the ter- nate its availability for some uses. For exam- ritory covered by their franchises which it is ple, New York banned the use of gas in presently profitable for them to serve.”38 As swimming pools and in buildings without adequate insulation. ” A few States have banned its use in decorative lighting.

‘4 Priest, Principles of Public Utility Regulation, 1288 ‘8 New York & Queens Gas Co. v McCall, 245 U S ‘5 Or Rev Stat $757020 (1974) 345, 351 (191 8). ‘ b N Y Pub. Ser Law $65 (McKlnney) ‘9 Priest, Principles of Public Utility Regulation, ‘7 WIS Stat Ann $196,03(1) (West) For a general a :237-238. discussion of a utility’s duty to serve, see Note, “Utili- 40 I bid., pp. 240-242. ty’s Duty to Serve, ” Columbia Law Review 62

(1962) 312; and Donald P. Hodel and Ronald G. 4 ’ New York Pub. Serv. Comm’n, Case 26286 [Apr. Wendel, “The Duty and Responsiblllty of Oregon 16, 1974]; and National Swimming Pool Institute v Public Agencies to Provide Adequate and Sufficient A/fred Kahn, 364 N.Y S 2d 747,9 P U.R 4th 237 (1974). E Iectrical Utillty Service, ” Oregon Law Review 54 See also “Ban on Heated Pools Leaves Californians (1975). 539 Boil lng,” New York Times, Feb. 5,1975 Ch. VI Legal Aspects of Onsite Solar Facilities ● 189

The legal principles involved in rate Until the late 1960’s, cost per unit of elec- regulation are similar to those discussed for tricity for at least some types of powerplants service discrimination. The same prohibi- declined steadily, Utilities could therefore tions on discriminating among customer argue that promotional rate structures categories apply, as do the ambiguities as to would, over time, bring new businesses that what constitutes “disc rumination.” 42 wouId justify additional powerplants. These new plants would then lower the bills of all A rate structure that adversely affects customers of the utility. More recently, the solar energy users, however, may be difficult lack of new sites for low-cost hydroelectric to challenge under current case law. Several power, changes in regulatory practices, and cases have upheld the legality of rate struc- increased environmental costs have forced tures that subsidize a particular class of the cost of new power to rise steadily.44 customers (al l-electric customers) despite antidiscrimination laws. I n 1965, a court in- In these circumstances, promotional rates terpreted an antidiscrimination statute as lose much of their appeal. A New York court barring only “unjust” discriminations, and recognized the common impact of rising concluded that only arbitrary d incrimina- fuel prices in a recent decision overturning a tions are unjust: subsidy for all-electric homeowners. 45 The subsidy, which was to run for a year, was in- If the difference in rates is based upon a reasonable and fair difference in conditions tended to lessen the impact of higher elec- which equitably and logicalIy justify a dif- tric rates on residential customers who had ferent rate, It IS not an unjust discrimina- previously been induced to buy all-electric tion 43 homes by favorable rates. The court held that the subsidy “constituted undue pref- Part of the difficulty results from the fact erence and advantage” in violation of the that the utility can argue that its cost struc- State antidiscrimination laws.46 ture justifies a discriminatory rate and the chalIenger is hard-pressed to rebut the ex- Several utility commissions have already tensive analysis which can be conducted by authorized programs to finance the installa- the utility about its unique cost structure, tion of insulation to conserve natural gas.47 although in cases requiring a calculation of Since it can be reasonably claimed that con- a fair backup charge for solar energy (and a servation by some consumers contributes to fair price to pay for excess onsite energy) the eventual economic benefit of all, earlier utilities can be as confused as the in- precedent in support of promotional prac- terveners. tices should be applicable. Some States

41 Colorado Pub Utll Comm’n Declslon No 87640 Environmental Concern. Structural Change In the (Oct 21, 1975), Leroy Fantasies, /rrc. v Swindler, 44 Process of Public Utillty Price Regulation, ” )ourna/ of APP DIV 2d 266, 354 N Y 5 2d 182, 4 P U R 4th 334 Law and Economics 17(1 974): 291 (1974), appeal cfenfed, 34 N Y 2d 519, 316 N E 2d 884 (1974) 4’ Lefkowitz v. Public Serv. Comm’n, NO 593 [N. Y. 43 88 N j Super 233, 236, 211 A 2d 806, 808, 60 Ct. App., Dec. 28, 1976), affg 377 N Y S 2d 671, 50 P U R 3d 210, 212 App Div. 2d 338 (Sup. Ct. 1975). 4’ 377 N.Y S 2d at 674 44 From 1956 to 1970, the average cost of electricity In the United Stdtes decllned from 261 cents per kWh 47 E g , Re Pacific Power & Light Co , Case No to 210 cents While average rates decllned, the costs U-1046-29, Order No 8567, 69 P U R 3d 367 (Idaho of supplylng electricity to certain types of loads and Pub Ut{l Comm’n 1967), In the Matter of the Appllca- to customers during peak hours Increased rapidly tlon of Mlchlgan Consol Gas Co for Authorization of Utilltles subsidize some customers by overcharging a Program for the Conservation of Natural Gas, 1 others Since 1970, costs have Increased steadily; the P U R 4th 229 (Mlch Pub Utll Comm’n 1973) average cost per kWh in 1975 was 3 21 cents, despite Related decisions by publlc utility commissions have an equally steady rise In consumption during the allowed the restriction of energy to approved uses same period Samuelson, “Reform of Electrlc Utility and the prohlbltlon of energy use by uses considered Rates, ” p 1475 See a/so Paul joskow, “lnflatlon and wastef u I. 190 ● Solar Technology to Today’s Energy Needs

have adopted legislation specifically au- The conference committee on the Na- thorizing conservation programs, elimi- tional Energy Act has, at this writing, taken nating any doubt about their validity.48 steps toward resolving these rate issues, but failed to completely clarify the situation. If rate structures that encourage conser- While most of the President’s proposals for vation are valid and mandated, subsidies for dictating rate reform at the Federal level use of solar energy, which employ a non- failed to gain conference approval, the con- depletable, nonpolIuting energy source, ferees did allow the Federal Energy Regula- should also be valid. Use of solar energy is tory Commission (FERC) to prescribe rules supported by the same public interest and requiring electric utilities to offer to sell public policy as conservation–decreased power to or to buy power from qualifying use of fossiI fuels. cogenerators or small power producers and State antidiscrimination statutes are not prevent discrimination against such pro- the only factor to consider in d incriminatory ducers. (Small power producers in this case practices by utilities. The Federal antitrust are facilities generating less than 80 laws may also outlaw rates or services that megawatts from sol id waste or renewable single out the owners of solar energy sys- resources; the definition of a qualifying tems for special treatment. The longstand- generator is left to the FERC. ) While this pro- ing antitrust exemption for State action will vision permits Federal regulation of the rela- not totally immunize public utilities from tionship between utilities and small solar antitrust Iiability.49 generating facilities, it leaves the difficult problem of determining just rates up to the There are several grounds on which utility FERC. rate and service discrimination toward solar users could be deemed anticompetitive, and ARE ONSITE SOLAR SYSTEMS SUBJECT therefore a violation of antitrust laws. A TO REGULATION AS PUBLIC UTILITIES? utility may be deemed a monopoly if it charges a very high price or even refuses to If an onsite solar system is found to be a provide backup service to solar customers. 50 public utility, it must file reports and ac- An antitrust violation might also be found if counts, 52 serve all customers who demand a utility subsidizes its entrance into the solar service within a given area, submit its rate heating and cooling market by distributing schedules to the utility commission for ap- its losses across all utility customers, giving proval,53 continue providing service until 5 it an overwhelming advantage. ‘ given permission to discontinue,54 provide safe and adequate service, 55 comply with

48 Cal Pub Utll Code $325007, 2781-88 (West); N J Stat Ann ~~ 482-4823 (West) ‘) Such conduct could be viewed as temporary 49 In Cantor v Detroit Edison Co., 96 S Ct 3110 price-cutting to put rival solar firms out of business. (1 976), the Supreme Court said that a privately owned See Puerto Rican American Tobacco Co. v American publ IC utll Ity IS not exempt from possible antitrust [obacco Co., 30 F 2d 234 (2d Clr 1929) Or, It ml~ht Iiablllty when It furnl~hes Its customers with Ilght be viewed as an Illegal tying arran~ement In situations bulbs tree ot charge, even though the Ilght bulb pro- where a solar customer’s receipt of favorable treat- motional practice had been approved (as part of the ment IS conditioned on hls acceptance of the utillty ut I I Ity’s rate structure) by the State public ut I I Ity com - service Tying arrangements are another classic an- m Isslon titrust violation See 15 U S C. $ 14 (1 970), /rrterrra- tional Busines$ Machine Corp. v United States, 298 50 Refusa/s to deal area classic kiolatlon of section 2 U S 131 (1936) of the Sherman A c?, 15 U. S C. $2 (Supp IV 1974) See, e g , Otter Tall Power Co. v United States, 410 U S 366 “ E g , Fla Stat Ann $366 06(1) (West) (1972), where a publlc utlllty wds found to have vlo- ‘) E g , Cal Pub Utll Code 454 (West) Iated section 2 of the Shermdn Act by refusing to sell electricity to a municipally operated distribution 54 E g , WIS Stat Ann 19681 (West) syJtem ‘ 5 E g., Cal Pub Utll Code 761 (West) Ch. VI Lega/ Aspects of Onsite So/ar Facilities ● 191

limitations on the issuance of securities, ” Ownership and apply for certificates of public conve- Most State statutes define a public utility nience and necessity. State utility reguIatory to include any person, corporation, partner- statutes universally require that every pub- ship, association, or other legal entity and lic utility obtain a certificate before begin- 59 their various representatives. A solar faciIi- ning operation or even construction of its ty owned by a landlord, or a private proper- equipment. 57 ty owner, as well as any partnership or cor- Meeting these requirements would be a porate entity would qualify as a public utili- prohibitive burden for most potential own- ty, if the other qualifications are met, ers of solar equipment, since the proceed- Where there is no sale of electric power ings are frequently long and expensive, Even involved, but rather the owner and user are if a solar owner were wilIing to undertake the same legal entity, State regulations gov- the trouble and expense to file as a utility, ern. Federal regulations concern only the he would have to recognize that an existing wholesale rate for interstate electricity utility will be able to maintain a monopoly sales, Rarely will owner-used energy be sub- in its geographical area unless the courts ject to Federal regulation as a public utility. determine that public convenience and ne- This is true whether the owner is a single cessity require otherwise family, a joint venture composed of the vari- A new utility is therefore rarely permitted ous users, or a corporation which supplies in an area already served by an existing utili- its own corporate needs. ty. Even where the existing utility is pro- Where the owner is not the sole user, viding woefully inadequate and inefficient State statutes vary, The general rule is that a service, it wi I be permitted to exercise company which supplies energy “to the pub- monopoly control over its service area if it lic” will be found to be a public utility, promises to correct its shortcomings. whereas a device which is not producing The initial factor in determination of energy for public use will escape utility whether an onsite solar system is a public reguIat ions, 60 Law in this area is very unclear utility is who owns the system? Ownership and the ambiguity may be a barrier to the in- can range from the privately owned solar troduction of solar equipment, system on a privately owned residence, to A facility can be judged to be dedicated cooperatively owned systems for a small to “public use” if its owners 1 ) demonstrate community, to a corporate-owned colIector a wiIIingness to serve alI who request serv- field on corporately leased or publicly 61 ice; 2) voluntarily submit to State regula- owned property to utiIity-owned systems on tion; or 3) attempt to exercise the power of private residences. Clearly, somewhere in 62 eminent domain. the continuum of owners the onsite solar facility and its owners became subject to reguIation as a public utiIity. ‘1 “The principal determinative charactlstlc of a public uti i Ity is that of service to, or read lnes~ to ierve an Indefinite public which ha~ a legal right to de- “ E g , [id Stat Ann ]66 O-I (West) mand and receive its services or corn mod I t I es ‘‘Motor “ ‘ E g , I I I t?E’V Stat , ch 1112 3, 56 Cargo, /nc. v. Boarcf of ~own.~hlp Trustee\, 5.2 Ohio Op 257, 258, 117 N E 2d 224, 226 (C P Summit County ‘“ See, e g , KentucA y Ut/i C 0, v Pub/Ic $erv Com- 19’52) See gerrera))y A J C Prle$t, “Some [J~ses of m n, 252 S W 2d 885 (Ky ) Publlc Utility Regulation, ” MIssI~sIppi Law journa/ 36

5 ’ f g , F la Stat Ann $ 36601, Mlch Comp 1 aws [1965) 18 See, e g , Peoples Gas Light & Coke Co v Ann $460-6, Cal Pub Utll Code ~ 21 6(a) Ame$, 359 I I I 132, 134 N [ 2W (19 35), Story v F?icharc]son, 186 Cal 162, 198 p 1057 (1921) ‘“ WI\ Stat Ann $19601 (West), Ill Rev Stat ch 111 2 ; Q 10, e g , A //en v California R /? Comm ‘n, 179 “ See Dow Chemical Co , et al , Energy Industrial Cal 68, 175 p 466(1918) Center Study, p 373 and cases cited therein 192 ● Solar Technology to Today’s Energy Needs

Even activities which do not clearly in- empting onsite owners from regulation, but volve a dedication to public use may be de- leaves many issues unresolved. The con- clared by the courts to be “so affected with ference agreed to exempt cogenerators and the public interest” that utility commission small powerplants producing up to 30 mega- jurisdiction is justified. In one recent case, watts of electric power from State utility the owner of a shopping center was not regulations (apparently granting the FERC allowed to sell energy to stores in the shop- the authority to overrule States in these ping center without being regulated as a issues) and exempts biomass generators ut i I ity. 63 smaller than 80 megawatts from the Public Utilities Holding Act. The act would, how- Electricity, Steam, or Heat? ever, apparently not permit exemptions for Another factor in determining whether an subsidiaries of utilities since small gener- onsite solar use is subject to regulation as a ators qualifying for the exemption must be public utility is the form in which energy is owned by organizations whose primary busi- supplied to the users —electricity, thermal ness is not energy generation, energy (steam or hot water), or chemical energy. Solar equipment may become avail- CAN A UTILITY OWN able which will produce energy in each of AN ONSITE SOLAR FACILITY? these forms. Again, State statutes vary, For example, some States do not vest juris- The above discussion has assumed that diction over production and sale of steam in the owner of the onsite solar system was 64 their utility commission. State statutes also the owner of the land and building vary greatly, however, and generalIy thermal upon which the solar system is located. Is it energy is not regulated simply because there permissible for utilities or other corpora- is no explicit mention of the issue in the tions to own onsite solar facilities on Iand statutes, which the utility does not own, such as the Still another aspect of this question is property of the user? whether the sale of energy by an onsite pro- The short answer to this question seems to ducer subjects the owner of the onsite be yes, although antitrust laws and State equipment to regulation. Sale to a presently policies designed to promote competition regulated utility should be interpreted as would probably prevent utilities from estab- would sale to any other category of user. lishing exclusive marketing rights for solar Under most State statutes, sale of excess equipment. Utilities probably would be re- steam or electricity to a specified public quired under existing law to compete with utility probably would not meet the test of other distributors of solar systems. dedication to public use which is required in determination of public utility status. In a The law is clear that utilities at least number of cases, industries that generate ex- would not be barred from the solar equip- cess electricity or steam or selI it to public ment market. A recent analysis of the ques- utility companies have been held not to be tion of permitting gas utilities to invest in public utilities.65 However, in some States onsite conservation equipment concluded the opposite has resulted. that Federal antitrust statutes would not be violated if the utility only purchased conser- The congressional revision of the Na- vation devices (in this case, insulation ma- tional Energy Act takes some action in ex- terial) from independent suppliers and did ‘ i Cottonwood Mall Shopping Center, inc. v Utah not actually manufacture or install a major 66 Power & Light Co., 440 F 2d 36 (lOth Clr 1971). share. ‘4 Mlch Comp Laws Ann $460501, Fla Stat Ann. Ej 36602 “ Willlam G Rosenberg, “Conservation invest- ‘5 See Dow Chemical Co , et al., op. cit., pp. ments by Gas Utilities as Gas Supply Option, ” Public 374-376, and cases cited therein Utilities Fortnight/y, Jan 20, 1977, pp 19-20 Ch. VI Legal Aspects of Onsite So/ar Facilities ● 193

Exemption from Federal antitrust statutes It is unclear whether an existing public is apparently permitted in some cases where utility wiII be permitted to own a solar an expansion of utiIity operations is under- system which is permanently placed on the taken at the suggestion of a State utility roof or other property of a customer. Since commission and not on a utility’s initia- such a system is probably a fixture, the utiIi- tive. 67 Precedents exist permitting utilities ty would be required to leave the solar sys- both to expand their business to include ac- tem in the home or office, even if the prop- tivities under regulatory authority and to erty is sold or leased. The most practical ap- own subsidiaries which are not reguIated. proach is for the utility to finance the purchase of the solar equipment and thus per- There have been cases where, at a utility’s m it its easy disposition as a fixture, but re- request, an unregulated industry was placed tain the usual metering, repair, and mainte- u rider reguIatory control. The Pacific nance relationships with the customer. Telephone Co., in California, for example, owned an unregulated subsidiary for a num- Nonutility corporations could also own ber of years which installed and operated onsite solar equipment. Probably, such a mobile radio telephones. The company sub- corporation would supply only equipment, sequently asked the California Public Utility and perhaps maintenance, but not energy. Commission (PUC) to place this activity Under most State statutes, provision of under regulatory control. The PUC accepted energy equipment is not subject to utility the application, but a private competitor ap- commission jurisdiction. pealed the decision. The California Supreme Court upheld the PUC approval, in a divided The specific arrangement between the decision. The court found that mobile tele- solar equipment leasing company or seller phone service was closely related to the and the property owner may alter the ques- utility’s regulated business and that the tion of utility regulation. For example, the equipment, used for telephone communica- inclusion of a service agreement between tion, fell under the jurisdiction of the the lessor and the lessee might increase the reguIatory authority. 68 likelihood of regulation, as would more At the same time, there are cases where widespread adoption of solar devices. Addi- utilities have not been able to place sub- tionalIy, to the extent that such an agree- sidiaries of this type under PUC reguIation. ment requires backup power from public For example, the New York Service Commis- utilities, the contracts and prices for these sion limited the activites of utilities in solid provisions would be indirectly subject to waste disposal ventures,69 and AT&T was regulation as part of the normal utiIity rate prohibited from expanding its unregulated reguIation. business as a part of a settlement.’” Congress apparently has taken a dim view of utility ownership and financing, since the committee of conference on the National b’ Cantor v Detro/t Edison Co., 96 Sup Ct 3110 Energy Act rejected the President’s proposal (1 976) that utilities be permitted to finance the in- “ Corrrrnerc/a/ Comrnunicat/orrr /nc v California stalIation of insulation and other expensive Pub/Ic Uti//ty Cornrn/ssion, 50 Cal 2d 512 (1958) residential conservation equipment. While “ P M Meler and T H McCoy, So/Ic/ Waste as an the conference encourages utilities to per- Energy Source for the Northeast, prepared for the form energy audits of residences, it prohibits Energy Research and Development Admlnlstratlon (Upton, N Y Brook haven National Laboratory, No utiIities from instalIing conservation devices 50550, 1976], p 96 other than furnace-efficiency modification, “) Un/tecf S?ate$ v W’estern E/ectr/c and AT&T, 13 clock thermostats, and load-management Rad Reg (P-H) $2143, 1956 Trade Reg Rep (CCH) equipment. Loans to cover these devices are 571,13-4 (D N J 1956) (consent judgment) Iimited to $300. (State commissions are per- 194 ● Solar Technology to Today’s Energy Needs

mitted to ask for an exemption from this changed in many areas of the country to prohibit i on.) allow municipal to share the cost of constructing nuclear-generatin facilities and The field remains quite ambiguous, how- g other centralized energy equipment, which, ever, and many possibilities remain open. It like solar energy systems, have high capital may be attractive, for example, for utilities costs. Prohibitions aganist such “joint ac- to operate solar equipment as a part of an tion” programs are often written into State unreguIated subsidiary. Such an arrange- constitutions. The constitution of the State ment would eliminate concerns, expressed of North Carolina, for example, was recently by some potential owners of cogeneration amended by referendum to permit joint- equipment, that equipment on their prem- action financing of new electric utility ises, owned by a regulated utility, would not plants, Such amendments have been contro- be able to sell energy on an equitable basis versial in some areas. For example, in 1977, because of special pressure to adjust utility the Governor of Indiana vetoed legislation rates. amending that State’s constitution to allow joint action programs. Municipal Utilities

Since municipal utilities can finance Cost-Sharing Issues plants with relatively low-interest, tax-free bonds, the capital costs associated with If a utility were to own or operate onsite plants owned by municipal can be lower generating facilities, contracts between cus- than those of plants owned by privately tomers and the utiIity wouId have to address owned utilities. Lowering capital costs is several important issues. They include: particularly important in the case of solar ● Who would pay the property tax on the energy systems where the bulk of the energy equipment? (This is particuIarly impor- cost results from the cost of capital. I n most tant because utility tax rates often are States, however, municipal utilities are pro- several times higher than those for hibited from expending funds for “private homeowners.) benefit” and this has been interpreted to mean that municipal utiIities cannot pur- ● How would costs of insurance be dis- chase shares in generating facilities which tributed? Would utilities be liable for are partly financed and operated by a damage to onsite equipment caused by private utility. the homeowner?

● These prohibitions may also prevent mu- Would a contract for onsite solar nicipal from owning or operating onsite equipment be binding on a new owner generating systems. In the case of solar if title to a buiIding were transferred? devices, however, it would seem that the ● How far would a utility’s maintenance municipal couId make a strong case that in- responsibility extend? Would a utility, stallation of a solar device would benefit for example, be responsible for keeping the public at large even though it was pri- a roof on which a solar collector was mariIy designed to meet the energy needs of mounted in weatherproof condition? a single building. In fact, several municipal ● Should a utility pay a customer for the utilities have experimented with onsite solar use of a roof or wall for installing a energy equipment in their districts. The legal solar collector? If so, would the fee point may be moot since, as one analyst put decrease for the use of walls and roofs it, “Who’s going to complain?” that did not permit optimum collection In any event, the laws preventing munic- of radiation? ipal from owning part shares in generating ● Could a customer demand that a utility facilities which will be partly owned and remove onsite equipment? If so, who operated by private utilities are being wouId pay for removal? Ch. VI Legal Aspects of Onsite Solar Facilities . 195

None of these questions pose insoluble and in heated underground caverns have problems, but all may require careful nego- been proposed (see chapter Xl), and the use tiation. All of the utilities interviewed by the of subsurface regions for such purposes may General Electric Co. said they preferred on- raise a number of difficult legal questions. site facilities on large buildings, because For example: questions would be easier to resolve than if large numbers of small buildings were in- Would a utility need to purchase miner- volved. 7‘ al rights to use subsurface water or rock for thermal storage?

WHAT RIGHTS WILL UTILITIES HAVE TO What aspects of water laws govern AQUIFERS AND OTHER GEOLOGICAL which aquifers can be used, the con- FORMATIONS USED FOR tamination permitted, the heating of THERMAL STORAGE? aquifers which might be used for potable water, etc. ?

Several techniques for storing large Would the owner of heated water have amounts of thermal energy in ground water protection from someone tapping this hot water supply? 71 General E Iectrlc Corp , Corrceputal Design and Systems Ana/ys/s of fhotovol?a~c Power Systems, April What environmental laws would apply 1977, ERDA contract E(ll-1 ) 2744, op cit to large-scale thermal storage? Chapter Vll THE IMPACT OF SOLAR ENERGY ON U.S. FOREIGN POLICY, LABOR, AND ENVIRONMENTAL QUALITY

Chapter VII-THE IMPACT OF SOLAR ENERGY ON U.S. FOREIGN POLICY, LABOR, AND ENVIRONMENTAL QUALITY

Page TableNo. Page Background ... *.. **. **...... * s.*.... 199 8. Primary EnergyRequired to Produce Developing Nations...... 202 ComponentMaterials for Solarand Implications for U.S. Policy ...... 203 Conventional PowerSystems ...... 221 Foreign Trade in Solar TechnoIogies ...... 208 9. EmissionsAssociatedWith the Energy Background ...... 208 Requirements of a Single Family House Foreign Competition in Solar in Omaha, Nebr...... 224 Technologies...... 209 10. Primary EmissionsAssociated With Energy ResourcesAvailable for The lmpact of SolarEnergy on Residential Commercial and Industrial American Labor...... 210 Consumers ...... 226 ManpowerRequirements...... 210 “PaybackTime’’ for the Emissions SomeQualitativeImpacts ...... 213 AssociatedWith the Manufacture of Long-TermImpacts...... 218 Solar EnergySystems...... 226 Net Energy Use of SoIarEquipment ...... 219 Land Required for Strip-Mining Coal. ... .231 Primary Energy Requirements ...... 219 PotentialAreasfor Collectors on Typical Energy UsePerDollarofGNP ...... 220 Buildings ...... 235 Thelmpact of On$iteEnergy on the Thermal and Electric Outputs of Environment ...... 222 . Flat-PlateCollectors in Omaha, Nebrv Direct Environmental Effects...... 222 as a Function of Tilt Angles and OnsiteSolarEnergySystems and Orientation ...... 240 Land Use...... 225 TheAdverse Environmental Effects of CollectorFields...... 231 Land Used by Conventional Generating Systems ...... 231 LIST OF FIGURES lmpact on BulldingDeslgns...... 232 Background ...... 232 Figure No. Page Roof Pitch and Orientation...... 236 l. Worid EnergySupply and Demand ...... 200 Space for Storage ...... 237 2. WorldwideAvailability of Sunliaht Other Building Impacts...... 241 Resources ...... _...... 2O4 3 A Small Housing Development Using Solar-Heating Devices ...... 228 4 Tracking Collectors Mounted Over LIST OF TABLES a Parking Lot ...... 229 5 VegetationGrowing UnderArrays of TableNo. Page SolarCollectors...... 230 l. Electricity Prices in Developing Nations ..205 6. Techniques for lntegrating Solar 2. Labor Requirements for a Conventional Collectors Into Conventional Designs

800 MWe Coal Plant...... 211 for Single Family Residences ...... 233 3. LaborRequirements of TwoTypes of 7. Techniques for lntegrating Solar DistributedSolarEnergySystems...... 212 Collectors Into Conventional Designs for 4. Skills Required for Constructing a Coal- Townhouses and LowRiseApartments ...234 Fired Electric Generating PlantandOper- 8. Presidential BuildingWith Optimized ating the System Over a 30-Year Period ...215 SolarRoof Pitch and Orientation...... 236 5. Detailed Breakdown of Skills Required 9. A Commercial Building Designed To for Conventional ElectricSystem ...... 216 Optimize Roof Pitch and Orientation .. ...237 6. Energy PaybackRelations for Onsite 10. A Proposed installation for a One- SolarConversionSystems in Albuquerque 220 AxisTracking Collector ...... 238 7. MaterialsRequired in Solar Energy 11. Use of Collectorson the Vertical Devices(kg/m2 ) ...... 221 Wall of a High Rise Hotel ...... 239 Chapter VII The Impact of Solar Energy on U.S. Foreign Policy, Labor, and Environmental Quality

BACKGROUND

Extensive use of solar energy throughout the world would relieve some of the international stress which results from competition over diminishing energy resources. Solar energy is one of the few energy resources reliably available throughout the world and, to the extent that it can be developed in lieu of conventional energy sources, it can reduce the uncertainties and trade imbalances which have resulted from energy imports. Moreover, solar energy technology can be implemented without the technical infrastructure and cadres of skilled engineers required to implement most other energy strategies— in developing countries solar energy may provide a technique for converting low-cost labor into low-cost energy. While it is difficult to anticipate how fast solar energy will be introduced into the world energy market, it appears that solar energy’s impact is likely to be quite small in the next few decades unless accelerated programs for developing this industry are undertaken.

It is likely that solar energy will grow more rapidly abroad than it does in the United States, since U.S. energy prices are relatively low, U.S. domestic energy supplies are relatively large, and U.S. labor costs are relatively high. However, U.S. policy in solar energy will probably play a critical role in in- fluencing the development of this technology throughout the world: the United States now probably leads the world in the quality of its solar engineering. The United States can influence utilization of solar energy in developing countries through its economic assistance programs and a major U.S. commitment to the use of solar energy for its own use would give a prestige to the field which may attract worldwide emulation. The history of the past two decades clearly indicates that these three effects resulted in a rapid transfer abroad of U.S. interest i n fission reactors.

The eventual need to develop renewable past two decades most of the developed na- sources of energy is beyond serious conten- tions of the world and the industrialized section, although there is disagreement about tions of developing nations have become the urgency involved. There are two parts of heavily dependent on the convenience and the problem: near-term depletion of low- low cost of petroleum and natural gas, and cost oiI and gas reserves, and the depletion consumption rates have become astro- of all fossil and uranium resources over the nomical. long term. A shortage of indigenous supplies of these Many recent studies have indicated that fuels has required many nations to import world demand for oiI and gas may exceed them and in many cases, dependence on 2 supplies by the middIe of the 1980’s, I n the these imports is heavy. This dependence is likely to increase during the next decade because of the shortage of acceptable alternatives, and the high costs and long construction times needed to convert to the alternatives which become available. The uncertainties associated with importing a 199 200 ● Solal Technology to Today’s Energy Needs

large fraction of a critical material are fuels. The use of coal resources may be amplified by the fact that world resources of limited by environmental problems, trans- petroleum are inequitably distributed. The portation costs, and other difficulties. OPEC cartel, for example, controls 68 per- Figure VI l-l indicates that if world energy cent of known world reserves of o i 1, and its consumption grows at its current rate, pro- Middle Eastern members alone control 55 ven world reserves wiII be entirely consum- percent of known reserves. ed by 2015, If the entire world consumed energy at U.S. consumption rates, world Coal and other fuels can be substituted reserves would be depleted by the end of for oil and gas even though the use of these this century, It is, of course, unlikely that energy sources is not as convenient as liquid production or consumption rates will continue to grow exponentialIy and new energy ‘ ()// ,)nd (;,]J /o(/rn,q/, De(- 29, 1‘)75 sources, such as fusion, may be available to

Figure VI I-1 .—World Energy Supply and Demand Measured World Recoverable Energy Reserves, 1974 I Quadrillion Btu] Oil shale Area Solid Crude Natural and Uranium Total fuels oil gas tar sands (nonbreeder) 2 Africa 361.7 526.6 201.7 81.4 1981 1,369.5 Asia (less U. S. S. R.) 2.608.7 2,202.4 432.6 8702 3.1 6,1260 Europe (less U S S. R.) 2,581,5 57.1 153.6 117.0 46.4 2,955,6 U.S.S.R. 3,325.5 333.6 577.9 139.0 Unknown 4,376.0 North America 5,070.9 301.0 380.6 9,111.0 422.7 15,286,2 South America 49.8 311.5 60.6 23.7 11,9 4575 Oceania 459,8 9.4 24.9 9.2 99.1 602.4 Total 14.457.9 3,741.2 1,831.9 10,3515 781.3 ’31 ,1732

‘ Accordlrw to the U S De~artment of the Interior Bureau of Mines North Amer)can tar sands and shale 011 reserves may be severely overstate: Development of most of these reserves IS not econom IC at present ‘ Enerqy content using breeders 60-100 t)mes as great Thortum resources neglected SOURCE World Energy Conference Survey of Energy Resources New York 1974

World Energy Consumption, Production, and Inventory Changes 260

gas consumption “ 100 80 60 Petroleum consumption

SOURCE Energy Perspectives 2 U S Department of the Interior, June 1976 pp 11 and 20 provide essentially inexhaustible supplies of energy are very long and thus potentially energy in the next 20 years, but it is difficult very vulnerable No nation can be comfort- to take great comfort from the available able if a commodity on which Its economy statistics. depends comes from so uncertain a source Moreover, in any situation where a state or a World supplies of fuels other than oil and group of states greatly dependent on Im- gas are also inequitably distributed Figure ports can assemble a substantial military VI l--i indicates that nearly half of known ca pa b i I i t y, a disruption, or threatened world energy resources are located In North disruption, of those supplies carries with It a America (although the share would be re- high risk of International violence It IS duced somewhat If oil shale assets are noteworthy that the U S response to the em- overstated) The United States, U S S R , and bargo of 1973-74 included thinly veiled Eastern Europe control 73 percent of the threats of military action known world reserves of coal 4 . Another potential source of energy- There can be Iittle doubt that growing related conflict concerns nuclear prolifera- uncertainties about energy supplies will tion The global spread of civilian nuclear have an Important Impact on international energy has been accompanied by a decline political stability during the next decade in- in the number of technological, economic, tensive efforts will be made to develop and time barriers to acquiring nuclear domestic resources and to ensure the securi- weapons An increasing number of countries ty and reliabllity of foreign supplies The lat- are already capable of producing their own ter objective, however, would appear to be nuclear arms The consequences of pro- Increasingly difficult to achieve The effort liferation are subject to debate, but they are to assure supplies and the vast transfers of unlikely to be positive from the perspective assets between nations which occur in the of U S or global interests. A strong argu- process, can create economic dislocatlons ment can be made that proliferation will in developed nations and frustrate the jeopardize regional and global stability, in- aspirations of less developed nations This, crease the Iikelihood of nuclear war, exacer- In turn, could lead to restructuring of world bate the threat of nuclear-armed, nonstate alIiances There has been specuIation, for terrorism, and greatly complicate U S. rela- example, that democratic institutions (in nations with new (potential or actual) nuclear tions such as Italy) may collapse under the weapons states. Because securlty concerns weight of accelerating Inflation and reces- are a key incentive to acquiring nuclear sion traceable, at least in part, to energy weapons, the probability of prolIferation costs Dr Henry Kissinger has warned that: will tend to be greatest in regions with the Not since the 1930’s has the economic highest potential for international conflict system of the world faced such a test. The disruptions of the 011 price rises, the threat In the past, the United States placed ma- of global InfIatlon, the cycle of contraction jor emphasis on aiding nuclear energy of exports and protectionist restrictions, the development programs around the world In massive shift In the world’s financial flows recent years, this program has been and the Iikely concentration of invested tempered by a concern about proliferation, surplus 011 revenue In a few countries, al I resu I t i ng in efforts to tighten export threaten to smother the once-proud dreams agreements, to prohibit the export of of universal progress with stagnation and facilities for reprocessing plutonium or despair enriching u ran i u m, and to discourage The sense of insecurity attached to im- foreign transfers of such technology. porting energy resources is magnified by the fact that in most cases supply lines for The United States, however, is in a weak position if it attempts to discourage the de- 4 Wilson, p 171 velopment of nuclear power in nations

2,{ - ‘i *.? I ) - 14 202 Ž Solar Technology to Today’s Energy Needs

where attractive alternatives are not ● ava i I able.

DEVELOPING NATIONS ●

Less developed nations are likely to be most vulnerable to energy shortages and a steep increase in energy prices. They will be less able to compete for scarce resources and less able to bear the additional financial burdens. (It could be argued that less developed nations wilI fare better than developed nations, since the less developed a nation is, ● the easier it will be to return to noncommer- panded flexibly and proportionately to cial fuels such as dung and wood ) Plans for meet growing requirements for energy. developing an indigenous industrial base Large facilities produce sudden large and modernizing agricultural methods have increments in capacity which are dif- already been disrupted by higher energy ficult to manage This problem fre- prices. Many irrigation systems in South quently results in prolonged periods of Asia, for example, stand idle because the expensive overcapacity fuels to operate them cannot be obtained.

The economic assistance programs of the Some of these advantages would be redeveloped nations are partly responsible for duced or eliminated if it were necessary to the dilemma. These programs have in many construct a centralized utiilty large enough to meet all energy requirements of the area cases attempted to promote the development of an industrial infrastructure which is under the assumption that solar equipment might supply no energy during some period as heavily dependent on scarce energy resources as U.S. industries. of peak demands There are a number of ways of eliminating the need for centralized The relatively small onsite solar tech- backup power in developing countries: nologies examined in this report should be particuIarly attractive to developing nations ● The facilities requiring energy could for a variety of reasons: s i m ply be shut down when energy was not avaiIable — this would reduce labor ● These nations typically have not in- productivity but would not be as signifi- vested in an extensive network of cant in a Iocation where Iabor was rela- transmission and distribution facilities tively inexpensive (equipment which frequently costs as much as the generating stat ions ● Many solar applications, such as water themselves); onsite technologies could pump i n g, will need no backup in re- provide power to dispersed sites mote areas since storage is very inex- without the expense and delay pensive associated with building such equipment. ● SmalI emergency generating equipment could be maintained to provide backup ● Onsite equipment does not require an power when solar energy fails. Energy enormous investment of capital in a from diesel generators is commonly single project, thereby reducing the used in remote villages and is very ex- overall risk of the investment and pensive, but the costs would be more avoiding expensive capita I-carrying manageable if the devices were only charges during construction. operated a few days each year Ch VII Impacts of Solar Energy ● 203

Solar energy should also be attractive to the less developed countries on grounds of broad social utilitv As a relatively labor-intensive means of power generation (both in terms of manufacture of components and installation), solar energy should help alleviate the endemic high unemployment and underemployment that plague most developing countrles

Village siting of solar facilities would help raise rural living standards This could, in turn, have the effect of reducing the rate of migration to urban areas in search of employment which is often available only in urban areas because only urban areas have adequate supplies of energy

Solar energy facilities can be constructed utilizing a variety of materials, which may be locally available.

Developing solar energy would not commit those countries to forms of energy production that they may not be able to sustain because of fuel shortages or the lack of secure funds for IMPLICATIONS FOR U.S. POLICY operating costs Solar energy may well become economically attractive in developing nations In many applicat[ons significantly before it does so in the United States for a number of reasons Most developing nations are located in areas where sunlight is plentiful (see figure VII-Z); labor costs–which frequently represent a substantial fraction of the total costs of a solar energy installation — are relatively low; and the cost of competing energy — when it is available— is frequently very high. Table VI I-1 sum- m a r izes the prices charged ror ectricity in many nations around the worId. The information IS difficult to Interpret since many governments subsidize the selling price (For reference, the fuel prices alone contribute over 3¢/kWh to the cost of electricity If petroleum is Imported at world 011 prices ) The table does show, however, that energy prices in many parts of the world are several 204 Ž Solar Technology to Today’s Energy Needs

Figure VII-2– Worldwide Availability of Sunlight Resources

Daily Radiation for June

Daily Radiation for December

SOURCE John A Duffle and Willlam A Beckman, So/ar Energy Thermal Processes, John Wiley& Sons, New York, 1974, pp 35,37 Ch. VII Impacts of Solar Energy ● 205

Table VII-I . —Electricity Prices in Developing Nations

Electricity prices (cents / k Whr)

Capital city Urban, Country Residence Commerce Industry noncapital Remote Comments Bureau: Asia

Philippines . 1.6-4.7 2.2-4.7 2.8-3.2 3.8-16 Remote: Regional national grid, 3.8; Private small COOPS, 16 Pakistan . . . 2.2-2.5 2.2-4.2 .4-1.5 Indonesia 7 10 .5 Sri Lanka. 4-2 Nepal ...... 2-4 Bangladesh. 1.1-1,9 Subsidized India...... 2.8 Afghanistan 1.7-6.6 Different rates for Hydro, Diesel, Gas Korea ...... 4.6-11 5.6-7 3-4

Thailand* . . . .70-5 ● BAHT/kWhr Bureau: Near East

Yemen . . . . . 13.3 Israel . . . 4.3 4.6-6.6 Egypt ...... 1.4-2.4 1-2.4 1.0 Subsidized (e. g., fuel 011 supplied at 1 /6 world price) Syria ...... 5 Morocco . . . 5.5-13 12.5 Portugal . . . . 3 4 4 Sudan ...... 8.6 Bureau: Latin America

Ecuador, . . . . 1.5-3.8

Haiti ...... 5.5-7.3 25/month for 25 watt bulb Colombia . . . 1-1.2 1-2.5 3-4 Costa Rica . 4.4-5.3 4.7-6 4.4-4.7 Guatemala . 4.4-6.4

Peru ...... 1.9 Guyana . . . . . 19-21.9 29.9 27 Bauxite manufacturer gets subsidized rate of 10 206 ● Solar Technology to Today’s Energy Needs

Table Vll-1.—continued Electricity prices (cents/kWhr)

Capital city Urban, Country Residence Commerce Industry noncapital Remote Comments

Dem. Rep. ● . 2-6 ● in RD ($RD?) Brazil ...... 5.6 6.9 3.7 plus 23% Fed. Tax Nicaragua . . . .87-11.3 should low residence be 8.7? Panama . . . . . 6-10 uniform in country Uruguay. . . . . 4-5 2-3 2-3 uniform in country Paraguay . . . . 5-8 6-8 6-8 Chile* ...... 68-1 1.4 CH $ Bureau: Africa

Benin . . . . . 13 13 13 13 Burundi . . . . . 5 5 5 5 Two cities: one hydro, one (smaller) diesel. Plans for small hydro for 3 towns (GEIL) Nigeria. . . . . 3-6 3-6 3-6 4-7 Cameroon . . . 19 19 — 23 Tanzania . . . 3-13 12-27 7-1o Heavy Industry, 1-3

Liberia ...... 6.5-8 6.5-8 5.5-7 Complicated billing Niger ...... 10-19 10-19 Average for Mission Residences, 12.5 Senegal . . . . . 7-24 11-25 7-14 Chad ...... 14-26 14-26 Average for Embassy housing, 2

Kenya ., . . . . 2.8 11.2 -15.8 6-14.2 Sierra Leone . 9 9 9 Upper Volta. 16-26 16-26 8*

Mauritania. . . 17

Ethiopia. . . . . 5-7.5 5-7.5 5-1o 10-12

SOURCE Mew for lnt~rnal(onal o~v~lw~~nt response to telegram requests for Information Summer 1977

related tensions lead to conflict (even if we attempts to improve relations with the Third were not directly involved in the conflict), World. and it has already been eroded by our grow- As the world’s largest consumer and im- ing reliance on fragiIe supply routes for porter of energy and the acknowledged energy supplies critical to our economy. leader in most energy technologies, the Short of open warfare, competition over United States will necessarily be the focus energy supplies could place a serious stress of international tensions generated by on traditional U.S. alliances and disrupt its energy issues. Washington’s relations with Ch. V// Impacts of So/ar Energy ● 207

other industrialized countries (many of them number of reasons, but two problems clear- U.S. allies) have already been strained by ef- ly are large factors: forts to impose controls on nuclear exports ● The failure of the United States to be and by a competitive scramble, following able to offer any logical alternatives to the 1973-74 embargo, to obtain reliable the proposed nuclear development pro- sources of oil imports. With the emergence grams, and of the United States as a major importer, petroleum has become a potentially serious ● The implication that advanced nuclear source of division within the Atlantic systems are reserved for advanced na- Alliance, and with Japan. By contrast, Soviet tions, particularly those with nuclear capabilities to export oil and uranium have weapons capabilities, while other na- augmented the U.S.S.R.’s hold over its tions are relegated to “second-choice” clients in Eastern Europe. energy alternatives not seriously considered by the United States for its own Its wealth and power have long made use. America the representative and symbol of It the industrialized state in the eyes of less is clear that accelerated development developed countries. Thus, inevitably, the of solar energy and other renewable energy Unitd States has been the focus of Third resources throughout the world wilI not be World resentment, a condition exacerbated able to play a large role in the difficulties by the scale of U.S. energy consumption in discussed here in the near future. But the an increasingly shortage-conscious world development of a reliable energy source, ap- and by recent American efforts to constrain plicable in a variety of countries, operating nuclear exports. largely independence of foreign supplies of resources or technology, would certainly A danger exists that energy problems may move things in the right direction. serve to reinflame some of the anxieties and Solar energy offers a particularly promis- ambitions which formerly dominated rela- ing avenue for improving U.S. relations with tions between the Communist and non- the Third World — an area in which Washing- Communist nations. For example, there has ton has not been notably successful in re- been fear that the U.S.S.R. may successfully cent years— because it is peculiarly adapt- exploit the Arab-Israeli dispute to obtain in- able to the needs of the developing coun- fluence over the disposition of Middle tries. Solar energy is particularly attractive Eastern oil, upon which most of the in- in this regard because it offers a means of dustrialized countries of the world are so directly contributin to improved well-bein dependent. Rising energy costs, in conjunc- g g at the village level. Americans have not tion with population, food, and resource been adept at providing technology suited pressures, may also frustrate the develop- to the rural conditions, low-skill levels, and ment hopes of many Third World countries, plentiful labor supplies which characterize thereby strengthening the hand of Com- the living conditions of much of the world’s munist movements in those countries and population. consequently placing new strains on U. S.- Chinese relations, Development of a set of solar energy systems which were genuinely useful to the Problems have also been created by the Third World would provide an opportunity current administration’s attempts to control for the United States to demonstrate its con- the proliferation of nuclear weapons tech- cern for the aspirations of developing na- nology by discouraging non-nuclear tions and to reinforce its global reputation weapons states from acquiring advanced for technological leadership and innovation. nuclear energy equipment such as uranium enrichment and reprocessing systems. Ef- The United States is in a position to forts in this area have been rebuffed for a assume leadership in the development of 208 Ž Solar Technology to Today’s Energy Needs

solar energy resources for a variety of either directly or through international lend- reasons. ing institutions such as the World Bank or the Export-Import Bank. In the first place, the United States leads the world in solar energy technologies. The U.S. Federal budget in solar energy is prob- Finally, a major U.S. commitment to the ably larger than the combined solar budgets development of solar energy resources both of the rest of the world. Soviet efforts in for its own use and in its economic solar energy are virtualIy nonexistent. assistance policy, would have a subtle but Secondly, the United States is in a posi- powerful effect on the attitudes of other nation to supply capital to developing nations tions toward this technology.

FOREIGN TRADE IN SOLAR TECHNOLOGIES

BACKGROUND More detail is available on photovoltaics than in other areas of solar technology. If solar energy can, in fact, provide a com- About 113 kW of photovoltaic devices were petitive source of energy in many parts of sold in non-Communist nations outside the the world, the potential for U.S. exporters United States in 1976 (a market of approx- should be substantial. There have not been imately $2 million) and a recent study has any systematic surveys undertaken of the ex- forecast that sales could reach about 88 tent of this market, either by the U.S. 7 MW ($44 million) by 1986. This is still much Government or by U.S. solar industries. too small to attract major industrial interest. Some observers are convinced that there is a potential market of many hundreds of mil- These projections will remain speculative lion dollars in annual sales to under- until an overseas solar marketing survey is developed nations alone, and see no reason conducted to look at the energy needs of why the United States cannot capture a developing countries, the kinds of special- large fraction of that market. ized solar technology that would be re- Other analysts are more conservative. quired to meet those needs, and the They note the limited capability of poor capability of the developing countries to countries to finance imports, and the fact pay for imports or to manufacture their own that much solar energy hardware is so sim- equipment, This information would be ple as to be unprotectable by patent. More- analyzed in the context of existing U.S. over, low labor costs in developing countries technology, and would indicate both how and the expense of transporting bulky solar extensive the market for off-the-shelf solar equipment suggest that many less devel- hardware is, and how existing technology oped countries will find solar energy an could be adapted to provide the specialized ideal import-substitution Industry. I t is not equipment needed by other countries. difficult to imagine a nation like Singapore, The development of a foreign market which has quickly mastered a variety of would also substantially benefit the medium-level technologies, developing the domestic solar energy equipment market, capabilities to fabricate some solar equip- since the additional overseas demand for ment. If this assessment is correct, the U.S. export market may be limited to relatively high technology solar components, e.g., ~ Characterization of the Present Worldw/de solar cells, electrical controls, and heat Photovo/taics Power Systems Market, the BDM and engines. Solarex Corporations (Draft report, May 1977). Ch. VII Impacts of Solar Energy ● 209

solar faciIities would result in larger produc- FOREIGN COMPETITION IN tion runs and more research, This should SOLAR TECHNOLOGIES reduce domestic prices and accelerate improvements made in devices sold in the Significant solar technologies have been United States, yielding the United States a developed in a number of other countries. long-term advantage, even if developing na- Japan, Israel, and Australia produce more tions began to produce their own systems in energy from the Sun each year than the a decade or so It is likely that foreign United States, primariIy because they have manufacturers would sometimes require used simple hot-water and space-heating U.S. assistance, for example, utilize U.S., devices for decades France, Germany, patents or Iicenses for solar devices, Japan, and perhaps Israel selI more solar equipment abroad a n n u a I I y than the U nited Estimates of a large potential foreign states market for solar energy are supported by recent studies conducted by the Department There are several reasons for this. First, of State. One study, published in November conventional energy in the United States has 1976, indicated a substantial potential been, for the most part, plentiful and inex- market for solar technologies in eight oil- pensive; consequently, this Nation has producing nations [Algeria, Indonesia, Iran, delayed emphasis on solar heating and hot Iraq, Mexico, Nigeria, Saudi Arabia, and water (except in Florida and southern Venezuela) The study showed that although California during the 1940’s and 1950’s) al I eight countries preferred manufacturing while countries such as Japan, Israel, and solar equipment themselves rather than im- Australia have been installing such devices porting it, none was making a sufficient for decades, Second, the United States commitment to solar research to produce spends proportionately more for research equipment which could compete with the than other countries with solar budgets, small solar electric-generating equipment most of which stress currently marketable and desalinization processes being technologies. Private industry in most other developed in the United States. State countries has been more deeply involved in Department studies have also indicated that solar technology than has its U.S. counter- a smaller but significant market for solar part, and it is private industry, not the devices exists in other oil-producing coun- Government, that usually determines an ex- tries and in underdeveloped oil-importing port market. Finally, the United States nations, This last group of countries, ac- spreads its financial resources among a cording to surveys, was anxious to develop broad range of solar technologies; many al I types of non petroleum energy sources other countries stress funding of fewer and willing to devote a substantial amount specialized projects, which leads to more of their capital if such sources have become rapid marketing of resuIts. economicalIy and technicalIy feasible. a [n the past year, France has doubled its Some i nd u st r i a I i z ed count r i es will solar budget to almost $10 million per year, develop their own solar energy industries putting special emphasis on developing 300 and, as a result, wilI not constitute a signifi- kW, 800 kW, and 3.5 MW solar electric sys- cant market for U.S exports The exception tems. West Germany, which spends about $6 may be certain high-technology compo- mill ion per year, also increased its funding ents. for solar energy substantially Japan is spending about $5 million per year in its government-sponsored Project Sunshine. Israel has boosted its solar commitment to 8 Mdrtln Prochnik, Of flcc of Nuclear Energy and about $2 mill ion. I ran has extended its solar Energy Pot ICI(JS, Department of State, private com- program, opening a 1 00-person solar in- mun I( at Ion, Mdrch 1977 stitute, Saudi Arabia has created a similar 210 Ž So/ar Techno/ogy to Today’s Energy Needs

center, although smaller, staffed by about in the process of locating a site for a solar 20 technologists. The Common Market has research institute with help from the United decided to build a 1 MW central thermal States and several European countries. power station, probably in Italy, and Spain is

THE IMPACT OF SOLAR ENERGY ON AMERICAN LABOR

Onsite solar technology appears to be difficult to deal with reliably, is how the more labor-intensive than contemporary technology wiII affect overalI manpower re- techniques for supplying energy; thus, in the quirements in the energy industry. Tables short term, the introduction of solar energy VI I-2 and VI I-3 compare the manpower re- devices might create jobs in trades now suf- quirements of a conventional coal-fired fering from serious unemployment. I n generating system with the manpower re- general, the new jobs will be distributed quired to construct and to operate each of widely across the country and wilI not re- two kinds of solar devices capable of pro- quire laborers to Iive in remote or temporary ducing equivalent amounts of energy. Only construction sites because most workers first order effects have been considered, and should be able to find jobs in areas close to the estimates made about solar devices are their homes. Work on solar equipment, for necessarily speculative. One overalI conclu- the most part, should necessitate only sim- sion seems inescapable, however: a large ple retraining programs, although there may fraction of the value of solar equipment is be shortages both of engineers and archi- attributable to direct labor costs. tects qualified to design solar equipment, and of operators trained in maintenance of The high labor intensity of solar equip- some of the larger and more sophisticated ment is not surprising, Most devices can be solar devices which have been proposed. constructed from relatively inexpensive material, and the small equipment exam- Assessing the long-term implication of ined here would not require extensive technological development on the work capital-carrying charges during construc- force, however, cannot be reliably under- tion. Factories for mass production of taken with con temporary economic photovoltaic devices, heat engines, and methods. Long-term labor impacts will de- other components of solar technologies will pend on forecasts of future growth rates probably employ sophisticated and expen- both in the economy and in U.S. energy sive equipment which will reduce labor in consumption — subjects about which there these industries, Much of the work of install- is great confusion and disagreement. ing solar equipment wiII continue to require Although making economic projections is direct onsite labor. hampered by imprecise methodology, it is possible at this point to outline some of the Table VI I-2 lists all labor requirements for critical issues which concern the effects of construction at the plant site, to build the solar energy development on labor. 800 MWe turbine generator in a factory, to operate the generating faciIity at an average of 60 per-cent of f u I I capacity for a period of MANPOWER REQUIREMENTS 30 years, to buiId and operate a coal mine large enough to support the plant, to trans- One of the most critical issues in port the 2.5 m i I I ion tons of coal per year evaluating the impact of a new energy needed to operate the pIant, and to con- technology on labor, and one of the most struct and maintain a transmission and Ch. VIl Impacts of Solar Energy . 211

Table VII-2. —Labor Requirements for a Conventional 800 MWe Coal Plant (in units of man hours per megawatt year) . . Operating Construction and Total maintenance — 800 MWe coal plant. ... 330 380 710 coal strip mine using western coal . . . 20 360 380 coal preparation plant. 3 290 293 coal transportation — 340 340 electric transmission 40 5 45 electrlc dlstribut!on 190 310 500 steel & concrete production 10 10 turbine/generator manufacturing. . . 170 0 170

Total ...... 763 1685 2348 — Assumptions: — 800 MWe coal plant operating at 60 percent peak capacitv for 30 years: — western’ coal’ strip mine with 525-miIe train line; — all data based on Bechtel data with the exception of the turbine generator manufacture. It was assumed that the turbine/generator cost of $150/kW of which 25 percent was labor and that this labor was paid at an average rate of $10/hr; — calculations divide the sum of construction manpower and 30 year operating manpower requirements by the total number of megawatt years of energy produced by the plant.

the range of labor requirements provided by

collector manufacturers contacted. It IS probable that the labor requirements of a mature solar industry will be close to the lower end of the range shown.

Table VII-3 presents an estimate of the labor required to build and maintain a flat- plate solar water heating system and a small tracking photovoltaic system in Albuquer- que, N. Mex. The hot water system requires 1.5 to 2.5 times more labor than the conventional coal-fired generating facility and even more if the utility must maintain a substantial faciIity for providing backup power. The range shown for the solar devices reflects Table VII-3. — Labor Requirements of Two Types of Distributed Solar Energy Systems (in man hours per megawatt year)

Operating & Construction maintenance Total

1. Solar hot water heaters (8m2 flat plate) ., — manufacture collector 800-2500 o 800-2500 —install collector. . . . . 1200 0 1200 —routine O&M ...... — 1200 1200

Total for hot water system ● 2000-3700 1200 3200-4900 Total for hot water system including backup 2340-4040 — 3540-5240

Il. Tracking silicon photovoltalc system: a. Electrlc only (50 m2) — manufacture colIector and cells ...... 2600-3300 — 2600-3300 — install collector. . . . . 1800-4600 — 1800-4600 —operate system...... 6800 6800

Total for tracking photovoltaic system ...... 4400-7900 6800 11200-14700 Total for tracking photovoltaic system including backup 4740-8240 — 11540-15040 b. Electric + 0.29-Thermal (Including backup). . . . . 2240-3740 3000 5240-6740 c. Electric + Thermal (Including backup). . . . . 1130-1750 1240 2370-2990

Assumptions: — 20 year system life; — installation includes 75 feet of piping costing 0.11 MH/ft to Install; — flat plates installed for 1.3 MH/m and tracking col- Iector installed for 1.3-3.33 MH/m2; — cells assumed to be 18 percent efficient, optical efficiency 80 percent. — labor for providing backup power is assumed to be 50% of the construction labor shown in table Vll-2— (e. g., 340 man-hours/ MW-year) — flat plates assumed to provide 930 kWh/m2 -yr (Albuquerque); cells provide 320 kWh/m2-yr electric and 1450 kWh/m2-yr thermal for PV system (Albuquerque); O&M labor for PV system assumed to be 0.25 hrs/m2-yr (see table Xl-7); — flat plate manufacturing labor based on data from several collector manufacturers; — concentrator manufacturing labor assumed to be .024 MH/lb of collector for PV concentrator given in table VII-7 (with concrete and sand excluded) with the labor to produce the raw materials added; .024 MH/lb IS approximate labor Input for automobile manufacturing based on employment and production for 1973 given in 1976 Sfatisfica/ Abstract of the United States, U.S. Dept. of Commerce, Bureau of the Census, pp. 369, 791. Ch. VIl Impacts of Solar Energy ● 213

Geographic Distribution

Employment in installation and operation of solar equipment can be expected to be Some collector designs (e. g., plastic col- distributed over a large part of the country. lectors) will almost certainly require less Initial installations of solar equipment are manufacturing labor but they will probably likely to occur in places with high insola- require more maintenance labor, while tion — the South and Southwest, Locations other designs which require less material with relatively low levels of sunlight, such as (e.g., tubular designs) may require more the Northeast, however, tend to have high manufacturing labor than simple flat-plate energy prices, Thus, while low insolation systems. levels make solar energy in the North expensive, competing energy sources are also expensive, so the net economic competitiveness of solar devices may be as high in the North as in more favorable climates, Employment in installing solar energy is, therefore, likely to be as geographically dispersed as the building industry.

One thing about solar employment seems clear— none of the small solar devices considered in this report wilI require the major The labor requirements per unit of solar dislocation of a work force, or the establish- energy delivered would be higher in areas of ment of temporary work camps as may be the country which do not receive as much required for construction of a pipeline, an sunshine as Albuquerque since each unit offshore drilIing operation, or a large central area of colIector wouId produce less output. generating facility in a remote location. The relatively small solar devices analyzed here It should also be noted that onsite will provide employment in close proximity systems which rely on utiIity systems for to where workers presently Iive, and there- backup would probably not reduce the fore will avoid the social disruptions asso- labor requirements for transmission and dis- ciated with large influxes of temporary tribution systems significantly. This is impor- workers. tant since a large fraction of the labor required by conventional utilities is due to Unlike most major manufacturing these energy distribution systems. A shift facilities, solar manufacturing at present is toward decentraIized solar energy systems spread across the country in literalIy hun- couId, therefore resuIt in repIacing cen- dreds of small companies. The future of tralized facilities with solar units requiring these businesses, however, is very uncertain. greater amounts of labor while leaving the If the demand for solar equipment increases labor-intensive distribution systems intact. substantially, the field may be dominated by

a small number of large manufacturing firms, much as the manufacturing of con-

ventional heating and cooling equipment is SOME QUALITATIVE IMPACTS dominated by a small number of firms. On the other hand, solar devices may be While the analysis of the overall labor re- designed for special climates and suffi- quirements of solar energy is very primitive, ciently site-specific for manufacturing to re- it is possible to be somewhat more confi- main geographically dispersed, much as dent about some qualitative aspects of solar facilities for manufacturing modular homes energy’s impact on the work force. are today. It seems clear that because of the 214 ● Solar Technology to Today’s Energy Needs

sophisticated technology employed, the to conventional boilers and generators, the manufacturing of components such as solar equipment would simply add work in photovoltaic devices, heat engines, and these areas at each installation, There may concentrating devices will occur in a be a shortage of engineers with adequate relatively small number of facilities. knowledge in areas critical to onsite power in general and solar devices in particular, Stability of Labor Demand Associated Designing a reliable and efficient onsite With Solar Equipment device for a large installation (such as an apartment or industry) requires experience If a major demand develops for solar with other types of equipment not now con- energy, it is Iikely that employment in the ventionally used in utilities or building area will be as stable as work in any typical building trade; the solar equipment will simply add jobs at each construction site. If a major retrofit market develops, there could also be major employment opportunities in this area; maintenance of solar equipment will also provide a stable source of jobs. Employment opportunities in manufacturing are more difficult to define, since the pattern of growth in the industry is presently Skill Levels Required unpredictable. Work opportunities will in- Most of the employment directly created clude glazing, metal extrusion, component by a shift to solar energy will be in installa- assembly, and chemical processing (for pho- tion of the equipment by the conventional toelectric devices, selective surface forma- building trades, and in the creation of new tion, storage systems, etc.). It is difficult to manufacturing industries. The skills re- anticipate whether the employment will be quired for installation of the equipment will created in a large number of dispersed fabri- be very similar to those required for conven- cating facilities, in large central plants, or in tional construction projects, although some both. brief training programs will undoubtedly be The skills required to maintain the type of desirable to familiarize workers with the simple solar equipment installed on homes new equipment and its installation. Most of and small apartments will be similar to the work will be in framing roofs, laying those required for conventional appliance footings, plumbing collectors and storage maintenance of utility gas and electric tanks, excavating trenches and pits for pipe- power equipment. Most of the personnel in runs and storage tanks, installing sheet these professions will require additional metal ducting, insulating pipes and tanks, specialized training in solar technology. and installing electronic control units. The There is a serious shortage of persons with work will be nearly identical to the installa- the skills needed to operate intermediate- tion of sophisticated air-conditioning and sized solar or conventional onsite energy heating systems in conventional buildings. equipment. Owners of small total energy Larger solar installations, such as those systems report difficulty in finding and serving groups of buildings and large in- holding persons trained in operation and dustrial operations, are Iikely to require maintenance of engines and heat recovery supervisors, managers, draftsmen, designers, units, energy control switching, and other and engineers in roughly the same propor- associated equipment. Maintenance of a so- tion as these skills are required in the con- phisticated collector system will present struction of conventional power-generating similar problems. Many now employed in facilities. In fact, since many large onsite the operation of total energy systems solar facilities are Iikely to be supplemental learned the requisite skills from the U.S. Ch. VIl Impacts of So/ar Energy Ž 215

military services. Such training appears dif- solar technology would initially affect only ficult to obtain in private industry. fuel utilization, and would affect transmission and distribution requirements only in Tables VI I-4 and VI I-5 demonstrate jobs an extreme case where all or much of local which must now be done to support conven- energy needs are met with solar equipment tional electric generating equipment. The It should not be assumed that an increase in impact of solar equipment on jobs will de- solar utilization would necessarily replace pend on the extent to which solar devices any of the employment indicated in tables displace fuel consumption (replacing jobs in VI I-4 and VI I-5, The expected increase in mining with jobs in solar technologies), the U.S. and worldwide coal demand is likely to extent to which the technology would cut be so large that employment in mining the demand for peak generating capacity would be unaffected by an expected pene- (replacing jobs in constructing and maintain- tration of solar energy into the market, ing generating equipment with jobs in solar Several observations can be made on the technologies), and the extent to which the basis of the tables, however: need for transmission and distribution equipment wouId be reduced. These effects are listed in the order of Ž SmalI solar installations are Iikely to their likelihood. It is most probable that employ more blue collar workers than

Table VIl-4.—Skills Required for Constructing a Coal-Fired Electric Generating Plant and Operating the System Over a 30-Year Period

1. Skills Required for Plant Construction (as a percentage of the 3,576 man-years required to construct the plant and the transmission and distribution network) — Coal-Fired Electric Transmission and Generating Plant Distribution Facilities Total

Non-manual construction 9% 13% 22% work . . (63°/0 engineers and 25% draftsmen and designers) 25% draftsmen and designers) Manual construction work . 49% 29% 760/0 (variety of trades) (mostly electricians)

Total construction work . . ., 216 ● So/ar Technology to Today’s Energy Needs

Table VI I-5.— Detailed Breakdown of Skills Required for Conventional Electric System*

(man-years per 800 MWe coal-fired plant and associated distribution and fuel facilities)

Annual Opera-

i I

1110 1110 31 186 217 218 254 472 67 83 150 I I 33 I , 6 6 6 6 3 3 4 269 1474 523 1997 109 60 271 8 18 1087 1148 240 240 12 396 2861 3656

I 240 12 450 12 36 843 1781 8

20 16 60 8032 81 10893

“ Based on Information In Manpower, Mater/a/s and Cap/ta/ Costs /or .Energy Re/a(ed Fac~/~fles, John K Hogle, et al , Bechtel Corp for Brookhaven National Laboratory Associated Unlvers(l(es, Inc , Contract No 354617S, April 1976

professional employees. Solar installa- table VI I-4 is closer to 1 to 3, The larger tions on individual buildings typically industrial and community solar systems require one supervisor for each 10 would, however, require much more workmen, 9 while the ratio for the con- professional work. ventional coal equipment shown in Nearly 50 percent of the jobs associated with operating and main- q FEA Project /ncjependence Task Force Labor taining conventional equipment is asso- Report ciated with coal mining and transporta- Ch. VIl Impacts of Solar Energy ● 217

tion. Jobs in these sectors could be the North and Northeast ‘‘) These are regions replaced with jobs in repair and where energy prices have risen very rapidIy maintenance of onsite equipment. in recent years. I t is possible that sizable near-term markets for solar equipment can ● About 40 percent of the work required be found in these areas in spite of their to build a conventional electric system re ativeIy unfavorabIe cIimates. and 30 percent of the work required to maintain it is associated with distribu- I n 1970, the plumbers and pipefitters had tion equipment, which is unlikely to be a nationwide unemployment rate similar to affected by solar technology. that of the sheet metal workers. A potential labor problem associated with implementa- Working Conditions tion of solar technology is the question of which union will subsume the categories of newly created jobs. Until recently there Expansion of the solar energy industry have been few solar installations so that few should not raise serious health or occupa- u n ions have staked out terri toritoriaI prerog- tional hazards, but some of the possible atives. For the most part, the solar energy problems are discussed below. The manu- field is still wide open to jurisdictional com- facture of some photovoltaic devices petition. The situation can be expected to employs cadmium and arsenic compounds change as more work in the area becomes which couId present hazards to workers available. An arrangement has already been assembling these units. Manufacture of negotiated between the Sheet Metal plexiglass and other plastics used in Workers and the United Association of photovoltaic devices can also involve han- Plumbers and Pipefitters which calls for dling potentially harmful chemicals. These joint crews in the installation of hot air col- manufacturing hazards are not unique, how- lectors using liquid storage systems, Juris- ever, because these compounds are widely dictional disputes could be a serious prob- used in other industries. Some steam-fitting lem in other areas, however, unless al I issues jobs will involve high-pressure steam lines, can be settled as amicably as this one has and some proposed thermal storage meth- apparently been. ods will require very hot oiIs, possibly explosive or toxic. These issues deserve serious Generally, union officials feel that an up- attention before such instalIations become surge of solar construction and instalIation common place. Devices using hazardous would radically alter the number, not the material may only be employed in larger, types of jobs available to union members. more centralized solar facilities and are Firms that now produce heating, ventilating, unlikely to be found in onsite residential and air-conditioning equipment— many of systems. Replacing jobs in coal mining for them already active in solar collector those in solar equipment maintenance, construction — would simply expand their however, would probably result in overall operations. Any new firms established improved working conditions. would be unionized in conventional ways.

While labor has occasionally resisted the Organized Labor introduction of new technologies into the building industry, this resistance has always organized labor is enthusiastic about been directed at technologies which reduce solar energy’s potential for creating jobs. jobs on each building site or which trans- Like many other construction trade unions, ferred employment from one building trade the sheet metal workers (SMWIA) have been to another. The disputes associated with the hard hit by unemployment: the SMWIA has a national unemployment rate of 30 percent to 35 percent, with unemployment reaching ‘” 1~ M( Monlgle, Siilhl’ I A, prlv,~te t ommu n I( ,~t Ion, 50 percent to 60 percent in some areas of 1977

28-842 0 -15 218 ● So/ar Technology to Today’s Energy Needs

introduction of plastic plumbing, prehung not expected to be sufficient to eliminate doors, and metal studs all resulted from one unemployment, labor-intensive industries of these effects. Solar equipment would add wiII be beneficial to both labor and society work at each site without displacing work in by productively employing a larger fraction other areas, It is, therefore, difficult to imag- of the work force. ine any group with a motive to resist its en- Other questions which must be addressed try into the market. incIude:

1. To what extent would the energy pro- LONG-TERM IMPACTS duced by solar equipment displace imports, nuclear, or indigenous fuel sup- The overall impact of generating a sub- plies? To what extent will solar energy stantial fraction of U.S. energy from small fulfill energy needs that might not solar devices is hard to assess, since current otherwise be met? (If solar energy economic theory has no satisfactory method fiIled such needs, employment could for such analysis. None of the major price grow i n areas of the economy not equilibrium models used to determine the otherwise possIble.) future of U.S. energy supply and demand adequately treat employment issues; most 2, To what extent will solar energy make the overwhelmingly simple assump- sources be able to reduce the need for tion that there will be full employment dur- instalIing additional electric gener- ing the entire period analyzed. As a result, ating facilities as well as reduce the many of these models tend to ignore the in- demand for fuel? fluence of alternative energy strategies on 3. If imports are reduced, and funds in- unemployment, The difficulties of predict- vested instead in U, S. solar industries, ing economic impacts are magnified by the how much direct and indirect employ- lack of information necessary to translate a ment would be created? How much workable theory or model into useful policy. wouId employment be reduced in in- In the absence of an adequate dustries now benefiting from the ex- methodology, the most critical questions in- port market stimulated by our pur- volving the impact of solar technologies on chase of foreign fuels? the work force cannot be answered with cer- 4. What kinds of growth rates can be ex- tainty. An example of one difficulty can be pected i n energy sources other than seen in the problems associated with inter- solar energy? W i I I this growth rate preting the implications of labor intensity. If be constrained by a shortage of rapid rates of growth are expected in both capital, resources, and demand, or by the U.S. economy in general and the energy a shortage of critical skills? Would production sector in particular, and if solar energy compete directly for unemployment is expected to be very low as scarce resources or would it be able to a result, any shift to a labor-intensive tap other capital or labor supplies? technology like solar energy could prevent wages from keeping pace with growth in 5. What kind of work force dislocations other sections of the economy, An industry could be expected in a shift from one with high labor intensity requires more man- energy source to another? Would new power for the same output than industries skills not now available in the building with low labor intensity. As a result, the trades be demanded? What kinds of average wage paid per worker must be lower transient unemployment could be ex- for the labor-intensive process. If growth is pected? Ch. VIl Impacts of Solar Energy ● 219

NET ENERGY USE OF SOLAR EQUIPMENT

Clearly solar energy devices cannot pro- Energy requirements of silicon cells could vide a useful contribution to the world’s probably be reduced below the lowest energy problems if more energy is used to number shown in the table if a technique is construct the devices than can be extracted developed for manufacturing thin cells from usefully from them. A brief examination of amorphous silicon material. The amorphous this question indicates that solar equipment cells may require as little as 1 percent of the can clearly be a net producer of energy. Un- silicon required in contemporary cells. fortunately, no straightforward metho- SiIicon celIs now require an energy consum- dology has been developed for computing ing crystal growing process and the resuIting the total amount of energy consumed in crystals must be sliced into wafers. Both manufacturing, instalIing, and operating a processes waste a considerable amount of piece of mechanical equipment. Two dif- s i I icon, ferent techniques will be used here: 1 ) com- It should also be possible to reduce the puting the primary energy required to amount of energy required in the manufac- manufacture the materials used in the solar ture of many other of the products shown in collectors and conversion devices, and 2) table VI I-8 if close attention is paid to computing the energy used by assuming that energy conservation. The energy content of the energy used per unit investment in solar U.S. steel, for example, has declined by 25 equipment is the same as the national percent since 1947, and the Germans use average energy use per unit of investment. about 68 percent as much energy as the The results of both approaches are shown in United States uses to manufacture stee].11 table VI I-6 The Aluminum Company of America (ALCOA) has apparently developed a smelt- PRIMARY ENERGY REQUIREMENTS ing process capable of nearly halving the energy used to manufacture alum inure. 2 It can be seen from table VI 1-6, however, that acceptable “energy-payback” times can be achieved even if the materials are manufactured using 1970 U.S. technology. It must be remembered that the energy content of the solar devices shown does not include any of the energy required in factories which assemble the collectors, the trucks which deliver the materials to the factory and the collectors to the installation site, the food consumed by installation workers, or a number of other “secondary” sources of consumption,

‘‘ M H Ross and R H Wllllams, Energy and Economic Growth, printed by the )olnt E conom[c Committee In Achlevlng the Goals of the Employment Act of 1946— Thirteenth Anniversary Review, Volume 2, Energy Paper No 2, Aug 31,1971 (91-592), p 7 ‘ 2 J C Meyers, et al , Energy ConSUr-nptIOn in Manufacturing, report prepared by the Conference Board for the Energy Policy Project of the Ford Foun- dation, Ball lnger, Cambridge, Mass , 1974 220 ● Solar Technology to Today’s Energy Needs

Table VI I-6 .—Energy Payback Relations for Onsite Solar Conversion Systems in Albuquerque

(See Tables VI I-7 & 8 for Assumptions)

Stirling Concentrating Flat plate Flat plate Pond thermal engine in photovoltaic photovoltaic thermal colIector tracking system array colIector dish (100x)

1. energy required to manufacture one square meter of collecting system (kWh/m2 450 425*-525 301 ● -8844 185-320 16-250 2. energy produced by the s stem annually 2 (kWh/m/year) —thermal ...... 1050 1440 — 930 400-800 —electrical + . . . . 2069 1100 1000 — — (primary energy) equivalent) 3. payback time computed from (1) and (2) above (in months) —payback from thermal energy ...... 5.1 4.4 (3.5)* — 2.4-4.1 0.5-3.8 —payback from electric energy ...... 2.6 5.7 (4.6)* 106 (3.6)* — — —payback from total energy ...... 1.7 2.5 (2.0)’ 2.4-4.1 0.5-3.8 4. allowed cost of system (in $/m2) for a 1- year energy payback time assuming that solar devices use the same energy input per dollar of initial cost as the U.S. average of new investments —thermal ...... 88 120 77 33-66 —electrical 172 291 83 (700$/kW) o —

—total ...... 260 411 83 77 33-66

● Assumes advanced manufacturing techniques. + Average efficiency of electric generation and transmission distribution assumed to be 290/..

NOTES: It IS assumed that the engine used IS 32% efftclent and that the optical systems In the concentrators are 807. efflctent Flat. plate slllcon cell arrays are assumed to be 120/. efflclent and concentrator cells are 20!/. efflclent (See volume 11, chapter IV for detailed assumptions )

ENERGY USE PER DOLLAR OF GNP the United States about 12 kWh were consumed for each added dollar of GNP. The One technique for counting all of the average kWh consumed per dollar of GNP energy which might enter a solar energy has averaged 9-10 during the past few years. system from secondary sources is to ex- (All quantities in 1976 dollars.) The link be- amine the average consumption of energy in tween GNP and energy consumption is the the United States per unit of GNP. 3 An examination of the incremental change in energy consumption per incremental change ‘ ‘ Technique suggested by Dr R D Huntoon, Presi- in GNP over the past 20 years shows that in dent, MEMO, Silver Spring, Md. Ch. VIl Impacts of Solar Energy ● 221

Table Vll-7.– Materials Required in Solar Energy Devices (kg/m 2)

Concentrator Concentrator Flat plate Flat plate Pond (thermal) + stirling + silicon s i I icon (thermal only) only engine photovoltaic photovoltaic

Steel . . . 30 27 0-3 4-8 0 Glass . . . 16 16 6 6-12 0 Concrete 79 79 0 0 0-40 Sand ...... 115 115 0 0 0 Polyurethane 0.3 0.3 0 0 0.6-6 Copper . . . . 0.4 0.4 0 4-8 0 Silicon cells . 0 0.0024 ’-0.007 0.24 ’-0.71 o 0

“Using advanced manufacturing techmques (not using amorphous slllcon) Energy Content SOURCES Concentrator data from H{ldebrandt, A F , and L. L Vant-Hull, ““Power with Heliostat s,” Science 197 (1977). p 1139 SIIIcon data from L P Hunt ( Dow Cormng Corp I Total Energy Use in the Production of SI I Icon Solar Cells from Raw Materials to F(n [shed Product The Conference Record of /he 72fh /EEE Photovo/ta/c S’pec/a//sfs Conference— 7976 Baton Rouge La Nuvember 1976 p 349 Other CO I Iector data from man ufaclurers

Table Vll-8.— Primary Energy Required to Produce Component Materials for Solar and Conventional Power Systems

Total energy require- Source of input Energy (in percent) ment Fuel (kWh/kg) Coal Oil Gas Electrlcity byproducts

Polyvinyl chloride resin, . 22 9.1 19.4 55,6 23,4 (7.5) Portland cement —wet process 2.1 30.4 13.7 39.9 16.0 — —dry process. . . 1.9 42.6 8.0 32.4 17.0 — Copper ...... 30 10.1 13.5 38.4 38.0 — Steel ... ., 5.1 81.1 6.6 13.5 8.4 (9.6) Glass containers . . 4.8 35.8 7.3 48.8 14.5 (6.4) Silicon . . . . . 12400- – – – ~100 — 1050

SOURCES The Data Base The Potential for Energy Conversion In Nine Selected Industries, FEA, June 1974, p 20

Silicon data from Hunt, L P subject of consider-able contention 4 but it is does the United States, although an ex- c I ear that the ratio is to some extent the am i nation of recent Swedish data seems to function of the society West Germany and indicate that since the late 1960’s the in- Sweden, for example, consume about two- cremental amount of energy consumption thirds as much energy per unit of GNP as per incremental amount of GNP in that country has been close to that of the United States. The statistics cited in the previous 222 Ž Solar Technology to Today’s Energy Needs

section at least indicate that it is possible to Since the allowed costs computed in this shift energy consumption from the manu- may correspond to costs which can prob- facture of primary materials to other areas ably be achieved with solar devices, the of the economy— areas where energy con- results of this method are roughly consistent sumption per unit of value may not be as with the previous method; both indicating great. that net energy should not present a barrier to the use of solar energy. (It should be noticed that if it is assumed that solar The allowable cost for solar energy manufacturing is more energy intensive than systems capable of “paying back” the an average process in the economy by some energy invested in them in one year (assum- ratio R. then a solar system with a cost equal ing the current U.S. ratio of incremental to the allowed cost shown in the table would energy to incremental GNP) is shown in require R years to pay back the energy it table VI i-6. contain s.)

THE IMPACT OF ONSITE ENERGY ON THE ENVIRONMENT

While solar energy equipment is not free Solar energy devices can change the of adverse environmental effects, providing amount of energy absorbed by the Earth’s energy from sunlight will have a much surface, and could have some small effect smaller environmental impact than conven- on the local thermal balance. The effect, tional sources providing equivalent amounts however, would typically be no greater than of energy. The primary environmental effect the change in local climate produced by of utilizing onsite solar energy will be reduc- covering land with equivalent areas of tion of the potential adverse environmental highways, buildings, or parking lots. effects associated with other energy In addition to these primary effects, a sources. number of the specific storage and energy The negative environmental effects of solar energy devices stem primarily from tions of this study wouldl have adverse two sources: (1) land use requirements, environmental effects because of noise, which could compete with other, more at- local heat and other minor emissions, and tractive uses of land, especially near use of toxic chemicals. These effects are populated areas, and (2) emissions asso- discussed in the chapers about individual ciated with the mining and manufacture of technologies. the materials used to manufacture solar equipment (manufactured steel, glass, DIRECT ENVIRONMENTAL EFFECTS alum inure, etc.). In general, solar devices manufactured using conventional energy Emissions Associated With Operating sources, create more pollutants while they Energy Equipment are being manufactured than an equivalent The primary direct impact of solar energy conventional plant (primarily because solar on the local environment will be the equipment requires a greater capital invest- elimination of adverse environmental ef- ment per unit of output) but this assymetry fects attributable to the burning of conven- is outweighed by the fact that the solar tional fossil fuels. The damage done to the devices produce much less pollution during environment by conventional energy their operational lifetimes. The net emis- sources is well known, although the magni- sions associated with solar devices are much tude of the long-term health and climatic ef- smaller than those of conventional fuel- fects is still being determined. The large burning plants. number of ways in which producing electric Ch. Vll Impacts of Solar Energy Ž 223

energy from a coal-f i red steam plant, for exchange on agricultural production and the ample, can adversely affect the environ- polar caps is difficult to predict. In addition, ment are suggested below: the effect of using solar energy to replace gas, oil, or wood home space and water Strip mining required to harvest the heating would be to reduce the thermal and coal resources can permanently change chemical pollution associated with these local topgraphy, alter stream beds, means. disrupt or contaminate ground water, and produce large amounts of rubble, Negative environmental effects can also no i se, and dust in m i n i ng areas. be expected from other conventional ap- Reclamation can be difficult, par- proaches to electric generators. Electricity ticularly in areas where water shortages provided from nuclear fission devices would exist. Underground mines have fewer avoid many of the environmental impacts external effects, but can create safety associated with the consumption of coal, and health problems for miners but the nuclear process produces thermal pollution and radioactive wastes with long Processing the coal can produce large lifetimes. Hydroelectric facilities eliminate amounts of solid waste and cause toxic most of the negative impacts of other elec- chemicals to be released into local tric sources, but can have a major impact on water. land use because of the need to flood land Transporting coal can require the use areas. Natural gas has fewer adverse en- of trains which burn oiI or use electri- vironmental i m pacts, but reserves are city from some fossil source In some drastically depleted, cases new rail Iines will be required. A comprehensive description of all en- Burning coal produces large amounts vironmental impacts of conventional energy of airborne particuIates, sulphur and sources is beyond the scope of the present nirogen compounds, hydrocarbons, study, but a brief comparison of the impact carbon monoxide, and a variety of on air and water quality by solar and con- other a i r contaminants In addition, ventional energy sources is shown on table large amounts of solid waste are pro- VlI-9). As a standard of comparison, table duced either as coal ash or as by- VI I-9 also shows the energy needed by a products of removing chemicals from typical single family detached residence in the smokestacks of the plants Omaha, Nebr., for 1 year (The exact charac-

Once generated, the electricity must be volume 11, chapter IV. It can be seen that transported along extensive networks use of natural gas is the environmentally of transmission and distribution lines preferred approach of providing heat and hot water to the house Even the solar total

Several recent studies have also indicated that continued large-scale consumption of fossil fuels could release so much carbon dioxide into the atmosphere that the gas wouId create aII green house” effect, raising the average temperature of the Earth’s atmosphere by as much as 6 “C (11 “F) i n 100 to 200 years.15 The impact of such a climate A home which burns synthetic gas would be responsible for considerably more air and water poIlution than a home supplied with 224 . Solar Technology to Today's Energy Needs

Table Vll-9.—Ernissions Associated With the Energy Requirements of a Single Family House in Omaha, Nebr.

(1 3-1 20) 13-120 (27-320) (1 3-1 20) 50-440

160-330 140-480 9 50-510

130-260 110-390 7 40-400

100-210 90-300 5 35-320

80-160 70240 4 27-250

60-120 50-180 3 20-190

50-100 40-150 3 20-160

NOTES — coal gass(flcatlon from unit fixed bed h[gh BTU plan! (see Synthellc Fuels Commerc(al(zatlon Program OP clt 1 net conversion eff(ctency of elecfrlc qenerat(on assumed to be O 29 and coal assumed to have 12000 BI u I b — coal plant uses f Iue gas scrubber SOURCE The numbers on this chafl are based In parl on Information prov(ded by K R Smlfh John Weyanl and John Holdren Fvd/ud/IcIr? of Corven/oo,) Powe/ Syslerns Un,v of Cal at Berkeley July 1975. p 119

processed to produce the synthetic gas. ing units releases 160 to 330 Ibs. of nitrogen Emission levels in this case, however, are oxides, 140 to 480 Ibs. of sulphur oxides, 9 stiII below those associated with burning Ibs. of hydrocarbons, 50 to 630 Ibs. of par- coal directly for use in electric heating. ticulate, and nearly 2 tons of solid waste per year. (These amounts include all direct As the table shows, any of the coal-based emissions associated with mining, process- processes for producing residential energy ing, transporting, and burning coal at gener- result in the release of large amounts of ating sites. ) The solar devices reduce these emissions into the environment, For exam- releases in direct proportion to the amount ple, the house heated with baseboard heat- they reduce electricity consumption. Ch. VIl Impacts of Solar Energy ● 225

The analysis has only considered en- VI I-10. Table VI I-11 presents the results of vironmental impacts resulting directly from this analysis by indicating the number of the burning of fossil fuels in mining, trans- months that several types of solar energy port, or generating processes associated systems would have to operate before the with the production and transmission of emissions associated with providing an energy A number of processes indirectly amount of energy equivalent to the energy connected to the construction and opera- derived from the solar device equals the tion of both conventional and solar equip- amount of emissions associated with the ment could also have adverse environmen- manufacture of the solar device. (The con- tal effects — mining and refining materials ventional system used for comparison is a used to fabricate generating devices, coal-fired electric generator. ) The resuIts are transport equipment, and other energy pro- roughly equivalent to the “energy-payback” duction apparatus. All of these require times computed previously. energy, and the production of the energy The tables show once again the im- resuIts in environmental damage. These portance of reducing the energy consumed secondary impacts are extremely clifficuIt to in manufacturing s i I icon photovoltaic analyze quantitatively because an accurate devices used without concentrators. assessment would require a model broad enough to encompass the entire economy. If solar energy or other energy equipment in- PROBLEMS ASSOCIATED WITH creases the demand for steel, it is not clear ONSITE FOSSIL BACKUP whether the indirect environ mental effects Solar energy systems which rely on onsite can be computed simply by calculating the combustion of fossil fuels as backup for energy required to construct this steel and solar space heating and air-conditioning or the damage charged to the account of the electric-generating equipment would have a energy source responsible, i.e., solar, since direct impact on air and water quality since the use of steel for energy equipment might emissions would be released whenever the reduce the use of steel for other types of backup systems were used. The total equipment. Alternatively, the production of amount of gaseous and solid polIutants pro- additional energy could increase demand duced by such onsite backup might be no for goods in the economy and in turn larger than the amounts produced by large stimulate energy consumption, thus increas- centralized generating plants providing ing environmental damage by other sources. equivalent backup services Emissions from the onsite combustion would generally be Emissions Associated With the Manufacture released much closer to popuIated areas of Solar Energy Equipment and, as a result, pollutants could have a Since solar energy equipment typically greater impact on health. has a higher initial cost than conventional systems, it is not surprising to find that ONSITE SOLAR ENERGY SYSTEMS larger amounts of pollution are associated AND LAND USE with their manufacture (assuming that the solar devices are constructed using energy The collectors employed in many of the derived from conventional energy sources). onsite solar energy devices discussed in this An estimate of the emissions associated paper can be either conveniently located on with the manufacture of various types of the roofs of serviced buildings or gracefully solar energy devices capable of producing integrated into the surrounding landscape. the same annual energy output can be ob- In a number of situations this will be im- tained by combining the information in possible, and collector fields will require tables VI I-7 and VI I-8 in the previous section and area which could probably be put to with the estimates of emissions associated other purposes. The resulting competition with different energy sources shown in table for land will be particularly serious for on- 226 Ž Solar Technology to Today’s Energy Needs

Table Vll-10.—Primary Emissions Associated With Energy Resources Available for Residential, Commercial, and Industrial Consumers (pounds per thousand kWh of heating value reaching consumption site)

Partic- Waste

S02 NOX CO HC ulates Solids Reference — 1. Residential systems —Natural gas . nil 0.3 0.7 0.03 nil nil (1) —Oil (0.2%` sulphur) . . . . 0.75 0.3 0.10 0.06 0.10 nil (1) —Electricity (from a ., 2.8- 3.3- 0.14- 0.11- 1,1- 431- (2) coal-fired baseload 9.6 6.6 0.6 0.19 10.2 533

generating plant) ● —Synthetic gas ., . . . . 0.22- 0.75- 70.10 0.063 - 0.49- 106- (1) 1.0 1.73 1.4 0.126 5,78 199 (3),(4), Il. Commercial and industrial systems —Natural gas nil 0.34 0.68 0.03 nil nil (1) –Oil ...... 0.75 1.71 1,71 0.68 0.34 nil (1) —Coal (western-stoker) 3.07 1.88 0,20 0.06 16.0 28.3 (1) —Coal (high sulphur) 4.10 1.71 2,39 0.06 0.20 123.9 (1)

“Assumes a Ilme-scrub&r, flue-gas, desulfunzatlon system. SOURCES: 1 Evaluation of the Feaslblllty for Widespread Introduction of Coal Into the Res{dentla[ and commercial .% CtOrS, Voiume 1, prepared by the EXXON Research and Engineering company for the Center fOr Environmental Qualltv Draft report, dated April 1977, p. 8 2- Evaluation of Conventional Power Systems, prepared by the Energy and Resources Program of the Unwerslty of California at Berkeley. July 1975, P 119 3 Kirk R Smith, John Weyant and John f-foldren ” Evaluation of Conventional Power Systems, Unlverslty of Call fornw at Berkeley, July 1975, P 136 4 Synthetic Fuels Commerclallzatlon Program Draft Environmental Statement, Synfuels Interagency Task Force on Synthetic Fuels, Volume IV, December 1975, PP IV-12 and IV-40

Table VIl-11 .–” Payback Time” for the Emissions Associated With the Manufacture of Solar Energy Systems

(expressed as the number of months the system must operate to displace energy which, if generated in a coal-burning electric generating facility equipped with a scrubber, would equal the emissions associated with the manufacture of the solar device)*

Solar Energy System

Pond Flat-plate Flat-plate Concentra- Concentrator with mission Type (thermal (thermal (silicon ing photo- high efficiency heat only) (only) photovoltaic) voltaic with engine. siIicon cells (electric only electric only thermal only

1. S0 2 ...... 03-1.4 0.6-1.1 3.3-106 6.1 2.9 1,1

2. NOX ...... 05-1,8 0.6-1.3 3.4-106 6.0 2.8 1.1 3. co ...... 0.5-15 3.7-7.5 5.1-109 26 14 5.1 4. Hydrocarbons. 0.3-8.0 2.0-4.1 3.9-109 15 7.6 2.9 5. Particulate. . . .08-4.4 1,7-3.4 3.7-108 24 13 5.0 6. Waste solids . . .02-0.6 0.3-0.6 3.2-106 2.5 0.9 0.3

‘These t(mes assume that emlsslons associated vwfh eleclrlc generation are the medan of the values given In table Vll 10 Ch. VII Impacts of So/ar Energy . 227

site solar systems where the required Iand is solar orientations would be extremely valu- close to populated areas. The land clearing able in assessing the potential market for required for collector fields under these cir- retrofitting existing structures with solar cumstances and the denial of alternative equipment. uses of open land close to Iiving areas con- Orienting new buildings to maximize op- stitute by far the largest negative impacts of portunities for collection of available this type of onsite solar technology. Conven- sunlight can create problems. I n most new tional energy sources also require substan- communities the orientation and placement tial land areas for mining, and for generating of buildings is dictated by the location of and transmitting power, but much less land sewers, water Iines, electric mains, local is required per unit of energy produced and topography, main access roads, etc. The the land, for the most part, is remote from direction of the Sun is rarely a considera- densely populated areas. tion. Proper orientation of buildings for The land use issues cannot be dealt with solar energy purposes could increase the in general terms, The eventual outcome of cost of houses in the community; for exam- each case wilI depend on the skill and imag- ple, services for providing utilities might ination of architects and planners as welI as have to cover greater distances, driveways the tastes and values of the individuals and might have to be extended to permit cars to communities served by solar equipment. enter garages or carports which were not facing the street, etc. These, and other Negative impacts of collector fields on aspects of community design, wouId pro- land use will be evaluated in three main mote energy conservation which inevitably areas: will become more important to buyers as ● building orientation and Iandscapi ng the price of energy increases (see figure VII-3). ● community design In some situations a building constructed Ž the environmental effects of colI ector to take maximum advantage of the Sun will fields. not supply enough roof or wall area for the The following discussion will point out required collectors. The site itself may be some of the anticipated problems in this shadowed during the day, or basic require- field, and outline some possible techniques ments of the building may limit available for resolving difficuIties. alternatives. I n a highrise buiIding, for example, the roof area will not be adequate for Land Use Impacts Associated With Building more than a simple solar hot water system, Orientation and Landscaping but more area can be obtained for solar collector if the south-facing wall is partially The environmental impacts of solar ener- covered by collectors (vertical collectors gy devices can be reduced in most cases by gather 50 to 75 percent of the energy which placing as many collectors as possible on would have been provided by collectors the roofs or walls of buildings. (The impact with the same surface area oriented at an on building design and appearance and the optimum angle on the roof). amount of area available for different types of architecture will be discussed in the next Since the combination of roof and wall section. ) In many cases, however, it will be areas may not adequately provide more impossible to find enough area on buiIdings than a small fraction of the energy re- for an efficient solar system Existing quirements of some buildings, additional buildings may be shadowed during the day colIectors must then be placed in arrays on or may have sloping roofs which are not the ground It may be preferable to locate properly oriented for efficient solar collec- these additional collectors close to the tion A detailed study of the number of buildings served by the solar equipment, buiIdings In different regions having proper since this wouId maximize alternatives for 228 ● Solar Technology to Today’s Energy Needs

Figure VII-3–A Small Housing Development Using Solar-Heating Devices

SOURCE Mother Earth News, No 45, May-June 1977, p IWO multiple use of the collector areas and reduce their disruptive effect on the com- minimize the cost of transporting the energy munity and maximize the likelihood of produced by the collectors. multiple land use. A variety of community designs maximizing the use of solar energy Many proposed multiple land uses would are possible, but problems are associated coordinate collector fields with other land with each. uses. For example, solar collectors could If it is not physically possible or shade the upper level of parking lots (as economically desirable to locate collectors shown in figure VI 1-4), or in other cases the close to building sites, the question of colIectors couId shade patios or play- locating sufficient collector areas arises. It grounds. Lawn or shrubs can be grown under must be determined, for example, whether the collectors as figure VI I-5 shows. the system should be located in a remote Wide spacing of collectors, or the place- area, generating only electricity, or whether ment of collectors on poles over parking the system should be located closer to the lots, will increase the price and possibly community or industry served, and gener- reduce the efficiency of the collector ating thermal energy as well. Remote loca- system. These effects must be carefully tion of the solar energy systems would per- weighed against the advantages of reducing mit the use of less expensive land, and the system’s land-use impacts. There is room would avoid the problems associated with for much creative work in this area which competing for scarce open areas close to wilI require a judicious mixture of engineer- population centers but it would increase ing, landscaping, and building design transmission costs and possibly reduce concepts. design fIexibility (see chapter IV).

Another possibility applicable especially Solar Collectors and Community Design in new developments, would be to central- To design a new residential community or ize the collector field and distribute the commercial area for the maximum use of community around it. Multiple land uses solar energy is easier than to implement would be encouraged by allowing central- solar collection in individual situations ized parking or some recreational areas to since, for example, plans can be made to be combined with collector fields but the orient buildings properly, height restrictions reduction in the density of the community can be used to minimize shading, and areas could result in added expense for other ur- can be set aside for collector fields to ban services (roads, utilities, etc.). Ch. Vll Impacts of Solar Energy ● 229

Figure VII-4– Tracking Collectors Mounted Over a Parking Lot

The prohibitive expense or simple 400,000 to 600,000 square meters of a area unavailabiIity of land close to population centers will be major constraints on the use of onsite solar facilities in or near existing highways. If all of these areas were covered communities. If solar collector fields are to with s i I icon photovoltaic devices and if ade- be integrated into population centers, fac- quate storage were available a continuous tors such as population patterns, the size output of 17 to 28 MW i n Omaha, Nebr, and and location of trees, the types of buildings 23 to 37 MW in Albuquerque, N Mex , could found in the area, etc., must be considered. be provided. While this wouId not be adequate for all of the community’s needs, it The use of solar energy in individual wouId greatIy reduce the land requirred for buildings can be encouraged by intelligent ground-mounted colIector arrays. community planning, In the computer- modeled residential community of 30,000 It may be very difficult to design a solar community in a heavily forested area and trees in existing neighborhoods may present prohibitive problems for some sites. A great 230 Ž So/ar Technology to Today’s Energy Needs

Figure VII-5.—Vegetation Growing Under Arrays of Solar Collectors

Photo by John Furbet a) Professor Francia’s Solar Steam Generating Plant, Genoa, Italy.

b) Flat-Plate Collectors at University della Calabria, Cosenza, Italy. SOURCE G Franc!a, Unlverslty of Genoa, Italy Ch. VII Impacts of Solar Energy . 231

deal of thought will have to be given to this in local temperatures simply because the ab- issue i n some parts of the country and there sorptivity of the region would be changed may be no easy solution by the presence of the collectors. The effects caused by solar arrays, however, are no different from the changes which would oc- THE ADVERSE ENVIRONMENTAL cur from other types of development (e. g., EFFECTS OF COLLECTOR FIELDS with a parking lot or with a farm field). Any harm to a relatively undisturbed natural en- If land must be cleared exclusively for use vironment in the immediate vicinity of as coIIector fields, the effect o n the IocaI en- populated areas must be considered to be vironment could be very great I m pacts in- particularly serious, because such areas are clude the loss of existing buiIdings, the rapidly disappearing. destruction of ecosystems, and the noise, dust, and disruption of the clearing activity. LAND USED BY CONVENTIONAL If the land were originally forested, the fun- GENERATING SYSTEMS damental ecology of the region would be affected While it is possible for vegetation to A conventional coal-fired electrical gener- grow under collector fields, so that some ating system requires land for mining, train low plants and smalI animals could continue lines to transport the coal, land for the gen- to Inhabit the area, the mixture of species erating facility, and land for transmission would no doubt be very different from those and distribution of power. which wouId have inhabited the region had it remained undisturbed Moreover the ac- Table VI 1-12 indicates the amount of land cess roads required to maintain the collec- which would be required for strip-mining tors would disturb any new species which coal and for transmitting power. Each did inhabit the area. If the land were square meter of strip-mined land in the originally grassland or desert, however, the Eastern United States yields enough coal to impact of the solar devices might be less, provide about 2,000 kWh of electric energy. although it in no way could be considered A silicon photovoltaic array placed over the negligible. Some change could be expected same square meter would need to operate

Table VII-12. —Land Required for Strip-Mining Coal

Eastern strip mines Western strip mines

1974 1985 1974 1985

Acres/year mined . . . . 57,348 69,704 7,140 16,330 kWh/m 2 ...... 2,150 2,144 5,744 10,627 Years of solar operation to provide equivalent power in the same land area: Albuquerque ...... 14 14 38 69 Omaha...... 22 22 60 111

Assumptions: — 29 percent efficiency of generating and transmitting electrlcity — Silicon photovoltaic cells on non-tracking racks spaced to avoid shading (land coverage ratio = 52 percent in Albuquerque and 43 percent in Omaha), — 12,000 Btu / lb coal — Coal production statistics based on OTA forecasts. 232 Ž So/ar Technology to Today’s Energy Needs

between 14 and 22 years to provide an Another interesting point of reference for equivalent amount of energy. In the West, the land use impact of solar equipment is where thicker coal seams are found, a the land covered by surfaced roads in the square meter of strip mine could provide United States. There were about 5.9 x 1010 between 6,000 and 10,000 kWh of power and m 2 of such roads in the United States in a colIector would need to operate 40 to 100 1975.17 Covering these surfaces with 10- years in the same region to provide an percent efficient cells would produce 11.4 x equivalent amount of power. 1012 kWh annually or 39 Quads. United States electricity consumption in 1976 was 2 x 10’ 2 kWh or 6.8 Quads.

Long distance electric transmission also The direct comparisons of solar and con- requires a considerable amount of land. The ventional land use cannot be conclusive, Electric Power Research Institute estimates, These comparisons do not account for for example, that by 1990 electric transmis- either the quality of the land impacted by sion Iines will require a right-of-way of 2. I x the two types of systems or the fact that the 10 10 m 2 (about 220 billion ft2 ). ” If this area impacts of onsite solar facilities are typi- were covered with 10-percent efficient solar cally closer to populated areas than coal cells, about 4 x 1012 kWh (1 3.6 Quads) of mines or larger transmission facilities. Land- electricity would be produced annually, It is use impacts in populated areas are generalIy possible to use the rights-of-way of transmis- more regulated by local zoning laws and by sion Iines for purposes other than transmis- the public opinion associated with highly sion — multiple land use is also possible with visible local activities, whiIe activities in the solar equipment but somewhat more dif- remote areas are generally exempt from f i cult and expensive to undertake. reguIation.

IMPACT ON BUILDING DESIGNS

BACKGROUND concern to them in evaluating a loan application for solar energy and 19 percent stated Unlike conventional heating and cooling that this would be a “primary concern.’” 8 equipment, solar colIectors mounted out- The difficulty is traceable in part to the side of the building can be highly visible. lack of examples of equipment on standard Concern about the appearance of solar in- types of housing and to the fact that most stalIations and the effect of this appearance on the resale value of the property to which publicized devices are either highly experimental (without great attention being paid it is attached, may be a significant barrier to to appearance) or are installed on expensive, the near-term commercialization of onsite solar energy equipment. In a recent survey custom-built homes. With some care, even buildings which are optimized for solar of lending institutions, 43 percent of the officials interviewed stated that concern energy by having large roof areas with steep slopes, large south-facing windows, thick about the “bulkiness or unusual appear- walls, and other special features, can be ance” of solar devices would be of some made attractive.

“ EPRI Technical Assessment Guide, August 1977. 18 Regional and Urban Planning Implementation ‘ 7 Federal Highway Administration, Department of Inc , financing the So/ar Home: Understanding and /rn- Highways, 1974. (Calculation assumes average sur- proving Mortgage Market Receptivity to Energy Con- faced road width is 40 feet ) servation and Housing Innovation, June 1976, p. 83 Ch. VII Impacts of So/ar Energy ● 233

integrating active and passive solar problems, and improper roof orientation or energy systems into building design will re- slopes could impair system efficiencies. quire some imaginative architecture and the The roofs of standard buildings are not results will depend on regional tastes. It is designed to optimize the efficiency of solar possible to design conventional buildings equipment. Roof pitches may be wrong, the with solar energy devices with a minimal im- roof area may be too small, the framing of pact on building appearance (see figures the roof may be insufficient to support a VI I-6 and VI 1-7). Collector colors can be collector, and the orientation of the struc- matched to root colors. ture may be incorrect. Table V I 1-13 indicates The feasibility of retrofitting existing the roof areas available in standard building homes with collectors as shown in the designs, and the areas which can be provid- figures will depend on local conditions. ed with roof slopes at more optimum angles Shading by improperly placed trees and for solar collection. A number of imag- other buildings present the most serious inative designs have been developed during

Figure VII-6– Techniques for Integrating Solar Collectors Into Conventional Designs for Single Family Residences

SOURCE Solar Dwelling Design Concepts op clt pp 79.83, 89

28-84’2 () - 16 234 ● Solar Technology to Today’s Energy Needs

Figure VII-7– Techniques for Integrating Solar Collectors Into Conventional Designs for Townhouses and Low Rise Apartments

SOURCE Solar Dwelling Design Concepts op clt pp 91-93

the past few years which can provide large cooling towers), it would be difficult to collector areas at proper orientations. Two argue that the addition of solar devices such designs are illustrated in figures VI I-8 would seriously degrade the appearance of and VI I-9. buildings. The less attractive collector systems, such as tracking colIectors and rack-mounted flat Wall collectors provide another means of plate collectors, can be shielded from increasing the collector area. Large, tall ground view with simple screens around the buildings, such as high-rise apartment build- building perimeter, but in some installations ings, are particularly well suited to wall col- it wilI be clifficult to mask the systems com- lectors. Wall collectors generate about 75 pletely. (See figure VI I-10). Screens would percent of the energy that the same collec- add to the cost, but would probably in- tor area wouId generate if tilted (in Omaha, crease the reliability of tracking systems by Nebr. ), so their use may be economical in also serving as wind screens. As society has apparently become accustomed to build- may not aIter the appearance of some types ings with all manner of gadgetry on roof of buiIdings, e.g. , glass-waIled offices, or tops (vents, antennas, and air-conditioning apartments (see figure V I 1-11 ) Ch. VIl Impacts of Solar Energy ● 235

Table VII-13 .—Potential Areas for Collectors on Typical Buildings* (in square meters)

Albuquerque Boston Ft. Worth Omaha

Shopping Center Building Roof Horizontal roof area . 28,800 28,800 28,800 28,800 Slanted racks on horizontal roof . . . . 15,261 12,171 16,520 12,626 Parking Lot Land area, ...... 90,000 90,000 90,000 90,000 Slanted racks above cars . , . . 47,691 38,034 51,624 39,456 196-Unit high rise Building Roof Horizontal roof area . . 1,883 1,883 1,883 1,883 Slanted racks on horizontal roof . . . 998 796 1,080 826 500/0 of southern wall. 1,500 1,500 1,500 1,500 Parking Lot Land area...... 7,840 7,840 7,840 7,840 Slanted racks above cars ...... 4,154 3,313 4,497 3,437 36-U nit low rise Building Roof Horizontal roof area . 1,270 1,270 1,270 1,270 Slanted racks on horizontal roof . . . . 674 537 729 557 Parking Lot Land area...... 1,440 1,440 1,440 1,440 Slanted racks above cars . . 763 609 826 631 8-Unit townhouse Building Roof Horizontal roof area ., 620 620 620 620 Roof slope at latitude 756 837 731 824 Typical roof slope 327 327 327 327 Slanted racks on horizontal roof 328 262 356 620 Parking Lot Land area, ...... , 320 320 320 320 Slanted racks above cars 170 135 184 140 Single family house Building Roof Horizontal roof area 83 83 83 83 Roof slope at latitude 101 112 98 111 Typical roof slope . 44 44 44 44 Slanted racks on horizontal root...... 44 35 48 36 Carport Horizontal roof area ., 28 28 28 28 Roof slope at latitude 34 38 33 37 Slanted racks on horizontal roof . . 15 12 16 12

“See volume 11, chapter IV for a detatled description of the bulldlngs 236 ● So/ar Technology to Today’s Energy Needs

Figure VI I-8.—A Residential Building With Optimized Solar Roof Pitch and Orientation

PHOTO: Reprinted from Popu/ar Science with permission 1976 Times Mirror Magazines, Inc

ROOF PITCH AND ORIENTATION The useful thermal output for heating and hot water is optimized when the roof in Table VI 1-14 indicates how the energy col- Omaha is sloped at an angle of 560 (which is lected by flat-plate collectors varies as a 150 greater than the latitude), and the col- function of the angle of the roof and orien- Iector is oriented due south. If the collector tation of the building. It indicates the “use- faces south but is tilted at an angle more ful” output of thermal collectors (e.g., the typical of residential roofs (a drop of 4 feet output which is actually applied to heating in a run of 12 feet) the performance would space and water), the total thermal output be reduced by 18 percent or, equivalently, (which includes thermal energy which must the amount of collector area required for an be discarded because the storage is filled), equivalent output would need to be in- and the electric output which could be pro- creased by 22 percent. If the house with a vided by a flat-plate silicon photovoltaic ar- collector tilted at the latitude angle (4 I 0, ray. In all three cases, the direct output is were oriented due west instead of south, the shown and the results are normalized for energy received would be reduced by 11 per- comparison with the optimum roof design. cent. If both effects were combined in a Ch. VIl Impacts of So/ar Energy Ž 237

Figure VII-9. —A Commercial Building Designed To Optimize Roof Pitch and Orientation

PHOTO Courtesy of J Bayless, President, Solaron Corporation, 1976

‘‘worst possible house for solar cilIection, ” This analysis indicates that a large frac- and a house with a standard “4/12“ slope tion of existing buildings could be retro- were facing due west, the energy received fitted with solar systems without either a per unit collector area would be reduced 39 major sacrifice in system efficiency or percent or the required collector area would alterations in the roof lines. It also means be Increased by 64 percent. [Even a house that architects have considerable latitude in with a collector on a horizontal roof would designing solar structures; deviating from receive more energy. ) A number of other optimum orientations will increase the cost combinations of roof pitches and building of collector systems, but designers may feel orientations are shown for comparison. that this added cost is justified if it allows a more attractive buiIding plan, if it improves the orientation of the building with respect The output of photovoltaic devices is to scenery, or if it reduces the overall con- much less sensltive to the roof orientation, A struction cost of the buiIding. south-facing roof tilted at the “4/12“ slope wouId receive 98 percent of the energy received by a house tiIted at an optimum SPACE FOR STORAGE Storage Tanks The size of required heat storage tanks varies with the type of storage sought: over- 238 ● So/ar Technology to Today’s Energy Needs

tor

night storage, backup capacity for 2 or 3 25,000 to 50,000 gallon tank; 2 or 3 day days to allow for cloudy weather, or season- storage capacity would be twice or three al storage. For overnight heating and hot times that, and seasonal storage would re- water needs (assuming an average house in quire a 3 to 6 m i I I ion gaIIon tank Omaha on a typical winter day), a 500 to All but the smallest of these tanks would 1,000 gallon water tank is sufficient, For 2 to probably be buried close to building sites, 3 days storage, that capacity would have to thus minimizing land and building space re- be doubled or tripled; seasonal storage quirements. In the case of new housing, it would require a 50,000 gal Ion tank, might be more practical to bury the tank For the 196-unit apartment building (again directly under the basement of the house, using the needs on a typical winter day in creating a sort of sub-basement. On most Omaha), overnight storage would require a sites, there should be adequate space for Ch. VII Impacts of Solar Energy Ž 239

Figure VI I-1 1 .—Use of Collectors on the Vertical Wall of a High Rise Hotel

SOURCE The Radlsson Hotel Comoratlon St Paul Mlnn expected operational date September 1978

even the largest tanks The huge tanks re- Electrical Storage Devices quired for seasonaI storage i n apartments, Advanced collector systems may produce for example, could be buried in an area electrical energy for a residential or com- covering less than half the area of the apart- mercial buiIding as welI as thermal energy, ment’s parking lot. and onsite storage of electrical energy in batteries may be a necessary component of A number of storage media other than such systems. water are avaiIable: oiIs, salt cornpounds, organics, and concentrated solutions. The The space required by the batteries is, by alternate fluids have the advantage of re- itself, not a major concern. Lead-acid bat- quiring less volume and hence less storage teries require about 1 cubic foot of space space< but the disadvantage of greater expense, flammability, or the requirement of separate speciaIly constructed tanks must cubic feet of space, most Iikely in the base- be considered Since the tank is buried, its ment of the home (less than a 3-toot cube). A size IS not an aesthetic factor, and water bank of batteries with this capacity would tanks are probably the most practical for the be dangerous, particularly in residential residential and commercial applications dis- uses where children are present, and should cussed here. be stored in a locked room or cage of some 240 Ž“ Solar Technology to Today’s Energy Needs

Table VI.14.—Thermal and Electric Outputs of Flat-Plate Collectors in Omaha, Nebr., as a Function of Tilt Angles (with respect to horizontal) and Orientation (with respect to south)

Orientation

South Tilt = Lat + 15° 590 .91 410 1.00 South Tilt = Lat 643 .99 399 .97 226 .99 14.6 21.3 South Tilt = Lat -10° 647 1.00 378 .92 228 1.00 13.6 22.6 South Tilt = Lat -23° (4/12 roof slope) 613 .95 335 .82 224 .98 11.9 23.7

Tilt = Lat 598 .92 364 .89 216 .95 13.2 21.3

Tilt = Lat -23° (4/12 roof slope) 470 .73 249 .61 195 .86 8.1 23.1 Horizontal 502 .78 260 .63 205 .90 8.7 24.0 S. Vertical 326 .50 324 .79 127 .56 6.3 13.8 W. Vertical 169 .26 158 .39 112 .49 5.0 13.0

Assumptions: — thermal output computed assuming a tubular flat plate (operating characteristics of the collector assumed in the analysis are shown in volume II chapter IV). — useful output of the collector was computed assuming that a heating and hot water system with 40 m2 of collectors is used in connection with 1,000 gal of hot water storage and serves the typical single family house whose characteristics are outlined in volume II, chapter IV. Electric resistance heating and electric hot water heaters were assumed to provide needed backup. — the photovoltaic system analyzed was a passively cooled silicon system with a cell efficiency of 0.14 at 28° C and a heat removal 2 factor (Ke) of 0,025 kW/m -“C. — the results are integrated over a full year.

SOURCE: Prepared by OTA. Ch. Vll Impacts of So/ar Energy ● 241

sort. The 196-unit apartment building would water tanks. More complex heating systems need a I most 3,000 kWh of electrical storage will require larger tanks as well as additional for one day’s needs (about a 15-foot cube). pumps, controlled valves, and heat exchangers. While the tanks can be buried outside In addititon to the security needed for a the building, space will be required for the large array of high-yield batteries, the sys- supporting equipment. In most cases the tem should be vented to protect against the space needs wiII be minimal. buildup of potentially explosive hydrogen and the toxicity of other gases which are by- More complex systems using heat engines products of lead-acid battery use (see chap- would require substantially more space, either in the building or in sheds close to the building served, A solar heat engine large enough to operate an air-conditioning sys- OTHER BUILDING IMPACTS tem, for example, would be approximately as large as the air-conditioner which it Onsite energy systems will undoubtedly operates An engine providing electricity as require more interior building space than welI as air-conditioning wouId be even conventional heating and cooling systems. larger. Space requirements within buildings Even the simplest hot water systems require could present serious difficulties in these space for pumps, controls, and larger hot cases. Chapter Vlll COLLECTORS

Chapter VIII.–COLLECTORS

Page LIST OF TABLES Background ...... 245 . Major Design Considerations , ...... 246 Tracking Versus Nontracking Systems. .. ..246 Table No, Page Installation...... 248 Degradation in the Performance of Flat- Working Fluid...... 249 Plate PhotovoltaicArrays Located in Cleve- Survival in Adverse Conditions ...... 249 land, Ohio, September-December 1975....248 Surveyof Collector Designs...... 250 SiteOrientation Chart...... 251 “Passive’’ Systems ...... 250 Characteristics of Competing Designs for Siting ...... 250 the 10MWeSolarCentral Receiver Basic Architectural Considerations .. ...251 Powerplant...... 280 Stationary Flat-PlateCollectors...... 286 Stationary Flat-Plate Collectors...... 255 Foreign StationaryCollectors on U.S. Pond Collectors. . :...... 257 Market ...... 286 Flat-PlateCollectorsAssembled Onsite. .259 StationaryTubularand CPC Collectors ...287 Factory-Assembled Modular Collectors. .259 One-AxisTracking Collectors ...... 288 Tubular Solar Collectors...... 261 Two-AxisTracking Collectors ...... 289 Concentrating Collectors...... 261 Assumed Coilectorlnstallation Costs for Nontracking Concentrating Systems ....26l VariousCollectorConfigurations, ActiveTracking and Concentrating ExcludingOverheadand Profit ...... 290 Systems ...... 264 Useful Radiation lncidenton Flat-Plateand FullyTracking Concentrating Collectors, Environmental Impacts...... 284 2 Working Fluids...... 284 FourCities, in kWh/m /year ...... 298 Manufacturing Hazards ...... 284 CollectorCharacteristicsAssumed in Preparing FigureVlll-39 ...... 299 Collector Costs ...... 285 . Comparison of the AnnualOutput of Five FOB Collector Prices ...... 285 CollectorDesigns, in kWh/m2/year...... 301 Collector Summary Tables...... 285 Output of SingleCoverand DoubleCover Collector Performance ...... 287 Pond Coilectors for Various Operating The Energy Available for Collection ...... 289 Conditions ...... 301 The Solar Resource...... 291 A-1. Empirically Derived Constants Used in the CollectorTracking Geometry...... 295 FormulaforEstimating Direct Normal Collector Losses ...... 295 Radiation,Given Measurements of Total Optical Losses...... 295 Horizontal Radiation...... 304 Thermal Losses...... 298 A-2. Comparison of 1962 Weather With Long- The Significance of the Loss Factors . . . . 298 Term Averages and Extremes ...... 304 A-3. Glossary of Symbols Used in Computing The Net Performance of Collectors...... 300 Collector Geometry, ...... 306 AppendixVlll=A.-Techniques Used to A-4. Coefficients of the Fourier Expansion Compute the Output of Representative of the Equation of Time Used in Equation Collector Designs ...... 303 A-15...... 309 Chapter VIII. —COLLECTORS—continued LIST OF TABLES—continued Figure No. Page Table No. Page 18. Russell Collector by Scientific-Atlanta, A-5. Transmittance of Transparent Covering inc., Installed at Georgia institute of Materials Which May be Used in Solar Technology ...... 269 Collectors...... 311 19. ITEK Distributed Collector Concept With A-6. Specular Reflectivities ...... 313 Inset Showing the High-Performance A-7. Maximum Possible Geometric Receiver Design...... 270 Concentration Ratios at Perihelion...... 320 20 The Varian Two-Axis Concentrator Using A-8. Maximum Possible Geometric GaAs Photovoltaic Devices ...... 272 Concentration Ratios ...... 320 21 An MIT Design for a Small Two-Axis A-9. Typical Thermal Loss Coefficients ...... 322 Tracking Unit ...... 273

A-10. Ratio of Collector Output When Average 22< Sales Price of Cast-Acrylic Fresnel Lens U-Value Used to Output of Collector With Versus Production Volume ...... 274 Variable U-Value for Flat-Plate Collectors 23, 1 kWe Focusing Photovoltaic Test in Omaha With Tilt Angle—Latitude...... 323 Bed & Sandia Laboratories, Albuquerque. l-Square Foot Fresnel Lenses Focus on 2-inch Diameter Solar Cells ...... 275

24. RCA’s 300We Photovoltaic Concentrator. .276 25. JPL Paraboloid Design With Stirling Engine at Collector Focus...... 276 26. Sunpower Systems Solar Powerplant. .. ..277

27. Francia 100 kWt Solar Powerplant...... 278

LIST OF FIGURES 28. Mitsubishi (7 kW+) Heliostat/ Receiver Test Bed ...... 279 Figure No. Page 29, Pilot Plant Heliostat Concepts...... 281 1. A Sample Site Plan Illustrating Techniques Pilot Plant Receiver Concepts...... 282 for Minimizing Heating and Cooling 30. McDonnell Douglas 10-MW Pilot Plant Requirements ...... 252 Design...... 282 2. The Operation of the Trombe-Wall 32. The 5-MW Central Receiver Demonstration Collector/Storage System ...... 254 Under Construction in Albuquerque, 3. A House Using a Trombe-Wall Collector N. Mex...... 283 Located in Eastern Maryland ...... 254 33. Cross-Section of Stationary Hemisphere 4. The Temperature Averaging Effects of Concentrator ...... 283 Masonry Wails of Various Thickness .. ...255 34. Variation of Direct Normal Component of 5. Typical Home With Solar Water Heating Solar Radiation With Time ...... 292 Using Flat-Plate Collectors ...... 256 35. Mean Daily Total-Horizontal Solar Radiation 6. Cross-Section of a Typical Modular Flat- (kWh/m2) ...... 293 Plate Solar Collector...... 257 36. Mean Daily Direct-Normal Solar Radiation 7a. Pond Collector With a Rigid Cover ...... 257 (kWh/m 2)...... , ...... 294 7b. Cross-Section of a Combined Pond 37. Perfect Fiat-Plate Collector Tilted at Coilector/Thermal Storage Pond Using Latitude Angle and a Perfect Fully Tracking an inflated Cover...... 258 Collector...... 296 8. Typical Air Collector Installation ...... 260 38. Comparison of the Maximum Energy 9. Various Tubular Collector Designs...... 262 Collectable by Four Types of Collectors 10. Fiat-Plate Collectors With Stationary Located in Albuquerque (1962 Radiation Boosters ...... 263 Data) ...... 297 11. One-Axis Compound Parabolic Collector. .264 39. Energy Balance for Five Collector Designs 299 12. Albuquerque-Western Tracking Collectors A-1. Collector Coordinates Showing the - installed on Modular Home ...... 265 Collector Direction ...... 305 13. Acurex Parabolic Trough ...... 266 A-2. The Geocentric and Collector Coordinates 14. Beam Engineering Parabolic Trough on a Showing Direction of Sun...... 306 Polar Mount ...... 267 A-3. The Specular Reflectance at 500 nm as a 15. (a) The Linear Fresnel Lens and the Function of the Collection Angular Aperture Absorber Tube are Both Visible in This for Several Reflector Materials ...... 312 Cross-Sectional End-View of the Northrup A-4. Monthly/Hourly Variation in Available Concentrating Collector. (b) Array of Thermal Power...;...... 315 Northrup Collectors is Mounted for Polar A-5. The Solar image on Three Typical Tracking ...... 268 Concentrating Collectors...... 317 16. Receiver Pipe inside McDonnell Dougias A-6. Characteristics of the image of Acrylic Prototype Linear Fresnel Lens Fresnel Lenses Designed by Swedlow Inc. Concentrator...... 268 for Solar Applications...... 318 17. General Atomic Distributed Cllector A-7. Geometry of a Simple Flat-Plate Concept ...... 269 Collector...... 324 Chapter Vlll Collectors

BACKGROUND

This chapter reviews the diverse assortment of techniques which can be used to collect sunlight on receiving surfaces. Technologies for converting the energy collected into mechanical or electrical energy are examined in chapters IX and X. Solar collectors are the only components of solar energy systems which are unique; all other parts of the systems—heat engines, storage devices, and the like—have a history of use in other applications. Collectors can, however, be relatively simple devices and have much in common with other types of heat exchangers. A variety of design approaches are possible using well-established technology. The major problem is reducing the cost of the devices with innovative designs or mass production techniques. Low-cost colIectors are critically important to the future of solar energy since collector costs dominate the cost of solar energy in almost all systems. Evaluating collectors at this stage in the history of the technology is an extremely treacherous undertaking. The field is changing at a bewildering rate and it is much too early to be dogmatic about the outcome. Since collector designs can be perfected without the need for sophisticated development laboratories, a large number of inventors have entered the field and an incred- ible variety of approaches have been proposed. Concepts have come from home inventors, university laboratories, and small manufacturing concerns, as well as large Government and corporate development laboratories. Many of these new ideas wilI never reach the marketplace and many that do will not survive the intense competition which is beginning to take place. There are presently about 200 independent organizations in the United States with a collector on the market. Many interesting designs have never been produced commercially and many of the designs which have reached the market have been available for such a short time that their long-term performance cannot be accurately evaluated. In particular, few systems have been tested extensively in adverse weather conditions. Moreover, many contemporary collector manufacturers are smalI firms which are unable to make reliable estimates of a selling price which can sustain the overhead and marketing costs of their concerns— several companies have failed in the past year. As a result, the claims made by many manufacturers of inexpensive devices must at this point be treated with great caution.

Uncertainty about the reliability and per- I n almost all cases, forecasts of the future formance of collectors may be alleviated to price of collectors are based on estimates a considerable extent when consensus of potential mass production and are not standards are developed by the industry for based on a detailed analysis of specific testing collectors and when testing labora- manufacturing processes, I n fact, the price tories are certified for conducting the of many of the products now on the market needed tests. (This uncertainty about system is unlikely to fall dramatically with mass quality is a major problem for consumers production–the cost of materials already and is discussed more extensively in chapter represents a significant fraction of the total I I 1, Policy Analysis.] cost of some devices. Significant price re-

245 246 ● Solar Technology to Today’s Energy Needs

ductions are more likely to result from the collectors, which use the earth for much of development of innovative designs. their support, will almost certainly provide the lowest cost solar energy. Nonfocusing I n spite of the uncertainties, colIector pro- collectors are also uniquely able to make duction is increasing rapidly. Manufacturers use of diffuse sunlight reflected from the at- reported production of 426,000 m2 of collec- mosphere and the ground. (Some diffuse tors during the first half of 1977 (4.5 million solar energy can be collected by concen- square feet), of which about 250,000 m2 trators which magnify the Sun’s intensity were low-temperature devices designed pri- only 2 to 3 times, ) Flat-plate colIectors are marily for heating swimming pools. Sales not able to provide temperatures high have been increasing by more than so per- enough to operate most kinds of heat en- cent every 6 months. Collector sales were gines, however, and cannot be used to pro- expected to amount to over $100 miIlion vide high-temperature process heat. (A heat during 1977. engine which can operate from the temperatures produced by flat-plate devices is dis- MAJOR DESIGN CONSIDERATIONS cussed i n chapter IX, Energy Conversion With Heat Engines. ) The enormous variety makes the selection of an optimum collector design a complex Some types of flat-plate collectors may decision. The choice can only be made by cost more per unit of aperture than tracking analyzing the space available for collectors devices. This is because flat-plate units re- on building roofs or in landscaping around quire a considerable amount of material for buildings, the local climate (including the each unit of collector area —the entire area availability of direct and indirect sunlight), must be covered by an absorber surface, in- and the compatibility of the collector out- sulation, and one or two layers of glass or put with storage equipment, engines, and plastic. The large heated area also means other elements of the solar energy system. that thermal losses for flat-plate devices are Clearly, no single design will be optimum for generally larger than those of systems which all applications in all climates. The follow- concentrate sunlight, even though the con- ing discussion reviews some of the major centrating systems typically operate at high- variables which must be considered i n se- er temperatures, lecting a collector. Systems which track the Sun and concentrate sunlight are able to produce the high temperatures needed to operate efficient TRACKING VERSUS heat engines or can be used to reduce the NONTRACKING SYSTEMS area of photovoltaic cells needed for electricity production. Their use with solar cells The vast majority of the collectors now on is important if the cost per unit area of the the market do not follow or “track” the Sun tracking collector is significantly cheaper or concentrate sunlight with an optical sys- than the unit area celI costs, and if the track- tem, but are “flat-plate” systems rigidly ing device allows the use of a high-effi- fixed to rooftops or frames in fields. This ciency cell. This is discussed in greater de- kind of collector has the advantage of sim- tail in later sections. plicity and reliability, and can be integrated into buiIding designs with relative ease. Although most concentrating collectors now on the market cost considerably more If sufficient land is available and large than flat-plate devices, it may eventually be quantities of low-temperature (500 to 90° C) possible to build concentrating devices thermal energy are required, shallow pond which cost no more (perhaps less) than standard fIat-plate systems since most of the ‘Stoll, R. (DOE) So/ar Collector Manufacturing Ac- area of concentrating collectors is covered tivity, November 1977 only with a thin layer of reflective surface or Ch. Vlll Collectors ● 247

lens material. The inability to utilize diffuse Dirt can scatter light and therefore inter- sunlight is compensated for, to a large ex- feres with the ability of the optical devices tent, by the fact that tracking devices can to focus light even when the amount of light maintain a better angle to the Sun than sta- absorbed by the dust is not important. Re- tionary systems. cent experience at Sandia Laboratories has indicated that the specular reflectivity of Systems have been proposed which con- tracking mirrors can be reduced by as much centrate sunlight without tracking — exam- as 15 percent in poor locations if the mirrors ples are simple stationary reflectors placed are not washed during a year. The effect is between tilted flat-plate collectors and the very sensitive to the location of the collec- “compound parabolic concentrator” under tors since precipitation can reduce dust ac- development at the Argonne National Lab- cumulation but no data is available on this oratory; and systems have been proposed in problem in most locations. Table VII l-l indi- which flat-plate colIectors track the Sun cates the degradation in the performance of without concentrating sunlight. I n most flat-plate photovoltaic collectors. It can be cases, however, tracking and concentration seen that the effect of dirt depends strongly are used together. on the cover material and the operating en- Tracking collectors can be conveniently vironment. The degradation of performance divided into two general categories depend- apparently is quite rapid during the first 3 ing on whether they track the Sun by tilting months, but levels off quickly. Performance around one or two axes. The one-axis track- at 9 months is not much worse than performing systems are typicalIy shaped Iike long ance at 3 months.2 A relatively simple hose- troughs which swing about the trough’s long down once or twice a year may be sufficient axis. These troughs cannot keep the receiver for most cleaning requirements. ’ Larger col- aperture perpendicuIar to the Sun’s direc- lector arrays may require specially designed tion, but provide better Sun angles than a equipment to faciIitate cleaning colIectors. fixed device. One-axis systems typically are The timing of cleaning cycles will depend used to magnify the Sun less than 50 times on a detailed comparison of the cost of and are not used to provide temperatures 0 alternative cleaning schedules and the cost above 3500 C (660 F); some simple, inex- of energy lost because of the dirt which can pensive systems are designed to produce accumulate as a result of each schedule. Un- fluids at650 to 1200C(1500 to 2500 F). fortunately, most types of tracking devices The advantages of concentrating collec- have not operated long enough to allow the tors are counterbalanced by the added costs collection of adequate information about of maintaining the optical surfaces and the degradation of performance over time. moving components, and by the cost of the Cleaning is, of course, also important for tracking unit itself. The tracking systems flat-plate collectors, but tends not to be as need not be very expensive since a single critical a factor in their performance since a tracker can be used to drive a large array of significant fraction of the light scattered by colIectors and wear on the moving parts wiII dirt can still be captured by a flat-plate ab- be minimal since a collector will rotate only sorber. 11,000 times in 30 years. Maintenance of the Wind Ioads present a particularly serious optical surfaces is Iikely to be the largest problem problem. Optical losses can be a dominant for tracking collectors since they factor in the overall efficiency of concen- can act like sails and much of the cost of trating collectors (the relatively poor optical tracking devices results from the need to efficiency of some concentrating collectors tends to offset their relatively good thermal 2A. F, Forestieri, NA5A Lewis Research Center, efficiency), and these losses can be signifi- private communication, November 1977 cantly increased if dirt or scratches accumu- ‘Rosco Champion (Sandia Laboratories), private late on mirror or lens surfaces. communication, February 1977 248 Ž Solar Technology to Today’s Energy Needs

Table Vlll-1.— Degradation in the Performance of Flat-Plate Photovoitaic Arrays Located in Cleveland, Ohio, September-December 1975

Heavy industrial Suburban environment environment

81 days 250 days 74 days 250 days Arrays not cleaned Cells encapsulated in glass -5.7 + 1.8 Cells encapsulated in silicone rubber (average of three products tested) -32 ~-30 -9 Performance after arrays scrubbed with a detergent solution Cells encapsulated in glass. . . . . + 1.8 0 Cells encapsulated in silicone rubber (average of three products tested) ...... -7 ~ -12 -2 -6 to -10

NOTE. Measurement error was - ~ 20/., so + 1.8% means only that no measurable degradation had OC. curred

SOURCE Forest lerl, A F “Results of Outdoor Real Time and Accelerated Testing” presented at ERDA National Photovoltalc Program Review, SIltcon Technology Program Branch, San Diego, Callf , Jan 18, 1977 (p 230) Forestlerl, A F private communtcatlon, November 1977 build massive supporting structures capable steam. The reliability of each approach can of withstanding high winds. A clever tech- only be established with carefuI testing. nique for reducing such costs would be a welcome innovation. INSTALLATION Another potential problem with tracking systems is the difficulty of integrating the The cost of installing collectors is an im- devices aesthetically into the architecture portant and often overlooked component of of a building; many of the experimental the cost of a solar system. The relatively tracking systems are far from attractive. The straightforward plumbing, carpentry, and architectural problem of integrating track- electrical work associated with installing ing systems gracefully into a building, how- collectors can represent more than half of ever, has not been adequately examined. the installed cost of a collector system. Finally, it can be difficult to design reli- These costs tend to be significantly higher in able couplings to carry very hot fIuids from the case of devices retrofitted onto existing a moving receiver. Several approaches are structures. possible. For temperatures below boiling, a flexible radiator hose may be adequate, It may be possible to integrate collectors although occasional replacements may be into the walls or roofs of new buildings in a necessary. For temperatures of 4000 to 6000 way that can lead to some savings in build- F, rubberized braided-steel hose can be ing materials and insulation. Plumbing and used. For higher temperatures, stainless wiring costs can be minimized with careful steel accordian bellows can be used. These building designs. Some additional construc- are commonly used to allow for expansion tion costs may be incurred if heavy collec- and contraction in industrial pipes which tors or collectors subject to high wind loads must carry very hot or very cold fluids or must be supported by the building. Ch. VIII Collectors ● 249

Collector systems which are not attached be transported over long distances. A variety to buildings incur the additional cost of of heat transfer fluids have been developed land-grading, concrete foundations, and the for chemical processing which can be used cost of purchasing needed land. I n many to transport heat from solar collectors, al- cases, the land cost can be eliminated by though there are disadvantages associated mounting collectors over parking lots or with their use. These fluids can be costly, other areas where the colIectors will not in- some are flammable, and others degrade terfere with use. with continued thermal cycling. The use of helium gas has been proposed for use in the The problem of installation costs has not receivers of very high-temperature colIector received the attention which this issue systems. merits. If an efficient and inexpensive chemical process can be developed which either converts light directly into chemical energy (photochemical reactions) or which uses WORKING FLUID thermal energy to drive a chemical reaction (thermochemical reactions), it may be possible to pump the appropriate chemicals di- A variety of fluids can be used to convey rectly into collectors to produce a higher the energy from a solar collector to the site energy material which can be stored for where the energy is needed or into storage. later use. At low temperatures, the prime candidates are air, water and mixtures of water, and antifreeze. (Pure water cannot be used in colder climates unless the system is de- SURVIVAL IN ADVERSE CONDITIONS signed to drain completely during cold, sun- less periods or the collector is made from A collector system should be able to with- flexible plastics or other materials which are stand strong wind and hail, and should be not damaged by expansion. ) able to operate after snowstorms. Some tracking collectors are designed to protect Air collectors have the advantage of themselves from inclement weather by turn- avoiding the problem of freezing altogether, ing the vulnerable surfaces down toward the and are not affected by the corrosion which building or the ground. can result from untreated water. Air can be heated to temperatures above boiling with- Another factor which must be considered out producing excessive pressures, and leaks is the collector’s ability to survive a failure in air colIectors do not lead to building of the pump control systems or plumbing damage. Air collector heating systems can which prevents the working fluid from carry- use inexpensive rock beds for heat storage, ing heat away from the collectors. If fluid thus eliminating the inefficiencies, tempera- flow stops, the temperature of even simple ture drops, and costs associated with heat colIectors can reach 1000 to 1500 C (the so- exchangers. However, the relatively low called “stagnation temperature” of the Col- density and specific heat of air (compared lector). These temperatures can melt critical to water) means that the collectors, storage, components of poorly designed systems or and heat transfer systems must be consider- cause expensive damage in other ways. The ably buIkier than the Iiqu id systems. colIector performance and certification tests designed by the National Bureau of Water can also be used as the working Standards will include a test of the per- fluid in high-temperature systems, but pres- formance of the collector after it has oper- surized systems can be expensive, especially ated without cooling fluids for some length if steam must pass through rotating joints or of time.

2 fl-fi42 () - 17 250 Ž Solar Technology to Today’s Energy Needs

SURVEY OF COLLECTOR DESIGNS

The following section examines a repre- Many of the more sophisticated passive sentative set of solar collectors. Some of solar designs are only applicable to new these devices are on the market and some construction since they affect the basic de- remain in the laboratory, but an attempt has sign of the building; many simple changes, been made to represent each generic cate- such as the addition of awnings, shutters, gory. The selection of particular collectors and lean-to greenhouses can be retrofit on as examples does not imply any judgment existing structures. Temperature control can about their performance relative to other also be difficuIt with some systems. devices, nor is the survey intended to provide a comprehensive listing of all available Siting designs. Extensive catalogs of solar collec- A wise decision about building placement tors have been published by the Energy Re- should take into account local topography, search and Development Administration sun angles, trees and other vegetation, (ERDA),4 the House Subcommittee on Ener- ground water, precipitation patterns, and gy Research, Development, and Demonstra- other aspects of the local climate and geog- tion,5 and the Solar Energy Industries Asso- raphy. There cannot be a simple, all-inclu- c i at ion. 6 sive formula for resolving these issues because each decision must be made on the “PASSIVE” SYSTEMS basis of specific site conditions. Table VI II-2 indicates some of the basic elements of The heating and cooling requirements of building siting decisions for four different buildings can be reduced if care is taken in the design of the building and the choice of climatic regions, and figure VII l-l gives an example of an efficient siting plan devel- a building site. With imaginative planning, most of the options should not add substan- oped by the AlA Research Corporation. The following features were used in developing tially to the cost or detract from the appear- the plan: 7 ance of structures. At some added cost, new buildings can be designed with more elabor- ● The use of windbreak planting; ate structural features (such as large south- ● facing windows and thick walls) which can The orientation of road alinement with further reduce heating and cooling require- planting on either side to channel summer breezes; ments. These features are all commonly cat- egorized as “passive solar” collection sys- ● The location of units in a configuration tems since they typically have no moving suggested by the topography; parts. ● The use of the garage to buffer the Passive systems are extremely attractive dwelling from northwest winter winds; because of their simplicity, very low initial ● The use of berms to shelter outdoor Iiv- cost, and freedom from maintenance costs. ing terraces; and

● ‘Catalog on Solar Energy Heating and Cooling Pro- The use and location of deciduous trees ducts. ERDA-75 ERDA Technical Information Center, to block or filter afternoon sunlight in Oak Ridge, October 1975 the summer. ‘Survey of Solar Energy Products and Services – May 1975. Prepared for the Subcommittee on Energy Research, Development, and Demonstration, U.S. ✎ House of Representatives, by the Congressional ‘The American I nstltute of Architects Research Cor- Research Service, Library of Congress, June 1975 For poration, Solar Dwelling Design Concepts, prepared sale by U S Government Printing Office, $460 for the U S Department of Housing and Urban ‘So/ar /ndustry Index. Solar Energy Industries Development, Office of Policy Development and Association, January 1977 $800 prepaid Research, May 1976 Ch. V/// Collectors

Table VI II-2.—Site Orientation Chart

Type of climate cool Temperate Hot humid Hot arid Maximize warming Adaptations Maximize warming effects of Sun in Maximize shade Maximize shade late effects of solar winter. Maximize Maximize wind morning and all after- radiation. Reduce shade in summer. noon. Maximize humidity, impact of winter wind Reduce impact of Maximize air movement Avoid local climatlc winter wind but in summer cold pockets allow air circuIatlon in summer Position on slope Low for wind shelter Middle-upper for solar High for wind Low for cool alr flow radiation exposure Orientation on slope South to southeast South to southeast South East-southeast for p.m shade Relation to water Near large body of Close to water, but Near any water On lee side of water water avoid coastal fog Preferred winds Sheltered from north Avoid continental Sheltered from north Exposed to prevailIng and west cold winds winds Clustering Around Sun pockets Around a common, Open to wind Along E-W axis, for sunny terrace shade and wind

Building orientation ● Southeast South to southeast South, toward pre- South vailing wind Tree forms Deciduous trees near Deciduous trees nearby High canopy trees; Trees overhanging building; evergreens on west; no evergreens use deciduous trees roof if possible for windbreaks near on south near buiIding Road orientation Crosswise to winter Crosswise to winter Broad channel; E-W Narrow; E-W axis wind wind axis Materials coloration Medium to dark Medium Light, especially Light on exposed sur- for roof faces, dark to avoid refIect ion —

SOURCE Solar Dwelhng Destgn Concepts op clt p 72

In warmer climates, a building should be Basic Architectural Considerations placed at the highest part of the terrain to take advantage of cooling winds (a form of A considerable amount of passive solar heating and cooling can be achieved simpl solar energy); in colder climates, it should be y located, ideally, in the cup of a hill, allowing by carefully designing the shape of a house, sunlight to reach the buiIding whiIe protect- and the placement of windows and thermal masses in the building (e. g., thick masonr ing it from chilling winds. y walls). Many older buildings incorporated When the terrain and local building codes these features in their designs. (The art of permit, siting at least part of the building taking such factors into consideration in de- underground or at ground level provides ex- signing a house seems to have been ne- cellent insulation. Trees are also an impor- glected when inexpensive heating fuels be- tant factor in site selection, acting both as a came available. ) windbreaker and a Iightbreaker. Deciduous trees shade the south side of the house for The size and location of windows is a ma- much of the year, alIowing sun Iight to pene- jor factor in determining the temperature of trate during the colder months. The same a house. Large, south-facing windows can shading principle is true of such plants as ivy collect a surprising amount of solar heat, on the walIs of the house, which is transferred to walIs and floors. 252 ● Solar Technology to Today’s Energy Needs

Figure VII I-I .—A Sample Site Plan Illustrating Techniques for Minimizing Heating and Cooling Requirements

SOURCE The AlA Research Corporation, “Solar Dwelllng Design Concepts” Ch. Vlll Co//ectors ● 253

Small, northern windows minimize heat loss. prince Edward Island, Canada, claim that The use of natural shading and orientation their building re mained at a comfortable to breezes provides i m proved cooling temperature throughout the severe winter of through windows. 1976-77 without using backup heating systems. 2 The basic shape of a structure is also important. Long ranch-style homes, for exam- Two slightly more elaborate techniques ple, require much more heating per unit of involve the use of “thermosyphoning” and floor space than cube-shaped, two-story thermal masses. The “thermosyphoning” homes, Roof overhangs should shade win- systems use natural or forced convection to dows during the summer when the Sun is heat building air in walls, ceilings, or win- high in the sky and allow sunlight to enter dow surfaces heated by the Sun. 13 A variety when the Sun is lower in the sky during the of techniques have used solar radiation for winter months. Dense interior materials with heating a mass with large heat capacity via a high heat-retaining capacity, such as ma- sunlight, and using direct radiant heating sonry, concrete, or stone, can be used to ab- from these masses after the Sun sets. The sorb surplus heat from sunlight during the thermal mass can be nothing more than a day, and return this heat to the room after dark wall or floor made of thick masonry, dark. stone, or adobe, or a water tank integrated into the wall or floor. The system designed Passive heating and cooling of buildings by Steve Baer of the Zomeworks Corpora- can be enhanced by taking advantage of the tion uses cylinders of water to provide the heat gained in southern walls and roofs, 1 thermal mass. 5 natural convection, and the heat-storage capabilities inherent in windows and walls. A system which has become known as the A number of recent publications have re- “Trombe-wall” collector (after Felix viewed these designs.8 9 10 Trombe, a French designer who has designed several such structures since 1967) is il- The simplest systems consist only of a lustrated in figure VII I-2. Figure VII I-3 shows window with insulated shutters. The shutters a house in Maryland which includes a are opened to permit sunlight to enter and Trombe wall, The owners estimate that the heat the house during winter days, and are passive solar system added approximately closed at night to prevent heat from escap- $2,500 to their construction costs. The de- ing. The shutters are closed during summer vice is expected to provide about 50 percent days because white or silver surfaces on of the building’s heat requirements. their outer surface reflect the Sun’s heat. During summer nights, the units open to The Trombe wall is essentially a vertical cool the building. Several innovative tech- hot air collector which uses a thick wall niques have been developed for controlling both for a receiver and a storage system. shutters and covers of this kind. Buildings The air can circulate with natural convec- have been designed which incorporate tion or with a fan. In most climates, the per- greenhouses into the southern wall. De- formance of the system is improved if ad- signers of one such system, located on justable vents are installed over the open-

‘B Anderson, (Total E nvlronmental Action), The \o/ar tfome t?ook, Cheshire Hooks, Church H Ill, Har- 12J Todd, et al , The )ourn,q} of th~ ,h’~b{ 4/chemists, rlsvllle, N H 1976 New Alchem}, Woods Hole, Mass , spring 1975 ‘Leek IC, et al , Other Homes and Garbage lle~l~n~ ‘‘T Price, ‘‘Low-Tee h no logy Solar Homes that tor Se/f-Sufflclent L/\T/rrg, Sierra C I ub Books, 1975 work ~vlth Natll re, ” Popu/ar Science, TI mes Mirror ‘”10$ Alamos Sc Ientiflc Laboratory F’assi~e Solar Magaz Ines, I nc , December 1976, pp 95-98, 143 Heating and Cooling Conference and Workshop Pro- 14S F3aer, Sunspot~, The Zomeworks Corporation ceedings, LA-6637-C, May 18-19, 1976 (1975) 1‘ Bruce Anderson, Solar Energ} I undarnentals In ) ‘A4 J H arisen, “The Bened Ictlne Monastery, ” So/ar Bulldlrrg De\/gn. Age, October 1977, p 24 254 ● Solar Technology to Today’s Energy Needs

Figure Vlll-2.— The Operation of the ings which connect the collector airspace Trombe-Wall Collector/Storage System with the interior of the house.16

(Sun The response of walls of various thickness is illustrated in figure VI I I-4, The ability of the thermal mass to average the external Solar temperatures is clearly illustrated. Analysis heated of the many varients of this system which air are possible have just begun, and an analysis of the economics of the systems is difficult Transparent cover heat : because of the scarcity of consistent cost in- . formation and the small number of systems which have been adequately instrumented.

The “Skytherm” house in Atascadero, Cal if., uses water beds covered by remov- able insulating panels on the roof of a building. During the winter, the panels are automatically removed during the day, allowing the water to be heated and replaced at night. Heat is provided to the living areas by direct radiation through a metal ceiling

“J D Balcomb, et al , “Thermal Storage Walls for Passive Solar Heating Evaluated, ” Solar Age, August 1977, p 22

Figure VII I-3.—A House Using a Trombe-Wall Collector Located in Eastern Maryland

PHOTO Courtesy of Andrew M Shapiro, “The Crosley’s House—With Calculations and Results,” So/ar Age, November 1977, p 31 23456 Days Days

I I 1 I 1 31 1 2 3 4 5 6 7 Days

SOURCE Balcomb, et al SImu Iat I(JII Analy 51s 1,f Passive Sol,)r Heat(Id Bulldir]qs -- Prf,limlnary resu Its So/a( En erg j , I )1 19 ( 1977 I I 1,if,+. 281 separating the interior of the house from the a 9-month period in which the average high water beds. I n dry climates with cool sum- temperature for the hottest month was 32° mer nights, the system can also provide C (90 0 F) and the average low temperature cooling. Heat is radiated from the water to for the coldest month was -1°C (30 0 F).18 the sky during the night when the insulating covers are removed, and the thermal mass is used to absorb building heat during the day STATIONARY FLAT-PLATE COLLECTORS when the insulating covers are i n place. 7 I n Flat-plate collectors have been used for some recent measurements, this house was several decades to provide hot water in shown to maintain an inside temperature between 180 and 240 C (65 0 and 750 F) during ‘8Phl I Ip W B Miles, “Thernlal Evaluation of a House U$i ng a Movable I nsu Iatlon Heating and Cool- i ‘H a rold Hay, privdte comrnu nlcdt Ion ing Syjtem, ” So/ar Energy, Vol 18, (1 976) 256 ● Solar Technology to Today’s Energy Needs

Australia, Japan, and Israel. Large numbers perature of the collector. The absorptivity of the devices were also sold in southern of the system is high for wavelengths where parts of the United States during the late the Sun’s intensity is greatest and low at 1920’s and early 1930’s, but sales declined wavelengths where the intensity of the ra- rapidly as low-cost natural gas and oiI be- diation from the heated receiver surface is came available. I n recent years, however, greatest, A number of such “selective sur- there has been a great resurgence of interest faces” are now on the market but the devel- in the systems, and a large number of de- opment of a high-performance, low-cost se- signs are being marketed or prepared for lective surface would be a great boon to the marketing. A typical installation is shown in colIector industry. figure VI 11-5. The heated surfaces are insulated on the The cross section of a typical collector is back and sides by standard types of insula- shown in figure VI 11-6. The fluid is heated as tion (e. g., fiberglass), and on the front by one it is passed over or through an absorbing sur- or two layers of glass or plastic. These trans- face. At some additional expense, this sur- parent or semitransparent covers can also face can be specially designed to maximize be made selective. Several common mate- the amount of sunlight it absorbs and to rials are nearly transparent to visible light minimize its radiation at the operating tem- from the Sun but absorb the infrared radi-

Figure Vlll-5.— Typical Home With Solar Water Heating Using Flat-Plate Collectors

--,

PHOTO Courtesy of American Hellothermal Corp Ch. VIII Collectors ● 257

Figure Vlll-6.— Cross-Section of a Typical Modular where relatively low-temperature flu ids are Flat-Plate Solar Collector required; the systems will probably be most useful when combined with long-term (6- month) thermal storage or when used for industrial-processing facilities since very little output is provided during winter months. Re- search on these devices has been conducted in Israel for many years. One of the first installations in the United States using such collectors was designed by the SOHIO oil company working with the Lawrence Liver- more Laboratory to develop a pond system which could be used for processing uranium. Two types of solar pond collectors are shown in figure VIII-7a and VIIl-7b. ated by the colIectors. (AlI common glass possesses this property. This is the basis of The basic Livermore collector design con- the “greenhouse effect” which heats closed sists of a reinforced concrete curb which cars and rooms with southern windows. ) forms the periphery of the pond. A layer of Special “heat mirror coatings, ” such as in- sand and a layer of foam-glass insulation are dium oxide, can be deposited on collector placed inside this curb and a watertight covers to further reduce losses Such coat- polyvinyl chloride (PVC) bag is placed on top ings reflect the infrared radiated by the hot of the rigid insulation. The upper cover of receiver, but permit most of the incident this bag consists of 12 mill (C).3 mm) clear sunlight to pass into the collector. PVC while the bottom layer is a 30 mill (0.8mm) black PVC. A single upper cover for Pond Collectors the collector is provided by a flexible fiber- Pond collectors can be used when suffi- glass material called Filon which is com- cient level ground is available near a site monly used to construct greenhouses. The

Figure VIIl-7a.— Pond Collector With a Rigid Cover

PHOTO Courtesy of University of Call fornta, Lawrence Llvermore Laboratory and the U S Department of Energy 258 ● Solar Technology to Today’s Energy Needs

1. Polyvinylchloride Pool Liner 2, Solar Reflector (North Side) 3. Outer Glazing of Collector 4. Collector absorber Surface and Inner Glazing 5. Bead Insulation 6. Earth Berm 7. Pool Water 8. Pool Extension Wall 9, Support Structure

Source J Taylor Beard, Ibid entire collector is inclined to provide a slope devices should be able to provide fluids at of 0.083 percent (1 inch in 100 feet) of col- about 900 C. PVC bags could not be used at lector length. One I imitation of this design is these temperatures, however. that the thin PVC bag probably must be re- A number of improvements to this basic placed every 5 years. It is estimated that this design are being investigated. The Teledyne- replacement wilI cost about $6/m2 of collec- Brown Company has proposed replacing the tor.19 concrete curbing with an extruded alum- A contracting firm in New Mexico has inum frame which could be assembled estimated that an 8,000 m2 colIector based rapidly on simple footings. This design on this design could be constructed for would also permit rapid replacement of the about $30/m2 . 20 (Smaller systems would, plastic film materials.21 A number of plastic however, be considerably more expensive materials are being examined which would per unit area.) This collector is typically improve on the performance of the PVC operated by filling the bag with water in the systems used in the experimental systems. morning and draining the heated water in Polybutylene (which is used for “boil in the the evening, instead of flowing water con- bag” processed foods) can be extruded into tinuously through the collector. It would be a thin (5 mill 0.1 mm) bag, saving material able to provide fluids at a temperature of costs and permitting operation at higher about sO 0 to 600 C during the summer and temperatures. A du Pont plastic called about 300 to 350 C on sunny winter days, If Hypalon can be used to provide a back ab- a second cover is added to the collector (at sorbing surface for the collector which a probable cost of less than $5/m2 ) the would probably last 10 to 20 years.

19Alan Casamajor, Lawrence Livermore Laboratory, private communication, November 1977 ‘][lr Gerald Guinn, Teledyne-Brown Company, ZOl bld private communication, November 1977. Ch. VIII Co//ectors ● 259

Two systems which use a pond collector Flat-Plate Collectors Assembled Onsite combined with a thermal storage pond have Thomason.–One of the oldest and simplest been built and are currently being tested in solar liquid collector designs used for heat- Virginia 22 23 (figure VI II-7). In one design, the ing buiIdings is the “Solaris ” system de- storage system is simply a trough in the signed by Harry E. Thomason. The first sys- ground lined with a plastic swimming pool tem was installed in a suburb of Washing- liner, The trough is filled with water and ton, D. C., in 1959. In this system, water is covered with a foot of styrofoam beads to pumped to the roof ridge and trickled down provide insulation. The thermal losses from channels of a black-painted, corrugated- such a pond should be acceptable, even aluminum absorber. The heated water is col- without insulation under the pond. The collected in a gutter at the cave. A single glass lector is a modified Thomason trickle col- cover is used. The system can only produce lector placed over the floating beads. The fluids with temperatures in the range of 300 top cover is a fIexible plastic (Monsanto 602) to 500 C. Special ductwork is required in the supported by air pressure from a small houses employing the system, since rela- blower. The pond uses a reflector along the tively large amounts of air must be moved north side to enhance its performance. through the house; the air used to heat the A similar, but somewhat larger pond col- house is cooler than air typically used in lector/storage system (1 ,340 ft2 , 80,000 forced-air heating systems. Systems are sold gallons) has been built to heat a well- with a 5-year guarantee. The performance of insuIated 5,000 ft2 home in StanardsvilIe, the system has been a subject of continuous Va.24 This system, which cost $6,000, is ex- controversy. pected to provide all of the heating needs of Calmac.–Another low-priced collector is the house. A unique radiant heating system the Calmac Sunmat. The absorber consists is used which permits the use of water only of a 4-foot-wide mat of black synthetic rub- 50 to 100 F warmer than the room tempera- ber tubes. At the building site, the mat is ture for heating purposes. spread on l-inch-thick fiberglass insulation Pond collectors provide a smaller fraction board and glazed over with translucent of their output during winter months than pIastic/fiberglass sheets. The Sunmat’s non- tilted collectors since the winter Sun is low metallic materials have been tested up to in the sky. For conditions typical of many 180° C, and the price of materials for solar heating systems, the output occurring double-glazed systems is $35 to $44/m2. during the coldest 6 months of the year is Assembling the system will, of course, add only 5 to 16 percent of the total annual out- significantly to system costs, but the put. (See table VII 1-13 at the end of this assembly is simple enough that unskilled chapter. ) As a result, the attractiveness of workers or homeowners couId do it. The Iife ponds used for heating would be greatly in- expectancy of the system remains to be creased if a low-cost technique for storing established. energy generated by the pond during the summer is developed. It is possible to build Factory-Assembled Modular Collectors the colIector on top of a pond. PPG.-Glass has been used longer than plastic as a flat-plate cover material, and ‘2] Taylor Beard, F A Iachetta, L V Lllleleht, and PPG built its Baseline Solar Collector ~ W Dickey, Annual Co//ect/on and Storage of So/ar Energy for the Ffeat/ng of Elu//dings, A nnua/ Progress around standard, hermetically sealed, Report, May 1976-J uly 1977 to ERDA under Contract double-pane window units. PPG’s collector No E-(40-1 }51 36, Publl( ation ORO,’51 36-77 consists of a flat, black, aluminum roll-bond ‘‘john W Dickey, “Total Solar Heat-Totally Non- absorber backed by 6 cm of fiberglass in- polluting, ” presented at E Ieventh Advanced Seminar, Society for Cllnlcal Ecology, San Francisco, Callf , sulation. Panels are 193 by 87 by 9.5 cm Oct 31, 1977 (76-3/16 by 34-3/16 by 3-3/4 in) and weigh 50 “John W Dickey, Ibid kg (110 Ibs) empty. They are available only .- 260 ● Solar Technology to Today’s Energy Needs

through distributors and contractors. PPG Honeywell/Lennox.–Where output tem- recommends that the collectors be used in a peratures of 950 C and higher are required, closed system with treated water to prevent higher efficiency can be achieved if a selec- corrosion. Collectors are sold with a 2-year tive-surfaced absorber is combined with two warranty which excludes glass breakage. covers. Lennox Industries markets a collec- (Although the insulation is optional, that op- tor of this type under license from Honey- tion has been assumed in the cost shown in well for around $145/m2 wholesale. Two the summary table at the end of this chap- sheets of antireflection-etc heal, low-iron ter. Other options include copper roll-bond glass, and a black-chrome selective coating absorbers, selective surface, and singlecover on the steel absorber are key features of the glass.) high-performance Honeywell LSC-18-I Solar Collector. Copper tubing, bonded to the Sunworks.–Sunworks sells a selective-sur- steel plate, provides the resistance of cop- face collector with a single glass cover for per to fluid corrosion without the expense of $84 to $114/m2. This design can achieve effi- an all-copper system. ciencies comparable to those of doublecover systems which do not use selective Panel dimensions are 183 by 91 by 16.5 surfaces. The absorber is copper tubing cm (6 ft by 3 ft by 6-1/2 in) and dry weight is soldered to a copper sheet and treated to 68 kg(150 Ibs). produce a selective surface. Because it is copper, a tapwater, flow-through system can Solaron.-The Solaron collector is an air- be used. Panels measure 91 by 213 by 10 cm heating device designed by George Lof, who (4 ft by 7 ft by 4 in), and weigh 50 kg (110 Ibs) has been designing solar collectors for empty. A 5-year warranty is offered, ex- nearly 30 years. The device (shown in figure cluding cover-glass breakage. VI 11-8) has a steel frame insulated with 3.75

Figure VII I-8.—Typical Air Collector Installation

SOURCE Solaron Inc Air to the collector Ch. VIII Co//ectors ● 261

in (9.5 cm) fiberglass and has two 0.125 in spaces the tubes, but puts a reflective (0.32 cm) low-iron, tempered-glass covers. trough behind them. KTA does not evacuate The absorber is a 28-gauge steel plate with a the outer-glass tube, but covers the array of high-absorbance ceramic enamel coating. tubes with a plexiglass cover which serves The collector is about 65-percent efficient both to reduce heat losses and protect the when the temperature of the air leaving the tubes. Owens-1 Ilinois, KTA, and General colIector is 490 C above the ambient a i r Electric apply a selective surface to the ab- temperature. 25 The company has attempted sorber while Philips applies a selective heat to make the collector easy to install by mirror of indium oxide to the outer-glass designing units so that they can be butted tube. together and bolted in place without additional fittings between collectors, The CONCENTRATING COLLECTORS wholesale price of the device is currently

$1 18/m2. 2’ Nontracking Concentrating Systems Boosted Flat Plates.–The simplest concen- TUBULAR SOLAR COLLECTORS trator is the boosted flat-plate collector. Another type of stationary collector be- One or more flat mirrors are mounted so ginning to reach the market has a tubular that they reflect light onto a flat-plate collector most of the time. The rows of collec- rather than flat-plate configuration. The tors run east to west and the mirrors are be- heat-transfer fluid is circulated through a tween the rows, In winter, when the Sun is glass or metal tube which is enclosed in a low in the sky, the light comes straight into larger glass tube The space between the inner and outer tubes is dead air or a vacuum, the collectors, missing the mirrors. I n summer, when higher temperatures are needed If a vacuum is combined with a selective surface, thermal losses are much smaller to operate absorption air-conditioning, the Sun is higher in the sky and strikes both the than with the conventional f tat-plate design. collector and the mirrors — thus increasing The tubular concept also eliminates insula- the concentration of Iight on the colIector. tion in back of the absorber. Such a collector can be lighter than the conventional Several varients on this basic approach double-glazed, fIat-plate type, have been proposed, Some of the tubular The outer glass envelope is produced by collectors, shown in figure VIII-10, for exam- the same machines which make fIuorescent- ple, use a stationary or cusp-shaped mirror Iighting tubes. Indeed, three of the four to achieve a low level of concentration. A manufacturers of tubuIar colIectors are also system proposed by K. Celchuck of JPL uses major makers of tubular lamps. The fourth, a shaped-mirror unit mounted between sta- KTA, is a small business which buys its tub- tionary flat plates, The mirror unit is man- ing from a large fIuorescent Iight tube manu- ually I if ted and rotated twice a year to en- facturer. sure maximum performance during the summer and winter seasons Each manufacturer boosts its collector’s performance differently (figure VI 11-9). Phil- Several recent theoretical and experimen- ips of the Netherlands and KTA silver the tal studies of the performance of simple bottom half of the glass tube. Owens-1 Illinois mirror booster systems have indicated that spaces the tubes and places a flat, white the output Of flat-plate collectors can be en- refIector behind them. General EIectric also hanced by factors of 1.45 to 1.6.2728

27A M Clauslng and A L Edgecombe, “Solar Col- 2 ‘The Solaron Corporation, 485001 Ive Street, Conl- lector Cost Reduction with Reflector Enhancement, ” merce City, Colo 80022, “Technical Data, Selres 2000 ISES 1977 meeting, p 37-25 Alr Type Solar Col Iector ” “R L. Reid, et al , “Measurements on the Effect of “George Lof, Solaron Corporation, private com- Planar Reflectors on the Flux Received by Flat-Plate munlcatlon, November 1977 Collectors,” ISES 1977 conference, p 37-12 262 ● Solar Technology to Today’s Energy Needs

Figure VlIl-9.— Various Tubular Collector Designs

Philips

0 ,/ /

Proposed optimum cusp designs (J. D, Garrison)

Solar rays

Corning Glass

SOURCES Manufacturers data Garrison, J D ‘Optlmlzatlon of a Fixed Solar Thermal Energy Collector, ” Proceedings of the 1977 Annual Meeting of the American SectIon of the International Solar Energy Society, Orlando Florida. June 6-10 1977, p 36-15 Ortabasl, U and W M Buehl, ‘Heat Pipe Solar Thermal Collec- tor, 1977 ISES meeting, p 36-30 Ch. VIII Collectors ● 26.3

—

Figure Vlll-10.— Flat-Plate Collectors ficiencies as high as 60 to 75 percent are With Stationary Boosters theoreticalIy possible using plexiglass cells 1 to 2 meters on a side,31

Compound Parabolic Collectors.-The Com- pound Parabolic Concentrator (C PC) collector (also called the “Winston” or “Baranov” collector) consists of a stationary refIective Prepared by OTA from data below trough with a receiver at the bottom Each wall is a section of a parabola, and the system is designed so that all of the light 0.5 received from a relatively large region of the sky will reach the receiver surface (see 04 figure VI 11-11). Sunlight received from a solar disk which is not on the main axis of the collector, however, produces a very ir- 0.3 regular image on the receiver and some care must be taken to ensure that this lack of uniform illumination does not create damage 0.2 1 . Collector with no reflector to the receiver. Systems with concentration ratios of 9 to 10 can be designed which are able to collect energy from the Sun’s disk for at least 7 hours each day with only 10 position adjustments per year.32 If the system is not seasonally adjusted, useful output will be available for less than 7 hours. (A two-dimensional concentrating system has also been designed, but this system must be moved at 15-minute intervals about one axis to follow the Sun during the day. ) The mirror shape developed for this design can also be used at the focus of other concentrating sys- Total-Internal Reflection Concentrator.–A tems to reduce the requirements for high- concentrator system using a plastic doped tracking precision. with fIuorescent dies has recently been suggested which may be able to achieve con- The CPC cuts costs by eliminating the centrations on the order of 100 x with no need for elaborate tracking systems, but it tracking. 29 30 The dye molecule reradiates uses more mirror area than a trough or dish light that it absorbs at a random angle. The of the same aperture because of the steep reradiated Iight striking the receiving sur- angles of its reflective sides. The CPC also face at an angle greater than the angle of uses more receiver pipes because of its total internal reflection continues to be lower concentration ratio. Moreover, multi- reflected until it reaches the edge of the ple reflections inside the collector can at- sheet covered with the receiver. (The fre- tenuate the sunlight before it reaches the

quency of the reradiated light can be se- receiver, These factors considerably inlected to optimize photovoltaic cell per- crease the cost of the CPC design. inexpen- formance.) If the dye has zero absorptivity sive techniques have been proposed for pro- at the reradiated frequencies, collection ef- ducing the required shape by extrusion or other shaping processes. Material costs of 29W H Weber and ] Ldmbe, Appl Opt 16, 2299 $5 to $20/m2 appear possible for collectors {1 976) ‘“A Goetzberger and W Breubel, Appl Phys 14, 121 ‘lA Goetzberger, op clt (1977) “Argonne, op clt 264 ● Solar Technology to Today’s Energy Needs

Figure VII I-I 1.—One-Axis Compound Parabolic Collector

used with photovoltaic systems. Fabricating ONE-AXIS TRACKING costs are difficuit to estimate at this point. One-axis tracking collectors concentrate Active Tracking and Concentrating Systems the Sun’s energy onto a I i near receiver. They typically are capable of producing tempera- Techniques used to track the Sun fall into tures in the range of 1500 to 3000 C, and three broad categories: there are many different ingenious designs. 1. Systems in which the concentrator and One-axis trackers can either follow the Sun the receiver both rotate (focusing can from east to west each day, or they can face be by means of a curved or segmented due south and tilt up-and-down to follow the mirror or a Fresnel lens); Sun. The terminology can be confusing because the axis of the east-to-west tracker 2 Systems in which the concentrating mir- runs i n a north-to-south Iine, and the axis of rors remain stationary and the receiver the south-facing collector runs in an east-to- shifts to follow a moving focal point or west line, Solar technologists usualIy refer line; and to these collectors according to their axis 3 Heliostat systems in which the mirrors orientations. Thus, for example, a parabolic rotate to focus light onto a stationary trough concentrator which follows the Sun receiver. from east to west is called a “north-south Ch. Vlll Collectors ● 26.5

Figure VIII-12. —Albuquerque-Western Tracking Collectors Installed on Modular Home

. .

PHOTO Courtesy of Albuquerque Western Solar Industries

trough, ” The “north-to-south” polar-mount they are designed for easy replacement on- collectors collect more energy than north- site. south or east-west troughs with horizontal axes Sandia: As part of its total energy program, Sandia Laboratories in Albuquerque Collector and Receiver—Both Tracking has built some high-performance parabolic troughs for use at 2300 to 3150 C. Sandia’s Parabolic Troughs. –AIbuquerque- Western: units, Iike most other Iinear-focus colIectors, Albuquerque-Western Industries, a modular may be mounted with the axis oriented housebuilder, is now producing parabolic either east-west or north-south. The receiver trough solar collectors as well as complete is a selectively coated pipe inside an evac- solar heating and water heating systems. uatd glass tube. The cost of the system in The company has installed systems on new commerciaI production has not been estab- modular houses (figure V I I l-l 2) and on ex- lished. isting conventional residences. The collectors (including tracker) sell for $48 to $51 per Acurex: Acurex Corporation is commer- square meter of aperture. This makes them cialIy producing two models of parabolic less expensive than most flat-plate collec- troughs. One is a high-performance para- tors Each trough is 51 cm wide and 2.44 m bolic trough similar to the Sandia design long (20 in by 8 ft) with a clear Tedlar plastic (figure VllI-13). The trough is formed by front window and a 3.2 cm (1 ,25 in) flat- clamping polished aluminum refIective black copper absorber tube inside The sheets to parabolic ribs. The sheets are eas- reflector is aluminized Mylar. The present ily replaceable and the units CO I lapse for unpressurized system is designed to produce compact shipping. Black chrome selective hot water at up to 880°C , Albuquerque- coating is used on the 3,35 cm (1.3 in) Western Industries is working on an im- diameter stainless steel absorber pipe which proved but more expensive collector which is inside a 5.08 cm (2 in) diameter glass tube wilI produce 1500 C, enough to run absorp- (not evacuated). The absorber tube is spe- tion air-conditioning or to store more heat cially designed to increase heat transfer to for winter heating, The Mylar reflector may the flu id. Each trough is 3.05 meters long have a relatively short life, and a new and 1.83 meters wide (10 by 6 ft), and eight material may need to be developed; but troughs (end-to-end) can be driven by each .’ ? - , 1.! r ) - 1,4 266 ● Solar Technology to Today’s Energy Needs

Figure VIII-13.—Acurex Parabolic Trough

Shadow Band Tracker Reflecting Lighting Sheet

Absorbing Receiver Tube Mot;r Drive PHOTO Courtesy of Acurex Corporation, 1977 tracker unit. The receiver pipes of the eight coated, anodized, polished sheet aluminum, collectors attach directly to one another, but other material may be used in the future eliminating much interconnect piping and to achieve better reflectivity. There is a 2-, reflector end losses. The other trough design 5-, and 10-year limited warranty on moving is basically similar but is designed for use at parts, reflectors, absorbers, and framework, lower temperatures (less than 1800 C). It is respectively. only 4 feet wide and the absorber tube is un- Beam Engineering: Beam Engineering covered. In a recent contract, Acurex sold makes a sheet aluminum parabolic trough 625 m2 of its collectors to New Mexico State very simiIar to the Albuquerque-Western University for $156/m2. trough, except that each Beam trough is smaller and has its own tracker (figure Solartec: Solartec Corporation is produc- VI 11-14). Costs are considerably higher but ing a 44X concentration parabolic trough Beam feels that large orders and the use of which heats pressurized water or other fewer trackers could lower prices signifi- fluids to over 200° C. Each 1.22 by 3.05 m (4 cantly. Each collector is 1.83 m long and by 10 ft) trough has an aperture of 3,4 m2 0.51 m wide (6 ft by 20 in) with a replaceable and weighs 25 kg. The 2.54 cm (1 in) hard clear Tedlar front window and a 5.08 cm (2 copper absorber pipe has a selective coat- in) black-copper absorber tube. ing. A smaller pipe within the absorber pipe improves fluid heat transfer by increasing Linear Fresnel Lens.–A linear Fresnel lens of the flow velocity, The mirror is presently extruded acrylic plastic forms the focusing Ch. VIII Collectors ● 267

Figure Vlll-14.— Beam Engineering Parabolic Trough on a Polar Mount

PHOTO Courtesy of Beam Englneenng element of the Northrup concentrating solar cient absorber. This advanced unit will pro- collector shown in figure VII 1-15. Northrup duce the higher temperatures necessary for Inc., a Texas Company whose principal busi- efficient absorption air-conditioning and ness has been manufacturing heating and heat engine operation. cooling products, has invested nearly McDonnell-Douglas Company has devel- $250,000 developing this unit. Several large oped several prototype high-performance DOE-assisted demonstration projects are us- linear Fresnel collectors under contract to ing Northrup collectors. Each unit is 3.05 m the DOE/Sandia Solar Total Energy Pro- long with a 30.5 cm wide aperture (10 ft by gram. Using Therminol heat-transfer fluid, 12 in). The recommended mounting is with the units have produced 3150 C steam. The the axis parallel to the Earth’s axis (“polar 3.8-cm- (1 ‘A-in) wide absorber tube is coated mount”) and with a center-to-center spacing with a black-chrome selective surface and of 60 to 75 cm between adjacent units. One placed in a glass tube to cut heat loss (figure tracker drives 24 units. Northrup offers a VIII-16). The collector design is still being limited warranty on all parts and workman- developed. The lenses used are manufac- ship of 18 months from shipment or 12 33 tured by Swedlow, Inc. The lenses used in months from instalIation, whichever occurs the prototype were cast in one 94 by 233 cm first. Currently, the collectors are much (37 by 92 in) piece and produced a concen- more expensive than flat-plate devices tration ratio of 21:1 Swedlow believes that capable of producing energy at equivalent 40:1 is about the maximum practical limit rates,

Northrup is also working on a higher per- ‘‘W R Lee (Swedlow, lnc , Staff As$lstant, formance linear Fresnel collector with a Marketing Vice President), private communication, greater concentration ratio and a more effi- Nov 17, 1976 268 ● Solar Technology to Today’s Energy Needs

Figure VIII-15 .—(a) The Linear Fresnel Lens Figure Vlll-16.— Receiver Pipe Inside and the Absorber Tube are Both Visible in McDonnell Douglas Prototype Linear This Cross-Sectional End-View Fresnel Lens Concentrator of the Northrup Concentrating Collector

(b) Array of Northrup Collectors is Mounted for Polar Tracking

PHOTO: Courtesy of McDonnell Douglas Astronaut~cs Co

General Atomic.–General Atomic Com- pany has patented a design for a trough consisting of reflective strips which can be rigidly fixed while still maintaining sharp focus (figure VIII-17). The design is sometimes called the Russell collector after one of its inventors. The troughs are oriented east to PHOTOS Courtesy of Northrup, Inc west and a glass mirror is bonded to a con- for linear Fresnel lens concentration. More crete form. The focal line moves in a cir- information on the Swedlow cast-acrylic cular arc as the Sun changes position, and Fresnel lens is presented in the discussion of the absorber pipe moves to follow it. The two-axis, full-tracking systems. pipe is a high-performance design and may incorporate a secondary reflector to raise Tracking Receiver—Stationary Mirrors the overall concentration ratio to 60:1.

These designs give the benefits of concen- General Atomic hopes that this design tration while keeping most of the collector can eventually be built to sell for less than area stationary. But since the aperture does $65/m2 installed after a large production in- not follow the Sun, early morning and late dustry is established but, of course, this cost afternoon performance suffers. has not been verified. The design is well Ch. VIII Co//ectors ● 269

Suited to casting in concrete. Sandia has ordered a 7-ft-wide by 400-f t-long prototype from General Atomic being tested in connection with its solar total energy system.34 scientific-Atlanta. Scientific-Atlanta, Inc.,

is a General Atomic licensee and IS producing 2.44 x 3.05 m (8 by 10 ft) collectors (figure VI 11-18). Rather than embedding mirrors in concrete, Scientific-Atlanta uses steel sheet-metal ribs on which the low-iron, back- silvered glass mirrors are fixed. The collectors bolt end-to-end to reduce optical end- Iosses and interconnection pipe expense The receiver is a high-performance, tubular- evacuated collector manufactured by Corn- ing Glass Works. Scientific-Atlanta installed a 50 m2 prototype at the Georgia Institute of Technology in 1975.

J4j Russel (General Atomic Co.], Private com- SOURCE Nontechnical Summary of D@trlbuted Collector Concepts ATR- mun!catlon, March 1977 76(7523 -07)-1 (1) ERDA

Installed at Georgia Institute of Technology Figure Vlll-18.— Russell Collector by Scientific”Atlanta, Inc.,

PHOTO John Furber 270 ● So/ar Technology to Today’s Energy Needs

AAI.-AAI is also developing a fixed trough the light is focused on it by an array of long, with a tracking receiver. The trough has a narrow mirrors which follow the Sun. The circular cross section and the concentration design has several advantages: the receiver ratio is 8:1. It is not designed to produce the pipe carrying heated liquids does not move; very high temperatures of the General the moving mirrors are all relatively small; Atomic design. The effective cost of the and al I mirrors are driven by a single tracker. system would be considerably less if the SunTech Systems (a subsidiary of Shel- trough could be used as a part of a building dahl) is producing a concentrator consisting roof. The axis is oriented east to west and a of 10 long, narrow reflectors which direct wide range of trough sizes is possible. The the Sun onto a single stationary receiver receiver is similar in construction to a long, pipe. Each reflector is 6.1 x 0.30 m (20 by 1 narrow, flat-plate collector mounted upside ft) and is slightly curved to concentrate the down on long arms above the reflecting Sun by four times onto the absorber. This trough. The refIecting surface is glass mirror. gives an overaIl concentration ratio of 40X. Two of these modules are placed end-to- Linear Heliostats/Stationary Receiver end and driven by a single tracker. The linear-segmented reflector concept This unit can withstand very high winds, was originally suggested by Professor F. and the slats are automatically turned up- Francia and tested in 1963 at the Universite side down when the Sun isn’t shining to pre- de Provence in Marseilles. ” The design has vent frost formation or snow accumulation. attracted the interest of several U. S. manu- Sheldahl received a $176,156 ERDA contract facturers. The basic approach is illustrated in 1976 to develop the design. A prototype in figure VII 1-19. The receiver is fixed and , has been installed at Sandia.

“Arrow & Francia, /ourna/ of Solar Energy, Vol 11, 1, Itek is doing research on a similar linear- 1967. segmented reflector. However, Itek’s receiv-

Figure Vlll-19.– ITEK Distributed Collector Concept With Inset Showing the High” Performance Receiver Design

Pyrex tube enclosure (6 inch diameter)

Insulation - (rein-k) / Movable Ch. Vlll Collectors ● 271

er is designed for hi gh performance at even focus ing light on a series of relatively small higher temperatures. AAl is also interested receivers. These smalI units typically are in this concept and has buiIt a prototype. ganged together into a single tracking unit. Determining the optimum size of the indi- TWO-AXIS TRACKING vidual concentrator device will require a substantial amount of engineering analysis Solar collectors capable of producing for each application, temperatures above about 3000 C must be able to track the Sun by rotating about two Ganged Concentrators.–Both mirrors and independent axes. The most common sys- Fresnel lenses can be used in a ganged con- tems are the equatorial and the azimuth centrator. Mirrors have the advantage of mount. The equatorial mount is advanta- being less expensive per unit of aperture and geous because all tracking during the day do not experience chromatic aberation if follows one axis (parallel to the Earth’s axis used to produce high-concentration ratios. of rotation). The change in the Sun’s eleva- (Mirrors will probably be preferred in sys- tion is only a maximum quarter-of-a-degree tems with concentration ratios greater than per day and can be compensated for by a 500 x ).3’ 37 The Varian Corporation has built simple adjustment of the declination axis a two-axis tracking device using an array of every few days. AlI other tracking systems 7 rows of 17 parabolic mirrors each 25 cm require active tracking along both axes dur- (10 in) square, mounted on a single tracking ing the day. The azimuth mount is often platform (see figure VI 11-20). Each mirror used because of its mechanical simplicity; provides a concentration of 1,000 x .38 this mount, for example, is used for most MIT and the National Patent Develop- radar dishes and for naval artillery. The ment Corporation are doing research on a azimuth axis is vertical and the altitude or moduIar, mirror-concentrater/photovoltaic elevation axis follows the Sun’s movement system in which the separate, round, para- from horizontal to vertical. bolic mirrors are connected to a common Two-dimensional concentrators fall into tracking system (see figure VI 11-21). A small three classes: secondary mirror in front of each of the main mirrors reflects Iight back through a 1. Systems which focus light on a small- hole in each main mirror onto a solar cell. point receiver which moves with the op- This reduces any shadows from the cell and tical system. cooling water pipes. A concentration ratio 2 Heliostat systems, where a large field of of 300-500:1 is felt to be optimum. The sys- individual mirrors focus on a central tem is designed to produce both electricity receiving tower from the photovoltaic cells and thermal energy from the liquids used to cool the 3 Stationary concentrators with tracking cells. The company hopes to be able to sell a receivers. complete system of unspecified size for less than $5,000— a system which wilI last at Collector and Receiver Both Tracking least 10 years with minimal maintenance,

Most early two-axis tracking systems used Fresnel lenses have the advantage of a single large reflecting dish which looked being somewhat less sensitive to tracking er- much Iike a radar antenna. These systems may prove to be the most attractive in applications where there is an incentive to focus 3’L W James (Varian), private communication, large amounts of energy on a single point May 6,1976 (e g., where a small heat engine or sophisti- “W R Lee (Swedlow, Inc ), private communi( a- tion, Nov 17, 1976 cated photovoltaic device is employed). In 36L W James (Varian Associates, Baton Rouge, La ), many applications, however, it is possible to phone conversation, April 1976 use a number of smaller concentrating units 3’Washington Post, June 5,1976, p Al 272 ● Solar Technology to Today’s Energy Needs

Figure VIII-20.—The Varian Two-Axis Concentrator Using GaAs Photovoltaic Devices

PHOTO Courtesy of The Varlan Corporation, 1977

rors than mirror systems, and they can be The best material for Fresnels will prob- designed to provide a uniform intensity ably prove to be some kind of acrylic plastic across the receiver surface. The lenses can even though this material is considerably be made from durable plastic materials and more expensive than glass. It is very difficult it may be possible to manufacture them to cast glass with the accuracy and sharp- very inexpensively in mass production facil- ness that is possible with acrylic, which is ities. The special designs required for solar not as viscous as glass when it is cast, Acryl- applications would not add to the cost of ics can be made which can withstand out- manufacturing the systems. 40 4‘ door climates for over 20 years.”42 43 44 Swed-

42R P Falconer (Lectric Lltes Co , V Pres ), private 40W R Lee (Swedlow, Inc ), private communica- communication, Oct 15, 1976 tion, Nov 17, 1976. “W R. Lee (Swedlow, I nc ), prlv,~te communica- *’L. W James, et al (Varlan), “Performance of a 1- tion, Nov 30, 1976. kW Terrestrial Array of AICaAs/GaAs Concentrator “L C Rainhart and W. P Schimmel, Jr (Sandia Solar Cells, ” 12th IEEE Photovoltaic Specialists Con- Labs), “Effect of Outdoor Aging of Acrylic Sheet, ” ference, Baton Rouge, La , Nov 15-18, 1976 SAND 74-0241 Ch. Vlll Collectors ● 273

Figure VIII-21 .—An MIT Design for a Small Fresnel Optics, Inc., of Rochester, N.Y. This Two-Axis Tracking Unit collector consis ts of a checkerboard of square Fresnel lenses mounted on the top surface of a flat box (figure VI 11-23. )

A collector using Fresnel lenses in a design similar to the MIT device discussed previously has been designed for use on an experimental basis by the RCA Corporation (see figure VI 11-24). This kind of design has a relatively low profile and can be integrated into a house or building more easily than any other type of two-axis tracking system. Large Paraboloid. -Large tracking parabolic dishes are commercially available but current commercial designs are much too expensive for any practical solar energy system application.

The Jet Propulsion Laboratory (JPL) of the California Institute of Technology has developed a conceptual design for a high-efficiency, low-cost paraboloidal solar powerplant (figure VII I-25). The reflecting surface is made of commercially available silvered mirrors which are curved sIightly by glueing them to concave pieces of foam glass. These curved pieces are then mounted on a metal framework and all are aimed at a single focal point, The entire framework tracks the Sun. The tracking paraboloid system is well suited for applications using a Stirling or Brayton engine and electric generator. JPL has estimated that it may be possible to low, Inc., has estimated the price at which mass produce and instalI these collectors for they could sell cast-acrylic Fresnel lenses at less than $120/m2 . 46 The mirror and foam various production levels. These estimates glass surface cost about $20/m2. This is ad- appear in figure VI I I-22. Swedlow has in- mittedly optimistic since precision tracking vested about $200,000 in solar lens research radar dishes now cost about $322/m 2,47 but at this writing, and the firm estimates that a the solar devices could be produced in large-scale production line could be oper- much greater quantities and would not need ating in 22 months if a decision is made to to be as precisely constructed or as reliable, initiate manufacture. 45

Sandia Laboratories, Albuquerque, has built a 1 kWe photovoltaic test bed using 46M K Selchuk, et a I , So/ar Stir/ing Power Genera- pressed-acrylic Fresnel lenses supplied by tion. Systems A na/ys is and Preliminary Tests, Pro- ceed ings of the 1977 Annua I Meeting of the American SectIon of the International Solar Fnergy Soc(ety, “it’ R ~.ee (Sw[’dlow, I nc ), private commu nlca- orlando, Fla , June 6-10, 1977, p 20-8 47 tlon, Oct 14, 1976 Selchuk, op cit., p 20-9 274 ● Solar Technology to Today’s Energy Needs

Figure Vlll-22.— Sales Price of Cast-Acrylic Fresnel Lens Versus Production Volume

Note:

SOURCE Urrsohclted Tecfmmal Proposal for Casf-Acry/lc Fresne/ Lenses for Scl/ar-Ce// Energy Generator?, Swedlow Report No 873, September 30 1976 Swedlow Inc Garden Grove CA pp 5-3

The Carousel Collector. -Another approach receiver as light rather than through an ex- to two-axis tracking is illustrated in figure pensive piping network as heat. VI 1 I-26. In this approach, a number of one- Francia Solar Heliostat Tower.–Professor axis tracking parabolic troughs are mounted Francia of the University of Genoa has had a together in a platform which rotates to 100 kW solar steam-generating station follow the Sun. The system illustrated is t operation near Genoa (S. IIario), Italy, since mounted on tracks, but it is also possible to 1967 (figure VI 11-27). All of the mirrors in the simply float the platform on a pond of field are linked together and driven by a water. ” A simpler one-axis tracking system single pendulum clock. A joint venture of can be manufactured along the same lines ANSALDO, S.A., a large Italian industrial by rigidly mounting the trough concen- organization, and Messerschmidt of Ger- trators on the rotating platform. many is now selling solar steam-generating systems of Francia’s design. The Georgia In- Heliostat/Central Receiver stitute of Technology in Atlanta bought a

The heliostat/central receiver arrange- 400 kWt test facility of this design from ment can be scaled up to very large sizes, ANSALDO. It began operating on the although small systems may also be useful. Georgia Tech campus in 1977.49 In addition Such a system has an advantage over most to the innovative linked-mirror field, the distributed collector field concepts in that Francia design appears to have an unusually the energy is transmitted to the central

4’S H Bomar (Georgia Institute of Technology), 48 Solar Energy Digest (9)1 (1 977) private communication, Nov 13, 1976 Ch. VIII Collectors ● .275 —.——-

Figure Vlll-23.— 1kWe Focusing Photovoltaic Test Bed at Sandia Laboratories, Albuquerque” 1 -square Foot Fresnel Lenses FOCUS on 2-in. -Diameter Solar Cells

PHOTO Courtesy of Sandla Laboratories 276 ● Solar Technology to Today’s Energy Needs

Figure Vlll-24.— RCA’S 300We Photovoltaic Concentrator

PHOTO Courtesy of RCA

Figure VI II-25 .—JPL Paraboloid Design With high thermal efficiency, Professor Francia Stirling Engine at Collector FOCUS has reported a net collection efficiency of 73 percent.50 Analysis at Georgia Tech indicates that even better results can be obtained by using molten salt or liquid metal instead of steam in this type of receiver.51

Francia’s design has been used by Mit- subishi Heavy Industries, Ltd., of Hiroshima

to build the 7 kWt test facility (shown in figure VI 11-28). Mitsubishi changed the heliostat design slightly. to allow the field to move its focus from one receiver tower to another. This improvement has been incor-

‘“G Francia, Large Sea/e Central Receiver Solar Test Facilities, ProceecJ; ngs of the International Seminar on Large Scale Solar Energy Test Facilities, Las Cruces, N Mex , Nov 18-19, 1974, pp. 101-136, p 130 SC)URCE Prepared by OTA usng manufacturer s iiatd “R W. Larson (Professor, Ceorgla Institute of Tech- SOURCE Prepared by OTA using JPL Information nology), private communication, September 1976. Ch. Vlll Collectors ● 277

Figure Vlll-26.— Sunpower Systems Solar Powerplant

—--7.

\ .

SOURCE Sunpower Systems Corp Tempe, Arlz 278 ● Solar Technology to Today’s Energy Needs

Figure VIII-27.—Francia 100 kW+ Solar Powerplant been directed to the design of large helio- (Closeup of heliostats showing tracking- stat/central-receiver electric powerplants Iinkage on back) designed primarily for desert regions. A number of variations on the basic design have been funded by DOE and the Electric Power Research Institute. Present plans call for a 100 MWe pilot plant, preceded by a 5 MWe test facility at Sandia Albuquerque and a 10MWe demonstration plant at Bar- stow, Cal if. (table VI 11-3).

Three companies designed complete systems, and Boeing contracted to design just the heliostats. The heliostats designed all have refIector areas of approximately 40 m2, but designs differ considerably (figure VI 11-29). Boeing’s design employs a thin layer of Kaptan stretched over a lightweight frame. The system is shielded from the weather with a transparent plastic bubble, . The Honeywell design uses six 2.1 x 3.1 m (7 by 10 ft) mirrors mounted on a common turntable. The mirror mounts are aluminum “egg crate” with plastic filling, The Martin Marietta/Georgia Tech design uses 25, 1.22 by 1.22 m (4 by 4 ft) mirrors mounted on a common tracker. This array forms a crude parabola with a concentration ratio of approximately 5.3:1. The McDonnell Douglas/ University of Houston design uses a single 37 m’ (400 ft2) mirror mounted on large-cell honeycomb material.53

The three receiver concepts also differ considerably. Martin Marietta is designing a high-efficiency cavity receiver to face a heliostat field to the north. The Honeywell receiver accepts Iight through an opening in its bottom, and the receiver tower is located n the center of the heliostat field. McDon- nell-Douglas is designing an open panel re- PHOTO Courtesy of Georgia Tech ceiver to be located slightly south of the center of the heliostat field (figure VI 11-30). porated into the test facility sold to Georgia Tech by ANSALDO. 52 The Department of Energy has selected the McDonnell-Douglas design for its initial Federally Sponsored Heliostat/Central Re- 10 MW demonstration. An artist’s concept ceiver Designs. –DOE’s biggest solar invest- of the completed 10 MW facility is shown in ment in collector development thus far has — “Data on these collectors was taken from Survey of 52G Beer and R Flores (ANSALDO S P A ), private Several Central Receiver Solar Therma/ Powerp/ant communications, Oct 28-29, 1976 Design Concepts, J PL, August 1975. Ch. VIII Collectors ● 279

Figure Vlll-28.— Mitsubishi (7 kWt) Heliostat/Receiver Test Bed

Specifications

Energy Collected about 7 kWt Mirror 0,3 x 0.4 m2, 120 pieces Heliostat 60 pieces Tower Height 3m Absorber Cavity type 0.5 x O 6 m2 Heat Carrier Air. max 800° C

SOURCE K Yanagl (Mroshlma Technical Institute Mltsublsht Heavy Industries Ltd ) Solar Energy Collecting Test Apparatus

. 280 ● Solar Technology to Today’s Energy Needs

Table Vlll-3.—Characteristics of Competing Designs for the 10 MWe Solar Central Receiver Powerplant

Boeing Honeywell Mart in-Marietta McDonnell-Douglas

4 4 4 Annual energy output 4.3 x 10 3.4 x 10 3.6 X 10 (MWh) Collector Subsystem Heliostat construction metalized plastic glass mirror, low- glass mirror, steel glass mirror, steel reflector, aluminum profile steel frame, frame, multifaceted, frame, multifaceted, and steel frame multifaceted, focused focused focused Number of heliostats 3,146 2,320 1,718 2,350 Reflective surface per 29 m2 40 m2 37.2 m2 30.8 m2 heliostat Total area reflective 91,234 m2 92,800 m2 63,866 m2 72,380 m2 surface Field size 308 m radius 565 m x 565 m 527 m x 527 m Receiver subsystem Receiver type vertical cavity horizontal cavity external absorber Tower height 146 m 137 m 101.4 m Receiver working fluid water/steam water/steam water/ steam Storage subsystem Storage mechanism latent heat sensible heat sensible heat Storage media salts HITEC/hydro- rocks/ hydrocarbon heat carbon heat transfer fluid transfer fIuid Electrical generation subsystem Turbine rating 15 MW 12.5 MW 15 MW Turbine fluid steam steam steam

SOURCE Department of Energy figure VllI-31, and construction of McDon- At least three organizations are currently nell-Douglas heliostats or a 5-MW system is working on this concept— Environmental shown in figure VIIl-32 Consulting Services, Inc., of Colorado, E- Systems Garland Division in Texas, and Stationary Concentratord ‘ g Receiver C.N.R.S. (the French national petroleum This concept uses a fixed-mirror/moving- company). E-Systems is a large, high-tech- receiver system with two dimensions of con- nology company which has built and in- centration. A section of a sphere made from stalled dozens of fully tracking parabolic mirror surfaces produces a radial Iine-focus communications dishes and also refinished pointing at the Sun (figure VI 11-33). Only the the huge, stationary spherical radiotele- receiver pipe moves to follow this line of scope reflector at Arecibo, Puerto Rico. As a high-intensity sunlight around the inside of result of the firm’s experience with both the stationary dish. Because the dish does types of collectors, it considers the fixed- not track, this system collects much less sphere design a more economical solar col- light in the early mornings and late after- lector even when the reduced performance noons than tracking dishes. Its success will is taken into account. SmalIer colIectors can depend on whether initial and operating be integrated into a building’s roof, and costs will be sufficiently below the costs of larger dishes could be mounted in an ex- tracking dishes to compensate for its disad- cavation to serve several buildings, a fac- vantages. tory, or a community. Ch. Vlll Collectors ● 281

Figure Vlll-29.– Pilot Plant Heliostat Concepts

Boeing

McDonnell Douglas Martin Marietta

SOURCE Prepared by OTA using manufacturer’s data 282 ● Solar Technology to Today’s Energy Needs

Figure Vlll-30.— Pilot Plant Receiver Concepts

McDonnell Douglas

Honeywell

SOURCE Prepared by OTA using manufacturers data

Figure VIII-31 .—McDonnell Douglas 10-MW Pilot Plant Design. The Heliostat Field Surrounds the Thermal Storage (Circular Tank), Tower, and Electrical Generation Subsystems. Note the Octagonal Shaped Heliostats Ch. VIII Co//ectors ● 283

Figure VIII-32. —The 5-MW Central Receiver Demonstration Under Construction in Albuquerque, N. Mex.

‘.e

‘

Photograph by John Furber

Figure VIII-33. —Cross-Section of Stationary Hemisphere Concentrator

Heat transfer . A

Fixed absorber

Turbine

SOURCE E. Systems Inc absorber facility 284 ● Solar Technology to Today’s Energy Needs

ENVIRONMENTAL IMPACTS

The two largest environmental effects of Glycol and other heat transport fluids the manufacture of solar collectors result degrade, and must be replaced periodically. from the emissions associated with the This disposal could also create environmen- energy generated to manufacture the detal problems.55 vices, and the impact of the collectors on land use in cases where the collectors cannot be integrated into the roof, walls, or im- MANUFACTURING HAZARDS mediate landscape of a building. These problems are discussed in some detail in Many of the plastics being used or pro- chapter VI 1. There will also be a number of posed for use in inexpensive solar collectors occupational health and safety issues asso- can create hazards for employees in plants ciated with the manufacture of specific col- manufacturing the materials, even though lector designs, most of the plastics are not harmful after they are fabricated and units installed. Plastics are used in collector covers, Fresnel WORKING FLUIDS lenses, thin mirror surfaces, piping, and a variety of other places in solar systems. Some of the chemicals used in solar Most of these materials are manufactured in domestic water heaters to slow corrosion in substantial volume today and the solar in- the collector and to prevent the working dustry would only have the effect of increas- fluid from freezing can be harmful if the col- ing the number of persons exposed to any lector fluid leaks through a heat exchanger risks that may now exist. None of the and mixes with the hot-water supply. I n most materials described below are uniquely re- regions, double-walI heat exchangers are required for the manufacture of solar collec- quired by local codes to protect against ac- tors. If it is determined that any of the cidental leakage when potentially harmful materials now in use create unacceptable chemicals are used. A lethal dose of ethyl- environmental hazards, substitutes could ene glycol which is commonly used as an undoubtedly be found. antifreeze in colIector fIuids is about 100 gm (1.3 lb) for an average adult. About 1/2 liter In simple flat-plate collectors, thin strips (18 OZ) of the glycol-water mixture used in of Styrofoam or similar materials are often typical systems would have to be ingested to used as insulation or backing; these com- obtain a lethal dose. It is unlikely, however, pounds contain styrine, which the EPA class- that the heat exchangers wouId leak so mas- ifies as a suspected carcinogen. Some sili- sively that undiluted collector fluid would cone elastomers and polysulfide-based com- appear in the hot tapwater without being pounds are used as sealants in solar collec- detected. Chronic ingestion of small tor units; silanes, contained in the silicone amounts of ethelyene glycol can, however, elastomers, are considered moderately to cause “moderately toxic systemic effects.”54 highly toxic during the manufacturing process. Organic sulfides, compounds found in Some of the working fluids proposed for polysulfide-based materials, can cause an use with higher temperature systems can acute reaction that could cause a person to also be caustic or toxic if leaks develop in become unconscious after one alcoholic the plumbing systems, but these chemicals drink. would not come into close proximity to potable water. Urethanes are contained in polyurethane foams, which are often used as insulation in

“J. G. Holmes, “Environmental and Safety implications of Solar Technologies, ” ISES 1977 meeting, p, 285 55J G. Holmes, op. cit Ch. V/// Co//ectors ● 285

plumbing connected to solar collectors. EPA which are considered moderately toxic. And suspects that urethane is a carcinogen. coatings or encapsulant on flat-plate solar cells may be made from plastic-based films, The transparent covers used on flat-plate which contain melamine, a moderately toxic collectors are often made of acrylic plastics material. or plastic films such as Mylar, Tedlar, Kynar, Korad, and Teflon. Some plastics contain Vinyl chlorides are used extensively in the methyl methacrylate, which is considered to manufacture of a number of inexpensive be moderately toxic by the EPA. Others con- collectors. Unfortunately, vinyl chlorides tain fluorocarbons which are only slightly (along with other plastics) cause disposal toxic, but can be an environmental problem. problems and can be hazardous. The mater- (See the discussion of fluorocarbons in ials are not biodegradable, and they may chapter VI 1.) produce toxic fumes if burning is used as a means of disposal. Research is underway to Concentrating lenses and reflecting mir- develop biodegradable plastics to help alle- rors are generalIy acrylic-based plastics, viate the plastic disposal problem.

COLLECTOR COSTS

FOB COLLECTOR PRICES ings, drive motors, and tracking controls, but exclude the cost of pumps, storage, and Unless otherwise noted, the collector controls. Prices for collectors other than flat prices cited in this chapter (including those plates are in dollars per-square-meter of shown in tables VII I-4 through VI 11-8) are useful aperture, while flat-plate collector FOB factory prices and do not include ship- prices are per-square-meter of gross collec- ping or installation. Estimates of collector tor area. This gross area includes the area instalIation costs vary greatly (see discus- blocked out by the “window frame” and sion in volume 11, chapter IV). Table VII I-9 thus makes the flat plates appear a bit less contains an estimate of installation costs costly than if they were priced on a useful which may be obtainable in a mature aperture basis. market. Each manufacturer was contacted direct- In a few cases involving larger systems, ly and asked for quantity factory prices to the companies indicated that they would in- contractors, excluding shipping, installation, stall only the entire system and would not and interconnecting piping. Since most col- sell collectors separately, Where a price lectors other than flat plate are not yet in range is given, the lower price corresponds mass production, manufacturers were asked to a large order while the higher price cor- for both present limited-production prices responds to a smalI order. As noted, some and what prices they projected in mass pro- manufacturers of flat-plate collectors, and duction. All prices were requested in con- the foreign distributors, will sell directly to stant 1976 dolIars and all inquiries were individuals at these prices, Most, however, made in 1976, sell only to distributors, contractors, and ar- chitect/engineering firms, COLLECTOR SUMMARY TABLES All pricing data in this section are in 1976 dollars. Prices include headers, but exclude The following abbreviations are utilized the controls, pumps, and interconnectin g in tables VII I-4 through VII I-8: pipe which most collectors require. Prices of tracking collectors include trackers, bear- Sel. Surf. –Selective surface absorber ab- 286 . Solar Technology to Today’s Energy Needs

Table Vlll-4.—Stationary Flat-Plate Collectors

Present wholesale Expected price price f.o.b. factory when in Design Company Type/feature ($/m2) mass product ion Status temperature

Thomason flat plate 32-43 commercial 67° C trickle system to consumer 1 glass cover Sun works flat plate 85-114 about same commercial 57 0-97“c sel. surf. product ion 1 cover, glass PPG flat plate 80-107 same commercial mass 57°-97 “c (opt. sel. surf. ) product ion 2 glass covers Al roll-bond (opt. Cu roll-bond) Reynolds flat plate 54-65 same commercial 57°-97 “c Alum inure (opt. sel. surf. ) 2 Tedlar covers N. V. Philips Mark II — $118 R&D 57 °-167°C Al or Cu roll-bond covered with evac. tubes heat mirror Unitspan Cu tube and sheet 86-92 about same commercial 57 °-97° C 2 glass covers to consumer Honeywell/ flat plate 145 or less less commercial 57 °-97°C Lennox Cu tube, steel sheet, 2 etched AR glass covers set. surf. Calmac Flexible mat o 35-44 about same commercial 57°-820°C Manufacturing black EPDM (Retail price; mass production Corp. tubes, 2 fiber- some on-site glass covers. fabrication required)

SOURCE Prepared by OTA using manufacturer’s data

Table Vlll-5.— Foreign Stationary Collectors on U.S. Market

Present wholesale price Foreign f.o.b. U.S. Design company Country U.S. Distr. Type distr. ($/m2) temperature

Miromit ...... Israel American flat plate 119-180 57 °-97°C Heliothermal 1 glass cover Corp. sel. surf. steel tube sheet SAV ...... New Zealand Fred Rice cylindrical 500 57°-97°C Product ions, colIector Inc. incorporates storage Amcor ...... Israel Sol-Therm flat plate 119-147 57°-970°C Corp. 1 glass cover steel tube & sheet

SOURCE Prepared by OTA using manufacturer’s data Ch. Vlli Collectors ● 287

Table VIII-6 . —Stationary Tubular and CPC Collectors

Geometric Present wholesale Expected price concentration price f.o.b. when in Design Company Type/feature ratio factory ($/m2) mass production Status temp.

Owens-l llinois evac. glass tubes — $215 (array aper- 107-130 pilot prod. 97 °-147° C sel. surf. on glass ture excl. headers demon. & inner tube. White and end caps) testing refIector KTA Cu absorber in — 85-104 58-80 commercial 57 °-97°C glass tube. Half product ion siIvered Philips Mark I evac. glass — — 129 R&D 57°-167°C tubes half silvered; heat mirror coating General Electric evac. glass tubes — — 48-81 pilot 57 °-167°C sel. surf. product ion stationary external mirror Steelcraft, Inc. alzak mirror CPC — 269 161-215 commercial 204° C evac. glass tube/ (end of 1976) (end of 1977) production sel. surf. receiver (excluding rack) (excluding rack) (end of glass cover 1976) M-7 International solid plastic CPC 5 — only slightly have proto- electri- for solar cells more expensive type; need city than conven- capital for tional solar tooling cell packaging

SOURCE Prepared by OTA using manufacturer’s data

sorbs light well but does not radi ate Opt. —Optional; available at extra cost. heat as well. Al — Aluminum. Flat Plate— Flat-plate solar collector. Cu —Copper. Heat Mirror— Selective heat mirror coating CPC– Compound parabolic cross-section on transparent cover allows sunlight concentrating solar colIector. to enter but reflects back infrared Evac. – evacuated. heat trying to escape. AR – AntirefIection coated.

COLLECTOR PERFORMANCE

The only accurate test of the value of a and type of storage devices used, local tem- collector is the amount of useful output peratures and wind velocities, and correla- which it can provide per dollar of Iife-cycle tions between energy demands, weather, investment, Unfortunately, there is no sim- and available sunlight: a system which ple way to determine this useful output operates effectively in a home-heating since the useful work done by a colIector system in Albuquerque may be extremely in- depends on the load, the quantity and qual- efficient connected to an air-conditioner in ity of sunlight which is available, the size Boston. 288 Ž Solar Technology to Today’s Energy Needs

Table VIII-7. —One-Axis Tracking Collectors

Present wholesale Geometric price f.o.b. Expected price concentrate ion factory ($/m2) when in Design Company Type/feature ratio (incl. tracker) mass production Status temperature

Albuquerque- parabolic trough 20 48-51 (incl. (developing ad- commercial 32°-1OO°C Western Inc. tedlar window 250 tracker to vanced design) product ion Cu pipe drive 20-28 troughs) Beam parabolic trough 235 or less “much less” commercial 93° C Engineering product ion Sandia Labs parabolic trough (see Acurex) 80% learning demonstrate ion 317°c evac. glass tube/ curve to very sel. surf. abs. low price AAI fixed trough; ~8 — 54-65 w/roof R&D 117°c tracking receiver cred. or 86-97 retrofit General Atomic fixed stepped 60 — R&D 497° C co. trough; tracking (installed) receiver Northrup, Inc. linear Fresnel ~ 10 133-180 commercial 93° C lens; sel. surf. (advance product ion on Cu absorber design) Suntech linear heliostat 40 215-270 46-108 prototype 177°-317°C Systems, Inc. testing Itek linear heliostat — 102 R&D 537° C linear cavity receiver Acurex Corp. parabolic trough 58 160-240 less commercial 60°-31 1‘C (6’ wide) anodized Al mirror product ion glass tube sel. surf. absorber Acurex Corp (see above) 140-210 86 commercial 600-1 77“C (4’ wide) product ion Solartec Corp. parabolic trough 100-172 about same commercial 204° C anodized Al mirror product ion Scientific (see Gen. Atomic) 145-161 about same commercial 204°-326°C Atlanta evac. glass tube/ product ion set. surf. absorber glass mirror

SOURCE Prepared by OTA using manufacturer’s data

It is only possible to evaluate a collector Evaluating the performance of integrated accurately by examining its performance as systems requires a technique for computing a part of an integrated system operating to the amount of output which can be ex- serve a particular building in a specific geo- pected from a collector under different con- graphic area. For this reason, primary atten- ditions. The calculations used to perform tion in this report has been directed to eval- this analysis are explained in some detail in uating the performance of integrated the appendix to this chapter. The basic ap- systems. proaches to the analysis of collector per- Ch. VIII Co//ectors ● 289

Table Vlll-8.—Two-Axis Tracking Collectors

Present wholesale Geometric price f.o.b. Expected price concentration factory ($/m2) when in Design Company Type/feature ratio (incl. tracker) mass production Status temperature

ANSALDO/ ganged kinematic 250-500 ? ready for 600° C Messerschmidt heliostat /tower order E-Systems, Inc. fixed dish — 50-53/m 2 R&D 260° C tracking receiver installed Sandia Labs multiple Fresnel 50-100 224* prototype 27°-100°C & lens w/solar celIs (w/o cells) (w/o cells) electricity acrylic lens JPL parabolic dish 1000 — 115 R&D 815° C 9.75 m square glass mirror Varian multiple parabolic 1000 650-1 ,000’ very low R&D 27°-1OO°C & dishes w/solar (w/o cells) electricity cel Is

2 DOE central power 437-492/m 2 70/m 477° c contractors station, helio- installed heliostats stat/tower govt. demo) 14/m 2 tower receiver

ANSALDO/ parabolic dish 1,800 less ready for 550” C Messerschmidt 832 m2 order 100 kWe National ganged glass 300-500 — 7 R&D 27°-100°C & Patent parabolic dishes electricity Development w/solar celI

ANSALDO/ Heliostat /tower 385 less ready for 600” C Messerschmidt 5MWth/1MWe (incl. tower& order boiler) Sun power parabolic/trough 96 175 about same commercial 500-2600C System Corp. carousel product ion

“ Estimated based on laboratory prototype excludlng des!gn and toollng costs SOURCE Prepared by OTA using manufacturer’s data

formance will be explained briefly in the THE ENERGY AVAILABLE following section and some general conclu- FOR COLLECTION sions will be drawn about the advantages and disadvantages of the major categories The amount of light energy which ulti- of colIector designs. mately reaches the receiver of a collector The next two sections examine the effects depends on two things: which are most important in determining 1. The quantity and quality of the sunlight collector performance and a final section of which reaches the Earth’s surface, and this chapter compares the performance of five generic types of collectors operating in 2. The tracking geometry of the collec- the four cities examined in this study. tors, 290 • Solar Technology to Today’s Energy Needs

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Ill I I I I

...... , ...... c...... - ...... (n ......

LL Ch. VIII Collectors . 291

The Solar Resource other particles suspended in the air), and The amount of light which can be collected by a solar device on the Earth’s sur- 2. The “direct normal” radiation–the face is limited by the cycle of day and night, energy received by a collector which clouds, atmospheric turbidity, seasonal tracked the Sun’s motion precisely, changes which result from the tilt of the keeping the Sun perpendicular, or “nor- Earth’s axis of rotation (the axis tilts toward real, ” to the surface of the receiver. the Sun during the summer in the northern Tracking systems which focus sunlight on hemisphere and the elliptical shape of the a receiver can only make use of “direct nor- Earth’s orbit brings the Earth closer to the mal” radiation. It can be seen that the basic Sun during the winter) and atmospheric dust solar resource varies by about 25 percent which may result from volcanic eruptions or around the national average in June (which local air pollution. It is also possible that is the sunniest month in most climates) and there are long-term cycles in the amount of by about 50 percent in December (which is energy generated by the Sun itself, and there typically the least sunny month). The pat- has been speculation that such cycles are tern of distribution of direct normal radia- responsible for cyclic ice ages and periods tion is somewhat unexpected since there of severe cold which fall short of ice ages seems to be more variation from east to (such as the cold period which gripped west than from north to south. Thus, there is Europe during the reign of Louis XIV]. greater similarity between the amount of There is very little information available direct normal sunlight available in Fort about long-term changes in the amount of Worth, Tex., and Columbus, Ohio, than energy produced by the Sun or about long- there is between Fort Worth and western term cycles in the net clearness of the parts of Texas. Earth’s atmosphere. It has been possible, Several warnings are necessary before however, to assemble continuous measure- proceeding more deeply into an analysis of ments of the intensity of energy reaching the the availability of sunlight around the coun- Earth on a clear day from 1884 to the ples- try. The data on which such analysis now ent by combining records taken at several must be based is of poor quality in most U.S. sites. The result is shown in figure parts of the country; continuous records of VIII-34. It can be seen that changes of 10 direct normal radiation are almost nonexist- percent are typical, but that larger changes ent. (One of the primary criteria in selecting can result from major volcanic eruptions the cities used in this analysis was the avail- even though these explosions took place ability of sunlight data. ) Stations which many thousands of miles from the site measure direct radiation are located in three where the sunlight measurements were of the cities chosen (Albuquerque, N. Mex.; made. Following the explosion of Krakatoa, Blue Hill, Mass. —a town close to Boston; for example, the sunlight reaching the Earth and Omaha, Nebr. ). Even in these cities, fell by nearly 20 percent. however, complete records are difficult to The variation in sunlight available for col- obtain. Most information about direct nor- lection in different parts of the United mal radiation must be obtained indirectly by

States is illustrated in figures VI 11-35 and 36. applyin g statistical ‘techniques to measure- These figures show the solar resource in two ments of the total amount of radiat;on ways: reaching a horizontal surface. (These techniques are discussed in the appendix. ) 1. The total amount of sunlight falling on Another limitation of the analysis is that it a horizontal surface (which includes used data taken in a single year— 1962 (1 963 both the energy received directly from for Boston). Better comparisons could be the sun and the “diffuse energy” re- made if results were averaged over a num- ceived by reflection from clouds and ber of years to eliminate unusual effects 292 ● Solar Technology to Today’s Energy Needs

Figure VIII-34. —Variation of Direct Normal Component of Solar Radiation With Time Northern hemisphere values: typical of air mass = 1.5 100% corresponds to approximately 0.94 kW/m2. The names on the graph refer to major volcanic eruptions. Figure Vlll-35.— Mean Daily Total-Horizontal Solar Radiation (kWh/m2) 294 ● Solar Technology to Today’s Energy Needs

Figure VllI-36.– Mean Daily Direct-Normal Solar Radiation (kWh/m2) 6.0 Ch. VIII Collectors ● 295

which may be due to weather patterns in and a fully tracking collector system with any single year. A comparison between 1962 two other collector geometries: the heliostat data and long-term averages given in the ap- system (in which an array of mirrors directs pendix indicates that, for example, in light to a central tower), and a one-axis Omaha direct normal sunlight was about 13 tracking trough which rotates around a percent below normal in 1962 while in polar axis (an axis which points at the north Boston it was about 15 percent above aver- star). age (see table VII l-A-2). . The heliostat system gathers less energy One of the limitations of the maps shown than other tracking devices because: 1) the in figure VI 11-35 is that they seriously under- heliostats are not turned to face the Sun state the radiation which is available for a directly (these devices must point in a direc- flat-plate collector installed in a northern tion between the Sun’s direction and the latitude. An optimum collector is not hor- direction of the receiver tower), and 2) be- izontal but tilted at an angle close to the cause in the computation used to prepare latitude angle, In northern climates, this op- the data shown, the heliostat devices were timum angle is quite far from the horizontal packed in a way that allowed some helio- plane in which the sunlight measurements stats to be shaded during part of the day. were made. This shading was somewhat greater than the shading which occurred with a comparable ground coverage ratio in a field of fully COLLECTOR TRACKING GEOMETRY tracking dishes; it is necessary for a heliostat to have an unobstructed view of both the A comparison of the sunlight available for Sun and the receiving tower. This small dis- tracking and nontracking collectors is advantage of heliostat systems may be com- shown in figures VI 11-37 and 38 for the four pensated in cost savings when integrated cities examined in detaiI in this study. Figure systems are evaIuated. VI 11-37 compares the energy available for colIection by a perfect flat-plate collector COLLECTOR LOSSES (e.g., one with no thermal or optical losses) tilted at the local latitude angle with the Up to this point, the analysis has shown energy available for a perfect, fully tracking only the amount of energy which could be collector (e. g., a fully tracking parabolic provided by perfect collectors with different dish). The annual output of these collectors tracking geometries. The energy provided by is summarized in table VII J-1 O. real collectors falls below this theoretical value because of imperfections in the op- Albuquerque is the only city examined tical systems, and because some of the col- where the energy avaiIable for a fully track- lected energy is lost to the environment ing collector exceeds the energy collectable without doing usefuI work. by a perfect flat-plate device. (It will be seen later, however, that when an analysis is done Optical Losses which includes the performance of real collectors, the ordering is usually reversed.) The Four types of losses decrease the optical difference between the solar resource avail- efficiency of f tat-plate systems: able for the two types of colIectors is, how- 1. Reflection from glass or plastic covers ever, so small in the cities studied that it is is typicalIy 8 percent for each cover perilous to make any kind of conclusive used and is greater when the sunlight statement, particularly given the poor quali- strikes the collector at an angle. Some ty of the data on which these comparisons thin-plastic films have lower reflective are based. losses than glass. These losses can be Figure VI 11-38 compares the solar re- reduced if antireflective coatings are sources avaiIable to a nontracking fIat-plate used, but this adds to the collector cost. 296 ● Solar Technology to Today’s Energy Needs

—...... -— - . . —. . -. . - . . . — ...... Figure Vlll-37.— Perfect Flat-Plate Collector Tilted at Latitude Angle and a Perfect Fully Tracking Collector

Boston 200

180

1 160

140

120

140

120 20

Omaha 200 200

180 180

160

140

● ’

OTA Ch. VIII Collectors ● 297

Figure VIII-38.—Comparison of the Maximum Energy Collectable by Four Types of Collectors Located in Albuquerque (1962 Radiation Data)

28-842 () -20 298 ● Solar Technology to Today’s Energy Needs

Table VllI-10.—Useful Radiation Incident on Flat-Plate and Fully Tracking Concentrating Collectors, Four Cities, in kWh/m2/year

Collector type Albuquerque Boston Ft. Worth Omaha

Perfect flat plate (tilted at local latitude) 2,217 1,481 1,742 1,665 Perfect fully tracking collector 2,500 1,373 1,543 1,458 Ratio (tracking/fIat plate) 1.13 .93 .89 .88

SOURCE. OTA

2. Reflections from the absorber surface system, however, is lost completely. Data on are typically 2 to 10 percent, depending the effect of dirt accumulation on perform- on the type of absorbing surface used. ance is very preliminary at present, and may be critical in determining the net cost and 3. About 2 to 4 percent of the energy re- performance of tracking devices. ceived is absorbed and heats each cover glass used. Thermal Losses 4. Dirt on the collector surface reflects when the absorber of a solar collector is additional light if the collector has not heated, it loses energy back to the environ- been cleaned. ment in three ways: direct radiation (mostly The energy actually available to heat liquids as infrared radiation) as it is lost from any in a single cover flat-plate colIector, there- hot body; conduction; and convection fore, is on the order of 80 to 90 percent of through the transparent covers. These losses the energy incident on the device. Losses are proportional to the absorber surface will be greater during the morning and eve- area and increase with the temperature of ning when the Sun strikes the collectors at collection. Concentrating systems have glancing angles and reflective losses are much less absorber area per unit of collec- greater. tor area (it is reduced by the magnification of the concentrating optics) and typically In tracking systems, losses can result from operate at much higher temperatures. I n imperfect reflecting surfaces, reflections most cases, however, the reduced absorber from lenses, energy absorption in lenses, in- area more than compensates for the inaccurate pointing of the focusing system, creased temperature. Concentrating systems and inaccurate placement of the receiver. It usualIy lose a smaller fraction of the energy is possible to produce mirrors which reflect reaching them to thermal effects than flat- over 90 percent of the Iight striking them but plate collectors. concentrating systems now on the market typically use light, inexpensive aluminum The Significance of the Loss Factors reflectors which typicalIy only reflect about 70 to 75 percent of the light striking them. The contribution of thermal and optical Dirt and dust pose a greater problem for losses to the net efficiency of several collec- concentrating systems than for the fIat-plate tor designs is illustrated in figure VIII-39. It devices since a significant amount of the can be seen that optical losses dominate energy in light which strikes dirt on the collector performance in all cases. The ef- cover of a flat-plate collector eventually fect of optical losses in flat-plate systems is, reaches the absorber surfaces and is ab- in fact, understated since the losses calcu- sorbed. Light deflected by dirt on a focusing lated assume that the Sun is directly over Ch. VIII Collectors ● 299

Table VIII-11.– Collector Characteristics Assumed in Preparing Figure VIII-39

1-ax is tracking parabolic Commercial trough with Flat-plate 1 -axis improved Fully Single collector tracking refIecting tracking cover (tubular parabolic surface and parabolic pond design) trough receiver dish Heliostat . Concentration ratio 1 1 60 60 1,000 500 Outlet temperature (0 F) (1) 90 200 300 600 1,500 950 Optical efficiency (including pointing inaccuracies, dirt, etc. ) (2) 0.75 0.68 0.53 0.65 0.81 0.83 Thermal loss coefficient (including convection, conduction and radia- tlon) in kW/m2°C (referenced to collector area) (3) 7.3 x 10– 3 2.0 X10-3 4.1 X1 O-4 1 .5X10-4 6.2x10-5 6.4x1 0-5

NOTES (1) In all cases the Inlet temperature was assumed to be IOO° F less than the outlet temperature (2) In all track{ng collectors, opt(cal efficiency Includes a 1OO. loss due to dirt (3 I In computfng thermal losses. It was assumed that the am b!ent temperature was 60” F

SOURCE OTA

Figure Vlll-39.— Energy Balance for Five Collector Designs (See table VIII- I 1 for Assumed Characteristics of Collectors)

B B

Flat Plate Commercial Improved Full y Tracking Heliostat Parabolic Parabolic Dish Trough Trough

A— Half of Maximum Sunlight B — 1/4 of Maximum Sunlight (.5 kW/m2 Incident on Collector) (.25 kW/m2 Incident on Collector) SOURCE OTA 300 ● Solar Technology to Today’s Energy Needs

the collector. The thermal losses shown in 3. The fully tracking dish produced the the figure are somewhat below average largest output in all cities, giving nearly since in most climates solar intensity seldom 25 percent more than the best single- is above the maximum possible solar intens- axis devices and nearly 60 percent ity, which is typically close to 1 kW/m2. The more than the f tat-plate systems. relative significance of thermal losses increases sharply as solar intensity de- 4. Measured in terms of useful collector creases — e.g., during periods of partial output, Albuquerque has almost twice cloudiness. Moreover, the ambient tempera- the solar resources as any of the other ture chosen for comparison was 600 F to cities examined. The performance of show the average performance of collectors collectors in Boston, Fort Worth, and throughout the year. During the winter Omaha was strikingly similar. months, the outside temperature will be lower and the thermal losses proportion- 5. The pond collectors typically have very ately higher. The thermal losses of the high low performance during the winter, par- temperature collectors are, however, some- ticularly if high outlet temperatures are what overstated since the inlet temperature desired. assumed is only 1000 F lower than the outlet temperature. It is clear, however, that ther- The results of this analysis indicate that mal losses are a relatively small fraction of concentrating systems can provide much the energy balance of high-temperature sys- more useful thermal output than simple flat- tems. plate devices of the same area.

Even parabolic trough devices which THE NET PERFORMANCE make use of known techniques for improv- OF COLLECTORS ing output were superior to the flat plate in each city. This consistent inferiority of the The results of an analysis which includes flat-plate system occurred in spite of the both a calculation of the sunlight available fact that the flat-plate device chosen for for a collector and the ability of a collector analysis was a relatively sophisticated and to utilize the sunlight available is summar- efficient system. This seems to indicate that ized in tables VII 1-12 and 13. This informa- optical advantages of flat-plate systems tion was computed using data on sunlight (chiefly their ability to gather diffuse sun- and ambient temperatures available for light) is more than offset by the advantages each city for each hour of the year 1962. offered by concentrating systems (e. g., Several observations can be made on the tracking and reduced thermal losses). A basis of these figures: valid comparison of systems can only be obtained, however, from a detailed economic 1. If systems are ranked in each city by the comparison of the systems operating in real- total annual thermal output produced, istic environments. the ranking is, with a few exceptions, the same in each city. The value of this, of course, will depend 2 The only concentrating system which on the costs added in the process of pro- produced less annual thermal output viding tracking; this can only be resolved in than the flat-plate system was the com- a detailed analysis of the relative costs of in- mercial parabolic trough system. tegrated systems. Ch. VIII Collectors ● 301

Table Vlll-12.—Comparison of the Annual Output of Five Collector Designs, in kWh/m2/year

Albuquerque Boston Ft. Worth Omaha Annual radiation on nontracking flat plate tilted at Iatitude...... 2,217 ,481 1,742 1,665 Annual direct normal radiation ...... 2,500 ,373 1,543 1,458 output of: Single cover pond...... 960 — — 630 Tubular flat plate...... 952 538 705 619 Commercial parabolic trough ...... 1,030 529 621 561 Improved parabolic trough design ...... 1,370 720 835 765 Heliostat ...... 1,443 791 887 833 Fully tracking dish ...... 1,901 1,023 1,150 1,085

SOURCE OTA

Table VIII-13. —Output of Single Cover and Double Cover Pond Collectors for Various Operating Conditions

Mean collector temperature* = 90° F Mean collector temperature = 140” F — Percent of output Percent of output Annual output occurring during Annual output occurring during (kWh/m 2) October-March (kWh/m 2) October-March

Albuquerque 958 23 447 13 Single cover pond collector Omaha 630 13 259 5

Albuquerque 804 24 470 16 Double cover pond collector Omaha 535 15 281 8

“It was assumed that the collector was operated with a constant fluld Inlet temperature I()” F lower than the mean collector temperature and a constarl~ output temperature 100 F higher than the mean collector temperature

SOURCE OTA Appendix VIII-A

Techniques Used to Compute the Output of Representative Collector Designs

The major variables which must be con- The basis for the Sandia analysis is the sidered in analyzing collector performance observation that the intensity of direct nor- were reviewed in a qualitative way in the mal radiation is correlated with the ratio main body of this chapter. This appendix in- between the amount of energy actually dicates how these effects can be quantified reaching a horizontal surface in a given hour and shows how the equations are derived and the amount of energy which would have which were used to obtain the detailed esti- fallen on the surface if the Earth had no at- mates of collector performance presented mosphere. This ratio is called the “percent elsewhere in this report. Following the tax- possible” sunshine and will be represented onomy of effects used in the earlier discus- by the variable PP. The Sandia work com- sion, this presentation begins with a discus- pared the intensity of direct normal radia- - sion of techniques for deriving estimates of tion (1DN) as a function of PP in several loca

the intensity of direct and indirect sunlight tions where measurements of IDN were avail- which can be captured by each collector able. It was found that the relationship geometry. It then provides a detailed discus- could be approximated with a simple seg- sion of the optical and thermal losses experimented straight-line formula which takes enced by each major colIector type. the following form: (A-1 )

AVAILABLE SUNLIGHT

Sunlight Data

As noted earlier, data about available sun- M light around the country is of extremely uneven quality. Very few stat ions have meas- where A, B, C, and M are constants which ured direct normal sunlight, and results of must be determined for each location. The these measurements have not been readily values of these constants which apply to the available. Information on the total amount three cities (for which consistent direct nor- of solar energy reaching a horizontal sur- mal sunlight data is avaiIable) are shown in face is available from about 80 locations table VII l-A-l. Notice that in Albuquerque it around the country and is archived in the was necessary to use different constants for National Climatic Center in Asheville, N.C. midday and periods early and late in the While this data does not distinguish be- day. In the analysis of sunlight data for Fort tween direct normal radiation and diffuse Worth, average values of the constants were radiation, statistical techniques have been used (A = 1.79, B = –0.55, C =0.85, and developed which can be used to approx- M = 1.00). imate the relative contributions of the two types of radiation. The technique used in The data actually used for the estimates this study is based on work completed re- of collector performance conducted as a cently by Sandia Laboratories. part of this study was taken at weather stations during 1962 (1963 in Boston). Table VII l-A-2 compares the average values of ‘ E Idon C Bees, Est/rnatjng the Direct Component of So/ar /?adiat/or-r, Sandla Laboratories Energy Report, direct normal, and total horizontal radiation SAND 75-0565, November 1975 measured at these stations (and reduced us-

303 304 Ž Solar Technology to Today’s Energy Needs

Table VIII-A-1 .—Empirically Derived Constants ing the methods previously discussed) with Used in the Formula for Estimating Direct average values of these quantities for a 15- Normal Radiation, Given Measurements of Total year period. The 15-year averages were com- Horizontal Radiation (see equation A-l) puted from data prepared by the National Climatic Center and the Aerospace Corpora- tion. The 15-year average values shown in Spring Summer Fall Winter the table contain correction factors which compensate for calibration errors recently Albuquerque* discovered in some of the older measuring Mid E-L Mid E-L Mid E-L Mid E-L equipment. While, as expected, the 1962 A 1.64 1.13 1.65 1.07 1.56 1.15 2.42 1.68 data does not precisely match the long-term B -0.43 -0.19 -0.35 -0.17 -0.47 -0.21 -0.78 -0.25 average, no systematic error is apparent— C 0.85 0.85 0.80 0.80 0.85 0.85 0.80 0.80 some of the 1962 averages are higher while M 1.07 1.07 0.95 0.95 0.97 0.97 1.09 1.09 others are lower than the 15-year averages. Since observing sites a few miles apart can Blue Hill take measurements of sunlight and tempera- A 1.60 1.86 1.93 2.10 ture which differ by 10 percent during the B -0.52 -0.56 -0.58 -0.71 c 0.80 0.70 0.75 0.80 same year (because of microclimates pro- M 0.89 0.81 0.87 1.03 ducing local patterns of fog, etc.), the 1962 data probably represent a reasonable esti- Omaha mate of insolation as it is reasonable to A 1.69 1.62 1.88 1.67 make, given other errors inherent in project- B -0.62 -0.50 -0.68 -0.48 ing the cost of solar energy. c 0.85 0.80 0.85 0.85 M 0.89 0.87 0.96 0.98 Direct Normal Radiation

“ln Albuquerque, It was necessary to have separate Sets of constants for mldday (Mld)andearlyand late ln the day (E-L) The amount of direct normal radiation incident on a collector which is not directly SOURCE Bees, Eldon, “Esttmatlng the Dlrecl Component of Solar Radiation,” Sandla Laboratories Energy Report, SAND 75-0565, November 1975 facing the Sun is reduced by a factor equal

Table Vlll-A-2.—Comparison of 1962* Weather With Long-Term Averages and Extremes

Average daily sunlight (kWh/m2/day) Albuquerque Boston Fort Worth Omaha

Direct normal 1962...... 7.0 3.9 4.3 4.0

15+ yr av** ● ...... 7.1 3.3 4.7 4.5 Ratio: average/1962...... 1.01 0.85 1.09 1.13 Total on horizontal surface, 1962 . . . 5.5 3.7 4.5 4.2 15 + yr av** ...... 5.8 3.5 4.7 4.2 Ratio: average/1962...... 1.05 0.95 1.04 1.00 Heating degree-days† 1962 ...... 4,310 5,754 2,434 6,272 1954-74 average ...... 4,374 5,769 2,423 6,145 1954-74 extremes...... 3,857-4,941 5,410-6,228 1,861-2,855 5,622-6,911

“Read as 1963 for Boston wherever 1962 IS used “” 15 + year average was compiled from the augmented SOLMET weather tapes produced by the National Cllmatlc Center and the Aerospace Corporation. †Heatlng degree-day information from “Local Cllmatologlcal Data–Annual Summary with Comparative Data. 1974” Nattonal Cllmatlc Center, Asheville, N.C Appendix VIII-A ● 30.5

must be considered, With the appropriate choice of geometry, however, the actual calculation can be quite simple. A technique is displayed here which permits a calculation

expressed in the same coordinates. The coordinates which are the most convenient (A-2) are the “collector site coordinates” illustrated in figures VI II-A-I and VIII-A-2. A glossary of symbols used in computing collector geometry appears in table VI 1 l-A-3. In these coordinates, the z-axis points at the zenith at the colIector site, the y-axis points south in the plane of the horizon, and the x- axis points west in the plane of the horizon.

Figure VI II-A.1.– Collector Coordinates Showing the Collector Direction and the Axis of Rotation of the Collector Direction (Zenith) z = z’ 306 ● Solar Technology to Today’s Energy Needs

Collector site

Y’

Earth’s equator

x and x‘

SOURCE. OTA

Table Vlll-A-3.—Glossary of Symbols Used The first step is to obtain an expression for in Computing Collector Geometry the direction of the normal to the collector (a) Variables describing the solar position L latitude of the collector site (north is positive) illustrates a completely general collector w solar hour angle (east is positive, due south is zero) solar declination (north is positive) local standard time on nth day of the year which are obtained by two rotations from the x,y, z system: 1 ) a rotation around the z- clock time using the applicable time zone of the region (eg. eastern standard time) on the nth day of the year the new x’-axis defined by the previous rota-

T e(n) a correction of Tn called the “equation of time” resuIting from the fact that the Earth’s orbit is not circuIar, computed for day n n the day of the year (0 < n < 365) (b) Variables describing the position of the collector

single-axis tracking system where y“ is the axis of rotation. The vector can now be transformed simply back to the x,y, z coordinates through two unit rotations which Appendix VII I-A Ž 307

reverse the rotations by which the x,y, z coor- This achieves the objective of expressing

dinates. With this transformation dinates and the cosine function can be computed: (A-4)

Using equation A-7, the tracking geometry of alI colIectors can be computed rapidly. The second step is to write the Sun posi-

FLAT-PLATE COLLECTORS done by examining figure VI II-A-2 which The typical flat-plate collector is These coordinates are obtained by rotating mounted on a sloping roof which faces the collector site coordinates x,y, z through south, or nearly so. The general formula” for a fixed fiat-plate collector which is tilted up latitude angle). The z’ axis points to true north. In these geocentric coordinates, the Sun’s position can be computed simply from

function of the seasons, and the solar hour stead of with the horizontal). When the col-

be written in geocentric coordinates as follows: SINGLE-AXIS TRACKING COLLECTORS

Single-axis tracking collectors can be mounted many different ways, but two widely used configurations have been used in this study

Polar Mount

The polar mount provides more annual This vector can be translated into collector output than other single-axis tracking site coordinates with a simple unit rotation mounts, but is generally more expensive to about the x’ axis giving construct than mounts where the rotational axis is horizontal. The polar mount can be (A-6) visualized by imagining a collector which rotates about a horizontal axis running from north to south and then tiIting the rotational axis up from the horizontal and toward the south by an amount equal to the latitude angle L (see figure VI 11-8). The cosine factor for polar-mounted tracking devices can be 308 ● Solar Technology to Today’s Energy Needs

and 13 = L, the latitude angle. Using these hours) since the Earth’s orbit is an ellipse values in equation A-7 and minimizing the and not a circle. result with respect to the collector angle of the nth day of the year in the local time zone (i.e. eastern standard time) and TN(n) is the cidence is then simply the solar declination time at which the Sun points due south on and this day (measured in the same local clock (A-8) time), the solar hour angle can be written on this day as follows: East-West Axis of Rotation (A-1 1 ) Collectors which rotate about a horizontal axis that runs east to west receive somewhat less sunlight than single-axis The time for solar noon can be computed polar-mounted collectors, but are sufficient- from the latitude of the collector site (L), the ly less expensive that they are more widely latitude to which the prevailing time zone is used. The cosine factor for this collector referenced (Lref) (Lref is 120°W for Pacific

standard time), and a correction factor Te(n) computed for each day to account for the maximized with respect to the tracking elliptical nature of the Earth’s orbit. Using these variables it is found that:

(A-9)

The equation of time is a complex function gebra it is found that of the day of the year and its specification (A-IO) requires solving equations for which no closed solution is possible. It can be approximated to limits of precision compatible Equations of Time with the rest of the analysis which will be The previous section showed how the col- employed here with four terms of a Fourier lector cosine factor could be computed series. This series is expanded as a periodic function of the length of the year since the from information about the solar position equation must have a period of precisely 1 (the declination and hour angle) and the col- year Coefficients of this expansion have lector position. Solar declination can be been computed by the National Bureau of computed simply since it varies approx- Standards 2 and are illustrated in table imately sinusoidally from plus 23.5 degrees VII l-A-4. The Fourier formula is, as follows: to minus 23.5 degrees with the maximum occurring at the summer solstice. Computation of the solar hour angle from local time is complicated by two factors: 1 ) the time shown on clocks with which the sunlight observations are correlated does not correlate with local solar time since each time zone covers a large spread of longitudes — the Sun can not be due south at noon in the entire time zone; 2) the times at which the Sun is directly south are not separated by ‘T. K usuda, NBSLD Computer Program for Heating precisely 24 hours (although the yearly and Coo/ing Loads in Bui/dings, NBS I R 74-574, No- average of these separations is exactly 24 vember 1974 Appendix VII I-A ● .309

Table Vlll-A-4.— Coefficients of the Fourier Expansion Using this “isotropic sky” assumption, it is of the Equation of Time Used in Equation A-15 possible to convert ldh computed in equa-

tion A-1 4 into an estimate of iD-- the intensi- A O -0.0002 B 0 0 ty of diffuse radiation on a tilted collector. A l 0.4197 B 1 -7.351 Following Liu and Jordan, ’ it is assumed that A 2 3.2265 B 2 -9.3912 the diffuse radiation reaching the collector A 3 0.0903 B 3 -0.3361 consists of two parts: (1) a part received directly from the sky (which is assumed to Diffuse Radiation radiate isotropically) and (2) a part reflected from the ground (which is proportional to The diffuse component of the solar radia- the fraction of the sky from which radiation could be reflected into the collector). Using tion reaching a horizontal surface (Idh) can be computed if information is available these assumptions, it is possible to compute i for a collector which has been tilted about the total energy incident on a d

horizontal surface (1TH) and the direct nor-

mal radiation (1D).

the horizon directly below the Sun,

This equation, however, carries no information about the distribution of diffuse radiation across the sky and thus there is not ground. The reflectivity varies greatly from a simple way to compute the amount of dif- location to location. It may be very high if fuse radiation that can be collected by a the area is covered with snow, and it can be device which is not horizontal, In fact, the artificially enhanced by placing ponds, or distribution of diffuse radiation over the sky reflective surfaces, in appropriate locations dome varies widely, depending on local close to the reflectors. For the purpose of weather conditions and on the time of day, this analysis, It is remarkable, however, that there is very which is a typical reflectivity of dry ground. little data in the literature about the distribution which can be expected. In the following discussion, the simplifying assumption Optical Losses that diffuse radiation is distributed uni- formly across the sky dome (the “isotropic in addition to the limits imposed by the sky” assumption) has been used, even geometry of tracking, the amount of light though it is known that under some condi- which reaches the receiver units in solar col- tions the bulk of diffuse radiation emanates lectors is limited by a number of losses due from a region in the sky close to the Sun. to imperfect optics. These losses include: 1) Very recent work’ indicates that this is a energy absorbed by transparent covers over conservative assumption which understates the receiver; 2) losses when light is reflected the radiation on a tilted surface by as much from mirror surfaces or transmitted through as 7 percent. lenses; 3) errors in pointing a tracking collector at the Sun; and 4) shading of collectors by adjacent collectors, or (in the case of ‘Thomas M Klucher, Var/ation of 50/ar Cc// 5en- sttt vlty and So/ar Rad/a tion on Inclined Surfaces,

presented at the Semiannual Review Meeting, ERDA 4 B Y H LIU and R C Jordan, “The Long-Term Aver- Slllcon Technology Programs Branch, Aug 23-25, age Performance of Flat-Plate Solar Energy Collec- 1977, Wllllamsburg, Va tors,” So/ar Energy 7, 53(1963) 310 ● Solar Technology to Today’s Energy Needs

some tracking units) by other parts of the collector. Designing an optimum collector T(0) is the transmissivity for a case where the requires balancing the features which can light is incident normal to the plane of the improve optical efficiency against other cover. If diffuse light strikes the collector design constraints. For example, adding cover glasses can reduce thermal loss but in- averaged over the section of the sky which is crease optical losses. Increasing the focal viewed by the colIector as follows: length of a concentrating collector can reduce dispersion and transmission losses in (A-1 7) lenses, but increases the size of the Sun’s image and can add to the bulk and contribute to the wind profiIe of the collector.5 Increas- ing the concentration ratio decreases thermal losses, provides a higher temperature thermal output, or reduces the amount of photovoltaic material required. Higher con- e of the sky viewed centrations increase the significance of by the collector. pointing errors. For a horizontal fIat-pl ate system receving TRANSMISSION LOSSES radiation from an isotropic sky, equation A-1 8 gives: Light is lost when it passes through transparent receiver covers. Some light is lost due to surface reflections (from both the front T (one cover) = 0.89 T(0) and back surface of the covers), and some (A-18) T (two covers) = 0.80 T(0) light is absorbed by the transparent material. These losses represent the bulk of optical losses in flat-plate collectors and can play a significant role in concentrating collectors which surround a receiver with a glass or plastic cover. IMPERFECT REFLECTIONS FROM MIRROR SURFACES The transmission coefficient for various types of materials is illustrated in table Materials proposed for use as mirror sur- VII l-A-5. These losses are computed only for faces in concentrating collectors vary normal incidence, however, and transmis- greatly in their cost and optical properties. sion decreases with increasing angles of in- An ideal material would be inexpensive, cidence. The analysis of the transmission at have a high reflectance, create little disper- angles of incidence other than zero can be sion (i. e., a narrow beam of incident light complex. The following formula fits empir- should be reflected without spreading), ical data with a fair degree of accuracy:6 resist impact from hailstones (no fracturing or denting), and not attract dust. Candidate materials include first-surface glass mirrors (which have high reflectivity but are vulnerable to tarnishing and scratching), second- surface glass mirrors (low-iron glass is preferred to reduce absorption), second-surface bulk acrylic mirrors, annodized aluminum 5Gene Nixon, cast acry/ic Fresne/ /ens so/ar concen- (relatively inexpensive and easy to form but trator distributed by Swedlow, Inc., obtained by OTA, May 26, 1977. a lower overalI reflectivity (60 to 80 per- ‘Empirical expression provided for OTA by Don cent)), and a variety of metalized plastic Watt films. The plastic films are much less expen- ●

Appendix VII I-A . 311

Table Vlll-A-5.—Transmittance of Transparent Covering Materials Which May be Used in Solar Collectors (Assuming the Solar Spectrum Resulting From Air Mass 1)

cutoff Normal Thickness wavelength Hem is, solar Material (in. ) Supplier um refIectance transmittance Quartz ...... 0.125 Sandia 0.26 0.064 0.94 Glass Shop Teflon 100 C ...... , ... . 0.001 Dupont 0.26 0.031 0.93 Pyrex (Corning 7740) ...... 0.134 Sandia 0.36 0.067 0.91 Glass Shop Acrylite ., ., ... ., ., ., . . . . . 0.0625 Petterson 0.35 NM† 0.89 0.125 0.87 Plexiglas “G” ., ., ., ., ., ., ., 0.0625 Petterson 0.35 NM 0.88 0.219 0.86 Tedlar, polished...... , . . . 0.004 Dupont 0.31 0.080 0.88 Swedlow centinuous cast acrylic...... 0.076 Swedlow 0.33 0.070 0.88 Swedlow coated acrylic,. 0.273 Swedlow 0.39 0.058 0.85 cell cast Israeli collector glazing ., . . 0.092 Peterson 0.31 NM 0.85 Glass for mirror ...... 0.125 Champion 0.31 0.070 0.85

cutoff Hemispherical Thickness wavelength Hem is. solar Material (in. ) Supplier um refIectance transmittance — Teflon 100 C ...... 0.001 Dupont 0.25 0.031 0.96 Aclar #22A ...... 0.002 Rain hart: 0.25 0.060 0.94 Allied Chem. Corning Ultramicrosheet . . . . . 0.0045 Butler: Corning 0.30 0.071 0.92 Tedlar, polished...... 0.004 Dupont 0.30 0.080 0.91 Lucite 147 ...... 0.120 Dupont 0.38 NM† 0.85 Mylar D...... 0.010 Dupont 0.33 0.112 0.85 Rhom-Haas Korad A...... 0.005 Brumleve 0.38 0.088 0.86 std. clear Fllon A748, Tedlar coated, ... , 0.028 Filon Corp. 0.38 0.082 0.84 Kalwall Sunlite Regular ...... 0.040 Kalwall Corp. 0.38 0.079 0.83 Mylar A. . . ., ...... 0.005 Dupon 0.38 0.19 0.78 Kalwall Sunlite Premium . . . . 0.040 Kalwall Corp. 0.38 0.087 0.79 Swedlow continuous ... 0.076 Swedlow Corp. 0.38 0.070 0.86 cast acrylic Swedlow coated acrylic . 0.273 Swedlow Corp. 0.38 0.058 0.85 (cell cast) — .-

†NM = not measured

SOURCE Solar Total Energy Program Se~laflflu~/ RePort April 1975 September 1975 SAN D76 0078 Sandla Labs, Albuquerque N Mex Apr!l 1976 p 98 99 372 ● So/ar Technology to Today’s Energy Needs

sive, but many appear to age rapidly and to on it into a cone smaller than 4 mrad wide. attract dust, and currently available mater- The second-surface glass mirror reflects ials have relatively low reflectivities. The over 90 percent of its Iight into a cone less search for an optimum reflecting surface than 2 milt-ad in width. will be an important development problem A final difference between surfaces is the for the next several years. variation of reflectance with the angle of in- Figure VI II-A-3 and table VI II-A-6 il- cidence of the incoming Iight. Class mirrors lustrate the optical properties of a number and first-surface aluminized du Pont experi- of different reflecting surfaces. It can be mental film show almost no variation over a seen that the materials vary greatly both in wide range of incidence angles, while other total reflectivity and in the amount of dis- materials such as the aluminized 1-3 Mil persion introduced. The reflectivity for glass Mylar-S film have very poor reflectance at mirrors can be as high as 96 percent, while small angles of incidence, 7 the inexpensive aluminum reflectors can have refIectivities below 80 percent. SHADING, BLOCKING, AND END LOSSES

The surfaces also vary in the amount of Three additional loss factors must be con- dispersion which they introduce. Mirrors sidered: which introduce large amounts of dispersion cannot be used to achieve high magnification (as is shown quantitatively in the next 7R. C Zenter (Boeing Aerospace Co ), “Performance section). The aluminized 1 Mil Teflon film of Low Cost Solar Reflectors for Transferring Sunlight material shown on figure VII l-A-3, for exam- to a Distant Collector, ” So/ar Energy, Vol 19, No 1, ple, reflects 75 percent of the light incident 1977, pp 15-21

Figure VI II-A-3.—The Specular Reflectance at 500nm as a Function of the Collection Angular Aperture for Several Reflector Materials, Together With

80 -

60 “

B Appendix VII I-A ● 313

Table Vlll-A-6.—Specular Reflectivities

Cone Wavelength Specular angle (MRAD) Material Supplier (um) Reflectivity containing Reference 67% of reflected Iight

1. Second-surface silvered glass Carolina A. Laminated glass . . . . . Mirror Co. 500 .92 0.15 (3)

B. Corning Micro- sheet, 0.11 mm...... Sandia 550 .78 1.1 (4) C. Corning 0317, no iron, 1.5 mm fu - Carolina — .96 small (2) sion glass. . . . . Mirror CO. D. Float glass with iron ...... —— — .82 smalI (2) Il. First-surface glass A. Double acrylic coat, silver . . . Sheldahl 550 .93 .21 (4) B. AL/ground glass overcoat ...... 628 .88 <1.7 (6) Ill. Polished aluminum A. ALZAK lighting sheet (Parallel to rolling marks) ...... Alcoa 505 .62 .29 (3) (Perpendicular to rolling marks). . . . . 505 .56 .42 (3) B. KINGLUX reflector sheet (Parellel to Kingston 498 .67 ,43 (3) rolling marks). . Industries (Perpendicular to Kingston 498 .65 .37 rolling marks)...... Industries Sun .81 —— (3) E. Household foil ...... —— Sun .65 —— (8) V. Metalized plastic films A 2nd-surf. alum. FEK-163 ...... 3M 500 .86 0.90 (3) B. 2nd-surf. alum. Teflon ...... Sheldahl 500 .80 1.3 (3) c. 2nd-surf. alum. Teflon laminated to alum. sheet ...... Sheldahl 550 .87 1.2 (4) D. Al/nylon, 1st surf ., . ——— Sun .80 —— (8) E. A1/Kapton-H, 1st surf. , 0.25 mm ...... 628 .87 5 (6)

References

1 Handbook of Chernlsfry and Physics The Chemical Rubber Co , Ed by R C Weast, 54th Edlflon, 1973-1974, p E225 2 L G Ralnhard (Sandla Labs, Albuquerque) private communtcatlon, Aug 10, 1977 3 R B Pettt and B L Butler (Sandla Labs, Albuquerque) Sern~annua/ Rev(ew ERDA Therrna/ Power Systems, Dispersed Power Systems, f)jsfr~bufed Co//ec(ors and Research and Deve/oprnent, Mirror Ma ferla/s and Se/ecf(ve Coatings SAN D7701 11, February 1977, p 6 4 So/ar Tofa/ Energy Program Sernlannua/ Report October 1975 and March 7976 SAND76 0205, Sandla Labs, Albuquerque, June 1976 5 Test report by Desert Sunshine Exposure Test, Inc , March 4, 1977, rendered to Kingston Industries Corp DSET Order No 17127S 6 R C Zentner (Boeing Aerospace Co ), “ Performance of Low Cost Solar Reflectors for Transferring Sunllg h! to a Distant Collector, ” So/ar Energy, Vol 19, No 1, 1977, Pp 15-21 7 L Drummeter and G Haas “Solar Absorptance and Thermal Emlttance of Evaported Coating s,’ Physics of Th(n FI/rm, 2, 1964 Ed by G Haas and R Thun, Academic Press 8 F Damels (Umverslty of Wlsconsln, dec ) L7(recf Use of fhe Sun Energy Yale Untverslty Press of Ballantine Books, Inc 1964 314 Ž Solar Technology to Today’s Energy Needs

1. “End losses” of one-axis tracking de- and must be computed separately for each vices which result from the fact that case. These losses can be reduced or elim- some part of the light reflecting from a inated if the collectors are widely spaced, trough or other one-axis tracking unit but such separation increases the demand will miss the receiver surface except for land use and can increase piping costs (in during the infrequent occasions when the case of distributed collectors) or add to the incident light is directly normal to the demands placed on pointing accuracy the colIector plane; (in the case of heliostat designs). In addition, the solar image will be larger from more dis- 2. Shading of collectors by adjacent col- tant heliostats, decreasing efficiency, or lectors; and concentration ratio. A balance must be 3. Blocking of the reflected beam of a struck in each application. In many cases, heliostat by other heliostats however, a shading problem will be negligible if the collector surfaces cover less than End Losses about one-fourth of the area provided for colIectors. If the collector reflecting surface is a flat Fresnel lens or a series of coplanar linear Heliostats slats, light incident on an area of the collec- The shading, blocking, and cosine factors receiver surface. (F is the focal length of the of heliostat fields are complex since the location and pointing angle of each helio- angle of incidence of direct sunlight meas- stat in a large field must be analyzed to de- ured with respect to a direction normal to velop an estimate of overalI system per- the plane of the collector. ) If the collector formance. An independent analysis of this length is L, then the fraction of the incident problem has not been attempted in this light lost in end effects (1’,(0)) is given by: report and the computations of heliostat performance rely on an analysis performed by the University of Houston in connection with the McDonnelI Douglas design pro- (A-19) posal for a 10 MWe pilot plant for a 100 MWe central receiver system. The results of this analysis are illustrated in figure VII l-A-4. If the system uses a parabolic trough, the The curves shown include the effects of at- calculation is somewhat more complex mospheric attenuation for clear days in the since points on the edge of the trough are southwest United States, and apply to a farther from the focal line than points at the field optimally designed for a site at 350 N base of the trough. It can be shown that in latitude. The designers attempted to design this case the fraction of the incident light a system which performed well during the lost in end effects is given by: periods near dawn and dusk, and which minimized seasonal variations. Mirror spacing is not uniform, but on the average about one- fourth of the area is actually covered with mirrors. where f = F/D is the “f-number” of the optical system. The curves of figure VII l-A-4 indicate the normalized power to the receiver and in- Shading Factors clude the cosine factors of the heliostats, The amount of energy lost when one col- shading and blocking effects, a receiver in- Iector shades an adjacent coll ector depends terception factor, and attenuation between on the exact geometry of the collector field the mirrors. Appendix VII I-A ● 315

Figure VIII-A-4. —Monthly/Hourly Variation in Available Thermal Power

1.0

Day number range Curve when the curve number is applicable* 1 158-186 2 127-157 and 187-217 3 97-126 and 218-248 4 66- 96 and 249-278 5 36- 65 and 279-309 6 5- 35 and 310-340 7 1- 4 and 341-365 *January 1 is day #1

SOURCE Raymon W Hallet, Jr and Robert L Gervals. Central Recewer Solar Thermal Power System Phase I lst”Quarter Tech- nical Progress Report McDonnell Douglas Astronautics Company (January, 1976), p 18 MDCG6318

These curves were used in the analysis by Limits on the Geometric Concentration Ratio approximating each curve with a six-Iine seg- ment polygon adjusted so that the area The amount of concentration of sunlight under the polygon was approximately equal possible with a given set of optics is limited to the area under the curves illustrated. The by the pointing accuracy of the tracking shapes of the polygons were also adjusted to system used, by the dispersion introduced reflect different day lengths at latitudes into the optics by imperfect refIecting sur- other than 35° N faces, and by the finite diameter of the Sun. 316 ● So/ar Technology to Today’s Energy Needs

(The intensity of the light actually reaching cells. With careful design the impact of the absorber will, of course, also be limited these effects can be reduced. For example, by the cosine factor, shading and blocking the facets of a Fresnel lens or mirror can be effects, and the reflection and absorption adjusted to spread the image to create a uni- losses discussed earl ier.) form illumination on the receiver surface. Measurements performed on a cast acrylic There is some abiguity about the proper Fresnel lens designed by Swedlow, Inc., are way to define the geometric concentration shown in figure VII l-A-6. CarefuI mirror ratio. I n the following discussion, geometric design or the use of a secondary mirror near concentration ratio (C ) is defined to be the g the focal point can also minimize the prob- ratio between the aperture of the colIector lem of uneven illumination. A precise com- and the area of the receiver which can be putation of the intensity distribution of the reached by the reflected or refracted sun- solar image requires compensation for the light. This definition assumes that the por- fact that the luminosity of the Sun varies tions of the receiver which can never be il- 8 over the solar disk. luminated are well insulated. This definition must be applied with some care in the case The size of the solar image reaching the of one-dimensional tracking systems since receiver in any practical system will be the concentration ratio will not be equal to larger than the angular diameter of the Sun the ratio between the solar energy reaching because of dispersion introduced by imper- the mirror or lens surface and the light fect reflecting or transmitting surfaces, by reaching the collector absorber (assuming imperfect concentrator shape, and because perfect optics), except when the Sun’s direc- of imperfect tracking. In addition, atmos- tion is directly normal to the plane of the pheric dispersion (e. g., hazy sky) can in- collector. At all other times, the effective crease the apparent diameter of the Sun by geometric concentration ratio for a perfect a factor of 2 or more. collector is equal to the geometric concen- The dispersion introduced by different tration ratio multiplied by the shading fac- types of reflecting surfaces was illustrated tor 1 in figure VII l-A-3. I n the following calcula- If the optical properties of the system are tions, the cone angle containing 90 percent perfect, the only limit on the geometric concentration ratio will be the angular diameter Lenses have some advantage in minimizing dispersion since an imperfection in a mirror from 9.16 milrad to about 9.46 milrad, surface which has the effect of tilting the changing as the Earth-Sun distance varies mirror surface by an angle A above the ideal over the year. The limits which this imposes mirror angle will result in an error 2A in the on the concentration ratios possible are il- angle at which light is reflected. A lens with lustrated for three different concentrating a similar error at each surface typically re- systems in figure VII l-A-5. The solar image sults in an angular error of less than 2A, de- reflected (or transmitted) from an extreme pending on the index of refraction of the edge of the lens or mirror has a width of lens and the angle between the lens surfaces. transmitted) from the center of the lens or Tracking errors can be treated with fair accuracy by simply assuming that the solar (where F is the focal length of the optical image is spread by tracking errors by an system). It can be seen that the intensity of the image will be greater in the image center. This can create difficulties if “hot- ‘D. L. Evans (Arizona State University), “On the Per- spots” place high stresses on small parts of formance of Cylindrical Parabolic Solar Concen- the receiver, and nonuniform illumination trators with Flat Absorbers, ” So/ar Energy, Vol. 19, No, can reduce the performance of photovoltaic 4,1977, Pp 379-385. Appendix VII I-A ● 317

mane on Three Typical Concentrating Collectors

Flat Fresnel Lens with Cylindrical Absorber SOURCE OTA

angle at. The angle a t will be chosen to be give a = 16.5 milrad (imprecise optics and twice the angle between the ideal collector direction and the actual collector direction, which is exceeded less than 5 percent of the time when the collector is operating. An estimate of the maximum concentration possible given tracking and optical dispersion ef-

If chromatic aberation is an important effect, ad should be increased accordingly. A simple tracking system can achieve a point-

ing accuracy such that at is below about 0.5 degrees or 8.6 milrad. Such a system could have a dispersion angle of 0.6 degrees or 10.5 milrad. A carefully constructed system dispersion and tracking, of 6 milrad.9 If the mean solar diameter is used, these cases

where f = F/D and the other variables used are defined in figure VII I-A-5, It will also be ‘Raymon W Hallet, Jr , and Robert L Cervals, Cen- tral Receiver Solar Thermal Power System Phase 1, Fina/ Report, McDonnel I Douglas Astronautics Com- (see figure VIIl-A-5). This variable can be pany (1 977) SAN 1108 computed from Rm /D as follows: 318 ● So/ar Techno/ogy to Today’s Energy Needs

Figure Vlll-A-6.— Characteristics of the Image of Acrylic Fresnel Lenses Designed by Swedlow Inc. for Solar Applications

Intensity distribution at the focus of an acrylic fresnel lens designed for one-axis concentration on a Iinear thermal receiver.

two-axis concentration on a photoelectric device. -

600

500

400

300

200

100

SOURCE Nixon Gene Cast AcrylIc Fresnel Lens Solar Concentrator paper distributed by the Swedlow Inc obtained by OTA May 26, 1977 pages 27 and 22 (A-22)

With perfect tracking and optics, all of the sunlight incident on a one-axis tracking col- Iector could be captured by a flat receiver with area Ar where

(A-23)

In computing the effective receiving area for a receiver with a circular cross section, it is assumed that the portions of the receiving tube which are never ilIuminated by the Sun are covered with an insulating material of sufficient quality that losses through the insulation are negligible, The angle measured from the center of the circular receiving by

fraction of energy lost as end losses fraction of energy lost in shading and blocking refIectivity of mirrors transmissivity of cover plates angle of solar incidence on collector Thermal Losses angle between zenith and Sun Not all of the solar energy reaching the colIector tiIt above horizontal receiving element of a solar colIector can be surface reflectivity of the ground removed as useful energy since some of the direct sunlight energy reaching the receiver wilI be re- total horizontal sunlight flected from the absorbing surfaces of the As the concentration ratio increases receiver and some of the absorbed energy above one, the fraction of the diffuse radia- will be conducted or reradiated back to the tion intercepted by the collector which atmosphere. As shown earlier, the thermal reaches the receiver surface drops rapidly, loss effects are usually much more signifi- and for concentration ratios above 10, the cant for flat-plate collector systems with diffuse sunlight can generally be neglected, relatively large receiver surfaces than they Ieaving are for concentrating systems with relatively 320 ● Solar Technology to Today’s Energy Needs

Table Vlll-A-7.—Maximum Possible Geometric Concentration Ratios at Perihelion

—— . 1 -D Concentrator 2-D Concentrator

SOURCE. OTA

Table Vlll-A-8.—Maximum Possible Geometric Concentration Ratios

1 -D Concentrator 2-D Concentrator ——

● ☛✎✎☛✎☛✎☛✎ 1330 1640 2140, 1553. 3283. 3449. 1257, 3337. 3023. 952 2787 2378. 725. 2207. 1849. 565. 1739. 1455. 450. 1384 1164. 366 1118 948. 303. 917. 785. 255. 764 660. 217 644 561. 187. 550. 483. 163. 474, 419. 143, 413 368. 126. 363 325 113. 321. 289 101 286 259, 91 256 233. 83. 231 211 75 209 .- — . SOURCE OTA Appendix VII I-A ● 321

small receiver surfaces. The thermal loss ef - perature TO remai ns constant. The heat col- fects have been treated extensively in a Iected is then number of recent publications10 11 12 13 14 15 and no attempt is made to reproduce the (A-28) analysis presented in these works. All that is done here is to summarize the results which are directly relevant to the analysis of this Here k is the thermal conductivity be- study. e tween the absorber surface and the fluid, For the concentrating collectors considered, THERMAL LOSSES AND HEAT COLLECTED U L/ke is less than 0.01 and can be ignored.

Two different, but rather simple, expres- For heliostats, UL was based on the outlet sions were used to compute the thermal temperature rather than the mean tempera- losses, For some cases, the fluid flow rate fr ture. was fixed. The heat Q colIected per unit C Typical thermal loss coefficients for a area of colIector is then variety of collectors are shown in table VII l-A-9. It should be noted that the thermal loss Here U is a thermal loss coefficient (the ef- L term of equation A-27 would be divided by fective conductivity between the heated the concentration ratio to obtain the heat fluid and the atmosphere). Fr is the “collec- lost by concentrating collectors. The expres- tor heat removal factor’’” which accounts sions used for determining the performance for the use of the fluid inlet temperature T, of photovoltaic collectors are somewhat instead of the mean absorber temperature in more complicated and are discussed in the calculation. T is the outdoor air tem- a chapter X. perature.

The other case modeled assumed that the Detai/ed Ca/cu/ation of F/at. P/ate Co//ector Output flow rate is varied so the fluid outlet tem- This section presents methods for computing the output of flat-plate collectors which assume that the thermal loss coeffi-

‘“John A Duffle ancf Wllllam A Beckman, op clt cient UL is constant and a method which ex- chapters 4-8 plicitly considers the dependence of UL on 1‘ Frederick F .51mon, F/at-P/a?e Solar-Col/ector Per- the wind velocity, collector tilt, absorber formance Evaluation with a Solar Simulator as a Basis for Co//ector Selection and Performance Prediction, temperature, and air temperature. The re- NASA TM X-71 793, presented at 1975 ISES Meeting, sults show that the approximations used

Los Angeles, Callf with UL constant are adequate for the long- 1‘M W Eden burn, Performance of a Focusing Cylin- term system performance which is central to drical Parabolic Solar Energy Col)ector: Analysis and this study. Computer Program, SLA-74-0031, Sandia Laboratories, Aprl I 1974 There are three primary sources of heat ‘‘G W Treadwell, W H McCulloch, and R S loss from the receiver of a solar collector: Rusk, Test Results from a Parabo/jc-Cy/indrica/ So/ar Co//ector, SAND 75-5333, Sandla Laboratories, July 1. Radiation – Any hot body radiates ener- 1975 14 Raymon W Hal let, J r , and Robert L Gervais, Cen- tral Receiver Solar Power System, Phase 1– Final temperature of the body in degrees Kel- Report PI/et P/ant Pre//minary Design (MCDG 6040), pp 310, 337,366, j anuary 1976 1‘Giovanni Franc la, “Large Scale Central Receiver constant: Solar Test Facilities” Proceedings, I nt Seminar on Large Scale Solar Energy Test Facilities, Las Cruces, N (5.67 x 10-8Watt/m2-K4). Mex , Nov 18-19, 1975 “John A Duffle, op clt pp 146-151 2. Conduction – Heat flows from the 322 ● So/ar Technology to Today’s Energy Needs

Table Vlll-A.9.—Typical Thermal Loss Coefficients

Collector type (kW/m2°C) Temperature range Reference

1 cover flat plate . . . .0074 < 150° F ( < 66” C) 1 2 cover flat plate . .0046 -.0063 < 200° F ( < 93” C) 1 2 cover fIat plate, selective absorber. . .0032 -.0046 < 250° F ( <1210 C) 1 Tubular flat plate. . .0011 -.002 < 250° F ( <121 “C) 1,2 Parabolic trough, unglazed...... 025 140°-3500 F (60°-1770 C) 3 Parabolic trough, glazed, sel. absorber, no .009 250°-6000 F (121 0-316 0 C) 4 vacuum...... Heliostat ...... 03 9000-1 ,100° F (482°-5930 C) 5,6 Parabolic dish ...... 076 1,4000-1 ,500° F (760°-8160 C) 7

1 Simon, Frederick F , op clt 2 A/r Corrdltlonirtg & Refrlgerat(on Bus/rress, July 1976 data for KTA collector 3 Acurex Aerotherm, “Technical Note, Concentrating Solar Collector Model 300201 ,“ received by OTA, 1977 4 Acurex Aerotherm, “Model 3001 High.Temperature Concentrating Solar Collector, ” speclf{catlons received by OTA, 1977 5 Hallet, Raymon W , Jr Ib{d 6 Franc la, Glovannt, Ibid 7 Estimate based on T’ scahng of heliostat value

heated collector surfaces through in- useful thermal output (QC) can be given as: sulation, covering glass, and structural (A-29) supports to the atmosphere. 3 Convection – Circulation of the air between the collector plates or motion of air outside the top cover of the collector causes thermal losses. Such circulation is generally present due to gravity, colIector aperture area even in enclosed spaces. Such losses sunlight intensity reaching the col- can, of course, be greatly reduced if the lector (see equation A-25) space between the receiver surface and thermal loss coefficient per unit covers is evacuated. area of absorber surface concentration ratio of the optical For long-term modeling, the heat loss can system used be treated as proportional to the difference the ambient air temperature between the average absorber surface tem- heat transfer coefficient between perature and the ambient air temperature; the absorber surface and the fIuid, i.e., the heat loss per unit absorber surface Equation A-29 makes the implicit assump- ductance between the absorber surface and tion that the temperature of the surfaces of the atmosphere and includes losses due to the absorber and the fluid temperatures al I three processes mentioned above. vary I i nearly over the area of the collector. When the collector inlet and outlet fluid The actual distribution of temperatures

temperatures T, and TO are known, the across the area of the collector depends on Appendix VII I-A ● 323

the details of the construction of the device F R is a constant, the collector output can be (placement of the tubes, the heat-conduct- given as follows: ing properties of metal surfaces, etc.). Several recent papers have examined this problem with some care,17 18 19 A simple technique for approximating this compli- Techniques for computing FR for different cated calculation which was used in the types of collector geometries are discussed analysis conducted for this study relies on in detaiI in Duffie.20 defining a correction factor, Fr. A similar approximation which can be This correction factor, sometimes called used to evaluate the performance of collec- the “heat removal factor, ” is defined to be tors covered with photovoltaic cells is the ratio of the useful thermal output of a discussed in chapter X. The values of UL ac- colIector (Qc) to the usefuI output of the col- tually used in the analysis were based on the lector, assuming that the entire collector ab- empirical performance data summarized in sorber surface was held at the inlet tempera- table VII I-A-IO. ture (T,):

(A-30) An iterative Solution to Collector Heat Loss

A typical flat-plate collector is shown in where fr is the mass velocity of the fluid figure VI II-A-7 and is used to illustrate the moving through the collector and CP is the detailed method used to compute heat specific heat of the collector fluid. The heat losses. The system is characterized by five removal factor defined in this way actually temperatures: changes slightly throughout the year as a function of operating conditions, but it can the temperature of the absorber be shown that in most cases of practical in- plate terest, these changes are negligibly small the temperature of the inside cover the temperature of the outside when TO -Ti is only a few “C. Assuming that cover the ambient air temperature ‘‘F F Simon, F/at-P/ate So/ar Co//ector Performance the effective black body tempera- Evaluation Performance Pred/ct/on, presented at the ISES Meeting, Los Angeles, Cal If , )uly 28-Aug 8, 1975 ture of the atmosphere ‘8 Duffle, op clt , pp 138-153 “E M Sparrow and R J Krowech, /ourna/ of Heat Transfer, Vol 99, 1977, pp 360-366 20 Duffie, op cit., pp 146-151

Table Vlll-A-10.—Ratio of Collector Output When “Average” U-Value Used to Output of Collector With Variable U-Value for Flat-plate Collectors in Omaha With Tilt Angle— Latitude

Collector Inlet “Average” type temper- U-value Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual ature (kW/m2°C)

1 cover 90° F(32°C) ,0069 .946 .954 .977 .999 1.007 1.005 1.005 1.0031.002 .999 .992 .970 .996 1 cover 120°F(49°C) .0072 .900 .913 .964 1.006 1.033 1.024 1.0191.0221.014 1.003 .993 .942 1,004 2 cover 120°F(49°C) .0041 .945 .956 .974 1.001 1.015 1.012 1.011 1.0121.007 1.002 .989 .967 .998 2 cover, 1 50° F(66°C) .0025 .978 .983 .991 1.004 1,014 1.012 1.011 1.011 1.007 1.004 .999 .986 1.003 selective absorber

SOURCE OTA 324 ● Solar Technology to Today’s Energy Needs

Figure VIII-A-7. —Geometry of a Here h are the effective convective/con- Simple Flat-Plate Collector ij ductive heat transfer coefficients (it being assumed that convective and conductive losses are linear with the temperature differ-

radiative heat transfer between the two surf aces.

supposing that energy radiated from one

is all incident on a second surface with tem-

reflected. An infinite series can thus be constructed and it can be shown that the net heat transfer rate per unit area is given by

The convective/conductive heat transfer coefficients are much more difficult to evaluate since a number of effects can contrib- (The typical temperature drop occurring ute to these losses and since the convective across a glass cover is less than 10 C, so each effects will depend on the precise geometry cover is assumed to be at a single tempera- and orientation of the collector. The coeffi- ture. ) The receiver and first cover are sepa- cients which apply to the spaces inside the rated by a distance d and the inside and 12 colIector (h and h ) are usualIy given by: outside covers are separated by a distance 12 23 d 23. In equilibrium, the heat flowing from the absorber to the first cover must equal (A-34) the heat flow between the two cover plates which must, in turn, equal the heat flowing from the top plate into the atmosphere. If ess (the ratio of the convective heat transfer the heat flowing from surface i to surface j is to the conductive transfer) and Ka is the con- called Q ij, the heat flows can be expressed ductivity of air. The problem then becomes one of establishing an appropriate Nusselt number for the process. Hollands, et al.,21 have suggested the following (basically empirical formula):

‘ l K,G. T Hollands, et al., )ourna/ of Heat Transfer, Vol. 98, May 1976, pp. 189-193, Appendix VII I-A ● 325

Rayleigh number cuss ion since they are easy to compute once the temperatures in the colIector are known, thermal expansion coefficient of air Since the heat loss coefficients k have a kinematic viscosity of air ij weak but complicated temperature depend- gravitational acceleration ence, it is usually not possible to obtain a thermal diffusivity of air closed expression for U . The most conven- angle of tiIt from horizontal L ient technique for computing U is to solve T – T L i+1 i an algorithm for the expression using a I digital computer. One such technique is presented below,

The solution is initiated with the assumption that the average temperature of the

receiving surface (Tl) is equal to the inlet fluid temperature T, and that the temperature rise across the thickness of the colIector is equalIy divided between the two

= then be used to compute the heat loss coef-

ficients kij which can in turn be used to ob-

tain a new estimate for the temperatures T3

and T2 using equation A-32. These new temperatures can then be used to compute a

new set of approximations to kij. The cycle is

continued until successive values of T 2 and

T 3 satisfy a convergence criteria. When the desired convergence is achieved, the param-

eter U'L can be computed, including the side

and back losses. This U'L can be used to compute the collector output:

and the output temperature of the fluid

moving through the collector is then T O = Tj

and C P is the specific heat of the fluid, With this estimate of TO, a new estimate of the average temperature of the colIector sur-

face can be computed as (T, + TO )/2 +

ficient between the fluid and the absorber

surface. The procedure for computing U L for a given ambient temperature and plate temperature can be used again to obtain a new

estimate of UL. This series can be continued until a convergence criteria for the average temperature of the collector surface is satis- “E M Sparrow, University of Minnesota, private communication, Febr 25, 1977 fied. A final value of U'L can then be com- “J R Lloyd, E M Sparrow, and E R C Eckert, Int. puted which meets all of the specified journal of Heat and Mass Transfer, 15,457-473, (1972) boundary conditions. 326 ● Solar Technology to Today’s Energy Needs

An Approximate Solution values for heat loss through the back and sides of collectors. The comparisons all Since the procedure just described is assume a constant flow rate of 10 cm3/sec quite lengthy and quite expensive to execute per square meter of collector area AC and a on a computer, an approximation was used fixed inlet temperature for collectors in to compute the heat loss in the analysis of Omaha. The “average” U-value used for the integrated systems conducted for this study. fixed U-value case was computed using the The approximation was simply to use equa- annual average daytime temperature and tion A-29 or equation A-31, depending on wind velocity. whether the system was modeled with a It can be seen from table I-A-IO that fixed-outlet temperature TO or with a fixed- VII the total annual output agrees to within flow rate fr This equation was used with an about 0.5 percent in all four cases run. The empirically derived value for UL which was assumed to be constant throughout the monthly totals vary by as much as 10 percent, but for the two-cover, selective ab- year. Measured values of UL for a variety of different collector designs are shown in sorber case which has thermal losses com- table VII I-A-IO. parable to the tubular flat-plate collector generally modeled, the monthly differences are always less than 3 percent. During the Table VIII-A-IO compares the monthly winter, the fixed U-value approach gives output of collectors calculated assuming a less output than the variable U-value ap- U-value independent of temperature with proach. This indicates that lower ambient the collector output calculated using the temperatures during the winter decrease the variable U-value procedure of the previous U-value more than the increase due to high- sect ion. Computation of the variable er wind velocities, even for single cover col- U -values using the iterative solution in- L lectors. cluded all corrections discussed in the previous section: it assumed FR = 0.95, it The fixed U-value approach reduced the used Duffie’s assumptions about radiative cost of computer computation by about 50 sky temperatures, and it assumed typical percent. Chapter IX ENERGY CONVERSION WITH HEAT ENGINES

Chapter IX.— ENERGY CONVERSION WITH HEAT ENGINES

Page Page Background ...... 329. Noise ...... 388 Thermodynamics...... 330 WaterUse in SteamCycles ...... 389 Cogeneration...... 332 Sodium and Potassium Vapor ...... 389 The RankineCycle...... 333 Cycle Performance ...... 336 Turbine Efficiency ...... 338 PerformanceWith Heat Recovery...... 340 PerformanceWith Backup PowerSources343 LIST OF TABLES State of the Art...... 345 Table System Costs...... 352 No. Page Costs of Organic RankineSystems...... 354 I. Organic Power-CycleWorking Fluids Used in SystemTesting or in The BraytonCycle...... 354 Development ...... 339 System Efficiency...... 360 2. Efficiency of Steam Rankine Devices OperationWith Fossil Backup...... 365 Operated From Storage at Reduced System Costs...... 365 Temperature ...... 345 TheStirlingand Ericsson Cycles...... 366 3. Ratio of EnergyRequired for Boiling Priniciples of Operation ...... 366 to Total EnergySenttoTurbine ...... 345 Design Alternatives...... 368 4. Small Steam RankineTurbines ...... 346 Performance ...... 376 5. Design and Performance Parameters of PerformanceWithWaste Heat...... 378 Current and Projected RankineAutomotive SystemCosts...... 379 PowerSystems ...... 347 State of the Art...... 381 6. ExperimentalOrganic RankineTurbines in the UnitedStates...... 348 Other Heat-Engine Designs ...... 383 7. Brayton Cycle Efficiencies...... 363 The Thermionic Converter ...... 383 8. Stirling Engine Characteristics ...... 378 ThermoelectricConversion ...... 385 9. Performance of Free-Piston Stirling The Nitinol Engine...... 385 Engine Designs of EnergyResearch and Osmotic-Pressure Engine...... 386 Generation, inc...... 379 EnvironmentalandSafetyProblems...... 387 10. Performance of SunPower Free-Piston Fluorocarbons ...... 387 Devices ...... 379 LIST OF FIGURES Figure No. Page 21. 50 MWe Closed-CycleGas Turbine ...... 359 Figure No, Page 22. Section Through a Combined Gasand 1. Cycle Efficiencies of Heat Engines ...... 331 SteamTurbine Powerplant...... 361 2. System Performance (Ratio of Electric 23. Artists’sRendering of Proposed Solar- and Thermal Energy Produced to Energy HeatedAirTurbineGenerating Facility ...362 Entering the System)...... 333 24. Temperature Dependence of Optimum 3. Rankine-Cycle Devices With Heat Cycle Efficiencies...... 363 Extraction ...... 335 25. The Effect of Waste-Heat Extraction 4. Temperature Dependence of Rankine- on the Performance of Gas Turbines ...... 364 Cycle Devices ...... 337 26. Closed Regenerated-Cycle GasTurbine. ..364 5. Rankine-Cycle Expander Efficiencies. ....338 27. installed Costs of Open-Cycie 6. Efficiency of Backpressure Steam BraytonTurbines...... 365 RankineDevices ...... 340 28. ldealStirlingand Ericsson Cycles...... 367 7. Schematic Diagram of the SolarTotal 29. Calculated Performance of a 225-HP Energy System lnstalled at Sandia Stiriing Engine as a Function of the Laboratories in Aibuquerque, N.Mex. ....341 Specific PowerandWorking Gas ...... 369 8. Electric and Thermal Performance of a 30. Phiiips Rhombic-DriveStirling Engine ....37O 12.5 MWe Generai Electric Extraction 31. Swashplate Stirling Engine ...... 371 Turbine ...... 342 32. Calculated Performance of a Philips 9. Designs for Providing Backup Power Rhombic-DriveStirling Engine ...... 371 for Solar Rankine-CycleSystems ...... 344 33. Free-PistonStirlingand Ericsson 10.TheSunstrand 100kW Organic Rankine Cycle Designs...... 372 Turbine ...... 348 34. SunpowerSystems Free-Piston Stirling 11. Components of the Solar Heated, Rankine- and Ericsson Cycle Design Approach. ....374 Cycle Electric Power/3-Ton Air-Conditioning 35. Free-PistonTotal EnergySystem ...... 375 System ...... 349 36. Free-PistonTotal EnergySystem ...... 376 12. Flow Diagram of the Soiar Heated, 37. The Philips Design for a Stiriing Rankine-Cycle Electric Power/3-Ton EngineTotal EnergySystem ...... 377 Air-ConditioningSystem ...... 350 38. Heat Balance for the Stirling and 13. United Technologies Design for Diesel Engine...... 379 Rankine CycleAir-Conditioner ...... 351 39. ElectricandThermal Output of a 14. Sun PowerSystemsFlow Diagram for Stirling Engine...... 380 5HP, Rankine CycleAir-Conditioner...... 352 40. Weight-to-PowerRatios of EnginesWith 15. Experimental Expander at General lnternal Combustion and of Stirl`ing Electric ...... 353 Engines ...... 381 16. installed Costs of Steam Rankine 41. Cost of Diesel Engines ...... 381 Turbines ...... 354 42. 200-Watt,SunpowerStirling Engine, 17. installed Costs of Organic Rankine Mounted in ConcentratingCollector .. ...383 Turbines ...... 355 43. identification of Thermionic 18. installed Costs of Field-Erected ConverterComponents ...... 384 Boilers ...... 356 44. Effect of ColiectorTemperature 19. Four Brayton-CycleSystems Compatible on Thermionic Efficiency ...... 385 With SolarApplications ...... 357 45. The Nitinol Engine...... 386 20. Components of a 500kW GasTurbine. ....358 Chapter IX Energy Conversion With Heat Engines

BACKGROUND

The basic resource of solar energy is a constant temperature thermal source at approximately 10,000° F.* If this resource is to be used for anything other than lighting, the energy received must be converted into a more useful form. This paper examines three separate technologies for accomplishing this conversion: 1. Thermal devices which use sunlight to heat a fluid and direct this heated fluid either directly for applications requiring heat (such as space-heating or industrial processes) or to operate heat engines; 2. Photovoltaic devices which convert light directly into electricity; and 3. Photochemical devices which use light directly to drive chemical react ions. This chapter compares the costs and performance of a number of specific heat-engine devices. Photovoltaic and photochemical processes are discussed in chapter X. A large number of devices for converting thermal energy into mechanical energy and electricity have been developed over the years, and many of these could be converted for use with solar power. The only energy conversion cycles with which direct solar power would not be easily compatible are those requiring internal combustion— diesel engines, for example, would be cliff i cult to convert to a direct-solar application.

The following cycles are considered in overall cycle efficiency is relatively low (5 to some detail: 20 percent) because of the low theoretical maximum efficiency of low-temperature Rankine-cycle systems using organic working heat engines, Low-temperature engines can, fluids such as Freon show the greatest prom- however, be operated from fluids produced ise for producing useful mechanical work by simple nontracking collectors and track- from solar-heated fluids with temperatures ing collectors with low-concentration ratios in the range of 650 to 3700 C (1490 to 6980 and can use relatively inexpensive storage. F). The technology is reasonably well-developed and prototype devices are currently Steam Rankine devices are probably the available in sizes ranging from kilowatts to most attractive contemporary heat-engine many megawatts. An Israeli manufacturer designs for temperatures in the range of has been selling small units for nearly a 3700 to 550“C (6980 to 1,0220 F). (Recip- decade, and devices are now available from rocating steam engines and saturated steam U.S. manufacturers. Small organic Rankine devices can also operate at lower tempera- devices are similar to air-conditioners work- tures. ) A variety of devices are available and ing in reverse and should be able to exhibit the technology is mature, although the mar- the reliability, simplicity, and low cost en- ket for small steam turbines has, until joyed by refrigeration equipment. Organic recently, been quite small and designs are Rankine devices are able to make efficient somewhat outdated. Rankine-cycle devices use of the temperatures available, but the operating with steam or other working fIuids *This is the effective “blackbody” radiation tem- at temperatures higher than 600“C (1,1100 F) perature of the Sun, not its actual surface tempera are possible, but the equipment must be ture made from special materials. 329 Ji,{. , $J ( ) - 2’2 330 ● So/ar Technology to Today’s Energy Needs

One difficuIty with Rankine devices oper- sol id-electrolyte devices (systems have been ating in conventional temperature regimes is tested which operate in the temperature that their generating efficiency falls sharply range of 7500 to 1,5000 F, but research is in if waste heat is recovered. a very early stage). Brayton-cycle (gas-turbine) engines operate The overall system efficiency of these at temperatures of 900“C (1 ,6520 F). Com- cycles is illustrated in figure IX-I. The tem- mercial devices are available in a variety of perature ranges which can be produced by sizes, although efficient devices are typical- different types of collectors are also shown ly only available in units producing more to indicate which collectors would be used than 1 MW. The technology is well under- to provide heat for the cycles. stood, although work is needed to develop reliable heat exchangers for solar receivers THERMODYNAMICS and regenerators needed to improve efficiency. The efficiency of Brayton-cycle The cost of most solar systems depends devices is lower than steam Rankine effi- critically on the cost of the collector field ciencies, even though the former operates and the area of collectors required will de- with much higher initial temperatures. The pend directly on the efficiency of the energy high temperature of the exhaust, however, conversion system employed. The efficiency permits recovery of waste heat without ex- of an ideal heat engine increases with the cessive loss of generating efficiency. temperature available. If heat is available at a constant temperature T and is rejected at Stirling-cycle piston devices are available h a constant temperature T , the maximum on a prototype basis and can operate at tem- C engine efficiency is given by the Carnot effi- peratures in the range of 6500 to 800°C (1 ,2000 to 1,4700 F). Development work is needed to design a reliable commercial de- (1) vice. The engines will probably initially be best suited for applications where individual (Both temperatures must be expressed as ab- devices generate less than about 300 kilo- solute temperatures. ) I n many cases, how- watts. They may be able to achieve very ever, heat will be available only in the form high efficiences (40 to 50 percent). of a heated fIuid which cools as energy is ex- Advanced Ericsson free-piston engines and tracted. If energy is extracted from a fluid highly regenerated Brayton devices with which cools from Th to T'h, while giving up multiple stages of reheat are being inves- heat to the engine, in this case, the max- tigated, and some units are in the development stage, Those cycles would operate in a temperature range of 7500 to 1,000“C (1,382 0 to 1,8320 F) and also show promise of achieving high efficiency. The free-piston device may be able to achieve high efficiency with a small, relatively simple engine.

Research is also underway on several other advanced concepts including: Ran- kine-cycle devices operating with liquid metals, therm ionic devices (prototypes of these devices are available which operate in temperatures of 1,0000 to 1,500 “C; efficiency is poor, but they reject heat at temperatures high enough to drive other engines in a bottoming cycle), and thermoelectric Ch. IX Energy Conversion With Heat Engines ● 331

Figure IX-1 .—Cycle Efficiencies of Heat Engines

* Local temperatures In the combustion chamber only Exhaust gas IS 9000 to 1,4000 F Note References for Indlvidual estimates can be found In relevant sections of this chapter SOURCE Prepared by OTA using manufacturer’s data

the collector system and for engine com- been established, however, and could be ponents. Materials have been developed quite high. which can be used with gas turbines at In spite of the theoretical increase of effi- temperatures in the range of 1,8000 F, and it ciency with temperature, there are a number may be possible to develop material (such as of reasons to believe that the use of the silicon nitride or silicon carbide) which can highest available temperature may not re- be used at temperatures as high as 2,0000 to sult in either the most inexpensive solar 2,5000 F in the next decade. ’ The cost of energy or even the highest efficiency. If systems using such materials has not yet both the cost and the efficiency of collectors or of storage devices increases rapidly ‘Arthur L Robinson, “Making Gas Turbines From with temperature, for example, there would Brittle Materials, ” Science, Vol. 188 (1975), p 40 be an optimum temperature which would 332 ● Solar Technology to Today’s Energy Needs

minimize overalI system costs. (The preced- thermal and electrical requirements defined ing chapter has presented evidence that col- by the waste-heat temperature. With other lector costs may be nearly independent of ratios, some part of the load would have to the temperatures produced, but this result be met either with a backup “boiler” or with can only be tested with more experience.) a heat engine using the highest possible Even if collector and storage costs are in- electric-generating efficiency. dependent of temperature, however it may The complexity of the situation can be not be desirable to operate at the highest een in figure IX-2. This figure shows how the available temperature because the efficien- energy required by several types of systems cy of real devices does not necessarily in- varies as a function of the ratio between crease with increasing temperature. It can electric and thermal demands. The most ef- be seen from figure IX-I, for example, that ficient system is the device employing an ef- the efficiency of steam turbines operating at ficient heat pump and an efficient heat 8000 to 1,0000 F can be higher than the effi- engine. Commercial heat pumps are not ciency of gas turbines operating at 1,4000 to able to produce temperatures above 100 “C, 1,8000 F. A final choice of designs will re- but most space-conditioning applications quire a net assessment of the economic at- and many industrial processes can use heat tractiveness of the integrated system. at temperatures below 100°C. The seasonal coefficient of performance of space-condi- COGENERATION tioning heat pumps is typically below 2, The analysis of efficiency becomes signi- however, and figure IX-2 shows that with this ficantly more complex when there is a need efficiency, cogeneration systems using en- both for electricity and thermal energy. gines with lower electric-generating efficien- There are several alternatives to choose cy could have better overall performance f rem: than high-efficiency engines driving heat pumps as long as the ratio of electric to ther- ● Generate electricity at the maximum mal demand is below about 0.8. The least- possible efficiency and produce the efficient system shown, however, is the rela- thermal energy with a separate collec- tively low-efficiency engine with a backup tor or with a fossil boiler; boiler for providing thermal energy. ● Generate electricity at the maximum All that can be concluded from this anal- possible efficiency and use a heat ysis is that great care must be taken in pump to produce the needed thermal designing systems to maximize efficiency. energy (i. e., the heat engine would re- The decision depends heavily on the ratio ject heat at the lowest temperature); or between electric and thermal loads and the ● Use a heat engine which rejects heat at way in which this ratio varies over time. If a temperature high enough to be useful electricity which exceeds local requirements for the thermal processes (cogenera- can be sold to a utility, the perspective of a tion). designer could change. Since the ratio between thermal and electric loads could be The optimum selection will depend criti- changed, in this way the overall efficiency cally on the nature of the thermal and elec- of the system would always be reduced by tric loads and on the details of the opera- increasing the electric to thermal ratio. In tional performance of available heat some circumstances, the greater value of engines. the electricity generated would compensate If ideal systems were available, the sec- for the extra cost. The addition of storage ond alternative would always define the equipment could also permit some adjust- maximum efficiency; the cogeneration sys- ment of the ratio between the thermal and tem could equal the maximum efficiency electric demands placed on the energy con- only if the load had a unique ratio between version system. Ch. IX Energy Conversion With Heat Engines ● 333

Figure lX-2.—System Performance (Ratio of Electric and Thermal Energy Produced to Energy Entering the System)

14 Steam rankine with NO extraction

ExtractIon steam Ranklne (steam at 300°F)

12 Gas turbine with waste heat boiler — – — (steam at 300°F)

————. Combined cycle (COP as shown) 1,0 Backup ‘boiler’ assumed 100% efficient

0.8

0.45 04 0.33

0 o 0.25 0.50 0.75 1.00 1.25

All thermal demand Ratio of electric energy delivered All electric demand I to thermal energy delivered

Note. It is possible for a heat pump to perform several units of useful work for each unit of energy consumed since the “energy consumed” by the engine does not count the energy In the ambient alr used as a source of heat “pumped” by the device SOURCE. Prepared by OTA using manufacturer’s data

The following review of each cycle in- THE RANKINE CYCLE eludes a brief description of the way the cycle works, an analysis of the prospects for using the cycle for cogeneration, an esti- The Rankine cycle has been used since mate of the cost and performance of dif - the early 19th century for everything from ferent design options, and a summary of the steamboats to nuclear powerplants. It con- current status of research, development, tinues to be the most commonly used for and manufacturing. generating stationary power. Designs have, 334 ● Solar Technology to Today’s Energy Needs

of course, improved over the years and a the turbine, a heat exchanger is used which variety of devices are currently available. condenses the turbine fluid and transfers energy to a separate piping system used in Typical Rankine cycles operate as fol- spaceheating or industrial processes. The lows: a liquid is pumped under pressure into temperature of the steam produced is con- a boiler (which could be a receiver in a solar trolled by the pressure maintained at the collector) where heat is added, boiling the end of the final turbine-expansion stage. liquid into a vapor (in some applications the This temperature can be changed somewhat vapor is also superheated); the vapor is then to adjust to different loads, but a large expanded over turbine blades or in a piston amount of control is not possible. The sys- to produce mechanical energy; the low-pres- tem is most useful in situations where there sure vapor which emerges from this expan- is a relatively constant demand for process sion process is condensed to a liquid and heat during the year; it does not require pumped under pressure to the boiler where costly condensing equipment or cooling the cycle begins again. In sophisticated towers since this operation is being per- systems, efficiency can be increased 4 to 5 formed by the industrial process or building percent by preheating the water returning to heaters. If there are periods when the heat is the boiler with hot vapor extracted from not required, however, condensing stages high-temperature stages of the expansion must be purchased to reject the unwanted process. Water is the fluid most commonly heat. The backpressure devices producing used in the cycle, but other liquids can offer steam at high pressure can significantly advantages at lower temperatures. reduce the amount of electricity generated There is no fundamental limit to the tem- by a given rate of steam flow. A very large peratures which can be used in the Rankine fraction of the total energy sent to the sys- cycle, but practical limits are imposed b} tem can be recovered as steam heat or elec- the steel alloys used in boilers and other tricity, however, since the only losses in the components. The highest practical tempera- system result from mechanical losses in the ture with current technology is about 1,1000 turbine, losses in the generator, and oil- F. Higher temperatures may be possible in cooler losses. These losses are quite small. the future using advanced materials, but a An alternative approach is illustrated in recent study by the Federal Power Commis- figure IX-3B. This system, called “extrac- sion concluded, “It would probably require tion” turbine (or “pass out” turbine by the 10 to 15 years to develop materials for use at temperatures above 1,2000°F.”2 It may be English and Europeans) is simply an ordinary possible to achieve much higher operating condensing Rankine device with provision temperatures if liquid metals are used as a for extracting steam at some intermediate working fIuid. stage in the turbine-expansion process. The device has the advantage of permitting Two techniques are used to extract heat great flexibility in the temperature and from Rankine-cycle devices for direct ther- quantity of steam produced but, of course, mal applications. Figure IX-3A shows a sim- it requires the purchase of condensers, cool- ple “backpressure” device in which lowing towers, and relatively expensive low- pressure vapor is simply sent directly to the pressure expansion stages. (Low-pressure process loads. If organic fluids are em- stages are physically large since the volume ployed, or if the process requiring thermal of the steam has increased at the lower energy could contaminate the water used in pressure, and thus these stages are more costly per unit output.)

Steam turbines are used in many indus- ‘John H. Nassikas, Chairman, Advisory Committee Report: Energy Conservation, Federal Power Commis- trial cogeneration installations, but are used sion, The National Power Survey, December 1974, p by less than 1 percent of the “total energy” 86. space-conditioning instalIations in the Ch. IX Energy Conversion With Heat Engines • 335

Figure lX-3.— Rankine-Cycle Devices With Heat Extraction

Boiler

Generator

Boiler

Pump

SOURCE Prepared by OTA using manufacturer’s data 336 ● So/ar Technology to Today’s Energy Needs

United States.3 This is due to the fact that The overall system efficiencies of a vari- their efficiency is low when there is a small ety of simple and regenerated Rankine-cycle demand for space heat, and that local or- devices (i.e., systems in which the working dinances frequently require experienced fluid is preheated by hot sections of the tur- operators to be on duty whenever pressur- bine before being sent to the boiler) are il- ized steam is used. Extraction turbines are, lustrated in figure IX-4. The extremely high however, frequently used in district heating efficiencies of large contemporary steam systems in Europe where a variety of designs plants result from the use of many reheat are employed. Stal-Laval apparently has a cycles (i.e., adding heat to the working fluid system which saves the expense of a con- at some stage during expansion) and ex- denser by using low-temperature steam to tremely high pressures. Such sophistication provide “heating of swimming pools, snow cannot be afforded in small systems. The at- melting in winter, pavement heating, etc.”4 tractiveness of organic working fluids depends on the power levels required and the One difficulty with all large steam tur- characteristics of available heat sources. bines is that all of these devices require Organics may prove to be more attractive complex procedures when they are started than steam in small systems working at rela- and when they are turned off. Usually an tively low temperatures, although ideal hour or more is needed and skilled person- steam cycles can produce competitive effi- nel must be present. The process is expen- ciencies. There are several reasons for this: sive and wastes energy. It could be a serious barrier to the use of these devices in solar applications where systems must be turned ● The organic working fluids remain on and off each day. The problem could be vaporized under temperature and pres- alleviated if fossil fuel were used to fire the sure conditions where steam would be system when storage was exhausted. gin to condense. In steam systems, the turbine blades can be eroded severely by the impact of droplets on the rapidly Cycle Performance moving blades. These droplets reduce system reliability and system life, as The Rankine cycle permits a great range well as efficiency. This problem can be of design options and the system efficien- reduced if the turbine is divided into cies vary widely. Efficiency depends prin- several stages with liquid removed be- cipally on the following design features: tween stages, but this adds to the sys- ● The maximum temperature and the tem’s costs condensing temperature of the cycle. ● The efficiency of the organic turbines ● The working fIuid used. proves to be greater than steam turbine efficiencies in many systems now oper- ● The efficiency of the turbine (or piston) ating at low-power levels (figure IX-5). expansion process and the mechanical efficiency of the system. ● The optimum turbine speed of organic systems is lower than equivalent steam ● A number of features, such as the systems (potentially saving costs). number of stages of expansion used, the use of feedwater heating, etc. Organic systems are relatively simple compared to multiple-stage steam de-

~1 971 Total Energy Directory and Data Book, ‘Dean T. Morgan and Jerry P. Davis (Thermo Elec- Volume 1, Total Energy Publishing Company, January tron Corporation), High Efficiency Decentralized Elec- 1971, pp. 40-66, trical Power Generation Utilizing Diesel Engines Cou- 4!. G. C. Dryden, editor, The Efficient Use of Energy, pled With Organic Working Fluid RankineCycle IPC Science and Technology Press, Surrey, 1975, p. Engines Operating orI Diese/-Reject Steam, NSF Grant 355. No. G 1-40774, November 1974, pp. 8-28. Ch. IX Energy Converison With Heat Engines . 337

Figure lX-4.—Temperature Dependence of Rankine-Cycle Devices

Maximum Cycle Temperature (°F)

SOURCES Low-Temperature organic and steam efflclencles computed by R E Barber “Solar powered Ranklne CYcle Engine Cycles —Character!stlcs and Costs, ” June 1976, with the followlng assumptions” Expander efficiency 80 Percent, PumP efflclencY 50 Percent, Mechanical eff Iclency 95 Percent, Condensing temperature 95° ● F, Regeneration efficiency 80 percent, High side pressure loss 5 percent, Low side pressure loss 8 percent “High-temperature steam efflclencles from National Power Survey Adwsofy Panel Report On Energy Conservahon, December 1974, page 102

vices and can be constructed inexpen- organic working fluid for maximum efficien- sively from low-cost materials if a non- cy and power; up to 35 percent greater corrosive working fluid is used. The sys- power output can be achieved with organic tems thus have the potential for long relative to steam, depending on heat-source life and high reliability at relatively low temperature characteristics. cost. The advantages of organics are counter- Thermodynamic properties can be opti- balanced to some extent by the fact that mized by selection of an appropriate many of the fluids being studied are toxic or 338 . Solar Technology to Today’s Energy Needs

Figure lX-5.—Rankine-Cycle Expander Efficiencies

efficiency #lo

1 10 100 1000 10000 Engine Size (kW)

Reciprocating steam Steam turbine organic turbine Reciprocating organic turbine

SOURCE. Prepared by OTA using manufacturer’s data

flammable. The systems are sealed, how- the search for the desirable materials is con- ever, and only small amounts of the fluid tinuing. In the temperature range of 7000 to should leak from the cycle in a properly 1,1000 F, there is no advantage in using maintained system. Another potential draw- fIuids other than water. back is the cost of the fluids, although fluid Many early organic systems have had re- costs tend to be only a small fraction of liability problems resulting from failures of overall system costs even if expensive fluids bearings and seals. These problems have ap- are used. (Water clearly has the advantage parently been overcome by several manu- of being cheap, plentiful, and nontoxic. ) The facturers, and high reliability is one of the characteristics of a variety of materials selling points of organic Rankine engines de- which have been considered for turbine ap- signed for use in isolated regions. Reliable plications are shown in table IX-I. systems are presently quite expensive, Refrigerants are attractive for applica- however. tions up to about 4000 F. They are nontoxic and the technology of Rankine systems us- Turbine Efficiency ing these materials is very well known since refrigerators are simply Rankine cycles Turbine performance is limited by the size operating in reverse. A number of other of the equipment as welI as by the temper- materials have been examined for applica- atures available. Figure IX-6 illustrates the tion at temperatures up to about 8000 F, and efficiency with which turbines of varying Ch. IX Energy Conversion With Heat Engines ● 339

Table IX-1. —Organic Power-Cycle Working Fluids Used in System Testing or in Development

Maximum boiler out let System Current temperature Freezing test development Fluid Developers ‘F point ‘F experience Flammablllty underway Comments

Freon 11 IHI (Japan) -250

Freon 114 -400 -137

Freon 22 425 -256

Isobutane -500 -217

Thiophene 550 -37

FC-75 -600 -76 (3 M Co )

Chloro- -600 benzenes

-600

625-650 -82

-700 75

SOURCE Thermoelectron Corp 340 ● Solar Technology to Today’s Energy Needs

Figure lX-6.— Efficiency of Backpressure Steam Rankine Devices

sizes can extract the energy available in the on a refrigerant, which demonstrated a tur- fluids sent to them. It can be seen that with bine efficiency of 72 percent.6 A small multi- current designs the efficiencies of small sys- vane expander developed by the General tems are quite low. This is in part the neces- Electric Co. has demonstrated efficiencies sary result of the fact that a clearance must as high as 85 percent. 7 It is clear, therefore, be maintained between the turbine blades that high-turbine performance is not neces- (or pistons) and their containment cylinders. sarily restricted to large devices. (This is not a limiting factor for single-stage impulse turbines. ) The fluid which can leak Performance With Heat Recovery through this aperture does not perform work The decline in generating efficiency and thus limits efficiency. In smaller sys- which is experienced by steam Rankine de- tems, the clearance area is a larger fraction vices operating with backpressure and ex- of the total useful turbine blade area and thus smaller systems are more seriously affected by these effects. The figure il- ‘Robert E. Barber, “Solar Air-Conditioning Systems lustrates, however, that several advanced Using Rankine Power CycleDesign and Test Results turbine and reciprocating engine designs of Prototype Three-Ton Units, ” Proceedings, the Sec- have been able to achieve relatively high ef- ond Workshop on the Use of Solar Energy for the Cooling of Buildings, Los Angeles, Calif , Aug. 4-6, ficiencies even at small sizes. 1976, p. 91. 7 High turbine efficiencies have been dem- S. E. Eckard and J. A. Bond, “Performance Charac- teristics of a Three-Ton Rankine Powered Vapor Com- onstrated even in very small devices. Barber- pression Air-Conditioner, ” Proceedings, the Second Nichols Engineering Company, for example, Workshop on the Use of Solar Energy for the Cooling has constructed a 2.5 hp turbine, operating of Buildings, op. cit., p. 110. Ch. IX Energy Conversion With Heat Engines “ 341

l’: I I . l-:=

-l-’ 1+ 1/ “’ .’- ““fh L “’.” ~ — — -k . : . A I “ I I .-c < :=,- F’ I ..—

, ,-

-UMAL -’ TJm I J

I I rl II II II IL I I I : I I I I I ; I I I I I I I I 1 I iI I I I , , I ; wI I

. II — . —.. —..- 342 Ž Solar Technology to Today’s Energy Needs

traction systems is shown in figures IX-7 and Figure IX-6, for example, illustrates the dif- IX-8. The efficiencies shown in these figures ficulty of using backpressure turbines with represent a highly simplified analysis of the relatively low-inlet temperature systems to cycle and are intended only to illustrate the produce process steam at high pressures and sensitivity of generating efficiency to temperatures. Generating efficiency falls changes in several important variables. off rapidly with increasing backpressure and

Figure lX-8.— Electric and Therma Performance of a 12.5 MWe General Electric Extraction Turbine Ch. IX Energy Conversion With Heat Engines Ž 343

the problem is exaggerated unless high- solar colIectors. With this approach, the per- turbine efficiencies can be achieved. formance of the cycle is not changed by a shift from solar to backup power. Figure IX-7 illustrates the operation of a backpressure device using toluene as a If a storage device capable of supplying working flu id which has been installed in temperatures close to those supplied direct- Albuquerque to test the concept of solar- ly from the solar collectors is not available powered “total energy” systems. The system at an acceptable price, it would be possible is equipped with a cooling tower since the to use a turbine with two different inlets: heat extracted from the turbine is used for a one for high-temperature fluids received heating and cooling application where loads directly from the collectors, and one for are Iikely to vary greatly from day to day. lower temperature fluids received from storage. (This is shown by the dotted line in The performance of an extraction device figure IX-9 A.) Steam turbines with multiple is illustrated in figure IX-8, using a format inlets have been avaiIable for many years, which has become standard for presenting although most are relatively large. data about such systems. Another approach which may be attrac- Steam Rankine devices have been se- tive under some circumstances would use lected by all three contractors working on a the “hybrid” system illustrated in figure IX- design for DOE’S 10 MWe solar central- 9B. In this design, solar energy at relatively receiver demonstration plants,8 9 10 The total low temperatures is used to boil the working energy test design developed by Sandia uses fluid and a fossil boiler is used to superheat the toluene-based Rankine cycle shown in the liquid to the turbine inlet conditions, figure IX-7. This system takes advantage of the fact that the majority of the energy absorbed by con- Performance With Backup Power Sources ventional Rankine cycles is absorbed at a It is possible to design Rankine-cycle sys- constant temperature while the liquid is tems which are capable of operating both converted into vapor. This system would from fossil fuels and from solar power. The take advantage of the relative simplicity of temperatures used are low enough to permit solar collectors operating at moderate tem- piping energy from boilers operated from peratures, while permitting more efficient different sources to a single Rankine turbine utilization of the high-flame temperatures device. In addition, the boilers can be exter- available from burning fossil fuels. nally fired so coal or other solid fuels can be The performance of these different ap- easiIy used for backup fuel. proaches can be summarized in the follow- Two approaches are shown in figure IX- ing simplified analysis. If the fraction of the 9A. The most efficient type of backup sys- thermal energy applied to the system which tems provide energy from a fossil-fired leaves as mechanical energy through the boiler or a storage unit at temperatures and high-pressure and low-pressure stages of the pressures which are as close as possible to those of fluids supplied directly from the mixture emerging from the high-pressure ‘Quarterly Report No 1, Central Receiver Solar stage is available to be sent to the low- Thermal Power System, Phase 1, january 1976, Martin pressure stage (the remainder being used to Marietta (ERDA Contract E(04-3}1 110) preheat the feedwater going to the boiler), ‘Central Receiver Solar Thermal Power System, the total electric output of the engine E is Phase 1, Final Report, January 1976, McDonnell- written as follows: Douglas Astronautics Company (ERDA Contract E(04-3-1 108) (3) ‘“Solar Pilot Plant, Phase 1, Conceptual Design Report, Dec. 18, 1975, Honeywell, Inc. (ERDA Con- tract E(04-3}1 109) Here Qb is the energy available from the 344 • Solar Technology to Today’s Energy Needs

Figure lX-9.— Designs for Providing Backup Power for Solar Rankine-Cycle Systems

A. Direct fossil backup

Fossil + 300° F/60 psia boiler -- To process loads , rq

Solar 950°F/1 250 psi / ~ collec -1, Hp ; tor \?:, p:ak~—’ m c “~ ~ ~ 600°F/350 psia 2 P v 2 v I 1 L–- -

Con- denser

~~.1

-- --– ~ From process loads Deaerator Pump ———— Storage discharge flow if storage can discharge at 950° F

B. Fossil boiler used for superheating

● To process loads ~—--- L-’-”l Generator Solar M. collec- — ● tor

M. (l~f) ?

denser

[ I & From process Pump L 4 loads Deaerator d! M. = mass flow from boiler

SOURCE. Prepared by OTA using manufacturer’s data Ch. IX Energy Conversion With Heat Engines ● 345

The performance of designs using a fossil fraction of the energy available from the system to superheat the steam can be esti- first turbine stage which is sent to the sec- mated from the efficiencies shown in table IX-2 and the ratios shown in table IX-3. This available for process loads. Using the same last table indicates the percentage of the notation, the energy available in the process energy entering the turbine which results heat Q P can be written as follows: from the boiling process. Boiling can represent a large fraction of the total energy re- (4) quirements. The boiling temperature for this system shown is 5720 F. Using fossil fuels only to provide superheat would effectively the temperature of the process heat stream. increase the efficiency of converting fossil These parameters are illustrated in figure IX- energy into electric output. 9B. A sample set of these parameters is illustrated in table IX-2 for a turbine oper- Table IX-3 .—Ratio of Energy Required for ating with 9500° F, 1,250 psia steam. The Boiling to Total Energy Sent to Turbine decrease in system performance resulting from the lower storage temperatures can be Boiling clearly seen. The performance can be im- temper- Ratio proved considerably if the fossil boiler is ature used to raise the temperature to the original extraction turbine 950° F/l 250 psia inlet conditions. (feedwater regeneration) ...... 572° F 0.76 0.79 Table IX-2. —Efficiency of Steam 950° F/1250 psia(no feedwaterheat) 572° F Rankine Devices operated From Storage 600° F/350 psia backpressure50 psia 486° F 0.91 at Reduced Temperature 400° F/150 psia backpressure50 psia 247° F 0.99

Single-feed water No feed water SOURCE: Prepared by OTA using manufacturer’s data. regenerator regenerator

State of the Art While Rankine-cycle engines are available in a variety of sizes, most of the development work in the United States in recent years has been directed to perfecting very Assumptions: generator efficiency = 95% large devices optimized for centralized utili- turbine efficiency = 800/0 ty applications. Because of the limited de- pump efficiencies = 700/o steam extracted for reheat at 300° F mand for small steam turbines, designs tend inlet conditions 950° F/l 250 psia to be somewhat antique, although interest in smaller devices has been greatly in- fraction of energy entering system which leaves as mechanical power in the first turbine creased in recent years. stage A number of companies are working on fraction of energy entering system which leaves as mechanical power in the second devices capable of improving the perform- turbine stage ance and reducing the costs of small 300° F energy available for process heat or low Rankine-cycle systems. Table IX-4 indicates pressure turbines per unit of energy available some of the steam turbines which were iden- from the high-pressure turbine tified by Sandia Laboratories in their review of devices for use in their total energy sys- SOURCE Prepared by OTA using manufacturer’s data. tem. Extraction turbines and backpressure 346 • Solar Technology to Today’s Energy Needs

Table IX-4.—Small Steam Rankine Turbines in 1972, which Ied to the construction of two (1973 Dollars) prototype steam vehicles–one built by Steam Power Systems and the other by Aero- jet Liquid Rocket Company. There has also Capacity cost Source (kW) ($ in thousands) been a considerable amount of interest and investment in this area by private com- 2 2.0 5 panies, including Lear, Carter Enterprises, 4.5 2 and Saab-Scandia of Sweden. Table IX-5 3 3.7 1 5 3.0 1 summarizes the performance of some of the 10 4.1 1 equipment which has been investigated. 3.8 5 2.5 5 Interest in small, combined-cycle systems 20 6.0 1 has come mostly from companies which 100 18.0 1 construct onsite generating facilities for 11.3 1 remote locations (pipeline pumping sta- 10.0 5 tions, offshore drilling rigs, etc.). interna- 9.6 6 9.0 2 tional Harvester, Solar Division, for exam- 250 50.0 3 ple, believes that a steam turbine which 400 17.5 1 operates on the heat exhaust from their 2.6 500 30.0 4 MWe “Centaur” gas turbines could produce 1000 100.0 2 an additional 1.3 MWe, resulting in increas- 70.0 3 45.0 4 ing generating efficiency from 26.6 percent to over 40 percent. Similarly, a steam turbine which operates on the heat exhaust SOURCE: Solar Total Energy Program Semiannual Report, April 1975- September 1975, Sandia Laboratories, Solar Energy from their 7 MWe “Mars” unit, could pro- Projects Division, April 1976, p. 96. duce an additional 3.3 MWe, resulting in in- Source Legend: 1 - Coppus Engineering Corporation creasing generating efficiency from 31.5 to 2- The Terry Steam Turbine Company 3- The Trane Company, Murray Division 43.5 percent. The Thermo Electron Corp. 4- Turbodyne Corporation, Worthington Turbine Division and several other companies are working on 5- The O’Brien Machinery Company 6- Carling Turbine Blower Company small steam turbines for similar applications.12 turbines are also available in the sizes of in- In addition to development work on im- terest to intermediate total energy applica- proved steam cycles, a considerable amount tions. Most interest in this research comes of attention is being directed to the develop- from several directions including: ment of organic Rankine cycles. Work in this 1. A desire to develop devices to improve area has also been stimulated primarily by a the fuel economy of diesel-generator desire to develop high-efficiency, combined- sets and gas turbines through the use of cycle, generating systems. Geothermal and a “combined-cycle” approach. even space applications have also motivated research in organic cycles. Several 2. Making use of waste heat from other in- large organic Rankine units are now in use in dustrial processes which is available at various parts of the world. DOE is support- temperatures of 2500 to 1,0000 F. ing work in organic Rankine devices of inter- 3. Interest in exploiting geothermal ener- mediate sizes by the Sunstrand Corporation, gy in the range of 2000 to 6000 F. Thermo-Electron Corporation, and Mechan- ical Technologies, Inc. A summary of the 4. Interest in developing new engines for automobiIes and other vehicles. ‘ ‘jet Propulsion Laboratory, An Autornobi/e Power Systems Evaluation, August 1975, p. 7-2. The Environmental Protection Agency z ‘ Donald L. Kearns, Regional Manager, Govern- and the State of California funded research ment Relations, International Harvester, Solar Divi- on steam-powered automobiles, beginning sion, letter dated Mar. 10, 1977. 650 1000

IL-4 IL-4 v-4’ IL-2 IL-4 IL-4 Series-P spool HAP PAP Series-P HAP Variable Variable Variable Fixed Variable Variable 135 49 184 30 68 50 Variable Variable Variable 12: 1 Variable Variable 2500 2400 1800 6000 3200 2000

246 228 244 210 193 228 212 33 20 27 35 10 20 32

71 N/D 75 N/D N/D 75 85 N/D 87 N/D N/D 87 68 N/D 75 N/D N/D 75

150 65 145 90 90 60 755 N/D N/D N/D 600 N/D 0.77 1.03 0.79 0.55 0.67 0.79 765 857 835 338 520 N ID

characteristics of some of the devices which unit for a truck diesel engine. 3 The turbines have been tested can be found in table IX-6. used by Thermo-Electron are typically axial impulse turbines and may have up to six The Sunstrand Corporation work started stages. These designs all utilize either in 1961, and a number of units rated from Fluorinol 50 or Fluorinol 85. 1.5 kilowatts up to 600 kilowatts have been operated successfully. One of the Sunstrand No large organic system is now being 100-kilowatt units has been modified to manufactured on a large scale, although a operate on 5500 F solar heat and has been number of prototype units have been suc- tested at the Sandia Albuquerque Labs. cessfully operated. Engines ranging in size from a few kilowatts to a few megawatts are Development work at Thermo-Electron commercially available from Sunstrand, Sun has been proceeding in several different Power, Kinetics Corporation, and other areas. Among the organic Rankine cycle firms, although none is produced in large systems (ORCS) applications are a 10 MW combined steam/ORCS unit, a 4.3 MW diesel/ORCS unit, a 1.25 MW ORCS bottom- ‘] Organ/c Rartkine Cycle System tor Power Genera- ing unit, a 400-kilowatt ORCS as a prime tion from Low-Temperature Heat Sources, Thermo- mover, and a 40-kilowatt ORCS bottoming electron Corporation, Sept. 10,1973. 348 • Solar Technology to Today’s Energy Needs

quantities. (A 100 kW Sundstrand unit is reliability guarantee results in a high initial shown in figure IX-10. ) The Ormat Corpora- cost. Several hundred of these units have tion of Israel has sold a number of small been sold over the last 10 years and millions organic Rankine-cycle devices for use where of hours of operating experience have been extremely high reliability is required (e. g., obtained. remote pipeline pumping stations). The high

Table lX-6.– Experimental Organic Rankine Turbines in the United States

Sunstrand Elliot ● Thermo- Thermo- Thermo- Aviation Turbo- Electron Electron Electron machinery

Working Fluorinol- Fluorinol- Fluorinol- fluid ...... Toluene Isobutane 85 50 85 Turbine Inlet 550° F 350° F 550° F 600° F 550° F Turbine type Single- 3-stage Single- 3-stage 1-stage stage double stage axial axial partial flow axial axial flow turbine turbine admission turbine impulse impulse turbine turbine Unit-rated 36 kWe 65 MWe 104 kWe 33 kW shaft 3 kWe capacity

● Developed for geothermal application. SOURCE: Prepared bv OTA using manufacturer’s data,

Figure IX-10.— The Sunstrand 100 kW Organic Rankine Turbine

SOURCE: Sunstrand Aviation, Rockford, Ill., “100 kW Organic Rankine Cycle Total Energy System.” Ch. IX Energy Conversion With Heat Engines ● 349

A number of firms are also developing these engines is demonstrating acceptable organic Rankine devices which could be lifetimes and reliabilities. A critical element used for small residential or commercial in- in this design work is finding an inexpensive stallations. Several of the designs now under safe working fluid with an acceptably long consideration are illustrated in figures IX-II life. A variety of other design details (blade through IX-I 5. Hundreds of hours of oper- shapes, etc. ) will undoubtedly also be im- ating experience have been achieved with proved for optimum performance. The tech- many of these devices, even when the units nology of steam turbines has been devel- are unattended; the expanders have run very oped over nearly a century. While organic quietly and without vibration. (The sound is systems can profit from this development similar to the hum of an air-conditioner. ) work, much remains to be done to realize The major development problem for their full potential.

Figure IX-1 1 .—Components of the Solar Heated, Rankine-Cycle Electric Power/3-Ton Air-Conditioning System

Prototy~ Integratd System

The Organic Turbine

SOURCE Robert E Barber, “Solar Air Cmd!tlon!ng Systems Using Rank!ne Power Cycles —Des@n and Test Results of a Prototype Three Ton Unit, ” PrO. ceedlngs 01 the Second Workshop on fhe Use of Solar Energy for the Coo/lng of Bulkftngs, Los Angeles, Calif., Aug 461975, PP 101 and 102 350 Ž Solar Technology to Today’s Energy Needs

Figure IX-12.— Flow Diagram of the Solar Heated, Rankine-Cycle Electric power/3-Ton Air-Conditioning System

T = 215° F SOLAR T = 205° F

WATER WATER

m—[ RANKINE CYCLE REFRIGERANT 113 1—1 AIR CONDITIONER REFRIGERANT 12 DESIGNED AND FABRICATED BY SOLAR COLLECTOR WATER BARBER-NICHOLS ENG CO DENVER, COLORADO r J COOLING WATER SOURCE: See figure IX-1 1. Ch. IX Energy Conversion With Heat Engines ● 351

Figure lX-13.— United Technologies Design for Rankine Cycle Air-Conditioner

BASELINE DESIGN CONDITIONS FLUID R 11 T = 20Qo F COOLING = 37 TONS — —b COP = O 36 TURBINE / COMPRESSOR 3------r k T = 45°F N = 28,560 RPM COLLECTOH STORAGE I SIMULATOR H20 + (COOLING LOAD) -1 T = 137’F T = 159° F T = 213CF I EVAPORATOR /

VAPOR d GEN “ II b L_d L . . . . . J i H20 STEAM T = 203° F EXP VALVE EXP VALVE FREON I PUMP T = 105’F I -8 - I T = 105° F - –--—

POWER LOOP COOLING LOOP

SOURCE” Fran Blancardl and Maurice Meader (Un[ted Awcraft Research Laboratories), “Demonstrat~on of a 3-Ton Rankine Cycle-Powered Air-Cond/t~oner, ” F’roceed)ngs of the Second WorksfIop on ftre Use of So/ar energy for the Coollng of Bul/dings, Los Angeles, Cal If., Aug. 4-6, 1975, p. 142.

Thermostat Electrlc Motor {v>. Y Alr I Multl.Vane L[qu[d u , Expander I I Separator t ftt 1

compressor T ( )-i

Hot Water I Press ; I LooP ‘ I Control L J Recetver

1 H Refrigerant Loop

Water Coollng Loop

SOURCE S E Eckard and J A Bond (General Electrlc Company), ‘“Performance Characterlstlcs of a 3-Ton Ranklne Powered Vapor.Compression Air. Condltloner,” Proceedings of Ihe Second Workshop on the Use of So/ar energy for the Coo/ing of f3ul/dmgs, Los Angeles, Callf , Aug. 4-6, 1975 p 129 352 • Solar Technology to Today’s Energy Needs

Figure lX-14.— Sun Power Systems Flow Diagram for 5 HP, Rankine Cycle Air-Conditioner

solar collector n n

EXPANDER

u R-1 14 180° 141 pSl 1 20” 33 psl \

/ \ \ I water 80° 165° 185° POWER OUTPUT Freon

/ ‘0’’”

condenser

water \I pump \ //\

\ [ (3 U water pump

80° Freon Ilquld pump ~ 1 water cooling ~ grid FOR FIVE NET HORSEPOWER ( \ R-1 14 2.86 GPH m Hot water 14 GPH I Cool water 28 GPH I

SOURCE: Sun Power Systems, Inc , Sarasota, Fla.

While improvements in design will cer- System Costs tainly be forthcoming, there is no apparent The costs of Rankine-cycle devices in technical barrier to developing a commer- small sizes is difficult to estimate, as rela- cial device. The General EIectric device, tively few installations are presently being based on a multivane expander, is an adap- constructed; however, the cost of installing tation of a system called “ELEC-PAC” which contemporary steam devices in the mega- was designed to be a simple, portable, total watt range can be estimated with fair ac- energy system used to provide electricity curacy. The costs can be divided into four and heat for mobile homes, boats, or recrea- general categories: tional vehicles. The device is shown in figure IX-I 5, together with some of the advantages 1. The cost of heat exchangers which may of the device claimed by G. E. be required to transfer heat from the collector circuit or storage device to It can be seen from the pictures in figure the working flu id in the turbine; IX-11, that devices large enough to provide 2. The cost of the turbine itself; adequate power to a single-famiIy home can be quite small. The entire device shown is 3. The cost of any condensing systems not much larger than the air-conditioner and cooling towers which are em- which it would be designed to replace. ployed; and Ch. IX Energy Conversion With Heat Engines ● 353

Figure lX-15.– Experimental Expander at General Electric

FEATURES AND CHARACTERISTICS OF INLET MULTI VANE EXPANDER

High Brake Efflclency Over a Wide Range of — Load(ng — Speed — Vapor Pressure

Tr)lerates Wide Range of Vapor Quallty PI — No Eros[on Problems — Nc) LIq utd Compression Problems

H g h Tcirque a! Zero Speed — Self Startlnq Under Load

Low Speed Compared to Turbine — Matches May Load Requirements

Stmplr3 Construct Ion — Nr, Valves or Gears — Simple Seals and Con/e~tlonal Bearings

PII~m IIs Slm~le Control System — Lc A N o se and VI brat 10 r – Gc,(,d LI fe Potenllal P2 SOURCE Eckard and Bond, op cIt , page 123 354 Ž Solar Technology to Today’s Energy Needs

4. The cost of a backup boiler to provide erected boilers and include the cost of main- energy when solar energy is not avail- taining all of the ancillary equipment able. (pumps, feedwater treatment, etc.) required for the operation of the system. Approx- It would be possible to reduce the cost of imately 10 percent of the cost shown is due the smaller turbine units if large numbers to devices designed to remove sulphur and are manufactured. The Jet Propulsion Lab- particulate from the boiler exhaust, and oratory estimated the costs of producing about 10 percent is traceable to systems for units in the 150-kilowatt size range if fuel-handling and storage. manufacturing were performed on the scale with which automotive engines are now pro- Costs of Organic Rankine Systems duced. There estimates show a wholesale price of $13/kW and a retail price of Estimating the potential cost of organic $17/kW.14 This is more than an order of Rankine devices requires a considerable magnitude lower than the cost of the units amount of speculation, since the few units manufactured with conventional turbine now on the market are essentially hand- manufacturing techniques. made. I n spite of this, there is a fair degree of agreement about the price of devices The cost of condensing units and cooling manufactured in relatively small numbers. towers required by condensing systems (in This pattern could change, however, if mass- addition to the turbine costs shown in figure production techniques were employed for IX-16) are illustrated in figure IX-17. Costs the smaller units. The figure shows estimates range from about $90/kWe to about indicating that production of 10,000 to $30/kWe. 20,000 units per year could reduce the costs The cost of providing backup power to an of units in the 5 to 10 kWe range to $200 to onsite solar system is shown in figure IX-18. $300/kW, a price which compares favorably The costs assume the construction of field- with the costs of even the larger steam- tur- bine systems. These costs are in general “An Automobile Power S ysterns Evaluation, Jet Pro- agreement with the costs of commercially pulsion Laboratory, Volume 11, pp. 11-12. available reciprocating and centrifugal air- Figure lX-16.– Installed Costs of conditioning systems. The comparison is a Steam Rankine Turbines reasonable one for determining the potential future price of mass-produced organic Rankine turbines since the mass-produced air-conditioners employ a nearly identical \ technology.

THE BRAYTON CYCLE

wc4wrw8umtulblrHo.nl bum hx The Brayton cycle (which uses gas at all @loV Iiulda phases in the thermodynamic cycle) has

cod bolw w been used extensively for jet aircraft and is Cmdmm!aw Wbhn commonly used by utilities to provide {~COndemm MfbhO power during peak demands. Its usefulness for peaking applications results from the low initial cost of the devices. Since they are

mlcmduwwJ tuli4bu relatively inefficient, however, they are {1a403 p@@ typically used only to help meet peak loads and are typically used by utilities less than

10 N 30 40 1,000 hours per year. .l.w!rlCO. !put MWe

T.rtlne COSIS (ncl.de I“stallallo” .. ”!,01s ..6 0..”,.1., c.o,ler coats ,.,1.0. suloiwr rem. ”.l wale< $re”lme”l !“elstrx~e .sh rerro”al bul!d W, PIPI!W !“slr. me.!, O“. ! The rising cost of liquid and gaseous fuels w.,* .“OSt Wk, ”X

Figure IX-17.— Installed Costs of Organic Rankine Turbines

1000 —

8’00 —

600 —

400 —

200 — /-” \ ‘ ---- —o 20,000 unltslyear ‘--@ / Notmcl.cfing installation I rl- 10 100 1000 10,000 System Size In Kilowatts

SOURCE A Milton Van Horn (Market Manager General Electrlc Advanced energy grou P Private communlcatlon, June 1, 1976) (estimates In 1975 dollars) B Price of electrlc chll Iers (assume 17°. cycle efflc Iency when operated as turbine generators) c Beno S!ernllcht (Mechanical Technology Inc ) Power, June 1975 p 71 D Sun Power Systems Inc (Dr M{nto. President, prlvafe communication April 19, 1976) E R E Barber “Solar Powered Organic Ranklne Cycle Engines Charactenst!cs and Costs “ June 1976 F Thermo Electron “ H Iah Efflc lenc~ Electrc Power Generation”, November 1974, paqes 59 and 510 (Increased by 9°. for lnflatlon since 1974) G Sun Po-wer Systems ~rlce estlmaie 1.21175 (200° F (n let)

cycle gas turbines has dramatically in- operational performance. A heat exchanger, creased operating expenses. There is, how- constructed from a material called Haynes ever, technology which shows promise of 188, survived 10,560 cycles with a high tem- permitting Brayton-cycle devices to operate perature of 1,5000 F. Tests will also be done from external heat sources, such as coal on a device using an Inconel 617 heat ex- (burned in a fluidized-bed boiler or a similar changer. 5 These materials will, however, be device) or from solar sources. The major bar- quite expensive. rier to the use of these devices has been the As was the case with the Rankine-cycle development of heat exchangers which are devices, the maximum temperatures avail- capable of transmitting high temperatures able for use with Brayton-cyc!e devices is into gaseous working fluids. Such materials limited by the performance of inexpensive now exist, but further work is needed to develop commercial devices. The Boeing Cor- “John P Gintz, Program Manager, Boeing Com- poration has recently completed a success- pany Engineering and Construction Division, C/osed- ful test which subjected the receiver to Cyc/e, l-ligh- Temperature Centra/ Receiver Concept for thermal-cycling equivalent to 30 years of Solar Electric Power, E PRI, February 1976. 356 ● Solar Technology to Today’s Energy Needs

Figure lX-18.— Installed Costs of Field-Erected Boilers*

1250psig 900°F

\ ———— 650 psig 750°F

\ \ 30 \ \ \ \ \ %

\ 20 \ -- -- + ‘- c oa I - - —-— - - - 1- -\_ -- oil ‘- ‘ -- --— —- ——— oil ——— —— 10

I I I I I I I 100 200 300 400 500 600 700 Millions of Btu/hour

● Includes coal handling, ash removal, fuel storage, sulphur removal, and electrostatic precipitator for particulate removal, boiler erection, foundation, buildings, instruments, auxillary equipment, ductwork and stack, electric material in boiler building, feedwater sampling and treatment, fuel and ash handling, and indirect distribution costs.

SOURCE Thermo-Electron Corp A study of Inplant Electrlc Power Generation of the Chemical, Petroleum Reflnlng, and Paper and Pulp Industries, June 1976, pages 317 and 319

materials. Temperatures of 1,5000 F are typi- means that heat can be recovered from the cal for Brayton devices. Temperatures as exhaust gases without reducing generating high as 1,8000 F can be used, but this signifi- efficiency to the extent that Rankine-cycle cantly shortens the expected operating life efficiencies are reduced. of the units. Four different Brayton-cycle systems The Brayton cycle has an advantage over which may be of interest for solar energy ap- Rankine-cycle devices when used in connec- plications are shown in figure IX-I 9. The sim- tion with a total energy or cogeneration ple cycle is the basis for most of the gas- system because the Brayton devices operate turbine power generated in the United at much higher initial temperatures. This States. Commercial devices are available Ch. IX Energy Conversion With Heat Engines Ž 357

Figure IX-19.— Four Brayton-Cycle Systems Compatible With Solar Applications

(A) SIMPLE CYCLE

r * waste.heat boiler solar collector r ‘Xhaus’”r A~r Inlet -1 and/or fossil burner l-l I r-l1 J generator \ Compressor 1 -@

Turbine

(B) REGENERATED CYCLE

air inlet

regenerator

compressor \

fess burner or

I I regenerator waste heat

(D) INVERTED CYCLE generator

\ \ J EzEl “

Alr waste heat ~ Exhaust Inlet bo{ler SOURCE Prepared by OTA using manufacturer’s data 358 ● So/ar Technology to Today’s Energy Needs

which range in size from a few kWe to over single-cycle gas turbine is shown in figure 50 MWe.16 IX-20. Ambient air is compressed, heated, and A variety of techniques can be used to im- expanded through a turbine. About two- prove the efficiency of the cycle. The air can thirds of the turbine’s power is required to be cooled during the compression stage, for provide the compressor with power, with the example, and the gas can be reheated during remaining power being available for oper- expansion in the turbine. The most effective ating a generator. The gas is heated in a con- technique for increasing efficiency, how- ventional device by igniting oil or natural ever, is to use the techniques in connection gas in a combustion chamber. In a solar or with a regenerator as shown in figure IX- an externally fired device this combustion 19(B). In this design, the compressed air is chamber would be replaced with a high-tem- preheated by the turbine exhaust before be- perature heat exchanger. A commercial ing heated in the combustion chamber or heat exchanger. Cycle efficiencies can be increased from 28 percent to nearly 38 percent in this way. The major barrier to the use

‘K. Samuels and J. T. Meador, M/US Technology of such devices, however, is the cost and fva/uation: Prime Movers, Oak Ridge National Lab- reliability of the regenerative heat ex- oratory (OR NL-HUD/MIUS-l 1 ), April 1974, p. 22. changers.

Figure lX-20.— Components of a 500kW Gas Turbine

‘URNER —————cl

I 7X STARTER DOG ~,rrt ,,.=nL ‘f

ACCESSORY [JA GEARBOX ‘, “ . . l“ e ) ‘1 L/ ‘ ,4 MAIN GEARBOX — )4

DRI

)+&Ls\:&’’,~A,z-~Hous,;TuRB’NEENTRyvOL”TE

OIL DRUM COMPRESS~R STATOR CASING

SOURCE. Electrical Research Assoclatlon, Llmlted “Electrlc Power Plant Intmatmal 1975-1976 edition” Surrey, England, 1975 (Acknowledgements to Centrax LTD) Ch. IX Energy Converison With Heat Engines ● 359

Commercial regenerative heaters can be used to improve heat-exchange character- guaranteed only if they are not turned on- istics. The closed cycle can also be used at and-off frequently, since the materials used higher pressures with the advantage that fail if they are repeatedly heated and smaller turbines can be used. No penalty cooled. This I imitation is, of course, in- need be paid in efficiency for using gases consistent with using the devices for meet- other than air. 1819 ing intermittent loads in utility peaking ap- While a few closed-cycle, gas-turbine plications, and it is inconsistent with the devices have been built in the United States demands of a solar installation where the (a closed-cycle device developed for NASA available energy is intermittent. Progress in by the Garrett Corporation has been oper- developing reliable regenerators is being ating or under test for about 15 years), made, however, and the Garrett Corporation several German and Swiss firms have had claims to have a device which is capable of devices operating from coal for a number of withstanding large numbers of on-and-off years. The cycle is being investigated for use cycIes without damage. 17 with gas-cooled nuclear reactors. A picture A third approach to the Brayton cycle is of a large, closed-cycle plant now being to close the cycle as shown in figure IX- checked out in Oberhausen, Germany, is 19(C). In this device, the gas emerging from shown in figure IX-21. A closed-cycle gas- the turbine is sent back to the compressor turbine system is being investigated by EPRI instead of being exhausted. The device must for a central receiver solar application .20 be fired externally since the circuit must be The “inverted” Brayton cycle illustrated closed. The closed cycle has a number of ad- in figure IX-19(D) may offer some advan- vantages, the most important of which is tages when used as a bottoming cycle for that it permits the use of gases other than air. Helium and other light gases can be ‘8 Samuels, op. cit , p. 42 ‘9R, M. E, Diamant, Total Energy, pergamon Press, 1‘Patrick G Stone, Garrett Corporation, private pp. 229-232 communication, December 1975 20G intz, op. cit.

Figure IX-21 .—50 MWe Closed-Cycle Gas Turbine HELIUM TURBINE INSTALLATION AT OBERHAUSEN, GERMANY

T INTER- 1 COOLER

LOW- HIGH. HIGH- LOW- PRESSURE PRESSURE PRESSURE PRESSURE COMPRESSOR COMPRESSOR TURBINE TURBINE * \ GENERATOR

HEATER ~ ,1 (RECEIVER)

h v RECUPERATOR

PRE- COOLER

i HELIUM CYCLE SCHEMATIC

SOURCE Glntz, John R (Boe}ng Company, Englneerlng and Construction Dlvlsion), “Closed Cycle High Temperature Central Receiver Concept for Solar Electrlc Power, ” February 1976, EPRI 360 ● Solar Technology to Today’s Energy Needs

any process generating hot air at ambient Another approach which can be used to pressures. 21 It may also have some advan- increase the generating efficiency of Bray- tages in small solar applications. The device ton-cycle devices is to recover the energy in operates by heating ambient air in a heat ex- the turbine exhaust in a boiler and use the changer before the gas is sent to the turbine. heated fluids generated in this way to drive The hot air expands through the turbine into a steam or gas turbine. Overall efficiencies a vacuum produced by a compressor (which as high as 48 percent in large units can be acts like a pump in this application), which achieved in this way.23 exhausts the gas at ambient pressure in an Waste heat can be recovered from gas open-cycle system or returns it to the heat turbines in two ways. The most commonly source in a closed-cycle system. The effi- used technique is simply to install a large ciency of the inverted cycles can be as high boiler in the path of the turbine exhaust. as similar devices operating at higher pres- Heat can also be extracted between com- sures. The advantage of such a device for pression stages if more than one compressor solar applications is that the heat exchanger is used. One system for removing thermal can operate at atmospheric pressure. This energy from a Brayton-cycle device is shown greatly reduces the demands placed on the in figure IX-22. materials which transfer high temperatures to the engine. The major disadvantage of Two approaches have been proposed for this approach is that the density of the gas is using Brayton-cycle turbines in solar ap- much lower than in a pressurized system plications. Small units could be mounted at and thus the turbine units must be relatively the focus of individual tracking-collectors, large. This is less of a restriction in small or they could be located at the counter- sizes, however, since small turbines must be weight position of these collectors with heat relatively larger per-unit-energy output to transferred to the units through a heat pipe. minimize the effect of gas escaping around Heat pipes using sodium vapor have been the ends of the turbine blades. Another developed which operate successfully in the disadvantage of the inverted cycle is that a temperature regimes necessary. heat-rejection heat exchanger is required in In a central receiver used for larger addition to the heat exchanger where exter- systems, it would be possible to pipe the hot nal heat is applied. This is not a problem in gases to a heat exchanger on top of a applications where a second heat exchanger receiver tower. This is the approach being is required for a heat-recovery system. Heat examined by EPRI (figure IX-23). exchangers will need to be relatively large, however, because of the low density of the gases used in the cycle. System Efficiency Few inverted-cycle devices have been The optimum cycle efficiencies of simple constructed, but a prototype, developed by and regenerative Brayton cycles are shown the Garrett Corporation for a gas-fired heat in figure IX-24 as a function of the temper- pump, has operated successfully since ature available. (It is important to recognize, November 1976. The designers claim that an however, that the comparison is made only efficiency of over 38 percent has been for turbines operating at full load; operating measured on this device in initial tests .22 efficiencies at part load may compare quite differently.) The great advantage of developing materials capable of operating at high temperatures can clearly be seen. The per- “D, C. Wilson, and N. R. Dunteman, The Inverted formance of actual units is summarized in Brayton Cycle for WasteHeat Utilization, ASME table IX-7. It can be seen that the efficiency publication, 73 CT-90, April 1973, ~Zpatrlck C, Stone, Garrett Corporation, Private communication, December 1976. 2’Morgan, op. cit., pp,4-9. Ch. IX Energy Conversion With Heat Engines ● 361

Figure IX-22.—Section Through a Combined Gas and Steam Turbine Powerplant

1 Gas turbine package 2 Load gear 3 Generator 4 Steam turbine 5 Crossover pipe to adjacent condenser 6 Waste heat boiler 7 Exhaust gas silencer 8 Stack 9 Inlet silencer 10 Air intake building with filter

t r, II I i 1111 ‘r- ”-n 111~

K.= — – - — --- - “ ‘[ - g;+1--ul~‘ - - ● .

1 2 3

SOURCE Electrical Research Assoclatlon Llmlted, E/ecfrfc Power Plant IfJternafloflal, 1975-1976 edltlon, Surrey, England, 1975 (With acknowledgements to A E G Kanfs )

, . 4 ,,. !1 362 ● Solar Technology to Today’s Energy Needs Ch. IX Energy Conversion With Heat Engines ● 363

Figure IX-24.—Temperature Dependence of simple-cycle devices decreases dramati- of Optimum Cycle Efficiencies cally in small sizes. The 2.7 MW “Centaur” gas turbine manufactured by International 40 Harvester, for example, can achieve 26.6- percent efficiency, while the small 20 kW Gemini unit achieves only 13.7 percent effi- 30 ciency. The inefficiency of smaller engines is decreased somewhat if regenerators are 20 used. A small turbine developed for automobile applications, for example, can develop 26.8-percent efficiency and, as noted 10 earlier, the small inverted-cycle turbine developed by the Carrett Corporation has shown 38-percent efficiencies in preliminary 0 tests. All of these efficiencies are, however, 500 1000 1500 2000 substantially less than the 47-percent effi- Turbine inlet temperature, ‘F ciency which apparently can be” achieved by the 50 MWe closed-cycle device.

SOURCE. Beno Stemlicht, “The Equipment Stale of LowLevel Heat Recovery,” Power, June 1975, page 73 The generating efficiency of a gas turbine I is reduced if waste heat is recovered in a

Table IX-7 .—Brayton Cycle Efficiencies

Cycle Cycle Efficiency’

Nominal Present Future Size (kW) (1976) 1980-85 Reference

Simple cycle 20 13.7 (1) 100 13.7 22-28 (1) (2) 800 22.8 (1) 2700 26.6 (1) 7200 31.5 (1) Regenerated cycle 20 26.8 38 (5) 100 32-35 (2) central station 35 (3) 2800 32.2 (8) Closed cycle 25-32 (4) (Regenerated) 35-39 (9) Combined cycle 4200 36.8 (8) (Simple cycle) 4550 40.2 (8) 57400 44.4 (8)

Combined CYCIe 3606 40.7 (8) (Regenerated gas turbine) 3860 43.6 (8) 73700 48.0 (8) 235000 47.0 (lo)

*Losses in the mechanical equipment WiII reduce the cycle efficlency by 3-8% sOURCE (1)

(7) (8)

(9) (lo) 364 ● Solar Technology to Today’s Energy Needs

boiler placed at the turbine outlet. Overall Figure lX-26.— Closed Regenerated-Cycle Gas performance of the simple-cycle gas tur- Turbin~ bines producing both thermal and electric energy is shown in figure IX-25. It can be . seen that, in contrast with the Rankine cycle, the efficiency changes very sIightly as a function of the temperature of the waste . heat recovered. . The regenerative cycles apparently exhibit a combined electrical and thermal efficiency similar to that of the simple-cycle efficiencies shown in figure IX-25, but the ratio between electric and thermal output increases as a resuIt of the regeneration. The performance of a closed-cycle Bray- ton-cycle system, which provides thermal energy to a district heating system requiring pressurized water at temperatures between 2000 and 3000 F and returns the water at 1220 F, is illustrated in figure IX-26. In this t I 1 1 case, it can be seen that the combined effi- 200 300 ciency can exceed 80 percent. Pressurized water temperature “F in a solar application where alternating (water return temperature = 1229F current is required, all of the efficiencies SOURCE. Dlamanl, et al , op CII , page 244

Figure lX-25.— The Effect of Waste-Heat Extraction on the Performance of Gas Turbines discussed above must be reduced by the efficiency of some type of power-conditioning 90 equipment. This is because the speed of Brayton-cycle devices changes rapidly as a 80 Combined electric and function of the incident power; thus, frequency control cannot be maintained in an ‘————— thermalefficiency 70 alternator, although the Brayton-cycle [ device can be locked into a utility grid fre- 60 t quency if it is attached to utility power. In I such cases, electric output power will be 50 1- proportional to the energy available from Thermal efficiency the solar collector. 40 1– This frequency control problem can be Electric efficiency 30 - solved for a stand-alone system by rectifying the output of the alternator and then using 20 Electric efficiency = (electric output)/(energy an inverter to produce a constant 60-cycle entering turbine) t output. The efficiency of this process will be 10 Thermal efficiency = (energy in steam)/(energy typically in the range of 85 to 90 percent. entering turbine) t Constant-speed mechanical devices are also ()~ available which can produce a constant 100 200 300 400 Steam pressure (psig) speed in an output shaft, given variable speed inputs. It is, for example, possible to SOURCE Calculations based on performance of Rolls Royce RB.211 operate a drive-flywheel combination and Gas Turbine (28,960 BHP), 2°10 electrlc efftclency loss due to backpressure controller in reverse. There have also been Ch. IX Energy Conversion With Heat Engines ● 365

ingenious proposals for providing frequency System Costs stability by continuously changing the The installed costs of gas turbines of number of fixed magnets in the alternator. various sizes are illustrated in figure IX-27. All of these schemes result in some loss of There is a clear economy of scale in these efficiency. devices, given current manufacturing techniques, although the effect is not as pro- Operation With Fossil Backup nounced as it was in the case of Rankine- It should be possible to design a Brayton cycle engines. The enormous advantage of cycle system which is capable of operating using mass-production techniques for the from either fossil or solar energy sources. In production of small equipment is also ap- a closed cycle, all that would be required parent from this figure. would be to insert an additional heat- The total cost of an installed Brayton exchanger and fossil burner into the piping device must include the cost of several com- circuit. In an open-cycle turbine, a fuel in- ponents in addition to the turbine. Waste jector could be included in the circuit for heat boilers (if used) would add $15 to $75 use when backup was needed. There might per kilowatt to the costs shown in figure be some difficulty in operating a fossil- IX-27 (depending on the temperature and burning device which was attached to the z pressure of the process steam required). ’ focus of a tracking collector because the ex- Miscellaneous equipment for controls and haust might accelerate the aging of optical components; however, this problem should not be insurmountable. 24 Sternllcht, op. clt

Figure lX-27.— Installed Costs of Open-Cycle Brayton Turbines

Saturn ~’ --’<”~ Centaur J -- ‘---- Mars*

● Under development – 100 Estimated cost of mass-produced r I regenerated engine (JPL Automobile Assessment, pages 11, 12)

..1. __ L.. _ . ___ ...... 1. 10 50 100 500 1,000 5,000

SOURCE Pr~ces based on estimates made by International Hame5ter for unl!s shown Re9enerafor Prices are assumed to be 20°. of the turbine price (see Stern llcht, op clt p 72) 366 ● So/ar Technology to Today’s Energy Needs

other equipment will add about 20 percent tional advantage of rejecting nearly all of to the cost.25 The cost of the equipment re- their waste heat in the form of heated li- quired to maintain a constant output fre- quids, and thus a heat-recovery boiler is not quency will vary with the size of the installa- required. The cycles are capable of oper- tion. The cost of power-conditioning equip- ating at a variety of different temperatures, ment is discussed in detail in the section on with the upper-temperature range limited electric storage. If a backup fossil capability only by the capabilities of the heat-ex- is required for the equipment, fuel storage change materials. They also have an inher- would add approximately $30 per kilowatt.26 ently low RPM and thus need not use expensive gear-reduction systems. Devices based THE STIRLING AND ERICSSON CYCLES on the Ericsson cycle also can be designed to operate at relatively low inlet tempera- Even if devices employing Rankine or tures and can span the entire spectrum of Brayton cycles were constructed from temperatures available from solar collec- perfect components (i.e., if there were no tors. The systems are particularly interesting friction or fluid losses around turbine for onsite-power applications since efficien- blades), these devices would not achieve the cy is not sacrificed by building units as small efficiencies of ideal heat engines operating as a few kilowatts. between the same temperature limits. This is There have been proposals for using Stir- because neither cycle accepts heat only at ling engines for vehicle propulsion, electric- the highest cycle temperature nor rejects power generation (including residential, heat only at the lowest temperature; an total-energy systems), artificial hearts, and ideal engine would maintain a constant tem- water-pumping applications.27 28 29 30 31 32 A perature during these heat-exchange proc- major study conducted recently by the jet esses. Propulsion Laboratory concluded that the Both the Stirling and the Ericsson cycles Stirling engine was one of the two most maintain a constant temperature during the promising systems for future automobile heat-exchange processes associated with ex- engines because of its potential for high effi- pansion and compression and thus are, in ciency, low emissions, and quiet opera- principle at least, capable of achieving the tion. 33 maximum permitted Carnot efficiency. Ex- Principles of Operation isting engines which approximate Stirling The operation of ideal Stirling- and Erics- and Ericsson cycles are externally fired, son-cycle devices is explained in some detail piston engines. (No real device actually in figure IX-28. Both cycles described here maintains a constant temperature during heat addition or heat rejection and thus the devices fail to operate on a true Stirling or “W, R. Martini, Developments in Stirling Engines, presented to the American Society of Mechanical Ericsson cycle.) In addition to the potential Engineers, New York, N. Y., Nov. 26-30, 1972 for high efficiency, they should also be ‘8 Stir/ing Tota/ Energy System (a Philips Corporation capable of long lifetimes, and quiet, reliable paper). operation. Z9W. R, Martini, IJnCmventjOm I Stir/lng Engines for the Artificia/ Heart Application, Proceedings, 9th ln- Also, since heat is applied externally, the tersociety Energy Conversion Engineering Con- engines are easily compatible with solar ference, San Francisco, Calif , Aug 26-30,1974. energy applications, and backup energy can ‘OG. M Benson, “Thermal Oscillators, ” Proceed- ings, Eighth Intersoclety Energy Conversion Engi- be provided from any type of fuel. In total neering Conference, Philadelphia, Pa., August 1973. energy applications, they have the addi- 313-5k W Stir/ing Engine Alternator, ERG, Inc., report to u.s Army, MERDC (1969). 32 Stir/ing Engine Driven Tota/ Energy System, ERG, jsEstimate made for OTA by the Ralph parsons Inc , report to Am Gas Association (1969). Company, “An Automobile Power Systems Evaluation, jet Pro- 26 Sukuja, et al,, Op. cit., PP3-26 pulsion Laboratory. Ch. IX Energy Conversion With Heat Engines ● 367

I I I

0ml 0m Id H

I I I ($?E

lid] J uolsld 6U!yJOM 368 ● Solar Technology to Today’s Energy Needs

would be capable of ideal efficiency. Both constant-temperature source and sink and cycles absorb and reject heat at a constant the working fluid, even though the fluid temperature and employ a permeable ther- volume is changing. mal mass, called a regenerator, to heat and Another design decision is the choice of a cool the working fluid without exchanging working gas. The cycles operate most effi- energy with systems external to the engine. ciently with a gas with high thermal con- This regenerator is the key to the system’s ductivity, low density, low viscosity, and a efficiency. In principle, it cools heated large change in volume when heated.34 It working fluids passing through it, absorbing can be seen from figure IX-29 that hydrogen energy from the fluid in the process, and achieves the best theoretical performance. restores all of this energy to the fluid when It was selected by Philips and Ford Motor cool fluid passes through it in the opposite Company for their prototype automobile direction. The only difference between the engine. two cycles is that in the Stirling cycle the re- Hydrogen is highly flammable and could generative heating and cooling of the work- create a fire hazard if it escapes, although ing fluid occurs in a constant volume while the quantities used in small engines are ex- the Ericsson cycle performs this function at tremely small. It may also be incompatible a constant pressure. with certain heater designs and some types It was noted earlier that the efficiency of of heat pipes. (Heat pipes may be needed to Brayton-cycle devices could be improved transfer thermal energy from a separate with regenerators and by heating and cool- heater.) A recent study by Philips and Ford ing the gas during expansion and compres- concluded that helium is a “requirement sion. It can be seen that the Ericsson cycle when operating with the heat pipe since represents the ideal limit of the Brayton hydrogen permeates the joints and ‘poisons’ cycle. the heat pipe.”35 Theoretical work has also been done on a variety of other working In actual cycles, of course, performance fluids, including dissociating fluids and boil- is limited by failure to follow the ideal cy- ing and condensing fluids. cle, by “heat leaks” between the hot and cold ends of the cylinder, by pressure losses Design Alternatives through heat exchangers and regenerators, by miscellaneous mechanical losses, and by Prototype designs capable of approach- imperfect heat exchange and regeneration ing the ideal cycles are illustrated in figures processes. Major development problems in- IX-30 and IX-31. The rhombic-drive device, clude the design of high-temperature heat shown in figure IX-30, has been used by the exchangers and regenerators which are easy Philips Corporation since the 1930’s. It uses to manufacture and have displayed accept- a pair of pistons in the same cylinder and an able Iifetimes. ingenious mechanical Iinkage to maintain the proper phase between them. The newer A problem unique to the Stirling and Philips design is shown in figure IX-31. This Ericsson cycles is the requirement for sys- system uses the working piston in one cylin- tems capable of ensuring that the working- der as the displacer for the adjacent cylin- fluid temperature remains constant during der, with four cylinders forming a closed the heat absorption and rejection processes. A variety of schemes for accomplishing this function have been proposed. One tech- “W. R. Martini, Developments in Stirling Engines, nique involves constructing pistons with a presented to the Annual Winter Meeting of the Amer- series of fins which slide between mating ican Society of Mechanical Engineers, New York, N. Y,, Nov. 26-30,1972, P.1 fins attached to cylinder ends maintained at “R. J. Pens and R. D. Fox, A Solar/Stirling Total Ener- constant temperatures. These fins ensure a gy System, published by Aeronutronic Ford Corpora- large heat-exchange surface between the tion. Ch. IX Energy Conversion With Heat Engines ● 369

Figure IX-29. —Calculated Performance of a 225-hp Stirling Engine as a Function of the Specific Power and Working Gas

125

1,500 rpm 32

400 rpm I

24 0 10 20 30 40 50 60 70 80

Specific Power (h~jiiter)

SOURCE Samuels et al op clt , paqe 54

loop. The phase is maintained with a The problem of these seals could prob- “swashplate” as shown in the figure. ably be overcome for continuous power applications if the seals were separately A major problem for both of these devices cooled or if the engine were designed to be is the seal which must be made between the sealed hermetically with an alternator. Such working fluid (usually helium or hydrogen), systems, however, have not yet been de- and the reciprocating shaft emerging from signed. It can be seen from figure IX-32, that the engine. The Philips design employs a if the energy available to these mechanical flexible membrane called a “roll-sock seal” drive systems changes, the engine speed will for this function, which links the piston shaft change. A constant a.c. output from the sys- to the cylinder wall with a flexible mem- tem can be achieved in one of two ways: 1) brane (see figure IX-30). the engine speed can be permitted to change and the variable frequency output The United Stirling Company of Sweden rectified and inverted (as was necessary in uses a SIiding seal in most of their designs. the case of the Brayton-cycle devices), or 2) progress is being made, but these seals ap- frequency control can be achieved by vary- parently still remain the major limit on ing the pressure of the system using tech- engine life and reliability. The seals could niques developed for controlling Stirling- present difficulties for total energy applica- cycle automobile engines. tions where they must be maintained at the temperature of the hot water used for space- Some of the difficulties encountered by conditioning; the life of the seals decreases the mechanical drive systems could be over- sharply at high temperatures. come if the free-piston systems shown in 370 ● Solar Technology to Today’s Energy Needs

Figure lX-30.— Philips Rhombic-Drive Stirling Engine

Regenerator

— co oler

Power piston ~ml

Buffer space or bounce space —-L II

Exhaust gas u /r=, I approx. 200°C

F ‘ ti ‘h B r-

J / Annular channel

Heating pipes H Cooling ribs

Burner air i i’m Regenerator

Displacer Cooling water 60° C Cold spac Piston 1 Hermetic rolling diaphragm seal Buffer space Displacer rod L Piston rod Pitch circle of synchronizing gears &“--:’yl[! Piston yoke 1/ Counterweight 1- ‘- Piston connecting rod Crankpin Crank radius Displacer connecting rod II *Displacer yoke – Rhombic gear unit L4 .-.=..-.r.l.r

SOURCE: “Towards Cleaner Air: A Passenger Coach Powered by a Philips Stlrllng Engine,” N, V. Philips, Netherlands, January 1971. Ch. /X Energy Conversion With Heat Engines . 371

Figure IX-31 .—Swashplate Stirling Engine Figure lX-32.— Calculated Performance of a Philips Rhombic-Drive Stirling Engine Expansion space General Design Data Heater . ,.-J Regenerator Item Value Cooler 3 Compress Ion space p’ Shaft power 22.4 kW Effective efficiency 40°zY Engine shaft speed 2000 rpm Working fluid helium Mean pressure 200 atm Max. cycle pressure 276 atm Dlacjram of Ihe double-actlnq type Stlrllrrg engine pr{nclple of Min. cycle pressure 141 atm the double. acflng engine There IS a hot space—expansion Expansion gas temperature 9650 K space—at the top and a cold one—compression space—at the Compression gas temperature 335 ‘K bottom of each of the cour cyllnders shown The hot space of a cyl lnder IS connected to the cold through a heater, a regenerator, Number of cylinders 4 3 and a cooler The pistons Pn of the cyllnders move with a Piston swept volume 55 cm suitable phase shift between them In the case of four cyllnders, Piston phase 900 as shown here, th IS shift IS 90” Pressure phase 630 Piston diameter 4.4 cm Piston stroke 3.5 cm piston rod diameter 1.7 cm Water temperature in 303 ‘K Water flow 0.9 !/s Heat pipe temperature 1,070° K Engine length 75 cm Engine diameter 45 cm Engine weight 100 kg

System Efficiency at Various Power Levels and Speeds Schematic diagram of a four cyllnder, double acting type Stlrhng engine with swash plate drive One of the four cyllnders and one Power of the four cooler regenerator units are shown In cross-section In these engines, the movement of the pistons IS transmitted to 5 10 15 20 25 kW the main shaft by a swashplate

130

SOURCE Pictures and captions taken from R J Meller and C L 120 Splgl, “The Polenflal of the Phlllps Stlrhng Eng\ne for Pollutlon Reduction and Energy Conservation “ presented at the Second 110 200 Symposium on Low Pollutlon Power Systems Development, ATM Dusseldorf, Germany, November 48, 1974 100 90

> 80 figure IX-33 are successfully devel- E g 70 oped. 36 37 38 These systems are thermal/me a a 60 - c chanical oscillators in which the working 5 100 J piston and the displacer piston simply + 50 “ ATM bounce in the working fluid at a frequency 40 determined by the properties of the gas and 30 - 50 the mass of the pistons. 20 - ATM 10 “ The designers of the ERG “thermal 1 1 1 1 oscillator” system claim to have developed o 500 1,000 1,500 2,000 Speed (rpm)

“W Beale, et al , Free Pfston Stir/ing Engines, Some SOURCE H A Jaspers and F K du Pre, “Stlrllng Engine Design Model Tests and Simulations, SAF Paper 690230, Studies of an Underwater and a Total Energy Syslem.’ North American Phlllps Corporation publication #739035, 1973 /ECEC j anuary 1969 Record, pp 588.593 “W Beale, et al , Free Piston Engines, A Progress Report, SAE Paper 730647, June 1969. a free-piston system in which the frequency “G. M. Benson, Thermal Oscillators, Proceedings, Eighth IECES Conference, Aug 14, 1973, Phlladelphla, of oscillation is independent of the load ap- Pa plied as long as the average working pres- 372 ● Solar Technology to Today’s Energy Needs

Figure lX-33.– Free-Piston Stirling and Ericsson Cycle Designs

Heat added ~- Displacer piston ~Regenerator Heat removed

Displacer -r I I Regenerators L+-Heatre’ec’ed piston

volume Phasor ! I Heat added Po;er L, piston cylinder 1 I

“m / L Bounce I

t I I .

Power 1 u piston

Displacer—Power Piston System Phasor—Displacer— Power Piston System

SOURCE: Diagrams of free-piston devices shown above based on slmtlar diagrams In G M Benson, “Thermal Oscillators,” presented to 8th IECEC meeting, August 14, 1973, Philadelphia, Pa. sure is maintained in a sealed unit. The percent of ideal efficiencies may be energy applied to the load is automatically achieved, but this clearly will be extremely adjusted as the pistons change stroke and difficult.) relative phase angle. 39 The use of the free- One unique problem with the free-piston piston designs avoids the problem of me- design is that no rotating shaft emerges from chanical linkages (having only two or three the system. The power is in the form of moving parts), the need for starters (the linear oscillations of the working piston. The machines start themselves when heat is ap- piston may not move very far; a 1 kW unit plied), and the problem of seaIing a recipro- can move as little as 1 inch. ’” “Linear alter- cating shaft. As a result, it may be possible nators” suitable for this application have to develop a system which is inexpensive to been successfully constructed, however, manufacture and has a long life and low an- and exhibited efficiencies comparable with nual maintenance. With pressures on the conventional alternator designs. ” 4243 order of 1,000 to 2,000 psi, and the use of gas bearings where the working fluid provides the necessary lubrication, efficiencies as ‘“G. M. Benson, op. cit., p. 1. high as 70 to 80 percent of ideal should be 41 Ibid, obtainable. (Some designers contend that 90 ‘ zWilliam Beale (Sunpower, Inc.), private communication, July 1976, “William Beale, A 100-kVatt Stirling Electric Cener- ator for Solar or So/id Fue/ Heat Sources, I ECEC 75, 39G. M Benson, op. cit., p. 10 Record, p, 1,020. Ch. IX Energy Conversion With Heat Engines ● 373

Power is produced either by moving a con- operating temperature permitted would also ductor (in a design similar to a loudspeaker increase the potential efficiency of the voice coil) or by moving a magnet or flux system. DOE is sponsoring research to devel- gate. One design approach is shown in op a ceramic heat exchanger for Stirling ap- figure IX-34. plications beginning in FY 1978.47 While these devices have great promise, An interesting sidelight to the Stirling- and relatively little work has been done on their Ericsson-cycle devices just described is their design in comparison with the more conven- ability to integrate engines and heat pumps tional designs. Their performance in opera- into a single device. Two approaches to this tional configurations has not been exten- design, using the free-piston concept, are sively tested, and disagreements about their shown in figures IX-35 and IX-36. This design practical achievable efficiencies and their can be modified to include electric genera- stability to varying loads and input condition by using the “phaser” pistons as linear tions cannot be resolved until more work is alternators, thereby making the device an done. Working devices have been built, attractive total energy system. The system is however, and high efficiencies measured in also attractive in that the performance of the laboratory. ” 45 the heat pump does not drop rapidly as outdoor temperatures decrease (as is the case The development of a heat-transfer sur- with conventional electric heat pumps). ’n 49 face which can transport energy at high rates into a small cylinder head has proved An Ericsson-cycle heat pump would prob- to be a difficult undertaking. The materials ably have a higher efficiency than commer- required for this purpose must withstand cial heat pumps, but the impact of the new high pressure, as well as exposure to oxi- cycle on overall system performance would dizing hot gases on one side of the heat- not be dramatic since most of the losses in exchange surface and hydrogen on the other current heat-pump systems result from the side. Devices capable of accomplishing this need to heat (or cool) the refrigerants to function can be made, but they must use temperatures far above (or below) room alloys which are relatively expensive in com- temperature so that the room air-flow will parison with the mild steel used in conven- be kept to comfortable levels. Heat ex- tional engines— and in many cases, the changers and the requirements of fans are designs appear to be difficult to manufac- the second greatest source of inefficiency. 50 ture. Heat pipes may be able to solve some These effects reduce the performance of of the problems faced in this area by pro- contemporary heat pumps by more than a viding rapid heat transfer in a system which factor of five. The efficiency of the com- does not produce a large pressure drop in pressors used in contemporary heat pumps the working fluid.46 The development of is typically 75 percent of the ideal Carnot ef - ceramic heat-exchange materials wouId be a ficiency. great asset to the technology, since ceramic It is also possible to operate a Stirling devices would be able to operate at very engine as a standard total-energy system, as high temperatures (i. e., 2,0000 F) and it may be possible to manufacture them with low- cost, mass-production techniques. The high “Paul R. Swenson, Consolidated Natural Gas Serv- ice Company, Cleveland, Ohio, “Compet[tlon coming in Heat Pumps: Gas-Fired May be Best in Cold “G M Benson, op clt , p 14 Climate, ” Energy Research Reports, 3(5], Mar 7, 2977, 4SBeale, private communication, j uly 1976 p2 4’S G Carlqulst, et al , “Stirling Engines Their Po- ‘g’’ Advanced Gas-Fired Heat Pumps Seen Cutting tential Use In Commercial Vehicles and Their Impact Heating Bills in Half, ” Energy Users Report 188 on Fuel UtlllzatIon, ” lnstn Mech .Engrs, 1975, p 35 (3/7/77), p 27, Bureau of National Affairs “W A Tomazlc and James E Calrelll, Ceramic Ap 50W, A. Spofford, “Heat-Pump Performance for p/ications In the Advanced Stirling Automotive Engine Package Air Source Units,” ASHRAE /ourna/, April (ERDA/NASA 1011/77/2, p 6) 1959, 374 ● Solar Technology to Today’s Energy Needs

Figure lX-34.— Sunpower Systems Free-Piston Stirling and Ericsson Cycle Design Approach

~ Cooling air fan

Cooling air outlet

~1-li U . . k ‘“J, ,J ,, ;::;: f’:d’”g

9 II “ dJJF,e:’:lnding A . l’”

Liquid filled — . . ,’ ,. ,... . cool ing fin Jli.,.. . -Spring suspension

II — Draft shroud

Cylinder sleeve _ “ “ ‘“+’’’’’” Displacer rod ~ Liquid filled I ‘T coolina fin

w L Cooiing air Displacer seal I Liquid filled ring cooling fin (air side) < IIN Cooling fin (gas side) II Displacer ● u’- JJ ,. Regenerator matrix Regenerator Ilk,: # -, matrix ..- .“ . . $ ,, ,.,, . . ,. i::~ ~~., . .~ Ceramic filler HI Annular gas II ( 7.”&II I 1 / passages (finned)

Heat addition

SOURCE: W T, Beale and C. F. Rankine (Sunpower, Inc.), “A 100 Watt Stirling Electric Generator for Solar or Solld Fuel Heat Sources,” IOth IECEC, August 1975, Proceedings, p. 1020. Ch. IX Energy Conversion With Heat Engines ● 375

Figure IX-35. — Free-Piston Total Energy System

Qout (warm) f Displacer / Cylinder ~-

1 1 1

/ Qin (hot) Compressor cylinder Qin (cold)

1 1 Bounce vol. Bounce vol.

TH Tc o3

. .

= o4

Note: Only phasor position determines working

and bounce gas pressures (P w + pb) SinCe opposed motion of hot and cold displacers (H + C)

produces a constant Pw.

SOURCE. G M Benson (ERG), Thermal Oscillators, op clt (U.S. patent No. 3,928,974). 376 . Solar Technology to Today’s Energy Needs

Figure lX-36.— Free-Piston Total Energy System

Heat rejection 41,700 Btu/hr t 88°F 90”F t LI ‘a K1~ ‘- / 24” ID

A 1,500° F metal lln- 1’ 1’ ~ 50”F 1’ Heat input 1 Cooling power 5,700 Btu/hr 1 36,000 Bt u/hr

\ ~ 45°F I I

— 200 Annuli 0.010” thick 1 , , , { I id Pmax. = 261.7 I Pmin. = 107.2 - 17.7” STR. ~ 17.7” STR. Operating I lb. frequency 10 H PAV = 148.1 psia L Optimized preliminary design for a heat-operated heat pump

SOURCE W R Martlnl (Unwers!ty of Washington, Rlchland), “The Free-Displacer-Free-Piston Stlrllng Engine—Potential Energy Conserver,” 1975 IECEC Record, pp 9951,002, 1976. shown in figure IX-37. Space heat is provided refrigerant inside the working piston as the from engine waste heat. Another approach, piston oscillates.52 The refrigerant enters currently being supported by the American and Ieaves this compression volume through Gas Association, uses the piston of an flexible metal tubes which provide a leak- Ericsson-cycle device to drive a sealed freon free path for the refrigerant through the 51 compressor. WilIiam Beale of Sunpower, helium-filled spaces surrounding the piston. inc., has proposed still another alternative which is being investigated by the American Performance Gas Association. His design would use the The performance of a number of the de- working piston in a free-piston device as the vices surveyed by the Jet Propulsion Labora- for a Rankine-cycle heat pump. compressor tory in its review of potential automobile The working piston contains a mass whose engines is summarized in table IX-8. All of inertia changes the volume available to the

“Dr. C. H. Benson, ERG, private communication, -5~W111 lam Beale, President of Sunpower, I nc, Feb. 2,1977. private communication. Ch. IX Energy Conversion With Heat Engines Ž 377

Figure IX-37 .—The Philips Design for a Stirling Engine Total Energy System

. Preheater

SOURCE H A Jaspers and F K du Pre, .SIfrllng Engine Design Stud/es of an Underwater Power System and a Tofa/ Energy Sysfern, (N V. Phll(ps publtcatlon)

these devices use mechanical linkages of The performance of free-piston devices some sort. The efficiency of operating en- reported by Energy Research and Genera- gines averages between 24 and 30 percent tion Corporation (ERG) is shown in table (about 45 to 50 percent of ideal Carnot effi- IX-10. These reports claim measured “in- ciency). dicated” efficiencies as high as 87 percent of ideal Carnot efficiency. In the device An optimized engine operating at its most operating between 1,4000 and 120°F, this efficient speed could, according to these results in a cycle efficiency of 60 percent. estimates, produce 43 percent efficiency The feasibility of achieving these efficien- operating between 1,4000 and 1600 F (about cies is corroborated by estimates made by a 65 percent of ideal efficiency). Achieving group studying Stirling engines in the joint this high efficiency, however, would require Center for Graduate Study at Richland, operating the engine at less than its max- Wash., and by Beale of Sunpower, Inc., imum designed power, thus increasing its although there appears to be some disagree- cost. The performance reported for free- ment as to how far development has pro- piston devices has varied considerably be- gressed towards this objective. 5354 cause many different heat exchangers, regenerators, and thermodynamic cycles are The performance, of course, is largely sen- being examined. Consequently, it is much sitive to design details, including the size too early to make a reliable estimate of the and design (and hence the cost) of heat ex- efficiency of commercial systems. The efficiencies of devices constructed to date by the Sunpower, Inc., group have been rela- 5]W R Martini, The T/rerrnohydrau/ic Converter, prepared for the joint Center for Graduate Study, tively low (10 to 30 percent cycle efficiency Richland, Wash , Mar. 4, 1975 or 16 to 48 percent of ideal efficiencies) 54W. Beale, Sunpower, Inc , private communica- (table IX-9). tion, July 1976, 378 • Solar Technology to Today’s Energy Needs

Table IX-8.—StirIing Engine Characteristics

He 3,200 4 200 3,000 253 1,000 1,260 108

24 30 29 30 35 32

35 76 88

2,000 N/D N/D

Auto

changers used, the gas pressure used in the water. This is shown quantitatively for sys- cycle, the exact thermodynamic cycle tems burning fossil fuels in figure IX-38. In a chosen, and other variables. solar application, the percentage of energy recoverable in the coolant water would be even higher, given that there would be no Performance With Waste Heat losses in the exhaust. The performance of Stirling- and Ericsson-cycle devices oper- As noted earlier, Stirling devices have a ating at different coolant temperature is great advantage in total energy applications shown in figure IX-39 for two different because a very large fraction of the energy assumptions about engine-generating effi- not used by the cycle appears in the cooling ciency. Ch. IX Energy Conversion With Heat Engines . 379

Table IX-9 .—Performance of Free-Piston Stirling Table IX-10.-Performance of Sun Power Engine Designs of Energy Research and Free-Piston Devices Generation Inc.

ERG ERG Allison

50 .41 1220 170 62 80 118 1.79 4.81 1985 144 50 13.1

with large heat-exchange surfaces, but heat exchangers are expensive.

There could be some difficulty in adapt- ing current designs to mass-production System Costs techniques since many current designs re- It is impossible to estimate the costs of quire complex heat exchangers which would Stirling and Ericsson cycles with any preci- need many separate welds and brazements. sion, since no practical devices are on the It should be possible to overcome this dif- market. The cost will also depend on the ef- ficulty with advanced heat-exchanger de- ficiency and the lifetime expected of the signs, but the question of costs cannot be re- system. I n general, efficiency is improved solved until a production unit is designed. Estimates made by the Jet Propulsion Laboratory in their survey of automobile- Figure IX-38.— Heat Balance for the Stirling power systems indicate that a “mature” and Diesel Engine Stirling engine, operating at a temperature 1000/0 fuel of 1 ,400“ F, would cost approximately Friction heat input $14/kW wholesale, and would sell for ap- Exhaust and 55 rad iat Ion proximately $18/kW at the retail Ievel. (This, of course, assumes production on the scale of current automobile product ion.) A further study of the adaptations needed to install a 42-percent efficient Stirling device in a solar energy application resulted in an Coollng estimate of about $38/kW for the engine, water II I $27/kW for the alternator (installed on the engine), and about $27/kW for miscellaneous switching equipment and controls.56 This results in a total cost of about $92/kW

55ArI Autorrrobi/e Power S ysterns Evacuation, Jet Pro- pulsion Laboratory, Volume 11, pp 11-12 Stirling Diesel “Richard Caputo, J PL, Program Manager, Comp-

SOURCE R J Me[jer (N V Phillps), ‘The Phll(ps Stlrllng Engine,” arative Assessment of Orbital and Terrestrial Power De Ingenieur (621 41), page 21 Systems, p.24 380 •Solar Technology to Today’s Energy Needs

Figure lX-39.— Electric and Thermal Output of a Stirling Engine

- — — a&ailabJa for process heat

— (electric output~(input energy)

70 —

— - — 60Y0 Carnot 60 — ———— —— —— ——~ —— 50.- c ~- 90°A Carnot 40 — } ~A~arn~ — --- ~ -- -—— — 30 — 60% Carnot

20 1-

10. I I I I I I I I 100 150 200 250 300 350 400

Cooling Temperature ‘F Assumptions: inlet temperature = 1400°F Generator efficiency = 90% energy not recoverable = 59’0

SOURCE, Prepared by OTA.

(all prices are given in terms of price per- The cost of free-piston devices could be peak- power output; average power would lower than those of the mechanically cou- be substantially lower). These prices also do pled systems because of their inherent sim- not include the cost of the receiver and heat plicity, but again the lack of commercial pipe needed to transmit solar power to the devices makes cost estimates difficult. The engine. Energy Research and Generation Corpora- tion has estimated that their free-piston Another estimate of the cost of a Stirling design is amenable to mass-production tech- engine/generator set was made by Philips niques and could be produced for about and Ford Aeroneutronics for their proposal $30/kW, with an additional $10/kW for the to construct a solar, total energy system in 58 linear alternator. Disney World. This estimate for an engine/- generator and switch-gear amounted to Another way of estimating the cost of the $400/kW, with an aside noting that this Stirling-engine devices, manufactured at could be reduced to $100/kW if large-scale moderate production rates, is to compare production were undertaken .57 ‘aGlen Benson, Energy Research and Generation Corporation, private communication, December 57pOns, et al., Op. citr p“ 13’ 1976. Ch. /X Energy Conversion With Heat Engines ● 381

them with the cost of conventional gasoline- Free-piston designs could weigh signifi- and diesel-powered engine-generator sets. cantly less than the mechanical devices Figure IX-40 indicates that the Stirling de- shown in the figure. Dr. Benson of ERG has vices with mechanical linkages should have estimated that their device could weigh as a weight per-unit-of-power which is some- little as 5 lbs/kW (2.3 kg/kW).59 where between gasoline and diesel engines. Assuming that the Stirling devices are State of the Art roughly of the same complexity, figure IX-41 Engines based on the Stirling and Ericsson can be used to estimate costs of about $75 cycles have been in operation since the ear- to $150/kW for shaft output Stirling engines ly 19th century, The Stirling engine was of about 100 kW capacity. patented in 1816 by a Scottish clergyman, John Stirling; Ericsson-cycle devices were Figure IX-40. —Weight-to-Power Ratios of patented a few decades later. (The Ericsson Engines With Internal Combustion and of cycle is named for the Swedish-American in- Stirling Engines ventor, John Ericsson, who, among his other 100 accomplishments, was the designer of the Union ship, The Monitor.) These early designs used air as the working medium and were expensive, heavy, and relatively inefficient—since the designers lacked both ma-

10 terials and analytical methods capable of A -’””s optimizing the design of thermodynamic B A cycles. c Stirllng engines B -)Petrol engines c Interest in Stirling engines was revived in 1938 by the Philips Corporation of the 1 Netherlands, when that company was 1 10 ~ 100 kW searching for an engine to burn a variety of fuels and provide quiet and reliable power A A Stlrllng enqlnes present laboratory types 60 B Laboratory models to be expected w Ith,n a few years to military radio receivers. The company, C Stlrlinq engines developed for vehicles one of the world’s largest multinational Welqht to-power ratios of engines with Internal combustion and of Stlrllnq engines firms, now has over 100 people working on SOURCE the development of Stirling engines. Many R J Meyer Comblnaton of Eleclr[c Heal Battery and Stirlrng Engine—An Alternative Source of Mechan mal Power, reprtntcd world patents for Stirling engines are held by from Denkschrlft Elcktrospe[r herfahrzeuge ‘ Volume 1 Ill 969 Philips, and the vast majority of work which has been done on Stirling devices in this century has been done either by PhiIips or under license from Philips. The company has sev- Figure 1X.41 .—Cost of Diesel Engines eral well-developed engine designs, some of

COST OF DIESEL ENGINES which have operated over 10,000 hours without failures.61 They have been used to power ~ Onar! diesels 700 1 ~= a number of vehicles including boats and a 600 t I r-l’ Llstner diesels small bus. The basic development engine ~ 500 * * 400 z f~u 300 z General Motors aasollne 59 C ;ng[ne generatars ~ diesels Benson, ibid. ‘“R, J. Meijer and C. L Spigt, The F’oter-rtia/ of the 100 All Is Chalmers 1 ‘t “+ 1 Philips Stirling Engine for Pollution Reduction and ~ diesels , — .~ . . -. .~ 1 10 100 1000 Energy Conservation. “Norman D, Postma, et al,, The Stir/ing Engine for Engine/Generator capac, ty )kW) Passenger Car Applications, Ford Motor Company SOURCE Prepared by OTA using manufacturer’s data publication. 382 ● Solar Technology to Today’s Energy Needs

has been a 25-hp device using two rhombic- mine-pumping operations (where their low drive cylinders. About 30 to 40 of these emissions, fuel economy, and quiet opera- engines have been built by Philips or are tion should be great benefit), in total energy under Iicense from Philips.62 systems for homes, and for automobiles and buses. 66 The United Stirling devices use a The U.S. National Bureau of Standards is “sliding seal” instead of the “roll-sock” seal testing one of the few Philips engines that is employed by most of the PhiIips engines. outside of the Netherlands to measure its performance in total energy applications.63 The Thetford Corporation of Michigan recently formed a joint venture with The Philips work stimulated interest in Sweden’s Forenade Fabriksverken (FFV) to Stirling equipment by a number of different manufacture a Stirling total-energy system companies. The General Motors Company for recreational vehicles which the company had an extensive program in the develop- hopes to have on the market in 1978.”7 ment of Stirling engines which began as a cooperative program with Philips. Research In addition to Philips and the United Stirl- and design studies were conducted on a ing Company of Sweden, MAN of Germany number of different engine designs in- has accumulated many years of experience cluding free-piston devices. The company with Stirling devices, some of it based on had accumulated over 28,000 hours of en- Philips’ designs. gine running-time experience between 1959 Much less work on Stirling and Ericsson and the abrupt termination of the project. b’ cycles is being done in the United States. In 1972 the Philips Company entered into The Atomic Energy Commission and the a contract with the Ford Motor Company to Heart and Lung Institute at the National in- develop a Stirling automotive engine. Work stitutes of Health initiated a program in has been underway since then. The program 1966 to develop an artificial heart. Several began with an attempt to use a swashplate designs were proposed using electric motors Stirling engine with a 1973 Ford Torino. and Rankine and Stirling engines. The pro- Problems have apparently developed with gram attracted several U.S. companies, in- the original approach, however, and prog- cluding Aerojet, Thermo-EIectron Corpora- ress is slower than had been expected. tion, ERG, Inc., Air Products and Chemicals, Inc., and Westinghouse Astronuclear (under The United Stirling company of Sweden contract with Philips).68 has also done extensive development work on Stirling equipment and is apparently Work on novel engine designs for trans- planning to have a device ready for field- portation and automotive applications is be- testing in Swedish iron mines by 1979.65 The ing performed by the Energy Research and company plans to market 40-, 75-, and 150- Generation Corporation, Sunpower, Inc., kilowatt engines shortly thereafter for use in and by a variety of university groups. The work at Sunpower is based, in part, on fun- ‘2 Pens, op. cit , p 11. ding from the American Gas Association “D. Diddion, National Bureau of Standards, private with the objective of developing a heat communication, December 1976 pump able to operate from natural gas. The “W H. Percival, Historical Review of Stir/ing Engine company is also working under an ERDA Deve/oprnent in the United States from 1960 to 1970, grant to develop an engine using a radioac- prepared for the ERD,A(EPA contract 4-E840595), July 1974, page 124, tive source to provide electric power for ‘sHallare, Bengt, Director of Corporate Planning and Marketing, United Stirling, et al., “Development 66W. H. Percival, U.S. representative of the United of Stirling Engines in Sweden and Their Application in Stirling Corporation, private communication, May 6, Total and Solar Heated Energy Systems. ” Paper 1977. delivered to the 1977 International Solar Energy Con- “Ann Arbor News, Mar. 25,1977. ference and Exhibit, Palm Springs, Fla., 1977. Pro- 6’William Beale, A Stir/ing-Hydrosta tic Drive for ceedings published by the Northrop University Press. Srna// Vehic/es, provided by Sunpower, Inc. Ch. IX Energy Conversion With Heat Engines Ž 383

spacecraft. 69 Figure IX-42 shows the Sun- Although a number of groups have in- power device installed in a solar collector. vestigated Stirling- and Ericsson-cycle devices, the engines must be considered to be Work on Iinear alternators suitable for at- in a relatively primitive state of develop- tachment to Stirling- and Ericsson-cycle ment. The alternative cycles have benefited devices for electric-power generation has from many years of careful design work, been performed by the Energy Research and while most Stirling designs have remained in Generation Corporation and by the Mechan- the laboratory. No Stirling engine is being ical Technology Corporation. Both groups produced on a large scale anywhere in the have tested operational designs, but neither world. firm has a unit on the market. Work on the use of Stirling engines for transport is also being done by the Sunpower Corporation, Energy Research and Generation Corpora- tion, and Polster.70 OTHER HEAT-ENGINE DESIGNS

“G Benson, Thermal Oscillators, op clt The Thermionic Converter 70N E Polster and W R Martini, “self-starting, ln- The thermionic device shown in figure trinslcal Iy Control led Stirling E nglne, ” IECEC Record, PP 1,511-1,518, 1976 IX-43 can operate at very high temperatures

Figure IX-42 .—200-Watt, Sun power Stirling Engine, Mounted in Concentrating Collector

Photo credff .Sunpower, /nc 384 ● Solar Technology to Today’s Energy Needs

Figure lX-43.— Identification of Thermionic Converter Components

Interelectrode Thermionically space emitted electrons \’———— ~ Vacuum or vapor

Hot emitter Cold collector

Qin — I

Heat v source —

n. -

Enclosure Electrical feedthru

— load SOURCE Thermoelectron Corporation

and can achieve extremely high-power den- engine. The heat flow is thus translated sities (on the order of 2 to 10 watts/cm2 of directly into a flow of electricity. receiver surf ace).” The hot emitter and the cooler collector of a therm ionic converter Therm ionic energy conversion has a are separated by a vacuum or by an ionized number of desirable characteristics: 1) no gas. A current can be sustained if the hot moving parts, 2) heat rejection at relatively side of the diode emits electrons at a greater high temperatures, 3) lends itself to modular rate than the cold side. EIectrons evapo- construction, 4) potential for efficiencies up rated from the emitter flow across the inter- to 40 percent, 5) heat input in an interelectrode gap to the collector, where they mediate temperature range (1 ,2000 to condense and are returned to the emitter via 1,8000 K), 6) the mechanical simplicity asso- the electrical load. Some of the thermal ciated with no moving parts implies relia- energy transferred from the hot to the cold bility, and 7) the high temperature of heat side of the diode is carried directly by elec- rejection makes therm ionic converters well trons, which are the “working fluid” of this suited for topping steam powerplants, because the heat rejected from the collectors is available at a high temperature to generate steam for conventional turbomachinery.

“William C, Reynolds and Henry C, Perkins, Engi- Efficiencies as high as 5 to 15 percent neering Thermodynamics, McGraw H ill, 1970, p, 309. have been reported for devices working be- Ch. IX Energy Conversion With Heat Engines • 385

tween 1,160” and 2200 F (13 to 38 percent of While a good base of high-temperature, ideal Carnot efficiency) .72 A curve of per- thermionic-conversion technology exists, formance predicted for advanced designs of thermionics has yet to achieve practical ap- therm ionic converters is shown in figure plication with fossil fuels because the emit- IX-44. It can be seen that high efficiencies ter temperatures currently required for com- are possible if the losses which now limit petitive power densities and efficiencies performance can be reduced. limit the operating life of the “hot shell” (i.e., the protective structure which isolates The feasibility of therm ionic conversion the converter, per se, from the combustion has been demonstrated with a variety of atmosphere) to several hundred hours. I n hydrocarbon, solar, radioisotope, and reac- order to reduce the operating temperatures tor heat sources. Stable in-pile operation has of converters to levels where the hot shell been achieved for over 16,000 hours. The will have greatly extended life while main- Soviet Union has progressed to the third taining converter efficiency, it is necessary generation in-core therm ionic reactor with to develop improved emitter and collector electrical outputs of over 7 kilowatts. surfaces, as well as decrease the plasma losses occurring as the electrons flow across Figure lX-44.— Effect of Collector the interelectrode space. Reasonable prog- Temperature on Thermionic Efficiency ress is being made in both areas.

Thermoelectric Conversion

Electricity can also be generated directly from a source of high-temperature thermal energy using a solid-state “thermoelectric” junction. 73 These devices, which operate on the same principle as thermocouples, are frequently used to power spacecraft using isotopes as power sources. Devices operating with an isotope source of 1,000“C (1,832 0 F) are capable of efficiencies on the order of 3 to 6 percent. 74

Emitter temp = The Nitinol Engine 1,700 K Thermal energy is converted into mechan- 1,600 ical work when a heated metal expands, A nickel titanium alloy called Nitinol de- 1,500 veloped by the Naval Ordnance Laboratory (Ni + Ti + N. O. L.) in 1958 has unique thermal properties which can be used to con- 1,400 struct a primitive heat engine— one design is shown in figure IX-45. Nitinol deforms easily at low temperatures but returns to its original shape with considerable force when 10 1 I I 700 800 900 1000 heated. Several working devices have been

Collector temperature (K)

SOURCE Thermo Electron Corporation 71P Rouklove, Tests and Evaluation of Mu/ti- hun~re~ kVatt Thermoelectric Generators at /PL, 12th IECEC Conference, p 1,287 “j E Boretz, Reactor Hybrid-Organ/c Ranhine Cy- 72 Huff man, Thermo-E Iectron Corp , private com- c/e E/ectric Power 5 ys terns for Space App//ca tfons, munication, j anuary 1977 12th I ECEC Conference, p 1,318 386 • Solar Technology to Today’s Energy Needs

Figure lX-45.— The Nitinol Engine

ar input

Nitinol w i ire loops

~ Cold bath

SOURCE The CoEvo/utIon Quarter/y, Spring, 1975, p. 70

constructed by Ridgeway Banks at the Law- of 380 atmospheres (about 4,000 m of rence Livermore Laboratory. water). Every cubic meter of water sent into the reaction chamber with a saturated NaCl Osmotic-Pressure Engine solution, therefore, has a potential energy of about 11 kWh. The fraction of this energy Thermal energy can also be converted to which can be retrieved in a practical system mechanical energy in the osmotic-pressure has not been established, although some cycle. The heat is used to distill a dilute preliminary design work has been done on solution into pure solvent and a concen- membrane reaction chambers. 75 76 Mem- trated solution. Energy can be recovered if branes suitable for use in these systems are the solvent and concentrated solutions are commercially available. Du Pont, for exam- pumped into different sides of a chamber separated by a semipermeable membrane. The solvent is forced across the membrane 75S. Loeb, “Production of Energy From Concen- with a pressure equal to the difference be- trated Brines by Pressure-Retarded Osmosis: 1, tween the osmotic pressures and hydraulic Preliminary Technical and Economic Correlations, ” pressures of the fluids on either side of the )ourna/ of Membrane Science 1 (1976), p, 49. 7 S. Loeb, et al., “Production of Energy From Con- membrane. The osmotic pressures can be ’ centrated Brines by Pressure-Related Osmosis: 11. Ex- quite large. A saturated solution of NaCI in perimental Results and Projected Energy Costs,” /our- water, for example, has an osmotic pressure rra/ of Membrane Science, 1 (1976), p. 249. Ch. IX Energy Conversion With Heat Engines . 387

pie, has a membrane called “Permasep,” de- ference of 400 atmospheres is developed signed for use in desalinization plants, across the surface. 77 Waste heat can be which costs about $4/m2 of active surface. recovered from the system via the con- One square meter of this surface is able to denser of the distillation unit. pass about 0.16 m3/day when a pressure dif-

ENVIRONMENTAL AND SAFETY PROBLEMS

FLUOROCARBONS creased ultraviolet irradiation results in increased incidence of nonfatal, nonmela- Many of the currently available low-tem- noma types of skin cancer in humans.81 In- perature heat engines employ fIuorocarbons creased ultraviolet radiation may also have identical to the refrigerants now used in some adverse effect on human eyes and home and small industrial refrigeration and eyesight,82 and possibly on growing plants, air-conditioning equipment: F-1 1 (CCI3F), as well. F-12 (CCl F ), and F-22 (CHCIF ). These 2 2 2 In addition to the ozone depletion caused substances have great chemical stability at low temperature, but this very chemical by the release of fluorocarbons into the environment, and the coincident human health stability may lead to severe environmental effects, direct health effects from exposure problems. Because fluorocarbons do not to fluorocarbons have been reported in decompose once released into the environ- various animals. These effects include in- ment, they remain in the atmosphere and fluences upon the respiratory and circu- eventually react chemically with the Earth’s latory systems in mice, rats, dogs, and ozone layer, possibly reducing the ability of monkeys. 83 Research into the environmental the ozone to shield the Earth’s surface from 78 and health consequences of fluorocarbons the Sun’s ultraviolet Iight. has received impetus from concern over the The environmental, biological, and health widespread use of fluorocarbon propellants effects of stratospheric ozone changes are in aerosol sprays.84 only now being discovered. Some scientists suggest that changes in stratospheric ozone Some fluorocarbons leak into the environment from facilities which manufacture re- levels could cause changes in the Earth’s frigeration equipment and from abandoned climate, including changes in temperature and wind patterns. 79 The health effects of or malfunctioning units. Estimates indicate, however, that less than 3 to 6 percent of the changes in the stratospheric ozone are not fluorocarbons lost into the environment fully understood. The decreased ozone layer results in an increased incidence of ultra- come from this source, even though the refrigerants market constituted 28 percent of violet radiation on the Earth’s surface. Some evidence supports a correlation between ultraviolet radiation and malignant mela- noma, the most serious, often fatal, form of 8’ IMOS Report, p. 70. 80 821 bid., p. 74, skin cancer. Studies have indicated that in- 83D. M. Aviado, “Toxicity of Aerosol Propellants in the Respiratory and Circulatory Systems [X, Summary 77S Loeb, op cit , 11, p 254. of the Most Toxic: Trichlorofluoromethane (Fll ),” “M. J Molina and F J Rowland, “Stratospheric Toxicology, 3:311-319, 1975. Sink for Cholofluoromethanes Chlorine Atom “See e g , M. B. McElroy, “Threats to the Atmos- Cata Iyzed Destruction of Ozone, ” Nature phere, ” Harvard Magazine, 78:1 9-25, 1976; J E igner, 249.810-812, 1974. Unshielding the Sun... Environmental Effects, Environ- 79NAS Report, pp. 72-78 ment, 17:1 5-18, 1975; A.K.A. ed, Unshielding the ‘ONAS Report, pp 81-89 Sun. . .Human Effects, Environment, 17:6-14, 1975 388 ● Solar Technology to Today’s Energy Needs

the total fluorocarbon market in 1972.85 86 Under the Toxic Substances Control Act Recent studies indicate that losses from (Public Law 94-469), the process of regu- refrigeration equipment can be reduced, lating use of fluorocarbons is beginning be- especially those from automobile, home, cause of the possibility of extremely severe and commercial air-conditioning units. 87 environmental effects. In the Federal Register of March 17, 1978, the Environmen- The use of a freon-based heat engine to tal Protection Agency, Food and Drug Ad- provide solar air-conditioning would in- ministration, and Consumer Product Safety crease the amount of freon in a typical Commission issued regulations stating that home by a factor of 2 to 3. A house using a it will be illegal to: a) manufacture aerosol freon-based engine to provide 100 percent cans containing fluorocarbons after Decem- of residential electrical and air-conditioning ber 15, 1978, and b) introduce such con- needs would need 5 to 6 times more freon tainers via interstate commerce after April than a conventional house. 15, 1979. Uses of fluorocarbons in refrigera- The environmental impact of this increase tion, including onsite solar energy systems, in fluorocarbon use (independent of other wilI be regulated later. Use of fluorocarbons fluorocarbon uses such as aerosol pro- in onsite solar energy systems is merely one pellants) is yet to be fully evaluated, but category of use in refrigeration units, how- because of the possibility of severe en- ever, and as such will not be subject to im- vironmental damage either from fluorocar- mediate regulation. bons or their consequent ozone depletion, these impacts are being analyzed. ” NOISE Although ozone levels fluctuate worldwide, it is believed that an overall depletion Because the equipment for onsite energy has occurred, perhaps because of fluorocar- production may be located in or near living bon usage.89 The effect of this level of de- or working quarters, the noise emitted by pletion is still controversial. It appears, how- these systems must be considered as an en- ever, that the use of fluorocarbons in onsite vironmental impact. Solar collectors and energy production will not be a major prob- energy-storage systems are silent except for lem. This is because only a low percentage the low rumble of intermittent pumps and of environmental fluorocarbons result from flowing water, but in systems which employ loss due to use as a refrigerant. Until a re- gas turbines and other types of heat engines, placement fluid for fluorocarbons is found, noise could be a problem. Without noise an attempt should be made to minimize suppression, a gas turbine of a size suffi- their escape into the environment. cient to generate all electricity for a single home would emit about as much noise as an unmuffled internal combustion automobile a’Ha/ocarbons: Environment/ Effects of Cho/c engine at full throttle. ’” However, the noise f/uorornethane Release, National Academy of from gas turbines is readily suppressible to Science, Committee on Impacts of Stratosphere levels quieter than a common household Change, Washington, D. C., 1976 (hereinafter, NAS Report), p. 16. Fluorocarbons and the Environment, furnace fan– less than 40 decibels.” This Report of Federal Task Force on Inadvertent Modi- suppression is a normal part of commercial fication of the Stratosphere (l MOS), June 1975, (here turbine installations. In a total energy inafter, IMOS Report), p.91. system (a system which employs waste heat OSIMOS Report at page 88, P. H. Howard and A from energy production for space heating Hanchett, “Cholofluorocarbon Source of Environ- mental Contamination, ” Science, 189:21 7-219, 1975. uses), noise suppression of the gas turbine 8TIMOS Report, P. 93 ‘“Manufacturing Chemists Association, Research Program of Effect of Fluorocarbons on the Atmos- 90108-1 20d Ba, at 10 feet, phere, Dec. 31, 1976, and NAS Report, “Patrick G. Stone, Garrett Corporation, Washing- OglMOS Report, P. 380. ton, D. C., personal communication, Feb. 11, 1977, Ch. IX Energy Conversion With Heat Engines ● 389

can be accomplished using a waste-heat solar systems have other advantages, and boiler, reducing the noise to acceptable should be considered prior to installation of levels without added installation costs. such a system. Water requirements would be about the same as for a fossil steamplant of similar capacity. WATER USE IN STEAM CYCLES

The solar energy systems of a small com- SODIUM AND POTASSIUM VAPOR munity or industrial plant, on the order of 15 MW(e), may employ water or steam in ener- Some of the proposed high-temperature gy conversion. storage schemes require heat pipes which Although this water will not be polluted use sodium or potassium vapor as their by chemicals during this process, it will working fluid. While only very small quan- return to the environment with added heat. tities of these substances are required, they In areas of water shortage, the requirement could have minor adverse environmental for replacing the amount of water lost could impacts, although both of these vapors are constitute a major problem. This is par- presently employed in street lighting, and no ticularly true in dry, sunny climates where adverse use impacts have been reported. Chapter X ENERGY CONVERSION WITH PHOTOVOLTAICS Chapter X.— ENERGY CONVERSION WITH PHOTOVOLTAICS

Introduction ...... 393 . 4. Market Forecasts for Photovoltaic Devices Photovoltaic cells...... 395 at Different Prices...... 410 Cells Designed for Use in Concentrated Years To Achieve Indicated Price Reduction Sunlight ...... 400 as a Function of Learning Curve and Optimizing Conventional Silicon Cells Assumed Growth in Demand ...... 412 for Use in Concentrated Sunlight .. ...400 The Distribution of Costs in the Manufacture of Silicon Photovoltaic Devices Using Interdigitated Back-Contact Cells ...... 400 ContemporaryTechnology...... 414 Gaiiium-Arsenide Cells...... 401 7. The MajorSt6psin Manufacturing a Silicon The Vertical Multifunction Cell ...... 401 Photovoltaic Device ...... :...... 419 Horizontal Multifunction Cells...... 402 8. EffectiveConvective Heat-Transfer Thermophotovoltaic Cell ...... Coefficients [k ] for a Variety of Cooling Multicolor Cells ...... 403 e Systems ...... 424 Concentrator Systems ...... 403 Photovoltaic Cogeneration ...... 406 LIST OF FIGURES The Credibility of the Cost Goals ...... 407 Markets ...... 408 Figure An Analysis of Manufacturing Costs...... 412 Page Silicon...... 412 Array of Silicon Photovoltaic Cells Providing PowertoPumpWater ...... 393 Thin Films ...... 420 A Typical Photovoltaic Device ...... 396 MaterialsAvailability and Toxicity...... 421 An lnterdigitated BackContact SolarCell Silicon ...... 422 and CrossSection...... 401 Cadmium ...... 422 The Vertical MultijunctionCell ...... 401 Gallium Arsenide...... 423 Thermophotovoltaic Converter ...... 403 Performance of Cellsin Real Environments. ..423 Experimental Concentrating Photovoltaic PassiveCooling...... 424 Array in Operation. The Array Employs ActiveCooling...... 424 Fresnel Lenses and Silicon Photovoltaic Cells ...... 404 Photochemical EnergyConverslon...... 425 Breakeven Costs for Concentrating PhotovoltaicCollectorsCompared WithFlat- Plate Devices. .,...... 405 Historical Learning Curves From the LIST OF TABLES SemiconductorIndustry...... 409 Table PhotovoltaicArray Prices for Several Market No. Page Projections...... 411 l. a) Key Milestones for National Photovoltaic Commercial Silicon Photovoltaic Cells ...413 Conversion Program; and b) Goals for Silicon Ribbon Being Grown by the ’’Edge- ConcentratorSystemsUsingSilicon Cells .394 Defined Film-FedGrowth” Process ...... 417 2. PhotovoltaicCell Efficiencies ...... 398 Thin-Film Cadmium Sulfide-CopperSulfide 3. Temperature Dependence of Photovoltaic SolarCells ...... 420 Devices ...... 407 Photochemical Energy Conversion...... 425 Chapter X Energy Conversion With Photovoltaics

INTRODUCTION

Photovo taic cells (often called “solar cells”) are semiconductor devices which are capable of converting sunlight directly into electricity. Generating electricity in this way has obvious advantages. The photovoltaic cells have no moving parts, and they do not require high-temperature or high-pressure fluids. Since they are extremely reliable, quiet, safe, and easy to operate, they are ideally suited to onsite applications. Photovoltaic energy production is unlimited by scarce materials, since cells can be manufactured from silicon, one of the Earth’s most abundant elements. There is no doubt as to the technical feasibility of generating electricity from photovoltaic devices. The units have been used for many years in the space program and to provide power in remote terrestrial sites. The array of silicon cells shown in figure X-1 provides power to pump water in a remote location in Arizona. The most immediate barrier faced by all photovoltaic systems is the present high cost of the devices. Photovoltaic arrays could be purchased in large quantities in late 1977 for about $11 per peak watt of output. * Electricity from systems using such cells costs $1.50 to $2.00/kWh.

Figure X-1 .—Array of Silicon Photovoltaic Cells Development work to reduce the cost of Providing Power to Pump Water photovoltaic energy can be divided into three general categories: 1. Reducing the cost of manufacturing the single-crystal silicon celIs which are now on the market;

2. Developing techniques for mass producing and increasing the performance of cells made from thin films of mate-

rials such as CdS/Cu2S or amorphous silicon, and

3 Developing high-efficiency cells which can be installed at the focus of magnifying optical systems,

It is technically possible to use any of these approaches to reduce costs to $1 to $2

. * Photovoltaic prices throughout this paper refer to the sel I Ing price of arrays of cel Is encapsulated to pro- SOURCE Solar Technology International tect them from the weather, f o b the manufacturing facility In 1975 dollars The peak output of a cell refers to the output which would be obtained If the cell were exposed to the Sun at the zenith on a clear day. 393 394 ● Solar Technology to Today’s Energy Needs

per peak watt (electricity costing $0.10 to X-1. The lower cost goals appear to be op- $0.40/kWh) during the next 3 to 5 years. The timistic but not impossible. achievement of costs below $1 to $2 per The DOE price goals assume that the ar- watt will require a considerable amount of rays will last approximately 20 years. (Pres- engineering development work. Progress in ently, terrestrial arrays are guaranteed for 1 any of a number of current research pro- year.) This seems to be an attainable objec- grams would give us considerably more con- tive, although more data is required on the fidence about the prospects for achieving degradation rate for arrays exposed to the substantialIy lower costs. environment for long periods of time. Sili- A set of goals for reducing the cost of con cells apparently fail only when the ma- silicon photovoltaic devices was established terial used for encapsulation cracks or somewhat arbitrarily during the crash Proj- leaks. Structural failures and corrosion have ect Independence studies conducted in occurred in improperly encapsulated de- 1973. The Department of Energy (DOE) be- vices, ’ and most clear plastics darken with lieves that, with some relatively minor ad- prolonged exposure to sunlight, cutting justments, these goals are achievable and is down the light reaching the cells. Glass or using them for planning purposes. The pres- acrylic encapsulation should, however, be ent goals are: $1 to $2 per watt by 1980-82, able to prevent these problems. $0. SO/watt by 1986, and $0.10 to $0.30/watt ‘A Johnson (M ITRE Corporation), private com- by 1990. Current goals are shown in table munication, 1977.

Table X-1

a) Key Milestones for National Photovoltaic Conversion Program —— Array price in 1975, Production rate, dollars per peak megawatts peak watt per year

1. End of FY 1977 ...... 11 2. End of FY 1978 ...... 7 3. End of FY 1982 ...... 1-2 20 4. End of FY 1986 ...... 0.50 500 5. End of FY 1990 ...... 0.1-0.3 50,000

SOURCE Photovoltaic program program summary January 1978, U S Department of Energy, Division of Solar Technology

b) Goals for Concentrator Systems Using Silicon Cells

Technical Commercial feasibility* equipment* ●

1975 dollars Silicon 1975 dollars Silicon per peak watt cell per peak watt celI (entire system) efficiency (entire system) efficiency — —— — 1. End of FY 78. . . 2 16% 15 13.5% 2. End of FY 80. . . 1 180/0 2.75 16% 3. End of FY 82. , . 0.50 200/0 1.60 180/0

“ Laboratory proof of concept + reasonable estimate of cost of commercial system based on concept “* F o.b. price of production technology.

SOURCE Annual Operation Plan, Systems Deflnltlon Prolect (FY 1978), Sandla Laboratory Ch. X Energy Conversion With Photovoltaics ● 395

PHOTOVOLTAIC CELLS

All photovoltaic installations will consist ial (i. e., from the valence band), giving it of small, individual generating units — the enough energy to move freely in the photovoltaic cell. Individual cells will prob- material (i. e., into the conduction band). ably range in size from a few millimeters to A vacant electron position or “hole” is a meter in linear dimension, A surprising left behind at the site of this collision; such variety of such cells is available or is in ad- “holes” can move if a neighboring electron vanced development since it has only been leaves its site to fill the former hole site. A in the past 5 years that serious attention has current is created if these pairs of electrons been given to designing cells for use in any- and holes (which act as positive charges) are thing other than spacecraft. Devices are separated by an intrinsic voltage in the cell avaiIable with a large range of efficiencies material, and voltages. Some cells are designed to withstand high solar intensities and high Creating and controlling this intrinsic operating temperatures, while others are de- voltage is the trick which has made semicon- signed to minimize manufacturing costs. ductor electronics possible. The most com- The variety should not give the mistaken im- mon technique for producing such a voltage pression that this is an area where large is to create an abrupt discontinuity in the amounts of private or public research fund- conductivity of the cell material (typically ing have been directed; indeed, many of the silicon in contemporary solid-state compo- projects described here are being conducted nents) by adding small amounts of im- by small research laboratories. purities or “dopants” to the pure material. This is called a “homojunction” cell. A typi- The photovoltaic equivalent of power cal homojunction device is shown in figure engineering is something of an anomaly in x-2. the generating industry since it involves manipulations in the miniature and silent An intrinsic voltage can also be created world of semiconductor physics instead of by joining two dissimilar semiconductor ma- steam tables, gears, and turbine blades. The terials (such as CdS and CU 2S), creating a following discussion provides only a very “heterojunction,” or by joining a semicon- brief excursion through this complex field. ductor to a metal (e.g., amorphous silicon to More complete discussions of the topics paladium) creating a “Schottky” barrier covered can be found in several recent junction. publications. 2345 All that can be done here A fundamental limit on the performance is to outline some of the major effects in- of all of these devices results from the fact fluencing cell cost and performance. that (1) light photons lacking the energy re- The energy in light is transferred to elec- quired to lift electrons from the valence to trons in a semiconductor material when a the conduction bands (the “band gap” light photon collides with an atom in the energy) cannot contribute to photovoltaic material with enough energy to dislodge an current, and (2) the energy given to electrons electron from a fixed position in the mater- which exceeds the minimum excitation threshold cannot be recovered as useful 2t-i ). Hovel, Semiconductors and Semimeta/s, electrical current. Most of the unrecovered Volume 11, Solar Cells, Academic Press, New York, photon energy is dissipated by heating the 1975 ‘C E Bacus, (ed ), Solar Cc//s, I E EE Press, New York, cell. 1976 The bulk of the solar energy reaching the 4 A Rothwarf and K W Boer, frog, in Solid State Chem., 10(2), p 77 (1975) Earth’s surface falls in the visible spectrum, ‘K W Boer and A Rothwarf, Ann. Rev. Mat. Sci. (6), where photon energies vary from 1.8 eV p 303 (1976) (deep red) to 3 eV (violet). In silicon, only 396 ● Solar Technology to Today’s Energy Needs

\ Rear Metal Contact

about 1.1 eV is required to produce a Electrons actually leave cells with photovoltaic electron, and in GaAs about energies below the excitation voltage be- 1.4 eV. Choosing a material with a higher cause of losses attributable to internal re- energy threshold results in capturing a larger sistance and other effects, not all of which fraction of the energy in higher energy are understood. a (An electron leaves a typi- photons but losing a larger fraction of lower cal silicon cell with a useful energy of about energy photons. The theoretical efficiency 0.5 eV.) peaks at about 1.5 eV, but the theoretical efficiency remains within 80 percent of this The same kinds of fundamental limits ap- maximum for materials with band gap ply to photochemical reactions in which a energies between 1 and 2.2 eV.6 7 light photon with energy above some fixed

‘M. Wolf, Energy Conversion, 11, 63(1 971 ). ‘M. Wolf, University of Pennsylvania, “Recent im- ‘Joseph J. Loferski, “Principles of Photovoltaic provements and Investigations of Silicon Solar Cell Solar Energy Conversion,” 2Sth Artnua/ Proceedings, Efficiency, ” U.S./U.S.S.R. joint Solar Energy Power Sources Conference, May 1972. Workshop, Ashkhabad, U. S. S. R., September 1977. Ch. X Energy Conversion With Photovoltaics ● 397

excitation threshold is able to produce a crystal grains which can be tolerated, and al I chemical reaction or a structural change commercial sit icon celIs are now manufac- which can be assigned a fixed energy. The tured from single crystals of silicon. It is theoretical limit to the performance of sev- believed that if polycrystalline silicon is to eral types of cell designs is shown in table be used, individual crystal grains must be at x-2. least 100 microns on a side if efficiencies as high as 10 percent are to be achieved. 11 12 It The performance of real cells (also shown is important that the grains be oriented with in table X-2) falIs below the theoretical max- the grain boundaries perpendicular to the imum for a number of reasons. One obvious celI junction so that charge carriers can problem is reflection of light from the cell reach the junction without crossing a grain surface (which can be reduced with special boundary, A number of research projects coating and texturing) and reflection from are underway to develop inexpensive tech- the electrical contacts on the front surface niques for growing such polycrystalline of the cell (which can be reduced with care- materials 13 14 15 and for minimizing the im- ful contact design). ’ Losses also result from pact of the grain boundaries. ” Efficiencies the fact that the photo-generated electrons as high as 6.7 percent have been reported and holes, which fail to reach the region in for vapor-deposited polycrystalline silicon the cell where they can be separated by the celIs with grains about 20 to 30 microns on a intrinsic voltage, cannot contribute to side’ 7 and a proprietary process capable of useful currents. , producing grains nearly a millimeter on a Photo-generated charges can be lost side reportedly can be used to produce cells because of imperfections in the cell crystal with efficiencies as high as 14 percent, structure, defects caused by impurities, sur- Work is underway to improve crystal grow- face effects, and other types of imperfec- ing techniques and to enlarge grains with tions. Losses are minimized if a perfect crys- lasers and electron beams. tal of a very pure semiconductor material is Perhaps the most intriguing recent devel- used, but producing such a crystal can be ex- opment is the discovery that an amorphous tremely expensive. Manufacturing costs can silicon-hydrogen “alloy” can be used to con- probably be greatly reduced if cells consisting of a number of smalI crystal “grains” can be made to operate with acceptable ef- ‘)A R Kirkpatrick, et al., Proceedings of the ERDA ficiencies. The size of the grains which can Semiannual Photovoltaic Advanced Materials Pro- be tolerated depends on the light absorbing gram Review Meeting, Washington, D C , Mar 22-23, 1977 properties of the cell material. If absorption ‘lA, Baghdad[, et al , ERDA Semiannual Photo- is high, photovoltaic electron-hole pairs will volta ic Advanced Materla Is Program Review Meeting be created close to the cell junction where ‘ ‘T. L. Chu, et al., IEEE Transaction on Electron the voltages exist; relatively smalI grain Devices, ED-24 (4), 1977, pp. 442445. sizes can be tolerated since the charges 14H. Fischer and W. Pschunder, (A EG-Telefunken), “Low-Cost Solar Cells Based on Large-Area U nconven- need drift only a short distance before being tional Silicon, ” IEEE Transactions on E/ectron Devices, sorted by the field. ED-24(4), 1977, pp. 438-441 ‘5L. D. Crossman, Research and Development of Silicon is a relatively poor absorber of Low-Cost Processes for Integrated Solar Arrays, (Third light and, as a result, cells must be 50 to 200 quarterly progress report, ERDA EC (11-1 }2721, microns thick to capture an acceptable frac- Energy Research and Development Admlnistratlon, tion of the incident light. This places Washington, DC., 1975), p. 38 rather rigorous standards on the sizes of “T H Distefano and J. J Cuomo, 1 BM, “Enhance- ment of Carrier Lifetime in Polycrystalllne Silicon, ” Proceedings, National Workshop on Low-Cost Poly- ‘J Llndmayer and J F Allison, Cornsat Tech. #3, crystal I ine Silicon Solar Cel Is, Dallas, Tex , May 18-19, 1973, p 1 1976. ‘OJ R Hauser and P M Dunbar, IEEE Transactions “T. L Chu, et al., op. cit pp 442-445 on E/ectron Devices, E D-24 (4), 1977, p 305 ‘“H` Fischer and W Pschunder, op clt , p 438 398 ● Solar Technology to Today’s Energy Needs

Table X-2.— Photovoltaic Cell Efficiencies — Perform- ance of com- Reference mercial cells

10-15 (1 ,2) — (4,5) — (6,7)

2-3 (8,9) — (lo) — (9)

— (11 )

— (12) — (1 ,13)

— (3)

12.5 (14,15,16)

— (17) — (18) — (19) — (20) — (21 ) — (22)

● Techniques for reporting efficiencies differ Wherever Possible, efficiencies were chosen which assume air mass 1 and Include losses due to reflection and contact shading

1. H. J. Hovel, Semiconductors and Semimetals, Vol. 2: mium Sulfide Solar Ceils,” (ERDA E (49-18)-2538, So/ar Cc//s (Academic Press, New York, 1975). Energy Research and Development Administration, 2. J. Lindmayer and C. Y. Wrigley, “Development of a 20 Washington, D.C. 1977). Percent Efficient Solar Cell,” (NSF-43090, National 10. G. A. Samara, paper presented as part of the Pro- Science Foundation, Washington, D. C., 1975), ceedings of the ERDA Semiannual Photovoltaic Ad- 3. J. V. DeBow, paper presented as part of the Pro- vanced Materiais Program Review Meeting, ceedings of the Energy Research and Development Washington, D. C., Mar. 22-23, 1977. Administration Semiannual Photovoltaic Advanced 11. J. 1. Shay, S. Wagner, H. M. Kasper, App/. Phys. Lett. Materials Program Review Meeting, Washington, 27,89 (1975). D. C., Mar. 22-23, 1977. 12. L. J. Kazmerski, S. R. White, G. K. Morgan, ibid., 29, 4. 1.1. Chu, S. S. Chu, K. Y. Duh, H. 1. Yoo, /EEE Transac- 268 (1976). tions on Electron Devices, ED-24 (No. 4), 442 (1977). 13. R. J. Stirn (Jet Propulsion Lab). “High Efficiency Thin- 5. H. Fischer and W. Pschunder (AEG-Teiefunken). “Low- film GaAs Soiar Cells”, 730-9 First Interim Report for Cost Solar Celis Based on Large-Area Unconven- DOE/NASA, Dec 1977. tional Siiicon, ” IEEE Transactions on Electron 14. 1. S. Napoli, G. A. Swartz, S. G. Liu, M. Klein, D. Fair- Devices. pp. 438-441. banks, D. Tames, RCA Rev. 38,76 (1977). 6. D. E. Carlson, IEEE Transactions on Electron Devices, 15. H. J. Hovel (IBM), “The Use of Novei Materiais and De- ED-24 (No. 4) 449 (1977). vices for Sunlight Concentrating Systems,” Pro- 7. D. E. Carlson and C. R. Wronski, App/. Phys. Lett. 28, ceedings DOE Photovoltaic Concentrator Systems 671 (1976). Workshop, Tempe, ARiz., May 1977, pp. 35-54. 8. K. W. Boer and A. Rothwarf, Annu. Rev. Mater. Sci. 6, 16. J. Gibbons (Stanford University), personal communi- 303 (1976). cation, October 1977. 9. A. M. Barnett, J. D. Meakim, M. A. Rothwarf, “Progress 17. M. D. Lambert and R. J. Schwarz, IEEE Transactions in the Development of High Efficiency Thin Film Cad- on Electron Devices, ED-24 (No. 4), 337 (1977). Ch. X Energy Conversion With Photovoltaics ● 399

Table X-2 references—continued 18. R. M. Swanson and R. N, Bracewell, “Silicon 21. J. J. Loferski (Brown University), “Tandem Photovol- Photovoltaic Cells in Thermophotovoltaic Conver- taic Solar Cells and Increased Solar Energy Conver- sion” (EPRI ER-478, Electric Power Research in- sion Efficiency,” The Conference Record of the stitute, Palo Alto, Cal if., February 1977). Twe/fth /EEE Photovo/taic Specialists Con/er- 19. J. Harris, et. a/. (Rockwell International). “High Effi- ence-1976, Baton Rouge, La., November 1976, pp. ciency AIGaAs/GaAs Concentrator Solar Cells,” The 957-961. Conference Record of the Thirteenth /EEE 22. H. J. Hovel (IBM). “Novel Materials and Devices for Pho fo vo/fa ic Specia Iis ts Conference- 1978. Sunlight Concentrating Systems,” /BM Journa/ of Washington, D. C., June 1978. Research and Development. Vol. 22, No. 2, Mar 1978, 20. L. W. James and R. L. Moon (Varian Associates). T. T. Rule, et. a/. (Arizona State University). “The “GaAs Concentrator Solar Cells” The Conference Testing of Specially Designed Silicon Solar Cells Record of the Eleventh IEEE Photovoltaic Specialists Under High Sunlight Illumination,” Twe/fth Conference, Scottsdale, Ariz., May 1975, pp. 402-408. IEEE- 1976. Pp. 744-750.

struct photovoltaic cells with useful effi- of areas, however, and a number of thin film ciencies. Efficiencies of 5.5 percent have cells may be able to achieve efficiencies been measured” and 15 percent efficiency greater than 10 percent. may be possible. 20 The hydrogen apparently Older designs of cadmium cells degraded attaches to “dangling” silicon bonds, mini- and failed relatively rapidly, but accel- mizing the losses that wouId otherwise erated lifetime tests on modern designs ap- result at these sites. Acceptable perform- pear to indicate that cells hermetically ance is possible, despite the large number of sealed in glass with proper electrical loading remaining defects, because the amorphous could have a useful life of decades.24 25 26 material is an extremely good absorber of light; test cells are typically 1 micron or less Research is also underway on a number of - in thickness. 21 The properties of this com other materials which may be used to manu- plex material are not welI understood. facture inexpensive thin film cells. Experi- mental cells have been constructed which

GaAs or CdS/Cu2S are also much better substitute iridium phosphide or copper in- absorbers of Iight than crystalline silicon, so idium selenide for the copper sulfide in the

cells made from these materials can be thin- CdS/Cu2S heterojunction, and efficiencies ner and tolerate smaller crystal grains than greater than 10 percent have been demon- was possible with the crystalIine siIicon. strated in single-crystal laboratory cells

Commercial CdS/Cu2S cells will probably be made with these materials. 2728 6 to 30 microns thick,22 23 and the crystal It is also possible to convert light energy structure produced with a relatively simple directly into electricity by exposing elec- spray or vapor deposit process is large trodes immersed in chemicals to sunlight. if enough to prevent grain structure from sig- the materials are properly chosen, a current nificantly affecting celI performance. can be produced without any net chemical change in the materials used. Conversion ef-

The primary drawback of most of the L “thin film” celIs is their low efficiencies. “J. Besson, et al , “Evaluation of CdS Solar Cells as Research is proceeding rapidly in a number Future Contender for Large Scale E Iectriclty Produc- tion,” The Conference Record of the E/eventh /EEE Plrotovo/taic Specialists Conference–1 975, Scotts- dale, Ariz , May 6-8, 1975 (Institute of E Iectrlcal and “D E Carlson, RCA Laboratories, “Amorphous Sili- Electronics Engineers), pp 468-475 con Solar Cells, ” IEEE Transactions on Electron z 5E w c reenwich and F A Shlrland (Westinghouse Devices, ED-24(4), 1977, pp 449-452 Research Labs), “Accelerated Life Performance Char- 20 and C R Wronskl, App Phys, Lett. 28, 1976, p acteristics of Thin-Film CU2 5 Solar Cel/s-CdS, ” fro 671 ceedings, E Iectrochem Ica I Society Solar Energy Sym- 2 ‘A R Moore, E/ectron and Ho/e Drift Mobr’/ity in posium, Washington, D C , May 2-7, 1976 Amosphous Si/icon (to be published) “j F jordan, Photon Power,lnc , private com- 22 Boer, op clt , p 319 munication, Apr 5, 1976 2]) F jordan, Photon Power, Inc., El Paso, Tex , 27S Wagner, et al , Appl. Phys. Lett., 26, 229, 1975 private communication, February 10, 1977 “j Shay, et al , App/. Phys. Lett,, 27, 89,1975 400 . Solar Technology to Today’s Energy Needs

ficiencies greater than 5 percent have been tensity. These effects would lead to an in- reported with polycrystalline CdSe-based crease in overall cell efficiency, except that photoelectrochemical cells.29 30 31 32 33 34 the increased current densities in the cell lead to increased resistive losses and other effects. The design of standard silicon cells CELLS DESIGNED FOR USE IN can be optimized for operating in intense CONCENTRATED SUNLIGHT sunlight by carefully designing the wires used to draw current from the cells, optimizing the resistivity of the cell material, chang- High efficiencies are important for cells ing the thickness of the cell junction, and used in concentrated sunlight, since in- otherwise taking pains in celI manufacture creased cell performance means a reduction (e.g., better antireflective coatings and sur- in the area which must be covered with the face texturing, higher quality silicon, pre- magnifying optical equipment, which domi- cisely designed gridlines, etc.). Efficiencies nates the system’s cost. as high as 17.9 have been reported for sili- Modified silicon cells, designed to per- con celIs operating at 1000 C in sunlight conform in concentrated sunlight are not in- centrated 200 times. 35 herently more expensive than ordinary cells, but are always likely to cost more per unit of Several ingenious techniques have been cell area since production rates will be suggested for improving performance of siIi- lower and since more care will be taken in con devices used in intense sunlight with their manufacture. However, since the cells novel designs. cover only a fraction of the receiving area, much more can be spent on any individual cell. Cells such as the thermophotovoltaic Interdigitated Back-Contact Cells device and the GaXAl1-XAs/GaAs cells may be considerably more expensive per unit area An “interdigitated back-contact” cell ex- than the silicon devices, but this cost may poses an unobstructed wafer of intrinsic not be significant since the devices can be (i.e., very pure) silicon crystal directly to the used with concentrations of 500 to 1,000 or sunlight. The junctions that produce the cell more and can be much more efficient. A va- voltages, and that are attached to electrical riety of approaches are being investigated leads, are entirely on the back of the cell. for achieving high-efficiency performance in (The name comes from the shape of the pos- concentrated sunlight. itive and negative electrical contacts on the back side of the cell. See figure X-3.) An effi- Optimizing Conventional Silicon Cells for ciency of 15 percent concentration, with Use in Concentrated Sunlight ratios up to about 280, has been reported for The current from a photovoltaic cell in- a preliminary version of this cell; it is be- creases almost Iinearly with increasing sun- lieved that straightforward design improve- light intensity and the voltage increases ments will result in cells which are at least slightly faster than the logarithm of the in- 20-percent efficient. ”

jgMark ‘j WrightOn, MIT, private communication, Mar 26, 1977. 30A. B, Ellis, et al., ). Amer. Chern. Soc., 98, 1635, 15L s NapOil, et al,, RCA, “High Level concentra- 6418, 6855(1 976) tion of Sunlight on Slllcon Solar Cel Is, ” RCA Review, “G. Hodes, et al , Nature, 216, 403,1976, Vol 38, No 1, March 1977, p 91 ‘2B. Miller and A. Heller, Nature, 262, 680, 1976. 16M D Larnmert and R. j Schwartz, pU rdue Un iver- “D. L. Laser and A. ). Bard, j. E/ectrochem, Soc., sity, “The Interdlgitated Back Contact Solar Cell: A 123, 1027,1976. Silicon Solar Cell for Use in Concentrated Sunlight, ” “K. F Hardee and A j Bard, ), E/ectrochem. Soc., /EEE Transactions on E/ectron Devices, ED-24(4), 1977, 724, 215,1977 pp 337-341, Ch. X Energy Conversion With Photovoltaics 401

Figure X-3.— An lnterdigitated Back Contact The Vertical Multifunction Cell Solar Cell and Cross Section The edge-illuminated, vertical, multifunction cell shown in figure X-4 consists of a stack of silicon homojunction devices quali- tatively similar to standard cells, illumi- I Hlgh-lifetlme bulk region I nated in such a way that the light enters the cells parallel to the junctions. Several recent calculations have indicated that these devices have the potential of achieving efficiencies as high as 30 percent,39 although very little work has been done on designing and testing optimized cells. The maximum measured efficiency to date is 9.6 percent for a device without an antireflective coating. 40

Figure X-4.—The Vertical Multifunction Cell (edge illuminated)

incident sunlight SOURCE I Lammert M D and R J Schwartz “The Interdlgltated Back Contact Solar Cell A Sll; con Solar Cell for Use (n Concentrated Sunllghl ” IEEE Transacf/ons ori E/ecfron Dev/ces, VOI ED-24 (1977) p 337 current

Gallium-Arsenide Cells

Gallium arsenide has a higher theoretical photovoltaic efficiency than silicon because its excitation threshold is better matched to the energy in the Sun’s spectrum.

CaAs cells can be used to achieve high efficiencies in intense radiation, particularly if they are covered with a layer of GaXAl1-XAs which has the effect of reducing surface and contact losses. Efficiencies as high as 24.5 percent have been measured for such devices operating in sunlight concentrated 180 times, 38

In addition, both theory and experiment show that the efficiency of GaAs cells is reduced less by high temperature than is the efficiency of siIicon celIs. ‘9H.J Hovel, IBM, “Novel Materials and Devices for Sunllght Concentrating Systems, ” IBM journal of Research and Development, 22(2), March 1978, “H Hovel, op clt , p 195 40T T Rule, et al , Arizona State University, “The “J Harris, et al , Rockwell International, “High Effi- Testing of Specially Designed Silicon Solar Cells ciency AI GaAs/G aAs Concentrator Solar Ce[ Is, ” The Under High Sunlight Illumination, ” The Conference Conference Record of the Thirteenth /EEE Photo Record of the Twelfth /EEE Photovo/taic Specialists voltaic Specialists Conference-1978, Washington, Conferenc&1976, Baton Rouge, La., November 1976, D C , June 1978 pp 744-750. 402 ● Solar Technology to Today’s Energy Needs

The high potential efficiency results from The extra manufacturing steps required to several features of the device:41 42 43 fabricate these devices will make them somewhat more expensive than conven- ● Since the vertical multifunction devices tional silicon cells, but this difficulty would are connected in series, they produce be offset if the high efficiencies are realized. higher voltages and lower currents than other concentrator cells with the same Horizontal Multifunction Cells power output. The low currents reduce the resistance losses. Series connec- There have also been proposals for using tions also mean, however, that consid- horizontal multifunction devices using sili- erable care must be taken to ensure con or GaAs. It may be possible to design a that all of the cell elements are illumi- cell array capable of producing relatively nated since an unilluminated unit will high voltages on a single chip, thereby react Iike a large series resistance. ducing the cost of interconnecting devices and reducing series resistance in connec- ● Like the interdigitated cell discussed earlier, the vertical multifunction de tions. The inherent efficiencies of these vices do not require contacts on the sur- devices are approximately the same as conventional cells, but it may be easier to use face (the aluminum connections can the approach to develop practical cells cover less than 1 percent of the surface which can more nearly approximate the area)” and thus front surface reflec- potential of the materials.46 tions are minimized. ● The multifunction device should be Thermophotovoltaic Cell able to make more efficient use of light The “thermophotovoltaic” cells shown in with relatively long and short wave- figure X-5 may be able to achieve efficien- lengths. cies as high as 30 to 50 percent by making an ● The multifunction devices should be end-run around the fundamental limits on able to perform better than conven- cell performance discussed earlier. This is tional silicon cells at high tempera- accomplished by shifting the spectrum of tures, and its performance at high tem- light reaching the cell to a range where most peratures improves in high light con- of the photons are close to the minimum ex- centrations; the cells should, for exam- citation threshold for silicon cells. The Sun’s ple, be only half as sensitive to temper- energy is used to heat a thermal mass to ature at 1,000 x suns as they are in un- 1,800 ‘C (the effective black body tempera- concentrated sunlight.45 ture of the Sun is about 5,7000 C). A large fraction of the surface area of this mass radiates energy to a silicon photovoltaic device. (Reradiation to the environment can 41B, L. Sater and C. Goradia, “The High Intensity occur only through the small aperture where Solar Cell –Key to Low Cost Photovoltaic Power, ” NASA Technical Memorandum ,NASA TM X-71718, the sunlight enters. ) A highly reflective sur- 1975. face behind the photovoltaic cell reflects 42C Goradia and B. L. Sater, “A First Order Theory unabsorbed photons back to the radiating of the P-N-N Edge-1 Illuminated Silicon Solar Cell at mass and their energy is thus preserved in Very High Injection Levels,” IEEE Transactions on the system .47 Electron Devices, Vol. ED-24, 4, p. 342,1977, “H. ), Hovel, IBM, “The Use of Novel Materials and Devices for Solar Concentrating Systems,” Pro- ceedings DOE Photovoltaic Concentrator Systems “H. J. Hovel, IBM, “The Use of Novel Materials and Workshop, Scottsdale, Ariz., May 24-26,1977. Devices for Solar Concentrating Systems,” op. cit., p. 446. L. Sater, “Current Technology Status of the 38 Edge-illuminated Vertical Multifunction (VM)) Solar “R. M. Swanson and R. N. Bracewell, Silicon Cell, ” November 1977 (unpublished), Photovo/taic Cells in Thermophotovo/taic Conversion, 45 Goradia and Sater, op. cit., p. 350. EPRI ER-478, February 1977. Ch. X Energy Conversion With Photovoltaics ● 403

Figure X-5.— Thermophotovoltaic Converter lowing the remaining photons to reach lower cell levels,48 Little experimental work has CONCENTRATED SUNLIGHT FROM PARABOLOID been done on these devices, but theoretical analysis has predicted that the light-filter devices could achieve efficiencies as high as 46 percent if two separate cells are used and 52 percent if three cells are used. ” MuIti- Iayer cells using Ge, Si, GaAs, and other materials with two or more layers may also be able to achieve efficiencies above 40 percent. 50 An ingenious scheme for separating colors has been recently proposed which uses a series of dyes capable of absorbing sunlight and reradiating the energy in a narrow frequency band matched to the band gap of each of a series of cell junctions. s’ 52 A considerable amount of development work will be required to design practical Thermophotovoltalc Converter devices, however, and the ultimate cost of fabricating the devices cannot be forecast SOURCE Swanson, R M and R N Bracewell (Stanford Umverslty) “Sll(con with any confidence. Photovoltalc Cells In Therm ophotovoltalc Conversion” EPRI ER. 478 ~1977) 48H. J Novel, IBM, “The Use of Novel Materials and Devices for Solar Concentrating Systems, ” op cit., p 38 49N. S Alvi, et al., Arizona State University, “The Potential for Increasing the Efficiency of Photovoltalc Multicolor Cells Systems by Using Multiple Cell Concepts,” Twelfth IEEE-7976, OP cit., pp. 948-956 Another approach to achieving high cell 50] ] Loferski, Brown University, “Tandem Photo- voltalc Solar Cells and Increased Solar E nergy Conver- efficiencies involves the use of a number of sion Efficiency, ” Twe/fth /EEE-1976, op clt , pp different materials to form cells optimally 957-961 designed for different colors of light. There “A Goetzberger and W Breubel, App/. Phys., 14, are two basic approaches: (1) the use of 1977, p 123. 52 selective mirrors to separate colors and The technique was originally suggested for use in connection with scintil Iation counters in R L Carwln, direct them to different cells, and (2) the use “The Design of Liquid Scintlllatlon Cells, ” Rev. Sci, in- of a vertical stack of photovoltaic cells ar- st. 23, 755 (1 952); and R L Garwin, “The CO I Iectlon of ranged so that upper layers absorb only high Light From Scintillation Counters, ” Rev. SCI. Inst. 37, energy (i.e. short wavelength) photons, al- 1010 (1 960).

CONCENTRATOR SYSTEMS

The contribution of photovoltaic cell replaced with problems of mechanical en- costs to the overall cost of an installed pho- gineering. In most cases, the energy required tovoltaic system can be greatly reduced if to manufacture a concentrator array is an optical system is used to concentrate many times lower than the energy required sunlight on the cell, even though cells de- to manufacture a flat-plate cell array with a signed for use in concentrators may cost simiIar area. more per unit area of cell surface than flat- plate cells. If such systems are used, prob- The variety of concentrating collectors lems of reducing cell fabrication costs are which can be used with photovoltaic de- 404 ● Solar Technology to Today’s Energy Needs

vices is reviewed in chapter XII. PhotovoI- ● One-axis tracking collectors are unable taic devices can be attached to most types to illuminate the entire receiver surface of tracking systems with minimal modifica- during most of the day. Thus, only a tions to the basic collector design. (A two- part of the receiver can actually be axis tracking system using Fresnel lenses to covered by cells. In general, it is focus light on silicon cells is shown in figure necessary to connect photovoltaic de- X-6. ) Attaching a photovoltaic device to a vices in a receiver in series to achieve concentrating collector can, however, pre- acceptable system voltages. Nonillumi- sent some unique design problems: nated photovoltaic devices have high Figure X-6.—Experimental Concentrating Photovoltaic Array in Operation. The Array Employs Fresnel Lenses and Silicon Photovoltaic Cells

SOURCE Sandia Laboratories, Albuquerque, N Mex., 1976. Ch. X Energy Conversion With Photovoltaics . 405

resistance and the output of a string of rs = ratio of solar energy reaching cells in cells connected in series would be the tracking collector to the sunlight greatly reduced if one element of the (direct and diffuse) reaching the flat- string were shaded. plate collector

r C = ratio of the cost of the concentrating ● It is desirable to maintain a relatively cell ($/kW in one sun) to the cost of a uniform illumination on most cells to fIat-plate cell array maximize cell performance. This is dif- C = cost of installing the flat-plate collec- ficult to accomplish with most collec- i tors ($/m2) tor designs. It is possible to design cells r = ratio of cost of installing a concen- capable of performing with acceptable l trator to the cost of installing a flat- efficiencies in the i Illumination patterns plate device of specific CoIIector designs. This can C =annual cost of maintaining the flat- be done, for example, by modifying the o plate system (cleaning etc.) in $/m2 of pattern of electric contacts on the front colIector surface of the cell, but the market for r = the ratio of the cost of maintaining such specialized cells would necessari- O the concentrating collector to the cost ly be limited. of maintaining a flat-plate system (per It is difficult to compare the attrac- m 2)

tiveness of concentrating and nonconcen- k l= the effective cost of capital

trating photovoltaic devices because of the cm ––the cost of flat-plate supporting

large number of variables involved; the only structures ($/m2) completely satisfactory way of making such C,= concentration ratio of collector a comparison is to conduct a complete Iife- This formula has been used to construct the cycle cost analysis of competing systems curves shown in figure x-7. operating in realistic environments (such as those reported elsewhere in this study). The following formula, however, can be used to Figure X-7.— Breakeven Costs for Concentrating obtain a crude estimate of the cost of a con- Photovoltaic Collectors Compared With Flat. Plate Devices centrating collector which would be competitive with a flat-plate device (assuming that no credit can be given for the thermal energy which can be produced from the concentration systems):

where the variables are defined as follows:

cc= allowed cost of the concentrating collector, excluding the solar cells ($/m2)

C fP = cost of fIat plate cell array ($/kW)

n fP = the efficiency of the f tat-plate array 0.10 r e = ratio of the efficiency of the concen- 0.20 0.30 0.40

trator photovoltaic system (including losses in the collector optics) to the effi- EFFICIENCY OF CELLS USED IN THE CONCENTRATOR ciency of the flat-plate array (including packing factors) (not including optical losses) 406 . Solar Technology to Today’s Energy Needs

Assuming that concentrating systems cost While the cost of mounting cells on track- so percent more than flat-plate arrays to in- ing collectors is clearly a major concern, stall and three times as much to operate on there is also cause for concern about the an annual basis, concentrator systems cost of mounting flat-plate arrays. If array would be competitive with $500/kW—15 prices fall below $300 to $500/kW, the cost percent efficient flat-plate arrays if the con- of supporting and installing the arrays could centrating collector costs about $70/m2 and begin to exceed the cost of the arrays concentrating cells are 20-percent efficient. themselves. The concentrator could cost about $180/m2 General Electric has proposed a design if concentrating cells are 40-percent effi- for a photovoltaic shingle which may be cient. (This example assumes that the op- able to substitute for a building roofing tical efficiency of the concentrators is 80 material. If costs reach $100 to $300/kW, it percent and the concentration ratio is at may also be economical to use photovoltaic least 10 times the ratio between concen- sheets as a part of a wall surface. I n most trator cell costs and the cost of fIat-plate ar- locations in the United States, the output of rays. ) The allowed cost of concentrators will a collector mounted vertically on a south-, be considerably larger if there is a useful ap- east-, or west-facing walI is 40 to 60 percent plication for the thermal energy available lower than the output of a collector fixed at from an active cooling system. an optimum orientation.

PHOTOVOLTAIC COG EN ERATION

The analysis thus far has considered only With photovoitaic systems, the critical the electric output of collector systems, but question is whether the electric-generating the attractiveness of photovoltaic devices efficiency which is lost because of operating can be increased significantly if effective the cells at higher temperatures is compen- use can be made of the thermal energy car- sated by the value of the thermal energy ried away by water pumped over the back produced. Cell performance degrades surfaces of collecting celIs. Such systems almost Iinearly with temperature at tem- are the photovoltaic analogs of cogenera- peratures of interest primarily because of a tion devices, and an analysis of the op- drop in the operating voltage of the cell (at portunities presented by such devices is high temperatures, thermally excited elec- much the same as those conducted for con- trons begin to dominate the electrical prop- ventional systems. I n both cases, the net ef- erties of the semiconductor device). This ficiency of systems can only be understood temperature dependence is commonly ex- by examining the combined demands for pressed in the following form: electricity and thermal energy in each proposed situation. There are clearly many useful applications for the thermal energy with temperatures in the 500 to 100‘C range where n (T) is the efficiency of a cell at tem- which can easily be extracted from most perature T (expressed in “C) and ß is the tem- photovoltaic cogeneration devices. About perature coefficient. The temperature coef- 23 to 28 percent of the primary energy con- ficient (ß) measured for a number of dif- sumed in the United States is used at tem- ferent cells is illustrated in table X-3. It can peratures below 108 oC.53 be shown in most cases that if a use for low- temperature thermal energy exists, it is preferable to accept these losses of efficiency 53 Battelle Columbus Laboratories, Survey of the Ap- plications of Solar Thermal Energy Systems to /n- and use the thermal output from celIs direct- dustrial Process Heat. Iy rather than to maximize cell performance Ch. X Energy Conversion With Photovoltaics ● 407

Table X-3.—Temperature Dependence of Photovoltaic Devices

Cell Base Concentrate ion ß= temper- efficiency resistivity ratio ature coef -

Material at 28° C(% ) C r ficient

Silicon ...... , 10.4 0.1 1 0.0035 Sandia cell Silicon . . . . . 11.8 0.3 1 0.0035 Sandia cell Silicon ., ...... 12.4 0.3 40 0.0032 Sandia cell Silicon ...... 12.2 2.0 1 0.0040 Commercial cell Silicon ...... 11.8 10.0 1 0.0046 Commercial cell GaAs ...... 17.0 1 0.0022 Varian GaAs ...... 19.2 100 0.0023 Varian GaAs ...... , . . . . 18.5 1000 0.0021 Varian CdS ., ...... 7.8 1 0.004-0.005 Univ. of Delaware —

SOURCES Silicon cell data from Edward Burgess, Sandla Laboratories, private communication. GaAs data from L James, Varlan private communication CdS data from John Meakln, Institute of Energy Conversion, Unlverslty of Delaware (private communlcat{on)

and attempt to use a photovoltaic-powered ciency at 1000 C and about 12-percent effi- heat pump to produce thermal energy, ciency at 2000 oC.56

GaAs and other high-efficiency cells are It is possible to operate flat-plate collec- less affected by high temperature operation tors at elevated temperatures, but cogenera- than are silicon devices .54 A commercial tion will probably be easier to justify for silicon cell operating with an efficiency of concentrating systems. Care must be taken 12 percent at 270 C has an efficiency of only to cool concentrator cells even if waste heat 8 percent if operated at 1000 oC 55, while a is not employed. If photovoltaic cogenera- GaAs cell with an efficiency of 18.5 percent tion proves to be attractive, concentrator at 280 C can operate with 16-percent effi- photovoltaic systems may continue to be economically attractive even if the price 54H j Hovel, IBM, Semiconductors and Sernirneta/s, goals for fIat-plate arrays are achieved. op cit , p 168 ‘SE L Burgess and J C Fossum, Sand ia Laboratories, Albuquerque, “Performance of n + -p Sillcon Solar Cells in Concentrated Sunlight, ” /EEE Transactions on E/ectron Devices, E D-24(4), 1977, p. 56L. James, Varian Corp , private communication, 436 1977,

THE CREDIBILITY OF THE COST GOALS

The most satisfactory technique for an- ing processes capable of dramatic cost ticipating the future cost of photovottaic de- reductions are based on techniques which vices wouId be to anticipate future manu- are now only laboratory procedures or facturing techniques and develop a precise which anticipate progress in research. It is cost estimate for each processing step; this possible, however, to make some estimates approach is taken in the next section. Un- of potential cost reduction by examining the fortunately, the results of such analyses are history of cost reductions achieved in sim- inconclusive since many future manufactur- iIar types of manufacturing. 408 Solar Technology to Today’s Energy Needs

A common statistical technique for MARKETS analyzing the history of cost reductions is 57 called the “learning-curve” technique. The learning curve cannot be used to esti- This technique attempts to correlate the mate the rate at which prices will fall price of a product with the cumulative pro- without information about the size of the duction experience of the industry manufac- market at each future price. Unlike most turing the product. In many cases, a rough other power sources, the demand for photo- correlation appears to exist, although the voltaic devices exists at a large range of rate at which prices decrease varies greatly prices, since the equipment can provide from one industry to another. The rate of power in remote areas where conventional “learning” is quantified by determining how alternatives are extremely expensive. The much the price decreases when the cumula- unique features of the equipment may lead tive production volume doubles: if a doubl- to the discovery of markets for energy where ing of accumulated volume results in a price no market now exists. The large elasticity of decrease of 10 percent, the system is said to markets, coupled with the fact that individ- be on a “90-percent learning-curve;” if a ual installations can be very small, has al- doubling of production volume results in a lowed an evolutionary growth in sales and a price decrease of 30 percent, the system is gradual reduction in cell prices, said to be on a “70-percent learn i rig-c urve.” The free-world market for cells at 1976 The most obvious place to look for a prices was about 380 kW58 of which about historical analogy for predicting the price 280 kW were soId by U.S. manufacturers. reductions possible in photovoltaic devices U.S. Government purchases during this is the semiconductor industry which pro- period were about 108 kW, of which about duces silicon devices using many of the 50 kW were used in satellites.59 Major com- techniques now used to construct silicon mercial markets have appeared in commun- photovoltaic devices. The history of prices ications equipment (68 kW), corrosion pro- in the transistor and silicon diode industries tection for bridges, pipelines and like ap- is illustrated in figure X-8. The results are dif- plications (28 kW), and aids to navigation ficult to interpret since the price reductions (20 kW).6O Sales during 1977 were expected clearly do not follow a simple linear learn- to be about twice 1976 levels. ing curve, but they do indicate that a learning curve of 70 percent is not impossible. Several market surveys for photovoltaic The analogy is far from perfect, of course, equipment have been completed during the since miniaturization techniques which past several years, and some of these are were used effectively to reduce the price of summarized in table X-4. The considerable semiconductor electronics cannot be used differences in the forecasts reflect differing in the manufacture of photovoltaic devices; judgments about the future cost of conven- the size of photovoltaic devices used in flat- tional energy and other forms of solar plate arrays cannot be reduced since power energy, about the rate at which an industrial produced by a unit area of photovoltaic sur- infrastructure capable of supporting Iarge- face is limited by the intensity of sunlight on scale production can be established, and the Earth’s surface. The learning-curve about the potential costs of support equip- method is probably valid for making crude ment (storage, controls, etc. ) and instalIa- estimates of future cell prices since learning curves of 70 to 90 percent have been ob- served for most products, even when minia- 58BDM Corporation, Characterization of the Present turization is not used in the manufacturing Worldwide Photovoltaics Power Systems Market, May process. 1977, p. 1-1. S9 I ntertechnology Corporation, Photo vo/ta ;C power Systems Market /identification and Analysis, Aug. 23, “Boston Consulting Group, Perspectives on Ex- 1977. perience, 1971. ‘“lntertechnology Corporation, op. cit. Ch. X Energy Conversion With Photovoltaics ● 409

Figure X-8.— Boston Consulting Groups’ Learning Curve

SILICON TRANSISTORS 1954 1960 1963 1968 $100.00

0.1 1 10 100

Industry Total Accumulated Volume (million units)

SILICON DIODES 1955 1959 1965 1968

3 10 100 1,000 10,000

Industry Total Accumulated Experience (million units) 410 ● Solar Technology to Today’s Energy Needs

Table X-4.– Market Forecasts for Photovoltaic Devices at Different Prices [in megawatts of annual sales]

— Array prices in dollars per peak watt

Marketing study 10 3 1 0.5 0.1-0.3

1. BDM/FEA DOD market ...... 10 75 100 — — Worldwide commercial market ...... 1.5 20 70 100 — 2. Intertechnology Cor- poration ...... , . . 0.5 13 126 270 — 3. Motorola ...... 1.5 20-30 — — — 4. Texas Instruments. . . . . 0.4 2.6 30 100 20,000 5. RCA...... 0.8 13 200 2,000 100,000 6. Westinghouse . . . . — — — 96,000

DOE planning, objectives . . 1.0 8 75 500 5,000

SOURCES ERDA brteflng on the “Photovoltalcs Program, ” Sept 9, 1977. BDM Corporation, “Characterlstlcs of the Present Worldwide Photovoltalc Power Systems Market, ” May 1977, p 1.1 Irrtertechnology Corporation, “Photovoltaic Power Systems Market Identlflcatlon and Analyses, ’ Aug 23, 1977 BDM Corporation, DOD Phofovo/tam Energy Conversion Systems Market /nventory and Ana/ys/s, Summary Volume, p 17. P D Maycock and G F Wakefield (Texas Instruments) “Business Analysis of Solar Photovoltatc Energy Conver- sion, ” The Conference Record of the E/evenfh /EEE P/rotovo/fam Specla//sfs Conference. 1975 Scottsdale, Arlz May 1975, pp 252.255 The Motorola Corporation tion. Some manufacturers, for example, equipment has the additional advantage of have been skeptical about the high forecasts allowing functioning power sources to be in- for small remote applications since many of stalled quickly and in sizes appropriate for these applications require a considerable each application. Moreover, an investment amount of expensive marketing and engi- in the photovoltaic power source does not neering. commit a nation to finding a reliable source of fuel or to maintaining a highly trained The surveys seem to agree that a signifi- group of operators—two serious problems cant fraction of sales during the next few for developing countries, years will occur in developing countries. Photovoltaic equipment is ideally suited to Other possible areas where sales of photo- places where no utility grid is available and voltaic equipment may increase rapidly dur- where labor for installing the equipment is ing the next few years include applications relatively inexpensive. Consumers in the by the U.S. Department of Defense (large, capital cities of many developing nations cost-effective purchases appear possible now pay as much as $0.20 to $0.25/kWh for during the next few years)62 and the armed electricity, and prices in more remote areas forces of other nations; the agricultural sec- are often higher (if power is available at tor, for irrigation and other pumping ap- alI). 61 The modular nature of photovoltaic

“Telegrams received from A I.D from posts in numerous developing nations during July and August ‘2BDM Corporation, DOD Photovoltalc Energy Cor-- 1977 [n response to a request for information about version S ysterns Market /nventory and A na/ys IS, 5um- local utlilty rates mary Volume, p. 17 Ch. X Energy Conversion With Photovoltaics ● 411

placations; and the transportation industry, Figure X-9. -Photovoltaic Array Prices for for highway markers and lighting. 63 64 Several Market Projections

If prices fall below about $0.50/watt, an explosive growth in sales could occur since at this price photovoltaic equipment might provide electricity which is competitive with residential and commercial electricity rates in many parts of the United States. 65 66 By the time prices fall to $0.10 to $0.30/kW, the photovoltaic electricity may be competitive with electricity sold at buIk rates to large industrial consumers. Estimating sales at these levels is extremely speculative since generating large amounts of power from photovoltaic devices would require a fundamental change in the ways in which the Nation now supplies and consumes electric energy. Moreover, when array prices reach these low levels, the overall cost and attractiveness of photovoltaic systems are likely to be dominated by factors other than the cost of the celIs themselves. Before turning to an analysis of integrated systems, however, it will be useful to examine the costs and capabilities of the assortment of photovoltaic devices which are or may be available in the near future.

Each of the projections of markets can be NOTE: With the exceptfon Of the “DOD sales” curves, It has been assumed used to predict the rate at which prices fall that the Federal Government spends $129 ml Illon for photovoltalc systems between 1978 and 1981, of which 40 percent IS actually used to purchase given an assumed rate of “learning.” Three cell arrays (the remainder being spent for des Ign, i nstallatlon, storage, con- forecasts and three different learning curves trol systems, and other supporting devices) The forecasts assume that cumulatwe production of cel Is through 1975 was 500 kW and that average have been used to construct the forecasts array prices at the end of 1975 were $15/Watt shown in figure X-9. It can be seen that with the RCA estimate of markets and a 70-per-

cent learning curve, the technique predicts The figure also illustrates the extreme sen- that prices will reach $500/kW in 1986. If sitivity of the forecast of potential price re- prices fall according to a 75-percent learn- ductions to the assumptions made about in- ing curve, however, the price will not reach termediate markets. If the BDM Corporation $500/kW until after 1990. Using the less op- forecasts of potential cost-effective military timistic Texas Instruments (Tl) estimates of applications are correct and the military markets, prices would not fall to $1,000/kW purchases devices for all cost-effective ap- untiI nearly 1990, even with the 70-percent plications, prices can fall to $500/kW by

learning curve, 1986, even if a 75-percent learning curve is assumed.

‘‘Intertechnology Corporation, op. cit. If the cost of photovoltaic devices is to be 64BDM Corporation, Photovo/taic Market, op cit. reduced through an expansion of the mar- “Westinghouse Corporation, Fina/ Report: Concep- ket, the industry will have to grow extremel tual Design and Systems Ana/ysis of Photovo/taic y Power Systems, Vo/ume /, Executive Summary, April rapidly for the cost goals to be met. For ex- 1977, p 45 ample, if prices follow a 70-percent learning “See volume I I of this study curve, the cost goals can be met if the pro- 472 ● Solar Technology to Today’s Energy Needs

duction rate of cells doubles each year. (The times required to achieve different price reductions, given a learning curve and production doubling time, are summarized in table AN ANALYSIS OF X-5.) Such expansions are possible but they MANUFACTURING COSTS could make it difficult for small companies now manufacturing cells to expand fast Silicon enough to meet demands. The vast majority of the photovoltaic [n spite of its limitations, the learning- celIs now being sold are single-crystal siIicon curve technique can provide some useful cells in fIat arrays. (See figure X-1 O.) The bulk guidance by establishing whether the cost of Federal funding to reduce the cost of goals anticipated for photovoltaic devices cells is being directed to silicon technology. exceed any historic rates (the goals are op- The Federal Low-Cost Silicon Solar Array timistic, but not impossible by this test), and (LSSA) project, managed by the Jet Propul- they can be used to explore the sensitivity of sion Laboratory (jPL) has made a careful price reductions to different forecasts of analysis of the component costs of each potential markets. step in the manufacturing process and is

Table X-5.— Years To Achieve Indicated Price Reduction as a Function of Learning Curve and Assumed Growth in Demand

—— Learning Number of times production rates Price reduction curve double each year

1/2 (PO/ P) (percent) 4 2 1

70 3.0 5.5 10.0 18.0 30 75 3.6 6.6 12.3 22.6 80 4.4 8.4 15.7 29.4

70 3.4 6.2 11.4 20.9 50 75 4.0 7.5 14.1 26.1 80 5.0 9.5 18.0 34.0

70 3.8 7.2 13.4 24.7 100 75 4.6 8.7 16.5 30.9 80 5.8 11.0 21.1 40.2

70 4.1 7.8 14.5 27.0 150 75 5.0 9.4 17.9 33.7 80 6.2 11.9 22.9 43.8

a Assumptions: Price in 1976 = PO = $15,000/kWe b Cumulative sales volume in 1976 = So = 500 kwe Annual sales in 1976 = B = 250 (kWe)e

= to = 1976 (base date)

aJ w, yerk~.s, (.ARc(_J solar, lnC ) Pr!vatf? Communtd(on bJ Llndmeyer, (Solarex Corp ) Private Comrnunlcatlon.

C A Cllfford, (Solarex Corp ) Private Communlcatlon. Oct 1976 SOURCE” Prepared by OTA `Ch. X Energy Conversion With Photovoltaics ● 413

Figure X-10.— Commercial Silicon Photovoltaic Cells

Silicon Concentrator Photovoltaic Cells Commercial Silicon Photovoltaic Cells

Scale in Centimeters Photos John Furber, OTA

Manufacturer: Manufacturer: 1. Solarex. 1-4. Spectrolab. 2. Arco Solar (Printed contacts) 5. Sandia Laboratories, 3. Motorola. 6. Solarex. 4, Optical Coatings Laboratory, Inc. (Space Cell Utilized In Sat elites)

systematicalIy examining techniques for about $1 O/kg and the amount of siIicon reducing costs in four major areas. wasted in the manufacturing process considerably reduced. b’ Perhaps even more im- ● Production of the pure silicon feed- portantly, current techniques for manufac- stock, turing silicon are extremely inefficient in ● Preparation of a thin sheet of silicon, their use of energy; approximately 7,000 kWh of energy is required to manufacture a ● Fabrication of cells, and cell with a peak output of 1kW (assuming ● Arrangement of the cells in a weather- that celIs are 100 microns thick and 82 per- proof array. cent of the silicon entering the manufacturing process is wasted). 68 This means that the JPL objectives for cost reductions in each device must operate in an average climate area are shown in table X-6. I n reaching for about 4 years before it produces as much these goals, maintaining high cell efficiency energy as was consumed in manufacturing wilI be criticalIy important since many costs the component silicon. in cell manufacture and in the instalIation of photovoltaic arrays are proportional to Several promising techniques for improv- overalI celI area and not to power. ing the purification have been experimentally verified, and it should be possible to SILICON PURIFICATION ‘7H Macomber, j PL, Proceedings, ERDA Serni- The purified polycrystalline silicon used a nnua / Solar Photo vo/ta ic Program Review Meeting, as the raw material of commercial cell Silicon Technology Programs Branch, San Diego, manufacture now costs about $65/kg. The Calif , January 1977, p 68. “L P Hunt, Dow Corning Corp , “Total Energy Use jet Propulsion Laboratory estimated that, if In the Production of S i I icon Solar Cel Is From Raw the goal of $0.50/watt is to be reached, the Materials to Finished Product, ” Twe/fth IEEE-1976, op. silicon material cost must be reduced to cit `, pp 347-352 414 ● Solar Technology to Today’s Energy Needs

Table X-6.—The Distribution of CoStS in the Manufacture of silicon Photovoltaic Devices Using Contemporary Technology [aii costs in $/peak W]

Non ingot Ingot technology technology

Representative 1978 1980 1982 1984 1986 data for 1976

Polysilicon ...... 2.01 1.16 .76 .28 .14 .06 Crystal growth and cutting . . . . . 4.18 2.50 1.43 .67 .23 .10 Cell fabrication ...... 5.97 1.87 1.01 .58 .34 .19 Encapsulation materials . . . . .78 .22 .12 .09 .07 .03 Module assembly and encapsulating . 3.99 1.25 .68 .38 .22 .12 Price . 16.96 20.00 7,00 4.00 2.00 1.00 50 —— Goal ...... ‘Does not Include Inflation— prices In 1975 constant dollars NOTE The detailed price goal allocations are for slllcon Ingot technology up through 1982 and for slllcon sheet Technology In 1984 dnd 1986 These al local Ions for use w It h In the LSSA Pro)ec I are subject to rev IS Ion ds better knowledge Is gal ned and s ho[) Id not be ( onstr ued as predicted prices

I t Is ex pec ted t hal after 1982, Ingot and sheet lec h ndogy mod u Ies w I I I be cost corn pet I t I ve, w I t h the poss I btl I t y that the $ 50/W goal ~ an be achieved by e It her technology Technology developments and future product I on c OS! parameters w I I 1 be malor factors I n determ I n I nq t hc~ most cost effective deslg ns SOURCE Jet Propulslorl Laboratory Low Cost SIIIC on Solar Array Pro)e( t Recel~ed by OTA June 1977 develop cell arrays capable of producing all plants capable of manufacturing silicon in the energy used in their manufacture in 3 to quantities large enough to achieve the re- 4 months. ” A significant amount of chem- quired cost reductions would need to be ical engineering and process development is established very quickly— probably within needed, however, to demonstrate that these the next year — and the investments required laboratory experiments can be scaled-up by will be large, compared to previous spend- many orders of magnitude to form the basis ing in photovoltaic manufacturing New sili- of a commercial faciltiy. con plants are Iikely to require more capital investment per unit of cell production than It is possible to produce photovoltaic any other stage in the celI production proc- celIs with siIicon less pure than the “semi- ess — between $20 miIIion and $40 miIIion conductor grade” material now used in cell for a single plant. There is no incentive to in- manufacture, but a careful analysis must be vest in such equipment of this magnitude made to determine whether the lower sili- solely for the purpose of selIing sit icon to con costs would compensate for the addi- the semiconductor industry because mate- tional system costs which would be incurred rial costs for these devices are already a by the reduced cell efficiency which results. small part of the device cost. Silicon prices, Manufacturing very high efficiency cells for therefore, are unlikely to fall by 1982 unless use in concentrators may even require sili- the Government takes some action. con which is of higher purity than the mate- riaI now used to produce most semicon- Improved sawing techniques may be able ductors. to cut silicon material requirements by two- thirds by producing thinner silicon cells and Silicon costs probably represent the single reducing the material lost as sawdust. 70 Im- greatest technical barrier to meeting JPL’s cost goals for nonconcentrating arrays in the ‘ (’A Kran, I HM, Proceeding, S yn?po~lun? on the early 1980’s. This is because construction of M,] ter/a/s .$cience$ Aspect of Thin / //n? $y~ tern~ for So/ar F rwrgy Con\ wsion, Tuscon, Arlz , Mdy 20-22, b9Hunt, Ibid, 1074 Ch. X Energy Conversion With Photovoltaics ● 475

proving the techniques used to grow crystals Crystal Growing and S/icing could also reduce losses. Development of a Ali of the silicon photovoltaic devices ribbon or thin-film, crystal-growing process now sold are manufactured from wafers could greatly reduce wastage. Development sawn from single-crystal boules (2- to 3-inch of an amorphous silicon cell with adequate diameter cylinders of silicon). These wafers performance would dramaticalIy reduce sili- represented about 35 percent of the cost of con requirements in cells since these cells photovoltaic arrays in 1976 (see table X-6) would probably require less than I percent The crystals are commonly grown by dip of the silicon used in commercial cells, Sili- ping a seed crystal into a silicon melt in a con requirements can also be greatly re- quartz crucible which is a few degrees duced if concentrator devices are used. above silicon’s melting point and by slowly withdrawing the growing cyrstal from the melt. The crucible and the crystal are FORMATION OF SILICON SHEETS counter-rotated to grow a straight crystal of uniform, circular cross-section The crystal Growing pure silicon crystals and sawing is pulled from the crucible until most of the them into thin waters now represents about molten silicon has been withdrawn and 25 percent of the price of arrays. 7 A number ’ removed from the melt. The entire appa- of active programs exist for improving the ratus is then aIlowed to cool so that the batch processes in which crystal ingots are crystal can be taken out of the airtight currently being produced and sawed into chamber, As the remaining molten silicon wafers 72 techniques have also been de- solidifies in the crucible, the crucible usual- signed for drawing single-crystal sheets or ly breaks, adding about $50 to the cost of ribbons directly from molten siIicon, but a the boule This procedure is called the considerable amount of engineering work “Czochralskl ” (Cz) or “Teal-Little” method. must be done before a commerciaI process The boule is sawed into thin wafers which if available. Development of an Ingot tech- are sent to the next stage of the cell fabrica- nique adequate to meet the $1 to $2 per tion process. Several commercial silicon watt cost goal appears to be assured, and celIs manufactured using this technique are improved ingot techniques may even be shown in figure X-10. A variety of new con- adequate to meet the 1986 cost goal. The cepts have been proposed for reducing the problems remainlng in this technology ap- cost of the crystal-growlng processes, some pear to be largely ones of improving me- Involve radicalIy new approaches where thin chanical designs, this is another area where tilms or ribbons are solifified directly from the program could be accelerated by the the molten silicon. Government Although crystal growing • I reproved sawing techniques might re equipment IS relatively expensive, unsubsi- duce the material lost in the sawin dlzed commercial Interest in this kind of g equipment In the next few years is Iikely to process; currently, nearly 50 percent of be greater than commercial interest in ad- the crystal grown is lost as silicon sawdust. ” Techniques are bein devel- vanced silicon refinement processes. Re- g search progress which makes it possible to oped which use muItiple saws wIth thin use polycrystalIine or amorphous materials saw blades, sawing wires, and other ad- wouId substantialIy reduce the cost of this vanced processes to decrease the mate- step In production rial lost In sawing and increase the number of silicon wafers produced ——.—— — from a single crystal by producing thin- 7‘“ Low-(’ost SI I IC on Sol at Array Pro]ect, ” Qudrter)y ner wafers. 74 75 Report-l, J Uly-september 1976, pp 1-4 “jet propulylon Ldbordtory, Low-cost $//icon .$o/dr “Texas Instruments, I nc , and L’drlan have F RDA Array F’ro/ect, Report-J, July- September 1976, pp contrdcts to Improve sawl ng technlquej See R G 4-57 Forney, et al J PL, op clt 7‘M~comber, ] P1 , op c It , p 71 7’LSSA Quarter/v Report, op clt , pp 4-117, 4-115 416 ● Solar Technology to Today’s Energy Needs

The molten silicon in the quartz cruci- adapted to the growth of semiconduc- ble from which the crystal boule is with- tor-grade silicon crystals. drawn can be continuously replenished, improvements in cutting circular leading to longer crystal draws and a wafers into the hexagons required for lower requirement for crucibles. (This close packing are possible through the process could also save a number of use of a Iaser-slicing technique being processing steps.) developed by Texas Instruments. The silicon material lost in sawing Table X-6 indicates that if current tech- could be recycled for further use if it is niques are converted to mass production, not contaminated in the cutting proc- silicon wafer blanks can be produced for ess. about $112/m2 ($0.80/watt if the cell is 14- Techniques can be used to increase the percent efficient) if polycrystalline material diameter of the crystals grown by using were purchased for $35/kg. This could be the standard Czochralski process. Crys- reduced to approximately $78/m2 if poly- tals now in use are typically 3 inches in crystal Iine material were purchased for diameter, but crystals 10 inches in $10/kg. A recent analysis conducted for diameter have been grown in labora- DOE by Texas Instruments estimated that it tories. An experiment is now under- would be possible to produce “solar-grade” way to grow three 12-inch diameter polycrystalline silicon for $10/kg (or crystals in one continuous heating cy- $214/kW at 14 percent efficiency),79 and for cle. 77 Choice of an optimum diameter approximately $5/kg if arrays are to be will depend on a detailed study of the manufactured for $1 ()()/k W. 80 manufacturing process. (Problems in cutting the crystals increase with Single Crystal Growth—Ribbons and Sheets crystal diameter. ) Research has been underway for at least The rate of crystal growth can be in- 15 years to develop a process by which creased if columnar grains can be toler- single-crystal silicon can be produced in the ated in cell wafers (research is required form of ribbons or sheets. Thin ribbons to determine the extent to which such would be appropriate for use in solar cells grains can be tolerated or their effects without the crystal-slicing steps required for minimized). boules. This would eliminate the costs involved in slicing the crystals and could Considerable energy and capital equip- make more efficient use of silicon. This ment could be saved if a process could wouId not only eliminate expensive oper- be developed for growing a crystal in a ating steps, but could reduce trimming mold. The Crystal Systems Company is losses when cutting round cells to hexagonal currently examining a concept in which cells. The Department of Energy has been a seed crystal is placed in one end of an funding Mobil-Tyco, Solar Energy Corp., insulated mold filled with molten sili- IBM, Motorola, RCA, the University of con. A temperature gradient is main- South Carolina, and Westinghouse to assess tained along the mold so that the crys- the merits of a variety of processes for grow- tal grows from the end with the seed ing single-crystal ribbons and sheets. 81 crystal to fiII the mold. 78 This technique is commonly used to grow metal crys- One technique for doing this is the “edge- tals, but has not yet been successfully defined, film-fed growth” process (EFG);

“Ibid. “M. GoIdes (President of SunWind Ltd ), private ‘“lbld communlcatlon, Aug 16, 1976 a’ E RDA, Semiannua/ Nationa/ Yo/ar Photovo/tage “R G Forney, et al , j PL, op clt Program Review Meeting, University of Maine, August 78R C Forney, et al , jPL, op cit. 1976 Ch. X Energy Conversion With Photovoltaics . 417

work began on this process about a decade process in figure X-11. Photovoltaic cells ago. The EFG process utilizes a graphite die made from EFG ribbons have shown effi- on top of a crucible of molten silicon. A nar- ciencies as high as 10 percent.83 Intensive row pool of molten silicon forms on the top work is proceeding on the EFC process but of the die by capillary action. A thin ribbon several difficulties remain: 1 ) contain i nation of silicon is slowly withdrawn from this pool.82 Such a ribbon is shown in the growth

82B Chalmers, “The Photovoltaic Ceneratlon of ‘~K, Ravi, et al., 12th IEEE Photovoltaic Specialists E Iectrlcity,” Scientific American, November 1976, p Conference, Baton Rouge, La., Nov. 15,1976 34

Figure X-1 1 .—Silicon Ribbon Being Grown by the “Edge-Defined Film. Fed Growth” Process

(Mobil Tyco Solar Energy Corp ) — —

478 Solar Technology to Today’s Energy Needs

of the ribbon by impurities from the die to allow the production of cells with accept- results in efficiencies lower than other able efficiencies. Some processes are yield- siIicon cells; 2) the graphite die is attacked ing individual crystal grains 1 to 10 mm on a by the molten silicon; and 3) the process is side, blurring the distinction between single currently quite slow. Ribbons 2- to 21A-cm and polycrystalline devices. Perfection of wide can now be grown at rates of 2 to 7 cm such processes could lead to more efficient per minute. The objective is a growth rate of use of the silicon feedstock and replaces the approximately 18 cm. per minute. a’ A recent expensive task of growing a perfect crystal analysis by IBM indicated that a large- with a casting, forming, or depositing proc- diameter Czochralski boule can grow silicon ess which may be much less expensive. crystal areas at a rate equivalent to 20 to 40 Some of the methods proposed would cre- simultaneously pulled ribbons .85 ate a thin layer of polycrystalline material on a solid backing, or substrate, thus Other ribbon techniques under investiga- eliminating the cost and material waste tion include the IBM “Capillary Action associated with slicing the silicon material Shaping Technique” (CAST) which uses a into wafers. Concepts include: wetted die, and the RCA “inverted stepa- nov” technique which uses a nonwetted die. 1. Dipping a substrate into molten silicon, Both techniques share many of the prob- covering the substrate with a thin lems of the EFG approach. a’ coating of polycrystalline siIicon. (Honeywell). Another process for manufacturing ribbons is the web-dendrite crystal growth 2. Continuously pulling a thin sheet of sili- process. Unlike EFG, this process requires no con from the surface of a pool of die, and the die contamination and die ero- molten metal where silicon vapor is be- sion problems are, therefore, avoided. Strips ing deposited. (General EIectric). of silicon 2 meters long, 0.15mm thick, and 3 Depositing silicon from a silicon-halide 22mm wide have been grown at rates of 2 to gas directly onto a hot substrate. It may 3 cm per minute; the objective is a growth be possible to combine the final stage rate of 18 cm per minute.87 Difficulties of silicon purification (distillation) with which remain with this process include: 1) this deposition process (Rockwell inter- the fact that careful temperature control is national and Southern Methodist Uni- necessary, which probably precludes the si- versity). multaneous growth of several ribbons from one melt; and 2) relatively slow growth rates. 4 Forming heated silicon material under pressure in rollers (University of Penn- sylvania). Polycrystalline Sheets 5 Casting blocks of poiycrystalIine Work is also underway to develop low- material and slicing the blocks (Crystal cost techniques for producing sheets of Systems, Salem, Mass.). polycrystalline silicon with crystal grains large enough in size and oriented properly CELL FABRICATION

The process of converting silicon wafers “lbld into an operating photovoltaic array with 1 “5A Kran (1 BM), “Single-Sillcon Crystal Growth by kW peak output involves a number of indi- Czochralski and Ribbon Techniques–A Comparison of C a pa bl I I t Ies, ” Proceedings, S yrnpos I urn on the vidual steps which now require many hours Material Sciences Aspect of Thin Film Systems for of hand labor,88 adding about $6 to the price So/ar [nergy Conversion, Tuscon, Ariz , May 20-22, 1974, Pp 422-430 “’’Low-Cost Silicon Solar Array Project, ” Quarterly ‘ 8 P D. Maycock and G F Wakefleld, Texas in- Report-1, july-September 1976, p 4-57 struments, “Business Analysls of Solar Photovoltalc “lbld Energy Conversion, ” Eleventh IEEE-7975, pp 252-255 -.—.

Ch. X Energy Conversion With Photovoltaics . 479

of a 1 watt cell. Processes include the crea- manufacture silicon wafers. This is because tion of the photovoltaic junction, the addi- significant cost reductions can be action of electrical contacts, and the applica- complished with plants much smaller than tion of anti-reflective coatings.89 Studies of 50 MW/year, and it is much less likely that mass-production techniques conducted for fabricating plants would become obso-

JPL by Motorola, Texas Instruments, and lete–even if breakthroughs dramatically RCA all indicate that this cost could be reduce the cost of manufacturing silicon reduced to $0.30 to $0.90/watt90 using wafers. known mass-production apparatus, if plants The laborious and expensive processes for capable of producing about 5 to 50 MW an- making photovoltaic celIs are also extreme- nualIy were constructed. The costs asso- ly inefficient in their use of energy. Silicon ciated with each step in the fabricating material, for example, is melted when it is process are shown in table X-7. Projecting purified, cooled, and shipped to the crystal- further price reductions, however, requires a growin facility where it must be melted fair amount of optimism. It can be seen g again to grow a crystal, again cooled, from table X-4, however, that cell prices heated at least once more during cell fabri- must fall to $1 to $2/watt before there will cation, and then cooled to ambient tem- be markets large enough to support several peratures for the third time. No attempt is competing fabricating plants of the size en- made to recover any of the heat wasted visioned in the JPL studies. It is likely that when the cells are cooled. The efficiency of manufacturers wilI show greater desire to in- this process could clearly be improved vest in fabrication equipment than in the significantly to reduce both the cost of the more capital-intensive devices required to ———— cell and the time required for the cell to “’F RDA “ Photovol talcs Program “ “pay-back” the energy used in its manufac- ‘(’h! acomber, J []l., op clt , pp 71-72 ture once it is installed.

Table X-7 . —The Major Steps in Manufacturing a Silicon Photovoltaic Device

— Surface Junction Other Module prep format ion Metalization processes fabrication Totals (alternate) —.— -.——

Motorola 0.282 0.080 0.082 0.042 0.385 0871 RCA 0.003 Ion 0.044 0.101 0,045 0.114 0309 (Spin 0.081 ) to & PO CI3 0.343 (Print 0.048) Texas Instru - ments 0.035 Spin 0.048 Thik Film 0.050 0.093 Hermetic 0.272 0391 (Ion O 092) Nonhermetic 0135 to 0.586

ASSumptions I) cells would be made uslnq wafers Sliced from ingots 2) Based upon an extrapolation of present technology with reasonable development but wlthout technologicalbreakthroughs 3) 50 MW/year productlon of a slngle deslgn. 4) 14 percent cell efficiency

‘ Does not Include cost of sllicln material nor wafers

SOURCE JPL L[, h CJst Slhr(,r) Sc~lar Array Prole t (r~t mred by OTA June 19771 420 ● Solar Technology to Today’s Energy Needs

MODULE ASSEMBLY AND ENCAPSULATION Figure X.12.—Thin-Film Cadmium Sulfide-Copper Sulfide Solar Cells Finally, the process of connecting cells together into arrays and encapsulating them to protect the cells from the weather must be reduced by a factor of 10 from current costs to about $0.12/watt.91 A variety of techniques have been proposed and the cost reduction seems feasible, but the exact technique which will be used is not yet clear.

Thin Films

The nonsilicon thin-film technologies which show the greatest potential for reaching the cost goals early in the 1980’s

are all based on the CdS/Cu2S heterojunction cell. Much more work has been done on the problem of reducing the cost of manu-

facturing CdS/Cu2S than on any other thin film.

Cadmium sulfide cells are produced commercially in the United States by Solar Energy Systems (SES) of Newark, Del. These cells are produced in batch processes92 and hermetically sealed in glass. Their efficiency is 3.2 percent with an array efficiency of 2.5 percent.93 SES is attempting to keep their array prices competitive with the market price PHOTO: Courtesy of the University of Delaware of silicon arrays. An eariy prototype cell is shown in figure X-12. No technical barriers to scaling up the Photon Power, Inc., of El Paso, Tex., is current manufacturing procedures are fore- developing a chemical spray process which seen, but a significant amount of “process forms cadmium sulfide solar cell panels di- development” will be required to bring rectly on hot float-glass as it comes out of prices below $1,000/kW.94 Researchers at the glass factory. Westinghouse estimate that a factory based Photon Power has completed a pilot plant on this process capable of manufacturing in El Paso for testing the technique. If the cells for $1 to $2/watt could be producing process works as well in large- scale produc- commercial products within 2 years of a tion as it has in laboratory tests, the facility decision to initiate the project.95 will be expanded into a smalI manufacturing plant which, it is hoped, will be able to produce arrays which can be sold for $2 to “See table X-6 $5/watt by 1980.9’ Low costs are possible ‘ 2 F A Shlrland, Westinghouse Research Labs, because all of the processes in cell manufac- private communication, Mar. 26, 1976 ‘3S DiZlo (President, SE S) private comr:]unication, turing (cell growth, junction formation, ap- Apr 7 1976. “Ibid.

95F. A Shirland, Westinghouse Research Labsr 9’G. Rodrick, (President, Photon Power, Inc.), private communlcatlon, Mar. 26, 1976. private communication, March 1978 Ch. X Energy Conversion With Photovoltaics ● 421

plying contacts, and encapsulation) involve determine how much of the cadmium not spraying a series of chemical layers onto hot initially captured on the glass can be recy- glass moving through the plant on a con- cled (this is important since cadmium is ex- tinuous conveyor. Laboratory devices pro- pensive and toxic) and to determine how duced with a similar process have yielded well the hydrogen chloride, sulphur, and 5.6-percent efficiencies, and cells with 8- to sulfurous acids can be recycled. lo-percent efficiencies appear possible. ” Even higher efficiencies may result if the The French National petroleum company, prom i sing resuIts of experiments mixing zinc Compagnie Francaise des Petroles, owns with cadmium can be integrated into the controlling interest in Photon Power. Libby- process. Owens-Ford and D. H. Baldwin Co., own minority interests. Photon Power is working with Libby- Owens-Ford (a part owner of the company) Patcentre International of Hartfordshire, to design a process which can be attached England is working on a spray process very to a float-glass plant. A preliminary calcula- similar to Photon Power’s. They report S. S- tion indicated that a plant costing about percent efficiency for their laboratory de- $140 million would be able to produce 2 vices, and hope to market a commercial GW /year for $0.05 to $0.15/watt.98 00 e product in 1980. ’ The major technical challenge in increasing output will be finding a way to increase the A number of other cells, usually based on speed of the spray application process from heterojunctions between an element in the 2 cm per minute in the pilot plant by group III and group V of the periodic table, about an order of magnitude to match the are being investigated as candidate thin film rate at which glass is produced from a flat- cells, but few are beyond the stage of basic glass facility.99 It will also be necessary to laboratory research. The present performance of some of these experimental devices “G A Samara (Sandia Laboratories, Albuquerque), is shown in table X-2. Proceedings, ERDA Semiannual Photovoltaic Advanc- ed Ma reria /s Program Review A4eetlng, Wash I ngton, D C , Mar 22-23, 1977 “j F jordan, Photon Power, Inc , International Conference on Solar Electricity, Toulouse, France,

April 1976 IOOG Kaplan, IEEE Spectrum, “Power/Energy Prog- “j F Jordan, Photon Power, Inc , private com- ress Report, ” IEEE Spectrum, Vol 15, No 1, january munlcatlon, April 1976 1978, p 51

MATERIALS AVAILABILITY AND TOXICITY

Enthusiasm about cells based on mate turing, it clearly will be necessary to ex- rials other than silicon must be tempered to amine these hazards with some care before some extent by uncertainties abou‘t the recommending an energy system which health hazards which they may present and wouId significantly increase the use of these about the limits imposed on their produc- materials near populated areas. Domestic tion by U.S. and world supplies of compo- supplies of both cadmium and gallium will nent materials. Both cadmium and arsenic, be sufficient to supply annual production used in GaAs cells, are toxic and while it rates in excess of several thousand may be possible to reduce the hazards they megawatts a year but production beyond present to manageable proportions and this level could tax domestic supplies and, in whiIe both materials are already used exten- the case of cadmium, known world reserves sively in commercial products and manufac- limit the ultimate potential of CdS/Cu2S 422 ● Solar Technology to Today’s Energy Needs

devices to about the level of current U.S. creased release of cadmium from mining, re- energy consumption. fining, and manufacturing of the cell, and it would increase the amount of cadmium SILICON present in products located near populated areas, thereby increasing the risk of ex- Silicon is nontoxic and in plentiful supply posure in the event of fires, accidents, or the (about one atom in five in the Earth’s crust is demolition of buildings. a silicon atom), although current production More stringent standards may be needed rates of purified silicon are not adequate to both in manufacturing processes involving support a large solar industry. The manufac- the material and in permitting usage of the ture of silicon devices with present tech- material in commercial products. At pres- niques involves the use of a number of ent, cadmium is not subject to any environ- hazardous chemicals (PH3, BCl3, H2S 2, HCI, 101 mental controls, but under both the Toxic HCN). Existing State and Federal laws Substance Control Act (P. L. 94-469) and the should be sufficient to ensure that releases Resource Conservation and Recovery Act of these materials into the air and water are (P. L. 94-580), EPA has jurisdiction over its kept to acceptable levels, although vigi- regulation which, if instituted, could include lance will be needed to ensure compliance both solar and other household uses. with these regulations. Meeting the standards may add to the cost of the devices. It is apparently possible to significantly reduce the cadmium released in the manu- CADMIUM facturing process, and it appears that with proper encapsulation CdS cells can be used Cadmium is a cumulative heavy-metal in residential areas with minimal hazard. 105 poison with a half-life in the human body of Exposure to the material would only occur 10 to 25 years. Cadmium poisoning is be- during fires, accidental breakage, or build- lieved to lead to accelerated aging, in- ing demolition. The acceptabiIity of such ex- creased risk of cancer, heart disease, lung posure can be judged better when meaning- damage, birth defects, and other prob- ful standards have been developed. Iems. 102 Chronic exposure to airborne cadmium can lead to emphysema and other res- U.S. production of cadmium in 1970 piratory problems. 103 Cadmium, however, is could support the annual manufacture of used in many commercial and industrial cell arrays with a peak output of 5,000 to products; it is used for corrosion protection 20,000 MWe (assuming cells are lo-percent on bolts and screws, in paints, plastics, rub- efficient). World production is about five ber tires, motor oil, fungicides, and some times greater than U.S. production.106 The types of fertilizers.104 Increased use of cad- higher figure applies to the spray process for mium resulting from large-scale manufac- manufacturing cells, which results in cells ture of CdS/Cu2S cells could result in in- about 6 microns thick. Significant increases in cadmium production may be achievable, however, if demand increases. Identified 10’] G. Holmes, et al , “Environmental and Safety U.S. reserves of cadmium are sufficient to implications of Solar Technologies,” Proceedings, produce cells with an annual output equal 1977 Annual Meeting American Section of the /nterna- to the current U.S. consumption of electrici- tiona/ Solar Energy Society, Orlando, Fla., june 1977, p. 28-7 ty. Known world reserves are about five 07 ‘O’N A Esmen, et al., University of Delaware, En- times greater than U.S. reserves. ’ vironmental Aspects of Cadmium Sulfide Usage in Solar Energy Conversion– Part P– Toxicological and Environmental Health Considerations – A 13ib/iog- ‘ 05 Esmen, op. cit raphy, NSF/RANN, SE/C I 34872 /T R73/5, june 1, 1973, ) ObH .j Hovel, IBM, Semiconductors and Section I I Semimeta/s, op. cit., p. 219. ‘OJHolmes, op. clt , p, 287. 107R A Heindl, Minera/ Facts and F’rob/ems, U.S. ‘04 Esmen, op cit., section II & IV Bureau of Mines, U S. G.P.O ,1970, p 515. . . -— —

Ch. X Energy Conversion With Photovoltaics ● 423

GALLIUM ARSENIDE small. A device with a concentration ratio of 1,000 would, for example, use only about Undisassociated GaAs is harmful but ap- 0.16 gm per m2 of collector area. This con- parently not highly toxic. A lethal dose for centration is 250 to 1,500 times smalIer than an average adult is about one-third kg (0.7 the concentration of A S 20 3 recommended lb). ’08 To ingest this much GaAs, a person by the U.S. Department of Agriculture for would have to eat the amount of CaAs in weed control. 111 about 20m2 (200 square feet) of fIat-plate arrays or the amount of GaAs in a field of con- Gallium supplies should not place a sig- centrating arrays covering about 3 acres, nificant constraint on the use of GaAs de- clearly a Herculean task. The coatings and vices. U.S. consumption of gallium in 1973 protective encapsulation placed on cells was 8.5 metric tons per year, most of which should be able to reduce any hazards asso- is imported. If this amount of GaAs were ciated with normal operation of GaAs de- used to produce 50-micron-thick cells used vices to acceptable levels. in tracking collectors producing concentration ratios of 1,000, the arrays would have a The major danger arises when the peak output of about 10 GWe at an efficien- material disassociates as a result of a fire or cy of 20 percent. These arrays would have some other accident, since many arsenic an average output of about 1 percent of the compounds are highly toxic and recognized average output of all electric-generating 109 110 113 carcinogens, The AS 20 3 which would facilities in the U.S. in 1977. Domestic be released in a fire could contaminate land production of gallium could be increased and water near the fire site. Since the cells substantially if an attempt is made to ex- wouId most probably be used in connection tract the gallium associated with coal, with high concentrations of sunlight, care aluminum, and zinc ores. A recent study in- must be taken to ensure that the materials dicated that the United States could pro- do not vaporize and escape if a breakdown duce about 600 metric tons/year of gallium in the cell cooling system occurs. The from these sources. ’ So the gallium re-

amounts of arsenic used in a concentrating source is ample. World resources-of gal lium collector, however, wouId be extremely are about 1.1 x 105 metric tons.}‘5

1‘aBased on l-13j0 of 4,700 mg/kg body weight cited ‘ 1‘USDA Herblclde Manual, 1965 In the Regtstry of Toxic Effects of Chemical Sub- ‘“Y C M Yeh, j PL, private communication, Apr. stances, 1975 Edltlon, U S Department of HEW, 25, 1975 N IOSH 1 l‘H. j Hovel, IBM, Semiconductors and ‘“’N I Sax, Dangeroqs Properties of lndustrla/ Semimeta/s, op. cit , ~ 219 Materials, Fourth Edition, Van Nostrand Reinhold Co , ‘“R N. Anderson,” Available Supply of Gallium and 1975, pp 420-421 Arsenic, NASA-Langley, Contract Order No L42953A, 1‘“George L Waldbott, Hea/th Effects of En- 1976 vlronmen?a/ Pollutants, C V. Mosby Co., 1973, pp. f‘‘H j Hovel, IBM Semiconductors and Semimeta/s, 202-203 Op Clt , p 220

PERFORMANCE OF CELLS IN REAL ENVIRONMENTS Since the output of cells varies as a func- front (and possibly also the back) of the ar- tion of temperature, it is necessary to com- rays provides adequate cooling. In concen- pute cell temperatures in order to obtain an trating devices, it is usually necessary to pro- accurate estimate of the output of cells in- vide more sophisticated cooling systems. stalled in various types of collectors. The These systems can be passive [i. e., large, temperature of the cells depends on the ef- finned radiating surfaces attached to the fective heat-transfer coefficient of the cell), or active cooling can be provided by system used to provide cooling. In simple pumping liquids across the back of the cell. flat-plate systems, the heat loss from the —

424 . Solar Technology to Today’s Energy Needs

PASSIVE COOLING I D = direct normal solar intensity (kW/m2) The heat-transfer capabilities of a variety Ø i = angle between the Sun and the nor- of passive heat exchangers have been mal to the cell measured, although much more work must be done to obtain adequate data in this area. The results, shown in table X-8, are expressed in terms of an “effective heat-

transfer coefficient” ke where

2 k e=[rate of heat removal (kW/m

of heat exchanger)]/(T – Ta) (x-3)

In this, ke varies with wind speed and thus depends not only on the type of heat exchanger attached to the cells, but also on the air circulation possible in each installation. Equations (X-2, X-3, and X-4) can be combined to yield an expression for cell efficien- Table X-8.— Effective Convective Heat-Transfer cy in terms of insolation level:

Coefficients [ke] for a Variety of Cooling Systems

Device Wind velocity ke(kWjm’OC) ACTIVE COOLING Air circulating passively through metal pan If water is pumped through a heat ex- in back of cells . . . . 0 0.015 changer attached to the cells, the value of 2 Same as above ...... ‘ ‘average’ 0.025 K e can be made as high as 3 to 10 kW/m “C. Flat plate with finned With such high rates of heat removal, cell 0 metal heat-reject ion temperatures can bz maintained at 150 F surfaces ...... ‘‘average’ 0.30 (65 ‘C), even at concentration ratios near Active water cooling 1,000. The removed thermal energy avail- with ‘ ‘simple flow’ . . — 1-3 able in the cooling fluid (Q ) is given by Active water cooling A with “impingement cooling’ ...... — 3-1o

SOURCE Table prepared by OTA from data supplied by F T Bartels, (Spectrolab, Inc ,) Mar 1976.

where I is defined as before. UL is the heat In order to obtain a relation between cell loss coefficient which differs with each col- temperature T and insolation level I, an lector design. This equation assumes the energy balance is written entire receiver area is covered with cells. Tf is the average temperature of the cooling (x-4) fluid (a more sophisticated equation con- where a is the absorptivity of the encap- sidering cell coverage ratios less than unity and the difference in inlet fluid temperature sulated cell and Ta is the ambient air temperature. The value of I is given by the is developed in chapter VIII. following relations for f tat-plates or concen- The cell temperature (T) is given by trating systems: I I and the cell efficiency (n) is given by

where: Ch. X Energy Conversion With Photovoltaics . 425

PHOTOCHEMICAL ENERGY CONVERSION

Photochemical energy conversion has lustrated in figure X-13. In this system, many of the advantages of photovoltaic hydrogen is produced at the platinum energy conversion and, in addition, the ad- cathode and oxygen is generated at an vantage that the chemicals may be stored anode made from a semiconductor material for later use. However, the technology is not such as T1O3 or CaAs. Some work has also as well developed as photovoltaics, and been done on systems in which both elec- much research remains to be done. The nas- trodes are semiconductors. Other tech- cent state of photochemical energy conver- niques for generating hydrogen have also sion is compounded by the fact that public been demonstrated. Researchers at the awareness and Government funding are California Institute of Technology have both low, and thus research has been for the demonstrated that hydrogen is released most part confined to a few universities, when light strikes a complex Rhondium Research at the University of In 1972, Fujishima and Honda announced compound. 20 North Carolina at Chapel Hill has Ied to the the discovery of a process by which light development of a ruthenium compound energy incident on an electrode suspended in water could be used directly to convert which can split water into hydrogen and ox- the water into hydrogen and oxygen without ygen when applied in a monolayer to a glass surface and exposed to sunlight. ’z’ All of any noticeable degradation of the electrode.116 The original Japanese work has these processes now exhibit very low efficiencies, and long-term stability has not generated a considerable amount of interest and a number of other materials have been been demonstrated. Almost no work has examined. 117 118 been done to determine the potential cost of such systems. A system being studied by research teams The photosynthetic process used by of the Allied Chemical Corporation and Massachusetts Institute of Technology is il- plants to convert sunlight into storable fuel sources is clearly a photochemical system with great potential. Work is underway to ‘“A Fu]ishlma andhK Honda, “Electrochemical better understand the basic chemistry of the Photolysls of Water at a Semiconductor Electrode,” Nature 238, july 1972, pp 37-38 process and, of course, there is increasing in- ‘ 1‘K L Hardee and A J Bard, /, Electrochern Soc., terest in the use of plant materials as a fuel ~~q, 215 (1977) source. The use of biological materials as an 1‘EM Wrlghton and J. M. Bolts, “Characterlzatlon energy source is beyond the scope of the of Band Positions Photoelectrodes for the Photoelec- current study. trolysls of Water, ” paper delivered to the American Chemical Society, San Francisco, Calif , September 1976, and /, Phys, Chem.,/X), 2641, 1976. 1]OM Simon, “UNC Professor Patents Solar Energy ‘‘qHydrogen Production From Solar Energy, SITREP Process,” C/rape/ Hill Week/y, june 1976. Energy R&D, Report No. 154, Navy Energy and Natural ‘“’’Gray Discovers Rhodium Compound at Resources R&D Off Ice, Feb 18,1977. Caltech, ” The California Tech, Oct. 7, IW7, pp. 1,4.

28-.LI. I2 O - 28 —

426 ● Solar Technology to Today’s Energy Needs

Figure X-13. — Photochemical Energy Conversion

Phoioelectrolysls

H 2 0

* Window

Light

PlatIn um Photocatalytic electrode

SOURCE Goodenough, J B (Professor, Oxford Unlverslty, England) “The Opt Ions for Using the Sun,” Techrrology Flev/ew (Ml T.) 79(l), OctoberlNovember 1976, pp 62.71 - .— —. —

Chapter Xl ENERGY STORAGE

Chapter Xl.— ENERGY STORAGE Page Page Major Design Choices ...... 429 Appedix Xl-A...... 487 .

Thermal Storage ...... 432. Appendix Xl-B ...... 488 . Overview ...... 432 Appendix Xl-C ...... *..496 Low-Temperature Storage 0oto 150°C(32o to 302°F) ...... 432 Sensible-Heat Storage in Water...... 432 Sensible-Heat in Rocks...... 441 LIST OF TABLES Latent-Heat, Low-Temperature Storage ..442 Concentrated Solutions ...... 445 Table No. Page Thermal Storage at lntermediate and I. Proposed Thermal Storage Materials .....433 High Temperatures ...... 447 2. Phase-Change TEC Materials in the Low- Refractory Bricks...... 447 Temperature Regime With Melting Points Steel Ingot Storage ...... 449 Above 75°C (167o F) ...... 443 Heat-Transfer Oii Thermal storage ...... 451 3. Candidate High-Temperature Thermal-Energy Refined Fuel Oii Thermal Storage ...... 451 Storage Materials Without Phase Change .449 Latent-Heat Systems...... 453 4. Commercial Organic and inorganic Heat- Environmental Concerns ...... 458 Transfer Agents...... 452 Thermochemical Storage...... 459 5. Properties of Latent-Heat Thermal Storage Background ...... 459 Materials ...... 456 Design Alternatives...... 461 6. Candidate Chemicat-Energy Storage Summary ...... 464 Reactions ...... 462 7. Conventional Hydroelectric Capacity Electric Storage ...... 464. Constructed and Potentiai at Existing Mechanical Storage Devices ...... 466 Dams...... 469 8. Economic Specification (5-hr Battery) ....471 Battery Storage...... 469 9. Load-Leveling Battries: Candidates and Lead-Acid Batteries...... 470 Advanced Batteries...... 472 Characteristics; Developers and Demonstra- tion Dates ...... 473 Power Conditioners...... 477 10. Loss Mechanisms of iron-REDOX Design Alternatives...... 477 Batteries ...... 477 System Performance...... 480 11. System Cost Estimates for Near-, Battery System Costs...... 481 Intermediate-, and Long-Term ...... 482 B-1. Thermal Properties of Soils ...... 492 12. A High-Temperature Thermal Storage C-1. Assumptions for Hot Fuel Oil Thermal Device Designed for Residential Use ... ..450 Storage, Single Family House ...... 498 13. Steel-ingot, Sensibie-Heat Storage System 450 C-2. Assumptions for Therminol-55/Rock 14. Steei-ingot Temperature Profiles at Various Thermal Storage ...... 498 Times in a Typical Cycle...... 450 C-3. Assumptions for Steel-Ingot Thermai 15. The High-Temperature Heat Storage System Energy Storage ...... 500 at the Sandia Total Energy Experiment. . . . 454 C-4. Containment Materials ...... 501 16. Design of “Therm-Bank” Space Heater , .. 454 C-5. Latent-Heat Storage Tank Assumptions. . 501 17. Philips Latent-Heat Storage System With C-6. Assumptions for NaOH Latent-Heat Vacuum Multifoil Insulation...... 455 Storage ...... 502 18. Thermodynamic Behavior of Candidate

C-7. Assumptions for NAF/MgF2 Latent-Heat Latent-Heat Storage Salts ...... 457 Storage ...... 502 19. Use of a Sodium Heat Pipe With a Latent- Heat High-Temperature Thermal Storage System ...... 458 LIST OF FIGURES 20. Typical Thermochemical Storage Technique ...... 460 Figure No. Page 21. High-Temperature Thermal Storage Cost

1. Possible Locations for Storage Equipment per kWht Versus Storage Capacity ...... 465 in Onsite Solar Energy Systems...... 430 22. An isometric View of an Underground 2. Vertical Tank in a Drilled Hole With Foamed- Pumped Storage Plant ...... 467 in-Place Insulation ...... 434 23. Conventional Hydroelectric Capacity Poten- 3. Installation of insulated, Underground, Storage tial at Existing Dams...... 468 Tank at Solar Heated and Air-Conditioned 24. iron-REDOX Battery Structure and Plumbing Burger King, Camden, N.J...... 435 Diagram ...... 476 4. installation of Fiberglass Underground 25. Model of iron-REDOX Battery Facility. .. ..478 Tanks ...... 436 26. The Elements of a Power Conditioning 5. Cost of Buried Tanks ...... 437 System ...... 479 6. Megatherm Pressurized-Water Heat-Storage 27. Efficiency of a Solid-State Inverter as a Tank ...... 439 Function of Load ...... 480 7. Predicted Performance of an Aquifer Used 28. Power-Conditioning Cost Versus Power .. 483 for Thermal Storage ...... 440 A-1. Permissible Cost of Storage Equipment 8. Potential Sites for Aquifer Storage as a Function of Energy Prices During Systems ...... 441 Storage Charge and Discharge ...... 487 9. Osmotic Pressure Engine ...... 446 B-1. Thermal Conductivity of Insulation...... 490 10. Heat of Mixing Engine ...... 447 B-2. Annual Thermal Losses From Uninsulated 11. Low-Temperature Thermal Storage Cost Storage Tank ...... 493

per kWht Versus Storage Capacity ...... 448 B-3. Rate of Heat-Loss to Ground ...... 493 Chapter Xl Energy Storage

MAJOR DESIGN CHOICES

Energy can be stored in thermal form by heating or chilling liquids or solids; in mechanical form by using mechanical or electrical energy to pump water to high reservoirs, spin flywheels or compress air; and in chemical form by driving battery reactions, producing hydrogen or other chemicals to generate heat, or by distilling solutions. This chapter discusses a range of storage technologies which could have a major impact on the cost and performance of onsite solar energy systems during the next 10 to 20 years; it does not attempt to review all possible storage technologies. Most of these approaches require specialized storage equipment, but in some cases it may be possible to integrate storage into mechanical structures which serve other functions. Careful architecture can increase the inherent ability of walls and floors, for example, to store thermal energy. Energy can be stored at a variety of points in an onsite solar system and some of the opportunities are presented in figure Xl-1. The options for the heat engine system are most complex: 1. Energy can be stored at relatively high temperatures before it is used by a heat engine. In this form, high-temperature storage is equivalent to a supply of fossil fuel. 2. Heat rejected by the engines can be stored at relatively low temperatures. 3. Electricity generated by the system can be stored in batteries or other electric storage devices.

It is unlikely that all three types of storage would be used in a single instal I at ion.

Storage systems can provide a useful buf- at night. It can also mitigate the rapid , fering role, regardless of whether solar temperature changes which can result energy is used, since the timing of demands from sudden fluctuations in the Sun’s and the timing of generation desirable for intensity during periods of partial peak performance of generating equipment cloudiness. seldom coincide, Most of the equipment dis- 2. Storage equipment can be used to cussed in this chapter was developed for sys- make more effective use of generatin tems in which solar energy played little or g equipment. As noted earlier, without no part. storage the output of generating equipment must be continuousl adjusted to Some of the uses of storage are: y meet fluctuating demands. This means 1. Storage in solar devices can be used to that generating equipment is either idle provide energy during cloudy periods or operating at part capacity much of and at night. Storage can also be used the time— resulting in higher electric to facilitate starting large solar turbine costs since capital charges must be systems in the morning by preheating paid on the equipment, even if it is not the equipment and to allow a gradual used. Operating plants frequently be cooling of the system when it is closed low full capacity also means that the

429 —

430 ● Solar Technology to Today’s Energy Needs

Figure Xl=1.—Possible Locations for Storage Equipment in Onsite Solar Energy Systems

Thermal Thermal Collector Loads

Low Temperature Storage I A

Chemical Transport

Thermal Heat Electric Collector Engine Loads

Thermal Loads

High Low Temperature Temperature Storage I Storage

Hot Water Transport Electric Transport

Photovoltaic Electric Cells Loads Cell Cooling

Electric Storage Temperature Storage I Thermal Loads I

Thermal Transport Ch. Xl Energy Storage ● 431

generators are not operating at peak ef- “stored” inexpensively in tanks of ice or ficiency. Most large coal and nuclear chilled water. plants cannot readily be adjusted to Storage in this form will not be used un- meet changing loads; demand fluctua- less prices to consumers are changed during tions must be met with generating the day to reflect the fact that electricit equipment which burns oil or gas— y costs less to generate during off peak hours fuels which are becoming scarce and at night than it does during the day when expensive. demands are large. These simple storage devices are extensively used in Europe and Generating capacity can be reduced with Great Britain, where such “time-of-day” storage equipment if the storage is filled rates have been in use for many years and while capacity exceeds demand, and dis- are beginning to be marketed in the few charged during periods of high demand. In parts of the United States where these rates electric utilities, this means that gas- and oil- are being introduced. 3 burning plants can be replaced by storage charged from coal or nuclear plants func- (The circumstances under which storage tioning at close to their top output all year. devices can be used economically in load- In the case of solar collectors, it means that Ieveling applications are discussed in appen- collectors can be sized to meet average dix Xl-B.) demands instead of peak demands. 3. Storage can improve the performance of heating, cooling, and other energy- With the exception of pumped hydroelec- consuming equipment in much the tric storage, no electric storage* device is same way that it can reduce the cost of now economically attractive to electric util- generating electricity. Without storage, ities. The rising cost of oil and gas as well as the equipment must be large enough to progress in storage technology may reverse meet peak demands. This means that this situation in the near future however, the equipment must be operated at less and the industry will demonstrate a number than its maximum capacity much of the of advanced systems during the next few time, increasing the need for generating years. The possibilities have been reviewed equipment and decreasing system effi- in two recent studies sponsored by the Elec- ciency. Storage can have the additional tric Power Research Institute (EPRI).l 2 benefit of permitting heat-pump devices and air-conditioning devices to Electricity which will eventually be used operate when ambient conditions are for electric resistance heating can be stored most favorable. Air-conditioning sys- very inexpensively by using the electricity to tems, for example, are much more effi- heat water or bricks in onsite storage de- cient at night when ambient air temper- vices. EIectric air-conditioning can also be atures are relatively low.

— * The term “electric storage” IS used throughout this chapter to mean storage which IS charged by and which discharges elect rlclty, even though the energy In the storage device IS not I n the form of electricity ‘Ralph Whitaker and j Im Blrk (E PRI), “Storage Bat- teries The Case and the Candidates, ” EPR/ /ourna/, October 1976, p 13 ‘An Assessment of Energy Storage Systems Suitable 3 Wi II iam H. Wilcox, statement delivered to the for Use by E/ectr~c Utllltfes, EPRI project 225, ERDA E Pennsylvania Public Utlllty Commlsslon (76 (11 -1 }2501 , ) Uly 1975 P, R.M. D -7), jUIY 25,1977 432 Solar Technology to Today’s Energy Needs

THERMAL STORAGE

OVERVIEW from storage could be expensive, however, if expensive catalysts are required. Chemical There are three basic approaches to stor- storage can be expensive if some of the ing thermal energy: chemicals which must be stored are in the form of gases requiring large pressurized ● Heating a liquid or solid which does not tanks. melt or otherwise change state during heating. (This is called “sensible-heat” A number of promising reactions are be- storage, and the amount of energy ing examined, however, and there is reason stored is proportional to the system’s to be optimistic that an attractive technol- temperature. ) ogy can be developed. Research in this area is in a formative stage. ● Heating a material which melts, vapor- izes, or undergoes some other change Table Xl-1 summarizes some of the mater- of state at a constant temperature. (This ials and approaches which have been sug- is calIed “latent-heat” storage. ) gested for thermal energy storage,

● Using heat to produce a chemical reaction ‘which will then release this heat LOW-TEMPERATURE STORAGE when the reaction is reversed. 0° to 150°C (32° to 302° F) Equipment for storing energy as sensible Sensible-Heat Storage in Water heat can be simple and relatively inexpensive if fluids are stored at temperatures be- A variety of techniques have been exam- low 400o F. One difficulty with sensible- ined for storing relatively low-temperature heat storage is that it can be difficult to en- thermal energy, but the use of water as the sure a constant output temperature. storage medium for liquid systems has been the dominant approach and is likely to re- If a constant temperature is desired to 4 5 main so for at least a decade. Most solar operate a heat engine, or for some other pur- heating and hot water systems use an in- pose, two separate storage tanks are re- sulated hot water tank located in the build- quired: one to store the hot liquids and one ing equipment room or buried in the ground. to store the low-temperature fIuids emerging Figure Xl-2 shows a cross section of a typical from the engine. instalIation, and figures Xl-3 and Xl-4 show Latent-heat storage can supply energy at the installation of steel and fiberglass tank. constant temperature from a single con- Tanks can be made from a variety of materi- tainer and can usualIy store greater amounts als, and the costs of a number of commer- of energy in a given volume or weight of cially available containers are summarized material. The materials used, however, are in figure Xl-5. It may be possible to reduce relatively expensive and problems are en- the cost of large tanks significantly by sim- countered in transmitting thermal energy in- ply lining an excavation with a watertight to and out of the storage medium.

Chemical storage techniques can be used ‘C L Segaser (Oak Ridge National Laboratory), at a great variety of temperatures and have Thermal Energy Storage Materials and Devices, OR NL- the advantage of allowing storage of reduc- HUD-M IUS-23, August 1975 tion products at ambient temperatures ‘George C. Szego, “Hot Water Storage Systems Croup Report, ” i n Proceedings of the Workshop on (eliminating the need for expensive insula- Solar Energy Storage Subsystems for the Heating and tion). Chemical energy can also be trans- Cooling of Buildings, NSF-RA-N-75-041, ASH RAE, Apr ported conveniently. Recovering energy 16-18,1975, pp 17-23. Ch. Xl Energy Storage 433

Table Xl-1 .—Proposed Thermal Storage Materials — —.. — Temperature Regime

200 o-350 oC (392°-662oF) 0“-15 “C (32 0-500 f=) 30 o-150 oC (86°-302oF) (heat engines and Storage (stores cooling (process heat and low- process heat, absorption 400 ”-1,000 oC(752o-1,832 oF) type for air-conditioning) temperature heat engines) air-conditioning ) (heat engines) — ..—— -. -— — ———

Sensible — water —pressurized water —fuel oil — rocks heat — rocks —organic heat-transfer —steel liquids (e. g., —heat-transfer salts Therminol, etc. ) (e. g., HITEC) — rocks —steel —pressurized water

Latent –C14/C16 — Inorganic salt, — NaOH — in organic compounds

heat paraffin hydrate eutectics (LIH, NaOH, KN02/

— 1 -Decanol (e. g., CaCI2 6H20) NaN02) —other paraffIns —organic compounds —eutectic salts — Inorganic salt, (e. g., paraffin & (LiF, NaF, etc. ]

hydrate eutectics CC14) — ice

Chemical —metal hydrides CO + H2‘CH4 + H2 0

react ion (e. g., LaNi5H 2) 2S03 = 2S0 2 + 02 —.

(and possibly insulating) material. Plastic in- much as a year for the earth around a large sulations (such as polyurethane) can simply storage tank to reach equiIibrium by heating be floated on the surface of the thermal lake and drying, and a considerable investment thus produced. of energy may be required to achieve this equiIibrium. ’ Earth insuIation is examined in Insulation can represent a significant part greater detail in appendix Xl-B. of the cost of small water tanks, but in very large devices (i. e., in systems capable of The value of a sensible-heat storage sys- holding more than about 30,000 kWht or tem is increased if it is able to return energy about 160,000 gal. ) the insulating value of at a temperature close to the temperature at dry earth surrounding the tank may be ade- which fluids were delivered from the collec- quate. The insulating value of dry soil 10 tors. meters (33 feet) thick is roughly equivalent One way of doing this is simply to use two to that of a layer of polyurethane foam 30 storage tanks, one of which holds water at a cm (12 inches) thick. Very dry, low-conduc- relatively low temperature (i. e., at the tem- tivity soil would be equivalent to 1.3 m (4.3 perature of fluids returned from heating ft) of polyurethane. The heat conduction of radiators) and another which holds fluids moist soil should decrease to this value as it emerging from the CoIIectors, This is more is heated by energy escaping from the tank expensive, although it does not necessaril and dries out. b Since most buildings are y require doubling the cost. In a large system, located in areas where ground water is quite several tanks may be needed to provide ade- deep, earth insulation may be able to pro- quate storage. All that is needed in this cir- vide the bulk of the insulation required for cumstance is to maintain one empty tank large thermal storage systems. It must be for shifting liquids from hot to cold storage. recognized, however, that it can take as

‘j Shelton, “Underground Storage of Heat In Solar Heating System s,” So/ar Energy, 17 (2), 1975, p 138 ‘Shelton, op clt , p 143 434 . Solar Technology to Today’s Energy Needs

Figure Xl-2. - Vertical Tank in a Drilled Hole With Foamed= in= Place Insulation (for cohesive soils only)

Vent Q

Welded nipples for input-output, heat exchangers, vents, instruments, etc.

Steel tank shell w/fiberglass coating

Alternate shells:

Fiberglass pipe asbestos cement pipe reinforced plastic mortar precast concrete pipe

~ 5’ – 15’ Diameter

Typical Capacities

4’ Diameter x 10’ Depth – 940 Gallons 6’ Diameter x 12’ Depth – 2,538 Gallons 8’ Diameter x 16’ Depth — 6,015 Gallons 10’ Diameter x 30’ Depth — 17,624 Gallons

Vertical tank in a drilled hole foamed-in-place insulation (for cohesive soils only)

SOURCE: E. E. Pickering, “Residential Hot Water Solar Energy Storage,” Proceedings of the Workshop on Solar Energy Storage Subsystems for the Heating and Cooling ot Buildings, NSF-RANN-75-041, Awl 1975, PP. 24-37

436 ● Solar Technology to Today’s Energy Needs

Figure Xl-4.— Installation of Fiberglass Underground Tanks

During Construction, a 1,500gallon underground water storage tank is eased into position at a prepared excavation. The tank, made of lightweight resin-reinforced fiberglass, is one of the two installed as part of the solar climate control system.

SOURCE: September 1976 Solar Engineering, page 23.

Such a device would require a control sys- tank systems involve the use of internal par- tem and a series of adjustable valves. titions or one-way valves inside the tanks.9 Another method being studied involves In most single-tank systems, the cold maintaining a gradient in the density of a water returning from a heating system mixes salt mixture inside the tank. Heated, high with the hot water in the storage tank, grad- concentrations of salt remain near the bot- ualIy lowering the temperature of the fluids. tom of the storage tank if the drop in density It would be desirable to maintain a tempera- due to heating is offset by the higher density ture gradient across the tank. A recent set of resulting from the salt mixture. System sta- measurements on the behavior of a typical bility has been difficult to maintain and ex- vertical cylindrical tank indicated that while periments are continuing. the water in the tank did not maintain a perfect “stratified” temperature gradient, Given that the technology of large ther- the hot and cold liquids did not mix com- mal-storage devices is simple, and its poten- pletely, and a substantial temperature gra- tial for energy savings so great, the small dient remained. ’ amount of work done in the area is astonish-

Most techniques suggested for increasing the temperature gradients possible in single- ‘Sui Lin, “An Experimental Investigation of the Thermal Performance of a Two-Compartment Water Storage Tank,” Proceedings, the 1977 Annual Meeting ‘Warren F. Philips and Robert A. Pate, “Mass and of the American Section of the International Solar Energy Transfer in a Hot Liquid Energy Storage Sys- Energy Society (l SE S), Orlando, Fla., june 6-10, 1977, terns, ” Proceedings, 1977 Meeting of the American p. 17-1. Section of the International Solar Energy Society, IOD. L. Elwell, “Stability Criteria for Solar (Thermal- Orlando, Fla , june 6-10,1977, p. 17-6. Saline) Ponds,” /SES, p. 16-29. Ch. Xl Energy Storage ● 437

0 N

o T a) m

‘al

0 o . m0 438 . Solar Technology to Today’s Energy Needs

Ing. Possibly the field is not sufficiently If a deep aquifer is able to withstand high romantic. pressures, it may be possible to store fluids at temperatures as high as 200‘C (3920 F), It is possible to store water at tempera- but it is more likely that somewhat lower tures above the boiling point if pressurized temperatures will be used. 16 tanks are used. A number of such pressurized storage systems are available in Euro- It should be possible to recover 70 to 90 pean markets’ and a device manufactured percent of the energy injected and to main- by the Megatherm Corporation of East Pro- tain a reasonable thermal gradient across vidence, R. l., is now available on the U.S. the aquifer (the warmest water will tend to market. The Megatherm device, which is il- fIoat to the top of the structure). lustrated in figure Xl-6, stores water at tem- Since the only investment required for peratures up to 280° F (138 ‘C).12 13 The such a storage device is a series of wells for device is sold to institutions which can use injecting and withdrawin water, storage interruptible electric service or take advan- g costs can be very low. There is some dis- tage of “time-of-day” rates (see chapter V). agreement about the cost of constructing Water storage is probably not an attrac- such systems, but costs could be as low as 17 tive option for storage above 1500 to 200‘C $0.03/kWh t -- with power costs in the range (300 0 to 400° F) since the pressure required of $5/kW.18 Pumping energy should be in the would greatly increase the cost and danger range of $0.01/kWh (1970 dollars). of operating such systems. Local ordinances Aquifers adequate for thermal storage ap- frequently require all water tanks which plications are found in wide areas of the operate at temperatures above 2000 F, con- country (see figure Xl-8). It should be possi- tain more than 120 gallons, or require more ble to use aquifers of brackish water as well than 2 X 105 Btu/hr inputs to comply with as freshwater wells and, since there is little ASME low-pressure heating boiler codes. ” net consumption of water in the storage Pressure above 50 psia may require the pres- process, the technique will not deplete the ence of a trained operating engineer. water resources of a region or lower water An EPRI study examined the feasibility of tables. The environmental impact of these using steam accumulators to store heat for systems has, however, never been system- later use in a standard steam-electric gener- atically addressed. ating plant and concluded that in this ap- While a number of theoretical studies of plication, storage systems using fuel oil as aquifer storage systems have been under- the storage medium were less expensive. 5 taken, 192021 there have been few field tests. It may also be possible to store very large One large-scale experiment has been under- amounts of low-temperature thermal energy by pumping hot water into contained underground aquifers, as illustrated in figure Xl-7. “W. Hauz and C F Meyer, “Energy Conservation: Is the Heat Storage Well the Key, ” Public Ut///eses Fortnight/y, Apr. 24,1975. ‘1A W Goldstern, Steam Storage /nsta//ations, “General Electric Corporation, Heat Storage We//s Pergamon Press, 1970. Using Sa/ine and Other Aquifers, presentation to the ‘*The Megatherm Corporation, East Providence, U.S. Department of the Interior, Mar 5, 1976 R.1 , )Uly 1976 1‘General E Iectric Corporation, op. clt 1‘Therma/ Energy Storage Materials and Devices, “C. F. Meyer and D K. Todd, “Conserving Energy OR NL-HUD-MIUS-23, August 1975, pp. 9-10. with Heat Storage Wells, ” Environmental Science and 14 ASME, “Heating Boilers, ” ASME Boi/er and Pres. Technology, 7, p512, sure Vesse/ Code, Section IV, New York, N. Y., 1968. 20C. F. Tsang, et al,, Numerica/ Mode/ing of Cyc/ing 1‘An Assessment of Energy Storage Systems Suitab/e Storage of Hot Water in Aquifers, EOS, 57,918 for Use by E/ectric Uti/ities, EM-264, E PRI Project 225, “C. F. Tsang, et al,, “Modeling Underground Stor- ERDA E (11-1 }2501, Final Report prepared by Public age in Aquifers ot Hot Water from Solar Power Sys- Service Electric and Gas Company, Newark, N j , Vol. terns, ” Proceedings, the I SES 1977 Annual Meeting, p. 11, Jllly 1976, pp 4-45 16-20. Ch. Xl Energy Storage 439

—

I x 440 . Solar Technology to Today’s Energy Needs

Figure Xl-7.— Predicted Performance of an Aquifer Used for Thermal Storage

Injection Temperature 200 i

160 I . 120 . A Daily cycle (24 hours) A Daily cycle (24 hours) O Semi-annual cycle, partial O Semi-annual cycle, partial 80 penetration penetration . v Semi-annual cycle, full v Semi-annual cycle, full penetration penetration ● Yearly cycle, full . Yearly cycle, full 40 40 . penetration penetration

0 0 1 1 I 1 1 1 2 3 4 5 1 234 5 Cycle Cycle Temperature at the end of each production period (min!mum pro- Percentage of energy recovered over energy Inlected versu> ductlon temperature) versus cycle number cycle number

SOURCE’ C, F Tsang, et al., “Modeling Underground Storage in Aquifers of Hot Water from Solar Power Systems, ” ISES Proceed{rrgs of the 1977 Annual Meeting, page 16-20.

DRAWfNG FROM: Walter Hauz and Charles F Meyer, “Energy Conservation: Is the Heat Storage Well the Key?,” Publlc UfWt~es Fortrr/ght/y, Apr 24, 1975, p 34. Ch. Xl Energy Storage ● 441

Figure Xl-8. - Potential Sites for Aquifer Storage Systems (Aquifers In the Shaded Areas Should Have Adequate Water Flow)

SOURCE: Geraghty, et al., Water At/es of the United Stares, Water Information Center, Port Washington, N. Y., 3rd Ed., 1973. taken near Bucks, Ala. Approximately 2.4 large volumes of heated water in plastic million gallons of warm water were injected bubbles suspended in a lake. into an aquifer and stored at a temperature of 105” to 1070 F (41 0 to 42 “C) and stored Sensible-Heat in Rocks for 30 days. About 65 percent of the energy Energy can be stored at low and inter- was recovered when the water was pumped mediate temperatures by heating rocks held 22 unfortunately, the out of the formation. in insulated containers. Rock storage is typ- water used in the test was taken from a local ically used with solar heating systems using river and contained small clay particles air to transfer heat from collectors to stor- which began to clog the aquifer after about age since the rocks can be heated by simply 2 million gallons (7.6 million liters) of water blowing air through the spaces between the had been injected. The test was stopped rocks. (If Iiquid is used in the collectors, a when injection pressures became excessive. more elaborate heat-exchange mechanism is The experiment will be repeated using required. ) Rock storage can be both simple water from an aquifer in the same region and inexpensive, but designing an optimum which does not contain clay particles capa- system can be difficult since the perform- ble of plugging the aquifer. If all goes well, ance is affected by the shape, size, density, about 20 million gallons will be injected specific heat, and other properties of the over a period of 2 months. rocks used. 23

Swedish engineers have recently suggested that it may also be possible to store

“W D Eshleman, et, al., A Numerical Simulation of 22 F MOIZ Department of C ivi I Engineering, Au bum Heat Transfer in Rock Beds, ISES, Proceeding of the University, private communication, November 1977 1977 Annual Meeting, p. 17-21.

‘2 R.842 () - 2~ 442 ● Solar Technology to Today’s Energy Needs

It may also be possible to store large Iiminary calculations have indicated quantities of sensible thermal energy in un- that performance of the storage bed derground rock formations using a tech- would be optimum if the rock particles nique which is essentially the solid-state are about 0.3 cm (0.1 inch) in diameter. equivalent of the aquifer storage discussed It has been estimated that energy could previously. A number of schemes have been 24 25 be stored in these formations at tempera- proposed for storing energy in this way: tures up to 500‘C (9320 F). The cost of the ● Digging deep parallel trenches into dry system will vary from site to site, but it may earth (or land which is “dewatered” be possible to build devices for $0.03 to with a pumping well) and filling these $0.09/kWh and $150 to $400/kW, if the stor- trenches with crushed rock. The age cycle involves removing air at a temper- crushed rock would be heated from a ature of 500‘C above the temperature at series of distribution pipes buried with which it was injected.2s If a temperature the crushed rock, and heat would be swing of only 50‘C is used, storage costs removed by blowing air through similar would be on the order of $.30 to $.90/kWh. buried pipes. Latent” Heat, Low=Temperature Storage ● Excavating a large area in sandy soil, depositing a layer of material which An enormous variety of phase-change ma- can prevent ground water from entering terials have been examined for possible use the excavation, and filling part of the in low-temperature storage systems .27 28 29 30 excavation with crushed rock. An in- The properties of a selected set of these ma- sulating layer would be placed on top terials are summarized in table Xl-2. Phase of the rock. (This scheme would lead to change materials used in low-temperature a significant change in local topog- applications are of three basic types: in- raphy. ) Hot air distribution pipes would organic salt compounds, complex organic be buried in the layer of crushed rock. chemicals (such as paraffins), and solutions of salts and acids. Water itself can be used ● Digging tunnels through layers of sand- as a latent-heat storage medium to store stone or other porous rock in naturally “coolness;” the latent heat of melting ice is occurring formations. I n one proposal, 0.093 kWh/kg. the rock is heated by sending hot air through pipes located in an interme- A successful latent-heat system must have diate plane in the rock formation. The the following properties: 31 air passes through the rock formation and is returned through a piping network on planes above and below the in- “Hardy, op. cit , p. 590. jection plane. Heat is removed in the “Maria Telkes, Thermal Energy Storage, IECEC 1975 same way when cold air is introduced in Record, p. 111 the intermediate plane. 28D. V Hale, et al , Phase Change Materials Hand- book, NASA-CR-61 36. Lockheed Missiles and Space ● Caverns of crushed rock could be pro- Company, September 1971 duced by drilling and blasting under- “C L Segaser, MIUS Technology Evaluation: Ther- ground rock layers if the rock layers mal Energy Storage Materia/s and Devices (ORN L- available were not suitably porous. Pre- HUD-M IUS-23), August 1975, p. 28 ‘OH C. Fisher, Thermal Storage Applications of the IceMaker Heat Pump, Oak Ridge National Laboratory, “M P Hardy, et al , ‘ Large Scale Thermal Storage 9-30-76. (Paper prepared for presentation at Penn- In Rock Construct Ion, Utilization and Economics, ” sylvania E Iectric Association, Harrisburg, Pa. ) 12th /ECEC Conference, p 583. “Harold Lorsch, Conservation and Better Utiliza- ‘5M Rlaz, et al,, “High Temperature Energy Storage tion of Electric Power by Means of Thermal Storage In Native Rocks, ” Proceedings, the I SES joint Con- and Solar Heating – Final Summary Report, ference Sharing the Sun–Solar Technology in the NSF/RAN N/SE/G 127976/PR73/5, j uly 31, 1975 Some Seventies, Volume 8, p 123 (1976) Pergamon Press phrases taken verbatim. Ch. Xl Energy Storage ● 443

Table X1-2.—Phase-Change TEC Materials in the Low-Temperature Regime With Melting Points Above 75°C [167°F] — Latent heat of Melting point phase change TEC material Class Lab test* “C “F (Cal/G) (Btu/lb) — — — ———. .

Mg(N03)2 6H20 . inorganic compound S 89 192.2 NA NA Ba(OH)2. 8H20. . inorganic compound G 82 179.6 63.5 114.3 N H4Br(33.4% ) CO(NH2)2 . . . . . inorganic eutectic G 76 168.8 NA NA Acetamide (CH3 CONH2 ) . organic compound s 82 179.6 NA NA Naphthalene (C10H 8 ) ., ... . . organic compound G 83 181.4 35.3 63.5 Propionamide (C2 H 5 CONH2 ) organic compound G 84 183.2 40.2 72.3

— —— —

NOTES NA — not available ‘S — satisfactory performance G — good performance

SOURCE Hoffman (Oak Ridge National Laboratories), prepared for OTA, 1976.

A melting point within the desired tem- tems is limited by the fact that the storage perature range. medium usualIy begins to solidify on the surface of heat exchangers; the layer of solid A high heat of fusion (this reduces stor- material acts as an insulator. Designs for in- age volume and material demands). creasing effective heat exchange areas have Dependability of phase change (a melt usually involved “microencapsulation” (in should solidify predictably at the freez- which the storage medium is separated into ing point and shouId not supercool). a number of smalI containers suspended in a heat exchange medium) or shallow trays. Small volume change during phase transition (a volume change makes The General Electric Company has recent- heat-exchange difficult, and can place ly proposed another approach. In their sys- stress on the storage containers; most tem, the phase-change materials is con- materials increase in density when they tained in a series of long, cylindrical con- freeze, but water and gallium alloys ex- tainers which rotate (typically at 3 rpm) to pand). keep the material mixed and to maintain a uniform temperature throughout the mix- Low-vapor pressure (some materials ture. GE claims that with this approach, have high-vapor pressures near their solidification begins at a number of nuclei melting points, placing stress on con- distributed throughout the Iiquid and not on tainers). the walls of the cylinders, If the latent-heat medium is a mixture, it must remain homogeneous; i.e., its INORGANIC SALT COMPOUNDS parts should not settle out. Inexpensive salt mixtures have the poten- has proven difficult to combine all of tial of requiring up to 100 times less volume these properties in a single system. for low-temperature storage than a simple The rate at which energy can be with- sensible-heat, water-storage system. The dis- drawn from many phase-change storage sys- advantage of all such systems compared 444 . Solar Technology to Today’s Energy Needs

with simple water storage is the need to use Many of the clathrates examined do not more complex heat exchangers, nucleating appear to melt in temperature regions useful devices, and corrosion-resistant containers for heating or cooling applications. (if corrosive salts are used). The two cate- A technique for encapsulating a proprie- gories of salt solutions which have received tary mixture of Glaubers salts, fumed silica, the most attention are inorganic salt and other chemicals (melting temperature hydrates and clathrate and semiclathrate 730 F (230 C) in a polymer concrete shell has hydrates. been developed by the Massachusetts insti- If the concentrations of the components tute of Technology working in cooperation of a mixture are adjusted so that the mixture with The Architectural Research Corpora- attains its lowest possible melting point, the tion of Livonia, Mich., and the Cabot Cor- mixture is termed “eutectic. ” In such a mix- poration of Billerica, Mass. The storage ture, melting occurs at a constant tem- elements are formed into units the size of perature. 32 standard ceiling tiles (2 ft x 2 ft x 1 in) and are designed to be installed as ceiling tiles in Inorganic salt hydrates are crystalline passively heated solar buildings. They store compounds of the general form S • nH O, 2 2 about 0.7 kWh/m of ceiling area, and where S is an anhydrous salt. The hydrate 2 should sell wholesale for about $32/m in ini- dissolves when these compounds are tial production (about 13 times the cost of heated, absorbing energy. standard acoustical ceiling tiles). The de- Clathrate and semiclathrate hydrates are vices thus have an effective storage cost of compounds in which water molecules sur- $39/kWh storage capacity. MIT does not ex- round molecules of materials which do not pect prices to fall rapidly; apparently mate- strongly interact with water. These materials rial costs already represent a large fraction melt in the range of 00 to 30‘C (30 to 860 F) of the cost of production. While the tiles and have heats of fusion which are in the can be hung on hangers similar to those now range of 78-118 Btu/lb; most have not been used for acoustical ceiling tiles, their greater studied in detail. 33 Materials suitable for use weight, which is 54kg./m2, requires the use of in connection with space heating (melting heavier gauge hangers. points in the range of 30° to 48‘C (86° to The tiles, which will be marketed under 1180 F) and heats of fusion in the range of 66 the trade name “Sol-Ar-Tile,” have been to 120 Btu/lb.) include Na S0 . 10H 0 2 2 4 2 demonstrated in a 900 ft passively heated (Glauber’s salts), Na HP0 . 12H 0, and 2 4 2 solar house built by MIT’s Architecture De- CaCl ● 6H 0. Materials suitable for storing 2 2 partment. Timothy E. Johnson, who heads “coolness” (melting points in the range of the project, reported in May 1978 that tiles 130 to 18‘C (550 to 750 F) and heats of fu- suffered no deterioration after accelerated sion in the range of 70 to 80 Btu/lb. ) include lifetime testing, in which the tiles underwent eutectic salt mixtures such as mixtures of 2,400 freeze-thaw cycles. The building uses Na S0 /10H 0/NaCl, and Na SO /10H O/- 2 4 2 2 4 2 specially designed window blinds which re- KCI.34 fleet sunlight from the southern windows to “See, for example, Walter J. Moore, Physica/ Chemi- the ceiling. Johnson claims that the phase stry, 3rd edition, Prentice-Hal 1, 1964, p. 148. change medium is nontoxic. 35 “M. Altman, et a[,, Conservation and Better Utiliza- tion of Electric Power by Means of Thermal Energy Storage and Solar Heating, Final Summary Report, ORGANIC COMPOUNDS NSF/RANN/SEGl 27976/PR73/5, University of Penn- sylvania, National Center for Energy Management Organic compounds can also be used for and Power, July 31, 1973, pp. 6-51 storing energy as latent heat. These mater- “Segaser, op. cit., p, 30. ials have the advantage of relatively high ‘ST. E. Johnson, MIT, private communication, May heats of fusion, and few of the materials ex- 1978, R. Stepler, “Solar Lab Soaks Up Sunshine With Exotic New Materials,” Popu/ar Science, June 1978, amined present problems of supercooling or pp. 96-98. high vapor pressures. Unfortunately, some Ch. Xi Energy Storage 445

of the most attractive organic materials also been proposed that a device similar in under consideration (e. g., paraffins) have a operation to an absorption air-conditioner relatively large volume change upon melt- could be used to provide heat from such ing (nearly 10 percent in some cases), are storage, using an “absorption heat pump.”43 flammable, and can cause stress cracking if All such systems would require three storage the containment vessel is not constructed tanks: one for the concentrated solution, from a material as strong as steel. Experi- one for water, and one for the dilute solu- mental paraffin storage systems, however, tion. The storage would not require insula- have been operated successfully. 36 tion.

Materials suitable for heating include ar- It is believed that approximately 65 Btu/- tificial spermaceti (manufactured by Lipo pound of LiBr) could be stored in a system Chemicals) and paraffin wax (possibly mixed which uses sunlight to distill a solution of 66 with carbon tetrachloride). These materials percent LiBr to 54 percent.44 A major draw- melt in the range of 350 to 50‘C (95 0 to back of using LiBr is the high cost of the ma- 1220 F), and have heats of fusion on the terial, but further study may reveal other order of 40 to 90 Btu/lb.37 Materials such as less expensive salts with acceptable prop-

Acetamide (CH 3 CONH 2 ), Naphthalene erties.

(CIOH 8) and Propionamide (C2H,COHN 2) can be used to store energy at slightly higher SALT STORAGE FOR OSMOTIC PRESSURE ENGINES temperatures, melting in the range of 820 to Energy can be generated from the os- 83‘C (180 0 to 1830 F) and having heats of fu- motic pressure developed between salt solu- sion in the range of 55 to 72 Btu/lb. 38 Mater- tions and freshwater. A system based on this ials suitable for storing coolness include principle is illustrated in figure Xl-9. The paraffins and olefins with freezing points in concentrated saline solutions produced for the range of 30 to 80 C and heats of fusion in use in such equipment can be stored in unin- the range of 65 to 85 Btu/lb. 39 sulated tanks which can be quite inexpen- Concentrated Solutions sive. A cubic meter of a salt solution comparable to water from the Dead Sea (27 per- Concentrated solutions can also be used cent salt by weight) can produce 1 to 2½ to store low-temperature energy without a kWh in a reverse osmosis engine. ” Figure phase change. It has been suggested, for ex- Xl-5 indicates that large tanks can be pur- ample, that solutions of LiBr utilized in ab- chased for less than $20/m3, and therefore sorption air-conditioner systems could be brine storage can be achieved for about $8 used to store solar energy in the “generator” to $20/kWh (or more if storage must also be 41 42 42 portion of an absorption unit. It has provided for the freshwater distilled from “A D Fong and C W Miller, “Efficiency of Paraf - solution). The use of covered ponds could f~n Wax as a Thermal Energy Storage System, ” Pro- result in substantially lower storage costs. ceedings, the 1977 Annual Meeting of I SE S, p 16-6, “lbld , p 33 SALT SOLUTIONS FOR ENGINES “C A Lane, et al , Solar Energy Subsystems Emp/oy- USING LATENT HEAT OF MIXING IrIg Isothermal Heat Storage Materials, ERDA- 117, UC- 94a May 1975 Engines can be operated from the latent 9 ‘ Segaser, op clt , p 33 heat released when concentrated solutions ‘“j Baughn and A jackman, Solar Energy Storage W(thin the Absorption Cyc/e. Paper delivered to the ASME meeting in New York, November 1974 ‘] Letter from Dr. Gary Vllet (University of Texas, 4‘M Semmers, et al , L/quid Refrigerant Storage in Austin) to Dr Albert R Landgrebe (ERDA), jan. 5, Absorption Air-Conclitioning. Paper delivered to 1975 ASME meeting In New York, November 1974 44Cary Vliet, ibid, “E H Perry, “The Theoretical Performance of the 45S Loeb, et al,, “Production of Energy from Con- Lithium-Brom ide-Water Intermittent Absorption centrated Brines by Pressure Reduced Osmosis: I I Ex- Refrlgeratlon Cycle, ” Solar Energy 17 (5), November perimental Results and Projected Energy Costs, ” jour- 1975, p 321 na/ of Membrane Science, (1), p. 264(1 976) 446 “ Solar Technology to Today’s Energy Needs

Figure X1-9.—Osmotic Pressure Engine

High Pressure Pump SOUROE: OTA.

of some types of salt are mixed with water ploratory survey indicated that photochemi- (see figure XI-10). Energy is released when cal reactions can be competitive with other water is introduced and aqueous solutions low-temperature thermal storage systems if are formed. ’b A study of this effect has they are capable of 25-percent conversion estimated that if energy is stored in the form efficiency and energy storage at more than of dry NaOH, the density of the energy 158 Btu/Ib. (88 cal/g), or 40-percent efficien- stored is 135 kWh/m3, and if energy is stored cy and 81 Btu/lb. (45 cal/g). in the form of dry ZnCi , CaCl , MgCl , LiBr, 2 2 2 One of the few low-temperature reactions and LiCl, the energy storage density is about which has been studied involves the use of 80 kWh/m3. metal hydrides. The reactions are of the general form M + (x/2)H ~ MH , where M CHEMICAL REACTIONS 2 X is a metal or alloy such as LaNi5, SmCo5, or There is growing interest in the possibility FeTi. These materials are capable of storing of storing energy for low-temperature ap- between 45 and 92 Btu per pound of hydride plications in chemical form, but work is in a (0.029 to 0.059 kWht/kg), if storage temper- very preliminary stage and no practical ature is heId at 2000 F and initial hydride systems have yet emerged. ” 46 A recent ex- temperature is 700 oF.49

Energy is stored when the hydride is “N. isshiki, et al., “Energy Conversion and Storage by CDE (Concentration Difference Energy) Engine and heated, releasing the gas, and recovered System, ” Proceedings, the 12th Intersociety Energy when hydrogen recombines with the metal. Conversion Engineering Conference, Washington, Recent investigations at the Argonne Na- DC., Aug. 28-Sept. 2, 1977 (American Nuclear Society, La Grange Park, ill.), page 1117. “G S. Hammond, “High Energy Materials by Charge Transfer and Other Photochemical Reac- 4’G. G. Libowitz, “Metal Hydrides for Thermal tions, ” ACS 122r7d Meeting, San Francisco, Cal if., Sep- Energy Storage, ” Proceedings, the 9th Intersociety tember 1976. Energy Conversion Engineering Conference, San Fran- 48S. C. Talbert, et al., “Photochemical Solar Heating cisco, Cal if., Aug. 26-30, 1975, p. 324 (Quoted in and Cool ing,” Cherntech, February 1976, p. 122. Segaser, pp. 37-38.) Ch Xl Energy Storage 447

Figure Xl-10.— Heat of Mixing Engine

To Process Loads 1

~ i-lot Water Storage 1 Condenser Mixing Heat Chamber Engine r To

SOURCE OTA. tional Laboratory have demonstrated the Refractory Bricks feasibility of hydride storage for both heating and cooling applications ‘0 Devices capable of storing energy in magnesium oxide bricks at temperatures up to The possible costs of several of the low- 600 oC (1 ,1120 F) have been commercially temperature thermal storage systems dis- available in England and Western Europe cussed in the previous sections are summar- for many years; the original patents date ized in figure Xl-11. The techniques used to back to 1928. They are in buildings so that compute these costs are explained in appen- customers can charge the storage from the dix XI-B, relatively inexpensive electricity available in these areas at night; during the day, homes and offices can be heated from the THERMAL STORAGE AT INTERMEDIATE systems in the same way that a baseboard AND HIGH TEMPERATURES resistance heater would be used. In 1973, both Great Britain and West Germany had Table Xl-3 lists the properties of some of installed enough such devices to provide the materials which can be used to store nearly 150,000 MWh of storage capacitys1 52 thermal energy at high temperatures. Rock for leveling the loads placed on their elec- storage was treated in the previous section. tric utilities. Devices such as the one shown The following discussion examines sensible in figure Xl-12 are beginning to appear on heat storage in refractory bricks, iron ingots, the U.S. market in areas where time-of-day and hot oils.

5 IGunter Mohr, Electric Storage Heaters, AE C- Telefunken Progress, (1970), 1, p 30-39 ‘“James H Swisher, Director of the Dlvlslon of 52) G Ashbury and A. Kouvalls, E/ectric Storage Energy Storage Sy5tems, Of flee of Conservation, Heat/rrg: The Experience in Eng/and and Wales and ~n ERDA, letter to OTA dated Mar 30, 1977 the Federa/ Repub/lc of Germany, ANL,’E S-50(1976) 448 Solar Technology to Today’s Energy Needs

Figure Xl-11 .— Low-Temperature Thermal Storage Cost per kWht Versus Storage Capacity

200

100

.20

.10 Single Tank Storage —“- MultlpleTank Storage . ‘ 0.05

‘, t,

100 1000 104 10’

Storage capacity (kWht)

NOTE: The storage untts would lose only about 5 percent of the energy stored In the Interval Indicated. This cost IS based on precast concrete and coated steel, and excludes 25 percent O&P Ch. Xl Energy Storage ● 449

Table Xl-3.—Candidate High-Temperature Thermal-Energy Storage Materials Without Phase Change

Sensible-heat storage between 77° F and 900° F

Density Price (1971 $) output Material (lb/ft 3 ) Btu/lb Btu/ft 3 ($/100 lb) (Btu/$)

Al ...... 168 200 34,000 29.00 690

A12 (S04 ) 3 . . . 169 202 34,000 3.11 6,500

Al 20 3 , ...... 250 200 50,000 2.20 9,100

CaCl 2 ...... 135 135 18,000 2.20 6,000 MgO ...... 223 208 46,000 2.80 7,400 KCI ...... 124 140 17,400 1.65 8,500

K 2SO 4 ...... 167 180 30,000 1.10 16,400

Na 2CO 3 . . . . . 160 265 42,500 4.00 6,600 NaCl ...... 136 180 24,500 1.33 13,500

Na 2SO 4 . . . . . 168 247 41,500 1.50 16,400 Cast Iron . . . . 484 102 49,500 10.00 1,000 Rocks ...... 140 160 22,500 1.00 16,000

SOURCE M Allrnan, et al @rrSe~at~Ofl a~~ ~~~er u~lllza~lo~ of ~~ectrlc power ~Y Means Of ~~er~al .Emrgy Storage and so/ar ~eatln~, Phase I .Su~~arY ~eport, NSF G127976, Unlverslty of Pennsylvania National Center for Enerqy Management~nd Power, Oct 1, 1971, pp. 2-10 rates have been introduced. The units heated steam is passed through the pipes for typicalIy sell for $20 to $40/kWh. 53 charging and discharging. It should also be possible to maintain a significant tempera- Some thought has been given to using ture gradient along the length of the storage these bricks to provide high-temperature unit for several days (see appendix Xl-B). The storage for a solar-powered gas turbine sys- predicted performance of a large device is tem. I n one proposal, helium from a receiv- illustrated in figure XI-14. Like the MgO ing tower would be passed through a pres- (magnesium-oxide) storage system, this de- sure vessel containing refractory bricks, simplicity, it o 0 vice has the advantage of great heating the bricks to about 530 C (986 F). It has virtually nothing to wear out, no heat ex- is estimated that such a device could be changers to clog, and no scarce or toxic ma- constructed for $11 to $14/kWht. 54 terials are required. It has an advantage over the brick storage system in that a pressure Steel Ingot Storage vessel is not required to contain the heat- transfer fluid —the steel pipes provide the A system for using steel or cast-iron ingots needed containment. For this reason, the to store high-temperature energy for use in a cost should be slightly less expensive per steam electric-generating plant has been unit of energy stored. 57 proposed by Jet Propulsion Laboratory (JPL). 55 56 This device, illustrated in figure It should be possible to build a steel ingot Xl-1 3, consists of an assembly of pipes with storage system with relatively Iittle develop- rectangular external cross sections. Super-

5’) G Ashbury, et al., “Commercial Feasibility of 56program Review, cC3fT)pari3tivt2 Assessment of ~r- Thermal Storage in Buildings for Utility Load Level- bita/ and Terrestrial/ Central Power Systems, OCtober I ng, ” presented to the American Power Conference, 1975- January 1976, jPL, p 16 Apr 18-20,1977, Chicago, Ill. “R H Turner, j PL, “Thermal Energy Storage Using “W D Beverly, et al , “1 ntegration of High Temper- Large Hollow Steel Ingots, ” Sharing the Sun: Solar ature Thermal Energy Storage into a Solar Thermal Technology in the Seventies, joint Conference, Brayton Cycle Power Plant, ” 12 IECEC Conference, p American Section, International Solar Energy Society 1195 and Solar Energy Society of Canada, I nc , Winnipeg, ‘% Beverly, op clt , p 1199 Canada, Aug. 15-20, 1976, Vol 8, pp. 155-162. 450 Solar Technology to Today’s Energy Needs

Figure XI-12.—A High-Temperature Thermal Figure Xl-13.— Steel-Ingot, Sensible-Heat Storage Device Designed for Residential Use Storage System

Return to solar collector during charging; return from load during discharge

A storage/heating unit installed in a home

- Distribution piping heating I elements (made of 80% Nickel/ Input from solar collector high density mineral wool 20°& Chromium during charging; input to thermal Insulation heat storage core mounted on # of magnesite bricks ceramic supports) ,. . load. . during discharge / I (nole diameters not to scale) finish cabin metal

Figure Xl-1 4.—Steel-Ingot Temperature Profiles at Various Times in a Typical Cycle

950°F Fully charged system temperature \ \ \ \ I \ \

warm alr out

quiet, low energy, squirrel cage fan (actuated by room thermostat)

An interior view of the unit showing the magnesium bricks, heating elements and air blower

SOURCE Control Electric Corporation Burlington, VT ment work since most of the properties of the system can be computed with considerable precision. Since the system uses high- Ingot system length -pressure steam, considerable care must be (Steam path is many ingots long) taken if it is used in onsite applications, but SOURCE: existing boiler codes should be able to en- R. H. Turner (JPL), “Thermal Energy Storage Using Large Hollow sure adequate safety. Lower pressures can Steel Ingots,” Sharing the Sun: Solar Technoloav“. in the Seventies. be employed if the system uses a heat- Joint Conference, American SectIon, International Solar Energy Society and Solar Energy Society of Canada, Inc. Winnipeg, transfer fIuid other than steam. Canada, Aug. 15-20, 1976, Volume 8, page 160. Ch. Xl Energy Storage 451

It may be possible to reduce the cost of high enough vapor pressure to sustain com- the system by replacing some of the volume bustion at temperatures in the range of 600 c of metal with concrete. Concrete costs to 1,0000 F (ignition temperature), This about a third as much as steel and could means that great care must be taken to en- easily be formed around a matrix of sepa- sure that the material is not overheated, rate steel pipes. The practical difficulties of Dikes will be needed to prevent the material constructing such a system have not been from spreading if a leak should occur. Some evaluated, however, The performance of the systems require an inert gas (such as nitro- system could be degraded significantly if gen) over the liquids in the tanks to inhibit the concrete separated from the steel tubes; reactions which might degrade the storage this may create problems even though con- material. The behavior of the rock-oil mix- crete and steel have nearly the same coeffi- tures over long periods of time remains an cients of expansion. Another difficulty open question, since little experimental would be the relatively poor heat transfer evidence is avaiIable. The rocks may tend to between concrete and steel. Concrete itself crack, and the apertures between them may has low conductivity, and cracks could fur- clog with degraded oil. ther reduce its conductivity. Refined Fuel Oil Thermal Storage Heat-Transfer Oil Thermal Storage A thermal storage system proposed by Some of the sensible-heat storage systems EXXON eliminates the problems of degrada- utiIize a mixture of rocks and a heat-transfer tion and clogging by using a relatively inex- fluid such as Therminol. The properties of pensive fuel oil without rocks.58 This system some common commercial heat-transfer liq- uses specially refined oil that does not de- u ids are Iisted in table Xl-4. Sandia Labora- grade with time, but it can only be used at tories in Albuquerque chose a system using up to 530° F (277 ‘C). The oil is estimated to Therminol-66 and rocks for storing energy in cost $146/m 3 (installed, excluding operations its total energy system. This system, shown and maintenance) and, if necessary, can be in figure Xl-1 5, has been operated success- used as fuel at any time.59 Its specific heat is fully since early 1976. A mixture of Caloria 0.795 kWh~Jm3“C.bo HT43 and granite rock storage was chosen An EPRI study estimates the installed cost by McDonnell-Douglas for storing energy of insulated tankage, including an inert gas generated by their central receiver design. system to exclude oxygen, to be $91/m3 of Martin-Marietta chose to use a sensible-heat oil for a two-tank system. Oil handling facili- storage system with two stages — a high-tem- ties, such as pumps, piping, and heat ex- perature stage for superheating, using changers, are power related, rather than HITEC as the storage medium, and a low- energy related, and cost $288 per installed temperature stage using a heat-transfer oil. kw of capacity .61 Each stage has two tanks for high perform- th ance.

All heat-transfer oils share a common set of problems. They all degrade with time, and their degradation is increased rapidly if they are operated above their recommended “An Assessment of Energy Storage System5 temperature Iimits for any length of time. Suitable for Use by Electric Utii[tles, EM-264, EPRI This degradation requires a filtering system Project 225. ERDA E (11-1} 2501, Final Report and means that the relatively expensive oils Prepared by Public Service E Iectrlc and Gas Com- must be continualIy replaced. The oils also pany, Newark, NJ “lbld , pp 4-40 can present safety problems, since they can ‘“ibid , pp 3-48 be ignited by open flames at temperatures in “ Ibid , pp 4-41 Converted from $144 kWe using O 4 the range of 3000 F (fire point) and have a kWe kWth and 1 25 O&P factor 452 ● Solar Technology to Today’s Energy Needs

Table Xl-4.—Commercial Organic and Inorganic Heat-Transfer Agents

Refined fuel Therminol- Therminol- Caloria-HT- Dowtherm- Humble- oilb a 5 5 5 55 66 43 A therm 5005 HITEC 5 (see text)

Dow E. 1. Producer Monsanto c Monsanto c EXXONC Chemical d Humble Oil Dupont EXXON C

Highest usable temp

(“C) = Tmax ...... 316 343 316 260 316 500 277 Lowest usable temp: (°F) ...... 601 649 601 500 601 932 531 (“c)...... -18 -4 — -11 -21 142 — (°F) ...... 288 Fire point (°C) ...... 210 193 — 135 246 — — Autoignition temp(° C) 354 374 404 621 — — — Specific heat (Btu/lb oF)3 (or cal/gm°C) . . 0.72 0.655 — 0.537 0.7165 0.4 0.70 Viscosity (lb/ft-hr)e . 1.1 0.649 — 0.65 1.01 — Thermal conductivity (Btu/hr-ft° F e . . . . . 0.065 0.0612 — 0.0645 0.0655 0.68 Density (lb/ft3 ) e . . . . 43 50 53 41.3 112 — Heat capacity (Btu/ ft3° F)e ...... 31 32.8 28.5 29.6 44.8 38.21 Cost ($/lb) ...... 0.38 0.81 0.26 0.71 0.25 cost ($/ft3 )...... 16.34 40.50 37.63 28.00g 4.13 Mills/Btu (assuming 0 AT = Tmax-50 Cand

perfect thermal gra- f dient)...... 1.1 2.3 S.2 3.5 0.99 0.26 Mills/Btu (assuming complete mixing and allowing T to fall max 2,0h to (Tmax/2) + 25” C) 2.2 4.6 6.4 7.0 0.53

a @mPlfed by Hoffman (ORNL) and Tas Bramlette (Sand la, Llvermore)

b Energy in 011,” IEEE Power Englneenng Soc(ety Summer Meeting, Portland, Oreg., July 1976

c Requires nonoxldlzlng cover gas

d Requires pressurization for temperatures above 260”C

e Propefly at maximum usable temperature.

f AT = Tmax – 83°C

g AT = Tmax – 150”C h AT max falls to (Tmax/2) + 75°C Ch. Xl Energy Storage 453

At least one design for such a hot-oil must be closely spaced to permit acceptable energy storage system for use with a 1,000 rates of heat transfer since sodium hydrox-

MWe nuclear powerplant has already been ide has a relatively small heat conductivity. completed, and the EPRI study classifies this JPL estimated that such a system could store technique as “a near-term solution with cer- 52 MWht if the temperature swing were be- tain economic advantages over other stor- tween 6500 and 4000 F and would cost age systems.”62 about $13/kWht.Gs A major problem with these systems is that the highly corrosive Latent-Heat Systems nature of NaOH (lye) demands expensive containment to prevent leaks. Heat-of-fusion systems using inorganic salt mixtures have a distinct advantage for The Philips Corporation has investigated a storing energy at high temperatures, since number of materials for possible use in a they can reduce storage volumes and pro- phase-change storage system. Lithium fluo- vide more energy at constant temperatures. ride has received the most attention be- The major disadvantages have been the cause of its extremely large latent heat of fu- costs of the materials required and the prob- sion, but other less expensive materials have lem of developing adequate heat transfer also been examined for use in the Philips between the storage material and the work- design. ” Other fluoride compounds, for ex- ing flu id. Two designs which have been used ample, have extremely large latent heats. in devices designed to store energy for space The properties of a variety of salt com- conditioning are illustrated in figures Xl-16 pounds which might be considered for use in and Xl-17, The Comstock and Wescott de- phase-change storage systems are illustrated sign uses relatively inexpensive materials: in table XI-5 and their thermodynamic be- NaOH mixed with corrosion inhibitors. The havior is illustrated graphically in figure unit shown consists of six moduIes contain- Xl-1 8. It can be seen that the sodium hydrox- ing sodium hydroxide which was heated ide material appears to have an advantage with electricity. The unit has been rede- in the temperature regime appropriate to signed to use steel pipes rather than the conventional Rankine cycle systems, while panels shown. 63 64 65 A similar approach has fluoride compounds (such as the NaF/MgF been proposed by JPL for use in a central 2 mixture) appear to have an advantage when station powerplant. I n their approach, a used in connection with engines operating bundle of tubes is imbedded in a long cylin- at very high temperatures such as Brayton or drical tank (in the central station design, the Stirling cycle devices. tanks were 60 feet long and 12 feet in diameter) filled with sodium hydroxide. The In general, the nitrates and nitrites are steam or other heat-transfer Iiquid is sent relatively inexpensive and do not corrode through the tubes to extract or to supply their containment vessels, but they tend to energy to the storage medium. The tubes decompose at temperatures above 4000 to 500 “C. The hydroxide eutectics can operate at high temperatures, but become corrosive ‘Zlbld , pp 3-51 The completed study IS referenced and thus require corrosion-resistant alloys. as R P Cahn and E W N Icholson, Storage of Off- Carbonates have good thermophysical prop- Peak Therma/ Energy In 0;/, Approved by I E E E Power erties, but also decompose at high tempera- General Committee, Paper No A76 326-9 Summer 1976 tures unless a cover gas of CO2 is used in the “Comstock and Wescott, Inc., “First Step of Heat tanks. Chlorides and fluorides have high spe- Storage Research Actlv[ty of Heat Storage Systems, ” cific heats, conductivities, and latent heats, EE/ L3u//, June 1959 “Comstock and Wescott, Inc , “Promlslng Heat Storage Material Found Through Research, ” E.E/ Bu//., “R H Turner (J PL), private communlcatlon, June 9, February 1962, p 49 1976 “R H Turner (J PL), private communication, June 9, “j Schroder (N.V Philips Aachen Lab ), Therrna/ 1976 Energy Storage, N V Phlllps publication 454 ● Solar Technology to Today’s Energy Needs

Figure Xl-15.— The High-Temperature Heat Storage System at the Sandia Total Energy Experiment

— A- photograph by John Furber

Figure Xl-16.– Design of “Therm-Bank” Space Heater

Heater terminale \ Inner tank cover

90URCE R E Rk., rrwn.l Smmp APPIIc@On W EnwvY ConsewMIII Comwoch md Wssc.11, Inc AD.(. 1975 Rwrlntad m timbl~. *I 4, SAN07$iMb2 P8C942 Ch. Xl Energy Storage ● 455

SOURCE N V Phlllps 456 Solar Technology to Today’s Energy Needs

Table XI.5.—Properties of Latent-Heat Thermal Storage Materials

Storage material NaF/MgF2 LiF/NaF/MgF 2 (mole %) NaOH (75/25) B2O3 46/ 44/ 10 NaN03 Lif

Melting point ‘C...... 320a 832b 450c 632d 31Oc 845c ‘F. ., . 608 1530 842 1170 590 1553 Density at m.p. (kg/m3) . 1784 2190b 1571 c 2105d 1916c 1829c (most bulky phase)* . . . . (Iiq) (Iiq) (Iiq) (Iiq) (Iiq) (Iiq) Heat of fusion ( A HPC). 0.0442c 0.174b 0.092d 0.226 0.0481 0.290 (kWh/kg) ., ...... 0.0442** (e) (c) (c) -4 -4 -4 -4 Specific heat at m. p. 5.89 x 10 a 4.1 x 1O-4*•• 4.48 X 10 d 4.88 X 10 5.06 X 10 6.69 X 10-4 sol id (C ) (kWh / kgoC) (below 295° C) p —— (e) ● ☛☛ (d) (above 295” C) Specific heat at m .p., -4 -4 -4 - -4 -4 liquid (Cp) (kWh /kg° C) 5.75 x 10 C 4.07 x 10 e 5.09 X 10 d 4.88X 10 4*•• 5.058 X 10 6.94 X 10 (c) (c) Heat capacity (m. p,-50° C to m,p. + 50” C) (kWh/ 3 m )...... * 262 471 205 578 189 655 0.55f 1,10-0.55g 0.20 2.20 0.57 5.56h 983 2400-1200 312 4641 1098 10,161 Material cost ($/ kWh capacity) (m. p. -50” C to m.p. + 50° C) ., ., 3.75 5.10-2.55 1.52 8,02 5.81 1551

. Volume of storage conta[ner must be large enough to accommodate most bu Iky phase . . Solld/solld phase change at 295° C (563° F) . . . Estimate based on speclf[c heat of other phase

aKubaschewskl, O , et al (National Physical Laboratory, Mlddlesex), Metallurgical Thermochemistry Fourth Ed Pergamon Press Ltd , 1967 bschroder, J (N V Phlllps Aachen Lab), “Thermal Energy Storage Using Fluorldes of Alkall and Alkallne Earth Metal s,’ Proceed/rigs of fhe Symposium on Energy Storage The Electrochemical Soctety, Inc , 1976 cJanz, G J (Rensselaer Polytechn IC Institute), Mo/(en Sa/ts Handbook Academic Press I nc , 1967 dw{cks, c E and F E Block (U S Bureau of Mines), Therrnodynarn(c Properties of 65 E/ernents — The/r Ox/ales, Ha//ales, Carb/ijes and Nlfrldes BuI Iettn 605, Bureau of Mines, 19(j3 eschroder, J ( N v Phlllps Aachen Lab), private communication, Jan 13, 1977. fchem(cal Mar~e(l~g Reporter VOI 210, No 10, Sept 6, 1976 100 lb drums of U S PharmacoPla NaOH In truckload quantities

9$0 !jsl kg IS a cost estlnlate made by N V Pfllllps, based on (he use of waste rnaterlals from fertilizer rnartufacturlng present cost IS $1 1 (J / kg

hLltfllum Corporation of America quotatton, SerX 15, 1976, for 99 5°0 LIF in lots greater than 5 tons This material IS proposed for use In Phil Ips space heat storage system m p — melt ng point (Ilq)— hqu[d phase

but tend to be higher in cost and can have systems are capable of storing a large corrosive properties. Phosphates and sul- amount of energy per unit weight. The stor- fates are very corrosive. age could be mounted directly on a tracking dish, or it could be physically close to an If the latent-heat storage system can be engine mounted at the top of a tower. located very close to the collectors, it may be possible to use a heat-pipe system to con- Heat pipes operate most effectively if vey the energy from a collector to storage. their working fluids have pressures in the Extensive surfaces would have to be affixed range of 1 to 10 atmospheres. Both sodium to the heat pipes to produce sufficient heat- and potassium have these pressures in tem- transfer surface area in the storage medium. perature ranges of 6000 to 1,000 “C. The This may be feasible since the latent-heat technology of sodium-vapor heat pipes has Ch. Xl Energy Storage 457

Figure Xl-18.—Thermodynamic Behavior of Candidate Latent-Heat Storage Salts

Temperature of storage (°C) 0 100 200 300 400 500 600 700 800 900 0

.05

.10

.15

.20

.25

.30

.35

.40 of heat engines

.45 Organic rankine engines I

.50

.55

Gas turbines .60 I J\

0 100 200 300 400 500 600 700 800 900 ‘c

SOURCE Table Xl 7 been thoroughly investigated, and pipes ceptable generating system is to be de- made of relatively low-cost “type-304” stain- signed. Such improvements are expected, less steel are predicted to have lifetimes of but design research and much more operat- 10,000 hours. ” ‘9 This lifetime corresponds ing experience is needed. to only a little more than a year of continuous operation for a generating system, and A Philips design employing a heat-pipe further improvements are needed if an ac- and a phase-change storage system is illustrated in figure Xl-19. When the storage is being “charged,” the liquid sodium flows to ‘8G A A Asselman, et al , “Heat Pipes, ” Philips Tech. Review, Vol 33, No 4 (1970), p 104 the collector where it is vaporized and re- “C A A Asselman, et al , “Hea~ Pipes, ” PhI/ips turns as a gas to the storage vessels. (EIectric Tech l?e~ Iew, Vol 33, No 5 (1970), p 168 pumps for moving sodium without moving 458 Solar Technology to Today’s Energy Needs

Figure Xl-19.— Use of a Sodium Heat Pipe operator, and they do not appear to present With a Latent-Heat High-Temperature Thermal any serious safety problems. Release of the. Storage System sodium from the system could be hazardous, but only very small amounts of sodium are required in the system per-unit-of-power output.

Unfortunately, there remains a substantial amount of disagreement about the performance capabilities of phase-change sys-

exchangers, average cycle efficiency corrosion resistance, and development of low- cost materials have been resolved .’” On the other hand, others are still having substantial development problems and feel that a considerable amount of fundamental development work is needed. Only more research and the fabrication and testing of real devices will resolve these debates.

Environmental Concerns The environmental problems associated with the use of high-temperature thermal storage devices have not been explored in detail, although a preliminary survey of the issues has been conducted. 71 Some of the oils proposed for use as heat transfer fluids or as storage materials can be Heat from solar collectors explosive. Care will have to be exercised in SOURCE: Drawn by OTA using N. V. Philips concept, the construction and operation of these systems, particularly if they are integrated into parts have been developed by the breeder systems close to populated areas. Most oil reactor program. ) The vapor condenses on storage tanks must be covered with an inert the storage containers, giving the energy of gas such as nitrogen to minimize the risk of vaporization gained at the collector and the explosion when the oil is heated. Leaking cycle begins again. When the system is be- tanks could result in fires; earthen dikes or ing discharged, the vapor is generated by the dams would be required around large tanks storage vessels and condensed in a heat ex- built above the ground. The risk would be re- changer sending energy to a heat engine. If duced if underground storage were used. auxiliary power is needed to supplement the Care would also be essential when the ther- solar energy, a separate heat exchanger can be built into the heat-pipe loop to permit running the engine from fossiI fuels. 70). Schroder (N V Phlilps Aachen Lab ), private If these low-pressure sodium or potassium communication, jan 13, 1977 “john G. Holmes, “Environmental and Safety im- heat-pipe systems could be developed, they plications of Solar Technologies” Proceedings, the would be very attractive. They should not 1977 annual meeting of the American Section of the require extensive maintenance or a trained International Solar Energy Society, p, 28-5 Ch. Xl Energy Storage ● 459

ma storage materials are discarded after a tion to transfer heat to a latent-heat storage system is dismantled or when fluids are re- system. 74 placed if they have been damaged or de- Developing procedures which will be graded with repeated thermal cycles. The useful for onsite applications may be dif- oils would typically be dumped into city ficult, since many of the reactions being ex- sewage systems. amined are quite complex. Frequently, the reaction in the collector is simpler to control than the reverse reaction, In this case, a THERMOCHEMICAL STORAGE series of distributed onsite collectors could be used to feed a common collection pipe Background network which operates an electric-gener- Recent interest in thermochemical reac- ating device at a central facility, I f hydrogen tions for storing energy has been motivated or other easily reacted materials are pro- primarily by a desire to find a way to store duced, the storage products could be used and transport energy generated by nuclear easily in onsite facilities without trained plants.72 73 Like the heat of fusion storage operators. systems, chemical storage has the advan- The basic chemical cycle employed is tage of being able to produce heat at con- shown in figure XI-20. A chemical (labeled stant temperature. It has the additional ad- “A” in the diagram) is preheated in a coun- vantage of not requiring insulated storage terflow heat exchanger and sent into the col- tanks. Some chemical systems could allow lector where it is separated into products storage densities many times higher than (“B” and “C” in the diagram) through a any other types of thermal storage. A variety chemical reaction. The heated-reaction of reactions have been examined, and there products are cooled to ambient tempera- appears to be no technical barriers to using tures in the heat exchanger. If the reaction a number of them in connection with solar requires a catalyst in the solar collector, it colIectors. may be possible to store the products at am- The problems remaining involve both the bient temperatures. If no catalyst is needed, need to understand much more about the it may be necessary to store each reaction fundamental chemistry of some simple reac- product separately. The stored products can tions which have never been examined in then be piped to other sites where energy is detail, and the engineering details of con- needed, When energy is to be extracted verting laboratory reactions into reliable from the system, the reaction simply pro- commercial products It is also possible to ceeds backward at a lower temperature (Ie use the energy stored in chemical reactions Chateler’s principle). In the diagram, “B” to transport energy from colIectors to a stor- and “C” recombine to form “A “ If the orig- age vessel The “Solchem” process, for ex- inal chemical (“A”) is valuable, it must then ample, being examined by the Naval Re- be piped back to the collector. In some search Laboratory, uses the SO3/SO2 reac- cases, the reaction must proceed through

In a recent paper, W. E. Wentworth and E 7ZR schu Iten, et al , The Concept of N’uclear Hvdro- Chen presented an elegant approach for gen Production and Progress of Woolf in the Nuc/ear Research Center )uellch, paper presented at the 1 St evaluating and comparing thermochemical World Hydrogen Conference, Mlaml Beach, Fla , Mar 1-3, 1976 ‘ ) Jon B Pangborn, “ }iydrogen Energy Technology- Update 1976,” In Energy Technology I I I proceedings “T A Chubb, “A Chemical Approach to Solar of the third energy technology conference, Energy, ” to be publlshed In Cherntech, 6, p 654, (Oc- Washington, D C , 1976, p 1972 tober 1976) 460 ● Solar Technology to Today’s Energy Needs

Figure Xl-20.— Typical Thermochemical Storage Technique.

Collector

to Energy I from sun

Storage

L Distribution

b # \ 4 Collection reaction User-site reaction

J reactions. Their work provides the basis for 1 The reaction should be nearly complete the analysis which follows. 75 within the temperature range of available collectors. (In practical terms, it The basic measures of merit for a ther- would be desirable to have 95 percent mochemical reaction are: 76 completeness at temperatures below 1,000 oC.) 2. The reverse reaction should be nearly “w. E. Wentworth and E. Chen, “Simple Thermal Decomposition Reactions for Storage of Solar Ther- complete at the temperature at which mal Energy, ” Solar Energy 18(3), 1976, p. 205. useful energy is to be extracted. (If the “I bid,, p. 208, reaction is to be used in connection Ch. X/ Energy Storage 461

with- a conventional powerplant, this Design Alternatives temperature would be approximately Most of the thermochemical reactions 500 “C; if a Stirling cycle or Brayton cy- which are now being examined for use in cle device were to be used, the tem- connection with high-temperature storage perature should be closer to 800 “C.). systems require fairly sophisticated reaction 3 The reversible reaction should be able apparatus which must be maintained by to release energy for the user at temper- trained personnel. As a result, these thermo- atures close to those supplied by the chemical systems will be limited to rela- collector. (The collector temperature tively large onsite systems, such as shopping should be as low as possible to mini- centers, industries, and communities. Re- mize material problems and to maxi- search may develop reactions which do not mize collection efficiency— in the fol- require such attention and the equipment lowing discussion, it will be seen that needed for existing systems may be simpli- this requirement will be met by reac- fied, but much more development work is tions which involve large changes in needed before assessment of this issue can entropy. ) be made. 4. The energy absorbed per-unit-volume METHANE–STEAM of the products stored should be as large as possible to minimize the vol- A variety of reactions have been proposed ume of storage. It would be most desir- for use in larger systems, and some of them able to be able to store the reaction are summarized in table Xl-6. The reaction products in liquid form. This would which has probably received the most re- both reduce storage costs and the cent attention is the methane/syn-gas reac- energy losses in pumping the stored tion. The methane reaction probably re- material. quires the least development since the technology required for each step of the storage 5. The reaction should be completely re- process is commercially available and the versible and no side reactions should chemistry is well understood. occur to produce contaminants in a closed-cycle system. These side reac- The Ralph M. Parsons Company, for ex- tions would tend to create products ample, has operated a device for converting which would accumulate and eventual- hydrogen and carbon monoxide to methane ly poison the system. for 3 years, producing nearly a million ft3/- day of methane. The equipment was de- 6. Reactions should be fast. signed as a part of a synthetic fuel plant, 7, None of the reactions involved should where the first step would be partial com- require extensive development of new bustion of coal to produce the “syn-gas”

chemical techniques. They should not combination of H2 and CO, and the second require expensive or elaborate equip- phase would use the Parsons’ “methana- ment. This is of paramount importance tion” process. 77 for onsite equipment not operated by trained personnel. One potential difficulty of the methane/ steam process for onsite application is the 8 The reaction products should not react difficulty of controlling the reaction. The strongly with water or oxygen, since it thermal output from the reaction which gen- would be difficult to seal the system crates heat can be throttled down to about against these materials. 50-percent peak capacity without major dif- 9 The materials used should be inexpensive and should not require chemicals for which shortages are likely to de- “Charles Luttman (Ralph M Parsons Co.), private communication, Aug. 6, 1976. velop. 462 ● Solar Technology to Today’s Energy Needs

Table X1-6.—Candidate Chemical-Energy Storage Reactions ——— Energy stored Cost of Temperature per unit mass stor- of reaction Temperature of (VOI. ) of storage in colIector ● user react ion ● age material mate- Reaction o C o F n T o C “F rial Comments Btu/lb kcal/liter $/kWh —

780 1,440 0.94 610 1,130 2,792 50 Products of the storage reaction are gases and thus VOlume IS large. Gas must be stored under pressure. Reactions are well known. Nickel catalyst required. CO

+ 3H2 CH 4 + H2 0 IS a methanation reaction.

589 1,150 60 Products stored as gas 590 1,090 532 110 0.16 Cost includes system cost S02 stored as liquid, 02 as gas,

435 850 512 1.1

335 635 446 740 0.62

390 740 567 470 0.07

. See text for explanation of terms In the anal ysls of “temperature effl[ IPII y Tc = 100‘ F has been used SOURCES W E Wentworth and E Chen, “Simple Thermal Decomposlt [on React Ions for Storage of Solar Thermal Energy, Sular Energy 18(3), 1976 T T Bramlette (Sandla Laboratories, Llvermore), Survey of High- Temperature Thermal Energy Storage SAN D75-8063, March 1976, pp 83-94 R S Hockett and R W Serth, “High Temperature Thermal Energy Storage System, ” 721h IECEC Conference, (1977), pp 510 ficulty, but control beyond the So-percent solved salt caverns constructed for this pur- reduction becomes difficult. Another major pose for about $3/1 ,000 SCF, and in mined problem is the relatively low-energy density caverns for about $5.6/1 ,000 SCF.78 The of the gas which must be stored. The H2 + energy storage costs would thus range from 6 CO mixture holds approximately 60 Btu/ft 3 about $17/10 Btu ($0.057/kWh t) of storage at atmospheric pressure, and methane holds capacity for gas field storage to about 3 6 approximately 240 Btu/ft . The price of $93/10 Btu ($0.32/kWhtO for mined caverns. tanks for storing the coal and gas mixture These underground storage systems wiII dominate the cost of this type of stor- would not be available in many sites, They age. If large amounts of gas are to be stored could probably be used only in connection and underground caverns or abandoned gas with a very large plant, and then only if ap- fields are available, underground storage is propriate geology could be located. With clearly the most inexpensive approach. A re- current technology, it would be necessary to cent JPL study estimated that hydrogen store the gas in pressurized tanks, In the could be stored in depleted gas fields and future, it may be possible to store hydrogen aquifers for about $1/1 ,000 SCF,* in dis-

‘The abbreviation “SCF” stands for standard cubic 78 Toshlo Fujlta (j PL), Underground Energy Storage feet If the gas IS stored under pressure, the volume for E/ectric Uti/i(les Ernp/eying Hydrogen Energy Sys- wou Id be less th~n the “SCF” tems, June 1976, p VIII Ch. Xl Energy Storage ● 463

in solid hydrides .79 A recent EPRI study in- cles, reported to ERDA last fall that it found dicated that hydrogen could be stored at 88 the following cycle the most promising: atmospheres for about $0.50/SCF80 (or (1) $28/kWh t) in the syn-fuel storage system. (2) Major development problems which must be overcome for the methane/steam cycle (3) include the design of high-temperature re- Two other high-temperature chemical ceivers using nickel-base catalysts. The re- storage cycles are being studied by Westing- ceivers must be capable of operating for ex- house in the United States and KFA in West tended periods with minimal maintenance. Germany. In all three cycles, the primary Another unresolved issue is the question of heat storage occurs in the dehydration and the extent to which the system will be stable 82 pyrolysis of H2SO4. Several reactions have when the load or solar influx changes sud- also been proposed by Debini and Marchetti denly. There may also be difficulties with (using CaBR and HgBr ) Westinghouse (us- side reactions which wouId lead to the ac- 2 2 ing a hybrid sulfuric acid process), General cumulation of reaction products that would Atomics (using an iodine-sulfur dioxide cy- poison the system. The seriousness of these cle), Schulten (using a methanol-sulfuric difficulties and the cost of overcoming them acid process), the Lawrence Livermore Lab- cannot be determined without operational oratory (using a zinc-selenium cycle), the In- testing. stitute of Gas Technology (using iron chloride), and others.83 A major problem with all MULTISTAGE PROCESSES FOR of the reactions examined is low efficiencies GENERATING HYDROGEN (typically 20 to 40 percent). In many cases, A number of multistage processes have the basic chemistry of the processes has not been suggested for generating hydrogen, but been well established. most are cumbersome for onsite applica- In addition to the calcium-bromide proc- tions and involve several different reactions, ess described above, reactions using cesium, some of which require the addition of Iow- tin, iodine-vanadium chloride, and iron chlo- temperature “process heat” in addition to ride-oxide have been proposed. The cal- the high-temperature processes. 8 Two ad- ’ cium-bromide reaction appears to be the vantages of these muItistage processes over most efficient, AlI require three or more single-stage hydrogen production are that processes and considerable quantities of lower temperatures can be used and that the process heat. 8485 The cost of such systems is two gases are released separately at dif- extremely difficult to estimate at present. ferent stages. One preliminary study showed that a 47-per- General Atomic Company, which in 1973 cent efficient thermochemical-process plant developed a computer program to find the for converting solar-supplied heat into hy- best combination of chemical reactions that drogen would cost $25 per kW of thermal in- could form closed hydrogen-producing cy - 82Data provided by ERDA, Off Ice of Conservation 8 ‘E isenstadt and Cox, op c It , A Techrroeconornjc “G Strlck land and J J Reilly, Operating Manua/ Analysis of Large-Scale Thermochemical Production of for the PSE&G Hydrogen Reser\oir Containing Hydrogen, (E PRI EM-287), December 1976, Pre//rm;nary Tita rJIum Hycfrlcfe, Brook haven National [Lab , A5se55ment 0/ Econom/cs of Hydrogen Procfuctlon February 1974 From Lawrence Liverrnore Laboratory, ZnSe Thermo- a’JUtJ/)zar)on ot C~ff-Peak Power to Produce /n- cherr~lca/ Cyc/e, Un Ited E nglneers, September 1976 dustr/a/ Hydrogen, EPRI 320-1, Final Report, prepared 84R F Chao and K E Cox, “An Analysls of Hydro- by I nstltute of (;a~ Technology, August 1975 gen Produc tlon vIa C Iosed Cycle Schemes, ” Pro- “M M E lsen~tadt and K E Cox, “ Hydrogen Pro- ceedings, THEME Conference, Mlaml Beach, Fla , duction From SoJ~r [ nergy, ” So/ar [nergy, 1 7(1 ), 1975, S13 1 -S1 32 (March 1974), cited In E Isenstadt and Cox p 59 a5Pangborn, op cit , p 174 64 ● Solar Technology to Today’s Energy Needs

put capacity .8’ Converting this to 1976 dol- withstanding high temperatures. The devel- lars and removing the contractors overhead opment of such a receiver presents a major and profit, which will be added in later, this problem. The system would also require rel- cost is $26 per kW of thermal input capac- atively large heat exchangers at both the ity, or $57 per kw of hydrogen- production collector site and in the system for reacting capacity. This cost does not include the cost the sulfur dioxide to generate heat. This of hydrogen storage tanks, which would cost results from the high molecular weight of a great deal. A big central system could pipe the materials used and the necessity of con- the hydrogen to gas customers in natural gas densing the products in the heat exchangers. pipelines, or store it in depleted natural gas The sulfur system could also present corro- wells, but these options may not be avail- sion problems since corrosive acids would able to the small onsite units. I n addition, form if any water entered the system; the much work remains to be done on the sys- safety problems associated with piping the tems, however, and it seems that the chemis- materials must also be examined. try required will be too complex for any but Examining the chemicals in table Xl-6, it the largest “onsite” facilities being exam- appears that one of the most attractive mained in this study. terials for high-temperature storage would be NH HS0 , since all of its reaction prod- SULPHUR DIOXIDE/SULPHUR TRIOXIDE 4 4 ucts can be stored as Iiquids at ambient tem- Some of these difficulties associated with perature and since its reaction temperatures the methane system can be avoided in the are not as high as those required for the S03 other simple chemical system which has re- system .87 Work has begun on this and a va- ceived major interest—the riety of other reactions, and it is clear that not all possibilities have been explored.

The sulphur compounds used in this stor- reaction. Its major advantage is that only age system could create environmental haz- the oxygen cannot be stored as a liquid at ards if the equipment leaks or is not proper- ambient pressure and temperatures; this rely maintained. Accumulations of sulfur- sults in a very substantial saving in the cost based gasses can be highly toxic and may be of storing the material. The system has no explosive under the right conditions. side reactions, and it requires relatively small catalyst volumes. Since the sulfur trioxide reaction reaches Summary completion at temperatures nearly 2000 F higher than the methane/steam system, a re- The costs of several of the high-tempera- ceiver and reaction chamber must be made ture thermal storage systems discussed in out of ceramics or other material capable of this section are summarized in figure XI-21.

ELECTRIC STORAGE

All of the storage devices examined thus engine. It is also possible to store the elec- far are designed to deliver heat which can tricity produced by heat-engine generators be either used directly to heat a building or or photovoltaic devices. EIectricity can be for some other purpose or to operate a heat “stored” directly in a loop of superconduct- ing (zero-resistance) wire, and although research is being conducted on such devices, sw Hauz, et al,, Publication 72 TM P-1 5, General Electrlc-TEMPO, Santa Barbara, Calif., April 1972, cited in E isenstadt and Cox. a7Wentworth and Chen, op. cit Ch. Xl Energy Storage ● 465

Figure XI-21 .— High-Temperature Thermal Storage Cost per kWht Versus Storage Capacity

200

100

1.00

.50

.20

Note: The storage units would lose only about 5Y0 of the energy stored in the interval indicated.

.10

100 1000 104 105 10’ Storage capacity (kWht) 466 ● Solar Technology to Today’s Energy Needs

they are unlikely to play a significant role in age reservoirs deep underground as llus- energy storage for some time. AlI other trated in figure Xl-22. Such a facility could forms of electric “storage” convert the elec- be located wherever minable rock exists at tricity into mechanical or chemical energy the required depths, but would cost consid- in such a way that electricity can be easily erably more than a standard hydroelectric removed. facility. Recent estimates of the cost of a pumped hydroelectric facility capable of producing 2,000 MWe for 10 hours range MECHANICAL STORAGE DEVICES from $270 to $350/kW.88 Looking in another direction, it has been The only large-scale electric storage sys- found that a very large amount of potential tems in use today are pumped hydroelectric hydroelectric capacity can be found in the storage facilities. A conventional installa- numerous small dams which already exist tion consists of two lakes connected with a around the United States. The generating device which is a combination pump and capacity of existing small hydroelectric sites turbine generator. Water is pumped into the could be expanded, and generators could be upper lake when energy is available to added to a number of dams which currently charge the storage and is discharged are used exclusively for other purposes, The through the turbine generator when the results of a preliminary survey of the op- system is discharged. Standard hydroelec- portunities presented by existing dams are tric facilities can provide storage since the summarized in figure Xl-23 and table Xl-7. flow of water through turbines can be re- The survey discovered that a generating stricted during periods of low demand, in ef- capacity of 26.6 GWe could be installed at fect storing water in the dam’s lake for later small dams (dams capable of producing less use. than 5 MWe of power) and that these small facilities could provide 159 billion kWh an- Hydroelectric storage facilities are likely nually. This represented approximately half to continue to be one of the least expensive of the new capacity identified. The extent to techniques for storing electricity, even if ad- which such dams couId be used for power vanced electric storage systems of other and storage cannot be determined without a types are developed. Unfortunately, the more detailed examination of the issue. United States has already exploited a significant fraction of the most attractive sites for It must also be recognized that solar hydroelectric facilities, and attempts to de- energy systems will not be able to benefit velop many of the remaining sites are likely directly from most of the added hydroelec- to face determined opposition on environ- tric capacity, since utilities will want to take mental grounds. A number of potential sites maximum advantage of new and existing hy- are protected under the “Wild and Scenic droelectric facilities for storage and for Rivers Act” and other legislation. A pumped meeting peak demands. Solar equipment hydroelectric facility is particularly unat- could benefit indirectly to the extent that tractive from an environmental standpoint, the new facilities improve the ability of util- and the lakes created are difficult to use for ities to meet fluctuating demands. Mechan- recreation. This is because the water levels ical storage of electricity can also be accom- in lakes created in a pumped hydroelectric plished with flywheels by compressing gas in system change significantly throughout the underground caverns for use in Braxton cy- day and the pumping continuously mixes cle engines, and in other ways. These tech- water from different parts of the lake. niques have been adequately reviewed elsewhere.

It may be possible to greatly expand the “Frank M. Scott, “Underground Hydroelectric number of potential sites for pumped hydro- Pumped Storage. A Practical Option,” Energy, Fall electric facilities by placing one of the stor- 1977, p 20. -—

Ch. XI Energy Storage . 467

Figure Xl-22.— An Isometric View of an Underground Pumped Storage Plant

Vent house

Ground— level / Upper reservoir ‘ Access building

Penstock shaft

Construction and ventilation shaft

Lower reservoir

Manifold Pens

Tail race tunnels and sucti (Not to scale)

SOURCE: Scott, Frank M. “Underground Hydroelectric Pumped Storage: A Practical Option” Energy Fall/1977 p. 20 468 . Solar Technology to Today’s Energy Needs

Figure Xl-23.— Conventional Hydroelectric Capacity Potential at Existing Dams

36,418

15 35,661

\ 9

i ‘--7

SOURCE McDOnald. R J Pr[ncfipal lnV=tI@o~ (us .ArmY cows O! Efwmeers Es!,mate of Na!lonal l+ydroeleclrtc Power POtentlal at Extst#ng Dams July 20 1977 Ch. Xl Energy Storage ● 469

Table XI-7.-Conventional Hydroelectric Capacity Constructed and Potential at Existing Dams —— Capacity Generation (millions of (billions of kW) kWh)

Developed ...... 57.0 271.0 Under construction . . . . . 8.2 16.8

Total installed ...... 65.2 287.8

Potential rehabilitation of existing hydrodams 5.1 24.4 Potential expansion of existing hydrodams . . . 15.9 29.8 Potential at existing non- hydro dams greater than 5,000 kW ...... 7.0 20.4 Potential at existing non- hydro dams less than 5,000 kW ...... 26.6 84.7 Total potential . . . . . 54.6 159.3

Total (developed and undeveloped). 119.8 447.1

SOURCE: McDonald, R J Principal Investigator (U.S. Army Corps of Engineers Institute for Water Resources), “Estimate of Na- tional Hydroelectric Power Potential at Exlstlng Dams,” July 20, 1977

BATTERY STORAGE ysis on this point must be performed for each type of battery. It is likely that there Batteries are able to store electrical en- will be an optimum size for each device. ergy by using a variety of different reversible electro-chemical reactions. The electri- Lead-acid batteries are the only devices cal energy must be introduced and with- currently mass produced for storing large drawn from batteries as direct current, how- amounts of electrical energy using electro- ever, and a “power-conditioning” device chemical reactions. Systems as large as must be included in any battery system 5,000 kWh are currently used in diesel sub- which receives and produces alternating marines. Batteries now on the market which current. Within large bounds, the cost of can be deeply discharged often enough to batteries per unit of storage capacity is in- be attractive for onsite or utility storage ap- dependent of the size of the system since plications, however, are too expensive for most batteries are built by combining a economic use by electric utilities. Extensive large number of individual reacting cells. work is being done to determine whether it Larger systems may benefit from some econ- is possible to develop batteries suitable for omies of scale because of savings due to use in utility systems. Work is being done on more efficient packing, lower building costs, advanced lead-acid battery designs and on and possibly lower costs of power condition- several types of advanced batteries which it ing for larger systems, but a separate anal- is hoped will be less expensive than lead- 470 ● Solar Technology to Today’s Energy Needs

acid batteries in the long term. This work The Department of Energy asked several has been thoroughly reviewed in several re- battery manufacturers to estimate how cent papers .89 90 91 92 much it would cost to manufacture a battery capable of storing 5 megawatt-hours, discharging in 10 hours, and lasting 500 to Lead-Acid Batteries 1,000 cycles, using essentially off-the-shelf components. The manufacturers’ responses When voltage is applied to a lead-acid averaged about $93/kWh, but responses battery, energy is stored by converting the varied from $41 to $138/kWh.95 This spread

lead sulfate (PbSO4) on the battery elec- reflects a range of battery capabilities. An trodes into a mixture of pure lead (Pb), lead independent survey conducted by the Bech- dioxide (PbO2), and sulphuric acid (H2S04); tel Corporation resulted in an estimate of the reaction is reversed when the battery is about $63/kWh.96 discharged. The industrial battery price of $80/kWh The current market for lead-acid batteries will be used in further analysis to represent capable of muItiple deep cycles is very Iim- “current” battery prices for community ited and prices are high. (Automobile bat- systems. teries cannot be used in power applications since the full charge in such batteries can- While the range of prices encountered for not be withdrawn repeatedly without dam- near-term batteries reflects the differing aging the battery. ) “Houselighting battery specifications, production rates, etc., there sets” are being manufactured for use with is rather remarkable agreement about what windmills and remote generating plants. batteries will cost in the intermediate term Units capable of 2,000 deep cycles cost ap- when comparable assumptions are used. Ta- proximately $385/kWh.93 94 Golf cart bat- ble Xl-8 shows recent estimates of the price and specifications of load-leveling batteries, teries sell for as little as $40/kWh, but are only capable of about 350 cycles. Industrial assuming a production rate of 1,000 MWh/yr in a dedicated production facility. These es- traction batteries, used in fork-lift trucks timates reflect a relatively rapid writeoff of and the like, have Iifetimes of nearly 2,000 97 cycles and are available for as little as plant costs. Westinghouse has estimated a selling price of $41.68/kWh by assuming ver- $80/kWh. tical integration of lead production and battery manufacture, present battery technol- 89An Assessment of Energy Storage Systems Suitable ogy, and more optimistic assumptions about for Use by E/ectric Uti/ities, Public Service Electric writeoff. and Gas Company under E PRI Project 225 and ERDA Contract No E (11-1 ~2501, Vols. I & 11, july 1976. A major disadvantage of contemporary ‘“Near-Term Energy Storage Technologies: The Lead- lead-acid battery designs is their relatively Acid Battery, a compilation of papers presented at the ERDA-E PRI-ILERO Workshop, Dec. 18-19, 1975, EPRI low storage capacity per unit weight. This is SR-33 due largely to the amount of lead used. 91j R, Birk, The Lead-Acid Battery for E/ectric Lead-acid batteries have a theoretical “en- Utilities: A Review and Analysis, presented at ERDA- ergy density” of about 0.175 kWh/kg, and E PRI Lead-Acid Battery Workshop 11, Dec. 9,1976 ‘*Ralph Whitaker and Jim Birk, “Storage Batter[es: The Case and the Candidates, ” EPR/ journa/, October ““A National Battery Energy Storage Test (BEST) 1976, pp 6-13 Facility Conceptual Design and Design and Cost “Prices quoted by Solar Wind Company, North Estimate,” BEST Facility Study Project Team, EPRI Orland, Maine The batteries are of Austrian manufac- 255, ERDA 31-109-38-2962, Technical Report 1, August ture and come in a clear polystyrene case with bu i It-in 1975, p I 11-11 pilot-ball charge indicators in each cell. 9’Bechtel Corporation, op clt “All prices quoted are based on the battery capaci- 97 Study of the Manufacturing Costs of Lead-Acid ty when discharged to rated depth-of- discharge flatteries for Peaking Power, Final Report, Unless otherwise stated, it is assumed that batteries Westinghouse Electric Corp , ERDA Contract No. operate with 80-percent discharge in a typical cycle. E(40-18}21 14, December 1976, Ch. Xl Energy Storage 471

Table X1.8.—Economic Specifications (5-hr Battery) ——— . .— . Specification C&Da ESB Globe-Union Gould Westing - houseb

d Price ($/kWh)c ...... 55 56 58 54 49 Life (cycles at 77” F), ., . . 2,000 2,000 2,000 2,000 1,750 (95° F) Price/cycle, ., ...... , . . . . 2.7 2,8 2.9 2.7 2.8 Efficiency (%)e . . ., ., 73 76 72 70 68 Replacement price ($/kWhr) 40 32 38 25 34 O&M cost (mills/ kWhr) 0.28 0.18 — — — —- —.-

aea~ed upon B50,0 depth Of d IsCharge to achieve 2,000 cycles Instead of 95°. of discharge to achieve 1,250 cycles at a price of $49/ kWhr (to be discussed) bDoes no[ reflect raw ~aterlals Integration and market optimism Included by Westinghouse (to be discussed) cAssumes 25c / lb lead

‘Installed cost el ncl udes Conversion eff Iclency Of 9000

SOURCE James R Blrk, “The Lead-Acid Battery for Electrlc Utlllt}es A Review and Analysls “presented at the ERDA / EPRI Lead-Acid Battery Workshop 11, Dec 9, 1976 thus a perfect battery would weigh about using aluminum electrodes covered with a 12,6 pounds per kWh. Commercial batteries lead coating. The device is currently being weigh more than this because of design inef- tested by EPRI.99 ficiencies and the need to provide packag- The current U.S. production rate of lead ing for the active materials Commercial could support all foreseeable needs of on- lead-acid systems weigh about 100 pounds site electric systems and should be able to per kWh of storage capacity, of which 60 to support the development of a nationwide 80 pounds is lead The cost of this rather battery system used for utility peak shaving substantiaI quantity of lead imposes a prac- (although the price of lead would undoubt- tical lower limit on the price of lead-acid edly increase if a very large demand devel- batteries oped). Present U.S. domestic lead consump- In 1975, when ERDA asked three of the tion is about 600,000 tons per year, and our largest battery manufacturers in the United reserves are estimated at 40 miIIion tons States to design the lowest cost battery for (World production is approximately 3.6 utility applications, the estimates of mate- mill ion tons and world reserves 141 mill ion rial costs ranged from $24 to $34/kWh.98 tons.)1oo Thus, at present energy densities, (The range is much smaller if allowance is current production rates could provide 15 to made for the differing Iifetimes of the de- 20 million kWh of storage per year or signs. ) Very high production volumes would enough to provide 4,000 to 5,000 MWe for 4 be required before the price of the complete hours every day. At this rate of production, battery would approach this minimum therefore, it would take 10 years to develop material cost. a battery system capable of meeting 10 percent of U.S. electricity demand for 4 hours The Axel Johnson Institute for industrial Research in Sweden has proposed a novel technique for reducing lead requirements by “A C Slrnon and S M Cauldar, “The Lead-Acid f3a t tery, Proceeding~, Symposium and Workshop on Advanced F3attery Resear( h and Design, Argonne Na- tlon~l Ldbordtory (AN L-76-8), Nldrc h 1976 ‘“OM/ner.?l\ \earbooA, U S Department of the ln- terlor, [3u reau of JMI ne~, 1973 472 ● Solar Technology to Today’s Energy Needs

per day. The lead used in the batteries is not energy storage is presently unknown. The consumed in the storage process, and after recognition of the possible adverse environ- the initial investment is made, the material mental impact of arsine and stibine and im- can be recycled indefinitely. plementation of appropriate safeguards– proper battery placement and ventilation – An ordinary automobile battery will last 3 reduces the risk of harm from these gasses. to 5 years, undergoing extremely shallow cycles several times a day, but would be capable of only 150 to 250 deep discharges. Advanced Batteries The electrodes in batteries used in golf carts, industrial forklifts, etc., are usually 2 Three basic categories of advanced sys- or 3 times as thick as those used in car bat- tems are under exam i nation: teries and are typically capable of 300 to 1. Aqueous or water-based systems which 500 deep cycles. Batteries capable of dis- operate with electrodes surrounded by charging 2,000 times are currently available a liquid electrolyte, as do lead-acid and this has become a design objective for systems. utiIity storage batteries. 2. Nonaqueous high-temperature systems, A practical limit to the depth of discharge which use a nonaqueous material to which can be obtained from a given battery conduct ions needed to complete the design can be obtained by watching the bat- electrochemical reaction. tery’s voltage. This voltage drops slowly during discharge and then begins to f al I sharply. 3. “RED OX” (reduction/oxidation) devices If the battery is discharged beyond this which reduce aqueous solutions to point, its life is shortened substantially. store energy. (REDOX batteries are “aqueous,” but they are usually con- ENVIRONMENTAL AND SAFETY PROBLEMS sidered separately. )

Lead-acid batteries produce potentially Table Xl-9 summarizes the characteristics hazardous gasses, such as hydrogen, arsine of several advanced battery designs.

(AsH,), and stibine (SbH3) when they are cycled. Hydrogen released in the atmos- AQUEOUS BATTERIES phere has no effect on air quality or human Zinc Chloride health, but is highly flammable and explosive in concentrations above 3 percent. This Zinc-chloride batteries are aqueous de danger can be eliminated by placing bat- vices which can store electrical energy in teries in well-ventilated compartments. aqueous chemical solutions at ambient tem- Arsine and stibine are toxic, colorless, perature. Research on this battery is under- gaseous compounds which form during the way in a joint venture of Gulf Western In- required, periodic, high-voltage charging of dustries and the Occidental Petroleum Cor- lead-acid batteries. For example, the recom- poration. Small (50 kWh) units have been mended threshold Iimit values for arsine and tested at Argonne National Laboratory, and stibine in workroom air are 0.05 ppm (0.2 it is expected that a 10 MWh battery will be mg/m3) and 0.1 ppm (0.5 mg/m3), respective tested in a realistic utility environment by

lO1 1980. Iy. Whether these levels will be exceeded when charging lead-acid batteries for home The small experimental batteries now being produced cost approximately $2000 a kilowatt hour, but when the system reaches ‘“’’’ Report on an Engineering Study of a 20 MWh production stages, cost is expected to be Lead-Acid Battery Energy Storage Demonstration reduced to $40 to $50. This is more expen- Plant,” for Argonne National Laboratory under Con- tract No. 31-109-38-2962, by Bechtel Corporation, Oc- sive than projections for lithium or sodium tober 1975, p. 5-5. battery systems, but this cost is offset to ,.

Table X1.9.—Load-Leveling Batteries: Candidates and Characteristics; Developers and Demonstration Dates

Lead acid (Pb/Pb02) 2030 110 11 075 25 10 -15 850 >20 2,000 Lead Gould Inc ESB Inc C&D 1979 1981 83 Batteries Globe-Union Inc.: K.W. Battery Co Sodium sulfur (Na / S) 300350 360 70 25 85 75 049 05 400 General Electric Co Dow 1981 82 Chemical Co Ford Motor Sodium-antimony co trichloride

(NA SbCl3) 200 350 50 20 80-90 25 235 002 175 Antimony ESB Inc 1981 82 Litium-metal sulfide 400450 430 85 35 80 30 4 27 10 1000 Lithium Atomics International DIV RockwelI International Corp.: Argonne National Zinc chlorine Laboratory 1980 b (Xn/Cl2) 50 210 45 10 100 40-50 Theor - 0.59c 1.7 Ruthenium Energy Development As- 1980 Practical - 0.84 (catalyst) sociates Z[nc-bromine 15 — (Zn / Br2) 30-60 195 40 90 30 Theor - 1.56 01 2.000 None Exxon Gould GE 1983 Post 1985 Practical - 1.65 Hydrogen-chlorine 03 (H2 /Cl2 ) 30-60 450 50 95 300 20 001 50 Platinum Ruthenium GE, BNL 1983 . Post 198’3 (catalyst) — 40d — REDOX am bient 90 40-60 $3-$10 005 200 None NASA-Lewis 1984 1986 1988 Iron REDOX ambient — 38 26 $1 >1 ,000 None GEL 1980

aAl SCJ known as Utw!zatlon of acllve m.ater, als

b5 n, rate ‘GE c al, dales fof IZ.I,IZI I a[whllstre 0! sol. t,onl

SOURCES EPRI Journal and K.n w Klund91 Battery Branch Of f#ce of Conservation EROA I \ 474 ● Solar Technology to Today’s Energy Needs

some extent by the fact that zinc-chloride tive materials which are inexpensive and batteries produce a constant voltage and widely available. Most of the development equipment necessary to convert the current work on this battery has centered on a solid to a.c. is cheaper than other systems, result- electrolyte material called “beta-alumina” ing in an overall competitive price. Zinc- (an alloy made of sodium, aluminum, and chloride batteries are capable of operating oxygen), 05 and the electrolyte costs consid- at ambient temperatures, but require a com- erably more than the active materials to- plex plumbing system for circulating the day. ’”’ Small 10-to-15 watt sodium/sulfur electrolyte and controlling the temperature celIs are now being run in excess of 3,000 of the system. ’02 ’03 The presence of chlorine cycles, and Ford hopes to test a 5-to-10 gases could create an environmental prob- MWh battery in late 1981. A second sod- lem if used in onsite systems. ium/sulfur concept is being developed by Dow Chemical, and is about 2 years behind Zinc Bromide the Ford research. Both systems still cost some $3,000 a kilowatt hour, but projections The zinc-bromide battery is another aque- are that the Ford system will be reduced to ous device being developed primarily for $30 by 1985-87, while Dow suggests that a utiIity load leveling and electric automo- $24.50 cost can be attained perhaps a year biles. Early work on these batteries was done later from its system. G.E. and EPRI spent by the G.E.L. Corporation of Durham, N.C. about $3.5 million developing this system Devices developed by the General Electric between 1967 and 1976, and expect to spend Corporation have operated for more than about $3.5 milIion in FY 78. 2,000 cycles of 2.5 hours discharges. ’04 Systems have been demonstrated which Researchers at G.E. believe that batteries are capable of 90-percent discharge and 77 based on this concept, capable of 65 to 80 percent-efficiencies. ’07 The major develop- percent efficiencies, should cost no more ment problem remains the beta-alumina than $17 to $26/kWh (excluding the cost of electrolyte. Poor quality material tends to pumps, controls, and marketing). The major crack and degrade and seals have been unre- problem is the development of a low-cost liable, Another issue, identified as a prob- and reliable membrane. Imperfect mem- lem by G.E,, is the difficulty which may be branes lead to a “self-discharge.” In the encountered in scaling the units up to a size most recent G, E. designs, the cell discharges where they can be used in large central util- at about 0.1 percent per hour. ity applications. It is expected that large bat- One potentialIy serious problem with zinc teries will be constructed from units of 10 to bromide is the caustic nature of the bromine 100 kWh.‘08 solution. Containment of this material can be expensive and great care must be taken Lithium-Metal Sulfides to ensure that this powerful chemical is Lithium-metal sulfide batteries are being properly contained. examined primarily by Argonne National Laboratories under a DOE contract. Ar- HIGH-TEMPERATURE BATTERIES gonne is now making 150 W/h cells capable

Sodium/Sulfur ““N P Yao and J R Birk, op cit , p 1107. Sodium/sulfur batteries, under develop- IObArthur L Robinson, “Advanced Storage Bat- ments by the Ford Motor Company, use ac- teries Progress But Not E lectrlfytng, ” Science, May 7, 1976, p 543 ‘(l’N Yao and j .R Blrk, op cit. ‘07S. P Mitoff, et al , “Recent Progress In the “] ‘t3echtel Corp , op cit. Development of Sodium Sulphur Battery for Utility ‘(”F G Will, “The Zinc-Bromide Battery: Possible Applications, ” Proceedings, 12th I ECEC Conference, Candidate for E Iectric Vehicles and Load Level ing, ” 1977 Proceedings, 12th IECEC Conference, 1977, p 250. ‘O’S P Mltoff, Op. clt Ch. X/ Energy Storage 475

of 500 deep cycles. I n 1982, a 5-to-1 O MWh In a standard REDOX battery, the two cell module is scheduled to be tested in storage tanks (called the “catholyte reser- Argonne’s Battery Energy Storage Test voir” and the “anolyte reservoir” in the dia- (BEST) facility. Argonne foresees a cost of gram) contain different chemicals. In one $29.16 per kWh at full production in design which has received recent attention, 1985-87. Like sodium/sulfur batteries, lith- the tank connected to the positive terminal ium-metal sulfide devices now cost about contains a solution of Fe+2 and Fe+ 3 ions, $3,000 a kwh to produce experimentally and the tank connected to the negative ter- and in small working applications. minal contains a solution of Ti+ 3 and Ti+4 ions. When the battery is completely dis- Both the sodium/sulfur and the lithium- charged, the one tank is filled with FeCl and metal sulfide batteries operate at tempera- 2 the other with TiCl . When the battery is be- tures above 300 “C, and the combination of 4 ing charged, negatively charged chlorine high temperatures and reactive materials re- ions drift across the semipermeable mem- quires hermetic sealing.109 There are accom- brane and combine with FeCl , producing panying seal problems. Questions have been 2 FeCl and giving up the extra negative raised about the safety of using the sod- 3 charge to the positive terminal. On the other ium/sulfur system in large numbers unless side of the membrane, chlorine ions are re- stringent precautions are taken to protect leased when TiCl forms TiCl , taking an against a rupture of the containment vessel. 4 3 electron from the negative electrode. The Since the lithium battery uses two metals, electric current from the positive to the the chemical reaction caused by a rupture negative electrode is matched by the flow of would not be as serious as it would in a chlorine ions across the membrane. It is im- sodium cell, which uses two Iiquids. portant that the membrane be able to pass Both lithium and sodium are flammable chlorine ions with minimal resistance, but and, under some conditions, explosive. 10 not allow either the iron or the titanium to The use of lithium and sodium batteries, pass. If iron or titanium leaks through the therefore, must include careful provision for membrane, the performance of the device is fire and explosion containment. gradually degraded. NASA-Lewis has been working on systems based on this design for REDOX BATTERIES a number of years, and it is hoped that a battery suitable for demonstration in utility ap- The REDOX battery presents a tantalizing plications will be available by 1985. opportunity for electric storage since devices based on the design may be able to Iron REDOX store energy in tanks of inexpensive chemicals; storage costs couId be $10/kWh or less. The iron-REDOX battery being developed The problem which has plagued the devel- by the G.E.L. Corporation operates on much opment of these systems for many years is the same principle as the REDOX system just the need for a semipermeable membrane described, but uses the same chemical at with some rather remarkable properties. The both electrodes, thereby greatly simplifying need for a sophisticated membrane could be the requirements placed on the mem- eliminated, however, if an iron-REDOX de- brane. 112 The basic components of an iron- sign is perfected. REDOX battery system are illustrated in figure Xl-24.

When the iron-REDOX system is com- ’09 Herbert P. Silverman, Lynn S. Marcoux, and Ed- die T. See, TRW, Inc , “Development Program for pletely discharged, the storage tanks are Solld E Iectrolyte Batteries, ” Final Report for EPRI, EM-226, September 1976 “ ‘K. W. Klunder, Office of Conservation, ERDA, 1 I°Chemlcal Rubber Company, Handbook of private communication Chemistry and Physics, 54th Edltlon, 1973-74, pp B-19, 1 12The C E L. Corporation, Durham, N C , Per- B-31 formance Status, January 1977 476 ● Solar Technology to Today’s Energy Needs

by resistive heating. With design improvements it may be possible to achieve overall efficiencies of 80 to 85 percent with moderate discharge rates. The system is not damaged by deep discharges.

The reaction chamber with its membrane will account for the bulk of the cost of the iron-REDOX system – the chemicals and the tanks needed to store them will probably cost less than $2/kWh. The cost of this reaction chamber is a direct function of the area of membrane required. G. E. L. estimates that the graphite electrodes they are now using can store about 1 amp-hour per square inch of electrode surface. After this thickness has been deposited, the deposited iron becomes uneven and physically unstable. If a large area is allowed per unit of power delivered, the system is more efficient but costs per kilowatt increase. The cost of reactors capable of delivering different amounts of power ‘ “Dr. R Zito, President, the G.E. L Corporation, per unit of membrane surface is shown in ta- private communication, September 1977. ble XI-10. An electric storage system de-

Figure Xl-24.— lron”REDOX Battery Structure and Plumbing Diagram

Catholyte

SOURCE: GEL, Inc , Durham, N C Ch. Xl Energy Storage ● 477

Table XI-10.— Loss Mechanisms of matures. To date, no chemical or mechan- iron-REDOX Batteries ical problems have been encountered which would cast doubt on the ultimate practical- Loss factors ity of the device. However, firm conclusions are not possible until information becomes Loss mechanisms Percent at Percent at 0.10 A / in2 0.4 A / in2 available from a demonstration of the full- scale system.

H 2 evolution . . ., . . . . . 1-2 2.3 pH regeneration . . . . ., 1-2 2-3 POWER CONDITIONERS Fe + 3 membrane diffusion . 2-3 0.5-2 Joule heating Design Alternatives —electrolyte 2-4 6-14 —thru membrane . . . . -o -o Most battery storage systems will require 14-20 Polarization effects ., . . 14-20 some kind of “power-conditioning” system Fluid pumping, ...... ‘1 -1 to supervise their connection with sources Fluid manifold conduction -1-2 -1-2 of charging energy and with the loads met Total loss...... 22-34 26.5-45 whiIe discharging.

Reactor cost ...... $68/ kW $18/kW This equipment can serve four functions: 1 SOURCE The G E L Corporation, Durham, N C., September 1977 Regulate the rate at which a battery is charged and discharged to protect the battery and extend its useful life; signed for use in a solar energy application may require a device capable of storing a 2 Serve as a switching system, and deter- large amount of energy for periods of 10 to mine whether the loads will be met di- 20 days, but there would be no need to dis- rectly from the onsite generating sys- charge the entire device over a short period. tem, from storage, from the utility, or The REDOX device would appear to be well from some combination of these (in suited for such an application. some cases it can also allow the storage to be charged from the utility); The devices will probably not show significant economies of scale until systems of 3 Rectify alternating current received more than a few hundred kwh of storage from the onsite generator or from the capacity are constructed. utiIity so that this energy can be used to charge the battery; and G.E.L. is presently constructing a 2.2 MWh iron-REDOX battery system with a peak out- 4 Invert the direct current produced by put of 250 kW for use in the Mississippi the battery or by the onsite generating County Community College total solar en- equipment, creating alternating current ergy system. This DOE-sponsored project whose voltage and frequency meet ac- should be operating by late 1979. The stor- ceptable standards of uniformity. age system will consist of 24 reactor mod- A system which can perform all of these ules rated at 11 kW. Each module will con- functions is illustrated in figure Xl-26. Not tain 130 to 150 bipolar electrodes and will alI devices will be as complex as the one measure approximately 120 x 60 x 240 cm shown, and designs wilI differ greatly from (2 ‘ x 4 ‘ x 8 ‘). The entire system will require one application to another. 60,000 to 80,000 liters (1 5,000 to 20,000 gallons) of electrolyte. A model of the sys- The most important design decision is tem is shown in figure Xl-25. Electrodes and whether to use an inverter. These devices membranes for the system have been devel- are by far the most complex elements of a oped for reproduction with acceptable elec- power-conditioning system and represent 85 trical and mechanical characteristics, but to 95 percent of the cost of a typical power improvements can be expected as the design conditioner. Inverters would not be needed 478 ● Solar Technology to Today’s Energy Needs

Figure Xl-25.— Model of iron-REDOX Battery Facility

...... * . . .-. .*X-. .K?. -...... - .... .s. ss.

SOURCE: G. E, L.. Inc Ch. Xl Energy Storage 479

Figure XI-26.—The Elements of a Power Conditioning System

DC Loads

Battery Interface

I Interface

I AC Loads

if local loads could be met by direct current, ● Direct current systems would require but these savings could be largely offset by more expensive switches and fuses, The the costs of converting a residence or indus- cost of wiring would be higher if low- try to d.c. operation. A quantitative assess- voltage d.c. were used, ment of this issue is beyond the scope of the It should also be recognized that a d.c, current study, but it is possible to outline system which relies on the utiIity grid to pro- the major factors which must be considered vide backup wilI need a rectifier. (Most in- If conversion to a d.c, system is converters can rectify as welI as invert and so templated: would not require separate rectifying equip- Over two-thirds of the power required merit. ) Rectifiers tend to cost about 30 per- in a typical residence is used in equip- cent as much as inverters of equivalent ment which could easily be converted power ratings. to d.c. operation. Incandescent lights, A typical inverter can provide some kind heaters, stoves, heating elements in of fauIt or short-circuit protection and can driers, etc., could all operate with provide a.c, synchronized with the utility direct current without major difficulty. grid. The cost, design, and performance of The only devices requiring a.c. are inverters vary greatly and are strongly de- fluorescent lights, systems with electric pendent on the quality of the a.c current re- motors, and electronic devices such as quired. Systems using grid backup wilI clear- televisions, radios, and the like. Most of ly be required to provide a well-filtered out- these appliances are currently available put which matches the grid in frequency and in d.c. versions, however, although some are more costly than their a.c.

equivalents. A complete Iine of residen- ‘“laclllty Systems E nglneerlng Corporation, 5/?oP- tial d.c appliances is available for PIng Center App/icat/errs of Photovo/ta/c So/dr Power mobiIe homes. Sys(ems, ERDA Contract (1 1-1 ~.2748, 1976 480 Solar Technology to Today’s Energy Needs

phase. Performance is usually specified in power supplies which are used in hospitals, terms of the voltage control, and the har- computer centers, and other installations monic content of the voltage produced. which cannot afford to lose power when grid electricity is unavailable. Much larger Older units frequently were nothing more units are in use and being developed for d.c. than a d.c. motor which drove an a.c. gener- transmission Iines. ator, but most modern devices use solid- state components based on silicon-con- The design of interface and regulator sys- trolled rectifiers. The solid-state devices are tems is quite straightforward and systems usually more reliable and require less main- are available in a variety of sizes. The com- tenance. Most of these systems are “line plexity and cost of the system will depend commutated” in that they rely on utility strongly on the speed with which the system power to establish the phase and frequency must shift from one power source to of their a.c. generation. Devices operating another, and on the system design. independently of grid power (self-commutated systems) are also available, but are System Performance more expensive. The efficiency of modern solid-state in- Interest in developing inverters of various verters is in the range of 92 to 95 percent sizes has come from a variety of places. when the devices are operating at more than Small inverters have been developed for about 25 percent of peak capacity. Below military applications, for smalI onsite gener- this point, the efficiency falls off quite ating plants (using windmills and conven- sharply since a fixed amount of energy is re- tional power sources), etc. Larger devices quired even at zero loads. Figure Xl-27 illus- are available from suppliers of interruptible trates the part-load efficiency of a typical

Figure Xl-27.— Efficiency of a Solid-State Inverter as a Function of Load

v 1 1 1 1 I 20 40 60 80 100

Operating point (0/~ of full load) SOURCE: MERADCOM, DoD Ch. Xl Energy Storage 481

sol id-state inverter. The mechanical inverter 2 An estimate based on present estimates systems mentioned earlier are typically less of the cost of lead-acid batteries and inefficient than the sol id-state units. verters produced in large numbers (1,000 MWh/yr) for distributed storage The overall operating efficiency of invert- applications. ers in small systems will probably be lower than the efficiency of inverters in large sys- 3 An advanced-concept estimate of fu- tems because there is less load diversity in ture prices which assumes that inexpen- the smaller systems. This can be expected to sive, advanced battery systems such as result in more operation at partial load. sodium/sulfur or lithium-metal sulfide are successfully developed. This price Voltage regulators are quite efficient at could also apply to very large contract all power levels; typical systems are 98- or Government purchases, where sales percent efficient. 115 overhead couId be reduced.

4. A very low-cost estimate which assumes BATTERY SYSTEM COSTS that low-cost advanced-concept systems such as iron-REDOX are success- Since there is considerable disagreement fully developed. about the future price of batteries and supporting equipment for onsite storage sys- The results of these estimates are summa- tems, cost estimates for battery storage sys- rized in table Xl-11 and figure Xl-28. tems wilI be given in four categories:

1. A near-term price, reflecting the costs The cost of a battery storage system con- of devices which could be purchased in sists of three major components: the cost of 1976. the battery itself; the cost of the power-conditioning system; and the remaining cost 1 ‘‘Bechtel Corporation, Energy Storage and Power which includes instalIation and the space re- Conditioning Aspects of Photovo/taic So/ar Power Systems, prepared for Spectrolab, I nc , under Sub- quired to house the system. The cost of each contract No 66725, October 1975. component is treated separately, . —

Table Xl-1 1 .—System Cost Estimates for Near-, Intermediate., and Lena-Term (Including 25-Percent Off) — Advanced concept or Long-term advanced Iead-acid tech- iron-REDOX Present technology nology wIth Iarqe firm con- Present market prices wtth mass production tracts (e.g., GSA) 1990-2000

Llfetlme (deep cycles) 2000 2000 2000 2000 0 & M cost (mills/kWh discharged) 028 028 (O 287) (c) Replacement cost (% of original) 85 60 100 100 Assumed discharge t I me (hours) 5 5 5 10

First costs (1) Commercial and multlfam{ly residentIal systems Battery cost ($/ kWh) BuIIding and other costsa ($/kWh) Power-cond!tlonIng costsb ($/kW) (2) Home systems Battery costs ($/kWh) BuIIdIng and other costs a ($/kwh) Power-condItIonInq costsb ($/kW) — — Ch. Xl Energy Storage . 483

Figure Xl-28.— Power-Conditioning Cost Versus Power

1000 0

~ 200 - ---- x

1 KW 1 MW

0.1 1 100 1000 100,000 1,000,000

Rated power (kW)

Below 10kW this data represents catalog prices and quotes for commercialIy available units

The unit at $10/kW (3kW) provides square wave output. The prices between 10 kW and 25 MW are prices for uninterruptible power suppIies less batteries which are generalIy more sophisticated t h an wiII be required for onsite electric systems The data for higher power levels represent projected prices for utility load-Ievellng systems

—The solid line segments represent prices for a single manufacturer as a function of size —– “Gemini Synchronous 8 kW Inserter, ” Windworks, P O Box 329, Mukwango. Wis

x Prices for current-fed inverter systems from Peter Wood. AC/DC power Conditioning and Control for Advanced Conversion and Storage Technology EPRI 390-1-1 (1975) The lower price IS for a Iine commutated system hiqher price IS for a comparable Isolated system Chapter Xl APPENDIXES Appendix XI=A A Technique for Estimating the Allowable Cost of Storage Devices

Computing the amount which can be E C = the cost of energy available for spent on storage equipment requires a care- charging storage ($/kWh) ful comparison of the Iife-cycle costs of sys- the efficiency of the storage tems with and without storage devices. It is equipment possible, however, to compute the approximate amount which can be spent on stor- M= the average annual operating cost age with the following simple algorithm: of the storage device ($/kWh of energy stored)

the installed cost of storage If the storage is not owned by the utility, capacity (in $/kWh) then the costs E and E represent the rates the average number of storage C d charged for electricity during peak and off- cycles per year peak periods. If the systems are owned by a

the fraction of the storage capacity utility, EC would represent the cost of energy used in an average cycle provided by a baseload plant used to charge storage and E would represent the cost of the effective cost of capital (see d energy provided by a peaking plant. The chapter IX) allowable cost of storage calculated in this the cost of energy available when way is iIlustrated for a variety of different storage is discharged ($/kWh) assumptions in figure Xl-A-1.

Figure Xl-A-1.– Permissible Cost of Storage Equipment as a Function of Energy Prices During Storage Charge and Discharge

Batteries: intermediate term

Pumped hydroelectric Brick storage onslle

Low temperature Thermal storage

487 Appendix Xl-B Analysis of Performance —

A perfect thermal-storage system would charged from the collectors at a tempera- return all of the energy supplied to it at the ture close to the temperature at which the temperature at which the energy was orig- fluids will ultimately be used. In general, inalIy supplied. I n real systems, of course, systems which use the stored heat only for energy is lost through the containers and the space heating and domestic hot water will transport system, and the temperatures of not be as sensitive to temperature degrada- fluids which discharge the storage are lower tion as systems which generate electricity or than those used to “charge” the storage with which drive air-conditioning systems direct- thermal energy. This temperature reduction Iy, but size and cost of even simple systems results not only from a net loss of energy to can be reduced if the temperatures can be the surroundings, but also from the mixing kept high. of hot and cold fluids in the storage vessel The designs chosen will depend crucially (if a single tank is used), unless stratification on the economics of the system. Insulation is achieved, and from the temperature dif- should be added until the incremental value ference which must be maintained across of the energy saved by insulation equals the any heat exchangers which are employed. incremental cost of adding insulation, Simi- One advantage of chemical storage sys- Iarly, the sophistication of systems designed tems is that the products of the reactions to maintain temperatures at constant levels can usually be stored at ambient tempera- should be increased until the incremental tures. In chemical systems, however, tem- value of the energy provided by these sys- perature losses are the necessary result of tems is less than the incremental investment the fact that reversible reactions must oper- needed to prevent the additional drop in ate with the forward reaction occurring at a temperature. temperature different from the reverse reaction. Energy is also lost during the process of STORAGE TEMPERATURE LOSS AND cooling the hot chemicals emerging from HEAT ENGINE EFFICIENCY the high-temperature reaction chambers down to ambient temperature. Some chemi- In the immediately foIlowing analysis, cal reactions also require the addition of losses through insulation and temperature “process heat” to stimulate intermediate drops across heat exchangers are ignored for processes, and this heat requirement lowers simplicity; they are included later. A de- the overall “efficiency” of the storage proc- tailed analysis of the effect of heat ex- ess. changers is contained in appendix A of Bramlette. 1 The significance of energy lost through in- The performance of heat engines can be sulation, parasitic loads due to pumps, proc- approximated by assuming that their me- ess heat, etc., is clear. This is energy which chanical or electrical output is some frac- cannot be recovered for usefuI work. On the tion (f ) of their ideal Carnot efficiency. other hand, the significance of storage tem- e

perature reductions which do not result in a Q out = fe Q ln (1-TC /Th ) net loss of energy requires more explana- (constant-temperature storage or two-tank system) tion: 1 ) heat engines are more efficient at where Q is the mechanical or electrical high temperatures, and 2) the performance Out energy generated by the heat engine, Q, of solar collectors decreases as the exit tem- n perature of fluids produced by the collec- I T T Bramlette, et al (Sandla I-a boratorles, Liver- tors increases; thus collector performance is more), Survey of E//gh- Temperature Therma/ Energy maximized if the storage system can be Storage, SAN D75-8063, March 1976

488 —

Appendix XI-B ● 489

was the energy originalIy sent to the storage,

T c is the temperature at which heat is rejected from the engine, Th is the temperature at which energy is sent to the heat engine (also the temperature of the storage medium), and TC and Th are absolute temperatures.

drops from Th to Th during discharge because of mixing or other effects, the energy produced by the heat engine will be given by:

at a temperature Th in the reverse direction and the enthalpy change associated with the at the user site. In this case: th i phase change. Cp is the specific heat. The specific heat is assumed to be constant for all temperatures in this simple approxima- It is now possible to define a uniform tion. figure of merit or “temperature efficiency” In the case of a thermochemical reaction, it is assumed that the reaction proceeds to techniques used with heat engines, It will

95-percent completion at a temperature Th simply be the ratio of Qout for the technique in the forward direction (in the solar collec- in question to Qout for a constant-tern pera- tor), and proceeds to 95-percent completion ture storage system.

—————. (phase change with perfect mixing) 490 Solar Technology to Today’s Energy Needs

The average efficiency of a heat engine heat loss rate (Q) from the cylinder just used with thermal storage is just: described would be approximately:

ture Th. Note that the heat engine will operate more efficiently than this average figure where Ts is the average temperature of the when the storage is fully charged and the storage material and T a is the ambient tem-

perature; RO is the radius of the cylinder with

“temperature efficiency” is not the same as insulation, and R I is the radius inside the in-

“round-trip storage efficiency” (QOut/Qln), sulation. which is the ratio of the amount of heat This equation can be simplified in most which can be recovered from a fulIy charged cases of practical interest by assuming that system divided by the amount of heat which the thickness of insulation (t,) is small com- is required to charge it. “Round- trip storage pared to R [i. e.: (R -R) is much less than R,] efficiency” affects al I energy storage sys- O O i and that the quantity k/h is small compared tems, while “temperature efficiency” is of with t,. This last condition is equivalent to concern primarily for systems which drive an assumption that the air or earth surround- heat engines from stored heat. While a tem- ing the tank provides no insulation, and is, perature drop sometimes signals a loss of therefore, a conservative assumption. Figure thermal energy, the “temperature efficien- Xl- B-1 shows that most common insulations cy” is a measure of how the engine perform- have k less than 0.05 Btu/hr ftoF. h will range ance is reduced as a result of heat being between the value for air with free convec- delivered at a lower temperature, and has 2o tion (l-5 Btu/hr ft F) to that of water with nothing to do with how much energy was forced convection (50 to 100 Btu/hr ft2oF). ’ first pumped into storage or how much sub- sequently leaked out.

Figure Xl- B-1 .—Thermal Conductivity of SENSIBLE- AND LATENT-HEAT Insulation STORAGE LOSSES 0.7 ~ , / In storage systems using sensible and latent heat there are three primary loss mechanisms: losses through the insulation; temperature degradation in heat exchangers; and temperature degradation due to mixing.

In all of the direct thermal-storage applications considered, it will be assumed that the storage vessels are cylindrical with a radius R and a height L which is equal to 4R. O 100 200 300 400 500 600 700 800 Mean temperature, Fahrenheit Losses Through the Insulation SOURCES: 1. ASHR.4E H8ndbook of Fundamentals. 1972, Page293. 2. “l%amglass Insulation” Brochure FI-132 (REV). Pittsburgh COr- The losses from such a tank will, in gener- ning Corp., April 1975. al, depend on the thickness (ti) and conductivity (k) of the insulation and the heat transfer coefficient (h) giving the conductive, convective, and radiative losses of the outer ‘F T Krelth, Prlrtclp/es of Heat Transfer, second edi- insulation surface to the air or ground. The tion, 1965, p 15 .

Appendix XI-B 491

It can be seen that k/h is small for either assumption. I n the remainder of this discussion, a cylindrical storage container with length L = 4R is assumed, unless stated otherwise. With the assumptions tj/R<<1 and ti<< k/h, the heat flow Q from the cylinder can be approximated as follows: Earth Insulation

In practice, the soil itself will provide As noted earlier, in an actual design, the some insulation for a buried tank. The in- insulation thickness wouId be chosen so that sulating properties of the soil will depend the marginal cost of adding additional in- strongly on local conditions, in particular, sulation wouId be equal to the marginal cost ground water flows, The heat conductivity of energy saved by adding this insuIation. of soil, for example, varies from 0.1 Btu/hr For simplicity, the Insulation used in the ftoF for dry sand or soil to 2 for wet sand or calculations which follow is based on the soil.3 Assuming that the storage tank is a premise that only 5 percent of the stored simple hemisphere, it can be shown that the energy wiII be lost during the desired storage heat leaving through the earth when equilib- interval of Ø hours (Ø would be 24 hours for daily storage, 168 hours for weekly storage, by:4 be used to determine the desired thickness of insulation.

The energy stored (E ) can be written ap- where rs is the radius of the storage and ks is s I proximately as follows (assuming that the the soil’s heat conductivity. If we write the specific heat does not change significantly heat flow through the insulation as Ui(Ts-To) with temperature). per unit tank area, where T, is the temperature inside the tank: I

I ! Note that it is assumed that losses to the surface are minimai. The system can be welI Alternatively, the volume required to store a insuIated on top, buried deeply, or placed given amount of energy is: under the building to minimize surface losses.

As shown in the equation above, Shelton I I found that the thermal losses to the ground were proportionaI to the perimeter rather than the surface area of the hemlsphere He 1 also showed that the earth is equIvaIent to a

k i is the thermal conductivity of the insulation being compared and R is the radius of the storage tank. The thermal conductiv ty the specific heat and latent heat of phase 1] ay Shelton, ‘ U ndergroun(i Storage’ ot Ii (’at I n change per unit volume The desired thick- Solar Heat I ng System\, \Ol

of different kinds of soil can vary by more For large storage tanks, the thermal losses than an order of magnitude, depending on are small even if no insulation other than the soil composition and moisture content (see soil is used. Figure Xl-B-2 shows the annual table Xl-B-1 ). A hot storage tank under or thermal losses from an uninsulated storage near a building or paved area tends to dry tank (as a percentage of the storage capaci- out the soil surrounding it. Moderately dry ty) for a hot water storage system operating soil of a type typically found near building between 1200 and 2000 F. While the losses sites has a conductivity of 6.0 Btu in/hr ft2 are large for small systems, by the time the “F. (About 40 times the conductivity of poly- storage capacity reaches 1 million kWh (typ- urethane. ) ical of the size needed to provide 100 percent solar heating and hot water for a high If it is computed that a thickness t of in- i rise apartment), the annual losses have sulation with conductivity k, must be used dropped to 6 percent of the storage capa- to reduce losses to acceptable levels with- city. out using earth insulation, burying the tank in soil can reduce the required thickness to tl’ where Shelton also shows, however, that the heat loss through the soil is much greater than the equilibrium for the first few months after the system is installed, as the soil

Table Xl-B-1 .—Thermal properties of soils

Very dry soila. ., ...... 0.1-0.2 Wet soila ...... 0.7-2.0 Dry sandb ...... 0.1 0.0054 19 Wetsand b ., . . . ., . . . . 1 0.042 25 Sandy clay (15% moisture)c. . 0.6 0.015 37 Concrete c ...... , 1.6 0.046 34 Organic soila ...... 0.8 0.021 36 Wet marshy soila . . . ,. .,.. 0.7 0.012 54 Granite rocka ...... 0.26 0.008 31 Concreted ...... ,. .,.. 0.54 0.025 22 144 Dry earth, packedd ...... 0.037 95 Sand d ., ...... ,. .,.. 0.19 0.011 18 95 Moist high-conductive y SOil e 1,2 0.026 46 102 Moist medium-low con ductivity soile ...... 0.4 0.013 30 100 Assorted soilsf...... , 0.3-1.3 90-110

SOURCE. Reproduced from Shelton (OP cit. ) p 143,

aR. E , Munn, Descr/pflve M/cromefeoro/ogy, 34. Academic PreSS, New York (1 ~). bR &lger, constant values for estimation of heat economy for the agricultural meteOrO1091St Met Rurr~schau, Heft 11 /12 (1948) CH Lettov, Theory of surface temperature and heat transfer osctllattons near a leVel ground Surface. Trarrs Am Geophys U 32, 189 (1951)

dGelger, Op C(ts , PP 57~”572

‘L R Ingersoll, F T Adler, H. J. Plass and A, C. Ingersoll, Theory of earth heat exchangers for the heat pump, Trarrs Arrr Soc lfeatlrrg !/ent//af/rrg .Errgrs 57, 167 (1951)

fGelger, op clts , p 374 Appendix X/-B ● 493

Figure XI-B-2.-Annual Thermal Losses From Uninsulated Storage Tank 100 ‘

1 I I 1 0.01 0.03 0.10 0.30 1.0 3.0 1 Storage capacity in millions of kWh NOTE. The thefmal lossas plo!led above are based on the resulta of ShOl~On uelw WOter an tk stof~ga medlurn IOr o wide range of edl conductlvitles Shefton’e results were modified by OTA to aseuma ● n average storage temperature of l@O”F, a ground temperature of 50.F, and a atorage tampemture swing of AT= SO”F.

‘Shelton, op. Clt Table XI. B.1.

Figure XI-B-3.– Rate of Heat=Loss to Ground

Time, days Rate of heat-loss to ground as a function of time after initial start-up. It is assumed that there is no heat demand, so that all the collected solar heat is available to maintain the storage temperature at near its peak level. This curve corresponds to a 6 ft radius ground or gravel hemisphere storage region with a maximum temperature of 170°F with initial surrounding ground temperature of 50°F, and a solar- heat collection rate of 94,000 Btu/hr for eight hours every day (except when maximum storage temperature would be exceeded). The ground’s volume heat capacity is 20 Btu/ft° F and its conductivity is 0-50 Btu/hr ft20F/ft. 5 I bld SOURCE: ‘1 bld J. Shelton (Williams College, Willlamstown MA). “Underground Storage of Heat in Solar Heating Systems,” Solar Energy. Volume 17, No. 2, May 1975, pages 137.143 494 ● Solar Technology to Today’s Energy Needs

Shelton’s early calculation only assessed the half-empty tanks as the storage is the thermal energy lost into the earth and charged and discharged Calculation of in- did not include an estimate of the losses sulation thickness is similar to the earlier from heated earth into the atmosphere. case. When ground-to-air losses were taken into account in a detailed analog simulation of a 27,000-gallon storage pond, it was found that total losses were approximately twice those caculated by Shelton.’ It should be possible to keep seasonal losses in thermal storage ponds at acceptable levels even if these added effects are considered, how- Even though each tank is half full, it is ever. Clearly, this is an area where further stilI assumed that heat is lost through the en- anaIysis is warranted tire wall The insulating value of the earth IS stilI equal to a thickness kR/6 of insulation. Reduction in Temperature Due to Mixing The additional cost of the extra tank could in the Storage Vessel be justified if the added performance permitted wouId lead to significant energy sav- It can be very difficult to compute the ing through increased heat-engine perform- temperature gradient which can be main- ance or if the cold tank can be enough cold- tained in a storage vessel. The result de- er than the lower Iimit of mixing storage that pends strongly on the design of the system the storage capacity of the fluid is signif- (e.g., use of multiple interior baffles, pump- icantly increased. The use of multiple tanks ing rates, tank orientation). A variety of in the same manner, but with only one tank clever approaches are currently being exam- empty at any time, wouId resuIt in lower ined and much more interesting work can be costs. The analysis in this paper assumes expected. I n the absence of the necessary that multiple-tank hot water systems for empirical or theoretical work, it is necessary low-temperature storage are 50 percent to make some very crude approximations. more expensive than single-tank systems of the same capacity. However, hot oil storage has been costed on the basis of two tanks Multiple-Tank Systems

The problem of temperature degradation due to mixing is a problem only for techniques employing sensible heat for storage Solid Storage Media It is clear that the best way to eliminate mix- Another approach is to use a solid mater- ing is to use separate tanks for the hot and ial such as stone or steel as the storage me- cold liquids. The major difficulty with this dium. As noted earlier, some thought has is, of course, the added expense of another been given to the possibility of using steel tank. ingots or other material for storing energy in In the case of a two-tank system of capa- specific heat at temperatures as high as city E s, each tank is as large as the one- tank 1,0000 F. One concept would use large steel volume calculated earlier. The volume of rectangular cylinders stacked together in an heat-storage liquid is the same as before, insulated container building. Heat would be and it is pumped back and forth between added and removed by passing steam/water through a series of holes penetrating each steel cylinder. The heat transfer from the hot 7, ‘TaYlor Beard, F A Iachetta, L U Lllleleht, and j end of the steel cylinders and the cold ends W Dickey, Annual Co//ect/on and Storage of Solar shouId be slow enough to permit a tempera- Energy for the Heat/rig of Bu//d/ngs, Report No. .?, prepared for ERDA under contract No E-(40-I k51 36, ture gradient of several hundred degrees to July 1977 be maintained across the storage. This Appendix Xl-B ● 495

would permit the withdrawal of high tem- where A is the area of the heat exchanger, perature steam at relatively constant temperature. the two Iiquids at the hot side of the heat ex-

An ideal material for such a storage sys- the cold side, and U is the overall thermal tem would have the following character- conductivity between the fIuids, The size, s: and thus the cost of the heat exchanger, will Very low cost, determine the temperature difference AT for a given rate of heat exchange. In an ideal High specific heat, system design, the heat exchange area Low thermal transfer from the hot to would be chosen so that the marginal cost the cold side of storage, of increasing the area would equal the marginal value of extra usefuI energy re- High thermal transfer from the charging sulting from a higher temperature emerging tubes to the storage medium, and from storage. Ability to withstand constant thermal cycIing without degradation If one or both of the liquids passing through the heat exchanger undergoes a The search for an Ideal material is in a phase change, the analysls becomes signifi- very prellminary stage and many promising cantly more complex. This situation could concepts have not progressed beyond spec- occur if a phase-change materlaI is used for uIation. storage or if water is boiled to steam whiIe passing through the exchanger Designing heat-exchanger systems using materials which sol id if y can be a serious difficuIty.

If heat exchangers are used both for charging and discharging, two separate temperature reductions would occur one during charging of the storage and one during discharge. One of these heat exchangers can be eliminated if the same fluid is used in the storage and coIIector system. Reduction in Temperature Due to Heat Exchangers Systems of the type shown in figure Xl-13 The rate of heat transfer in a counterflow have a great advantage in that they do not heat exchanger In which no phase change require any heat exchangers (the whole stor- occurs in the materIaIs and In which changes age device being, in effect, a large heat ex- in the specific heat are negIigible can be changer). Liquid thermal-storage systems written as follows: can also be built without heat exchangers if the storage medium is also the heat-transfer fluid. Appendix XI-C

Costs of Designs Chosen for Analysis

LOW-TEMPERATURE DESIGNS variety of types of tanks suitable for storing heated or chilled water or other fluids. The design chosen for hot water storage is These prices exclude pumps and piping, It 3 a tank which is buried in the ground, sur- can be seen that for the range O to 1,000 m rounded by a layer of polyurethane insula- it is possible to have a tank installed, in- 3 tion (where necessary) and a vapor barrier cluding excavation and backfill, for $80/m 3 which protects the insulation from ground or less. The baseline design assumes $80/m moisture. (See figure xi-2). If the collector for this size range. The assumed cost is uses a fluid other than water, a heat ex- plotted as the dashed line in the figure. changer is also required. Heat exchangers would also be required if the storage were pressurized while the other parts of the sys- Insulation tem were not under pressure. The primary Insulation costs depend strongly on the costs are divided into three categories: the temperature of the storage and the length of tank itself, the excavation and backfill, and time needed for storage, The insulation the insulation. Costs presented here exclude chosen for analysis is polyurethane. This the contractor’s overhead and profit (25 per- material can be foamed on in place for ap- cent), which is added later. 3 9 proximately $0,24/board foot ($101.71/m ). (A thin polyethylene vapor barrier adds neg- Excavation, Backfill, and Soil Compaction. ligible cost.) This cost might be reduced if a Figure Xl-5 shows as a solid line the ex- plant dedicated to producing storage equip- cavation, backfill, and compaction cost per ment manufactured preinsulated tanks. The cubic meter of tank volume as a function of conductivity of urethane protected by a tank volume. Costs were derived from good vapor barrier is approximately 0.13 Btu Meansa using the following assumptions: inch/hr ft2 oF. Excavated volume is 1.3 times the tank volume to allow for clearance, insulation, etc. Backfill volume is 0.3 times tank vol- Analysis ume. Because there is a mobilization and Two cases are considered: 1 ) a case which demobilization charge for heavy equip- applies to storage for use with systems ment, smalI jobs can be done less expensive- designed to supply domestic heating and ly by hand labor. For tanks greater than 3.35 hot water (thermal energy supplied between m 3 excavation is done with a track- , 2000 and 1200 F and returned at 900 F); and mounted, 3½-cubic-yard, front-end loader. 2) systems designed to supply absorption air- Backfill is done by bulldozer for tanks conditioners and other industrial process- greater than 28 m3, Soil compaction in all heat loads (thermal energy supplied be- cases is done in 12-inch layers with vibratory tween 2700 and 2200 F and returned at 2000 plate compactors. F). Case I requires a storage volume of 3 0.02013 m /kWht if mixing is assumed, or Hot Water or Oil Tanks 3 0.0146 m /kWht if there is no mixing in a Figure Xl-5 also plots installed tank costs, single tank. The cost of insulation in these excluding excavation and insulation, for a

‘Bui/dIrJg Construction Cost Data 1976, Robert ‘John L Renshaw of john L Renshaw, Inc (an in- Snow Means Company, Inc , R S Godfrey, ed , pp 18, sulating firm [n the metropolitan Washington, D C 22, 258 area), private communication, August 1976. 496 Appendix Xl-C ● 497

10 cases is $101.71 Vi, where VI is the volume tural Metal Products.” Cost of onsite of insulation in m3. assembly and installation (excluding the contractor’s overhead and profit, which is Case 1: C, added later) is assumed to be 32 percent of the cost of the components from the factory. This comes from the Department of where E is the storage capacity in kWh and th Commerce tables for “Sectors 11, 12: All New Construction.’” Thus, in cases where that if the above equations yield a negative better estimates of assembly and installa- result, the earth alone provides sufficient in- tion were not available, bare materials costs sulation and C, = O. have been increased by 211 percent for ma- The installed cost of buried tanks is terials which require additional factory assumed to be $80Vs for tanks less than work, or 32 percent for systems which do 1,000m3. For tanks with volumes greater not. than 1,000m 3, an appropriate cost per cubic meter was taken from figure Xl-22.

Case 1: Ct = $80x 0.02013E Oil Storage for Residential Organic Case I 1: Ct = $80 X 0.03221 E Rankine Devices (Systems larger than 1,000m3 would substi- The highest temperatures used in the tute an appropriate tank cost for $80 in the baseline-design organic Rankine engines for last equation. ) the single family house are 4200 F (216 oC). For storage at this temperature, a sensible- heat storage system using fuel oil has been chosen. The oil is Iiquid at all temperatures of interest and thus can be used as a heat- HIGH-TEMPERATURE DESIGNS transport system for conveying heat from the coIIector to the tank as welI as serving as Since very few of the concepts which the storage medium. Heat exchangers are have been suggested for high-temperature only needed to transfer heat to the heat thermal storage have ever been fabricated engines used to generate electricity, The as complete systems, it is difficult to esti- storage system operates at atmospheric mate what they would cost if they were pro- pressure. Since heat engines operating at the duced commercially. An attempt has been small temperature differences available for made to select for the analysis systems the single family system are already oper- which are as simple as possible, both be- ating at relatively low efficiencies, the sys- cause such systems show the greatest prom- tem is not able to tolerate a large drop of ise of reaching the market in the next temperature at the input of the heat engine, decade and it is much easier to estimate the For this reason, separate tanks are used for potential cost of these systems. The analysis hot fluids emerging from collectors and cold is fairly conservative, and may be used to liquids returned from the thermal loads to provide an upper limit for future high-tem- ensure a constant high temperature to the perature thermal storage costs. inlet. The assumptions and resuIting costs are summarized in table XI-9 Costs are com- in cases where the materials require fac- puted as shown in table Xl-C-1. tory work done off site, the bare materials cost is multiplied by 1.6 to account for overhead, wages, and profit in the factory. ‘“’’ Input-Output Structure of the U S Economy 1963, ” Survey of Current Business. U S Department of This number is obtained from the Depart- Commerce, National Economics Dlvlslon, November ment of Commerce input-output tables for 1967, pp 16-47 “Sector 40: Heating, Plumbing, and Struc- ‘ ‘ Ibid

28-842 0 - 33 498 Solar Technology to Today’s Energy Needs

Table Xl-C-1 .—Assumptions for Hot Fuel Oil Table Xl-C-2.—Assumptions for Therminol-55/ Thermal Storage, Single Family House Rock Thermal Storage [600 “F heat engine] [420” F organic engine]

Two-tank system: no heat exchanger to collectors; Two-tank system 70% rocks by Volume No heat exchanger to collectors Heat engine temperatures: 600° to 100” F (316° to 38° C) Heat engine temperatures (organic Rankine) = 420° to a 90” F (216° to 32oC) Heat exchanger temperature drop to heat engine: aHeat exchanger temperature drop to heat engine: 10” C (18° F) 10oc (18” F) Storage temperature swing: 618° to 118°F (326° to 48oC) Storage temperature swing: 439° to 108° F (226° to Heat capacity of Therminol-55: 31 Btu/ft3° F (0.577 42 “C) kWh/m3° C) Heat capacity of storage medium (refined fuel oil) = Heat capacity of rocks: 27.3 Btu/ft3° F (0.509 kWh/m3° C) 30 0.795 kWhth/m C b System heat capacity: 28.4 Btu/ft3° F (0.529 kWh/m3 Thermal conductivity of insulation (foam glass): k = “c) 0.5 Btu in/ ft2hr° F bThermal conductivity of insulation (foam glass): k = Ground temperature = 55° F (13” C) 0.6 Btu in/hr ft2° F Credit for earth’s insulation: equivalent to insulation a 2 thickness of (0.0833)R Heat exchanger constant = 4.5 kW/m ° C aHeat exchanger constant = 4.5 kW/m20C Ground temperature: 55° F (13° C) Credit for earth insulation: equivalent to insulation clns.tailed cost of insulation” (foam glass) = $1 14/m3 Of 3 thickness of (0.1)R insulation = $3.24/ft c lnstalled cost of insulation (foam glass) = Installed cost of buried tanks and excavation = $160/ m 3 of oil $114/m3 of insulation = $3.24/ft3 a Installed cost of storage medium (refined fuel oil) = lnstalled cost of heat exchangers to heat engine = $146/m 3 $80/m2 of heat exch. 3 alnstalled cost of heat exchanger to heat engine = $80/ Installed cost of rocks = $0.01/lb x 140 lb/ft x 70% = m 2 of heat exchanger $0.98/ft3 storage = $34.61/m3 Installed cost of Therminol-55 = ($.38matl + $.05 Tanks, excavation, oil = 2.092E$ shipping)/lb x 43 lb/ft3 x 30% = $5.55/ft3 = $195.89/m 3 storage Heat exchangers = 1.78P$ Installed cost of buried tanks and excavation = $160/ m3 of storage:

NOTE Costs exclude contractor’s overhead and profit (ZSo/O), which IS added later. “E’” IS storage capacity in kWhth. “d” Is Tanks, excavation, Therminol, rock = 2,655E$ storage Interval In hours. “R” IS storage tank radius “P” IS Heat exchangers = 1.78P$ discharge rate In kwth

aR w Hall~t and R L Gervals, Cert(ra/ Rece~ver Solar Thermal power System, Phase 1, F(na/ Report, MDC G6040, McDonnell. Douglas NOTE: Costs exclude contractor’s overhead and profit (250/.), which Astronautics Company, January 1976 IS added later. “E” IS storage capacity in kWh “8” is .sfor- age interval In hours “R” is storage tank ra~us. “P” IS dis- %ee figure Xl-B-1 charge rate In kWth cMeans Bu//d/ng Cons frucf/on COSf Data, 1976, P. 111 aHa[let and Gervals, MDC G6040. b%e figure Xl- B-1

cMeans, 1976, Q . 111 Therminol-55/Rock Storage The TherminoI-55/rock-storage system is similar to the hot fuel oil system just exam- system. This is assumed to be acceptable ined. Two tanks are used to maintain a high since the heat engine will operate at this discharge temperature and thus a high “tem- pressure, and thus an operator familiar with perature efficiency” (for heat engines). The the engine should be able to supervise the rocks are assumed to occupy 70 percent of steam transport system. The ingots could be the storage volume. The assumptions and re- integrated into the structure of the building sulting costs are summarized in table XI-C-2. or buried in the earth. Earth burial is assumed for the following calculations, al- Storage in Steel Ingots though individual installations may present The steel-ingot system can eliminate the other opportunities. Excavation and backfill need for heat exchangers, but this requires costs are taken from figure XI-5. The Jet Pro- the use of 150 psia steam in the collector pulsion Laboratory (JPL) has calculated that ..— —

Appendix XI-C ● 499

a system operating between 9500 and 1000 F for use with a solar system which operates (510 0 and 38 “C) can be discharged by about between 6500 and 4000 F for a cost of ap- 68 percent of its total sensible-thermal ca- proximately $3.7/MBtu ($12.63/kWhJ. pacity before the output steam starts to fall The system which will operate with the below 950° F.12 The analysis therefore Stirling cycle will have a very similar design. reduces the thermal capacity of the steel ac- The costs of the two systems are estimated cordingly and assumes that al I of the disin paralIel in the following discussion. charge steam is at 9500 F. The following cost assumptions were also taken from the JPL The heat of fusion storage system is as- study: steel ingots at $.15/lb; welded headers sumed to be produced in factory-assembled at $50/hole ($25 each end); rail transporta- modules. Each modular tank contains within tion of materials at $.01/lb; miscellaneous it a bundle of sealed, long, narrow, cylinders (flow valves, controls, sensors, weather- full of the storage material. The cylinders proofing, etc. ) at $.0067/lb of ingots. It also occupy three-fourths of the tank volume, is assumed that the ingots are piled in a and heat-pipe fluid circulates in the space stack whose shape is close enough to a cyl- around the cylinders, as shown in figure inder (with length = 4R) that the insulation IV-20. During charging, the heat-pipe fluid is calculations can be done using equations heated directly in the solar collector, and already developed for cylindrical tanks. The during discharging, the heat-pipe fluid con- assumptions used are shown in table Xl-C-2. denses at the heat engine, eliminating the expense of separate heat exchangers. Each cylinder is assumed to be 4 feet long and 3 High-Temperature Phase Change Storage inches in diameter. There are 60 cylinders Several designs for storing thermal energy per tank, and the tanks are 59 inches long in the heat of fusion of sodium hydroxide and 27 inches in diameter. The cylinder have been examined, and operating units of walls are 0.040 inches thick. This is thick at least two different approaches have been enough to contain the weight of the storage constructed. 3 These units use electricity to material if adequate room is provided for charge the storage to about 9000 F. Total expansion during phase changes. The vol- system cost for these devices is estimated ume of containment material per cylinder is to be between $1 .35/MBtu and $1.50/MBtu thus 302 cm3, and each cylinder can contain 3 ($4.61-512/kWh th). Examining figure XI-19, it 5,260 cm of storage material. The charac- can be seen that the available energy for use teristics of potential container materials are at 9000 F is approximately twice the avail- shown in table Xl-C-3. able energy for the temperature swing be- The cylinders are assumed to be made of tween 6200 and 4200 F which is required for stainless steel. Although stainless steel is not the heat engine. The price appropriate for completely resistant to corrosion by pure the on site application wouId thus be approx- fluorides, N. V. Philips reports that by add- imately $3/MBtu ($10.24/kWht) JPL has ing a small amount of aluminum to the melt, designed a sodium hydroxide storage system all corrosion is eliminated. Corrosion testing was done for more than 14,000 hours at 850 “C with ordinary 18/8 stainless steel. 5

“R H Turner () PL), “Thermal Energy Storage Using Each tank is a double-wall pressure vessel, Large Hollow SteeJ Ingots, ” Sharing the Sun: So/ar insulated by a vacuum and multifoil super- Techrto/ogy in the Seventies. J olnt Conference, Amer- ican Section, International Solar Energy Society and Solar Energy Society of Canada, Inc , Wlnnlpeg, Can- ada, Aug 15-20, 1976, Vol 8, pp 155-162 14) Schroder (N V Phliips Aachen Lab ), “Thermal ‘ ‘R E Rice, Therma/ Storage for Application to Energy Storage and Control, ” journa/ ot Engineering Energy Conservation, Comstock and Wescott, Inc , for /ndustry, August 1975, pp 893-896 April 1975, Cited In Bramlette, et al , (Sandla Labora- “j Schroder (N V Philips Aachen Lab ), private tories, Llvermore) SAN D75-8063 communlcatlon, jan 13, 1977 500 . Solar Technology to Today’s Energy Needs

Table Xl-C-3.—Assumptions for Steel-Ingot sumed to be ¼-inch stainless steel, fabri- Thermal Energy Storage cated at $2.00/lb. 8 The two heat pipes are assumed to add $200 each to the cost of Steam Rankine engine: no heat exchangers each tank. 9 Heat engine temperatures: 950° to 10O”F (510° to 38oC) Storage temperature swing: 950° to 100” F (510° to 38°C) The installed cost of the cylinders is esti- o Storage temperature swing: 950” F to 100” F (510 C to mated using the materials costs in tables 38” C) Storage medium: cast steel ingots, 60 ft long, 1 ft wide, Xl-4 and Xl-C-4, adding $().1()/kg for shipping, 1 ft high; 9 axial holes, 2 in diameter per ingot and multiplying by the factor of 2.11 to ac- Headers: 2 in diameter, low-alloy, seamless pipe count for factory and onsite fabrication and Schedule 50, formed into thermal stress expansion loop and welded to ingot holes instalIation. The cost assumptions are sum- Steel heat capacity = 58 Btu/ft3° F marized in tables Xl-C-5 through Xl-C-7. System heat capacity (20% holes; 32% unrecoverable) = 0.608 kWhth/m3° C

BATTERY STORAGE COSTS

The costs of battery storage used in the analysis conducted in this study are summarized in figure Xl-28 and table XI-11. There appears to be a reasonable concensus that costs as low as $55/kWh are feasible in the “intermediate term, ” but a considerable amount of disagreement about how far prices will fall in the long term. The Bechtel summary of battery costs estimated that advanced batteries could be produced for $10 to $25/kWh20 while other sources have estimated that prices below !$25/kWh are unlikely .21 22 The “long-term” cost $11/kWh shown in the table reflects an assumption aSee figure Xl- B-1 that a low-cost iron-REDOX system has been b Means, 1976, p 111. developed.

NOTE Costs exclude contractor’s overhead and profit (2s0/. ), which IS added later. “E” IS storage capacity In kWh Neither estimate of O&M cost given in storage Interval In hours. “R” IS radius of the p~~e ‘;~I’; ;; table Xl-8 would add appreciably to the possible to use concrete or some other Inexpensive material instead of steel, the cost could be reduced by a factor of three overall costs of battery storage. Even if or more O&M costs for advanced batteries are a factor of 2 higher, the O&M costs would still be insulation. This type of insulation has a ther- minor. Consequently, 0.0284/kWh has been mal conductivity of 0.0049 Btu in/hr ft2 oF. 16 used for all three cases in table Xl-11. The cost of the metallic foil insulation is 2 estimated at $2.00/ft of surface area, and a ‘ Ibid, the resultant thermal conductivity is so low “Ibid that even seasonal storage results in “very ~OAn Engineering Study of a 20 M W, .200 MWh f-=d- small heat losses.’” 7 The tank walls are as- Acid Battery Energy Storage Demonstration P/ant, Bechtel Corporation, ANL Contract No. 31-109- 38-2692, October 1975. “N. E. Polster and W R. Martini (University of *’James Birk (E PRI), private communication, Jan. Washington), Self-Starting, Intrinsically Control/cd 20,1977. Stirling Engine, 11th I EC EC. ZZAn Assess~enr of Energy Storage S ysterns suitable “R L, Pens and R. J. Fox (Aeronautronic Ford Corp. for Use by Electric Utilities, Fina/ Report by PSEG on and Walt Disney Productions), A So/ar/Stir/ing Tota/ ERDA Contract No. E (11-1 }2501, Vol. 11, July 1976, Energy System, unpublished, 1976. pp. 4-60. Appendix XI-C . 501

Table Xl-C-4.—Containment Materials

Density Yield strength ● cost Material (kg/m 3) (N/m2) ($/kg)

3 8 8515-70 carbon steel. . . . 7.8 X 10 3.1 x 10 .22 ab 304 stainless steel . . . 7.9 x 103 2.4 X 108 1.76 abcde. . Steelite-21 . . . . . 8.3 X 103 5.7 x 108 40.00 ce Inconel ...... 7.8 X 103 2.7 X 108 11.00 Hastelloysabcde...... 9.0 x 103 3.8 X 108 26.00

‘ Room temperature values

aOxldatton resistant bHlgh.temperature al IOY CReSIStant to chemical attack dReslstant to most fluorldes

eReslstant to fluorldes If Al IS added to the fluorlde

SOURCES T T Bramlette (Sandla Laboratories, Livermore), compiled for OTA, 1976. Note e added by J Schroder (N. V. Philtps Aachen Lab ), Dnvate communl - cation, Jan 13, 1977

The salvage value (or reduced replace- than a 50 kWh cell, and batteries in the 20 ment cost) for near-term batteries is prin- kWh size range may cost 20 to 25 percent cipally the value of the lead in the battery. more than batteries for large storage facili- The replacement price for intermediate- ties. Detailed design studies now underway term batteries is based on a crude average may change this estimate. 24 of the fractional replacement prices projected in table Xl-8. Most of the advanced Table Xl-C-5 .—Latent-Heat Storage Tank batteries use inexpensive materials which Assumptions wouId have negligible salvage value. Conse- quently, no salvage value is assumed. If one of the batteries containing Iithium were Volume of stainless steel in tank wall = 0.04477m3 Surface area of tank = 38.48ft2 used, the replacement price would clearly Tank wall cost = (0.0447 m3)(7,900kg/m3)( 2.2lb/kg) ($2/lb) be less than the inital price, since lithium = $1,560 Insulation cost = (38.48ft2)($2.00/ft2) = $77 can be effectively recycled. Heat pipe cost = $400 Battery storage systems for utility ap- 60 cylinders per tank Cylinder cost = (302cm3)(.0079kg/cm3)($1.86/kg) plications are expected to use a large num- (2.1 1) = $9.36/cylinder ber of cells which have individual storage NaOH cost + (0.00526 m3)(1,784kg/m3)($0.65/kg) 23 (2.11 = $12.87/cylinder capacities of 5 to 40 kWh. These are the NaF/MgF2 at $0.50/lb = (0.00526m3)(2190kg/m3) systems for which virtualIy alI of the avail- ($1.20/kg)(2.11) = $29.17/ cylinder able cost projections apply. It is expected NaF/MgF2 at $0.25/lb = (0.00526m3)(2190kg/m3) ($0.65/kg)(2.11) = $15.80/ cylinder that smaller systems will require somewhat Volume of storage material per tank = 0.3156m3 smaller cells to obtain reasonable system Overall volume of tank = 0.60m3 voltages Detailed studies of the relative Total installed tank, NaOH: $3,371 plus excavation and backfill cost of such systems have not been com- Total installed tank, $0.50 NaF/Mg F2: $4,349 plus ex- pleted. However, the direct product cost cavation and backfill ($/kWh) for a 7 kWh mass-produced cell Total installed tank, $0.25 NaF/Mg F2: $3,547 plus ex- would probably be about 14 percent higher cavation and backfill

J ‘james R [31rk, The Lead-A c/d Battery for E/ectr/c Uti//t/e~ A ReL Iew and Ana/ysIs, presented at the ER- 24Nlck Maska lick (Westinghouse Corporation), pri- DA EPRI Lead-Acid Battery Workshop 11, Dec 9,1976 vate communication, Jan. 31, 1977 502 ● Solar Technology to Today’s Energy Needs

Table Xl-C-6.—Assumptions for NaOH Table Xl-C-7.–Assumptions for NaF/MgF2 Latent-Heat Storage [600° F heat engine] Latent-Heat Storage [1 ,400°F heat engine]

cost :

(.50 NaF/mg F2 $/kg)

Total storage cost : (.25NaF/ F2 $/kg)

aHallet and Gervals, NDC G6040 NOTE Costs exclude contractor’s overhead and profit (250/.), which b IS added later. ‘(E” IS storage capacity In kWht IflSulatlOn See table Xl-7 IS adequate for seasonal storage aHallet and Gervals, MDC G6@$0 bsee table XI-7 CR L. Pens and R J FOX. 6 percent of the cost of the inverter. The cost of the interface varies from about 10 to For purposes of this study, we increase the 20 percent of the inverter cost for systems in large system prices by 10 percent for the the kilowatt range to about 2 percent of in- commercial and multifamily residential sys- verter cost for systems in the megawatt tems, and 20 percent for home systems. range. Estimates of current and potential power-conditioning costs are shown in figure XI-28. The prices chosen to represent “near- term, ” “intermediate,” and “speculative” POWER-CONDITIONING COSTS technologies are chosen somewhat arbitrarily to represent the spectrum of estimates As noted earlier, the bulk of the cost of shown. The “near-term” prices selected are power-conditioning apparatus results from somewhat lower than the average prices of the cost of the inverter system. Estimates of contemporary power-conditioner devices the cost of voltage regulators vary from 1 to since many of the units now available are Appendix Xl-C .503

26 overdesigned for solar application, and the power conditioner and the load. ’ I n the many of the small systems shown operate at integrated system cost runs, it has been voltages much lower than would be required assumed that power conditioners have a for solar applications (low-voltage systems peak capacity 1.5 times their rated capacity. are usually more expensive than higher voltage devices with similar power capabilities). BUILDING AND OTHER COSTS In the intermediate term, it can be assumed that at the lower power levels, in- I n addition to the battery and power con- creased production volume will lower ditioner costs, there is a significant cost prices, although in many of today’s systems, associated with instalIation, electrical wir- standard components such as inductors and ing, and instrumentation, and the room in capacitors represent a significant fraction of which the battery system will be housed. No the cost, and this will limit the production detailed estimates of these costs were avail- economies possible. At higher power levels, able for systems of the size considered in systems wilI probably continue to be essen- this study, It was assumed that the batteries tially custom-designed, but increased engi- would be located in the basement of homes neering experience shouId lower costs some- or in the equipment rooms of apartments what, as assumed for the intermediate case and shopping centers. Unfinished basement of figure Xl-28. space in such buildings costs about $5.00 to in the longer term, it can be assumed that $7.50 per square foot. “Building and Other power-conditioner units in the smaller sizes Costs” were assumed to be twice the cost of can be made for substantialIy lower prices the space and it was assumed that the bat- by mass-producing units designed with teries we arranged so there were 2 to 3 kWh power transistors so that the use of com- per square foot of floor space for present ponents such as inductors is minimized. lead-acid battery systems. It is assumed that Westinghouse has estimated that such units “advanced battery systems” wiII have higher could be produced for $50 to $70/kW.25 At energy densities, and require less space. intermediate and higher power levels, mar- REDOX batteries do not have a high energy ket size and component size will probably density but it should be easier to integrate prevent automated production, and the the liquid storage tanks which make the price may go up for some sizes as suggested system bulky into building space than it by the curve sketched for the “long-term” wouId be to find space for more complex case i n figure Xl-28 systems requiring high temperatures or potentially hazardous materials It was It should be noted that the prices dis- therefore assumed that the building and cussed so far have been in terms of rated other costs associated with the REDOX capacities which are related to the normal systems would be no greater than those of load of the system. Most systems can actual- other batteries. It was assumed that the ly supply 1.5 to 3 times the rated capacity, “building and other costs” and power condi- depending on the specific characteristics of tioner costs scale with battery capacity in the same way (see table Xl 1-11 )

J 5P F Plttmdn, Progrdrn A4andger for Westinghouse F let trlc Corporat Ion Re$earch I aboratorie>, F/rra/ Report on Conceprud/ Lies/gn and S y$tems An~/\\l\ of Photovo/talc Power $ ysterns, ERDA Contrdct No I (1 1-.2744), December 1976 Chapter Xll HEATING AND COOLING EQUIPMENT Chapter Xll.— HEATING AND COOLING EQUIPMENT

Page Table No. Page Introduction ...... 507 4. Cost of Maintaining Commercial Heating Electric Air-Conditioners and Heat Pumps.... 507 and Cooling Equipment ...... 523 System Performance...... 510 Potential for Improving Performance .. ..511 LIST OF FIGURES Direct Fossil-Fired Heating and Air-Condi- tioning Equipment ...... 514 Figure No. Page Heating Equipment...... 514 Potential for Improving Performance .. ..517 l. A Typical ’’Split System” Heat-Pump Installation...... 508 Absorption Air-Conditioning ...... 519 2. A Typical Packaged Outdoor Chiiler ...... 509 System Performance...... 520 3. 1976 Air-Conditioning Performance of Conventional Gas and Electric Water Heaters. 522 Units Smaller Than 65,000 Btu/Hour ...... 510 Operating Costs...... 522. 4. Performance of the Carrier Split-System Heat Pump ...... 512 Adaptation of Conventional Equipment to 5. The Seasonal Performance of Heat-Pump Solar Power ...... 523 Units as a Function of Local Climate .. ...513 Solar Heat Engines...... 524 6. Estimated Cost of lncreasing the Solar Absorption Equipment ...... 524 Performance of Air-Conditioners From The Adsorption Cycle System ...... 524 the lndustry Average COP of 2.0 to the Performance Levels Indicated ...... 513 7. Some Examples of Proposed Advanced Heat-Pump Cycles...... 515 8. Residential Heating Systems...... 516 LIST OF TABLES 9. Efficiency of Gas Furnaces ...... 516 10. A Fossil-Fired Heat-Pump System ...... 517 Table No. Page 11. Basic Single-Effect Absorption Refrig- l. Cooling Coefficients of Performance for eration Cycle ...... 519 Systems Smaller Than 65,000 Btu/Hour. ...5lO 12. Estimated Refrigeration Unit Cost Per Ton 520 2. California Standards for Cooling Equipment 511 13. Coefficient of Performance Versus 3. Average Cost of Maintenance Contracts for Supply Water Temperature...... 521 Residential Heating and Cooling Equipment 522 14. An Adsorption Chiller...... 525 Chapter XII Heating and Cooling Equipment

INTRODUCTION

This chapter has two major objectives: to estimate the cost of providing space conditioning from conventional electric equipment as well as from oil- and gas-fired devices, and to analyze the performance of systems which can be coupled with solar devices. Technologies examined include electric and absorption air-conditioners, heat pumps, and conventional gas- and oil-fired boilers. Systems examined are compatible with loads varying from that of a single family residence to the requirements of a district heating system. Much of the data needed to perform a careful study of the cost of providing heating and cooling from conventional equipment is not easily available. Some of the relevant data remains proprietary and, in a number of cases, adequate measurements of performance in realistic operating environments have never been taken. A detailed study of the performance of many heating and cooling devices is now underway at the Building Environment Division of the National Bureau of Standards. A more accurate comparison of systems wilI be possible when that study is completed. Given the uneven quality of the information utilized, no attempt should be made to use the results to judge the relative merits of different conventional approaches to space-conditioning. The object of the cost computations is simply to provide a reasonable background against which to test the economic merits of solar equipment. These computations are based on the most reliable information now avaiIable to OTA, but the lack of precision is f reel y acknowledged.

ELECTRIC AIR-CONDITIONERS AND HEAT PUMPS

A typical residential air-conditioner/heat- are provided i n the same unit and can be pump installation is iIlustrated in figure connected directly to the ductwork (or Xl 1-1, and a large central chiller is shown in chilled water system) of the building. I n figure Xl 1-2. Both units employ the same “split-system ” devices, refrigerant is sent to basic refrigeration cycle, although the an air-handIing unit inside the building. (This smaller units usually cool and dehumidify system is illustrated in figure Xl l-l. ) Another room air directly while the larger systems distinction which is frequently made in- typically produce chilled water which is volves the technique used to compress the piped to fan-coil units in various parts of the refrigerant vapor. Smaller units typically use building. The cooling systems have three a simple piston system for compression and basic components: 1 ) a unit which permits a are called “reciprocating” units. Larger u nits refrigerant to expand, vaporize, and absorb may use centrifugal pumps or screw com- heat from the room air (or water system); 2) a pressors for this purpose. compressor which compresses the heated vapor (increasing its temperature); and 3) a Heat pumps use the same three basic condenser located outside the building components as the air-conditioners de- which rejects the heat absorbed from the scribed above, but the cycle is reversed. I n room air into the atmosphere (condensing the heating cycle, the indoor air absorbs the compressed vapor to a Iiquid). I n heat from the refrigerant and heat is ac- ‘‘s i ng I e-pa c k age’ units, alI three functions quired by the refrigerant from the outdoor

507 508 Solar Technology to Today’s Energy Needs

Figure XI I-I .—A Typical “Split System” Heat-Pump Installation

SOURCE. Carrier CorDoratlon

fan unit (the “condenser” in the cooling the water reservoir, while others recover model). this energy and pump it into rooms requiring heating. Solar energy can also be used to Heat pumps which can extract useful provide a source of heated water. Systems energy from outdoor air temperatures as which extract heat from water are called low as 00 F are now on the market, although “water-te-air” heat-pump systems, while system performance is seriously degraded at units extracting energy from the air are low temperatures. The electricity used by called “air-to-air” systems. the system can be considerably reduced if a While less than half of the residential source of heat with a temperature higher units in the United States were equipped than that of the outside air can be found. with air-conditioners in 1974, the demand Lakes or ground water, for example, are 1 for air-conditioners is growing. in 1974, usualIy above ambient air temperatures dur- about 45 percent of all single family homes ing the winter and can be used to provide a and 34 percent of all multifamily dwelling source of input heat if they are available. units were equipped with some type of air- Many buildings have sources of heat (such 2 conditioner. A DOE forecast estimated that as Iighting, mechanical equipment, rooms with large southern exposures, etc. ) which IGordian Associates, Inc , Evacuation of the A;r-tG can be recovered and used to heat a storage Air Heat Pump for Residential Space Conditioning, reservoir. A number of small heat pumps prepared for the Federal Energy Administration, Apr can be located throughout a building. Some 23,1976, p. 114 of these pump heat from warm areas into ‘Ibid , p 115 Ch. XII Heating and Cooling Equipment 509

Figure Xll-2.– A Typical Packaged Outdoor Chiller

ROOM THERMOSTAT IN CONDITIONED SPACE

a * ST - STARTER FD - FUSEO DISCONNECT

SOURCE Carrier Packaged Outdoor Air-Cooled Llquld Chillers Carrier Corporation 1974, Form 30GA-5P

4 by 1985, air-conditioning will be installed in system. The growth of the market has been 75 percent of all residential and commercial slowed by the sensitivity of buyers and buildings and will require about as much en- builders to the initial cost of the equipment ergy as electric heating. 3 (which is higher than conventional electric- resistance heat), and by the fact that Heat pumps are likely to have a far regulated gas prices and promotional elec- smalIer impact on overall U.S. energy con- tric prices have made the cost of operating sumption unless some dramatic change oc- competitive heating systems artificially IOW curs in public acceptance of the units. Less Concerns about reliability have also been a than 1 percent of U.S. homes currently have problem. Some of the heat pumps marketed heat pumps, and only about 7 to 8 percent in the early 1960’s were extremely unreli- of the new housing starts in 197.5 used the able, and sales of the units fell steadily be-

‘Nationa/ P/an for Energy Research Development and Demonstration, Vo/ume /, ERDA-48, p B 10 ‘Gordlan Associates Inc , op clt , p v 510 ● Solar Technology to Today’s Energy Needs

Figure Xll-3.— 1976 Air-Conditioning Performance tween 1965 and 1970. While most of the reli- of Units Smaller Than 65,000 Btu/Hour ability problems have been resolved, a recent study showed that the problem has not vanished. The compressors examined in the study failed at a rate which varied from 3.6 percent to an astonishing 23.3 percent per 1 00% years A 5-percent annual failure rate is con- 1976 Industry Average 2.00 sidered tolerable for this kind of space- conditioning equipment, and apparently 50% - very few manufacturers were able to meet this standard. In spite of their relatively small share of

the U.S. space-conditioning market, heat I I I I I 1.5 2.0 2.5 pumps are likely to be in direct competition .“ with solar equipment during the next few decades. They would tend to appeal to the same category of buyers, those willing to consider Iife-cycle costing, and are Iikely to offer the lowest Iife-cycle cost of any non- Tables Xl l-l and Xl I-2 give some indica- solar space-conditioning system if the price tion of the performance which can be ex- of heating oil and natural gas increases pected from different cooling devices, The significantly. 1976 industry average COP was 2.00. Heat pumps were about 5 percent less efficient than the average air-conditioner, SYSTEM PERFORMANCE There are a variety of reasons for this. Heat The performance of heat pumps and air- pumps cannot be optimized for maximum conditioners now on the market varies great- cooling performance as somewhat more ly. Figure Xl I-3 indicates the performance of complexity is required in the coolant piping, air-conditioners smaIIer than 5½ tons now and the valve which switches the direction on the market. The difference in perform- of the refrigerant when the system is ance reflects both the quality of design and changed from heating to cooling introduces the cost of the unit. High-performance units some inefficiencies. may also result from a fortuitous combina- Under some circumstances, small window tion of components. Manufacturers cannot units are capable of better performance afford to design condensers optimalIy suited than central air-conditioners; central units for all compressors to which they may be attached, and some combinations of these units (in the absence of information of com- Table XII-1 .—Cooling Coefficients of parable quality about the variety of systems Performance for Systems Smaller Than 65,000 Btu/Hour (1976 industry averages) examined here) may therefore result in a high-efficiency system. As a result, while Average COP there are a few units on the market with very high efficiencies (figure XII-3, for example, All ARI listings 2.00 indicated that 10 percent of the units on the Split-system cooling 2.00 market have a coefficient of performance Single-package cooling 1.90 (COP) greater than 2.5), this performance is Single-package heat pumps 1.94 not avaiIable in alI size ranges. Split-system heat pumps 1.90 — ——— .— SOURCE George D Hudelson (Vice PresldentEnglneerlng, Carrier Corporation), testimony before the Caltfornla State Energy Resources Conservation and Development Commlsslon, Aug 51 bld 10, 1976 (Docket No 75, CON3) Ch. XlI Heating and Cooling Equipment ● 511

inside and outside air. This is due both to the fact that the theoretical capacity of a unit varies as a function of these parameters, and because most units must either be fully on or fully off. The load control achieved by “cycling” the system from full capacity to Central Air-Conditioners zero output requires heating or cooling Heat pumps (cooling mode) 1.96 2.2 large parts of the system before useful space Air-conditioners 2.05 2.34 conditioning can be performed. Using energy to heat or cool the units decreases Room Air-Conditioners the system’s efficiency. The dependence of All systems with capacity greater a typical residential heat-pump unit COP on than 20,000 Btu’s 2.05 — the outdoor temperature is shown in figure Other heat pumps 2.08 — Xl 1-4. The fact that the heat pump’s capacity 2.20 — Other air-conditioners to produce heat decreases as the outside All systems using voltages greater than 200 v. — 2.40 temperature decreases results in a highly Other heat-pump systems — 2.43 temperature-dependent heating mode, A Other air-conditioners — 2.55 system large enough to provide 100 percent .— of the heating load at the lowest anticipated “No system m~y be sold n fhe State atter this date with a COP below the standard temperature would be prohibitively expensive in most locations, and a most common compromise is to assist the heat pump with must pump chilled air or refrigerant over electric-resistance heat whenever its capaci- significant distances, and require more ty falls below the heating demand. The energy to operate the pumps and fans need- average COP of a heat-pump system during ed to transport chilled air or liquids to and from the space to be cooled. The perform- the winter season is called the seasonal performance factor (SPF). This parameter is ance of large, central chilling units them- shown in figure Xl I-5 as a function of local selves (such as the one shown in figure Xl 1-2) climate. As expected, the average COP of is better than window units, however. The heat pumps is lower in northern parts of the larger units typically employ more efficient count ry. motors and more sophisticated designs; many units are able to achieve better per- The performance of water-to-air heat- formance at part loads by adjusting the flow pump systems can be significantly higher of refrigerant (Many of these improvements than air-to-air systems if heated water is couId, of course, be incorporated in a available. When 600 F water is available, smaller unit at some increase in the initial most commercial units have COPS in the cost. ) The advantages of larger systems are range of 2.5 to 3.5,6 but units with COPS as offset, however, by losses incurred in other low as 2.0 and as high as 3.7 are on the parts of of the system. market. A large number of designs are employed, and overall performance varies greatly from Potential for Improving Performance one installation to another. Some systems Research which could significantly im- may require significant amounts of pumping prove the performance of these devices is energy to either move chIIled Iiquids or air currently underway in the laboratories of a to different parts of a buiIdIng or to operate number of heat-pump and air-conditioner a cooling tower which may be located on manufacturers. Figure Xl I-6 summarizes a re- the roof ‘)LIIreC ~or} of Cert/f/ed UnJtJry A )r-( ond~t)oners, The performance of electric-cooling and Unitar} He, 1‘j76 512 ● Solar Technology to Today’s Energy Needs

Figure Xll-4.– Performance of the Carrier Split-System Heat Pump

I I I I I 1 I I 1 I 1 I I I o 10 20 30 40 50 60 70 80 90 100 110 120 Ambient Temperature

Model 38CQ020 ARI ratings: Heating mode nominal capacity 21,000 Btu/hour. COP at high temperature is 2.9, COP at low temperature is 1.7. Cooling mode nominal capacity is 19,000 Btu/hour. COP is 2.1. Assumptions used in computing Heating mode entering indoor air system performance: is 70- F (db) heating demand includes energy used for defrost balance point at 30’ F. Cooling mode entering indoor air is 80 F (db) and 67 F (wb). Fan power is 0.2 kW. Energy use includes: compressor motor demands; resistance heat; the demands of indoor and outdoor fans; and the energy used in defrost cycles. The air-flow was assumed to be 700 cfm. Assumptions made about decrease in efficiency due to part load conditions were not explained in the literature. SOURCE Carrier Spilt-System Heat Pump Outdoor SectIons Carrier Corporation 1976, Form 38CQ-l P Ch. XII Heating and Cooling Equipment 513

Figure XII-5.– The Seasonal Performance of Heat-Pump Units

SOURCE What IS a S/rig/e Packaged l-leaf Pump and How Can It Save You Money?, Carrier Corporation, Catalog No 650.069

Figure Xll-6.— Estimated Cost of Increasing the Performance of Air-Conditioners From the Industry Average COP of 2.0 to the Performance Levels Indicated (estimates assume production rates equivalent to current production rates)

2-piece cooling

20 21 22 23 24 25 26 System Coefflclent of Performance

SOURCE George D Hud~lson (Vice Prewdent - Englneerlng Carrier Corp } Presenlatlon to the solar Emmy Resources Conservation and Develop ment Commlsslon of Call forma Aug 10 1976 Docket No 75 CON 3 514 ● Solar Technology to Today’s Energy Needs

cent series of estimates of the increase in percent. A series of designs being con- air-conditioning COP achievable without sidered by the General EIectric Corporation changing the basic design of the air-condi- is indicated in figure Xl 1-7. Researchers at tioning system and using a compressor unit G.E. believe that it would be possible to which is currently available, and the cost of achieve an approximate 50-percent increase producing these new designs. Equipment in- in the average COP of both heating and corporating these new designs could be cooling for an increase in the initial cost of made in the next few years. The re- the unit of about 20 to 30 percent 7 It should quirements which will be imposed on air- be noted that performance can be improved conditioners and heat pumps sold in the by increasing low-temperature performance, State of California during the next 5 years high-temperature performance, or both, The are shown in table Xl 1-2. speed with which these new units appear on the market will depend strongly on the company’s perception of whether the public is Looking further into the future, a number willing to invest in equipment which can of systems have been proposed which could reduce their annual operating expenses over increase the COP of air-conditioning the long term. These attitudes, of course, systems and heat pumps by as much as so may be infIuenced by legislative initiatives.

DIRECT FOSSIL-FIRED HEATING AND AIR-CONDITIONING EQUIPMENT

HEATING EQUIPMENT nace bonnet divided by the heating value of the fuel.8 Typical values for direct-combus- The majority of residential and commer- tion furnaces are 70 to 75 percent; heat loss cial buildings in the United States are principally results from heated stack-gasses heated with direct-fired oil and gas furnaces lost during combustion, This definition does and boiIers. There is considerable controver- not give a complete measure of the fuel re- sy about the typical operating efficiencies quired to heat a living space over the heat- of these systems. One reason is that remark- ing season. A more useful definition which ably Iittle is known about the performance accounts for this, and which is increasingly capabilities of these systems in actual oper- being used, is the seasonal performance fac- ating environments, and the literature in the tor or seasonal efficiency. This measure compares performances of various space- area is filled with inconsistent information. heating systems. It is defined as the ratio of Some indication of the difficulty can be seen by examining figure Xl 1-8, which in- the amount of useful heat delivered to the dicates the performance estimates made by home to the heating content of the fuel the a variety of different organizations. Per- furnace used over the entire heating season. formance undoubtedly varies with the age Typical gas furnaces have seasonal efficien- of the unit, its installation, its position in the cies in the range of 45 to 65 percent (figure building, and a variety of other variables Xl 1-8). Seasonal efficiency accounts for all which are difficult to hold constant. factors affecting the heating system’s per- Another reason for the controversy is the formance in its actual operating environ- inconsistency in the definition of efficiency. Until recently, the most common value quoted was the steady-state or full-load 7Conley, General Electr c Corp , private com- combustion efficiency, which is defined as municatlon, 1977 the ratio of useful heat delivered to the fur- ‘Hlse and Holman, op clt Ch. XII Heating and Cooling Equipment ● 515

0 1

cd oJ -

1- 1-

7 516 ● Solar Technology to Today’s Energy Needs

Figure XII-8. – Residential Heating Systems

OIL Steady-State Efficiency (3) Columbus, Ohio (1) New England (429—well maintaine (2) New York (72—as found) (4) Washington, D.C. (8) U.S. Seasonal Efficiency (4) Washington, D. C. (4) Maryland mversion) (5) New York (6) U.S. (7) Us. (8) Us. (9) Us. (10) Philadelphia

GAS Steady-State Efficiency (3) Long Island Seasonal Efficiency (14) Baltimore (12) Canton, Ohio (10) Philadelphia (13) Philadelphia (4) Washington., D.C. v o 20% 40% 60% 80% 100%

SOURCE: J. H. Leggoa, “Seasonal Efflclency of Home Fuel 011 Furnaces” Phdadeiphla Electric Company PapeC Aug. 26, 1976.

ment. In addition to stack gas losses (the is indicated in figure Xl 1-9. The seasonal effi- largest contributor) these factors include ciency of many installations is reduced by loss of heated room air through the chimney while the furnace is off, cycling losses, pilot Figure Xll-9.— Efficiency of Gas Furnaces light (gas furnaces only), and heat losses through the air distribution ducts when in 9 unheated spaces. Cycling losses are a result 80 Oak Rtdge’ of operation at part loads, which causes t heat to be lost in raising the temperature of the furnace before useful heat can be 60 delivered to the living space. A recent measurement of this part-load performance 40

‘G Samuels, et al , MIUS Systems Ana/ysis– /rtitia/ Comparisons of Modular-Sized Integrated Utility Sys- 20 20 40 tems and Convention/ Systems, ORNL/H UD/Ml US-6, 60 80 100 June 1976, p 24. Ch. XII Heating and Cooling Equipment 517

installing units which are larger than neces- or a heat pump (figure Xl l-l O). The heat re- sary, meaning that the systems are always jected by this engine can be used to main- operating at relatively inefficient part-load tain a source of heated water, which can conditions. 10 then provide the heat pump with a source of thermal energy at a temperature higher than In addition to the fossil fuel required for the ambient air. Studies of this approach the burner, gas and oil furnaces and boilers require electric energy to operate fans and Figure XII-10.—A Fossil-Fired Heat-Pump System pumps. A typical small gas furnace will require about 13 watts per 1,000 Btu/hour Hot Alr 11 capacity, A large central boiler and hot- T O Builldlnq water distribution system wiII also require r about 13 watts per 1,000 Btu/hour of heating Outdoor Heat Pump 2 Heat capacity to pump heated water. Compressor Exchanger 1 % I Potential for Improving Performance I

The performance of gas furnaces can be increased by improving fan controls, using Heat Engine systems which preheat the air entering the furnace with the heat in the chimney, installing an electric ignition system to replace the I pilot, and a variety of other rather straightforward changes in design, A recent study conducted by the Oak Ridge National Lab- oratory estimated that fuIl-load combustion efficiencies of gas furnaces could be in- SOURCE OTA creased from 75 to 82 percent if these changes were implemented.13 The combustion efficiency of oil-burning furnaces can have been underway for some time in in- also be improved by using improved burner dustrial laboratories and a number of proj- heads and by ensuring that the burners are ects in this area have been supported by the welI maintained American Gas Association. An entirely different approach to the A variety of different heat-engine designs problem, using fossil fuels to operate a heat have been considered. Designs employing pump, has been under investigation for Stirling and Ericsson cycles are being exam- some time under the sponsorship of the ined by RCA, the N.V. Philips Corporation, American Gas Association. These designs Sun Power, Inc., Energy Research and Gen- burn fuel to operate a small onsite heat eration, Inc., and by the University of engine, which in turn drives the heat-pump Washington. 14 15 16 A number of workin compressor. g systems have been designed and tested. An advanced fossil fuel heating concept involves using the fuel to power a small heat “W Beale (Sun Power, Inc.), private communica- engine directly coupled to the compressor tion, June 1976 “G Benson (Energy Research and Generation, Inc ), Therrna/ Osci//ations, presented at 8th I ECEC meeting, ‘“H Ise and Hol man, op clt Aug 14, 1973 ‘‘W R Martlnl, Developments in Stirling Engines, ‘ ‘Sears Fall-W Inter Catalog, 1976, p 955 presented to the Annual Winter Meeting of the Ameri- ‘‘1 bld can Society of Mechanical E nglneers, New York, N.Y , ‘ ‘Hlse and Holman, op cit , p 3 Nov 26-30, 1972 518 Solar Technology to Today’s Energy Needs

A number of advanced, gas-fired, heat- tween 1,4000 and 1000 F could therefore pump systems are being examined by the in- achieve a cycle efficiency of 40 to 63 per- dustry, with the support of DOE and the cent. (ERG has reported a measured in- American Gas Association:* ** dicated efficiency which represents 90 per- ● An absorption system capable of pro- cent of Carnot in a free-piston device ducing both heating and cooling is operating i n roughly this temperature re- 18 being developed by the Allied Chemical gion. ) The Garrett Corporation has Corporation and the Phillips Engineer- reportedly achieved a cycle efficiency of 38 ing Co. percent, using a small regenerated gas turbine. ● A concept which uses a subatmospheric gas turbine is being developed by the If it is assumed that seasonal performance Garrett Air Research Corporation. factors for heat pumps can be in the range of 2.5 to 3.0, the overalI system COP (or ratio ● A free-piston Stirling engine is being of heat energy delivered to the Iiving space developed by the General Electric Cor- to the heating value of the fuel consumed) poration (the project received about $1 of a heat pump combined with a heat engine miIIion from the American Gas Associa- which is 38 to 60 percent efficient can be in tion and about $2 million from DOE in the range of 0.95 to 1.8, If waste heat from 1 977). the engine is used, the effective COP can be ● Systems based on diesel engines and as high as 2.2. Rankine-cycle devices are also being ex- A 38- to 60-percent efficient engine com- amined. bined with an air-conditioning cycle with a The technology of the engines used to drive COP of 2.5 could achieve system COPS of the compressors was discussed in greater 0.95 to 1.5. These coefficients cannot be detail in the previous chapter. An interesting compared directly with COPS of electric feature of the heat-fired, heat-pump systems heat pumps. In order to obtain comparable is that their performance does not decrease “system efficiency” for an electric system, with temperature as fast as the performance the electric COPS must be reduced by the ef- of conventional heat pumps. ficiency of converting primary fuels to elec- While working systems have been de- tricity and transmitting this energy to a heat- signed, commercial production is unlikely to pump system. The average generating effi- begin for the next 5 to 10 years. ciency in U.S. utilities is approximately 29 percent, the average transmission losses, ap- The performance of the engines being proximately 9 percent. Under these assump- considered for use with fossil-fired heat tions, an electric heat pump with a heating pumps is discussed in greater detail in the COP of 3.0 and a cooling COP of 2.5 would section on Solar Heat Engines in this chapter. have an effective “system” COP of 0.79 for Stirling and Ericsson cycle, free-piston heating and 0.66 for cooling. There are a devices may be able to achieve efficiencies number of questions about the system’s in the order of 60 to 90 percent of ideal Car- performance as an integrated unit, its not efficiency.17 An engine operating be- reliability, safety, noise, ease of maintenance, etc., which can only be resolved after much more experience has been obtained. *“Advanced Gas-Fired Heat Pumps Seen Cutting Heating E3111s in Half, ” Energy Users Report #188, Mar 17, 1977, p 25 * * Paul F Swenson, “Competltlon Coming In Heat Pumps Gas-Fired May Be Best In Cold Climate, ” Energy Research Reports, Vol 3, No 5, Mar 7, 1977, “lbld p2 “Patrick G Stone (Garrett Corporation), private ‘ ‘Benson, 011 clt communication, December 1976. Ch. XII Heating and Cooling Equipment 519

The devices do offer the prospect of a much at al 1. The heat-engine devices just discussed more efficient approach to converting fossiI could, at least in principle, be used in con- fuels to useful space-conditioning, nection with a coal-burning, fluidized-bed boiler or other system, and thus might pre- A major question concerning any onsite sent a promising long-term alternative. One system requiring oil or gas is whether these advantage of electric systems is that they fuels will continue to be available at accept- may be able to use a greater variety of able prices, or whether they wilI be available primary fuels than onsite systems.

ABSORPTION AIR= CONDITIONING

An “absorption-cycle” device for using absorbed heat rejected into the atmosphere direct thermal energy to operate air-con- (this cycle is on the right side of figure ditioning systems has been available for Xl 1-11). The absorption cycle accomplishes some time. A standard cycle is illustrated in this recompression by absorbing the low- figure Xl 1-11. The refrigeration cycle is very pressure water vapor in a concentrated salt similar to cycles used in other types of air- solution. This concentrated solution is con- conditioning systems (vapor-compression). A tinuously produced in a distilling unit which chilled liquid (usually water instead of a is driven by the heat from the fuel. refrigerant) is permitted to expand and cool The cooling performed by the absorption air. This water is then recompressed and the system can be separated into two distinct phases, and it would therefore be possible to store the concentrated salt solution for use Figure XII-11 .—Basic Single-Effect Absorption when required by the cooling load. This con- Refrigeration Cycle - cept is discussed further in chapter Xl, Energy Storage. The major limitation to such a procedure at present is the cost of the working fIuids,

An enormous amount of time and money has been invested in the search for better working fluids. Lithium bromide/water solu- 1 tions are used most frequently at present. Refrigerant (Liquid) Ammonia/water solutions are also used. Absorption units are inherently more ex- I pensive than electric systems 1 ) because of the larger number of heat exchangers required, and 2) because the unit’s cooling towers must be large enough to reject both heat from the combustion process and heat removed from the space which was cooled. (In electric systems, the heat from generation is rejected at the electric generator I I site ) Heat Heat Input Reject!on (Coollng Load) SOURCE: National Science Foundation. Double-effect units are also more expensive than single-effect devices because even smaIIer numbers are produced An anaIysis 520 Solar Technology to Today’s Energy Needs

of the components required indicates that marketed a small (1 5-ton) Iithium bromide, double-effect machines could cost about 20 double-effect, absorption machine. The de- percent more than single-effect units in the sign was taken from work supported in part same capacity range. The prices shown in by the American Gas Association, and was figure XII- 1 2 indicate that double-effect apparently capable of achieving very high units operating at 3050 F instead of 3600 F efficiencies. It was removed from the would cost nearly twice as much because market after only a few hundred were sold, capacity would be decreased. Little work apparently because the company felt that it has been done to produce an optimum de- could not overcome problems with the sys- sign for low-temperature systems, and DOE tem’s reliability at a reasonable cost. The is currently funding several projects in this unit was sufficiently different from single- area. effect units that gas company maintenance personnel had difficulty repairing the de- The only small absorption units now on vices. The unit at least demonstrated the the market are the Arkla single-effect de- feasibility of small double-effect units. vices, manufactured in 3- and 25-ton sizes. There are currently no small double-effect System Performance machines on the market. In the early 1960’s, the Iron Fireman Webster Division of the The coefficient of performance (COP) of Electronic Specialties Corporation briefly contemporary absorption air-conditioners is

Figure Xll-12.— Estimated Refrigeration Unit Cost Per Ton, 12,000 Btu/hr(contractor’s cost)* 700 I I I I I 1 I I I

1. Single Effect Absorption, 195° F Supply Water 2. Single Effect Absorption, 250° F Supply Water 600 3. Double Effect Absorption, 305° F Supply Water 4. Double Effect Absorption, 360° F Supply Water 5. Electro-Mechanical Vapor Compression–Reciprocating 6. Electro-Mechanical Vapor Compression-Centrifugal 500

400

$/Ton

300

200

100

L o 40 80 120 160 200 240 280 320 380 400 Unit Size in Tons .Industry Average- 1976 Costs

NOTE Prices do not Include Inslallat!on or subcontractor O&P costs SOURCE prepared for OTA by H CorbY r) Rooks April 1976 Ch. XII Heating and Cooling Equipment 521

shown in figure Xl 1-13. A typical single- The COPS also do not include the ineffi- effect device has a COP of 0.65 and double- ciency of the boiler which must be used effect units can have COPS of 1.1. These when the absorption units are used with COPS must, however, be carefully qualified. fossil fuels. Typical boilers used in such ap- (As in the case of fossil-fired heat pumps, plications lose about 20 to 22 percent of the these COPS should be compared with the heating value of the fuel burned in hot “system” COPs of electric system s.) gasses escaping up the chimney. The COPS shown in the figure would apply to units The COPS shown in figure Xl 1-13 include operated from solar-heated fluids or by neither the electric energy required to oper- steam generated by a waste-heat boiler-con- ate pumps which move chilled water to the nected to a direct or other heat engine. They building loads and cooling water to and must be reduced by 20 to 22 percent when from the cooling tower, nor the electricity used to represent the performance of direct- required to operate the fan in the cooling fired devices. tower. These ancillary units require about 0.14 kW per ton of cooling in a typical in- It is reasonable to expect that improve- stalIation. 20 ments in current designs could lead to significant improvements in performance. A new series of absorption units, soon to be marketed by Arkla, will probably achieve a 20 Samuels, et al , op cit , p 20 COP greater than 0.7 for a single-effect de-

1.2

1.1 0 With-85 Cooling Tower Water to Unit 44° Chilled Water Temp. From Unit 1.0

.7 COP .6 . .5

.3 ‘.

0 I I I I I I / I I I 1 I I I I I A 100 140 180 220 260 300 340 380 420 440 Temperature of the Supply Water (“F) SOURCE Prepared for OTA by H Corbyn Rooks, April 1976 522 ● Solar Technology to Today’s Energy Needs

vice with no substantial increase in price. An construct double-effect absorption devices experimental machine, which was a modi- with COPS in the range of 1.35.23 fied version of the single-effect Arkla de- Absorption units have good performance vice, has been tested with a COP greater at partial loads because their effective than 0.8. 21 capacity can be varied by simply changing The Iron-Firemen double-effect device the rate at which the salt solutions are discussed previously was able to achieve a pumped through the systems. This type of COP of 1.2 (not including boiler losses and control works until the load falIs to about 35 electric energy requirements) .22 Some engi- percent of the peak load, at which point neers believe that it would be possible to substantial inefficiencies are experienced.

CONVENTIONAL GAS AND ELECTRIC WATER HEATERS

Residential hot water heaters are very in- COPS of gas units to 0.80. z efficient. ’ A gas water heater has a COP of The efficiency of water heaters varies about 0.50, and an electric water heater a somewhat as a function of loads, but for 25 COP of about 0.75. 2 ’ 27 Better insulation simplicity it is assumed that water heaters and other improvements could increase the have a constant “average” efficiency. COPS of future electric units to 0.85 and the

OPERATING COSTS

The costs of operating conventional heat- nance contracts must increase the actual ing and cooling equipment (exclusive of fuel maintenance costs by a margin sufficient to costs) are not well documented, and no ex- cover overhead and profit requirements. tensive study has been conducted on the Table XII-3. — Average Cost of Maintenance subject. The estimates used in later analyses Contracts for Residential Heating are shown in tables Xl I-3 and Xl 1-4. The costs and Cooling Equipment used in this study were taken from the costs ——. . .— of purchasing a service and maintenance Annual cost contract for equipment installed in the Washington, D. C., area. The actual costs will Gas furnace and eleotric air-conditioning vary as a function of geographic location, $60 quality of the equipment, location of the Air-to-air heat pump $50 equipment in the building, design of the Baseboard electric heat and window systems, etc. The costs must be considered air-oonditioners $30 conservative since the selIers of mainte- —— ————.... .— SOURCE Gordlan Associates, Inc Evaluation of the Air-to-Air Heat Pump for Resldentlal Space-Condltlonmg. April 1976

2’joseph Murray, Chief Engineer of Applied Sys- 24 tems, Airtemp Corporation, private communication, CiIlman, op clt Sept 23,1976 2’APS, Efficient Use of Energy, p 83. ‘Z)oseph Murray, private communication, 1977 “J J. Mutch, Residential Water Heating, Fue/ Con- 2’G.C Vllet, et al , A Thermodynamic Approach to servation Economics and Public Policy, pp. 8 and 55 the Developments of a More Efficient Absorption Air- 27 Arthur D Little Co,, Study of Energy-Savings Op- Conditioning System, University of Texas at Austin – tions for Refrigerators and Water Heaters, draft, pp Center for Energy Studies S-12,1 3,14 Ch. XII Heating and Cooling Equipment ● 523

Table XII-4. —Cost of Maintaining Commercial Heating and Cooling Equipment* (Parts and Labor)

Low Rise

Heating (106 Btu/hour) Gas ...... $1,000 $1,000 Oil ...... 1,250 1,250 Electric ...... 1,000 1,000

Cooing (50 tons) Gas...... 3,8OO-4,5OO 6,300-7,500 Electric ...... 3,000-3,6OO 5,000-6,000

High Rise

Heating (2 units@ 2x106 Btu/hour) Gas ...... 2,000 oil ...... 2,500 625 Electric ...... 2,000

Cooling(200tons) Gas ...... 5,000-6,000 2,000-2,500 Electric...... 4,000-5,000 1,700-2,000

Shopping Center

Heating (2 units@ 8x106 Btu/hour) Gas ...... 2,500 150 Oil ...... 3,000 190 Electric ...... 2,500 150

Cooling(2000tons) Gas...... 19,000 800 Electric ...... 15,000 600

‘Actual costs wIfl vary greatly as a function of equipment quality, ln- stallatron, bulldlng features, etc Costs based on “very rough’ estimates of Robert NoYes of R E Donovan Co, Inc a service corn. pany[nthe Wasthlngton DC area Sept 23 1976

ADAPTATION OF CONVENTIONAL EQUIPMENT TO SOLAR POWER

Conventional heating and cooling equip- can provide a source of thermal energy for ment can be integrated with solar energy in liquid and air-heat pumps, for absorption two basic ways: 1 ) electricity or mechanical air-conditioning, forced-air heating, and to energy generated by solar energy devices heat domestic hot water. can be used to supplement electricity purchased from a utility, and 2) direct use of The direct use of solar-heated fluids for thermal energy generated by solar devices space heating or for the heating of hot water 524 ● Solar Technology to Today’s Energy Needs

requires no sophisticated equipment, and SOLAR ABSORPTION EQUIPMENT the problems of designing these systems are discussed elsewhere. Absorption cooling equipment can be easily converted for use with solar-heated fluids, and the modifications being sug- SOLAR HEAT ENGINES gested for high-performance solar applica- Direct use of solar-heated fIuids can oper- tions should not require major design ate heat engines such as Rankine cycle tur- changes. As a result, absorption equipment bines or Stirling engine devices which are will probably represent the majority of units coupled mechanically to heat pumps and used in solar air-conditioning systems in the air-conditioners. The direct-drive systems near future. The water sent to the absorp- have a substantial theoretical advantage tion generator can be heated either from a over systems operating from solar-generated conventional boiler or from a solar collec- electricity in that the losses associated with tor. The coefficients of performance used a motor and generator can be avoided. This for solar absorption equipment will be the can be a substantial gain, since typical effi- same as those used for the steam-driven ab- ciencies of small motors and generators are sorption equipment, since no boiler losses in the range of 80 to 90 percent and com- are involved. bined losses can amount to 30 percent. Total energy systems, which use the solar- The Adsorption Cycle System powered engine to drive both a generator The adsorption cycle was originally and a heat pump, could be driven directly developed by Carl Munters of Stockholm, from utility electricity when solar energy is and is often known as the Munters system. not available by using the electric generator The system is basically a desiccant system, as a motor to drive the compressor. Direct- drying the air with various kinds of salt drive systems have a potential disadvantage crystals, silica gels, or zeolite. Heat and if they cannot be designed as a single-sealed moisture are typically exchanged between unit, since seals on rotating shafts could an exhaust airstream and a supply airstream reduce overall system reliability. It may be using a heat exchange wheel and a drying possible to develop completely sealed en- wheel as shown in figure Xl 1-14. The air is gine-compressor units, but this wilI require a taken from the room and passed over the lengthy development program, drying wheel which contains the desiccant. In passing through this wheel, the air is dried All of the heat engine alternatives are dis- and heated to about 180oF. It then passes cussed in detail in the chapter discussing the through the heat exchange wheel, where it conversion of solar energy into electricity. cools to near room temperature. The air is The operating characteristics of conven- finally passed through a humidifier, where it tional heat pumps and air-conditioners in- picks up moisture and cools to 550 to 600 F. tegrated into solar energy designs using The exhaust airstream takes ambient air and direct-drive connections will need adjust- humidifies and cools it slightly to keep the ment to eliminate the inefficiency of the heat exchange wheel as cool as possible. motors used in conventional systems. For After passing through the heat exchange the purposes of the calculations which wheel, the air is still not hot enough to drive follow, it is assumed that the motors used on the moisture out of the drying wheel, so ad- conventional systems are 80 percent effi- ditional heat from a solar or gas source is cient. Systems connected electrically are added. This hot air then passes through the assumed to be identical to conventional drying wheel, where it evaporates moisture equipment, and conventional performance from the desiccant, and the moist, heated characteristics are assumed. air is exhausted to the atmosphere, Ch. XII Heating and Cooling Equipment ● 525

Its advantage is that it takes no refrigera- on the rotating wheels, and the wet pads. tion unit, but the wheels are large and re- Variations of this adsorbent system are be- quire power to drive. After years of developing properly supported by DOE. It has ad- ment, problems still exist with desiccant vantages, but still requires development systems, including the desiccant, the seals prior to demonstration. between the supply and discharge airstream

Figure XII-14. —An Adsorption Chiller

Heat Gas Burner Exchange Humidifiers or Solar Heat \\ Wheel I

Ambient

56.5o/53o

SOURCE Based on a drawtng by W F Rush, statement relative to H R 10952 (Institute of Gas Technology, Illlnols Institute of Technology, Chicago, Ill ) Nov 14, 1973