Small Wind Energy Systems for the Homeowner

DOE/GO-10097-374 FS 135 ENERGY January 1997 EFFICIENCY Small Wind Energy Systems AND

RC ENEWABLE for the Homeowner

ELE NERGY In the 1920s and ‘30s, farm families assess your wind resource and possible throughout the Midwest used wind to sites, discuss legal and environmental generate enough electricity to power their obstacles, and analyze economic consider- lights and electric motors. The use of wind ations such as pricing. A power declined with the government- subsidized construction of utility lines and Benefits of Wind Power

R fossil fuel power plants. However, the energy crisis in the 1970s and a growing A wind energy system can provide you concern for the environment generated an with a cushion against electric power price I interest in alternative, environmentally increases. Wind energy systems help N friendly energy resources. Today, home- reduce U.S. dependence on fossil fuels, owners in rural and remote locations and they are nonpolluting. If you live in a remote location, a small wind energy sys- G across the nation are once again examining the possibility of using wind power to pro- tem can help you avoid the high costs of vide electricity for their domestic needs. having the utility power lines extended to

H your site. This publication will help you decide whether a wind system is practical for Although wind energy systems involve a O you. It will explain the benefits, help you significant initial investment, they can be US E etz, PIX 00042 ren Gr ren War Unlike yesteryear's windmill, today's wind turbines use technological innovations that have substantially reduced the cost of electricity generated from wind power.

NT O ME F E T N R E A R This document was produced for the U.S. Department of Energy (DOE) by the National Renewable Energy Laboratory (NREL), a DOE national laboratory. P G

E Y D The document was produced by the Information Services Program, under the DOE Office of Energy Efficiency and Renewable Energy. The Energy Efficiency

A N and Renewable Energy Clearinghouse (EREC) is operated by NCI Information Systems, Inc., for NREL / DOE. The statements contained herein are based on C I I T R E information known to EREC and NREL at the time of printing. No recommendation or endorsement of any product or service is implied if mentioned by EREC. D E M S A TAT ES OF Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 20% postconsumer waste

competitive with conventional energy Conditions for Grid-Connected sources when you account for a lifetime of Systems reduced or altogether avoided utility • You live in an area with average annual costs. The length of the payback period— wind speeds of at least 10 miles per hour the time before the savings resulting from (4.5 meters per second). your system equal the cost of the system • Utility-supplied electricity is expensive itself—depends on the system you choose, in your area (about 10 to 15 cents per the wind resource on your site, electricity kilowatt hour). costs in your area, and how you use your • The utility’s requirements for connect- wind system. ing your system to its grid are not pro- hibitively expensive. Is Wind Power Practical for You? • Local building codes or covenants allow Small wind energy systems can be used you to legally erect a wind turbine on in connection with an electricity transmis- your property. sion and distribution system (called grid- • You are comfortable with long-term connected systems), or in stand-alone appli- investments. cations that are not connected to the utility Wind turbines for grid. A grid-connected wind turbine can Is Your Site Right? reduce your consumption of utility-sup- The U.S. Department of Energy (DOE) domestic or rural plied electricity for lighting, appliances, has compiled wind resource maps that are and electric heat. If the turbine cannot available from the American Wind Energy applications range in deliver the amount of energy you need, Association and the National Technical the utility makes up the difference. When Information Service (see Source List). The size from a few watts the wind system produces more electricity DOE maps are good sources for regional than the household requires, the excess information and can show whether wind to thousands of can be sold to the utility. With the inter- speeds in your area are generally strong connections available today, switching enough to justify investing in a wind watts and can be takes place automatically. Stand-alone system. wind energy systems can be appropriate applied economically for homes, farms, or even entire communi- Wind-turbine manufacturers can use com- ties (a co-housing project, for example) puter models to predict their machines’ for a variety of power that are far from the nearest utility lines. performance at a specific location. They Either type of system can be practical if can also help you size a system based on demands. the following conditions exist. your electricity needs and the specifics of local wind patterns. However, you will Conditions for Stand-Alone Systems need site-specific data to determine the • You live in an area with average annual wind resource of your exact location. If wind speeds of at least 9 miles per hour you do not have on-site data and want to (4.0 meters per second). obtain a clearer, more predictable picture • A grid connection is not available or can of your wind resource, you may wish to only be made through an expensive measure wind speeds at your site for a extension. The cost of running a power year. You can do this with a recording line to a remote site to connect with the anemometer, which generally costs $500 to utility grid can be prohibitive, ranging $1500. The most accurate readings are from $15,000 to more than $50,000 per taken at “hub height” (i.e., the elevation at mile, depending on terrain. the top of the tower where you will install • You have an interest in gaining energy the wind turbine—see the section on independence from the utility. “Wind System Basics” that follows). This • You would like to reduce the environ- requires placing the anemometer high mental impact of electricity production. enough to avoid turbulence created by • You acknowledge the intermittent trees, buildings, and other obstructions. nature of wind power and have a strat- The standard wind sensor height used to egy for using intermittent resources to obtain data for the DOE maps is 33 feet meet your power needs. (10 meters).

In favorable locations, a wind turbine can reduce your consumption of utility-supplied electricity.

Moderate wind energy Good wind energy Excellent wind energy 13.4 to 14.6 miles per hour 14.6 to 15.7 miles per hour More than 15.7 miles per hour (6.0 to 6.5 meters per second) (6.5 to 7.0 meters per second) (More than 7.0 meters per second)

This map gives general information on the average wind resources available across the country. Of course, the actual wind resource on your site will vary depending on such factors as typography and structure interference.

You can have varied wind resources Additional Considerations within the same property. If you live in complex terrain, take care in selecting the In addition to the factors listed previously, installation site. If you site your wind tur- you should also: bine on the top or on the windy side of a hill, for example, you will have more • research potential legal and environ- access to prevailing winds than in a gully mental obstacles, or on the leeward (sheltered) side of a hill • obtain cost and performance informa- on the same property. Consider existing tion from manufacturers, obstacles and plan for future obstructions, • perform a complete economic analysis including trees and buildings, which could that accounts for a multitude of factors block the wind. Also realize that the power (see the case study), available in the wind increases proportion- • understand the basics of a small wind ally to its speed (velocity) cubed (v3). This system, and means that the amount of power you get • review possibilities for combining your from your generator goes up exponentially system with other energy sources, back- as the wind speed increases. For example, ups, and energy efficiency improve- if your site has an annual average wind ments. speed of about 12.6 miles per hour (5.6 meters per second), it has twice the You should establish an energy budget to energy available as a site with a 10 mile help define the size of turbine that will be per hour (4.5 meter per second) average. needed. Since energy efficiency is usually less expensive than energy production, making your house more energy efficient first will likely result in being able to spend less money since you may need a smaller wind turbine to meet your needs.

3 Potential Legal and Environmental The Economics of Wind Power Obstacles for Home Use Before you invest any time and money, A residential wind energy system can be a research potential legal and environmental good long-term investment. However, obstacles to installing a wind system. because circumstances such as electricity Some jurisdictions, for example, restrict rates and interest rates vary, you need to the height of the structures permitted in decide whether purchasing a wind system residentially zoned areas, although vari- is a smart financial move for you. The case ances are often obtainable (see “Wind Sys- study that follows illustrates the many fac- tem Basics,” which follows). Your tors and calculations you will need to con- neighbors might object to a wind machine sider. Be sure you or your financial that blocks their view, or they might be adviser conduct a thorough analysis concerned about noise. Consider obstacles before you buy a wind energy system. that might block the wind in the future (large planned developments or saplings, Grid-connected-system owners may be for example). If you plan to connect the eligible to receive a small tax credit for the wind generator to your local utility com- electricity they sell back to the utility. For Wind is derived pany’s grid, find out its requirements for 1996, it was 1.6 cents per kilowatt hour. interconnections and buying electricity The National Energy Policy Act of 1992 from solar energy. from small independent power producers. and the 1978 Public Utilities Regulatory Policy Act (PURPA) are two programs that When the sun heats Pricing a System apply to small independent power pro- When you are confident that you can ducers. PURPA also requires that the util- the earth's surface install a wind machine legally and with- ity sell you power when you need it. Be out alienating your neighbors, you can sure you check with your local utility or unevenly, it creates begin pricing systems and components. state energy office before you assume any buy-back rate. Some Midwestern rates are differences in Approach buying a wind system as you very low (less than $.02/kWh), but some would any major purchase. Obtain and states have state-supported buy-back rates air temperature review the product literature from several that encourage renewable energy genera- manufacturers. Lists of manufacturers are tion. In addition, some states have “net and atmospheric available from the American Wind Energy billing,” where utilities purchase excess Association (AWEA, see Source List); how- electricity for the same rate at which they pressure, which ever, not all small turbine manufacturers sell it. (The Energy Efficiency and Renew- are members of AWEA. Manufacturer able Energy Clearinghouse—see Source causes wind. information can also be found at times in List—has more information on net billing.) the periodicals listed in the Reading List. Once you have narrowed the field, Also, some states offer tax credits and research a few companies to be sure they some utilities offer rebates or other incen- are recognized wind energy businesses tives that can offset the cost of purchasing and that parts and service will be available and installing wind systems. Check with when you need them. Also, find out how your state’s department of revenue, your long the warranty lasts and what it local utility, public utility commission, or includes. your local energy office for information.

Ask for references of customers with Wind System Basics installations similar to the one you are All wind systems consist of a wind tur- considering. Ask system owners about bine, a tower, wiring, and the “balance of performance, reliability, and maintenance system” components: controllers, invert- and repair requirements, and whether the ers, and/or batteries. system is meeting their expectations. Wind Turbines Home wind turbines consist of a rotor, a generator mounted on a frame, and (usually) a tail. Through the spinning blades, the rotor captures the kinetic energy of the

4 The highest average wind and converts it into rotary motion to Experiments have shown that relatively drive the generator. Rotors can have two small investments in increased tower wind speeds in or three blades, with three being more height can yield very high rates of return common. The best indication of how in power production. For instance, to raise the United States much energy a turbine will produce is the a 10-kW generator from a 60-foot tower diameter of the rotor, which determines its height to a 100-foot tower involves a 10% are generally found “swept area,” or the quantity of wind increase in overall system cost, but it can intercepted by the turbine. The frame is produce 25% more power. along sea coasts, the strong central axis bar onto which the rotor, generator, and tail are attached. The There are two basic types of towers: self- on ridge lines, and tail keeps the turbine facing into the wind. supporting (free standing) and guyed. Most home wind power systems use a guyed on the Great Plains, A 1.5-kilowatt (kW) wind turbine will tower. Guyed-lattice towers are the least meet the needs of a home requiring expensive option. They consist of a simple, but many areas 300 kilowatt-hours (kWh) per month, inexpensive framework of metal strips sup- for a location with a 14-mile-per-hour ported by guy cables and earth anchors. have wind resources (6.26-meters-per-second) annual average wind speed. The manufacturer will pro- However, because the guy radius must be strong enough vide you with the expected annual energy one-half to three-quarters of the tower output of the turbine as a function of height, guyed-lattice towers require to power a wind annual average wind speed. The manufac- enough space to accommodate them. turer will also provide information on the Guyed towers can be hinged at the base so generator maximum wind speed in which the tur- that they can be lowered to the ground for bine is designed to operate safely. Most maintenance, repairs, or during hazardous economically. turbines have automatic speed-governing weather such as hurricanes. Aluminum systems to keep the rotor from spinning towers are prone to cracking and should out of control in very high winds. This be avoided. information, along with your local wind speed distribution and your energy bud- Balance of System get, is sufficient to allow you to specify Stand-alone systems require batteries to turbine size. store excess power generated for use when the wind is calm. They also need a charge Towers controller to keep the batteries from over- To paraphrase a noted author on wind charging. Deep-cycle batteries, such as energy, “the good winds are up high.” those used to power golf carts, can dis- Because wind speeds increase with height charge and recharge 80% of their capacity in flat terrain, the hundreds of times, which makes them a turbine is mounted good option for remote renewable energy Tilt-up tower in the normal on a tower. Gener- systems. Automotive batteries are shal- operating position ally speaking, the low-cycle batteries and should not be used higher the tower, the in renewable energy systems because of

Tilt-up tower in the lowered more power the their short life in deep cycling operations. position for maintenance wind system can or hurricanes produce. The tower In very small systems, direct current (DC) also raises the tur- appliances operate directly off the batter- bine above the air ies. If you want to use standard appliances

turbulence that can that require conventional household alter- indpower exist close to the nating current (AC), however, you must gey W ground. A general install an inverter to convert DC electricity Ber rule of thumb is to to AC. Although the inverter slightly low- Towers can be hinged so they can be lowered to the ground for maintenance or during very high winds. install a wind tur- ers the overall efficiency of the system, it bine on a tower with allows the home to be wired for AC, a def- the bottom of the rotor blades at least 30 inite plus with lenders, electrical code offi- feet (9 meters) above any obstacle that is cials, and future home buyers. within 300 feet (90 meters) of the tower.

5 The power available For safety, batteries should be isolated from living areas and electronics because they contain corrosive and explosive sub- in the wind increases Wind turbine stances. Lead-acid batteries also require proportionally protection from temperature extremes. to the cube of its In grid-connected systems, the only additional equipment is a power conditioning Tower velocity (v3). unit (inverter) that makes the turbine Accessible output electrically compatible with the disconnect switch utility grid. No batteries are needed. Work with the manufacturer and your local util- Power ity on this. processing unit Circuit Energy breaker panel meter Hybrid Wind Systems According to many renewable energy experts, a stand-alone “hybrid” system 120/240 VAC indpower loads that combines wind and photovoltaic (PV) gey W technologies offers several advantages Ber over either single system. (For more infor- A wind system that hooks into the existing power grid makes economic sense if mation on solar electric—or photovoltaic— electricity is expensive and the electrical systems, contact the Energy Efficiency and load coincides with windy weather. Renewable Energy Clearinghouse—see Source List. ) If the batteries run low, the engine- generator can be run at full power until In much of the United States, wind speeds the batteries are charged. Adding a fossil- are low in the summer when the sun fuel-powered generator makes the system shines brightest and longest. The wind is more complex, but modern electronic con- strong in the winter when there is less trollers can operate these complex systems sunlight available. Because the peak oper- automatically. Adding an engine-genera- ating times for wind tor can also reduce the number of PV and PV occur at dif- modules and batteries in the system. Keep ferent times of the in mind that the storage capability must Wind turbine day and year, hybrid be large enough to supply electrical needs systems are more during noncharging periods. Battery likely to produce banks are typically sized for one to three PV array (optional) power when you days of windless operation. need it. Tower The Future of Wind Power For the times when neither the wind By investing in a small wind system, you generator nor the PV can reduce your exposure to future fuel modules are produc- shortages and price increases and reduce DC source Wind charge center PV charge DC-AC ing electricity (for pollution. Deciding whether to purchase a controller controller inverter example, at night wind system, however, is complicated; Engine generator when the wind is not there are many factors to consider. But if (optional) blowing), most you have the right set of circumstances, a (System controls stand-alone systems well-designed wind energy system can not shown) provide power provide you with many years of cost- through batteries effective, clean, and reliable electricity. Battery bank and/or an engine- indpower DC 120/240 VAC loads loads generator powered gey W by fossil fuels. Ber Hybrid systems, which use both wind and photovoltaic components to capitalize on the strengths of each technology, can offer more reliability than either system alone.

6 Case Study: Wind Power Economics of a Home System Note: In this analysis, we have assumed a certain over 20 years, her total inflation-adjusted cost set of conditions, such as wind regime, mainte- for buying a wind system is $19,678. nance costs, etc. Your analysis will differ for your Net Present Value of Both Options set of circumstances. This case study is for illus- However, our example is still not complete. tration purposes only. Economists tell us that future dollars are A New England homeowner is considering worth less than present dollars. It is better to taking out a 20-year loan to purchase a have money now, rather than in the future, so $10,000 wind system (turbine, tower, inverter, we can use it to invest and earn more money. and battery storage) for generating her own Even though inflation increases her annual electricity, instead of paying her full electric- electricity payments after 20 years to $1,894, ity bills for the next 20 years. those are future dollars, so they are worth less than today's dollars. Economists refer to this Assume that the wind turbine she has chosen devaluation as the net present value factor, the is rated at 3 kilowatts with the turbine 80 feet rate at which future dollars are discounted (24 meters) above the ground, and that she compared to present dollars. This discount lives in a Class 4 wind regime (average wind rate is equal to the rate of return that she could speed of 12.5 to 13.4 miles per hour [5.6 to make on an investment of equivalent risk and 6 meters per second] measured at 33 feet liquidity to a wind turbine. In this evaluation, [10 meters] above the ground). Given these assume her opportunity for return on invest- assumptions, the turbine can produce an esti- ment with today's dollars (i.e., the discount mated 9000 kilowatt hours (kWh) per year, or rate for her future dollars) is 10% a year. 750 kWh per month. Also assume, for the sake of simplicity, that she will use all of the Therefore, projecting her electric utility pay- electricity herself and will not sell any back to ments into the future to, say, the end of the the utility. Therefore, the value of the electric- first year, the dollars are worth 90% of what ity to her is equal to the retail price she pays they were at the beginning of the year. At the end of the second year, the dollars are worth the utility; in this case, 12 cents per kWh. 90% of what they were at end of the previous Today's wind power Continuing to Pay Electricity Bills year. (Notice the value of her future dollars If she continues to pay her electricity bills depreciates at a compounded rate.) Consider- without the wind turbine, the retail value of ing these adjustments, her annual electricity systems are durable, the electricity is $1,080 the first year. In later payment in the 20th year is actually worth years, the price of electricity increases. For only $156 in today's dollars. Thus, her total reliable, and this analysis, we assume that the cost of elec- cost of buying electricity for 20 years, tricity increases at the same rate as inflation— adjusted for inflation and present value fac- efficient, capable of 3% a year. Thus, the 9000 kWh will cost $1,112 tors, is only $8,927 in today's dollars. in the second year, $1,146 the third year, and Another way to think of it is that her pay- so forth, until the total inflation-adjusted cost ment in the 20th year is really a deferred pay- producing clean, of electricity for 20 years is $29,020. ment. She does not have to pay $29,020 today. Purchasing a Wind System Since the utility company allows her to pay cost-effective power. She can obtain the least-expensive loan by her bills as she uses the electricity, she does not taking out a second mortgage on her home. have to make any large capital expenditures. She can borrow $10,000 at 8%, and make pay- So she has more of her money to invest for ments of $1,019 for 20 years. But she can 20 years. This would not be true if she had to deduct the portion of her payments that go pay for 20 years of electricity up front. toward interest at her 30% combined federal But net present value factors also apply to and state tax rate. Thus, after taxes, her purchasing a wind system, because she is annual payment is $779 for the first year, and making deferred payments on her loan. Her increases to $996 as the interest deduction payments of $1,154 in year 20 are really worth decreases in later years. only $95 in today's dollars, for instance. However, there are other costs to owning a Therefore, her total cost for buying a wind wind turbine. Her property taxes will be system, adjusted for inflation and net present higher because the wind turbine increases the value, is only $6,426 in today's dollars. value of her property. She will pay additional The Final Analysis insurance since her standard homeowner's So in real terms, she saves $2,501 over 20 years policy does not cover liability from the wind by purchasing a wind system, as opposed to tower. And she will hire a local mechanic to continuing to pay her electricity bills. An climb the tower and grease the bearings added benefit is that she would avoid the every year. Altogether, she figures these oper- release of 40 tons (40 metric tons) of carbon ations and maintenance (O&M) costs will be dioxide, 800 pounds (363 kilograms) of nitro- about 1 cent/kWh or $100 per year in today's gen oxide, and 280 pounds (127 kilograms) of dollars. Let us assume for this analysis that sulfur dioxide into the atmosphere—the taxes, insurance, and labor rates increase at amount of pollution that a utility company in the same rate as inflation. Thus, annual O&M the Northeast would emit to supply her elec- costs increase to $175 in the 20th year. So, tric load for 20 years, on average.

7 Source List Reading List The following organizations can provide you with infor- Periodicals mation to help decide whether a wind energy system is Backwoods Home right for you. 1257 Siskiyou Boulevard, #213 Alternative Energy Institute (AEI) Ashland, OR 97520 West Texas A&M University (916) 459-3300 Box 248 This publication is devoted to independent living, including Canyon, TX 79016 independent energy systems. (806) 656-2296 Home Energy Fax (806) 656-2733 2124 Kittredge Street, No. 95 AEI conducts field trials at its Wind Turbine Test Center and is Berkeley, CA 94704-9942 a source of information on small wind turbines. (510) 524-5405 American Wind Energy Association (AWEA) This source provides information on reducing energy con- 122 C Street, NW, 4th Floor sumption. Washington, DC 20001 Home Power (202) 383-2500 Fax (202) 383-2505 P.O. Box 520 Ashland, OR 97520-0520 AWEA is a source for DOE wind maps, lists of manufacturers (916) 475-3179 and dealers, information on wind power tax credits, and other wind energy information. This periodical provides practical information, case studies, and advice on designing, installing, and living with small National Technical Information Service (NTIS) power systems. U.S. Department of Commerce 5285 Port Royal Road Books Springfield, VA 22161 A Siting Handbook for Small Wind Energy Conversion (703) 487-4650 Systems, Battelle Pacific Northwest Laboratory, National http://www.ntis.gov Technical Information Service, U.S. Department of NTIS has over 3 million publications that are available to the Commerce, 5285 Port Royal Road, Springfield, VA 22161, public. They offer a free catalog that lists a selection of these 1980. documents. The Wind Power Book, J. Park, Chesire Books, Palo Alto, For free information about many kinds of energy efficiency CA, 1981. This book is currently out of print, so check and renewable energy topics, contact: your local library for availability. The Energy Efficiency and Renewable Energy Wind Power for Home & Business: Renewable Energy for the Clearinghouse (EREC) 1990s and Beyond, P. Gipe, Chelsea Green Publishing P.O. Box 3048 Company, P.O. Box 130, Route 113, Post Mills, VT Merrifield, VA 22116 05058-0130, 1993. (800) 363-3732 Wind Energy Resource Atlas of the U.S., Battelle Pacific Fax: (703) 893-0400 Northwest Laboratories. Available from the American E-mail: [email protected] Wind Energy Association or the National Technical EREC provides free general and technical information to the Information Service (see Source List). public on the many topics and technologies pertaining to energy efficiency and renewable energy. You may also contact your state and local energy offices for information on region-specific information on small wind energy systems.