Federal Technology Parabolic-Trough Solar Alert Water Heating Renewable technology for reducing water-heating costs A publication series Parabolic-trough solar water heating is also explains energy savings performance designed to speed the a well-proven technology that directly sub- contracting (ESPC), a method for financing adoption of energy- stitutes renewable energy for conventional Federal facility energy conservation and energy in water heating. Parabolic-trough renewable energy projects. ESPC is avail- efficient and renewable collectors can also drive absorption cooling able for parabolic-trough systems and offers technologies in the systems or other equipment that runs off a many important advantages. thermal load. There is considerable potential Parabolic-trough collectors use mirrored Federal sector for using these technologies at Federal facil- surfaces curved in a linearly extended ities in the Southwestern United States or parabolic shape to focus sunlight on a dark- other areas with high direct-beam solar radi- surfaced absorber tube running the length ation. Facilities such as jails, hospitals, and of the trough. A mixture of water and Prepared by the barracks that consistently use large volumes antifreeze or other heat transfer fluid is of hot water are particularly good candi- pumped through the absorber tube to pick New Technology dates. Use of parabolic-trough systems helps up the solar heat, and then through heat Demonstration Program Federal facilities comply with Executive exchangers to heat potable water or a ther- Order 12902's directive to reduce energy use mal storage tank. Because the trough mir- by 30% by 2005 and advance other efforts rors will reflect only direct-beam sunlight, to get the Federal government to set a good parabolic-trough systems use single-axis example in energy use reduction, such as the tracking systems to keep them facing 1997 Million Solar Roofs Initiative. the sun. This Federal Technology Alert (FTA) from the Federal Energy Management Application Program (FEMP) is one of a series on new Use of parabolic-trough systems is more energy-efficiency and renewable energy limited by geography and system size than technologies. It describes the technology of are other types of solar water heating, but parabolic-trough solar water-heating and where parabolic troughs are usable they absorption-cooling systems, the situations often have very attractive economics. As in which parabolic-trough systems are likely concentrating systems, parabolic troughs use to be cost effective, and considerations in only direct radiation, so are less effective selecting and designing a system. This FTA The U.S. Department of Energy requests that no alterations be made without permission in any reproduction of this document. Warren Gretz, NREL/PIX01019 Warren where skies are cloudy and much more Renewables Program at the National collectors to provide domestic hot water likely to be effective in areas such as the Renewable Energy Laboratory (NREL). for the Federal Correctional Institution in Southwestern United States that have good (See Federal Program Contacts on page 20.) Phoenix, Arizona. Although this project was solar resources dominated by direct-beam IST can more specifically assess negotiated prior to granting of the IDIQ sunlight. It is also more cost effective to prospects for a trough system at a particular contract, it is being built on an ESPC basis. build large systems that will be used on a facility. The FEMP Help Desk can provide The facility, which houses about 1200 continuous basis. Parabolic-trough solar manuals and software for detailed economic inmates, now depends on electric-resistance water heating (and air-conditioning) is evaluation and more information on ESPC water heating. The new solar system was therefore most effective for large, 7-days-a- financing. (See manufacturer’s information specifically designed to avoid peak demand week, domestic hot-water users, such as and Federal Program Contacts.) ESPC, charges from the utility by using a 21,000- Federal hospitals, prisons, or barracks. (For which IST can provide under the Super gallon (79,494-liter) thermal storage tank most situations, about 500 gallons per day ESPC IDIQ contract, allows Federal facili- controlled to deliver solar heat during facil- of hot water use is a minimum for a viable ties to repay contractors for solar water- ity peak periods. This will allow the system parabolic-trough system.) Troughs also heating systems through bills for energy to meet a projected 82% of the facility’s work well for district space or water heating savings instead of paying for initial con- hot-water use. The solar system will dis- systems serving multiple buildings from a struction. The Super ESPC with IST offers place 15 billion Btus per year of fossil fuel central steam or hot-water plant. The cost many significant advantages: combustion, avoiding more than 80,000 of the collector system is a main economic • No financial outlay by the facility to kilograms of nitrogen oxides and nearly factor, but as with any capital-intensive determine feasibility 100,000 kilograms of sulfur dioxide pollu- energy conservation or renewable energy tion over the project’s life. • No need to seek competitive proposals installation, the critical factor is likely to be current cost of energy. Facilities that • Pre-identified savings Implementation Barriers • No responsibility for operation and pay high utility rates for conventional water There are no technological barriers to maintenance heating will always be the best prospects for using parabolic-trough solar water heating. cost-effective parabolic-trough solar water • The current system stays in place as a However, trough collectors are by nature heating or air-conditioning. backup for high reliability limited geographically to areas with high • Guaranteed savings direct-beam solar resources. They are also Technology Selection • The facility pays only for energy savings by nature more cost effective for facilities The FTA series targets energy efficiency it realizes that use large amounts of hot water 7 days and renewable energy technologies that • The facility can benefit indirectly from a week. But, because they directly replace appear to have significant untapped Federal- tax incentives available only to private conventional energy use, parabolic-trough sector potential and for which some Federal companies collectors will provide energy savings and installation experience exists. Many of the • The facility can get credit for energy use environmental benefits proportional to their alerts are about new technologies identified reduction in compliance with Executive use. From a financial perspective, however, through advertisements in the Commerce Order 12902 (mandatory 30% reduction relatively high conventional water-heating Business Daily and trade journals, and by 2005) without reducing hot-water use costs will be the biggest enabling factor. through direct correspondence soliciting ESPC financing also provides advantages • Switching to a more economical conven- technology ideas. This FTA describes a such as tax breaks for private investors that tional water heater or other related effi- renewable energy technology with known are important to project economics. ciency measures can be included in and energy, cost, and environmental benefits that financed by the ESPC project. Improvements in reflective and absorbent has substantial untapped potential for the coatings and development of triple-effect Federal sector. The U.S. Department of Case Studies absorption cooling will incrementally Energy has signed a "Super ESPC" indefi- improve economics, but there are no known nite delivery/indefinite quantity (IDIQ) This FTA describes two examples of technological developments that could dra- contract with Industrial Solar Technology parabolic-trough solar water heating instal- matically lower the cost of parabolic-trough Corporation (IST), the only current manu- lations by IST on a payment-for-energy- solar water-heating or absorption-cooling facturer of parabolic-trough collectors. This savings basis. systems. Much higher sales volume would contract encourages Federal facilities to use The first case study is the parabolic- likely lower costs, but that would depend parabolic-trough technology by greatly trough system at the Adams County on the new technology being able to consis- facilitating financing and implementation Detention Facility in Brighton, Colorado, tently compete with low-cost conventional through ESPC. which has been operating since 1987. The energy. Parabolic-trough solar water heating First, a preliminary analysis should be 7200-square-foot (669-square-meter) collec- is likely to remain most cost effective where conducted on whether solar water heating tor system displaces about 2 billion British natural gas is not available or is relatively generally or parabolic-trough systems thermal units (Btus) per year of natural gas expensive, and where consistent high- particularly would be cost effective for any water heating, about 40% of that needed for volume use provides economies of scale. situation on the basis of energy load, con- the more than 800 inmates. ventional energy costs, and the location’s In the second case study, IST is just solar radiation. Software that performs this starting construction of 18,000 square feet task is available from FEMP's Federal (1672 square meters) of parabolic-trough Federal Parabolic-Trough Solar Water Heating Technology Renewable technology