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