thetical example on the Solar Energy Industries Association Internet Web site (http://www.seia.org/legdepre.htm) calculates the resulting combined savings as more than 40%. Similarly, more than half the states and some local governments do provide incen- tives for solar thermal collector or solar cell system purchases. The State of Hawaii cur- rently allows a 35% tax credit for solar pro- jects for commercial buildings. Total tax credits for projects there can cut installation cost almost in half for a third-party investor in an ESPC project, and accelerated depreci- ation can add further savings.
Other exam- ples include an Arizona 6% loan program for renewable energy and energy efficiency equipment acquisition and a Texas corporate income tax deduction for solar energy equipment acquisition. A good source of information on state incentives is a DOE- North Carolina State University Internet web site: http://www-solar.mck.ncsu.edu/ dsirexls.htm. that they were there and working. The exis- tence of the system has no particular impact on their daily operations. Maintenance is minimal and performed by IST. Down-time is minimal. One system was down for 2 months after a backhoe broke the delivery line to the facility and the facil- ity delayed repair.
Another system was down for 3 weeks with a hose problem when IST personnel were tied up on another project. The third project had about 5% of the reflectors damaged by a freak wind storm, but IST had the system back up within a week. Very deep snow occasionally interferes with the tracking systems. Because the conventional water-heating system is still in place, system downtime causes no service disruption. Under an ESPC, facilities are also fully protected from any downtime because payments are based either on annual energy audits or directly on energy delivery meters.
Facility managers were generally quite impressed with how well the systems oper- ated and with the service provided for the systems. The extent of the energy cost sav- ings they were getting was not always that clear to them, but they thought projects were delivering about what was projected. Staff for the recreation center indicated that they are now considering expanding the center or building a new parking lot and that the col- lector field location could turn out to limit available options for those projects. There were no problems with vandalism of the collector fields, even when near heavy traf- fic by school-age children, nor were there problems with impacts on birds or animals.
displace 10% of total natural gas use for hot water and space heating. But for the other two projects, as they would for most facili- ties, the parabolic-trough system substitutes for about half of the conventional energy that would otherwise be used for water heat- ing. One new project is sized to provide 80% of water-heating energy, but the larger system and storage size for that project is justified by a need to avoid high time-of-day peak pricing by the local electric utility. Maintenance, Environmental, and Other Impacts Managers noted very little impact on their operations or on their facilities.
Maintenance of the parabolic-trough sys- tems is all handled by IST under the Super ESPC and the systems have no impact on other systems except extending the life of conventional water-heating equipment by reducing its use. Every unit of energy delivered by the solar collector directly eliminates conven- tional energy use—and the associated pollu- tion and global warming impacts.
Because of the inherent efficiency loss in heating water with conventional fuels, the environ- mental benefits of substituting parabolic- trough solar water heating for natural gas, propane, or fuel oil are actually about one and two-thirds times as great as the amount of energy provided (assuming a 60%- efficient heater) and about three times as great when substituting for electric water heating (assuming 30%- to 40%-efficient electric production at the power plant). Additional Considerations On the negative side, the facility loses use of the land occupied by the collector field.
On the positive side, because the con- ventional water heater is used less, polluting and global warming air emissions are reduced (on site for gas or oil heaters; at the power plant for electric heaters). Technology Performance IST has installed parabolic-trough solar water-heating systems for three state or local prisons and one local indoor-pool recreation center. All were installed on a payment-for-energy-savings basis. The fol- lowing is based on discussions with opera- tors of a city pool in Colorado that has had a parabolic-trough collector system since 1985, a county jail in Colorado with a system since 1986, and a state prison in California with a system since 1990.
A new system at another county jail in Colorado has only been operating a short time. Case Study 1 — Adams County Detention Facility, Brighton, Colorado Energy Savings The three projects each produce about what was projected, about 200,000 Btu per year per square foot of collector. All three displace natural gas use. Assuming backup water-heater efficiency of 75%, this means they save about 267,000 Btu (200,000/.75) of natural gas per year per square foot of collector. (New projects incorporating improved technology are about one- third more efficient for production of about 267,000 Btu per square foot, displacing about 356,000 Btu of gas per square foot of collector.
[See Laboratory Perspective on page 13]) For the California prison—a very large facility with a district heating sys- tem—the parabolic-trough system was built without storage and only large enough to The Adams County Detention Facility in Brighton, Colorado (about 30 miles [48 kilometers] northeast of Denver), was originally designed for about 500 inmates but is currently housing more than 800. The facility uses an average of about 18,000 gal- lons (68,000 liters) of hot water per day for kitchen, shower, laundry, and sanitation facilities. The facility's existing water- heating system included six natural-gas- fired boilers.
In 1986, IST installed a 6000-square-foot (555-square-meter) parabolic-trough collec- Field Experience Facility managers indicated that the parabolic-trough collector systems were largely "transparent" to them and their staff. That is, they did not know all that much about the collectors, and said staff just knew 17