Table 1. Effective Levelized Cost of Energy ($/MBtu) for Solar Water Heating with Parabolic-Trough Collectors at Selected Locations available on a roof. Parabolic-trough sys- tems therefore require large, unshaded installation areas near the place of use. Installed cost per square foot of Albuquer- Dallas, Denver, Phoenix, Sacramento, San Diego, collector que, NM TX CO AZ CA CA Energy Savings Performance Contracting $6.16 7.26 $6.26 $6.72 7.39 8.14 Industrial Solar Technology (IST) of Golden, Colorado, has installed parabolic- trough solar water-heating systems for sev- eral state or local facilities including prisons and an indoor-pool recreation center.
IST is also building a major domestic water- heating system for a Federal prison. (See case studies on pages 15 and 17.) The sole current manufacturer of para- bolic-trough solar water-heating systems, IST has installed all of its systems so far on a payment-for-energy-savings basis. IST or a third-party investor typically builds, operates, maintains, and owns the system. The owner then bills the customer facility for the amount of energy delivered by the solar water-heating system at a rate slightly less than currently being charged by the facility's utility for supplying conventional energy. The Federal Emergency Management Program (FEMP) of the U.S.
Department of Energy (DOE) has now set up a program of Energy Savings Performance Contracts (ESPCs) that allows Federal facilities to install energy efficiency measures or renew- able energy equipment under payment-for- energy-savings arrangements similar to those which IST has used. Many facilities have used ESPCs and found them highly advantageous.
ESPCs are Federal/private-sector partner- ships in which an energy service company (ESCO) installs and operates a system, bearing all up-front design, installation, and hardware costs (including financing) and the government repays the ESCO out of budgeted utility dollars for a share of energy savings resulting directly from the project during the contract term. The agency never pays more than what its utility bill would have been without the ESPC project. Once the contract is completed, the government takes title to the equipment and retains all subsequent savings.
The disadvantage of ESPCs is that the government does not immediately retain all savings generated, as it would if the project were funded by direct appropriations. The advantages of ESPCs, however, make them an attractive alternative for implementing energy savings, $6.78 8.15 $6.94 $7.30 8.09 8.92 $7.39 9.04 $7.61 $7.87 8.78 9.71 $8.00 9.93 $8.29 $8.45 9.48 $10.50 $8.61 $10.82 $8.96 $9.03 $10.18 $11.28 $9.21 $11.71 $9.64 $9.61 $10.88 $12.07 Array size 6000 7800 7200 4800 6600 7200 (sq.
ft.) % of load met 57% 53% 54% 54% 53% 55% Calculations are based on F-chart analysis of energy savings for a 7,200-square-foot (669-square-meter) collector system designed to meet domestic hot-water need of 17,000 gallons (64 kiloliters) of hot water (140˚F/60˚C) per day (4652 MBtus) in the Denver, Colorado, area, adjusted in size to meet approximately the same percentage of the hot-water load. Locations were selected that have both reasonably good solar resources and a large number of Federal facilities nearby. Other assumptions include:
Federal ownership and operation; backup by natural gas with costs inflated at 3.0% per year; 2% operation and maintenance costs inflated at 3.0% per year; continuous operation for a 25-year life with no salvage value; and present value of savings calculated on the basis of an annual nominal discount rate of 6.6% (equal to real discount rate of 3.4%). See "Costs" on page 16 for costs per square foot for some actual facilities. Note that costs include the cost of backup heating. Thus, the levelized costs for Phoenix (which has higher conventional energy costs) are higher than for Denver, even though the solar resource is better. Table 2.
Effective Energy Cost for Water Heating Based on 1995 National Average Federal Facility Utility Prices Boiler Effective Energy Cost Efficiency* Energy Cost* Electricity 6.1ў/kWh $17.87/MBtu 98/91%* $18.23/19.64 per MBtu* Propane 64ў/gal 6.99/MBtu 75/59% 9.33/11.85 per MBtu Fuel oil 60ў/gal 4.33/MBtu 80/59% 5.41/7.34 per MBtu Natural gas 35ў/therm 3.54/MBtu 75/59% 4.71/6.00 per MBtu * (state-of-the art/typical) The first, state-of-the-art boiler efficiency figures (and corresponding effective energy costs) are based on what is available for large modern boilers and are higher than those available for individual home water heaters.
The second, "typical" boiler efficiency figures are from the Gas Appliance Manufacturers Association October 1997 Consumers' Directory of Certified Efficiency Ratings for Residential Heating and Water-heating Equipment , pages 120, 142, and 144. Data are mid-range for a 50-gallon, first-hour rating, except for fuel oil boilers, which are for a 100-gallon rating. Efficiencies are for fuel conversion and do not include losses from the boiler or water heater, which also apply to heat supplied by solar collectors. Sources: Energy costs are from Table 6-A, p.
47, Federal Energy Management Program Annual Report to Congress on Federal Government Energy Management and Conservation Programs Fiscal Year 1995. highest level bands on Figure 5 or the two highest level bands on Figure 6 (4 kWh per square meter or more) are far more likely to be good candidates for parabolic-trough systems. (See Appendix A for specific data for nearly 70 locations with direct solar radiation.) Handling wind loading is the predomi- nant design challenge for parabolic-trough collector systems. High winds can exert tor- sional loads that are absorbed well by the ground, whereas roof-mounted troughs may require costly reinforcement to accommo- date the stress.
Also, trough systems require large installation areas that may not be 8