environmental concerns with manufacture and disposal are less for this coating than for previously used black-chrome coatings. How Do You Figure? To obtain a preliminary analysis of whether solar water heating would be cost effec- tive for a facility, use the Federal Renewable Energy Screening Assistant (FRESA) software package. It’s available from the Federal Renewables Program at the National Renewable Energy Laboratory (NREL). (See Federal Program Contacts.) Federal Renewables Program staff can also do the analysis, if provided the following data:
Application The two most important factors in deter- mining economic feasibility for any solar water-heating system are the cost of build- ing the system and the cost of operating conventional water-heating systems. Parabolic- trough collectors, in particular, require high direct normal solar radiation, high hot-water use levels, continuous hot-water use, and in the case of use for air-conditioning, a long cooling season. Therefore, parabolic-trough solar water-heating or air-conditioning sys- tems could benefit many hospitals, prisons, barracks, and other Federal facilities in the southwestern United States.
Federal facilities have two options avail- able for procuring a parabolic-trough solar water-heating system. The traditional option is directly purchasing the system. A simpli- fied procurement and budgeting option is using ESPCs, as provided for in IST's IDIQ contract. • Hot-water use in gallons per day • Fuel type and cost • Zip code • Incoming cold-water temperature • Outgoing hot-water supply temperature • Area of southern exposure roof or nearby grounds available for system • Tilt and direction of roof area. One can do a rough calculation before asking for FRESA or a more detailed F-Chart analysis.
Divide 51.4 by the solar insolation for the area (single-axis tracking in kilo- watt-hours per square meter per day as given in Appendix A). This should provide the number of years it would take for the system to pay for itself based on an installed cost of $22 per square foot. The FRESA system does include solar resource data based on your zip code, but to obtain comprehensive solar resource data request the NREL Solar Radiation Data Manual for Flat-Plate and Concentrating Collectors or the CDROM of the National Solar Radiation Data Base (Appendix A).
To estimate hot-water use, check the hot-water-use records; install a meter and track usage; or project demand based on average use for various facilities as found in the American Society of Heating, Refrigerating and Air-Conditioning Engineers' Handbook of Applications. Typical usage per day per occupant in gallons is 20–30 for housing, 30 for hospitals or prisons, 5 for dining facilities, and 3 for other uses. Application Screening In either case, the first step toward deter- mining if a solar water-heating system would be viable for a facility (or facilities) is to assess the hot-water needs.
How much hot water at what temperature do the various facilities use (or are new facilities expected to use), on what kind of schedule? How much does it cost for the energy to heat that water? Could costs be reduced with a more efficient conventional water heater? What options are there for reducing hot-water use or lowering the temperature of water provided? The next step is to obtain a preliminary estimate of whether solar water heating will be cost effective. The FEMP Federal Renewables Program at the National Renewable Energy Laboratory has devel- oped a computer program entitled Federal Renewable Energy Screening Assistant (FRESA) that can make such a preliminary assessment.
See the How Do You Figure sidebar for a list of the necessary informa- tion. IST can provide a similar rough assess- ment specific to using parabolic-trough collectors. In order to directly purchase a parabolic- trough-collector solar water-heating or air- conditioning system, a positive FRESA To determine incoming water temperature, which may vary considerably with the sea- son, call the water utility or check the supply with a thermometer. In some instances, the average annual air temperature also roughly indicates water supply temperature.
These temperatures are important because solar water heating is more efficient when incoming water temperatures are lower (less heat loss to the environment); whereas, cold air temperatures reduce efficiency. To calculate system output information more rigorously than the preliminary analysis provided by FRESA, use a computer program such as F-chart, or consult with Federal Renewables Program staff or a solar water-heating system supplier. The optimum size for collectors and storage will depend on fuel cost, available solar resource, and the hot-water use pattern, but expect capacity on a good summer day to roughly match usage. The resulting system should meet about half of annual demand.
Precise optimization of system size will require both a calculation of output and an evaluation of system economics. To evaluate the economics of a contemplated system in detail, use the FEMP Life-Cycle Costing Handbook and associated BLCC software, available by calling the FEMP Help Desk. (See Federal Program Contacts.) One can also consult with the Federal Renewables Program or a private engineer. assessment should be followed up with a formal feasibility study, including life-cycle cost analysis (Appendix D) in accordance with 10 CFR 436A and a request for pro- posals.
A simpler economic criteria than life-cycle cost analysis is the payback period— the time it would take for energy cost savings to repay the investment cost. Executive Order 12902 directs that agencies shall build any energy-saving project with a simple payback of less than 10 years. This is generally a more rigorous criterium than life-cycle cost analysis, so there will be many projects with positive life-cycle cost analysis but with greater than 10-year sim- ple payback. These may also be built, but Executive Order 12902 would not apply.
Assuming a payback of less than 15 years and a system life of 30 years, one can expect 15 years or more of "free energy." If, however, a project is built under ESPC, as IST's IDIQ contract allows, it is not necessary to do formal cost analysis or 14