6 3 billion square feet (280 million square meters). In fiscal year (FY) 1995 the Federal government spent $3.6 billion for 365 tril- lion British thermal units (Btu) of energy for those buildings and facilities. Water heating accounts for a substantial portion of energy use at many Federal facilities. Nationwide, approximately 18% of energy use in resi- dential buildings and 4% in commercial buildings is for water heating. Federal facilities with large laundries, kitchens, showers, or swimming pools will likely devote even more energy to water heating.
Parabolic-trough solar water- heating systems can efficiently provide half or more of the hot-water needs of many NREL/PIX01019 Federal facilities—cutting back on utility charges and on pollution. As for any solar water-heating system, Gretz, parabolic troughs are most likely to be cost effective for facilities that otherwise must Warren heat water with expensive conventional Figure 4. Parabolic-trough array for domestic hot-water service for the Jefferson energy. As Table 1 on page 8 shows, County Detention Facility, Golden, Colorado.
parabolic-trough collector systems can pro- vide hot water at a levelized cost of $6 to solar water heating is therefore an effective Application Domain $12 per million Btu for most Southwestern technology for serving large, 7-days-a-week, The Federal government provides energy areas. Parabolic-trough solar water-heating domestic hot-water users such as Federal to approximately 500,000 buildings and is therefore well worth investigating for eco- hospitals, prisons, or barracks.
facilities with a total floor area of about nomic viability if the available conventional water heating uses electricity or fossil fuel North-South Axis Kilowatt-hours per square meter 6 to 7 5 to 6 4 to 5 3 to 4 2 to 3 Map prepared by the NREL Resource Assessment Program 02279804m Figure 5. Average daily direct-beam solar radiation for horizontal, north-south, single-axis tracking parabolic trough collector systems. A north-south axis is better in summer and on a yearly average basis than an east-west axis.