now on the market. However, such systems (including collectors) cost too much at present to compete with gas-fired absorption air conditioners in regions where natural gas is available (gas-fired, rather than electrical, units dominate this market).

The use of solar energy to supplement conventional fuels in nonresidential cooling will be made generally feasible if low-cost solar collectors that provide low-pressure steam become available, since large cooling units are now generally run on low-pressure steam (usually obtained from combustion of natural gas). Such collectors are now under development for industrial process heat applications. If this development effort is successful in meeting its cost goals (see below), it will greatly improve the feasibility of solar space cooling in large buildings.

Impact on Utilities

If electricity is used to provide backup energy for a solar heating and cooling system, there is potential for a significant and adverse impact on the utility. It would be inefficient and uneconomic to use electrical generating capacity only to provide occasional supplemental energy, whether to solar energy systems or to other sources of intermittent demand such as all-electric homes. The Electric Power Research Institute investigated this question from the perspective of minimizing the total cost of the system including the building and the utility and concluded that solar heating and cooling systems are not inherently less efficient in their use of electrical generating capacity than conventional all-electric homes.15

INDUSTRIAL PROCESS HEAT

Another potentially important direct use of solar energy is to provide industrial process heat for use in small- and medium-size applications, as in laundries, food processing operations, and crop drying. At present about half of industrial process heat in the United States is supplied by natural gas, which is increasing in price and becoming less readily available. The temperature requirements of industrial processes range from warm water to very high-temperature (more than 1000°F) gases, but the heat is used mostly in the form of low-pressure steam.

Lower-temperature (less than 200°F) processes can be served by flat-plate collectors, so here the performance of present solar technology for fuel saving is adequate. However, for most industrial hot water applications the cost of present solar systems is not competitive with that of fossil fuels at current prices. If natural gas and fuel oil become much more expensive or government regulations limit their availability to industries, and at the same time environmental restrictions preclude on-site combus-



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