d. Compressed Air (1) Applications and Goals Under this program the feasibility of underground compressed air storage for electric utility applications will be investigated. Compressed air can be generated during off-peak load periods by a motor-compressor and stored underground. The stored compressed air can then be used during peak-load periods by being mixed with fossil fuels in the combustion chamber, burned, and expanded through a turbine generator. Since in normal operation the compressor consumes about two-thirds of the power output of the turbine, the rating of the gas turbine operating from the stored compressed air would be increased by roughly a factor of three. The compressed air can be stored in (1) naturally occurring caverns, porous-ground reservoirs, and depleted gas or oil fields, or (2) man-made caverns, such as dissolved-out salt caverns, abandoned mines, mined hard- rock caverns, or well casings. (2) Technology Requirements A development program would require adaptation and modification of existing equipment for use with air storage, and the design and development of suitable couplings and, possibly, unique valving. Uncertainties to be resolved include the cost of the air-storage facility, its performance, and leakage rate. The key to implementation is in selection of a suitable site and engineering. This program would investigate: • Locations for suitable sites through geological surveys for underground storage. • Geologic factors associated with various types of underground space. • New approaches to underground cavern construction. • Energy losses in storing and moving air. • Alternate air-storage concepts. An underground compressed-air storage system within a utility network could be demonstrated within about the next five years. Plants for utility applications would be in the 200 to 2000 MW range and would usually require additional transmission facilities unless sites can be located along existing lines or within or near large urban load centers.
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