(3) Scope of the Program Studies are being carried out to evaluate the overall feasibility and cost-benefit rates of underground pumped-air storage to identify and evaluate possible natural underground sites, including aquifers, and to determine the need for compressor-power turbine development. More detailed evaluation and experimental work on underground storage facilities will be pursued and, if needed, the design and development of a compressorpower turbine will begin. e. Pumped Hydro (1) Applications and Goals An underground pumped storage system operates by pumping water from a lower reservoir to a higher reservoir using off-peak electricity. The water is stored there until peak power is needed. The water is then released and flows back to the lower reservoir through an electric producing turbine-generator. The cycle is repeated as needed. This is similar to conventional pumped storage, except the lower reservoir and power plant are located in deep caverns or mines and the upper reservoir is at or near the surface. The siting of these underground plants should have greater public acceptance than for conventional pumped storage facilities. The sizes of these plants are in the 200-2000 MW range, and usually require additional transmission facilities unless sites can be located along existing lines or within or near large urban load centers. (2) Technology Requirements Equipment needed for underground pumped hydro is commercially available as it is in widespread use for conventional hydroelectric facilities. Several manufacturers are developing equipment capable of handling very high heads in a single lift, in order to improve the economics of the system. Underground construction and mining technologies are available and can be adapted for this system. (3) Scope of the Program Work is required to improve the turbine and shaft equipment, to obtain higher efficiencies, and on reservoir characteristics. This
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