UNDERGROUND STORAGE OF OFF-PEAK POWER.

Underground storage of pressurized hot water in association with a steam power plant as a means of off peak power storage is shown to be an alternative to pumped hydroelectric storage. Steam is flashed from the hot water and directed to peaking turbines for handling the peak load; at low load times, surplus steam is condensed in the water to recharge the system. The saturation pressure of the hot water is borne by the overburden pressure of the formation in which the storage cavity is prepared. For cavities operating in the pressure range from 70 to 140 bars the effective energy storage is 18 to 21 kwhr per cubic meter of cavity volume, and the loss in useful energy due to storage ranges between 5 percent and 9 percent. The estimate of a facility to provide 1000 Mw for 10 hr is 309 million.