The power plant operates by moving water between an upper and lower reservoir. When energy demand is high, water is released from the upper reservoir to the generating plant, and the water is discharged into the lower reservoir. When demand is low (such as at night), water is pumped into the upper reservoir to be used as stored energy at a later time. This is accomplished by pump-generators which serve a dual role: the pumps can reverse for use as generators. The plant can go from a standstill to operational in eight minutes, which allows it to meet
peak energy demand. It consumes more electricity pumping than generating electricity, but pumping occurs during periods of low demand with unused surplus energy available at lower costs from the electric grid. The upper reservoir,
Courtright Reservoir, has a storage capacity of and is at an altitude of .
Wishon Reservoir, the lower reservoir, has a storage capacity of . It is at an altitude of . Connecting the reservoirs, from upper to lower, is first a headrace tunnel which turns into a steel
penstock, which drops in elevation and splits into three individual penstocks, which each feed a separate pump-generator. After the water has passed through the generating turbines, it is discharged into the lower reservoir via a tailrace tunnel. The difference in elevation between the reservoirs has an effective
hydraulic head (drop of the water) of . The
underground power station is near Wishon Reservoir and houses three 404 MW
Francis pump turbine-generators. ==See also==