Helms Pumped Storage Plant
The Helms Pumped Storage Plant is located 50 mi (80 km) east of Fresno, California in the Sierra Nevada Mountain Range's Sierra National Forest. It is a power station that uses Helms Creek canyon on the North Fork of the Kings River for off-river water storage and the pumped-storage hydroelectric method to generate electricity. After being planned in the early 1970s, construction on the plant began in June 1977 and commercial operations began on 30 June 1984. It has an installed capacity of 1,212 MW and is owned by Pacific Gas and Electric  Company. Design and operation. 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 stand still 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 is at 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 long head-race tunnel which turns into a long 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 long tail-race 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.