Helms Powerhouse, California

The powerhouse for the Helms Pumped Storage Project is located at the end of the roads into the southern Sierra, on the edge of the John Muir Wilderness Area, 8,100 feet above sea level. Owned and operated by Pacific Gas and Electric (PG&E), it is the fifth largest pumped storage project in the country. The project uses similarly sized upper and lower reservoirs, three miles apart, connected by a tunnel, with an underground powerhouse near the lower reservoir, capable of producing more than 1,200 megawatts. Both the upper reservoir, known as the Courtright Reservoir, and the lower reservoir, known as the Wishon Reservoir, predated the pumped storage project. They were built in the late 1950s, as part of a string of hydropower plants along the North Fork of the Kings River, known as the Haas-Kings River Project. The pumped storage component was started in the late 1970s, linking the reservoirs by blasting a four mile long, 27 foot wide diagonal tunnel between them, and building an underground pump/turbine plant in a ten-story tall chamber at the end of the tunnel, near the level of the lower reservoir. The project involved up to 700 people working underground for four years, and was finally completed in 1984. The pumped storage operation was built primarily to provide grid stability in conjunction with the Diablo Canyon Nuclear Power Plant, which PG&E was building at the same time. That plant, 170 miles away on the Central Coast, featured in the film The China Syndrome, is now the state’s only operating nuclear power plant.