Imagine generating electricity by taking large quantities of water from lower elevation reservoirs and pumping it up 1,000 feet before releasing it through turbines as the water flows down.
For more than 20 years, Southern California Edison (SCE) has been doing just that at its John S. Eastwood Pump Storage Plant located 1,100 feet below ground in the High Sierra Mountains.
“We call the water at Eastwood and throughout the Big Creek hydroelectric generating system the hardest working water in the world,” said Joel Preheim, SCE manager at the Northern Hydro Office, who worked with the team that assembled much of Eastwood’s pump storage equipment. “At Eastwood, that water works even harder.”
When demand for electricity is low, generally at night, SCE pumps the water from a lower elevation reservoir to an upper reservoir. When electricity demand is high, the stored water is released down through the turbine to generate 200 megawatts of power.
The Eastwood plant is part of the Big Creek system that draws from a watershed of 1,200 square miles in the Sierra Mountains about 250 miles north of Los Angeles and began operating in 1911. The system includes nine power houses, 23 generating units, six major reservoirs and 27 dams that help to generate 1,000 megawatts of cost-effective, renewable and environmentally sustainable hydro power.
To build the Eastwood plant, workers drilled down, cutting through more than 1,100 feet of solid granite rock, before then drilling 4,300 feet back into the mountain to create the massive 184-foot-long and 80-foot high cavern, which houses the plant’s pumping and power generating equipment.
“Working conditions were challenging, and workers often worked in limited light,” said Preheim. “To make the elevator shaft, a ‘Mole’ was used. This is a large rotating metal disc, 22-feet in diameter with metal blades embedded with diamonds, and rotated at approximately five revolutions per minute to bore through the granite.”
It was engineer John S. Eastwood who in 1894 believed falling water could be used to create hydroelectricity. He surveyed the Sierras to find the best combination of water flow and geography to build a chain of power plants of unprecedented size.
During construction of Eastwood, SCE biologists closely worked with the California Department of Fish and Game and U.S. Wildlife to ensure that the locations used in and around the construction site were restored to their pristine condition after completing the project.
Like the Eastwood pump storage function, the entire Big Creek system uses gravity to generate power. The reservoirs can store more than 560,000 acre-feet of water. From start to finish, water flowing through the Big Creek system travels more than 50 miles and falls 6,637 feet.