NEW YORK - PG&E Corp's 404-megawatt Unit 1 at Helms hydropower station in California returned to service by Thursday afternoon, the California Independent System Operator said in a report.
The unit shut by Oct. 5 for unplanned reasons.

The 1,212-MW Helms pumped storage hydropower station, which entered service in 1984, is located near Fresno in Fresno County. There are three 404-MW units at the station.

One MW powers about 700 homes in California.

The other units remained available for service.

Pumped storage plants store and produce electricity to supply peak power demands by moving water between reservoirs at different elevations.

At times of low demand and low power cost, the plant uses electricity from the grid to pump water into the higher reservoir. When demand and prices are higher, the station releases the water back into the lower reservoir through a turbine, generating energy.

PG&E's regulated Pacific Gas and Electric Co subsidiary owns and operates the station.

PG&E, of San Francisco, owns and operates more than 6,200 MW of generating capacity, markets energy commodities and transmits and distributes electricity to almost 5.3 million customers and natural gas to 4.2 million customers in northern California. (Reporting by Scott DiSavino; Editing by Lisa Shumaker)