PG&E California Helms 1 hydro unit off line - Cal ISO

LOS ANGELES, Oct 24 (Reuters) - PG&E Corp's (PCG.N: Quote, Profile, Research, Stock Buzz) 404-megawatt Unit 1 at the Helms Pumped Storage hydropower station in California went off line for unplanned work by Wednesday afternoon, the California Independent System Operator said in a daily report.

No reason for the shutdown nor estimate of the unit's return was given in the report.

The 1,212 MW Helms station is near Fresno. There are three 404 MW Units 1-3 at the station.

The other two units were listed as available for service.

One MW powers about 700 homes in PG&E's service territory in northern and central California.

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 owns and operates more than 6,000 MW of generating capacity, markets energy commodities, and transmits and distributes electricity (5 million) and natural gas (4.1 million) to customers in California.