UPDATE 1-PG&E shuts Calif. Helms 1 & 2 hydro units

(Updates with company comment)

NEW YORK, May 8 (Reuters) - PG&E Corp (PCG.N) shut the 404-megawatt Units 1 and 2 at the Helms pumped storage hydropower station in California shut for planned work by Thursday afternoon, a spokesman for the company said Friday.

He could not say when the units would return to service but noted the work, which involved removing water from a storage tank, should be completed in time to meet the peak summer demand.

Earlier in May, Units 1 and 2 exited outages begun in early March.

Unit 3 meanwhile shut by Sept. 28 also for planned reasons.

The 1,212 MW Helms station, which entered service in 1984, is located near Fresno in Fresno County. There are three 404 MW Units 1-3 at the station.

One MW powers about 700 homes in 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.