May 23 (Bloomberg) — PG&E Corp., the owner of California’s largest utility, activated its second energy-storage project, using batteries from Japanese manufacturer NGK Insulators Ltd. to balance power on the electric grid.

The Yerba Buena Battery Energy Storage System Pilot Project cost $18.1 million and went into operation this month in San Jose, California, PG&E spokesman Paul Moreno said today by e-mail. The sodium-sulfur batteries have 4 megawatts of capacity and can store electricity for more than six hours. They’re charged when power demand is low and inject it back into the grid when demand grows.

Energy storage systems will improve the reliability of the grid and help utilities integrate intermittent renewable-energy generation, PG&E said today in a statement. The San Francisco-based company operates a similar 2-megawatt battery system near its Vaca-Dixon solar plant in Solano County, California, Moreno said.

The Yerba Buena project was funded in part by a $3.3 million grant from the California Energy Commission.

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