In another sign of an unprecedented year for new lithium-ion battery storage stations in the United States, NextEra Energy Resources LLC has added a 230-MW energy storage system at its existing 250-MW McCoy Solar Energy Project in eastern Riverside County, Calif.

Part of the massive Blythe and McCoy solar-plus-storage complex, the McCoy battery project connected to a nearby substation in early May, the NextEra Energy Inc. affiliate revealed in a fresh filing with the Federal Energy Regulatory Commission. (Docket No. ER15-1375)

NextEra has a 15-year agreement to sell the output from the four-hour battery storage system to Southern California Edison Co., starting Aug. 1. "Prior to that date, the output from the battery storage system will be sold in the [California ISO] market," Joel Newton, senior FERC counsel at NextEra Energy Resources, said in the May 26 filing.

In January, the company connected 115 MW of four-hour energy storage at another section of the complex, the Blythe Solar II (NextEra) project, also under contract with the Edison International utility.

Underpinned by a series of agreements with SCE and PG&E Corp.'s Pacific Gas and Electric Co., the complex is one of the largest emerging contiguous battery-backed solar photovoltaic facilities in the world, with a combined 523 MW/2,092 MWh of storage scheduled to be online by August, according to S&P Global Market Intelligence data.

NextEra's progress is part of a major push to bring online a new fleet of energy storage projects this summer to assist with grid reliability in California and throughout the Southwest. Vistra Corp., for instance, plans to add another 100 MW/400 MWh by August at its existing 300-MW/1,200-MWh Moss Landing Energy Storage Facility on California's Monterey Bay.

NextEra and Vistra are among a host of developers thinking even bigger on batteries as California and other states seek to wean themselves off natural gas generation. Vistra has a county permit to ultimately expand its Moss Landing project, which is co-located with a natural gas-fired power plant, to 1,500 MW/6,000 MWh, while NextEra is one of three developers that recently proposed gigawatt-sized solar-plus-storage projects in Nevada.