The battery is being installed on the SDG&E substation property.
The nation's largest battery storage for energy is being constructed in Escondido — part of the shift away from fuel-burning power plants to cleaner energy, which can't be switched on when needed.
San Diego Gas & Electric has contractors building the 30-megawatt lithium-ion array on the 1.5-acre Escondido lot that the company already owns. There's already a substation in that industrial park tucked into the southwest corner of where the SR-15 intersects Highway 78 (a second, 7.5-MW storage plant is being sited in El Cajon).
The facility will contain 24 steel cabinets of lithium-ion batteries that can hold about 1.25 megawatts each.
"We expect to have it done at the end of January, or early in 2017," said SDG&E spokeswoman Christy Ihrig, who confirmed it is the largest battery storage facility in the U.S.
"Thirty megawatts is enough power for about 20,000 homes for up to four hours." The battery array will let the utility store energy during off-peak hours and then circulate it during high demand hours, including early evening when many people get home and start turning everything on, she said.
Virginia-based AES Storage touts the batteries as a cleaner, less costly approach than the use of "peaker plants" — power-generating plants that fire up or fire higher at peak demand times. According to the battery-maker, power from storage costs less than peaker-plant power.
"It's a more flexible and reliable system that lets us store energy from clean energy sources like solar and wind power," Ihrig said. Peak demand times don't line up with clean-energy peak-production times. The battery arrays are in temperature- and humidity-controlled containers that look much like the containers that go from semi-trailers to ships. But the containers are laden with high-tech software and monitors and security features beyond padlocks.
Escondido approved the project in September, according to city records. Because the site already has a substation and is in an area zoned for heavy industrial use, the application to the city didn't face any serious challenges. No one in the area around the storage plant raised concerns or objected, according to file documents.
In 2013, the California Public Utilities Commission ordered SDG&E, Pacific Gas & Electric, and SoCal Edison to create facilities to store energy. The goal at the time was for California's three largest power providers to be able to store 1325 MW of power by 2020.
SDG&E put out a request for proposals in October 2014 and selected AES to construct the project this year.