Sunrun and Tesla announced Monday, September 21, that their fleets of home batteries dispatched more than 580 megawatts of peak power to California’s grid on the evening of September 9, the largest residential distributed power plant dispatch on record.
The companies coordinated 580 megawatts of residential battery capacity, combining 517 megawatts from 110,000 Tesla Powerwalls with 63 megawatts from additional batteries. More than half of the Powerwalls, 55 percent, are owned and operated by Sunrun, which also dispatched more than 30,000 of its customers’ batteries from other manufacturers.
The discharge ran for a three-hour evening period at the request of the California Energy Commission and utilities, amid scorching temperatures and elevated electricity demand. Sunrun said the extra capacity was meant to increase the grid’s operating margin and put downward pressure on real-time energy prices, providing enough power for every household in Sacramento County during peak hours.
Sunrun CEO Mary Powell said the company’s distributed home batteries are operating at a scale larger than many peaker power plants combined, adding that the dispatch shows the benefits of distributed energy go well beyond individual households by helping control the cost of electricity for all Californians.
The event was coordinated through the California Energy Commission’s Demand Side Grid Support program and the California Public Utilities Commission’s Emergency Load Reduction Program, with participating batteries located statewide. It builds on Tesla Energy’s own September 9 dispatch, when about 69,000 Powerwall owners sent more than 500 megawatts to the grid during the same heat wave. Tesla has also been expanding its energy business, including a $35 monthly lease for two Powerwalls in Texas, and the two companies previously teamed up on a fixed-rate clean energy plan in the state.
The companies said an even larger event is possible. The September 9 dispatch did not include additional batteries in Southern California Edison territory, which delivered more than 140 megawatts the following evening, and the fleets could have delivered over 720 megawatts had both events occurred on the same night. A Brattle Group report commissioned by the companies put potential net cost savings to Californians at $206 million by 2028.
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