No smokestack. No new land. No power plant at all, technically — just 140,000 home garages, working together. On September 9, that fleet of ordinary home batteries pushed a record 580 megawatts onto California's grid during a punishing heat wave.

  • 580 MW delivered during a three-hour evening window
  • 140,000+ home batteries pooled together statewide
  • 110,000 of them Tesla Powerwalls, contributing 517 MW
  • $206 million in projected net savings for Californians by 2028
  • 2 consecutive evenings the fleet was dispatched, September 9-10

How a neighborhood of garages beat a power plant

Sunrun and Tesla coordinated the dispatch as part of a "virtual power plant" — a network of privately owned home batteries that utilities can call on when the grid is under strain, the same way they'd fire up a natural gas peaker plant. A typical peaker plant produces 50 to 250 megawatts. This event beat several of them combined, using hardware already installed in people's homes.

Of the batteries involved, roughly 110,000 were Tesla Powerwalls — Sunrun says it owns or operates 55% of those — contributing 517 MW. Another 30,000-plus batteries from other manufacturers in Sunrun's fleet supplied the remaining 63 MW. Combined, that's enough capacity to power every household in Sacramento County during peak hours.

Triggered automatically as the grid strained

The batteries fed power back through two existing California programs: the California Energy Commission's Demand Side Grid Support program, which triggers automatically once wholesale electricity prices cross $200 per megawatt-hour, and the Emergency Load Reduction Program, which utilities can call directly during a crisis. Southern California Edison called on the fleet again the very next evening, pulling another 140-plus MW.

"Sunrun's distributed home batteries are operating at a scale larger than many peaker power plants combined." — Mary Powell, CEO, Sunrun

Why utilities are betting on garages over gas

Peak electricity demand typically lasts only a few hours a day, a handful of days a year — which normally means utilities pay to build or maintain gas plants that sit idle the rest of the time. A distributed fleet of home batteries covers the same peak windows without that overhead, and a Brattle Group analysis cited by Sunrun projects up to $206 million in net savings for California ratepayers by 2028 from this kind of dispatch.

Participating homeowners get paid for the power they contribute, adding a financial incentive on top of the grid benefit. The September event builds on a much larger ambition: in June, Tesla, Sunrun, and Renew Home announced plans for a 16.8-gigawatt virtual power plant aimed at offsetting data center demand — with this residential dispatch serving as a live proof that the model already works at real scale, no new transmission lines required.

As heat waves get more frequent, the open question is how far the model scales beyond California, where the pricing programs and battery density already line up. For now, 580 megawatts from ordinary homes is a number every grid operator watching this summer's heat waves is taking seriously.