The US’s largest virtual power plant now runs on 75,000 home batteries

Sunrun just turned thousands of homes into the US’s largest virtual power plant to help keep the lights on in California this summer.

The company’s virtual power plant, CalReady, has more than quadrupled in size, linking together around 75,000 home batteries from over 56,000 Sunrun customers with solar + storage. As summer heat pushes California’s grid to the brink, CalReady is ready to step in with up to 375 megawatts (MW) of backup power, enough to power around 280,000 homes, the equivalent of all of Ventura County.

This massive battery network isn’t just about keeping homes cool during a heat wave. It also helps to lower electricity bills and cut pollution by sending clean energy back to the grid when needed most: between 4 and 9 pm, from May through October. That’s when demand spikes and fossil fuel plants usually kick in.

Sunrun CEO Mary Powell calls it a “customer-led energy revolution.” The idea is simple: homeowners can become part of the grid solution instead of depending only on giant power plants. And they’re getting paid for it. Customers in CalReady can earn up to $150 per battery for sharing their stored solar energy. Last year, Sunrun customers made over $1.5 million from the program. This year, they could bring in nearly $10 million.

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In 2024, CalReady enrolled over 16,000 households and pushed out an average of 48 MW to the grid during heat waves. Now, it’s expected to deliver 250 MW per two-hour event, with bursts up to 375 MW.

What makes CalReady special is that it doesn’t need new land or expensive infrastructure. It uses what people already have – solar panels and batteries at home.

“CalReady’s decentralized nature eliminates any potential single point of failure while offering greater resilience and flexibility for the state’s evolving energy needs,” added Powell.

Thanks to California’s growing rate hikes, more people are turning to solar and battery storage. By the end of 2024, over 60% of new Sunrun customers added battery storage to their solar systems; in California, that number was nearly 90%.

Read more: Sunrun sets a record in California with the US’s largest virtual power plant

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