California-based photovoltaic systems provider Sunrun has announced that it has completed turning thousands of homes into the US’s largest virtual power plant. The firm’s CalReady system links domestic battery storage with solar panels to help keep the lights and AC on throughout the year.

According to Sunrun, Calready has more than quadrupled in size since it was first set up, linking around 75,000 home batteries from more than 56,000 Sunrun customers. Interestingly, this is not a one of its kind project in the US, with other players, like Tesla, also offering similar solutions. 

Sunrun's solar panels. Image: Sunrun.

The setup should provide around 375MW of backup power to power about 280,000 homes, the equivalent of all of Ventura County. It will help alleviate the pressure on California’s power grid, which tends to suffer in the summer heat. 

Massive battery network

Calready is not just a massive battery network, however. It is also intended to help lower power bills and cut pollution thanks to its 100% use of solar energy.

When not consumed, this power is stored in the batteries, enabling it to be fed back into the grid when demand is high. This is typically between 4pm and 9pm between May and October of each year.

This is when electrical demand records a spike, which typically means fossil fuel power plants need to kick in to provide supply. To this end, Sunrun CEO Mary Powell explains, Calready is something of a “customer-led energy revolution.” 

The concept is straightforward: Customers join the grid network instead of relying on more traditional power plants. They also benefit by getting paid for being part of the network.

At present, CalReady participants can earn up to $150 per battery for sharing their stored solar energy. Last year alone, Sunrun customers earned more than $1.5m from the program. If all goes to plan, that could rise to more than $10m in 2025. 

In 2024, Calready signed up more than 6,000 households and pushed an average of 48MW to the grid during heat waves. It’s expected to deliver 250MW per two-hour event, with bursts up to 375MW.

A customer-led energy revolution

One of the best parts about Calready is that it doesn’t need new land or expensive infrastructure to work. Customers only need to have solar panels and storage batteries to get the ball rolling.

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

With California’s growing rate hikes, initiatives like Calready will likely see healthy growth in the coming years. This will force more Californians to turn to solar and energy storage to help with their bills. 

By the end of last year, more than 60% of new Sunrun customers added battery storage to their solar systems. In California, that number was nearly 90%. Calready is currently only available in California. However, once successful it would only be a matter of time before it expands to other states.