More than 85,000 Tesla Powerwall batteries in California supplied over 600 megawatts to the electricity grid on October 6, accounting for most of a collective discharge that reached 745 megawatts, according to figures announced by Sunrun. This represents a new record for home batteries in the state, 28% higher than the previous record of 580 megawatts, set less than a month earlier.
The operation took place during a heat wave and at the request of the California Energy Commission and utility companies. The batteries discharged during the evening peak in demand to help reduce grid consumption and real-time electricity prices. Sunrun says the October 5 operation was the first this year in which the Demand Side Grid Support and Emergency Load Reduction Program programs were activated simultaneously in the service areas of all participating investor-owned utilities.
Shared figures and overlapping batteries
Tesla Energy announced on October 8 that more than 85,000 Powerwall owners sent over 600 megawatts to the grid, describing the event as the largest in the history of its virtual power plant program. Sunrun, meanwhile, said that “the two companies” supplied 669 megawatts on October 5 and 745 megawatts on October 6, without detailing the contribution from Sunrun customers compared with Tesla customers.
This means that the two companies are partially crediting the same fleet; Sunrun is the largest sales channel for Powerwall in the United States. In the previous record during September, 517 megawatts of the total 580 megawatts came from approximately 110,000 Powerwall units, and Sunrun owned or managed 55% of them.
What does the recorded capacity reveal?
Mathematically, capacity exceeding 600 megawatts spread across approximately 85,000 homes equals nearly 7 kilowatts per home, a capacity exceeding the continuous output of 5 kilowatts from the Powerwall 2. This indicates the growing prevalence of Powerwall 3 units, which have a capacity of 11.5 kilowatts, or the presence of more than one battery in some homes. This is a calculation based on the published figures, not a detail that Tesla confirmed for each home.
Sunrun says that 745 megawatts is enough to cover the consumption of all homes in San Francisco and San Jose combined during peak hours. California’s grid programs also include more than 120,000 home batteries operated by or participating with the company. Customers receive financial compensation for discharging their batteries when needed, according to statements by Mary Powell, Sunrun’s chief executive.
What the figures do not explain
These achievements are measured in megawatts, meaning instantaneous capacity, rather than megawatt-hours, which indicate the total energy delivered and how long it lasted. Therefore, discharging 745 megawatts for 20 minutes has a different impact from maintaining the same capacity for three hours. According to the article, the September event continued within a three-hour evening window, but details about the megawatt-hours and duration of the October event were not published.
The incident demonstrates in practice that the value of home batteries is not limited to reducing their owner’s bill; they can also be aggregated through software as a virtual power plant that responds to a single signal on a large scale. However, this model depends on compensation programs such as DSGS and ELRP; the article notes that most states do not offer similar incentives.
The next step in San Jose
A distributed power plant funded by Google and developed in cooperation with PG&E in the San Jose area plans to enroll approximately 21,000 devices with Tesla and Everyday Electric, formerly known as Renew Home, with initial discharges scheduled to begin during October. The project represents the first tangible part of a 16.8-gigawatt virtual power plant plan dedicated to data centers, announced by Tesla, Sunrun, and Renew Home in June. However, according to Sunrun, the participation of Tesla and Everyday Electric remains subject to a nonbinding letter of intent.