The 580MW of residential BESS capacity comprised 517MW from Tesla Powerwalls and 63MW from additional BESS. Approximately 110,000 Powerwalls participated in the event, with more than half owned and operated by Sunrun. Sunrun also dispatched over 30,000 customer batteries from other manufacturers.
The dispatch was coordinated through two statewide grid service programmes that regular readers of Energy-Storage.news may be familiar with, the CEC’s Demand Side Grid Support (DSGS) programme and the California Public Utilities Commission’s (CPUC’s) Emergency Load Reduction Program (ELRP).
Participating batteries were located throughout the state, with customers in all three investor-owned utility service territories taking part.
The DSGS dispatch was triggered when the California Independent System Operator’s (CAISO’s) day-ahead locational marginal price exceeded US$200-per-MWh. The ELRP dispatch was called by utility PG&E to coincide with the heatwave for BESS within its territory.
The 9 September event did not include the companies’ additional BESS participating in the ELRP programme in utility Southern California Edison’s (SCE’s) territory, suggesting even larger dispatch events are possible from the combined fleets.
The following evening on 10 September, SCE requested a three-hour dispatch during peak hours, with Sunrun and Tesla delivering more than 140MW of battery capacity to the grid. Had the dispatch events from both evenings occurred simultaneously, the companies would have been able to deliver over 720MW in a single dispatch.
A report by consultancy firm The Brattle Group, commissioned by Sunrun and Tesla, found that these types of programmes could provide up to US$206 million in net cost savings to Californians by 2028. The report stated these savings would benefit all grid-connected customers, whilst participants also receive direct compensation for the power they share with the grid.
The dispatch event provides validation for an existing initiative by Sunrun, Tesla, and energy management platform Renew Home to unlock more than 16.8GW of flexible capacity for hyperscalers and utilities from home batteries, solar, smart thermostats, and electric vehicles.
The three companies announced earlier this month they will enrol nearly 21,000 existing flexible energy devices into a new, Google-funded distributed power plant with PG&E. The resource is expected to begin supporting the grid as early as autumn 2026.
Two VPP-related bills cleared California’s legislature this month. Senate Bill 905 would create a grid utilisation metric to measure load factor across each segment of the state’s distribution network.
Senate Bill 913 would direct the CPUC to establish a valuation methodology for customer-sited BESS exporting electricity to the grid during periods of system stress.
Governor Gavin Newsom is expected to sign both bills into law. However, his administration has simultaneously blocked efforts to extend funding for the DSGS programme.