More than 140,000 residential batteries across California were coordinated during the Sept. 9 heat wave to deliver a record 580 MW to the grid over three hours. Roughly 110,000 Tesla Powerwalls supplied about 517 MW, while 30,000+ other systems added ~63 MW. The energy was dispatched through state demand-response programs and was large enough to meet peak Sacramento County household demand; Sunrun also supplied a further 140+ MW on Sept. 10.
Sunrun and Tesla Mobilize 140,000+ Home Batteries to Deliver Record 580 MW During California Heat Wave
Photo Credit: Sunrun
During the September 9 heat wave, California's grid received an unusual and decisive boost when more than 140,000 residential batteries — coordinated like a single virtual power plant — supplied a record 580 megawatts over a three-hour evening window.
How the Fleet Responded
According to reporting from Electrek, roughly 110,000 Tesla Powerwalls produced about 517 MW, while more than 30,000 other home batteries supplied the remaining ~63 MW, bringing the total to over 140,000 systems called into service. That distributed response was large enough, Electrek noted, to meet peak household demand in Sacramento County.
Programs and Operations
Utilities tapped the distributed storage through state demand-response pathways — notably California's Demand Side Grid Support program overseen by the Energy Commission and the Public Utilities Commission's Emergency Load Reduction Program. When enrolled in a virtual power plant (VPP), a program operator or utility can draw some stored electricity from participating batteries during the hottest evenings or other emergencies in return for compensation or bill credits for homeowners.
Why This Matters
During moments of acute stress on the grid, distributed batteries can provide fast, clean capacity without firing up rarely used gas peaker plants. For homeowners, batteries serve multiple purposes: maintaining essential loads during outages, shifting energy use to lower-cost periods, and participating in programs that offer financial incentives while supporting broader grid reliability.
Electrek also reported that Sunrun delivered another 140+ MW on September 10 at Southern California Edison's request, showing these dispatches were used on consecutive days to bolster grid reliability — not only to provide home backup.
"Sunrun's distributed home batteries are operating at a scale larger than many peaker power plants combined," said Sunrun CEO Mary Powell.
Broader Context
- Residential storage is scaling quickly: Tesla alone has installed hundreds of thousands of Powerwalls globally.
- Other projects, like Sonnen's VPP in Puerto Rico, demonstrate how coordinated home batteries can stabilize grids and support renewables.
- Large, distributed batteries are changing how solar and wind output is used and reducing reliance on fossil-fuel peaker plants.
Consumer Options
Homeowners exploring battery systems can compare options and installers through services such as EnergySage, which partners with companies like Qmerit to help buyers find competitive installation quotes. More affordable, plug-and-play options also exist for smaller backup needs.
Source: Electrek reporting on California dispatches (September 9–10).
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