California Home Batteries Power Grid During Heatwave

On September 9, 2026, residential battery energy storage systems (BESS) across California made history. Coordinated by Sunrun and Tesla, these home batteries discharged over 580 megawatts (MW) of peak power directly to the state's grid. This event marked the largest distributed power plant (VPP) dispatch ever recorded¹.

The substantial power injection was critical during an evening three-hour window. At this time, extreme temperatures drove high electricity demand, straining the grid with air-conditioning loads. The combined output was enough to power all households in Sacramento County during peak hours¹.

How Home Batteries Supported the Grid

The September 9 event was a direct response to requests from the California Energy Commission (CEC) and utilities². It involved pooling power from more than 140,000 home batteries across California¹.

This 580 MW capacity included 517 MW from approximately 110,000 Tesla Powerwalls and 63 MW from over 30,000 batteries from other manufacturers in Sunrun's fleet. Over half (55%) of the participating Tesla Powerwalls are owned or operated by Sunrun¹.

The dispatch happened through specific programs designed to leverage residential energy storage. These included the California Energy Commission's Demand Side Grid Support (DSGS) program and the California Public Utilities Commission's (CPUC's) Emergency Load Reduction Program (ELRP). The DSGS program automatically activated when the day-ahead electricity price exceeded $200 per megawatt-hour (MWh). Utilities directly called the ELRP event as the heatwave reached its peak¹.

Virtual Power Plants in Action

The September 9 dispatch showcased a Virtual Power Plant (VPP) in full operation. VPPs are software-coordinated networks of home energy storage systems. The grid can call upon these systems during peak demand, allowing them to behave like a conventional power plant³.

One key benefit of VPPs is their ability to reduce the need for expensive and often less environmentally friendly gas "peaker" plants. These older plants are typically brought online only during periods of extremely high demand. Sunrun CEO Mary Powell noted that their distributed home batteries operate at a scale larger than many combined peaker power plants. The following day, September 10, Sunrun dispatched another 140+ MW at Southern California Edison's request¹. If both September 9 and 10 dispatches had occurred simultaneously, over 720 MW could have been delivered in a single event².

Benefits for Homeowners and the Grid

Homeowners who participate in VPPs can earn compensation for sharing their stored energy with the grid¹. This compensation can come as cash or bill credits. The exact earnings depend on factors like battery size, program type, and seasonal grid demand³.

Some homeowners earn $300-$500 annually through the DSGS program or $200-$600 through ELRP³. DSGS is largely closed to new enrollment in 2026. Other VPP programs offer upfront incentives, such as Generac's program providing up to $1,000 upfront⁴. The Sacramento Municipal Utility District (SMUD, for example, offers a "My Energy Optimizer Partner+" program for qualifying battery customers. This program provides an upfront enrollment incentive of up to $6,000 for projects submitted on or after September 23, 2026. For more details on incentives, see our guide on California solar incentives.

VPP programs typically maintain a backup reserve, often around 20%, to ensure the home still has power during a grid event. Homeowners can also often opt out of specific VPP events if they prefer³.

California's Evolving Grid Resilience

California has been actively expanding its energy storage capabilities. By May 2026, the state had deployed 17,000 MW of grid storage. This significant expansion helps buffer demand spikes during heatwaves, reducing the probability of rotating outages from supply shortages compared to previous years⁵.

The state's electric grid is now better prepared for extreme weather events. This is due to rapid clean energy deployment, expansion of battery storage, and strategic emergency reserves⁵. As of September 14, 2026, wind, water, and solar met 56.2% of all electricity demand on the CAISO grid in 2026. These renewable sources even exceeded 100% of demand for 18.5% of all hours in 2026⁶.

The economic benefits of VPP programs extend beyond individual homeowners. A report by The Brattle Group, commissioned by Sunrun and Tesla, estimated that VPP programs could provide up to US$206 million in net cost savings to Californians by 2028. These savings would benefit all grid-connected customers².

Companies like Sunrun, Tesla, and Renew Home are collaborating on an initiative to unlock over 16.8 GW of flexible capacity. This capacity comes from home batteries, solar panels, smart thermostats, and electric vehicles, all designed to support utilities². This widespread integration of distributed energy resources marks a significant shift in how the grid operates and responds to demand.

Sacramento Homeowners: SMUD Rates and Battery Incentives

The fact that the September 9 dispatch provided enough capacity to power all households in Sacramento County during peak hours shows the scale of the dispatch which came from customers of the three big investor-owned utilities, not SMUD¹. Sacramento County is served by the Sacramento Municipal Utility District (SMUD), which operates with its own rates and solar policies, distinct from those governed by the California Public Utilities Commission⁷.

SMUD's standard summer Time-of-Day peak energy rate, from June 1 to September 30, is $0.3765 per kWh between 5 p.m. and 8 p.m. on weekdays. This peak rate is almost three times higher than the off-peak rate⁸. SMUD also increased its Solar and Storage Export Compensation Rate to 9.6 cents per kWh as of June 1, 2026, for eligible excess electricity sent back to SMUD⁷. These rates and programs directly influence the financial benefits for homeowners with solar and batteries in the Sacramento area.

The events of September 9, 2026, demonstrate the growing importance of California home batteries. They are proving to be a reliable and scalable solution for managing grid stress during extreme weather events. The coordination of residential energy storage into virtual power plants offers both environmental benefits and financial opportunities for participating homeowners.

Sources:

1. Tesla and Sunrun's virtual power plant dispatch record 580 MW to California grid, Fred Lambert, 2026 (electrek.co)

2. Sunrun and Tesla deliver record 580MW to California grid amid heatwave, April Bonner, 2026 (energy-storage.news)

3. What Is a Virtual Power Plant (VPP)? How California Homeowners Get Paid to Share Stored Energy (2026) (cainitiative.com)

4. California Virtual Power Plant Program, Generac Power Systems, Inc (generac.com)

5. California Energy Leaders Report Progress on Grid Reliability Ahead of Summer 2026 (energy.ca.gov)

6. More Than 56% of California Electricity Demand Supplied by Wind, Water, & Solar in 2026, Z. S. (cleantechnica.com)

7. Sacramento Solar 2026: SMUD Rates, Batteries & Savings, 2026 (nationprousa.com)

8. Why Your SMUD Bill Is So High in Summer | Battery Storage Sacramento (empoweryourhome.com)