Clean Energy SF: San Francisco, fog then sun, est. 2026

Vol. 1 - No. 14 - Thursday, September 24, 2026 - Free to readers

Grid ยท Analysis

The bay's home batteries, dispatched together as one power plant

Across the city, home batteries are being pooled and dispatched together on hot evenings. Here is who sends the signal, who pays your household, and how the grid counts the help.

Filed October 29, 2026 By the Clean Energy SF editors Reading time: 6 minutes

I. How a garage battery becomes a plant

Start with the hardware. A home battery (often a wall-mounted unit of roughly 10 to 15 kilowatt-hours, enough to run an efficient house for a few evening hours) normally charges from rooftop solar or cheap overnight power and holds it for your own use. The shift happens when you let an aggregator, a company like Sunrun, control the discharge. You keep a reserve for outages, and the aggregator borrows the rest during a handful of events each year.

That signal usually travels through the California Public Utilities Commission's Emergency Load Reduction Program (a state pilot that pays customers to cut use or send power back when the grid is tight). PG&E offers a residential version branded Power Saver Rewards, and aggregators plug their battery fleets into the same framework. Events tend to land on hot, still evenings from roughly May through October, called late in the afternoon and running into the night, which is exactly when a fogbound city can still bake inland.

II. Who pays, and roughly how much

The money is the part readers ask about first. At last public report, the Emergency Load Reduction Program paid on the order of $2 per kilowatt-hour sent back or saved during an event, which is many times the retail price of electricity. A household that discharges a few kilowatt-hours across a single evening event might see a credit in the low tens of dollars, and a season with a handful of events might add up to something in the low hundreds. Treat those figures as rough, because the exact rate and the number of events move year to year.

Where the dollars land depends on your contract. If you enrolled directly, the credit shows up on your PG&E bill; if Sunrun or another aggregator manages your battery, the company collects the grid payment and passes along a share, sometimes as an upfront payment, sometimes per event. Read the enrollment terms before you sign, because the split, the reserve the company keeps for you, and the penalty for opting out of an event all vary by program.

III. How the grid counts the help

For the people running the system, the interesting number is not any one battery but the pool. The California Independent System Operator, or CAISO, the nonprofit that balances supply and demand for most of the state, now plans around a net demand peak that has slid into the evening, roughly the 6 to 9 pm window, as rooftop solar fades while air conditioning and cooking stay on. That evening ramp is the stress point a battery pool is built to shave.

CAISO counts aggregated batteries mostly as demand response and emerging distributed resources, folding their promised output into its forecasts and, during tight conditions, its calls for help. The honest caveat is that measurement is hard, since the grid has to estimate what each home would have drawn without the battery, and that baseline is an educated guess. Sunrun has said its California fleet delivered on the order of tens of megawatts during recent heat events, a real contribution, though still small next to the thousands of megawatts a late-summer evening demands.

IV. Worth watching this month

1. CAISO typically posts dispatch and demand-response performance data after the summer season, so late-year reports should show how battery pools performed during this year's hot evenings.

2. The CPUC's Emergency Load Reduction Program is a multi-year pilot under periodic review, and any proposed change to the roughly $2 per kilowatt-hour incentive would surface in its public filings.

3. PG&E's Power Saver Rewards enrollment usually reopens ahead of summer, so watch the program page in the spring if you want in for next year.

4. CleanPowerSF and the SFPUC continue to expand local storage and demand programs, and their board materials are the place to catch any San Francisco specific offer.

5. Watch your own battery app's event log after the next hot spell, the plainest proof of whether your household was dispatched and roughly how much it sent back.

Frequently asked questions

Will the grid drain my battery when I need it?

No. When you enroll, you set a reserve the aggregator cannot touch, so a share of the battery stays yours for outages. Only the portion above that reserve is available for events.

Do I need rooftop solar to join?

Not always. A battery that charges from the grid overnight can still enroll in some programs, though pairing it with solar changes the economics and may change which programs you qualify for.

How many events happen in a year?

It varies with the weather. A mild summer might bring only a few calls and a hot one more; the program is built for a modest handful of evenings, not daily use.

Is this the same as a Flex Alert?

Not exactly. A Flex Alert is a voluntary statewide request to cut use, while these programs pay enrolled customers and can dispatch their batteries automatically. The two often fall on the same hot evenings.

References