Grid · Analysis

California's summer grid now banks on the evening, not the peak

Solar pushed the risky hours past sunset. Here is how the capacity rules changed, what batteries fixed, and the heat waves that tested the whole arrangement.

BY THE RENEWABLE ENERGY LA EDITORS · FILED OCTOBER 7, 2026 · 6 MIN READ ·

Why the risk moved to sunset

Solar does its most work in the middle of the day. When thousands of rooftops and desert farms push power onto the system at once, the net load (total demand minus what solar and wind are covering) sags in the early afternoon and then climbs steeply as the sun sets. Grid planners drew this shape years ago and called it a duck, and the steep evening climb is the duck's neck.

Here is the catch. The neck now lands in the hours when solar fades but demand stays high, roughly 5 to 9 p.m. on a hot day. People come home, the basin is still holding the afternoon's heat, and for a couple of hours the grid has to replace a lot of solar quickly. That window, not the old mid-afternoon peak, is where a hot evening gets tight.

How the capacity rules adapted

California's answer runs through resource adequacy (the rules that make the companies selling power buy enough capacity ahead of time to cover demand). The CPUC (California Public Utilities Commission) sets much of this for the state, and the obligations are counted months in advance so the capacity is contracted before summer arrives.

Older rules leaned on a single monthly peak hour. The newer framework the CPUC adopted, often called Slice of Day, asks the companies to show they can cover every hour of a representative day, not just the highest one. That is a direct response to the evening problem, because a plant or a battery only counts if it can deliver in the hour the grid is actually short, which is now after sunset.

What the batteries changed

Batteries are the piece that made the evening manageable. California has added a very large amount of grid battery storage in a few years, on the order of 13,000 megawatts across the CAISO (California Independent System Operator) grid at last public report, per the California Energy Commission, up from a few hundred megawatts early in the decade. Most of it charges on cheap midday solar and discharges into the evening ramp.

Think of it as a close-to-purpose-built fix for the duck's neck, storing the surplus at noon and handing it back at seven. It is not unlimited. Most of these batteries hold roughly four hours of output, so a heat wave that keeps demand high deep into the night still leans on gas plants, imports, and whatever conservation residents offer. Batteries moved the risk, they did not erase it.

The heat waves that tested it

Early September 2022 brought the hardest test, when a long heat wave pushed CAISO demand to a record, on the order of 52,000 megawatts, higher than anything the system had seen. On the worst evening, the grid operator sent a wireless emergency alert to phones across the state asking for immediate conservation.

Demand dropped within minutes and rotating outages were avoided. The lesson stuck. The dangerous hours were in the evening, after solar had fallen off, and both batteries and a message to millions of people were part of what kept the lights on. Los Angeles sits a little apart here, because the Los Angeles Department of Water and Power (LADWP, the city's municipal utility) runs its own balancing area outside CAISO, but it watched the same heat and did the same evening math.

Worth watching this month

1. LADWP's board meets roughly twice a month, and its agendas (posted on the utility's site) are where power-supply and storage contracts surface first, usually routine but occasionally worth a closer look.

2. The CPUC keeps refining the Slice of Day rules, so watch its resource adequacy proceeding for any filing that changes how the evening hours are counted, a slow process that matters more than it looks.

3. CAISO posts live net-demand and battery-output data each day, and October is a good month to watch the evening ramp without summer stress, a routine read.

4. Heat is not finished in Southern California in October, so a late Santa Ana event could still bring a Flex Alert for the 4 to 9 p.m. window, worth noticing if your evening comfort or bill depends on it.

5. The California Energy Commission updates its storage totals from time to time, so a new figure above the current roughly 13,000 megawatts would signal the evening buffer is still growing.

Where this dispatch reads

California ISO, Today's Outlook (grid operator), www.caiso.com/todays-outlook, Live supply, demand, and battery output, including the evening net-peak ramp, updated through the day.
California Public Utilities Commission, Resource Adequacy (.gov), www.cpuc.ca.gov/industries-and-topics/electrical-energy/electric-power-procurement/resource-adequacy, The capacity rules, including the Slice of Day framework that requires coverage in every hour.
California Energy Commission, Tracking Progress (.gov), www.energy.ca.gov/data-reports/tracking-progress, State tallies of installed battery storage and how fast it has grown this decade.
Flex Alert, run by the California ISO (grid operator), www.flexalert.org, When and why the grid asks for voluntary evening conservation, and what the hours mean.
Los Angeles Department of Water and Power, Power System (utility), www.ladwp.com, Board agendas and power-supply programs for the city's municipal utility, which runs its own grid.

Questions readers have asked

Why do I get conservation texts in the evening now, not the afternoon?

Because solar covers much of the afternoon, the grid is tightest after the sun sets, roughly 5 to 9 p.m. on hot days. That is when demand stays high and solar is fading, so that is when you are asked to cut back.

Is Los Angeles on the same grid as the rest of California?

Not exactly. LADWP runs its own balancing area and is not part of CAISO, though both face the same heat and the same evening ramp. The two systems do trade power and coordinate.

Do batteries mean we no longer need gas plants?

For now, gas and imports still matter. Most grid batteries hold about four hours of output and rely on midday solar to charge, so a long, hot night can outlast them at last public report.

What is a Flex Alert?

It is a voluntary call from the grid operator asking people to cut electricity use during the evening, usually 4 to 9 p.m. It is not an outage, it is a request meant to head one off.