California’s Heat Wave Is a Big Moment for Batteries

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California’s Heat Wave Is a Big Moment for Batteries
WIRED, September 9, 2022
By Gregory Barber

“Scorching temperatures in the Golden State are a test case for a more flexible energy grid.”


During a late summer heat wave in California, golden hour becomes danger hour. In the offices of the California Independent System Operator, which manages the state’s grid, things get tense. Their mission is to keep the electrons going where they’re supposed to go—otherwise, it’s rolling blackouts for millions.


That risk arises from a brief, but important, mismatch between supply and demand. A growing share of the state’s energy is derived from solar panels, which made up about a fifth of its supply last year. But as the sun goes down and those panels stop receiving photons, demand for electricity keeps soaring. People get home from work and plug in their EVs, then flick on the air conditioning to clear out the afternoon stuffiness. Maybe they make dinner and run the dishwasher. Meanwhile, back at work, the lights in the office are probably still humming.


These were the concerns during this week’s heat emergency, when dozens of cities broke all-time temperature records and energy demand soared. But this time around, the California ISO had some extra juice to work with: a relatively new fleet of grid-scale batteries. They are designed to hold their power for about four hours—just long enough to cover the evening gap. At peak output, about 6 percent of the energy supply comes from these discharging batteries, up from 0.1 percent in 2017, according to an analysis by BloombergNEF. Capacity nearly doubled in the past year. Just after 6 pm on Tuesday, batteries surpassed the output of the state’s last remaining nuclear plant, peaking at just under 3,000 megawatts.


There was also a second push, this one on the demand side. At around 5:45 pm, the phones of millions of Californians buzzed as a solid block of text arrived, imploring them to delay all those evening rituals to save energy. Apparently, they did. In the next 20 minutes, more than 2,000 megawatts of demand disappeared from the grid, according to Anne Gonzales, a California ISO spokesperson. It happened so quickly that many energy pundits were stunned. “I was pleasantly surprised to see how everyone came together,” says Ryan Hanna, an energy researcher at the University of California, San Diego.

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About the Author:

Gregory Barber is a staff writer at WIRED covering energy and the environment. He graduated from Columbia University with a bachelor’s degree in computer science and English literature and now lives in San Francisco.