California’s grid passed the reliability test this heat wave. It’s all about giant batteries

California’s power grid emerged from a nearly three weeklong record-setting heat wave relatively unscathed, and officials are crediting years of investment in renewable energy — particularly giant batteries that store solar power for use when the sun stops shining.

“This was a good early test that we passed in very good shape,” said Elliot Mainzer, president and CEO of California Independent System Operator (CAISO), on Monday. “Investments in new clean energy and in dispatchable battery storage played a major role.”

CAISO last issued calls for voluntary conservation two years ago, during a 2022 bout of extreme heat. Since then, roughly 11,600 megawatts of new renewable energy sources have come onto California’s electricity grid.

That includes 10,000 megawatts of battery power, enough to power 10 million homes for a few hours. California is now home to the most grid batteries in the world outside of China, Mainzer said.

“Batteries performed very well in this event, they were charged and ready at the right times for optimization on the grid,” he added. “That made a big, big difference.”

Many Californians remember a suffocating heat wave in August 2020 that prompted rolling blackouts for several hundred thousand Californians, and some will remember another two years ago that prompted a series of voluntary Flex Alerts.

Those periods were likely on their mind over the last few weeks, when sweltering heat enveloped California. This prolonged heat wave was the hottest 20-day period on record in Sacramento and set an all-time temperature record of 124 degrees in Palm Springs.

But emergency alerts or calls for voluntary conservation were ultimately avoided this time around.

Apart from battery storage, Mainzer also credited that success to less extreme temperatures in Southern California as well as noticeable slightly lower electricity consumption in the peak demand hours, from 4 p.m. to 9 p.m.

That said, he was quick to urge caution and continued diligence ahead of what is likely to be a very hot summer and fall.

“It’s going to be a long summer,” he said. “So that continued awareness and for customers to go to FlexAlert.org for tips on conservation that they can do without inconveniencing themselves goes a long way.”

State law in California require 90% of all retail electricity sales to be from renewable energy sources by 2035 and 100% by 2045. Right now, fossil fuel powered electricity makes up roughly 40% of all generation.

To get there, the CAISO said in a report last year that the state should expect to spend at least $7.5 billion on new transmission, or high voltage long distance power lines. For a multitude of reasons, those can take upward of a decade to build.

It’s just one of the many challenges to defending California’s grid against extreme weather, a symptom of climate change, while ridding the electricity sector of planet warming pollution in the first place.

Yet Rob Gramlich, president of power sector consulting firm Grid Strategies, said the state has taken a number of positive steps to get on the right path — from permitting reforms to a big, early bet on batteries.

“It’s really great news all around, the fact that they’re keeping the lights on with clean, carbon free energy,” Gramlich said. “I think the state was smart to take an early bet on battery storage. A lot of states were skeptical, but California went in big and it’s working.”