Californians coped with a second day of rolling power outages Saturday as heat-related electricity demand nearly outstripped supply, utilities said.
More than 307,000 electricity customers statewide were without power, although Southern California Edison said the flow for its customers taken temporarily offline had been restored by early evening.
The rolling blackouts were a surprise for some because the power grid's manager, California Independent System Operator, tweeted late Saturday that it was "expected to cover electrical demand with no stage emergencies planned at this time."
Then the ISO contacted Southern California Edison, one of the state's largest utilities, and "requested that we use a rotating outage to drop customer service and maintain grid stability," said Edison spokesman Robert Villegas.
The state was in the midst of a stage-three emergency as a result of high demand, he said, and power was cut to about 70,000 Edison customers for 16 minutes.
By 6:44 p.m. the emergency was back down to stage two, he said.
In Northern California, Pacific Gas and Electric had cut power to roughly 250,000 customers, NBC Bay Area reported.
The utility said in a statement Saturday that it might be required to conduct rotating power outages Saturday from 5 p.m. to 10 p.m. at the behest of the ISO.
PG&E cited not only increased demand as a result of a heat wave but thunderstorm-related cloud cover in Southern California that impacted its solar operations.
The Los Angeles Department of Water and Power said on Friday that it would not be participating in rolling outages.
"We own our own power plants and transmission lines and had enough supply to meet demand," the taxpayer-run utility tweeted.
The state's other large utility, San Diego Gas & Electric, said it cut power to thousands of customers at the request of the ISO, but service was restored to affected customers within a half hour.
By evening, the 47,770-megawatt California grid was about 5,000 megawatts from maxing out, according to the ISO's data.
Demand was boosted by residential usage in the second day of what forecasters have said could be a weeklong heatwave in the West and Southwest, with temperatures in many areas of Southern California reaching the triple digits.