California's rolling blackouts in mid-August, the state's first since the 2000-2001 energy crisis, resulted from a "climate change-induced extreme heat storm" across the U.S. West along with poor planning for higher levels of variable renewable energy and actions by participants in the California ISO's day-ahead energy market that "exacerbated the supply challenges," top state energy officials said in an Oct. 6 letter to Gov. Gavin Newsom that accompanied their preliminary report.

"There was no single root cause of the outages, but rather, a series of factors that all contributed to the emergency," said the letter, which was signed by Elliot Mainzer, the new president and CEO of CAISO, the state's primary wholesale grid operator, California Public Utilities Commission President Marybel Batjer and California Energy Commission Chair David Hochschild.

That combination "was an extraordinary event," the letter continued. "But it is our responsibility and intent to plan for such events, which are becoming increasingly common in a world rapidly being impacted by climate change."

The CAISO-ordered service disruptions affected nearly 500,000 customers of the state's three big regulated electric utilities on Aug. 14 and 321,000 the following day, according to the report. More than half of the blacked-out customers were in Pacific Gas and Electric Co.'s Northern and Central California service territory.

Promising a final report by the end of this year, the regulators recommended a series of "immediate actions" to ensure electric reliability in 2021 and beyond, part of a sweeping review of grid reliability in the state.

Resource adequacy reboot

Those actions include updating resource and reliability planning thresholds to better account for extreme climate-driven events, such as the massive wildfires that have ravaged the state in recent years, and to maintain reliability as the state moves toward a zero-carbon grid by 2045.

To do so, the state must fill a growing capacity gap in the early evening hours, when some 20,000 MW of large- and small-scale solar resources fade offline at sunset. Both rounds of August blackouts occurred in the early evening.

The report also calls for the CPUC and CEC to accelerate procurement and regulatory reviews in order to bring additional resources online by 2021, focusing on new demand response resources and speeding up timetables for flexible capacity already under development. That includes large battery storage projects that could help plug the twilight gaps as solar generation recedes. More than 4,600 MW of storage is under active development in the state, much of it at existing and new solar farms, according to S&P Global Market Intelligence data.

Demand underestimated

In the meantime, California has been forced to extend retirement dates for several aging natural gas-fired power plants because of grid reliability concerns. But the state's natural gas fleet performed poorly during the August blackouts, experiencing up to 2,000 MW of unplanned outages and another 400 MW of planned outages, according to the report. Ahead of the rolling blackouts on Aug. 15, wind generation also declined by 1,200 MW.

Participants in CAISO's day-ahead market contributed to the August reliability issues as well, underscheduling electricity load by thousands of megawatts under actual peak demand, the report said. CAISO plans to update its market guidelines "to ensure they accurately reflect the actual balance of supply and demand during stressed operating conditions," the officials wrote to Newsom.

The final report will include additional analysis on how scheduling coordinators for utilities and other load-serving entities missed the mark and on the performance of specific resources during the heatwave.