CAISO warned residents Sunday that rolling blackouts could continue for days and called emergency meetings of its Board of Governors to address the system deficiencies.

“A persistent, record-breaking heat wave in California and the Western states is causing a strain on supplies, and consumers should be prepared for likely rolling outages during the late afternoons and early evenings through Wednesday,” the ISO said in a news release. “There is not a sufficient amount of energy to meet the high amounts of demand during the heat wave.”

CAISO declared a Stage 3 emergency for two hours Friday night, ordering rolling blackouts across the service territories of the state’s three big investor-owned utilities. Hundreds of thousands of customers in Northern and Southern California were without power for an hour or more.

The ISO triggered a Stage 3 emergency again Saturday night for 20 minutes when, it said, 1,000 MW of wind power and a 470-MW power plant dropped offline.

“The load was ordered back online 20 minutes later at 6:48 p.m., as wind resources increased,” CAISO said.

Pacific Gas and Electric said it began restoring power to 220,000 residents on California’s coast and in the Central Valley after the brief outage but warned that restoration could take additional time.

Earlier in the day, CAISO had assured residents on Twitter that the “ISO is expected to cover electrical demand with no stage emergencies planned at this time.”

The CAISO board met Sunday in closed executive session and scheduled a public teleconference for Monday at 11 a.m.

Friday was the first time the ISO, which encompasses 35% of electrical load in the Western Interconnection and covers 80% of California, went to its highest emergency level since market manipulation schemes and rolling blackouts plagued the state during the Western energy crisis of 2001. A similar heat wave in 2006 strained the system but did not cause blackouts.

“The ISO requires load curtailments [and] use of interruptible load, and requests out-of-market and emergency energy from available sources,” CAISO said in an alert. “Maximum conservation efforts are requested.”

A Stage 3 alert means the “ISO is unable to meet minimum contingency reserve requirements, and load interruption is imminent or in progress.” Notices are issued to utilities of potential interruptions, CAISO says on its website.

CAISO spokeswoman Anne Gonzalez said the ISO had ordered 1,000 MW of load shed.

PG&E said it had been directed by CAISO to “turn off power to approximately 200,000 to 250,000 customers at a time in rotating power outages given the strain on the power grid during the statewide heat wave. Other power utilities in the state are being directed to take similar actions.”

Southern California Edison and San Diego Gas & Electric also shut off power to tens of thousands of customers. Roughly 750,000 account customers — and at least 2 million residents, based on average household size — lost power between 6:36 p.m., when the emergency was declared, and 8:54 p.m., when CAISO lifted its declaration.

Customers of public utilities including the Los Angeles Department of Water and Power and the Sacramento Municipal Utility District were not affected by the blackouts. The utilities operate their own power lines and generation resources.

The transmission grids of the three large IOUs are operated by CAISO.

Lead-up to Blackouts

On Friday afternoon, CAISO issued a Stage 2 alert after capacity dipped below its 15% reserve margin. It said it had taken all possible mitigation measures and was still unable to meet its energy requirements.

The heat wave drove temperatures into the triple digits in Sacramento, Phoenix, Las Vegas and other areas of the inland West on Friday and is predicted to last into next week. Temperatures in Los Angeles and typically cooler cities such as Portland, Ore., rose well beyond summer norms.

ERCOT, which instituted rolling blackouts during an extreme cold snap in February 2011, weathered the heatwave amid record-setting demand in Texas over the weekend. Dallas, Austin and other cities topped 100 degrees Fahrenheit.

Throughout the West, families working and learning from home during the coronavirus pandemic cranked up their air conditioners, straining the system.

CAISO’s day-ahead forecast predicted a peak of 46,258 MW on Friday, but the ISO raised it to 46,824 MW in the afternoon. Available supply, at its peak, was about 53,000 MW but declined to 48,378 MW as solar power dropped offline when the sun set.

The ISO said it was “declaring a Stage 3 electrical emergency due to high heat and increased electricity demand. The emergency initiates rotating outages throughout the state. A Stage 3 Emergency is declared when demand outpaces available supply. Rotating power interruptions have been initiated to maintain stability of the electric grid.”

“The Stage 3 emergency declaration was called after extreme heat drove up electricity demand across California, causing the ISO to dip into its operating reserves for supply to cover demand,” it said. “The California ISO is working closely with California utilities and neighboring power systems to manage strain on the grid and to restore the power grid to full capacity. As portions of the grid are restored, local utilities will restore power in a coordinated fashion.”

“Although a Stage [3] emergency is a significant inconvenience to those affected by rotating power interruptions, it is preferable to manage an emergency with controlled measures rather than let it cause widespread and more prolonged disruption,” CAISO said.

On Thursday and again on Friday morning, CAISO issued a “flex alert” urging customers to voluntarily conserve power, including by setting thermostats at 78 F. It restricted utility maintenance operations and then issued a warning midday Friday followed by the first emergency alert at 3:25 p.m.

The Stage 2 emergency, announced Friday afternoon, was the ISO’s first in 15 years.

Unexpected Early Test

The shortfall tested the state’s transition from fossil fuels and nuclear power to renewable resources. The percentage of renewables serving load fell from about 30% midday to single-digits after sunset as natural gas plants ramped up to meet demand.

Gas generation began the day providing roughly 11,500 MW to the CAISO grid but was pumping out nearly 26,000 MW after an exceptionally long, steep ramp from 10 a.m. to 7 p.m.

Renewables in CAISO’s system, mainly solar power, peaked at more than 13,000 MW at 2 p.m. but began to fall off just as demand increased late in the afternoon.

Imports from other Western states gradually decreased throughout the day to about 3,500 MW at 4 p.m. as the heat wave drove demand in neighboring Nevada, Arizona and other states. Imports recovered in the evening, helping to alleviate the shortfall.

CAISO and the California Public Utilities Commission have repeatedly warned that the combination of retiring natural gas plants and constrained imports could result in capacity shortfalls starting as soon as this summer and grow significantly worse in the next three years. (See CAISO, CPUC Warn of ‘Reliability Emergency’.)

However, the ISO reported in May that it expected to be able to get through this summer without a shortfall such as Friday’s. (See CAISO Predicts Adequate Summer Capacity.)

Resource adequacy in the West has become a major topic for organizations such as WECC and the Northwest Power Pool. The added problems of catastrophic wildfires and the COVID-19 pandemic have exacerbated those concerns. (See WECC Tackles Wildfires as Reliability Threat.)

Robert Mullin and Rich Heidorn Jr. contributed to this report.