Why California has blackouts: A look at the power grid

In August 2020, hundreds of thousands of Californians briefly lost power in rolling blackouts amid a heat wave, marking the first time outages were ordered in the state due to insufficient energy supplies in nearly 20 years.

The state has been working to avoid a similar scenario as California is in the midst of an unprecedented heat wave that officials said is on track to be the state's hottest and longest for September.

For more than a week, the California Independent System Operator (ISO) -- which oversees the electrical grid serving 80% of the state -- has been calling on residents to conserve their energy use in the later afternoon and evening amid extreme temperatures that have sent electric demand on the grid to record levels.

Thanks to those efforts, the company has so far avoided having to order an outage to reduce demand and stabilize the system even in the face of record demand. The power grid saw a record demand of 52,061 MW on Tuesday, as the ISO warned that power outages were imminently possible "as electricity supplies run low in the face of record heat and demand." Prior to this current heat wave, the previous record was 50,270 MW in 2006.

Had reserve supplies been exhausted, the ISO would have ordered utilities to begin rolling power outages to bring demand within available supplies and avoid cascading blackouts.

"Outages are a significant inconvenience to those affected, but it's preferable to manage emergencies in a controlled manner rather than let it cause a wider spread, longer lasting disruption," the ISO said in a statement.

Factors impacting the grid

Several factors impact the capacity and function of the power grid.

Increased demand and extreme heat: The power grid is being strained amid what California officials have called an unprecedented prolonged heat wave.

"California and many other western states are experiencing simply unprecedented temperatures," California Gov. Gavin Newsom said this week. "These triple-digit temperatures throughout much of our state are leading, not surprisingly, to record demand on the energy grid."

Heat waves drive up demand due to increased air-conditioning use.

"Typical summer peak load in CAISO is 30 GW, but super-hot day can be nearly 50 GW. That 60%+ increase is virtually all air-conditioning," Severin Borenstein, a renewable energy expert at the University of California, Berkeley, and an ISO board member, said on Twitter.

Californians have been urged to raise their thermostats in the afternoon and evening hours, when demand on the grid is greatest, among other actions to reduce their energy use at night.

California buys electricity from other states to boost its supply, but during a widespread heat wave, there's less energy for other states to sell. Rising temperatures due to climate change are expected to drive up air-conditioning demand across the country, according to Climate Central.

Renewable energy supply: The state's grid is powered, in part, by renewable energy, including solar power and hydropower.

The solar supply decreases toward the end of the day, prompting the calls to reduce energy use after 3 p.m. or 4 p.m. There can also be uncertainty with solar supply due to factors such as cloud cover and smoke from wildfires, as the state battles several blazes.

"We've seen situations where smoke and cloud cover can have an effect. If it's over a populated area, it could have more effect of reducing demand, where if the smoke and cloud cover is over the solar fields, it can have an effect on the availability of supply," Mark Rothleder, the ISO's senior vice president and chief operating officer, told reporters during a press briefing Thursday.

Prolonged drought and wildfires, which are becoming more prevalent and severe due to climate change, can also cut into power supplies. The U.S. Energy Information Administration had forecast that California could lose half its normal hydroelectric generation this summer due to drought. Wildfires can also trip off transmission lines, limiting the flow of electricity.

The current heat wave "is just the latest reminder of how real the climate crisis is, and how it is impacting the everyday lives of Californians," Newsom said in a statement. "While we are taking steps to get us through the immediate crisis, this reinforces the need for urgent action to end our dependence on fossil fuels that are destroying our climate and making these heat waves hotter and more common."

Breakdowns and human error: The state also uses natural gas to power its grid. Though during this heat wave, several plants, including gas-fired ones, partially broke down, The Associated Press reported.

Multiple generators also have been "forced out of service due to the extreme heat, making energy supplies tighter," the ISO said.

Human error may also play a part in power supplies. Though the ISO has not issued them, several Northern California cities did see rolling blackouts this week due to a "communication breakdown" between the grid operator and local power authority, The Sacramento Bee reported.

"I think every time you go through a period where you're where your grid and both your human and physical infrastructure gets stretched right to the edge, you can look back and learn from that," Eliot Mainzer, president and chief executive officer of the ISO, told reporters Thursday.

Mainzer said the latest heat wave has shown the importance of procuring new clean energy resources, ensuring backup generation and having a sophisticated alert system that can help cut down on energy use in real-time.

"We're seeing really the onset of what [is] now a new normal of heat and volatility and uncertainty in the system," he said.