Despite low solar power, California’s electric grid ran smoothly during the eclipse

This animation depicts the shadow of the moon as it sweeps across the continental United States.

The sun may have gone into eclipse mode Monday, but the California electric grid did not.

Power system officials across the state reported no major reliability issues, even though solar power took a dramatic dip as the moon obscured a large portion of the sun Monday morning.

That provided a real challenge for California grid operators, given that Monday marked the first eclipse seen throughout the contiguous United States since 1979, when solar power represented just a blip on the nation’s energy landscape.

The California Independent System Operator oversees the operation of about 80% of the state’s electric power system, transmission lines and electricity market. The Cal-ISO control room was ground zero Monday to see how the power system would react.

Cal-ISO officials spent months planning for the eclipse. Leading up to Monday’s event, they expressed confidence the energy needs of the state’s residents would be met.


As it turned out, no news was good news.

“We didn’t have any major challenges on the system, even minor challenges,” said Eric Schmitt, Cal-ISO vice president of operations. “We are very pleased about how smoothly it went.… All the resources performed the way they were supposed to perform. Our planning was excellent, [and] the market performed well.”

Under normal circumstances, solar production from utility scale power plants — as well as installations many California homeowners have placed on their rooftops — increases at a steady rate as the sun comes up in the morning and reaches its peak production around noon.

But the eclipse resulted in a sharp decline in solar production as the moon began to cover the sun at 9:02 a.m. in California, with production coming back online as the eclipse passed.

Cal-ISO expected a loss of about 4,300 megawatts of solar production by the time the eclipse ended at 11:54 a.m.

For perspective, 4,300 megawatts of electricity is enough to power between 3.2 million and 4.3 million homes.

Schmitt and Cal-ISO executive director of systems operations Nancy Traweek said they won’t have official numbers until later in the week, but estimated the loss at about 3,400 megawatts. They said the lower number could be partly because there were cloudy skies along the state’s coastline.

But the real challenge for grid operators came by dispatching other sources of energy to substitute for the loss of solar. The state relied on hydroelectric power and thermal sources — largely natural gas — to make up the difference.

The power system also leaned on the Energy Imbalance Market, a wholesale market made up of Western states that allows authorities to buy and sell megawatts of power to satisfy demand within the hour it’s needed.

“Early on, we were importing, as you would imagine, a few hundred megawatts, and now as the sun returned … we started to export on the Energy Imbalance Market,” Schmitt said.

California utilities did not report any problems Monday.

“All systems performed well — just how we forecasted them to,” said Allison Torres, San Diego Gas & Electric communications manager.

California is home to six times more solar electric capacity than any other state, and for Handa Yang, a PhD candidate at the Center for Energy Research at UC San Diego who studied the eclipse, Monday’s results indicate more solar will not overwhelm the power system.

“I think the grid can handle a surprising amount of solar penetration — more so than we originally thought — and it will be able to handle more once we get more battery storage online,” Yang said.

Battery storage is considered by many grid experts as an effective way to take solar and wind production and use it when the sun doesn’t shine or the wind doesn’t blow.

Nikolewski writes for the San Diego Union-Tribune.


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