When California experiences a partial solar eclipse on Monday, the dimmed skies in the Golden State will create a dip in solar generation — an amount large enough to power a large city.
But Californians aren’t likely to notice the shortfall. That’s because during the eclipse, when the sun moves partially behind the moon, the California Independent System Operator plans to turn to reserves in natural gas, wind, geothermal and hydroelectric.
“We are confident we can handle this. We have the capacity,” said Steven Greenlee, spokesman for the Cal-ISO, a nonprofit that manages California’s power grid. “Most customers should see no difference to the power supply.”
The eclipse will cast a 70-mile-wide shadow in a path through 14 states from Oregon to South Carolina, according to NASA. Those outside the direct path will see a partial eclipse, from 76 percent in Northern California to a 58 percent eclipse in Southern California.
The state is expected to lose an estimated 6,000 megawatts of solar generation during the eclipse, which is projected to darken the skies from 9:02 a.m. to 11:54 a.m. The amount of lost solar generation is roughly enough to power 6 million homes.
Cal-ISO began its preparations more than a year ago, reaching out to European countries that experienced a 2015 eclipse, including Germany, which also uses solar power. Among the lessons learned: Have more reserves.
So power plants will be on standby for additional generation in California.
“We know it’s a substantial amount of generation that we will have to make up,” Greenlee said. ”We have to be on our toes.”
Part of the issue for grid operators and utilities will be the rapid ramp-down of solar generation that flows into the power grid as the eclipse begins and the fast ramp-up of power back to the grid when the eclipse ends — rates that could stress the system, according to Cal-ISO.
The Cal-ISO, which runs the state’s power transmission grid — much like air traffic controllers tell planes when to take off and land — will be in charge of where the extra resources will come from if they are needed that day.
Cal-ISO could also issue a Flex Alert asking Californians to conserve their power consumption, a step officials don’t expect to happen if weather conditions are normal. For example, if a heat wave descends upon the state and electricity demand is greater than usual, grid managers might issue a conservation alert.
As a precaution, Pacific Gas & Electric Co. intends to pause all non-essential, routine work on generation equipment so it’s available should they need to reroute generation, spokeswoman Jennifer Robison said.
The California Public Utilities Commission is using the eclipse as opportunity to ask Californians to lower their energy use that day — part of its overall strategy to educate Californians about energy conservation.
“When the sun starts to step out of the picture, we can all step in,” said Michael Picker, CPUC president.
The state Department of General Services doesn’t plan to ask state agencies to reduce their energy use unless the Cal-ISO issues a Flex Alert, spokeswoman Lynda Gledhill wrote in an email.
Although an eclipse isn’t a common event, the Cal-ISO and the state’s utilities have some experience at managing power supplies when solar isn’t producing at its peak. For example, Southern California Edison, whose territory stretches from Fresno to San Diego County and from the Pacific Ocean to the Arizona border, often adjusts when a foggy marine layer or desert monsoons obscure the sun.
“It’s of the scope we generally manage,” said SCE spokesman Robert Villegas. “One of the nice things about the eclipse is we know about this in advance.”
