What the eclipse will mean for solar power
The ancient Greeks thought a total eclipse of the sun was a sign the gods were angry and bad things were to come. But for millennia, it has just been a game of hide-and-seek between the sun and the moon with little impact on Earth’s mortals.
Not this time around, as the sun, moon and Earth head toward their dark rendezvous Aug. 21.
Something has changed on the ground. There are thousands and thousands of solar panels across the country that will suddenly be switched off as the sun slips behind the moon.
The eclipse will cast a 70-mile-wide shadow across the country knocking out photovoltaic (PV) solar arrays from Oregon to South Carolina, briefly turning off as much as 9,000 megawatts (MW) of generation. That’s equal to 11 of Xcel Energy’s biggest Colorado power plants.
The last time there was a nationwide total eclipse was in 1918, long before solar energy was a thing.
While the eclipse is national, its shadow will fall heaviest in the West where solar has been deeply embraced. Four of the six top states for solar installations — California, Arizona, Nevada and Utah — are located in the region. Some days, California gets as much as 40 percent of its electricity from solar arrays.
The West alone could see the loss of as much as 7,000 MW spread over time, according to Brett Wangen, director of engineering at Peak Reliability, the organization responsible for assuring the dependable operation of the region’s power grid.
Wangen said the “biggest risk” is in California, where 80 percent of the state is served by the California Independent System Operator (CAISO). The impact on Colorado will be limited.
Between about 9 a.m. and noon on the day of the eclipse, CAISO expects to lose 4,194 MW of utility-scale solar and 1,365 MW of rooftop solar, according to Steven Greenlee, a spokesman for the agency.
CAISO is no stranger to solar-power losses on cloudy and rainy days where there can be a drop of 800 MW to 1,200 MW within minutes. “The difference with the eclipse is the magnitude,” Greenlee said.
“We’ve been preparing for several months, and the best tool in our toolbox has been pre-planning, talking to all the market participants,” Greenlee said, referring to utilities, independent power producers, and natural gas suppliers.
The Los Angeles Department of Water and Power (LADWP) projects it will lose about 605 MW of power from its arrays in the Mojave Desert, according to the department. “We expect to use the same operating principles we use on cloudy days,” the LADWP said, “carrying additional reserves with sufficient ramp capability to keep up.”
Peak has been meeting with the top four solar power producers in the region, CAISO, LADPW, Pacificorp and Arizona Public Service Electric Company, to coordinate for the eclipse, Wangen said. “There is a lot of coordination going on above and beyond what we normally do.”
Utility officials say they have a handle on the event, identifying potential outage areas and arranging for backup generation. “We know minute to minute when generation will be falling off and coming back,” Wangen said.
It will be a test and an important one for solar power. The next total eclipse across North American will be in 2024, If the trends continue, there will be a lot more solar arrays on the ground. In 2016, there were about 40 gigawatts of installed PV capacity. By 2024, there could be three times as much, according the industry trade group, the Solar Energy Industries Association.
In the future, managing eclipses will become a crucial exercise. The ancient Chinese would shoot fire arrows to scare off the menace to the sun. In some cultures, they banged pots and made noise to ward off the threat. Thankfully, Xcel Energy’s plans don’t include such indignities.