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Sparks

Saturday’s Eclipse Will Wreak Havoc on America’s Solar Power

Ever wonder how an eclipse affects solar? We’re about to find out.

Matthew Zeitlin •
10/13/2023
An annular eclipse.
Heatmap Illustration/Getty Images

The annular solar eclipse Saturday morning will darken a stripe of the United States stretching from Texas’s Gulf Coast to the Four Corners to the northwest corner of California and Southern and Central Oregon. A broader stretch around this already massive area will experience 65 percent to 90 percent of that darkness.

NASA eclipse mapNASA

While Saturday’s solar eclipse will only be partial — with 90 percent obscuration — compared to the full eclipse in 2017, the effect on electricity will be greater. That’s because of the spectacular growth of solar power.

The eclipse’s swath includes a huge portion of the United States’ solar power, especially in Texas and California, which will affect these areas’ electric grids. ERCOT, the energy market that covers nearly all of Texas, projected that its power capacity will dip from 79.2 gigawatts at 10 a.m. CT to 71.6 gigawatts at 11 a.m., whereas on Sunday capacity is projected to go from 77.6 gigawatts at 9 a.m. to 78.6 gigawatts at 11 a.m. ERCOT said in a statement that it anticipates the eclipse affecting solar output from 10:15 a.m. to 1:40 p.m..

Solar eclipses aren’t new, of course, but the amount of solar power, especially in the western United States, has grown tremendously since 2017. Back then, California’s grid had 10 gigawatts of solar installed and 5.8 gigawatts on rooftops; now it’s 16.5 gigawatts installed on the grid and 14.4 gigawatts of solar on the roofs of homes and businesses.

In California, the state’s system operator projected that solar output could fall by a whopping 9.7 gigawatts at the eclipse’s maximum, assuming the sky is clear before the eclipse, reducing solar capacity by about a quarter. That’s enough generation to power some 2.7 million homes disappearing off the grid.

As the eclipse ends, solar production will surge by 10.8 gigawatts, which the California Independent System Operator estimated was 10 times the normal rate that solar ramps up at as the sun rises and moves across the sky.

“An eclipse is a unique and rare event that captures the public imagination and requires a lot of coordination,” CAISO said in a statement.

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Matthew Zeitlin profile image

Matthew Zeitlin

Matthew is a correspondent at Heatmap. Previously he was an economics reporter at Grid, where he covered macroeconomics and energy, and a business reporter at BuzzFeed News, where he covered finance. He has written for The New York Times, the Guardian, Barron's, and New York Magazine.

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Heatmap Illustration/Getty Images

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