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How Will California’s Solar Grid React to the Eclipse?

Like many thrifty business owners, officials at the Riverbanks Zoo in Columbia, South Carolina, were banking on reducing their carbon footprint and saving money when they installed rooftop solar panels during a big expansion in 2015. In fact, since the panels went up, the zoo has saved more than $ 8,500 on its electric bill by using less energy from South Carolina’s fossil fuel power plants.

But at 2:41 pm on Monday, August 21, their solar panels will go dark as the shadow of the moon blots out the sun’s energy-producing rays. The zoo is in the path of the solar eclipse’s totality, but the lack of solar power won’t lead to any Jurassic Park-like escape scenarios.

“We do not expect any glitches as far as things shutting down,” says zoo spokeswoman Susan O’Kane. The zoo—like millions of other solar power users in the eclipse’s path—will simply switch to electricity generated from coal, gas, and nuclear power.

Sure, the eclipse won’t cause any major service disruptions. Nationwide, solar only accounts for 1 to 2 percent of the total energy supply. But it will create a substantial dimming in solar power generation, according to an analysis by the North American Reliability Corporation, an agency that works with electric grid operators. And not just in the darkest part of the shadow, but across swaths of the country hit by partial totality.

With thousands of rooftop solar panels and big desert solar farms, California will be hardest hit, according to Anne Gonzales, a spokeswoman for the California Independent System Operator in Folsom. The state generates more than a quarter of its electricity from solar farms and rooftop panels. So even though no Californians will experience full totality—the eclipse’s path intersects with the west coast in Oregon—a partial eclipse will be enough to drop solar power supplies by 6,000 megawatts during the entire two and a half hours of the eclipse. That’s enough power to run about 6 million homes. “The eclipse will impact all of our solar fields to some degree depending on the location,” Gonzales says. “The moon will cover 76 percent of the sun’s rays in Northern California, and that drops to 58 percent in Southern California.”

The biggest challenge for the state won’t be supplementing that 6,000 megawatts with other sources. Instead, it’ll have to focus on managing the sharp drop off and return of solar energy. California will start losing solar generated power when the shadow first hits at 9:02 am PT, keep seeing the dip until the peak shadow time around 10:22 am, and then ramp back up as the shadow diminishes until 11:54 am on Monday, Gonzales says. “There’s a strong ramp down and a sharp ramp up,” Gonzales says. Solar power “will come back strong and quickly.”

As the shadow advances, California’s electric grid will lose 70 megawatts a minute. Making up the difference will be a balancing act of high-tension electricity choreography conducted by grid operators across the country. They have to make sure that power plants aren’t down for maintenance, for example, and that pressure in natural gas feeder lines remains constant to prevent hiccups in the other power generation units. Californians won’t really know where that power comes from until that day: Power flows back and forth between states based on rapidly fluctuating market prices. The state’s utilities buy whatever’s cheapest at the time.

North Carolina’s power grid will face a similar juggling act to make up for its 4,000 megawatts of lost solar power, according to the NERC report. That’s because the Tarheel State has made huge gains in solar in the past few years, according to John Moura, NERC’s director of reliability assessment and system analysis. “It’s not an Armageddon scenario nor will it lead to significant problems, but it will lead to some interesting phenomena,” Moura says.

Grid officials have been preparing the eclipse for the past year, revising their original estimates of solar power losses upward after meeting with NASA officials who told them that the effects of the moon’s shadow will be felt well beyond the path of totality.

Moura said that lessons learned will help local utilities, plant operators, and grid managers prepare for the next big eclipse to hit North America on April 8, 2024. By then, solar power will make up a bigger share of the US energy portfolio, rising from 15 gigawatts today to 120 gigawatts in 2024.

Moura and other experts say battery storage technology will have to make big strides in order to help the solar industry survive events like an eclipse, as well as unexpected cover from smoky wildfires, dust storms or increasing humidity, rains and cloudiness that may occur in a changing climate. Monday will be “a test run” for the 2024 eclipse, Moura says. “We don’t see this on the grid very often.”

In the meantime, visitors Monday to the Riverbanks Zoo will get to help researchers from nearby University of South Carolina who are studying what happens to animals when the sun goes away for a few minutes. When the next eclipse falls across the US in 2024, solar-powered zoos, homes, businesses and cars better have their batteries charged.

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