What happens to solar power during an eclipse? On Aug. 21, California will find out

California relies more on solar energy than any other state in the union.

So what happens if the sun doesn’t shine?

That answer will come Aug. 21 when a solar eclipse will cast its shadow over the usually Golden State. It will hit late in the morning during peak solar production time on what normally is one of the hottest days of the year.

Last year, California’s solar facilities — from tiny rooftop units to giant desert plants — generated enough electricity to power about 4.7 million homes, according to an industry association. Obviously, most of that clean power was generated when the sun is high.

The eclipse will darken our skies during a time when solar power can account for as much as 40 percent of the load on the statewide electricity grid. Power experts believe as much as two-thirds of that clean energy will be lost as the moon’s shadow rolls across the state.

Californians won’t experience a total eclipse. That will happen farther north in Salem, Ore., but we will still see a significant impact.

“We have to have things ready so we can fill up this gap quickly,” said Anne Gonzales, a spokeswoman for the California Independent System Operator or Cal ISO, which manages the power grid.

Cal ISO officials are preparing for a minute-by-minute process of ramping up production from natural gas and hydroelectric plants starting at about 9 a.m. as the sky starts to dim until about 10:20 a.m when moon’s shadow will block about three-fourths California’s sunshine.

“Think of it as pushing a gas pedal,” Gonzales said.

The process will continue in reverse with gas and hydro plant shutoffs as the sun returns until the eclipse is over shortly before noon.

Cal ISO officials are working to make sure that the natural gas plants have enough fuel for the day. And the hydro plants at the state’s dams and reservoirs are preparing for strategic water releases to turn turbines as needed, say Cal ISO officials.

The recent wet winter has left state’s reservoirs with plenty of water, giving them the flexibility for such water releases.

State officials won’t know exactly how much the eclipse will affect California until they can see the weather forecasts a few days before it’s due to hit.

If the eclipse happens in the middle of a heat wave that drives up the demand for electricity to run air conditioners, more substitute sources will be needed, Gonzales said.

But so far, Cal ISO officials haven’t asked people to use less electricity to avoid blackouts.
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