Solar Eclipse Will Impact California’s Solar Output by 6,000 Megawatts

California will experience a drop in the production of solar power when the moon eclipses the sun on August 21. Energy entities like the California Independent System Operator (California ISO), which manages most of the state’s electric grid, are preparing for that reduction.

The eclipse will be most pronounced in the Pacific Northwest where a total solar eclipse will occur. California will experience a partial eclipse.

The expected time of the partial eclipse in California will be between 9:02 AM to 11:54 a.m., with peak obstruction at 10:22 a.m.

A study by California ISO expects that Northern California will see 76 percent of the sun blocked. In Southern California, the sun will see 62 percent of the sun’s rays blocked in the Los Angeles Basin and 58 percent in the San Diego region.

Electricity from solar photovoltaic and solar thermal will likely be produced throughout the eclipse, but at lower levels than normal.

California has 10,000 megawatts (MW) of installed commercially operational gird connected solar capacity within California ISO’s grid balancing area. The expected loss of power is predicted at about 4,200 MW of California’s large scale solar electricity, according to California ISO.

About 1,400 MW of rooftop is expected to be curtailed, which will add pressure on the grid since it is a backup power source.

In total, more than 6,000 MW of solar power will have to be made up.

The eclipse illustrates how California ISO handles the power demands of the grid. Typically, California ISO ramps down non-solar energy, like natural gas-fired power, when the sun rises. It does the opposite when the sun sets.

During the eclipse, the California ISO will conduct a second, smaller version of the ramp up and ramp down to fill the gap in solar power.

California ISO plans to maintain grid reliability by coordinating with Southern California gas and thermal generators and the state’s hydropower plants to make sure enough resources are ready to handle power needs during the eclipse.

While the ISO has enough energy supply to make up for lost solar production during the eclipse, consumers should always use energy wisely. Conservation is always of value, reduces emissions and makes the grid more reliable.

The California Public Utilities Commission (CPUC) has a website,, for more information on conservation during the eclipse. The website a partnership between the California Energy Commission, the CPUC and the California ISO.

The California ISO has a webpage on eclipse-related matters. The webpage includes links to fact sheets, forecasts, safe viewing tips, and a live feed showing the path of the eclipse as it moves across the United States.

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California Energy Commission

The California Energy Commission is the state's primary energy policy and planning agency created by the Legislature in 1974.
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