Total solar eclipses occur as a result of a peculiar, cosmic coincidence—the sun and moon, because of their relative sizes and distances from our planet, appear the same size in the sky.

But utilities and grid operators will be leaving nothing to chance on Aug. 21, when the next total eclipse is set to darken the heavens over the U.S.

The last time the U.S. witnessed a coast-to-coast total eclipse was in 1918, when grid management was a somewhat different business, to say the least.

In the last 10 years, solar photovoltaic generation in the U.S. has grown from almost nothing to more than 52 million MWh per year, according to the U.S. Energy Information Administration.

As a result, utilities and grid operators such as California ISO have been preparing for the eclipse for the best part of a year. At its peak, the eclipse will knock out about 6 GW of solar generation in California alone.

The missing megawatts with be replaced with hydro and gas-fired capacity, and CAISO has been coordinating with gas-fired generators to ensure capacity will be available. The grid operator will host a conference call with market participants two days before the eclipse.

If all this work has been a strain, market watchers haven’t noticed. “I haven’t heard anyone express anxiety about it,” says a renewables-focused investment banker.

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