Governors' Wind Energy Coalition

Unlike most eclipse-watchers in the United States, Eric Schmitt wouldn’t mind seeing a few clouds in the sky when the moon starts blotting out the sun on Monday.

“A cloudy morning might even be helpful for us,” he said.

That’s because, as the vice president for operations at the California Independent System Operator, which oversees the state’s electric grid, Mr. Schmitt will be dealing with an unusual challenge. As the eclipse carves a long shadow over California on Monday morning, it is expected to knock offline more than 5,600 megawatts’ worthof solar panels at its peak — a big chunk of the 19,000 megawatts of solar power that currently provide one-tenth of the state’s electricity. The California I.S.O. plans to fill the void by ramping up natural gas and hydroelectric power plants.

Then, a few minutes later, when the eclipse passes, all those solar panels will come roaring back to life, and grid operators will have to quickly make room for the sharp rise in generation by scaling back gas and hydropower. A cloudy day, Mr. Schmitt explained, might help blunt those wild swings in solar energy.

For months, the nation’s grid overseers have been preparing for any disruptions in solar power that the eclipse might cause, by running models and training operators in simulators for worst-case scenarios. Because solar still provides less than 1 percent of electricity nationwide, regulators are confident that the lights will stay on, other energy sources will compensate and the costs will be minimal.

But many operators also see the event as a rare trial run for a future in which solar power will become far more prevalent — and they will have to accommodate a fast-growing source of energy that, unlike older coal or nuclear plants, can wax and wane considerably during the day, and drop off at night.