Don’t look up, at least not without your eclipse glasses. That’s the advice from NASA as millions of people across the western U.S. will experience an annular solar eclipse on Saturday morning, Oct. 14, when the moon will obscure most of the sun.
In California, about 68%-89% of the sun’s rays will be obscured during the eclipse, which means the amount of sun shining on solar panels throughout the state will be reduced. Annularity, where the moon covers nearly all of the sun and produces a “ring of fire” effect, will occur along a band stretching from Oregon to Texas.
“The reduction in rooftop and utility solar locally in California would be similar to the impacts of a cloudy day for a brief period. The challenge is that typical cloudy days do not expand across the entire western United States,” said David Siuta, an SCE Meteorology senior advisor. “The fact that the eclipse will occur in the morning when temperatures are not likely to be warm is good news.”
The last solar event impacting SCE’s service area was a total eclipse in 2017. The California Independent System Operator, which manages the grid and utilities, was well-prepared, so impacts to the grid were minimal.
But today, CAISO manages a much more extensive portfolio of solar power. For example, in 2017, the grid relied on about 10,000 megawatts of large, grid-scale solar generation. Now, it has 16,500 MW. Rooftop solar power generation has grown even faster, from 5,700 MW in 2017 to 14,350 MW today. Taken together, the amount of solar power supplying the grid has about doubled since the last eclipse.
At the eclipse’s peak from 9:20-9:30 a.m. Saturday, the drop in solar generation will leave a gap of nearly 15,000 MWs compared to a blue-sky day, according to CAISO estimates. Making up the difference will be a mix of technologies. California’s grid now has more battery storage capacity than it did during the 2017 eclipse. And because the state has enjoyed a wetter-than-normal year, hydropower is more abundant. CAISO plans to use both resources to fill in gaps from the eclipse. Finally, the eclipse will occur on a Saturday, when electricity demand is typically lower than during the week.
However, the biggest challenge for CAISO will be to maintain grid balance. Grid-scale solar can be controlled, but rooftop solar will cause a swift increase in load as the eclipse begins and a speedy drop-off as the eclipse wanes.
“Our main concern from an operational standpoint is to make sure that forecasts reflect the changes in load and supply and our operators and solar generation partners are prepared to respond to CAISO’s instructions to manage what’s expected to be a very fast ramp in load (electricity on the grid),” said Leo Kim, SCE senior manager of forecasting and distributed energy resources.
Though not anticipated, CAISO could also implement demand response programs to ensure the grid continues to supply power to customers throughout the state.
For more information about SCE's commitment to a clean energy future, visit edison.com/countdownto2045.
