Solar Eclipse Will Darken California Skies And Challenge The Electric Grid

During a total solar eclipse, the moon blocks the sun from the Earth’s view. On August 21st, the total eclipse will last less than two minutes.

Scientists say it’s the best time to see the sun’s corona, or outer atmosphere. The corona is 200 times hotter than the surface of the sun and difficult to observe except during an eclipse.

The eclipse may provide other awe-inspiring sights, says Paulett Leiwer, a solar physicist with NASA's Jet Propulsion Lab in Pasadena.

“The moon...has mountains on it and so you get little beads of light shining through," says Leiwer. "When it’s [the sun] totally blocked sometimes we can see these orange tongues called prominences that are lying right on the surface of the sun that extend somewhat beyond the moon."

What makes this eclipse different is its path across the U.S. It will move from the Pacific Northwest to the Carolinas. This path of totality across North America hasn't happened since 1918.

“That’s what’s so special," says Leiwer. "They happen, but often they’ll just...maybe cut across a little corner of Antarctica. A lot of them, of course, they fall in the middle of the ocean since the planet is mostly ocean.”

Millions of people are expected to travel to see the full eclipse.

This video depicts the path of the solar eclipse across the US. (Credit: Genna Duberstein / NASA's Goddard Space Flight Center)

Californians will only see a partial eclipse. The sun will look more like a crescent. Seventy-six percent of the sun’s light will be blocked in Northern California, 62 percent of the sun's light will be blocked in Southern California.

The eclipse begins at 9:02 a.m. and lasts until 11:54 a.m. During that time, California will lose 6000 megawatts of solar power, or enough to power about six million homes.

That presents a challenge for the electric grid. 

“We are going to then have to bring up non-solar generation in order to make up that gap and so it’s not something we’ve seen at this magnitude before,” says Steven Greenlee with the California Independent System Operator, which operates the electric grid.

Greenlee says California will have to rely on hydropower and natural gas. The eclipse will also test the grid’s ability to handle rapid power fluctuations.  

"The ramping up and down during the eclipse is going to happen much faster than what we've seen before," says Greenlee. 

Greenlee says the system will be able to handle the eclipse. Cal-ISO has been planning for it for more than a year. But grid operators may not be able to predict other factors that could stress the system at the same time of the eclipse. Greenlee says if it’s a really hot day or if wildfires take out transmission lines or other more unpredictable events stress the system, Californians might be asked to conserve. 

Scientists say Sacramentans should pay attention to the solar eclipse. The next opportunity won't come around until 2045.