Eclipsed: Can the grid survive when solar power goes dark?

Electricity providers are bracing for Monday’s solar eclipse, which will take thousands of megawatts of solar power off the grid as it passes over the USA.

America’s last total solar eclipse took place in 1979, when solar was a much smaller part of the overall energy supply. Europe handled a similar event in 2015 with a minimum of fuss, as the amount of solar power fell from 13GW to 6GW as the eclipse began.

US providers are ready. California’s grid operator will bring in extra supply from natural gas power plants and hydroelectric dams, according to the Financial Times, in expectation of having to fill a gap of 6000MW – enough power for six million homes.

Randy Wheeless, a spokesman for North Carolina-based energy, told the FT that the eclipse was “a unique challenge because it’s right in the middle of the afternoon, when you could possibly lose a large amount of solar”.

Jon Major, a physicist who works on solar panels at Nottingham University, told Professional Engineering that the impact would likely be 'minimal' because eclipses could be easily planned for. “The change will be minuscule compared to the change between generation in June and December which will be more of a consideration,” he said.

Perhaps because he’s based in the UK and not California, he also pointed out that a week of cloudy weather would likely cause a bigger hit than a 10-minute eclipse.

What about satellites?

Above the clouds, eclipses are also a consideration for satellites, which often rely wholly on solar power. "Many, if not all of NASA’s earth-orbiting fleet rely on the Sun,” NASA planetary geologist Noah Petro told PE. “However, the eclipse won’t affect them in orbit around the Earth, as they are used to be in the dark, relying on their batteries.”

John Connolly, a chief exploration scientist at NASA, told PE that eclipses "are a big deal in the world of spacecraft design.” He explained that solar-powered spacecraft have their power and energy storage system designed around the longest ‘eclipse’ that they will see in their lifetime, which could be determined by how long it will spend on the ‘dark side’ of a planet.

“We need to design the energy storage system of a spacecraft to store enough energy so that the spacecraft can remain operating even when the solar arrays are not producing power, and we need to design the solar arrays so that they can charge the batteries to the level of energy needed,” he said.