The first total eclipse of the sun impacting the contiguous United States since 1979 will pass through the heart of America on August 21, carrying with it a challenge for electrical grid operators increasingly dependent on solar power.
According to modelling by global weather risk consultancy MDA Weather Services, total U.S. solar generation potential will be reduced by more than 50 per cent as the shadow of the moon passes over North America, with a full blackout across a maximum width band of about 256 kilometres following a trajectory from northern Oregon to South Carolina.
More than 11,000 MW of renewable energy supply potential will be knocked off U.S. power grids for over 20 minutes, according to MDA Weather Services.
“The peak impact is 20 minutes but the wider impact actually runs several hours,” says Stephen Jascourt, a senior scientist with MDA Weather Services.
Certain power grid regions will be affected more acutely than others. In Duke Energy’s Carolinas service area, for example, the potential for solar generation is expected to drop from 90 per cent plus at 13:15 EDT to just eight per cent at 14:45 EDT.
“Potential” is a key word in solar capacity because solar energy always has to contend with passing cloud cover and time of day effects on actual power output.
Jascourt explains that while the impact of the eclipse on the total amount of power produced in the U.S. from sunrise to sunset will be less than the impact of clouds on average day, the problem is that all regions will grow dark roughly at the same time.
“Because it’s so concentrated everywhere at the same time, there’s not an ability to compensate from one region to another region by moving power around the transmission grid,” Jascourt says.
That means power producers will have to bring other resources online that otherwise wouldn’t need to be brought online, especially as people reach for light switches, creating additional load on the grid.
“California has a report online describing what they will do. Each region has different additional power resources they can bring online,” Jascourt says.
California, which has seen its share of solar power on the grid soar to 10 per cent from 0.4 per cent in the last five years, boasts about half the country’s solar capacity, according to the US Energy Information Administration.
On Aug. 21, that will translate into a 6,000 MW shortfall during the hours of the eclipse, enough to power a large city.
To compensate, California’s utility operators are reserving spare capacity from gas and hydroelectric power plants, as well as coordinating with industrial sources to temporarily curb demand.
Europeans, who saw 90 per cent of new energy on the grid come from renewable sources in 2016, have already weathered eclipses successfully in the past. U.S. operators are reportedly taking lessons from them.