A rare eclipse set to traverse the US on Monday has sparked a tourism bonanza, as people flock to towns in its path to see the sun’s corona encircle the moon.
The control rooms of the nation’s electric utilities will be also be watching.
That is because thousands of megawatts of solar energy will disappear as skies darken.
In California, the grid operator is lining up additional supply from natural gas power plants and hydroelectric dams to accommodate the drop. PJM Interconnection, the grid spanning from Illinois to New Jersey, expects up to 2,500MW of solar power to be lost and will rely on replacement generation.
The contingency plans reflect the expansion of solar energy in the US in the years since 1979, the last time a total solar eclipse awed the country. The rise has been especially dramatic in California, which seeks to get half its power from renewable sources in 2030 in a bid to cut greenhouse gas emissions.
California lies south of the “path of totality”, where day briefly turns to night, but more than half its sunlight would be obscured between roughly 9am and noon on Monday, the California Independent System Operator (ISO) said.
As people flip on lights and solar plants and rooftop photo-voltaic systems lose their fuel source, the California grid operator said it would have to fill a gap of 6,000MW — enough power for 6m homes.
“We’ve told the market that we’re going to need extra generation on that morning,” said Steven Greenlee, an ISO spokesman.
The grid managed by ISO has added about 2,000MW of solar generation in each of the past four years, bringing installed solar capacity to almost 10,000MW. Solar plants around the state can now meet as much as 30-40 per cent of demand.
Solar energy drops off daily when night falls, and unexpectedly when clouds form. “But this is greater in magnitude, and it’s faster,” Mr Greenlee said. Grid managers are drawing lessons from Europe, which in 2015 underwent its first total eclipse of the solar power era without incident.
California’s public utilities commission is using the eclipse as a teachable moment. The agency has invited residents to pledge to unplug toasters and phone chargers to diminish the need for fossil fuel power during the solar shortfall. “When you Take the Pledge, you are joining a movement of Californians who are taking action during the eclipse to give the sun a break by saving energy and reducing GHG emissions,” it said on a special eclipse website.
In the absence of affordable electricity storage, the use of gas and hydro plants as back-up power sources highlights dependence on a diverse portfolio of energy sources. The challenge of intermittent output from solar and wind power plants could intensify if the California legislature passes a bill requiring 100 per cent of electricity to come from renewable sources by 2045.
Elsewhere, carbon emissions will receive a bump from the tailpipes of millions of eclipse enthusiasts driving towards the path of totality, which cuts eastward through 14 states from Oregon to South Carolina. Highway patrols have warned of traffic jams on back roads, motels in obscure hamlets are booked solid and online vendors have exhausted supplies of safety eyewear.
Hopkinsville, Kentucky branded itself “Eclipseville” and expects an influx of 100,000 people. It has planned a three-day festival around a celestial event that lasts less than three hours.
“We have people coming from 45 different states and 19 different countries. This is definitely going to be the largest event our community has ever hosted,” said Brooke Jung, a consultant to the town.
The eclipse will exit the US south-east by late afternoon. Duke Energy, a utility there, plans to host eclipse watchers at a South Carolina nuclear power plant on Monday, serving hot dogs and ice cream and playing songs such as “Blue Moon” and “Here Comes the Sun”.
“It’s like a solar eclipse craze,” said Randy Wheeless, Duke spokesman.
Duke also manages solar farms in North Carolina, the state with the second-most solar capacity after California. Mr Wheeless said about 2,000MW of solar output may be lost as the eclipse passes.
He compared the effects of the eclipse to a thunderstorm, though one that was long predicted and darkens a whole region at once. “It presents a unique challenge because it’s right in the middle of the afternoon, when you could possibly lose a large amount of solar,” he said.