When the solar eclipse takes place on Aug. 21, the moon will block more than 90 percent of sunshine across North and South Carolina. That much darkness presents a puzzle for Duke Energy employees managing solar energy.

Solar energy production will decrease as demand for lighting increases in North Carolina while the sun is at least partially obscured by the moon from about 1 p.m. to 3 p.m. This is normally a peak time for solar energy production. Sammy Roberts, Duke Energy director of system operations, estimates solar energy output will fall from about 2,500 megawatts (MW) to 200 MW in 1 1/2 hours.

This will be the United States’ first coast-to-coast solar eclipse since 1918 and the first to affect the solar energy supply in North Carolina.

Because of their flexibility, Duke Energy operators will have natural gas plants ready to step in during the eclipse. In addition to replacing the lost energy with a flexible fuel source, operators can gradually decrease solar production before the sky darkens depending on weather conditions, Roberts says. Doing so would allow them to slowly increase natural gas energy production.

North Carolina is home to more solar generating capacity than any state except for California. Duke Energy manages energy from more than three quarters of the roughly 3,200 MW of solar power in the state. With a diverse mix of energy sources and a plan in place, the company expects to meet customer demand during the eclipse.

In California, which has nearly six times as much solar as North Carolina, system operators anticipate losing about 6,000 MW during the eclipse. According to the California ISO, operators have a similar strategy to replace the lost energy with natural gas and hydropower.

Duke Energy’s Oconee Nuclear Station in Seneca, S.C., is in the path of totality and has hosted a series of educational events that ends with an eclipse viewing party on its lawn.