On August 21, the United States will experience its first coast-to-coast solar eclipse since 1918. In places like the Carolinas, the moon will block more than 90 percent of the states’ sunshine. That much darkness presents a first-of-its-kind puzzle for many organizations and employees managing solar energy.

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So, what exactly does this mean for the grid?

In North Carolina, for instance, solar energy production will dramatically decrease as demand for lighting increases while the sun hides behind the moon from about 1 to 3 p.m. This is normally a peak time for solar energy production, and Sammy Roberts, Duke Energy director of system operations, estimates solar energy output will drop from about 2,500 megawatts to 200 megawatts in 1 1/2 hours.

Just as punching the gas pedal to climb a steep hill is tough on a car, dramatic shifts in energy supply or demand are challenging for the grid. But unlike a car, which has a gas tank, the grid doesn’t have an effective way to store large amounts of energy. Energy production must mirror customer demand at any moment.

System operators are constantly monitoring demand and making decisions about what source – natural gas, solar, nuclear, hydropower, coal, wind, etc.– is the most efficient for that moment.

Because of its flexibility, 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, which would allow them to slowly increase natural gas energy production. In other words, they will gently press rather than punch the gas pedal.

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