Duke Energy makes plans for when sun goes dark :: WRAL.com

EDITOR’S NOTE: The following article originally appeared in Duke Energy’s Illumination blog.

When a total solar eclipse glides over the country on Aug. 21, the moon will block more than 90 percent of the Carolinas’ sunshine. That much darkness presents a first-of-its-kind puzzle for the Duke Energy employees managing solar energy.

Solar energy production will dramatically decrease as demand for lighting increases in North Carolina 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.

During the Aug. 21 eclipse, about 98 percent of sunlight will be blocked at Duke Energy’s new 500-acre solar plant in Monroe, N.C.

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. So, what does that mean for the grid?

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, Roberts said, which would allow them to slowly…

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