Yesterday’s eclipse enthralled the nation, leaving two things in short supply: eclipse glasses and solar energy. But at least on the energy front, utilities successfully planned for the event, giving some insight into the growing reliability systems with large amounts of intermittent energy.
“We were able to balance the Duke Energy system to compensate for the loss of solar power over the eclipse period,” Sammy Roberts, Duke Energy director of system operations, said in an emailed statement to Utility Dive. “Our system reacted as planned, and we were able to reliably and efficiently meet the energy demands of our customers in the Carolinas.”
Duke Energy has 2,500 MW of solar capacity connected to its system in North Carolina. Given the weather conditions yesterday, utility officials said they would normally expect 1,808 MW of solar output during the afternoon, but were getting only about 109 MW during the eclipse’s peak.
In the PJM territory, the grid experienced a drop of approximately 520 MW of wholesale solar generation from just before the eclipse reached its peak. The grid operator also estimated that electricity from behind-the-meter solar generation decreased by approximately 1,700 MW.
PJM Interconnection also said other factors made dealing with the drop-off of solar power easier. The operator said it had expected a reduction in power from rooftop panels, but several factors — including lower cooling loads, increased cloud cover and changes in behavior related to the eclipse — resulted in a net decrease in demand of about 5,000 MW throughout the eclipse.
According to the U.S. Energy Information Administration, more than 21 GW of solar capacity was expected to be impacted. Europe experienced a total eclipse in 2015 that impacted 90 GW of solar capacity — with 40 GW in Germany, supplying 40% of that country’s electricity demands.
Utility-scale solar provides less than 1% of the United States’ electricity use, and there were less than 20 utility-scale generators in locations where the sun was wholly obscured yesterday. But state renewable portfolio standards, falling costs and interest in rooftop generation means the country’s grid will continue to add carbon-free, intermittent generation.
Utilities and ISO officials were closely watching yesterday’s event to prepare for the next total eclipse in the United States in 2024.