The solar eclipse event on August 21 received a lot of news coverage before, during and after the moon passed in front of the sun. But only a sliver of that media attention was focused on the issue of its impact on the nation's electric grid.
Most of what was written in advance about solar power on the grid suggested that, while solar would go "offline" for a few minutes during the event, utility operators were planning for the event and would have sufficient alternative backup power available, primarily hydropower and gas-fired generation plants, which can be brought online very quickly. In fact, a large percentage of the nation's gas-fired generation is in place to deal only with peak demand events.
One reason for the initial concern, however, was the speed at which solar power would be lost—in a matter of minutes, rather than hours, as would be the case with weather events. Another was that, while the focus of concern was on utility-scale solar, many utilities have customers with rooftop solar, which would stop producing power, and would then have to pull the power they needed from the grid, adding even more stress to the grid. And a third concern was that the loss of power would occur during the day, when demand for electricity is at its highest.
However, one reason for optimism was that the industry knew of the event well in advance and had time to plan. It turns out the optimists were correct.
While there were nine states in the path of the eclipse with large amounts of solar power capacity (California, Nevada, Arizona, Texas, Utah, New York, New Jersey, Massachusetts, and North Carolina), the two of most concern were California and North Carolina, which rely on a significant amount of solar generation.
The California Independent System Operator (CAISO), which delivers 80 percent of the power to the state and which has 40 percent of the nation's solar energy capacity and can produce up to 10,000 megawatts of electricity during full sunshine, ended up losing half of its solar production for a brief period during the eclipse. During that time, however, the shortage was seamlessly replaced by hydroelectric and natural gas power plants, along with power drawn from surrounding states as part of pre-existing agreements.
North Carolina, which generates the second greatest amount of solar in the nation, ended up losing 1,700 of its 2,500 megawatts of solar capacity during the eclipse. However, Duke Energy, which supplies most of the power to the state, was prepared, and brought a sufficient number of natural gas-fired generators on-line during the event.