Solar power and the Great American Eclipse of 2024

A total solar eclipse traversed North America on April 8, 2024, on a path from Mexico, across the U.S. from Dallas to northern New England, and into Canada. No total eclipse has covered such a large extent of the U.S. in recent years (a 2017 eclipse was the first in the U.S. in 26 years); meanwhile, an increasing amount of solar photovoltaic power plants have been built. The "Great North American Eclipse" of 2024 thus provided an opportunity to examine how a total solar eclipse affects solar power and the broader grid, using New England as an example.

According to New England's regional grid operator ISO New England, "the April 8 solar eclipse led to a steep and significant decrease in solar energy production, but due to extensive planning by ISO New England operators, the event caused no disruptions to the power system." All of New England experienced at least a partial eclipse where the moon blocked at least 80% of the sun. Parts of Vermont, New Hampshire, and Maine experienced totality.

During the two hours around the eclipse's peak, ISO-NE reports that regional solar production dropped by as much as 4,000 megawatts. 

Chart from ISO-NE (source)

Most of the drop-off -- about 3,300 to 3,500 MW -- came from small-scale, distributed photovoltaic panels connected directly to distribution systems which ISO-NE says "make up the vast majority of solar resources in New England", while grid-connected solar system production dropped by about 650 MW. The timing of the eclipse, relatively late in the afternoon, meant that only about 1,350 MW of solar production returned to the system after the eclipse passed.

ISO reports that its market yielded negative real-time prices as the eclipse approached, followed by a price spike over $100 as the eclipse passed overhead, and then price moderation toward the day's average value.

ISO-NE reports no power system or reliability disruptions from the eclipse, thanks to the system operator's planning for the eclipse, and operations which dispatched natural gas and hydroelectric generators to make up the solar power blocked by the moon.