Magical eclipse created temporary solar power void

THE SUN AND THE MOON put on a magical light show on Monday afternoon across New England, and the folks who run the regional power grid performed a little magic themselves, offsetting the temporary eclipse of most solar power in the region with more electricity from natural gas generating plants and imports.

Officials at ISO New England estimate roughly 4,000 megawatts of electricity, or about a third of total electricity demand at the time, was being generated by solar just prior to the eclipse. As the sun disappeared, the solar power went with it, leaving a gaping hole that needed to be filled quickly.

The hole was filled by calling on natural gas power plants to step up production and by importing electricity from neighboring regions. The real-time data on the grid operator’s website showed that natural gas-generated electricity went from 34 percent of the region’s needs just prior to the eclipse to a high of 47 percent at the peak of the eclipse. Net imports of electricity went from zero to 6 percent. Renewables, meanwhile, went from providing 18 percent of the region’s electricity pre-eclipse to as low as 8 percent at the peak of the eclipse.

Such drastic swings in electricity production often happen because a power plant or a group of power plants suddenly go offline because of some sort of failure. In those instances, the grid operator has to make up the difference on the fly, with many generating plants requiring significant time to get up and running. With the eclipse, the challenge was far more manageable because the timing of when the moon would move between the earth and the sun was known precisely.

Grid operators prepared for the eclipse in advance and executed their power-replacement strategy without a hitch on Monday.

The eclipse’s effect on solar generation was just another reminder of how solar power is changing the way the power grid operates. It used to be that demand for electricity from the grid grew during the afternoon and early evening and then tapered off overnight as people went to sleep. But solar power is changing that dynamic. Because of the rise of solar power, increasingly more power is needed from the grid at night than during the day.

On Monday just prior to the eclipse, ISO New England estimates roughly 4,000 megawatts of solar power was being generated – 3,400 megawatts behind the meter and 650 megawatts from grid-connected solar resources. The behind-the-meter generation is called that because it is used on site and not delivered to the home or business by the local utility, which in turn obtains the power from transmission lines connecting to power plants across the region.

As this behind-the-meter solar generation increases, demand for electricity from the power plants that make up the grid falls – at least until the sun goes down and demand for power from the grid spikes upward.

ISO New England said the first time demand for power from the grid was higher at night than during the day was on April 21, 2018. It happened 33 more times through the end of 2021, and then the shift began to accelerate as more and more homes and businesses embraced solar. It happened 45 times in 2022 and 73 times in 2023 – a fifth of the year – and shows no sign of slowing down.

The shift in demand for power from the grid occurs most frequently in the spring (March, April, and May are the top months) but also in November, January, and December. The only time of the year it doesn’t happen is the heart of the summer when air conditioning in the afternoon and early evening typically pushes electricity usage higher.