THE GROWTH of solar power is dramatically changing the way the New England power grid works, altering when electricity from power plants is needed.
For decades, demand for power from the grid has grown during the afternoon and early evening and then tapered off overnight as people go to sleep. But increasingly, on more and more days, demand for power from the grid is higher at night than it is during the day.
The cause of this shift is solar power, most of which is generated and used at homes and businesses with solar panels. This electricity is called behind-the-meter power 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, the operator of the power grid, 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 began to take off 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 power demand 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.
On April 9, 2023, the demand for electricity from the grid hit a low of about 6,814 megawatts, breaking the previous record low of 7,580 megawatts on May 1, 2022.
ISO New England estimates solar capacity in the region was 6,542 megawatts at the end of 2023, up 9 percent from the previous year. Massachusetts accounted for 57 percent of the total and Connecticut 17 percent.
Overall, the growth of solar is a very good thing. It means less electricity is needed from power plants that tend to run on natural gas and other fossil fuels. But the growth of solar is also changing the way the grid operates.
Dan Dolan, president of the New England Power Generators Association, said the grid historically has relied on power plants that operate almost continuously. But as solar grows, the need for electricity from those power plants will steadily decline in the afternoon and then spike upward suddenly when the sun goes down. That means plants that are designed to operate most efficiently with continuous use will now be called on to cycle on and off during the day.
“Today, this is something that we can deal with,” Dolan said. But as the post-sunset spike in demand steepens, he said, problems are likely to surface. Batteries may help deal with the problem, but he believes the grid may become more dependent on power plants capable of powering up and down quickly.
If offshore wind takes off, that may change the power grid dynamic even more.
