Rooftop solar growth makes giant New England gas plant obsolete as region hits 500th Duck Curve day

Rooftop solar in New England has grown so much that the region's grid operator, ISO-NE, just logged its 500th "duck curve" day on September 21, 2026. A duck curve happens when solar panels on homes and businesses push midday electricity demand from the grid so low that the demand graph dips like a duck's belly. The first one happened back in 2018, but they're now piling up fast: it took nearly five years to reach the first 100, and only about seven months to go from 400 to 500.

This surge of home solar, which ISO-NE estimates supplied about 8.4% of all electricity New Englanders used in 2025, has real consequences for the region's power plants. ISO-NE told federal regulators that growing rooftop solar was a main reason it saw no clear need to keep an LNG gas-storage terminal running for grid reliability. That terminal supplied the region's largest gas plant, the 1,413 MW Mystic Generating Station, which retired in 2024. Home solar also keeps setting records for cutting midday demand, with output hitting a peak of 7,068 MW this past April.

Looking ahead, ISO-NE expects home solar to keep growing, but more slowly than before. It now projects about 270 megawatts of new rooftop solar capacity per year through 2035, down sharply from earlier estimates, because the federal solar tax credit has ended. Even so, the grid operator still expects home solar to cut overall grid demand by 6% this year. If you're weighing solar for your own roof, this shows the technology is already reshaping how the region gets its power, even as incentives shift.