Mild weather and rooftop solar power have created a first-ever situation on New England’s electric grid: On Saturday, April 21, there was less power used in the middle of the day than in the middle of the night.

“We were expecting this to happen at some point as more behind-the-meter solar gets installed in New England and the weather conditions were just right. While this kind of dip in demand is new for New England, it’s a common occurrence in California,” said Mike Knowland, Forecast and Scheduling Supervisor for ISO-New England, the group that oversees the six-state power grid.

At 1:30 p.m. on April 21, according to ISO-NE, the grid had to supply slightly less than 10,000 megawatts of electricity, while another 2,300 megawatts was being provided by solar panels on roofs around the region – the most solar production ever in New England.

By contrast, at about 3:30 a.m. that morning, when no solar power was available, demand had dipped to its overnight low of slightly more than 10,000 MW – higher than the midday low.

This inversion from historic patterns may become common, ISO-NE said, because it expects the amount of behind-the-meter solar power – that is, panels that don’t send power into the grid but are used locally, serving to reduce demand on the grid – to more than double to 5,800 megawatts by 2027. “The ISO anticipates more occasions when demand may dip extremely low, particularly during the spring and fall …. Demand is typically low already during those seasons, and conditions are ripe for high solar output.”