Continued installations of consumer-sited solar power have poised New England for a new record number of "duck curve" days, or periods when wholesale demand for grid electricity is lower during the middle of the day than during the night. The shift has consequences for the rest of the grid, including on the portfolio of other generating resources needed to meet demand, related emissions, and power pricing.
Historically, consumer demand for electricity has been highest during the day and lowest during the night, based on household, business, and other social patterns of energy use. But as behind-the-meter solar generation was added to the system, midday demand for grid power was reduced. On April 21, 2018 -- a mild sunny day on a spring weekend -- conditions combined to cause grid demand to be lower at midday than at night. Based on graphs showing grid demand reduction in yellow, such as the chart below produced by ISO New England, this phenomenon has become known as the "duck curve".
Since 2018, the duck curve phenomenon has become more frequent, as shown in this chart produced by ISO-NE.
In 2024, the region experienced 107 duck curve days -- a new record. So far in 2025, ISO-NE reports 100 duck days, with a projection to exceed last year's record by the end of December.
The "duck curve" is also reaching new depths of midday load. On April 20, 2025, system demand reached an all-time low of 5,318 megawatts -- which the grid operator projects to be less than half the level of load it would have seen without behind-the-meter solar.
With midday behind-the-meter solar producing power, other grid resources need to ramp down their production to keep supply and demand in balance -- and then need to ramp back up as midday sun fades. This requires the grid operator to ensure a sufficient volume of dispatchable generation capable of responding to these shifts, like natural gas-fired power plants (or large volumes of energy storage which have not yet materialized in the region).
