In a regional first, the New England Independent System Operator reported May 3 that the region’s customers had used less grid electricity at midday April 21 than while they were sleeping that night.
On Saturday, April 21, the right combination of sunshine and mild weather led to light consumer demand on the high-voltage electric power system, coupled with record-high output from the more than 130,000 solar power installations in the region. The result was that midday grid demand dipped below overnight demand for the first time ever in New England.
The ISO explains that only a tiny fraction of the region’s 2,400 MW (nameplate) of solar power is sold in the region’s wholesale electricity marketplace. Instead, almost all regional solar power is distributed—generated locally or installed directly on site at retail customers’ homes or businesses. New Englanders using distributed solar power use commensurately less electricity from the regional power system. As the grid operator, ISO New England experiences distributed solar power as a reduction in grid demand, as illustrated in the graph.
ISO New England’s system operators expect such dramatic midday dips to crop up more often as more solar comes on line. Mike Knowland, ISO Forecast and Scheduling Supervisor, notes, “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.”
While distributed solar power was reducing demand, the seven large solar farms that do sell their power in the regional wholesale electricity market were at near-100% production Saturday afternoon, helping to meet the demand that remained on the regional power system. At their height, they were producing about 93 MW of their roughly 100 MW of nameplate energy production capability.