According to ISO-NE, New England now increasingly experiences the "solar duck curve", as growing amounts of solar generation depress demand for grid power on sunny days, driving the need for other fast-ramping resources to come online to meet consumer demand as the sun sets. The "duck curve" name comes from traditional graphs depicting how behind-the-meter solar affects demand for grid electricity, such as this one prepared by ISO-NE for the Easter 2023 record low:
Historically, demand for electricity peaked during the midday and evening, and was lowest at night. While underlying consumer demand for power is changing somewhat, change is occurring even faster for the wholesale power system, as growing amounts of behind-the-meter solar photovoltaic (PV) generation reduce the need for other power plants to operate while it's sunny. ISO-NE reported first seeing the "duck curve" indicating grid demand was lower in the afternoon than overnight on April 21, 2018. At the time, solar power exceeded 2,300 megawatts for the first time.
Historically, demand for electricity peaked during the midday and evening, and was lowest at night. While underlying consumer demand for power is changing somewhat, change is occurring even faster for the wholesale power system, as growing amounts of behind-the-meter solar photovoltaic (PV) generation reduce the need for other power plants to operate while it's sunny. ISO-NE reported first seeing the "duck curve" indicating grid demand was lower in the afternoon than overnight on April 21, 2018. At the time, solar power exceeded 2,300 megawatts for the first time.
In 2018, the grid operator could see what was coming next:
ISO New England’s system operators will remember April 21 as a milestone for electricity demand in New England, with these dramatic midday dips expected 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.”
More behind-the-meter solar continued to be added to the system. By April 2021, ISO-NE reported that solar power had reduced grid demand enough to produce the duck curve 26 additional times, like this example from March 27, 2021.
Prior to April 2023, the region's previous record low occurred on May 1, 2022, when mild temperatures, sunny skies, and a Sunday combined to yield a grid demand of 7,580 megawatts, which was then the lowest demand for grid electricity on record in New England since ISO-NE began operating the system in 1997. For the 2022 record low, ISO-NE estimated that behind-the-meter solar resources produced over 4,000 megawatts of electricity, while grid demand dropped below 7,600 megawatts. On May 5, 2012, the grid operator said that New England had already seen nearly as many “duck curve” days, during which demand from the bulk power system is at its lowest in the afternoon hours and not overnight, in 2022 as in all previous years combined.
By the end of 2022, ISO-NE had tallied 45 duck-curve days for the year, more than the previous four years' combined total. The grid operator has said that this "points to the growing contribution of BTM PV to New England's energy mix -- particularly in the spring, when solar production is at its strongest."
Behind-the-meter solar continues to be installed across New England. For the April 2023 low, ISO-NE estimates even greater production from behind-the-meter solar generation, exceeding 4,500 megawatts throughout much of the afternoon. This changes the shape of the duck curve. Comparing duck curves over time, the depth of the "belly" of the duck is trending upward, as larger amounts of behind-the-meter solar resources come online (and come offline). In addition to deepening the duck's belly, the frequency of duck-curve days is expected to continue to increase; according to the grid operator, the region is on pace to set another new record for the number of duck-curve days in 2023.
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