ISO New England Successfully Manages Peak Demand During June Heatwave, Highlighting Grid Resilience and BTM PV Impact
Key Insights
ISO New England successfully managed a capacity deficiency during a June 24 heatwave, maintaining grid reliability as demand peaked at 26,024 MW.
The peak demand, the highest since 2013, was mitigated by activating reserve resources and reducing exports, avoiding public conservation appeals.
Behind-the-meter photovoltaics significantly reduced the actual peak demand by over 2,000 MW, shifting it by three hours.
Despite high reliance on carbon-emitting resources during the peak, the event underscored the critical role of diverse energy sources and grid management.
ISO New England system operators successfully navigated a significant capacity deficiency on Tuesday, June 24, 2025, ensuring grid reliability across the region during a severe heatwave. Consumer demand for grid electricity unofficially peaked at 26,024 megawatts (MW) between 6 and 7 p.m., marking the highest level recorded in New England since 2013. This figure aligned closely with ISO-NE’s pre-season forecasts for above-average summer weather, though it remained below the region’s all-time peak of 28,130 MW set in August 2006.
The peak demand coincided with an average regional temperature of 95.6° Fahrenheit and a dew point of 68.0°F, driving extensive air conditioning use. Concurrently, approximately 2,550 MW of generating capability was unavailable, leading to a shortfall in operating reserve requirements. In response, ISO-NE system operators initiated measures at 5:22 p.m., including the activation of reserve resources and a reduction in electricity exports to neighboring regions. These actions included implementing a Power Caution and declaring an Energy Emergency Alert Level 1 (EEA 1), the lowest of three alert levels, to maintain the reliable flow of electricity.
Conditions improved later in the evening as consumer demand subsided and some generators returned to service. ISO New England subsequently canceled the Power Caution and EEA 1 declarations at 9 p.m. Notably, no appeals for public conservation were issued, as the short duration of the event and the availability of reserve resources sufficiently addressed the deficiency. Anticipating tight operating conditions, ISO-NE had issued a precautionary alert on Monday, June 23, advising market participants to suspend any testing or maintenance that could impact grid reliability, an alert that was canceled 48 hours later.
During the peak demand period, carbon-emitting resources supplied approximately 74% of the total energy consumed. Natural gas, the predominant fuel source in the region, maintained an average production of nearly 12,000 MW throughout the day, while nuclear resources averaged 3,350 MW. Oil and hydro resources also increased their output around the peak hour. Crucially, ISO-NE estimates that without the contributions from behind-the-meter photovoltaics (BTM PV), demand would have peaked around 3:40 p.m. at 28,461 MW—three hours earlier and over 2,000 MW higher than the actual peak. At that earlier time, non-carbon-emitting resources, including BTM PV, nuclear, hydro, wind, telemetered solar, battery storage, and demand response, collectively provided a maximum of about 40% of the region’s energy.