Summer 2025 recap: Reliability maintained as grid sees highest peak in over a decade

New England’s power grid operated reliably in June, July, and August, including during a heat wave that contributed to tight system conditions and the highest consumer demand for electricity in over a decade.

Demand peaked for the summer at 26,586 megawatts (MW) on June 24 between 5 and 6 p.m., when the regional average temperature was 97° Fahrenheit (F) and the dew point, a measure of humidity, was 67°F. The peak exceeded ISO New England’s forecast for above-average summer conditions. It was also significantly higher than last year’s summer peak of 24,871 MW on July 16, 2024, when the temperature was 91°F and the dew point was 70°F.

For the summer as a whole, temperatures averaged 70.6°F, or 0.5°F above normal. New Englanders consumed about 3% less electricity — 32,470 gigawatt-hours (GWh) in June, July, and August of 2025 versus 33,305 GWh during the same period in 2024.

Wholesale energy prices increased year-over-year, largely due to higher natural gas prices.

Reserve shortage prompts charges

Heat and humidity, high demand, and some unexpected generation reductions and outages left the region short of the resources needed to maintain required operating reserves for more than three hours around the evening peak on June 24. Power continued to flow throughout the region without interruption despite the reserve shortage. The event triggered approximately $97.1 million in charges under the capacity market’s Pay-for-Performance rules.

The rest of the summer proceeded without incident. The ISO did issue a precautionary alert July 16 in anticipation of tight system conditions during another stretch of hot, humid weather. But system conditions remained stable, and the alert was lifted the following night.

June 24’s peak demand (26,586 MW) was the region’s sixth highest summer peak since at least the year 2000. The highest summer peak before that (27,379 MW) was on July 19, 2013, when the temperature was 95°F and the dew point was 72°F. The region’s all-time peak demand (28,130 MW) occurred on Aug. 2, 2006, when the temperature was 94°F and the dew point was 74°F.

Wholesale prices up compared to 2024

Real-time wholesale electricity prices averaged $49.65 per megawatt-hour (MWh) this summer, up 33% from the summer 2024 average of $37.45/MWh. Prices were also higher in the Day-Ahead Energy Market, at $53.31/MWh, compared to $39.03 last summer.

The increases are attributable in part to the elevated cost of natural gas, the region’s primary energy fuel. Average natural gas prices for summer 2025 were $3.22 per million British thermal units (MMBtu), an increase of 80% from summer 2024, when the average price was $1.79.

Resource mix and emissions

Natural-gas-fired resources produced 59% of energy consumed in the region in summer 2025. Nuclear power contributed 22%, followed by wind and grid-connected solar at about 8% and hydroelectric power at 5%. Imports supplied about 2%, while oil and coal combined produced about 1%.

ISO New England estimates carbon dioxide (CO₂) emissions associated with the region’s electricity use through an analysis that combines data on electricity generation by fuel type with emissions factors based on US Environmental Protection Agency data and generator data reported directly to the ISO.

CO₂ emissions for the summer months increased by about 5% or 448,000 metric tons from the previous year. Nearly 300,000 metric tons of CO₂ was emitted in July alone, a result of increased generation from natural-gas-fired resources that month. July’s average temperature was 74°F, five degrees higher than both June and August. July’s energy consumption was roughly 2,000 GWh higher than the other months.

Meanwhile, emissions from oil- and coal-fired resources nearly doubled compared to last summer. Because the region’s wholesale electricity markets select the lowest-priced resources needed to meet demand, oil- and coal-fired resources tend to run more frequently when natural gas prices rise, and less frequently when natural gas prices are low.