As Mainers sweltered under a heat dome last week, amped-up air conditioning and other power needs heading into the July 4th holiday spiked electricity demand across New England.

The heat wave started July 1, when the regional peak load registered 23,729 megawatts that evening — well above the 18,000 MW on a typical summer day, according to the Independent System Operator of New England.

Demand peaked last Thursday at 25,351 MW, then dipped to 24,358 MW on Friday and 21,481 MW on Saturday. By Sunday, the heat wave had passed and demand dropped to a near-normal 18,250 MW.

Central Maine Power Co., which serves more than 670,000 customers in southwestern Maine, saw peak demand surge to 1,733 MW on Thursday and drop to 1,403 MW on Sunday, a spokesperson said.

“The peak last Thursday was the highest demand so far in 2026, but it was below what we anticipated for highest demand this summer,” said Mary Cate Colapietro, spokesperson for ISO New England, a nonprofit that manages the power grid in Maine, New Hampshire, Massachusetts, Connecticut, Rhode Island and most of Vermont.

ISO New England expects to have sufficient energy supplies this summer, when the region typically sees its highest demand for electricity, Colapietro said.

Forecasted peak demand this summer is 25,228 MW in typical weather and 26,473 MW in above-average weather, she said. The grid’s capacity is about 29,000 MW. The region’s all-time highest summer demand was 28,130 MW on Aug. 2, 2006.

Very hot and humid weather could present challenging conditions, particularly if it’s combined with unexpected lost power generation, equipment breakdowns or other factors.

Changes in electricity demand also show how power use is changing, Colapietro said.

Peak use in New England is currently in the summer, but that will change as more people choose electric-powered heat pumps and vehicles, she said. By the early 2030s, the region’s highest demand is expected to be in the winter.

Growing residential or behind-the-meter solar installations are reducing energy demand in the region and pushing peak grid hours from midafternoon to early evening, when the sun is lower in the sky and solar production is reduced, according to ISO New England.

HEAT DOME BLANKETED EASTERN U.S.

Maine was one of more than 20 states caught in a massive, record-breaking heat dome that blanketed the Eastern U.S. last week. The searing weather pattern stretched from Kansas to Maine, bringing extreme humidity and dangerous heat.

Heat index values — how the air feels with humidity — soared above 100 degrees in southern and western Maine. The National Weather Service in Gray issued extreme heat warnings for much of the state.

Amid the rising temperatures, CMP saw a nearly nine-fold increase in the number of Maine customers who received high-usage alerts, said spokesperson Dustin Wlodkowski.

The company sent alerts to 122,390 customers from July 1-6, compared to 12,513 customers from June 1-6, he said.

CMP has offered the alerts for several years via email or text to help customers track electricity use. The alerts are sent when a customer’s use is 50% higher than their 30-day average for three consecutive days, Wlodkowski said.

CMP crews restored service to more than 45,000 customers who lost power from July 2-4, fixing more than 80 transformers that were disabled by strong thunderstorms or high temperatures.

The company also initiated controlled power outages to protect critical equipment, which affected a total of 3,440 customers in Kennebunkport, Ogunquit, Wells, Gray, Raymond, New Gloucester, Durham and Pownal. Most occurred on Friday. The longest lasted 5.5 hours. Customers were notified of the cause.

CMP BILLS DOWN STARTING JULY 1

Last week’s spike in power use came as CMP announced that the average monthly electric bill for its residential customers would decrease by about $11 on July 1, after the Maine Public Utilities Commission approved the company’s 2025 compliance filing in June.

The filing completed the recovery of storm repair costs in prior years, resulting in an average $8 monthly reduction in residential delivery bills. It also reduced charges related to Efficiency Maine product rebates and home upgrades, lowering bills an additional $3.

CMP transmission and distribution charges make up 48% of electric bills within its service area. The remaining 52% includes charges that fund various programs (7% of bills) and unregulated supply costs (45% of bills) paid to third-party companies that generate electricity.

In January 2026, supply costs increased by about $11 per month for a residential CMP customer with average usage who selected the Standard Offer. This year’s Standard Offer providers are NextEra Energy Marketing, New Brunswick Energy Marketing Corp. and Constellation Energy Commodities Group Maine.