November 5, 2025

Monthly wholesale electricity prices and demand in New England, September 2025

Wholesale power prices averaged $33.90 per megawatt-hour (MWh) in the Real-Time Energy Market in September 2025, up 6% compared to the previous year.¹ Day-Ahead Energy Market averages were $34.21/MWh, up 6% from September 2024.

By the numbers

September 2025 and Percent Change from September 2024 and August 2025	September 2025	September 2024	August 2025
Average Real-Time Electricity Price ($/megawatt-hour)	$33.90	5.6%	−17.4%
Average Natural Gas Price ($/MMBtu)	$2.02	11.6%	−20.2%
Peak Demand	17,226 MWs	1.0%	−25.3%
Total Electricity Use	8,824 GWh	0.1%	−14.5%
Weather-Normalized Use²	9,008 GWh	−1.6%	−17.7%

Drivers of wholesale electricity prices

In general, the two main drivers of wholesale electricity prices in New England are the cost of fuel used to produce electricity and consumer demand.

Power plant fuel

Fuel is typically one of the major input costs in producing electricity. Natural gas is the predominant fuel in New England, used to generate 55% of the power produced in 2024 by New England’s power plants, and natural-gas-fired power plants usually set the price of wholesale electricity in the region. As a result, average wholesale electricity prices are closely linked to natural gas prices.

The average natural gas price during September was $2.02 per million British thermal units (MMBtu).³ The price was up 12% from the September 2024 average Massachusetts natural gas index price of $1.81/MMBtu. The Mass. index price is a volume-weighted average of trades at four natural gas delivery points in Massachusetts, including two Algonquin points, the Tennessee Gas Pipeline, and the Dracut Interconnect.

Wholesale electricity and natural gas prices

Electricity demand

Demand is driven primarily by weather, as well as economic factors. Energy usage during September increased 0.1% to 8,824 GWh from the 8,813 GWh used in September 2024. The average temperature during September was 65˚ Fahrenheit (F) in New England, unchanged from the previous September. The average dew point, a measure of humidity, was 55˚F in September, up 1˚ from the previous September. There were 19 cooling degree days (CDD) during September, while the normal number of CDD in September is 34 in New England.⁴ In September 2024, there were 12 CDD. There were 48 heating degree days (HDD) during September, while the normal number of HDD in September is 96 in New England. In September 2024, there were 47 HDD.

Consumer demand for electricity for the month peaked on Sept. 6 during the hour from 3:00-4:00 p.m., when the temperature in New England was 80°F and the dew point was 68°. Demand reached 17,226 MW. The September 2025 peak was 1.0% higher than the September 2024 peak of 17,055 MW, set during the hour from 6:00-7:00 p.m. on Sept. 1, when the temperature was 79°F and the dew point was 68°.

Peak demand is driven by weather, which drives the use of heating and air conditioning equipment. The all-time high winter peak was 22,818 MW, recorded during a cold snap in January 2004 when the temperature was −1°F and the dew point was −20°. The all-time peak demand in New England was 28,130 MW, recorded during an August 2006 heat wave, when the temperature was 94°F and the dew point was 74°. Air conditioning use is far more widespread than electric heating in New England, so weather tends to have a relatively greater impact on the summer peak than the winter peak.

Monthly peak demand and total and weather-normalized energy use

Resource mix and emissions

The mix of resources used in any given time period depends on price and availability, as well as supplemental resource commitments needed to ensure system stability. Natural-gas-fired and nuclear generation produced about 84% of the 8,945 GWh of electric energy generated within New England during September, at about 57% and 27%, respectively. Renewable resources generated about 13% of the energy produced within New England, including 4.2% from wood, refuse, and landfill gas; 2.9% from wind; and 5.6% from solar resources. Coal and oil-fired resources generated 0.1%. Hydroelectric resources generated 3.1%. The region also received net imports of about 49 GWh of electricity from neighboring regions.

The mix of resources used to produce the region’s electricity is a key driver of carbon dioxide (CO₂) emissions. The ISO estimates these emissions through an analysis that blends data on electricity generation by fuel type with an emissions factor for each fuel that is based on data from the Environmental Protection Agency.⁵

September estimated CO₂ emissions in New England, by fuel source (metric tons)

New England power plants produced an estimated 2.42 million metric tons of CO₂ in September 2025, an approximately 6% decrease from the previous September.

Estimated CO₂ emissions from natural-gas-fired plants — typically the region’s largest source of power system emissions, due to the significant amount of electricity these resources produce — decreased 5% year over year, at 2 million metric tons. These resources accounted for 82% of the power system’s total emissions.

Together, oil- and coal-fired resources produced an estimated 4,569 metric tons of CO₂ in September 2025 (less than 1% of the total), up from an estimated 1,107 metric tons in September 2024. 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.

CO₂ emissions from other resources — mostly refuse and wood — were estimated at 422,914 metric tons, a 9% decrease from September 2024. These resources accounted for about 17% of the power system’s estimated CO₂ emissions for the month.

Estimated year-to-date emissions through Sept. 30 increased 3% year over year, which was largely driven by a colder winter, increased demand, and higher natural gas prices resulting in more oil- and coal-fired generation. Regional CO₂ average annual emissions from electric generation have declined significantly in the last decade. The ISO New England Electric Generator Air Emissions Reports provide a more comprehensive analysis of New England electric power generator air emissions and a review of relevant system conditions.

September year-to-date estimated CO₂ emissions in New England, by fuel source (metric tons)

1. One megawatt (MW) of electricity can serve about 750 to 1,000 average homes in New England. A megawatt-hour (MWh) of electricity can serve about 1,000 homes for one hour. One gigawatt-hour (GWh) can serve about 1 million homes for one hour.

2. Weather-normalized demand indicates how much electricity would have been consumed if the weather had been the same as the average weather over the last 20 years.

3. A British thermal unit (Btu) is used to describe the heat value of fuels, providing a uniform standard for comparing different fuels. One million British thermal units are shown as MMBtu.

4. A degree day is a measure of heating or cooling. A zero degree day occurs when no heating or cooling is required; as temperatures drop, more heating days are recorded; when temperatures rise, more cooling days are recorded. The base point for measuring degree days is 65 degrees. Each degree of a day’s mean temperature that is above 65 degrees is counted as one cooling degree day, while each degree of a day’s mean temperature that is below 65 degrees is counted as one heating degree day. A day’s mean temperature of 90 degrees equals 25 cooling degree days, while a day’s mean temperature of 45 degrees equals 20 heating degree days.

5. The factors used to calculate estimated CO₂ emissions were updated in September 2025. ISO New England analysts regularly review and refine the methodology used to develop these emissions factors, in order to reflect the characteristics of New England’s generating fleet and improve the accuracy of the estimates.