January 26, 2024

Monthly wholesale electricity prices and demand in New England, December 2023

Prices down in both day-ahead, real-time markets in December

Wholesale power prices averaged $37.15 per megawatt-hour (MWh) in the Real-Time Energy Market in December 2023, down 69% compared to the previous year.¹ Day-Ahead Energy Market averages were $38.14/MWh, down 67% from December 2022.

By the numbers

December 2023 and Percent Change from December 2022 and November 2023	December 2023	December 2022	November 2023
Average Real-Time Electricity Price ($/megawatt-hour)	$37.15	-69.4%	0.4%
Average Natural Gas Price ($/MMBtu)	$3.22	-76.8%	-6.7%
Peak Demand	17,702 MW	-1.4%	2.6%
Total Electricity Use	10,023 GWh	-3.7%	9.3%
Weather-Normalized Use²	10,573 GWh	0.5%	16.7%

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 52% of the power produced in 2022 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 December was $3.22 per million British thermal units (MMBtu).³ The price was down 77% from the December 2022 average Massachusetts natural gas index price of $13.86/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, 2003-2023

Electricity demand

Demand is driven primarily by weather, as well as economic factors. Energy usage during December decreased 3.7% to 10,023 GWh, from the 10,405 GWh used in December 2022.

The average temperature during December was 39˚ Fahrenheit (F) in New England, up 4˚ from the previous December. The average dewpoint, a measure of humidity, was 31˚F in December, up 7˚ from the previous December. There were no cooling degree days (CDD) during December, which is typical for New England.⁴ In December 2022, there were 0 CDD. There were 812 heating degree days (HDD) during December; the region’s normal number of HDD for the month is 995. In December 2022, there were 932 HDD.

Consumer demand for electricity for the month peaked on December 7 during the hour from 5 to 6 p.m., when the temperature in New England was 31°F and the dewpoint was 17°. Demand reached 17,702 MW. The December 2023 peak was 1.4% lower than the December 2022 peak of 17,956 MW, set during the hour from 5 to 6 p.m. on December 12, when the temperature was 30°F and the dewpoint was 16°.

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 dewpoint 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 dewpoint 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 79% of the 8,391 GWh of electric energy generated within New England during December, at about 53% and 26%, respectively.
Renewable resources generated about 11% of the energy produced within New England, including 5.2% from wood, refuse, and landfill gas; 3.7% from wind; and 1.8% from solar resources.
Hydroelectric resources generated 10.2%.
Coal resources generated 0.3%, while oil-fired resources generated 0.1%.

The region also received net imports of about 1,741 GWh of electricity from neighboring regions.

December generation in New England, by fuel source

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

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

New England power plants produced an estimated 2.39 million metric tons of CO₂ in December 2023, a 5.5% decrease from the previous December.

Estimated CO₂ emissions from natural gas-fired plants—typically the largest source of emissions, due to the significant amount of power these resources produce—rose 21% year over year, from 1.44 million metric tons to 1.74 million metric tons. These resources accounted for 73% of the power system’s estimated emissions.

That increase was offset by a 93% decrease in estimated emissions from oil- and coal-fired resources, which produced less electricity for the month due in part to the year-over-year drop in natural gas prices. Together, oil- and coal-fired resources produced an estimated 33,484 metric tons of CO₂ in December 2023 (about 1.4% of the total), compared to more than 450,000 metric tons in December 2022. 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 are high, and less frequently when natural gas prices are low.

CO₂ emissions from other resources—mostly refuse and wood—were estimated at 611,964 metric tons, down 2.7%% from December 2022. These resources accounted for about 25% of the power system’s estimated CO₂ emissions for the month.

¹One 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.

²Weather-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.

³A 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.

⁴A 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.

⁵The factors used to calculate estimated CO₂ emissions were updated in January 2023. 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.