Electricity demand in the eastern and midwestern United States increased in June as a heatwave settled across the Midwest, mid-Atlantic, and Northeast regions of the United States.
Demand across the Eastern Interconnection—which covers much of the mainland United States east of the Rocky Mountains except Texas—peaked at 502,670 megawatts (MW) in a single hour on June 21, compared with the hourly June peak of 467,609 MW in 2023.
Areas within the Eastern Interconnection set or neared record temperatures for June. Bangor, Maine, reached 96 degrees on June 20, a temperature not seen since 1931. In the Philadelphia, South Jersey, and Delaware area between June 19 and June 24, 20 heat records were broken. The Baltimore–Washington D.C. area also saw record breaking temperatures on June 22 and 23. Weather is a large driver of electricity demand in the United States, especially in summer months when homes and businesses use electricity for air conditioning.
The Eastern Interconnection consists of multiple Independent System Operators (ISOs) and Regional Transmission Operators (RTOs), which manage electricity dispatch across large areas. Of these, PJM, the Midcontinent Independent System Operator (MISO), the Independent System Operator for New England (ISO-NE), and the New York Independent System Operator (NYISO) were most affected by the recent heatwave.
Electricity demand in the PJM region, which covers a large area from New Jersey to Illinois, peaked at 147,976 MW on June 21, 19% more than the June hourly peak demand last year. During the heat wave, peak electricity demand each day was between 1% and 24% more than the maximum of any June day in the previous five years. PJM forecasted peak summer demand in its 2024 PJM Summer Outlook to be 151,000 MW.
PJM posted multiple alerts and warnings that were in affect from June 17 to June 26, so transmission and generator operators could be aware of areas of potential grid instability and could take steps to avoid cutting electricity to customers.
Although overall demand in the Midcontinent Independent System Operator (MISO) area did not peak, the northern part of the operating area experienced more demand than usual. Observed temperatures in Detroit, a demand center in the typically cooler northern portion of MISO, were higher than observed temperatures in New Orleans, a typically warmer demand center in southern MISO on June 17, 18, 19, and 22. It was hotter in Madison than in New Orleans on both June 17 and 18. Demand for electricity in the northern part of MISO (Wisconsin and Michigan) exceeded demand in the southern part (Arkansas, Mississippi, and Louisiana) for every hour of June 18 through midday June 20.
The heatwave also affected the Northeast. Demand in the ISO-NE electric grid territories peaked on June 20 at 23,266 MW, and NYISO peaked on June 21 at 28,245 MW. Both of these amounts neared last year’s peak summer demand for these territories and the peak summer demand forecasted in their 2024 summer assessments. ISO-NE forecasted peak summer demand to be 24,553 MW, and NYISO forecasted peak summer demand to be 31,541 MW.
