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Today in Energy

August 1, 2019

Heat wave results in highest U.S. electricity demand since 2017

hourly electricity demand in the Lower 48 states
Source: U.S. Energy Information Administration, U.S. Electric System Operating Data

Reposted August 7, 2019 to correct notation in the first figure.

From July 15 through July 22, 2019, a heat wave extending from the Midwest to the Atlantic coast brought extremely high temperatures and humidity to those regions. The high temperatures resulted in elevated demand for electricity to power air conditioners, dehumidifiers, fans, and other cooling equipment. In the hour ending at 6:00 p.m. ET on Friday, July 19, hourly electricity demand in the Lower 48 states peaked at 704 gigawatts (GW), according to data from the U.S. Energy Information Administration’s (EIA) U.S. Electric System Operating Data. Electricity demand has not been this high since July 20, 2017, nearly two years ago, when electricity demand in the Lower 48 states hit 718 GW.

Demand for electricity was relatively high throughout each day of the heat wave. Typically, electricity demand in the summer is highest midday or in the late afternoon and lowest in the middle of the night. On a typical summer night, electricity demand for the Lower 48 states is usually lower than 400 GW, but during the heat wave, nighttime electricity demand remained between 430 GW and 450 GW. For this reason, more power generating plants operated continually during the heat wave.

Although demand for power was relatively high nationwide during the heat wave, actual demand generally stayed within expectations of regional grid systems. In New England, hourly power demand peaked at 23,865 megawatts (MW) at the hour ending at 7:00 p.m. ET on Saturday, July 20. This level was lower than the New England Independent System Operator’s summer peak forecast of 25,323 MW, based on summer forecasts it made in May 2019.

Similarly, peak power demand in the Electric Reliability Council of Texas (ERCOT) region during the heat wave reached 70,177 MW on the evening of July 16, which was lower than ERCOT’s summer peak forecast of 74,853 MW, issued in early May 2019.

hourly electricity demand in selected regions
Source: U.S. Energy Information Administration, U.S. Electric System Operating Data

However, in the PJM Interconnection, which extends from the Mid-Atlantic states to the Chicago area, peak power demand was higher than the summer peak forecast that grid operators issued in early May. Hourly power demand in PJM Interconnection peaked at 152,315 MW at 6:00 p.m. CT on Friday, July 19. In early May, PJM issued a summer peak forecast of 151,000 MW. In that hour of peak demand, generators in PJM dispatched 155,263 MW of power, supplying more than 3,000 MW to adjacent grids.

By Tuesday, July 23, when temperatures had dropped, demand for electricity also subsided. On that day, demand for electricity in the Lower 48 states peaked at 589 GW, a level more consistent with hourly peak values of a typical summer day.

daily electricity demand in the Lower 48 states
Source: U.S. Energy Information Administration, U.S. Electric System Operating Data

Daily electricity demand in the Lower 48 states during the heat wave was the highest it has been so far this year, reaching a high of more than 14,000 gigawatthours on July 19, the highest daily value in nearly two years.

EIA’s U.S. Electric System Operating Data provides hourly electric system operating data, including demand, generation, and interchange, from all electricity balancing authorities that operate the electric system in the Lower 48 states.

Principal contributor: Mark Morey