Under extreme heat, the largest U.S. power grid sees record electricity demand.

Persistent heatwaves in the eastern United States are pushing the nation’s largest power grid to its limits. The electricity demand of PJM Interconnection on July 2 is likely to break the historical record set in August 2006; meanwhile, the risk of blackouts is rising, electricity prices are soaring, and the grid’s vulnerability is again drawing widespread attention.

On July 4, Bloomberg reported that PJM Interconnection LLC covers 13 states from Washington, D.C., to Chicago, serving a population of 67 million. The grid stated that demand on July 2 is likely to exceed the previous historical peak of 165.563 gigawatts. The U.S. Department of Energy has ordered all generating units to operate at maximum capacity, including backup power—this is the second time this summer that the emergency measure has been triggered.

The shock from the heat has already reached daily life and the markets. New York City’s power utility, Consolidated Edison, temporarily cut power to nearly 10,000 users in the southwestern part of Queens due to equipment failures, and asked tens of thousands of users to voluntarily reduce their electricity use. In some parts of the PJM region, electricity prices this week briefly surged to more than $2,500 per megawatt-hour on Monday. More than 197 million people are under extreme heat warnings or heat advisories, spanning from Kansas to Maine.

PJM Grid Under Pressure, Demand Approaching Full Capacity

This week, PJM has issued a series of emergency alerts. If demand on July 2 is ultimately confirmed to be a record, it would mean the grid’s operating load will exceed 90% of its capacity. However, as temperatures rise, there is a shortfall in some generation capacity—about 9.5 gigawatts of generating units are offline in the Mid-Atlantic region, including those concentrated in data centers in Northern Virginia. One gigawatt is equivalent to the installed capacity of a traditional nuclear power plant.

Notably, PJM had previously said that setting a summer demand record is “unlikely, but not impossible.” Official final data can only be confirmed after a 60-day accounting of demand response resources. On Thursday, data showed instantaneous load between 5 p.m. and 6 p.m. was approximately 162.7 gigawatts, though that figure was somewhat suppressed.

On Friday, as holiday travel leads to some pullback in electricity demand, overall electricity use is expected to ease slightly; however, with hot and humid conditions persisting, cooling demand may rise again. Sustained high-load operation will further increase the risk of failures in power-generation equipment and critical infrastructure.

Reports say, a severe heatwave has been lingering across the eastern United States this week, bringing triple-digit Fahrenheit temperatures to multiple cities. In New York City, the temperature in Central Park hit 98 degrees Fahrenheit (36.7 degrees Celsius) on Friday afternoon, while on Thursday the city reached 100 degrees Fahrenheit—its highest level since 2012. Weather forecasts indicate that hot and humid conditions are expected to continue throughout the weekend, covering the eastern half of the United States.

The heat also directly affects Independence Day celebrations. The “U.S. Great States Fair” held at the National Mall in Washington—a two-week patriotic-themed festival—was forced to close for several hours on Friday due to the heat. Organizers said on social media that the event will resume in the evening.

Frank Pereira, senior forecaster at the U.S. Weather Prediction Center, said, “Today’s weather will be quite difficult,” and noted that temperatures from the Plains and the Midwest to the Mid-Atlantic and the Northeast are “well above normal.”

Data Center Expansion Combined with Extreme Weather Structurally Intensifies Grid Pressure

This heat crisis is not an isolated incident; it reflects deep structural pressures facing the U.S. power grid. Before this round of heatwave hit, major U.S. power grids had already been under sustained pressure due to the data center construction boom—an expansion wave that broke the two-decade-long period of stagnation in electricity demand. The Northern Virginia region served by PJM is at the core of the U.S. “data center corridor.”

Extreme temperature fluctuations make the grid more prone to failures during peak hours, affecting key scenarios ranging from residential air conditioner usage to power for hospital lighting. In addition to cutting power to some users, Consolidated Edison also asked users to reduce their use of washing machines, clothes dryers, and microwaves, and to use only one air conditioner if they have two.

Jigar Shah, a former U.S. Department of Energy official, said: “We need to treat grid flexibility as part of day-to-day operations, not just a tool for crisis response.” Analysts believe that this heatwave stress test will further amplify calls for power-grid reform, driving additional generation capacity and improving system flexibility.

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