US heatwave pushes regional power grids to operational limits amid record AI data center demand, forcing curtailment alerts.
The soaring temperatures pushed the Mid-Atlantic's electrical grid to the brink on Thursday, July 2, when air-conditioning demand across 13 states—combined with data centers' unprecedented electricity consumption—threatened to overwhelm the regional power supply. The situation raised the prospect of PJM, the grid operator, cutting power to hundreds of data centers in the region, forcing them to rely on diesel generators to maintain operations.
The risk was real. PJM's emergency procedures dashboard displayed more than 40 alerts and warnings throughout Thursday. At approximately 5:30 p.m., the operator issued a "Transmission Security - Emergency Use of Back-Up Generator Warning," instructing transmission owners and electric distribution companies such as Dominion Energy to "prepare" to disconnect data centers from the grid. But it never happened, according to Daniel Lockwood, a PJM spokesman.
PJM had predicted demand would reach 166,241 megawatts by 6 p.m., pushing against the grid's estimated scheduled capacity of 172,780 megawatts. Actual demand peaked at 162,569 megawatts between 5 and 6 p.m., falling short of PJM's all-time record of 165,563 megawatts set in 2006.
Despite holding the line Thursday, the heat wave required PJM to call for maximum generation and monitor demand continuously. Dominion Energy's zone, covering much of Northern Virginia, hit a maximum hourly demand of 25,217 megawatts just before 6 p.m. Thursday, surpassing the previous record of 24,678 megawatts from the January 2025 cold snap.
Auxiliary generators were ordered to full output. The City of Manassas, for example, ran 31 diesel generators from 1:30 p.m. until 10 p.m. Thursday. "Operating our peaking generators helps reduce the amount of power the city must purchase from the regional transmission system during peak demand periods and supports PJM's efforts to maintain reliable electric service throughout the region," said Ana Davis, an assistant city manager. "This is a normal operational response to a PJM system request during periods of elevated electricity demand."
The U.S. Department of Energy issued an emergency order on Tuesday, June 30, authorizing PJM to take whatever steps necessary to prevent rolling blackouts, including directing data centers to run on generators if required. The order acknowledged that shortages and surging demand were "driven primarily by data centers." PJM created emergency procedures in response but has not invoked them. "We have not issued such an emergency procedure and don't expect to; this is meant as a last resort to avoid power outages for other customers," Lockwood said.
According to the DOE order, PJM normally maintains a 26% reserve margin, but that drops to 3.8% under extreme conditions when demand spikes and generating equipment fails. The operator had also issued alerts directing utilities to halt all maintenance on power lines and generators to ensure full functionality.
Local residents and advocacy groups watched the crisis unfold with alarm. Prince William County has more than 50 completed data centers, while Loudoun County has more than 200. "It's either breathe dirty diesel particulates or risk a blackout, or, as I am predicting, we will experience both," said Elena Schlossberg, executive director of the Coalition to Protect Prince William County. "That is what I have nightmares about."