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Largest US electric grid ramps up warnings amid hot temperatures

By Thomson Reuters Jul 15, 2026 | 1:35 PM

By Tim McLaughlin

July 15 (Reuters) – Largest U.S. grid operator PJM on Wednesday issued a series of warnings as temperatures soared and transmission line congestion increased ​the spot price of wholesale electricity.

PJM, which serves ‌67 million people in the Mid-Atlantic, South and Midwest, issued warnings about low voltage and heavy energy loads on transmission lines. PJM data also showed transmission line congestion, including around northern Virginia, home ‌to ​the largest collection of data centers ⁠in the world.

On Tuesday, PJM ⁠reported that the cost to secure enough electricity supplies to cover the highest-demand days on the grid would be more than $16 billion, according to its latest annual ​capacity auction results. But without price caps, the cost would have been nearly $30 billion, PJM said.

The auction fell ⁠short of meeting PJM’s reserve ⁠margin target by about 7 GW, weakening ​the grid’s buffer against wild weather and other unforeseen events.

“This year’s ​auction confirms an unacceptable trend: data center load ‌growth is outpacing new electricity supply, degrading reliability, and keeping prices at the cap,” said Claire Lang-Ree, a climate and energy advocate at National Resources Defense Council.

For Wednesday, PJM ⁠forecast electricity demand would reach 164.1 gigawatts about 6 p.m. EDT as air conditioning use surged. Temperatures in PJM’s region hovered ⁠around 90 degrees ‌Fahrenheit (32 degrees Celsius) in Chicago, Philadelphia ⁠and Washington, D.C., for example. PJM set an-all ​time ‌demand record of 168.2 GW on July ​2.

With heavy ⁠transmission line congestion, spot electricity prices surged to more than $300 per megawatt hour around noontime Wednesday. Earlier in the day, prices were around $30 per MWH, before residents and businesses cranked up their air conditioning use.

(Reporting By Tim McLaughlin, Editing ​by Nick Zieminski)