BOSTON—PJM, the largest U.S. electric grid operator, on Wednesday detailed price spikes and warnings of massive transmission line congestion as it braced for record-breaking demand driven by a heat wave ahead of July 4 celebrations.
Spot wholesale electricity prices Wednesday afternoon surged to more than $600 per megawatt hour in PJM's Virginia zone, home to the world's largest collection of data centers. Earlier in the day, prices were about $40 per MWh before temperatures soared toward 100 degrees Fahrenheit.
Demand on the grid topped 160 gigawatts on Wednesday afternoon, approaching an all-time high. PJM's record of 165.5 GW is expected to be broken on Thursday evening, according to PJM forecast data.
PJM serves 67 million people in the Mid-Atlantic, South and Washington, D.C. areas. Even before this week's heat wave, PJM had been straining to overhaul a system pushed to the brink by surging energy consumption by data centers and electric vehicles.
The grid operator on Wednesday afternoon issued an alert asking power plants to maximize their output and to review whether any generators offline can be fired up for service.
PJM's low-voltage alert signaled that the risk of rotating outages is higher as voltage levels on transmission lines weaken. The grid operator also has forewarned power plants to bring generators out of maintenance so they can be ready to meet surging demand.
Georg Rute, CEO of Gridraven, said extreme heat, low wind and surging demand are coinciding at a time when transmission lines have the least margin for safety. That is contributing to spikes in electricity prices, as the cost of moving power rises amid heavy congestion.
Temperatures this week are forecast to hover around 100 F from Boston to Washington, near Northern Virginia’s vast data center hub, driving a surge in air-conditioning demand that will further strain PJM and other regional power grids.
New York ISO (NYISO), the grid operator for New York state, asked electricity customers to moderate their use of air conditioning and major appliances. NYISO is preparing for Thursday demand of more than 32 GW, just shy of the record set in 2013 of 34 GW.
PJM's biggest test will come about 6 pm EDT on Thursday when grid demand is expected to be 166.3 gigawatts. That would break an all-time demand record set 20 years ago, according to PJM's latest forecast.
To meet unexpected shortages, PJM reported 18 GW of reserve power resources that can be brought online within 30 minutes.
Spot electricity prices will likely spike to more than $1,000 per MWh Wednesday evening as PJM operators manage congested power lines around Virginia's data center hub and dispatch expensive power plants mainly fueled by gas and coal to meet the day's highest electricity consumption.
Coal plant generation this week has produced up to 22% of PJM's electricity supply, with output approaching 28 GW. That's about 75 percent higher than the average so far in 2026, according to PJM generation data.
In the Midwest, another record for electricity demand could be broken as early as Wednesday evening. Forecasts by the Midcontinent Independent System Operator (MISO), the regional grid operator for 15 U.S. states in the Midwest and the South, indicate that the demand record of 127.1 GW could fall.