PJM Hit 162,401 MW in the June Heat Wave, Its Highest Peak in 14 Years, as Prices Spiked Past $1,300/MWh

A heat wave that settled over the eastern United States in the last week of June pushed electricity demand in the PJM Interconnection to levels not seen in 14 years. PJM, which operates the grid and wholesale market across 13 states and the District of Columbia and serves about 67 million people, reported preliminary hourly peak loads of 161,770 MW on June 23 and 162,401 MW on June 24, both between 5 p.m. and 6 p.m.

Those are the third- and fourth-highest peak loads in the operator's history. At the June 23 peak, EIA data show that natural gas supplied 44% of PJM's generation, nuclear 20%, coal 19% and solar 6%, with the rest from hydro, wind, oil and other sources. PJM issued a Hot Weather Alert on June 19 covering June 22 through June 26, and required generation and transmission owners to defer scheduled maintenance and return units to service.

PJM deployed demand response in select zones on June 23 and June 25 and across its whole footprint on June 24. Generator outages ran about 5 GW higher than PJM had assumed in its summer outlook, according to the operator. PJM's executive director of system operations noted that the temperature-humidity index, which combines temperature and humidity to measure heat stress, reached 84 across the footprint on multiple days and stayed there for hours at a time.

Humidity matters for electricity demand because it affects how hard air conditioners work and how long they run. PJM attributes the higher peaks to a combination of extreme heat and growing demand from data centers. Data center load is relatively flat across the day and the year, so it adds to the baseline on which weather-driven demand sits. The heat wave came weeks before PJM's capacity auction for the 2026 to 2027 delivery year, scheduled for July.

The timing of the peaks, between 5 p.m. and 6 p.m., and the price spike at 7 p.m. on June 23 reflect a pattern that grid operators see increasingly in summer.