As June’s extreme heat pushed PJM energy demand to the third- and fourth-highest all-time peak loads, PJM worked successfully with its generation and transmission owners to maintain the reliable flow of power to customers across 13 states and Washington, D.C.
PJM coordinated reliable operations keeping fans and air conditioners on for 67 million people in its footprint amid conditions that stressed the grid at peaks over 160 GW – the highest peaks in 14 years. These efforts included extensive communications in advance and during the events
As noted in a presentation at the PJM Operating Committee July 10, reserve margins at the peak were sufficient through the hot weather that impacted the region June 22–26.
PJM made use of all the generation available and was also able to level off demand in the late afternoon by calling on customers who are paid to reduce their energy use in times of high system demand. These customers, collectively called demand response, will remain a vital resource for dealing with escalating peak energy use.
PJM anticipated these conditions in its annual summer outlook, noting that demand response could be needed to meet reserve requirements in extreme scenarios. Forecasting leading up to the event was also extremely accurate, with very low error margins on June 23–25, the hottest days with highest electricity use.
Generator outages were approximately 5 GW higher than PJM anticipated in its summer outlook, but PJM maintained its reserve requirements – an important metric to avoid power interruption and escalating emergency procedures – at all times during the June heat wave.
PJM follows a set of established procedures to prepare for hot weather events and has become increasingly proactive in providing advanced communications to transmission and generation operators, curtailment service providers (who manage demand response programs), neighboring systems and other stakeholders.
The week before the heat wave arrived, PJM required transmission and generation owners to begin deferring scheduled maintenance and return generating units to service to keep critical infrastructure online from June 21 to June 26. PJM originally issued a Hot Weather Alert June 19 for the period between June 22 through June 26 to prepare resources for the approaching weather affecting all of the PJM region.
PJM then issued a Maximum Generation Alert for the PJM RTO effective June 23 through June 25. This procedure notifies transmission and generation owners to keep equipment online and to be in a state of readiness to be dispatched, alerts neighboring regions that electricity exports from PJM may be scaled back, and indicates that demand response may be used by PJM operators if necessary.
On Monday, June 23, the heat wave produced a preliminary hourly peak load of 161,770 MW between 5 and 6 p.m. The next day, June 24, demand driven by temperatures 95 degrees and higher in many parts of the PJM region produced a preliminary peak load of 162,401 MW between 5 and 6 p.m. These represent the third- and fourth-highest peak loads recorded in PJM.
Thunderstorms with wind on Wednesday and Thursday brought cooler temperatures and lower preliminary peak loads of 153,414 MW on Wednesday and 145,918 MW on Thursday.
PJM successfully deployed demand response resources on June 23 and June 25 in select zones and across the PJM RTO on June 24, helping to reduce load by more than 4,000 MW during the most extreme peak loads.
PJM has made it clear that the system needs all available generation it can get – of all types – to help meet growing energy demand. The system will also need to make use of the load flexibility tools at its disposal, including demand response, particularly during extreme conditions and in a tightening supply and demand environment.
These supply and demand conditions have two primary causes. Power plants are retiring due primarily to state and federal decarbonization policies and economic pressures. At the same time, demand is increasing due primarily to the electricity needs of data centers that power the digital economy and artificial intelligence.
PJM recorded its all-time summer peak load record at 165,563 MW in 2006. PJM’s 2025 Long-Term Load Forecast predicts that summer peak will climb to 220,000 MW over the next 15 years. The June 24 peak of over 162,000 MW is nearly 10,000 MW higher than the 2024 peak and 15,000 MW higher than 2023. This is a result of both extreme hot weather and the growing demand from data centers. PJM’s David Souder, Executive Director – System Operations, noted that the temperature-humidity index (THI), a combination of temperature and humidity that best assesses heat stress on humans, reached 84 across the footprint on multiple days and stayed there for several hours at times. PJM has reached 85 only twice in its history.