A severe heatwave affected the eastern United States in late June 2025, breaking numerous temperature records and pushing electricity demand in PJM and MISO to the highest levels in nearly a decade, with peak hourly demand reaching 160.6 GW in PJM and 116.4 GW in MISO. A new report by Energy Ventures Analysis on the Operation of PJM and MISO Power Grid During the June 2025 Heatwave shows that despite significant stress on grid operations, system reliability was maintained through the full dispatch of available thermal resources. Below are the key findings of the report:
- Coal and Natural Gas Were the Backbone of Reliability: Coal and natural gas generation were indispensable during the event. In PJM, coal output more than doubled (from 14.5 GW to 31 GW) and gas increased by 70% (from 41 GW to 71 GW). MISO Central saw similar trends, with coal and gas capacity factors rising to 63% and 60%, respectively. These resources provided the majority of the incremental generation, helping to balance the system when electricity demand peaked and variable renewable generation was unable to respond due to time-of-day and weather limitations.
- Impending Retirements Threaten Future Response Capability: A critical portion of the coal fleet that operated during the heatwave is slated for retirement by 2030. In every region analyzed (PJM, MISO Central, MISO North, and MISO South), the remaining coal units would have been unable to match the coal generation level achieved during the most recent heatwave. Without adequate firm replacements, extreme future events may result in electricity shortages and reliability emergencies.
- Extreme Price Volatility Highlighted System Constraints: Real-time prices surged. LMPs at PJM’s Western Hub peaked at $1,904/MWh, and MISO’s Indiana Hub hit $1,046/MWh, compared to typical June averages below $30/MWh.
- PJM’s Export Capability Was Severely Reduced: Historically, PJM exports ~5 GW during summer months. During the heatwave, exports fell below 1 GW as internal needs consumed all available generation—a sharp departure from prior years and an indication of tightening margins for regional reliability coordination.
We encourage you to read the full report here: Operation of PJM and MISO Power Grid During the June 2025 Heatwave