On August 26, amidst broiling heat across the Midwest, the Midcontinent Independent System Operator (MISO) issued a maximum generation event with power demand soaring to 122 gigawatts (GW). MISO – with service territory stretching from Louisiana up through Minnesota – needed every megawatt of power it could generate and then some. MISO even needed to import eight gigawatts of power from PJM, enough to meet the demand of six million homes.

In moments of peak demand, it’s instructive to see which resources rise to the occasion. So instructive it caught the attention of the Federal Energy Regulatory Commission’s (FERC) Mark Christie who took to Twitter with analysis of what kept the lights on and what that reality should mean for the nation’s energy policy.

In MISO, coal and natural gas supplied roughly 70% of demand during the heatwave’s most intense hours. Together with nuclear power, these dispatchable resources met 90% of demand when it was needed most.

On the PJM grid next door, where demand reached 148.3 GW, dispatchable resources also met 90% of demand.

As Commissioner Mark Christie observed, highlighting the importance of dispatchable capacity, “MISO and PJM expect substantial retirements of dispatchables in coming years, and that’s before impact of EPA power plant rule, which will force many more.” He continued, “Two lessons: 1. Loss of dispatchables threatens reliability. 2. Interregional transmission supports reliability IF there is surplus power to transmit, but if neighboring grid operators lean on each other for imports, both fall down when neither has surplus power to export.”

As Christie has warned again and again – and pointed out here – the very resources that are doing the lion’s share of work during both summer and winter peaks in power demand are the very resources targeted by the U.S. Environmental Protection Agency (EPA) for closure.

Regulatory Policy is the Largest Threat to Reliability

EPA has come for the coal fleet with a suite of rules that would wipe out the vast majority of the nation’s plants by 2032 and is using unachievable technology mandates to make it all but impossible to add new coal or natural gas baseload generation. EPA is also now teeing up a rule to go after the existing natural gas fleet.

Where exactly EPA expects grid operators to get the power they need in the years ahead remains a mystery. For their part, the grid operators have made it abundantly clear EPA’s rules are unworkable and are going to leave them woefully short of needed capacity.

There are no silver bullet solutions to replace the critically important GWs provided by the nation’s coal fleet, or meet the soaring new demand coming from electrification, robust industrial activity and the explosive growth of power-hungry data centers.

While renewable capacity is growing rapidly, the delta between nameplate capacity and what these resources can provide during periods of peak demand is startling.

Windless summer days – as MISO saw on August 26 – along with roasting temperatures that stretch into night – when the sun isn’t shining but people crank up their air conditioning and plug in their EVs – can leave tens of billions of dollars of investments in wind and solar resources all but useless when they’re needed most. And as Commissioner Christie underscored in his tweets, vast new transmission infrastructure – should it actually be permitted and built – can only come to the rescue if neighboring grids have excess power to export. If both MISO and PJM are short of power during peak summer or winter demand, as the grid operators project they will be, there will be no cavalry to ride to the rescue.

Summer and winter peaks are a critical test for our energy systems. Utilities and grid operators build for just these moments. But as their hands are tied by EPA rules that don’t reflect on-the-ground reality, their jobs are becoming all but impossible. The bottom line is this: government policy has now become the single largest threat to grid reliability.