PJM Interconnection issued a capacity advisory for Oct. 19, warning of tight electricity supplies as generators and transmission facilities went offline for maintenance and construction.
During the preceding week, more than 61,000 megawatts of generation capacity were out of service. That left PJM operating with only about 66% of its generating fleet available, according to David Souder, the grid operator’s executive director of system operations. More than two-thirds of the outages were planned maintenance or construction, while about 15,000 MW were unplanned, based on preliminary figures.
For data center operators, tighter power reserves can complicate plans to bring new facilities online and maintain reliable electricity supply. PJM must balance those large, steady loads against generator and transmission outages for maintenance, while preparing for winter demand.
PJM worked with generators to return about 10,000 MW to service. Souder said canceling maintenance could leave facilities unprepared for winter.
Maintenance season under pressure
In a recent post, Souder said spring and fall maintenance periods were becoming harder to manage as data centers and other large electricity customers maintained steady, year-round demand. Unseasonably hot or cold weather can also arrive earlier or last longer than expected.
The problem extends beyond PJM. “Across much of the country, the times when demand is getting close to available supply is shifting to where more spring and fall periods can be tight,” said Rob Gramlich, president of Grid Strategies.
“We are also seeing a gradual shift to winter peaking with the expansion of electric space heating and increasing frequency of polar vortex type weather incidents,” Gramlich said.
Generator retirements, delayed replacement capacity and transmission constraints also affect available supply, said Neil Osnato, founder of Persistence Analytics, a grid-analysis firm.
“The grid doesn't just need enough capacity to operate. It needs enough capacity left over to take equipment out of service, maintain it and bring it back before the next period of stress,” Osnato said.
Emergency measures and demand response
PJM issued emergency procedures on Oct. 13 and 14 to maintain sufficient generation during unseasonably warm weather. The operator also activated demand response on both days, according to Souder.
Through Oct. 14, PJM activated demand response on nine days in 2026, compared with eight days across the entire 2015-2024 period. Across 2025 and 2026 combined, activations occurred on 15 days. The figures count days when demand response was activated, not the amount of electricity curtailed.
Demand-response participants, including residential and industrial customers, are paid to reduce electricity use when called on by PJM. The operator has also restricted exports to neighboring systems during tight conditions.
“An emergency procedure can preserve reliability today without proving that the underlying system has regained its operating margin,” Osnato said.
The Department of Energy issued an order allowing PJM to direct data centers and other large electricity customers to run backup generation under specified conditions. Souder said it was the ninth DOE order of 2026. PJM had not used the authority to direct large loads to run backup generation as of Oct. 15.
DOE has also authorized generators to operate temporarily outside environmental permit limits during emergencies.
New capacity will take time
PJM is streamlining generator-interconnection reviews, developing a process to match new large loads with new supply and pursuing a Reliability Backstop Procurement to secure additional generation. FERC accepted the procurement proposal in September but suspended it for five months, setting an effective date of February 28, 2027, subject to further proceedings.
PJM also created an accelerated process for state-sponsored projects and is refining forecasts of proposed large loads. The operator estimates that about 11,000 MW of data center load is already connected to its system.
New generation and transmission projects require permitting, equipment, construction and commissioning before they can serve customers. Transmission upgrades also require work on existing lines, adding to outage-planning demands. Souder said the capacity PJM needs is not expected to come online immediately.
Shane Snider is a senior news writer at TechTarget, covering AI infrastructure, hyperscale data centers, cloud platforms, and the power and energy systems driving modern compute expansion. You can reach Shane at [email protected] or on LinkedIn.
