The alert, in effect through Wednesday, followed a request from PJM for federal emergency authority. The U.S. Department of Energy’s order allows PJM to direct power plants to operate as needed, even if that means exceeding air-pollution limits. It also lets the grid operator ask data centers and other large electricity users to switch to backup generators before PJM considers rolling blackouts or reducing electricity exports beyond its territory.

PJM told the Energy Department that demand, maintenance outages and electricity exports could leave the system within 900 megawatts of its required reserve margin — roughly the output of one large power plant. The operator said it expects generation capacity to be reduced by 62,000 megawatts during the alert and has recalled or canceled outages where it can.

The order covers a system serving about 67 million customers across 13 states, from New Jersey to Illinois and from the New York-Pennsylvania border to North Carolina. Energy Secretary Chris Wright said the measure would make additional generation, including backup power, available to help maintain reliable electricity service.

PJM spokesperson Jeffrey Shields said grid operators around the country are confronting similar pressures. Electricity demand is growing faster than new generating capacity can be added, he said, while unpredictable weather is shrinking the windows available for routine maintenance.

The alert is notable because autumn is typically a period of moderate electricity use and scheduled repairs. It is the second time this fall PJM has asked operators to keep equipment available during a forecast demand spike; the first alert came Sept. 17. PJM said that episode was driven in part by exports to areas experiencing unusual heat and by planned maintenance outages.

The supply concerns also come after PJM fell 6,800 megawatts short of its target for standby capacity in a July procurement auction. That reserve power is intended to be available during periods of peak demand.

Jon Gordon, a senior director at renewable energy industry group Advanced Energy United, said the shortfall reflects tightening supply and criticized PJM’s handling of applications from new power projects. The grid operator paused its interconnection queue from 2022 until earlier this year as it worked through a backlog and changed its process for approving projects.

PJM reopened the queue in April and accepted 811 proposed projects representing 220,000 megawatts of potential capacity. The new process gives priority to projects considered more likely to be completed, including those with land secured and financial commitments in place.

David Masur, executive director of PennEnvironment, said the current strain reflects insufficient planning. While the queue was closed, older fossil-fuel plants continued to retire, and longer manufacturing lead times for turbines and transformers have delayed new capacity, he said.

Masur and other clean-energy advocates argue that renewable power and battery storage could add supply more quickly and with less pollution than relying on emergency measures or new natural-gas plants. Emergency dispatch that allows higher pollution levels could mean dirtier power, while decisions made under tight supply conditions may also increase costs for customers, he said.

PJM says it is working with state and federal officials to expand supply, including by speeding connections for new plants and addressing state permitting barriers. The system’s immediate challenge, however, is maintaining adequate reserves while demand, outages and exports compete for available power.