PJM Says Data Centers Are Shrinking Maintenance Windows and Power Reserves

The lower-demand seasons that once gave PJM Interconnection room to maintain the power grid are becoming reliability-risk periods. On October 15, the grid operator said round the clock demand from data centers and other large electricity users is reducing its ability to take generators and transmission lines offline while retaining enough reserve capacity for unusual weather or equipment failures.

PJM coordinates electricity across all or parts of 13 states and the District of Columbia. David Souder, its executive director of system operations, described the new demand profile as a “12-month, 24/7 phenomenon.” Demand is growing faster than new generation and transmission capacity, he said, leaving dwindling reserves and “little room for error.”

Why constant demand changes maintenance planning

Grid maintenance depends on more than scheduling crews. A generator undergoing an overhaul cannot supply electricity, while work on a transmission line can reduce the routes available to move power from operating plants to customers. Operators therefore concentrate planned outages in spring and fall, when electricity use has historically been lower than during summer cooling and winter heating peaks.

Large data centers alter that operating pattern because their electricity consumption varies less with the weather than residential and many commercial loads. A sufficiently large block of continuous demand raises the system’s baseline, narrowing the gap between expected consumption and available generation during the very periods reserved for maintenance.

The practical tradeoff is increasingly difficult. Deferring work preserves near-term capacity, but maintenance and construction still must be completed before later peak seasons. Proceeding with planned outages leaves fewer resources available if temperatures depart from forecasts, another generator trips offline or transmission constraints limit where electricity can be delivered. PJM also says unusually warm and cold conditions are arriving outside their traditional seasons, further weakening the assumption that spring and fall will remain quiet.

That combination became concrete in October. PJM forecast demand at or around 111,500 megawatts for October 13 and expected to come within 900 megawatts of its reserve margin the following day, with anticipated generation outages reaching 61,591 megawatts. The Department of Energy issued an emergency order effective October 13 through October 16 after determining that emergency conditions existed in the region.

The order authorized PJM to dispatch specified generating units as needed and, as a last resort before or during the highest listed energy-emergency level, direct certain backup resources at large commercial and industrial sites to operate. It was a temporary response to elevated demand combined with extensive planned generator and transmission outages, rather than a substitute for additional permanent supply or grid infrastructure.

A connection proposal ran into a jurisdictional boundary

PJM’s longer-term challenge is deciding how quickly very large customers can connect when adequate new generation has not arrived with them. Its proposed Interim Resource Adequacy Service covered new loads of at least 50 megawatts. Qualifying customers could have connected without matching new generating capacity if they accepted possible curtailment during grid stress.

The structure attempted to make flexible service a condition of early connection. In system terms, a load that can be reduced during a shortage does not create the same firm capacity obligation as one that must be served continuously. PJM said the proposal was also intended to keep existing customers from bearing higher costs or reduced reliability as large-load demand outpaced supply.

However, the Federal Energy Regulatory Commission rejected the core framework. It found that several provisions appeared to place obligations directly on retail customers, determine which retail users would be curtailed and establish a form of retail compensation. Those matters fall substantially within state authority, even though PJM and federal regulators oversee important parts of the regional wholesale market and transmission system.

The rejection exposes a division of responsibility with direct consequences for households and businesses. PJM can identify a regional capacity problem, but it cannot unilaterally decide the retail-service priority of a data center or write every mechanism needed to shield other customers from the resulting costs. States have authority over key retail terms and curtailment priorities, while federal regulators must determine whether regional tariffs are lawful, fair and compatible with wholesale-market rules.

Existing customers face two related risks if those rules remain incomplete. New infrastructure built for large loads can create cost-allocation disputes, particularly if projected demand does not materialize as expected. At the same time, connecting firm demand without sufficient supply can consume reserves that protect the entire system during weather excursions and equipment outages.

PJM says it is working to accelerate connections for new electricity supply and is asking policymakers to address state permitting barriers outside its jurisdiction. Until added generation and transmission catch up, the immediate constraint remains physical: equipment still needs scheduled downtime, but the low-load breathing room that once accommodated it is steadily disappearing.

By Thomas Caldwell — AMI’s senior editor for mechanical and mobility engineering, covering vehicle electronics, systems integration, electrification, chassis systems, propulsion, and safety policy.