Maybe the kids are back to school, but grid operators haven’t said goodbye to summer just yet.

PJM Interconnection set a peak power record for September on Tuesday of 144,370 megawatts, with outages in Michigan, Indiana, Ohio and Pennsylvania. The power demands in PJM on Tuesday and Wednesday were higher than all but one day in summer.

The problems for the nation's largest grid operator started with unseasonably hot weather across much of the country, but were then exacerbated by equipment problems and offline generators. PJM had utilities in the affected areas of the four states cut electricity to some customers to prevent a cascading outage.

“Extreme heat in the western region of PJM resulted in record demand for September at a time when many power plants and some transmission lines were off for seasonal maintenance,” Terry Boston, PJM CEO, said in a statement. “Our only option to prevent a potential equipment overload and failures that would cause a much bigger interruption was to call for emergency relief in the form of controlled outages.”

Demand response played a vital role, according to PJM, which spreads across thirteen states. EnerNOC reported that its dispatch for this event could be the company’s largest ever as it approached about 2,000 megawatts at more than 5,000 sites. On Wednesday, PJM dispatched nearly 6,000 megawatts across its territory, the largest demand response PJM has ever seen.  

In many areas of the U.S., such as Texas and the Midwest, a relatively normal summer meant that there were few capacity emergencies. But the peak in September illustrates that demand response is increasingly needed not just in the hottest days of summer, but also for unseasonable weather, and to respond to capacity issues when generators are offline during weather events all year long.

PJM is also reinforcing transmission lines in the face or retiring coal generation in coming years to meet electricity needs.

The new peak record is far above last year’s September peak of 129,959 megawatts, although it was still below the July 18 peak of 157,509 megawatts.

The peak demand for electricity on Wednesday was 142,071 megawatts. By comparison, the peak demand for this summer on July 18 was 157,509 megawatts. Last year, the highest demand for electricity in September was 129,959 megawatts.

Source: PJM