The regional electricity grid serving the midstate and areas from the East Coast to Illinois reported its largest-ever demand response Wednesday from power customers who have signed up to reduce power if needed, grid operator PJM Interconnection said.
PJM estimates more than 5,900 megawatts of demand response resources were called on Wednesday.
Montgomery County-based PJM relies on demand response to lower usage and make sure there is enough electricity on the grid just as it does power generation sources during periods of high demand.
Customers sign up to reduce power as needed in return for financial compensation with third-party companies that PJM can call on to help lower overall consumption when supplies get tight.
The response for load reduction Wednesday, when abnormally high temperatures continued in its territory, was the largest PJM has ever received, spokesman Ray Dotter said.
Because individual customers sign up with third parties, it would be more difficult to calculate exactly how many consumers had cut back on power use under agreements, he said last week.
Last Tuesday's heat combined with local equipment problems in parts of PJM's territory led to localized emergency situations in which the grid operator had to direct utilities to cut power to some customers. It did not include the midstate, Dotter said.
PJM said in a statement that extreme heat came at a time when many power plants and some transmission lines were off for seasonal maintenance.
July's peak usage was more than 157,000 megawatts, though the July 18 figure is the only one from this summer that tops Tuesday and Wednesday of last week, PJM said.
Reported peak power demand Wednesday was about 142,000 megawatts, compared with a September record-setting figure of more than 144,000 megawatts Tuesday, PJM said.
Extra demand of more than 14,000 megawatts Tuesday compared with the month's peak usage last year was like adding a major city to the grid, Dotter said.
Typically, temperatures and demand are both lower this time of year, he said.
"You don't expect that in September," Dotter said.