Unusually hot weather this week created two of the highest electricity use days of the year in the 13-state region served by PJM Interconnection, operator of North America's largest electric power grid. Demand response, consumers' voluntary reduction in power use, played a vital role in keeping the power grid stable and air conditioners running.

Although September typically brings lower temperatures and lower demand for electricity, soaring temperatures this week pushed electricity use to record levels for the month. Demand for electricity Tuesday and Wednesday was higher than any day this summer except July 18.

Consumer use of electricity on Tuesday reached a record-setting 144,370 megawatts. To put it in perspective, under non-severe weather conditions, one megawatt could power roughly 800 to 1,000 average-sized American homes. Electricity use was headed even higher on Wednesday until PJM called for demand response.

Through demand response, customers voluntarily reduce their electricity use in exchange for payment. An estimated 5,949 MW of demand response resources (the largest amount of demand response PJM has ever received) were called on Wednesday, comparable to five nuclear plants or generators. Demand response resources act like generation resources on the system.

"Generation performance and demand response played significant roles in balancing the supply and demand on the grid during unusual conditions this week," said Andy Ott, PJM executive vice president – Markets.  "PJM continues to see the value and success of demand response participating in PJM markets."

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

Tuesday's unusual, extreme heat, combined with local equipment problems, created localized emergency conditions in Indiana, Michigan, Ohio and Pennsylvania.  PJM was forced to direct local utilities in those areas to immediately and temporarily reduce demand by small amounts to avoid the possibility of an uncontrolled blackout over a larger area that would have affected many more people.

Of the 144,370 MW being served on Tuesday, an estimated 150 MW were cut back to keep the grid stable.

9/16/2013