All 45 Carolinas power plants have been operating amid a record heat wave in the Charlotte-area. And the company reported an all-time record of 18,988 megawatts of demand on August 8.
It activated the programs the following day, which was hotter, and reduced demand to 18,907.
Duke's system in the Carolinas, when completely healthy, can produce about 21,000 megawatts. But outages are commonplace, and the system could not crank out that much power all the time.
About 150 commercial and industrial customers have signed up to be volunteers to be shut off in times of high demand in exchange for power bill rebates.
"We literally interrupt the service," said Duke spokesman Paige Sheehan. "It's something they build into their business plans."
Duke was asking customers to conserve by tweaking thermostats and turning off unneeded lights. Peak demand times usually occur in the late afternoon and early evening during hot weather. Residents are returning home and businesses are still open.