We've had record-breaking temperatures in Charlotte over the last few days. During past heat waves, Duke Energy has occasionally asked people to go easy on their electricity use. That's not the case right now. People have been cranking up their air conditioners over the past few sweltering days. Duke Energy spokeswoman Paige Sheehan says that's just fine. "The system is designed for this kind of load and it's performing very well," says Sheehan. When demand for energy is highest, Duke relies on an additional set of power plants. "During the hottest time of a day we can turn a hydro facility on, run some water through those turbines and generate power instantly," says Sheehan. "The problem with hydro is that you can't run it too much because you'll run out of power." That was one of the problems during a heat wave three years ago. North Carolina was in the middle of a two-year-long drought and lake levels were too low to get much electricity from the hydro-power dams. Also, the utility had to throttle back two of its coal plants that rely on rivers for cooling. But the drought is over and the region's lakes are full enough that Duke expects all of its plants will be available to bear the load this summer.