Frigid weather -- including a record low of minus-13 degrees Fahrenheit in Denver -- was at the heart of the problem, sending power demand soaring as homes and businesses turned up their heaters.
When the weather gets that cold, it can freeze wellheads -- the equipment that controls the flow of gas from the Colorado and Wyoming fields that Xcel power plants rely on to generate about half of the company's electricity. That's what happened Saturday. Heneley said he believed it was the first time the company resorted to power cuts in the winter to avoid collapsing the grid.
The outages affected about 300,000 Xcel customers in the Denver area, with customers in Eagle, Grand Junction, Vail and Aspen also briefly losing service.
Heneley said that demand on Excel's portion of the Colorado power grid peaked Saturday somewhere between 4,100 megawatts and 4,400 megawatts, which is far off the summertime peak of 6,500 megawatts.