Something very unusual has been happening to the U.S. electricity sector over the past three years.

The U.S. economy keeps growing. People are buying bigger homes and plugging in ever more electronic gadgets. And yet power companies have been selling less and less electricity since 2011:

electricity sales

That may not look like a particularly steep drop, but it's a massive break from the past. Ever since World War II, electricity sales in the United States have, for the most part, gone up and up and up. They've only ever declined in a handful of years associated with nasty recessions —1974, 1982, 2001, and then again in 2008 and 2009.