With apologies to Arthur Conan Doyle, of course.
The Department of Energy estimates that American energy usage will grow only 10% in the 25 years to 2040. As noted previously, this is despite a projected near doubling of GDP, a 20% increase in population, a 30% increase in vehicle miles traveled and much more.
They expect the number of households to increase from 115 million to 143 million, a 25% increase. They expect the square footage of new houses to climb from 1,686 sq. ft. to 1,858. But they expect residential energy consumption to climb by less than one quad, from 20.73 to 21.48 quads.
The DOE expects the industrial and agricultural sectors combine to grow from $6.616 trillion to $10.994 trillion by 2040, a 60% increase. But they expect energy consumption in the two sectors to grow from 26.81 quads to 33.53 quads, only 25%.
The explanation is simple, if not entirely credible. They expect energy intensity, as measured by thousand BTU per 2005 dollar in GDP to drop from 6.79 to 3.99 between now and 2040.
I hope to post soon on the plausibility of this.
3000 Quads 
They are expecting to have higher energy prices, with energy taxes to push down consumption.