The United States Uses 39% of the Energy It Produces, Wastes 61%...

This graph produced by the Lawrence Livermore National Lab is no doubt one of my favorites (others are this graph that shows the rapidly falling cost of solar, and this one that shows all solar PV efficiency records since 1975). It gets updated yearly and shows all of the main energy sources in the U.S., what they are used for, and how much of that energy goes to useful work ("Energy services") and how much is wasted ("Rejected energy"). It can seem a bit depressing at first to learn that more than half of the energy in the U.S. is being wasted, but we have to remember that the laws of physics will always prevent us from reaching 100% efficiency. But even taking that into account, there's still a huge low-hanging fruit to be harvested with measures that boost energy efficiency and cut waste. For the environment, it's often better to cut 1 watt of demand (1 negawatt) than to add 1 watt of renewable energy supply, and it often costs less too... One thing to note is just how inefficient the transportation sector's use of petroleum is. By going electric, massive gains could be made in efficiency, but it would also allow transportation to run on cleaner sources of power as we add more renewable sources to the power grid (and even dirty sources would be used more efficiently than with the internal combustion engine).