Good catch, adriantumble. Of all the energy that starts on the left, 58% of it ends up as “rejected energy” on the right. That’s huge! What does this mean? Does it mean we did a bad job and wasted a bunch of energy? Well, not necessarily. Laws of the universe (the second law of thermodynamics) say there is a limit to how much of the energy on the left we can actually use. Some of it must be rejected.
A great infographic. I found it interesting that transportation consumed the most energy, even more than residential and commercial combined. Not sure what “rejected energy” is on the right, but if it’s produced but unused energy, that’s pretty stunning too.
When talking about global energy use, a common unit to discuss is the quad. This is short for one quadrillion BTUs. In SI units that is 1.055 x 10^18 joules or 1.055 exajoules.
We’ll use the United States as an example (because data for the U.S. are easy to get). The U.S. uses 94.6 quads per year. The sources of this energy are shown on the left. 40.4% of this is used to generate electricity. The rest is used directly. The final uses are shown on the right: residential, commercial, industrial, and transportation.
You notice that petroleum is used almost entirely as a transportation fuel. If the U.S. could convert to an electric vehicle base, the flow of energy to transportation could come from the “electricity generation” box, which involves renewable sources like solar and wind. These renewables are a small fraction, but if they could be made cheaper, their fraction would increase.
