From the Annual Energy Review by the Energy Information Administration (a unit of the U.S. Department of Energy), a chart showing the sources and uses of electric power:
Via Lou Grinzo at the Energy Collective. Click through on the chart to see a larger version (or get the PDF) from EIA.
The chart is too aggregated to do detailed analysis, but good for some “big picture” looking. Grinzo offers a few comments, here are two of his remarks that seemed particularly worthy of note: “Conversion losses practically leaps off the screen,” and “Transmission and distribution losses are tiny.” As Grinzo suggests, the conventional view usually gets it backward: mostly ignoring conversion losses and often exaggerating the relevance of line losses. (See Grinzo’s post for the rest of his commentary.)
Cogeneration offers some efficiency benefits by reducing the energy wasted both in conversion and in line losses, but you can’t see that on the chart. I was surprised to see, in another table in the Annual Energy Review, that the “useful themal output” from combined heat-and-power plants (cogeneration plants) has been falling beginning about 2001. I guess I haven’t been paying attention. Is this due to the expiration of PURPA contracts? Something else? I don’t know.
Here is another chart from the EIA, this showing primary energy consumption by sector (again, click through to the source chart at the EIA for a larger version):