A post on 2GreenEnergy inspired me to talk about a flaw in Well to Wheel studies of vehicles that has been bothering me at a low level for years. Such studies attempt to quantify the emissions of vehicles based on the entire life-cycle of the fuel they use. For plug-in vehicles, this requires understanding the source of the electricity they use.
Put simply, every study I’ve read uses the average electricity generation mix. But all good economists think at the margins: The electricity going into EVs will be marginal generation: that which is built (or runs for additional hours) to meet the new source of demand. Since few new coal plants are being built in the US, and those that are here do not have much extra capacity, the marginal new electricity that will be used to power EVs will be mostly Gas, Wind, and Solar, since these dominate the mix of new generation being built, and among existing plants, only Gas has the ability to increase existing capacity factors substantially.
Since all these sources of electricity are cleaner than the average mix, studies that focus on the average utility mix understate the emissions reduction benefits of EVs. The answer may be different in China, where they are still building coal (as well as nuclear and renewable) generation at a breakneck pace.