The electric motor in a plug-in hybrid does not emit tailpipe emissions, but substantial emissions may be produced “upstream” at the electrical power plant. Upstream emissions for any particular PHEV will vary greatly depending on where the owner lives and when the vehicle is charged

Upstream emissions will be higher in areas where electricity is generated primarily from burning coal, lower when natural gas is used, and near zero when it is produced from nuclear, hydro-electric, wind, or solar power. Many areas get power from several sources, and the percentage of electricity produced from "clean" power can vary by season and even by time of day.

We currently provide GHG emission estimates for gasoline-only operation based on the Department of Energy’s GREET model.  EPA is in the process of developing a method for calculating a useful and meaningful estimate of upstream GHG emissions for PHEVs during electric operation. We will provide this information on fueleconomy.gov as soon as it becomes available.

The diagram below shows the fuel mix used to produce electricity in each state. This may differ from the mix prevalent for your local utility.

Net Electricity Generation by State and Fuel Source, 2009 (Gigawatt-Hours)