One of the questions that we have been asked from users of the Plug-in Electric Vehicle (PEV) calculator is how we get the results for the carbon footprint comparison. Users that compare a high efficiency gas engine or hybrid vehicle sometimes see a higher carbon footprint with an PEV. To be fair, the calculations are only based on the EPA accepted standard carbon emission estimate for 1 kWh of electricity and the standard emission estimate for 1 gallon of gasoline. This does not take into consideration scenarios where a user could be providing his own electricity from a renewable source, such as solar energy. Nor does calculation take into consideration that electrical energy is getting cleaner year after year or that a critical mass of PEVs is needed to achieve some of the really significant energy savings possible with V2G. We are looking to add more variables into the next release of the calculators. Let us know what you think.