I carried out some research at the beginning of the year into the environmental impact of electric cars compared to gasoline cars. It is part of a bigger survey that I'm doing, measuring comparable electric and gasoline cars to monitor their real world environmental impact over a long period of time.
I'm hoping to be able to include the Nissan LEAF in the next round of testing which takes place later on this summer. The aim is to pair it up with a Ford Focus to see how both cars compare in real world tests.
The figures take into account electricity losses through the grid and the environmental impact of the batteries. They measure both the gasoline car and the electric car using the European standard measurement for CO2 emissions per kilometer (one kilometer is approximately 0.6 miles).
Here's the video of the tests: http://www.youtube.com/watch?v=dSVc2SrXVIk
The tests showed that an electric car is responsible for less CO2 than a gasoline car, even if the electric car is charged up from a coal fired power station. Granted, the carbon saving isn't as much as if it were being charged from a solar array or a wind turbine but it is at least a step in the right direction.