In October 2012, the BBC published an interesting article with the results of a study about comparing the life cycles of vehicles equipped with conventional engines (petrol, diesel) with those of vehicles equipped with electric motors.
This study done by professors of Norwegian University of Science and Technology (Hawkins, TR, Singh, B., Majeau-Bettez, G. and Strømman, AH (2012), Comparative Environmental Life Cycle Assessment of Conventional and Electric Vehicles. Journal of Industrial Ecology. doi: 10.1111/j.1530-9290.2012.00532.x) is available at this address
In short: where electricity is produced with only fossil fuels, the use of electric cars is counterproductive.
If we take the average European scenario, where the production of electricity from fossil fuels is partial, then there would be a benefit in the use of electric cars.
The comparison with gasoline engines would be positive as long as the electric cars have total mileages of about 100 thousand Km To have a positive comparison with diesel engines, electric cars are expected to reach total mileages of the order of 200 thousand Km
What are the basic reasons that lead to these conclusions? As reported in the study, currently the construction of an electric vehicle (and its batteries) has an overhall energy about twice the production of a conventional vehicle. And we must add a greater use of potentially toxic minerals, such as copper, nickel, aluminum.
To balance this initial disadvantage, an electric vehicle in operation must be supplied with energy produced at least partially by renewable sources. Otherwise the gap above can not be recovered.