But what about charging it?
The problem with this, and any other electric car, is that at some point you have to charge it up. And right now when you do that you're probably burning coal/gas/oil to generate the power, so you're still chucking a load of CO2 into the atmosphere.
Until we sort out clean power generation the electric car is not going to be a practical solution - biofuels and hydrogen are the way forward in the meantime.