My favorite question. Let me start by saying my primary reason for this project is economics, I will save money – it is just a wonderful side effect that it happens to be better for the environment.
Absolutely no gasoline comes from renewable sources. In Maine (where I live) almost 50% of our electric supply is generated from non-CO2 emitting sources (wind, solar, hydro and nuclear). As time goes on this percentage will only increase.
Where I live is roughly 2000 miles from where the oil comes into the US. That means that gasoline must be transported from the Louisiana/Texas area to Maine. A heavy truck with a full load of fuel may get 10 mpg, meaning the truck will burn 200 gallons of fuel just to get the gas into my state. Then I must drive to the gas station to get the gas into my car, thereby burning more fuel. Electricity is sent directly to my home over transmission wires emitting no carbon.
The “average Joe” does not have the ability to generate their own gasoline. In time I am certainly able to install a wind generator or PV cells and generate my own electricity, reducing my dependence on the carbon emitting grid supply.
Slate did a fantastic article that compared the all electric Tesla Roadster with a 2006 Toyota Corolla. It is a very good article that goes into a fair amount of detail.