So, you want to join the hipsters who are powering their electric vehicles from the sun? That's cool, but how much energy will you need, and how many new solar panels will you need to make the switch? The best way to answer this question would be to talk to your local solar panel installer, but 1BOG has some rough estimates that will help you get started. Like they say, "It's hard to add solar panels later – make sure you buy the right number up front."
In order to drive around 12,000 miles a year (the U.S. average), you'll need about 200 to 250 kWh per month, given a car with a four- or five-mile-per-kW efficiency of cars like the Mini E, the Nissan Leaf and the Chevrolet Volt. 1BOG (which stands for One Block Off the Grid) ran some numbers for driving a Leaf in Los Angeles, and figured that you'd need to install three extra 200W solar panels at a cost of $1,808 after rebates and tax credits. Given the money saved by not paying for gas, the payback time to buy these additional solar panels is about three-and-a-half years. Get all of the details here.