Electric cars are rated in miles per kilowatt-hour. The Leaf will go about 4 miles on a kwh of energy. The Volt and C-Max are larger and go about 3 miles on a kwh.
A kwh costs about 12 cents so it costs 3-4 cents per mile to drive an electric car.
A gas powered car that gets 36 miles per gallon costs about 8 cents per mile to drive (assuming gas is $2.90/gallon). So electric cars start out with a significant $/mile cost advantage.
A solar array that produces enough energy to power an electric car 12,000 miles per year would cost $7,500 to $10,000; $5,250 to $7,000 after tax credits.
Over 10 years, that would average $525 to $700 per year for "fuel". That's 4.4 to 5.8 cents per mile. After that, no cost for your electric "fuel".