If a Tesla battery is 100kWh and it gets like 350 miles - and you can get 6 hours of sun on a 350 watt panel per day on average - that means 2 panels could charge your car about once per month, right?
15kWh * (220 miles / 50 kWh) = 60 miles of charge a day.
If your commute is less than 30 miles each way you don't touch the grid to charge. Of course if you plan on getting or have an electric car you can always get a larger system.