Yeah I went off Google's estimate of electric cars tend to get 3-4 miles per kWh (which I guess will actually vary massively)

And the car panel will be less optimal as the panels will be flat. Although unlike roof panels you could potentially move the car around to stay in the sun for longer.

For me, this would actually be an ideal car. I need a car for where I live, but I only use it a couple of times a week and almost always journeys of 5-6 miles or less. I'd only need to charge the car from mains in the depths of winter!