I suggest that you ballpark how many Teslas you expect to be on the road during a given time and place (say, a 1-mile stretch of highway during rush hour), and compute how much square footage of flying solar panel you're suggesting putting into the air, assuming 100%-efficient transmission of power given the current best efficiency of solar panel. (From there it's easy to compute what it would take given less than 100%-perfect transmission.)
I'm not just being rhetorical... try it. It's fun.
I'm not just being rhetorical... try it. It's fun.