Nothing stops anyone from doing this, except that it's ineffective. See comments here https://news.ycombinator.com/item?id=46455027 https://news.ycombinator.com/item?id=46454978

This guy's impractical homebrew rig gets "20 to 30 miles per day" when unfolded and the car is not in motion. That unfolding is necessary as there just isn't enough surface area on a car roof to make it worthwhile.

https://www.dartsolar.com/

https://www.reddit.com/r/TeslaLounge/comments/194ajsm/my_tes...

It's still far more practical to 5x or 10x the number of solar panels, mount them on a fixed structure like a house roof, where they never have to be folded or moved around, and park the car next to it, to charge.