In any case, getting 5-10 extra miles just by parking your car under sunlight while you are shopping would be nice!
The question is the cost.
The question is the cost.
The thing they're good for is running AC in the car when it's parked, without affecting the range. (Prius does this, I think the new Ioniq 5 has this)
With 4 sq m of solar cells, 1 kW / sq m of sunshine at high noon, and 20% of conversion efficiency, it's 800 W. So it's about 2 hours to gain 5 miles under ideal conditions. Think really big shopping :)