There's something that people really fail to grasp with solar, and that's the fact there is bugger all energy in the sun, and you need a huge surface area to get any meaningful energy.
A home solar array often takes up a significant chunk of the roof area, and the amount of surface area a car typically has means that even perfectly efficient solar panels wouldn't collect enough energy to significantly contribute to the vehicle's range.
There's a good reason why vehicle manufacturers don't bother adding them.