Just thought I would add my experience with my Volt. They car is fun to drive on top of all the savings.
28,741 total miles (EV and gas miles) so far and we have not needed one oil change yet. This also adds up in the savings.
Someone did put PV on a gen1 Prius, and a recent article was out for a converted classic VW van with a system.
It just isn't worthwhile for the gains. In order not to be an aerodynamic drag, the panel needs to be installed flat, which reduces its efficiency. The power it generates results in a tiny improvement to hybrid MPG, and there will soon be affordable long range BEVs with 150+ mile ranges. Then, when the car's battery is full, the PV's potential is wasted.
Better to put them on the house where they'll reduce your electric usage, or make you some coin adding power to the grid, whenever the panel can make power
I believe the leaf has a small panel on the roof, that aids the use of the electronics in the car, therefore less battery usage. It's too small to be considered as a way to top the battery up, but in the near future I can imagine panels being the entire roof length and possibly on the doors/bonnet and tailgate for when the sun is at certain angles. Maybe then if you went away for a holiday and left it on your driveway during summer, you might have a full charge when you get home!