A friend of mine has a solar panel on top of his old small hatchback. The car itself is petrol powered, but he has a surprisingly expansive 12V system all over the small cabin, including some Li-ion battery packs. This powers everything from a fridge to charging stations for go pro's and a raspberry pi. Before the solar panel he sometimes had to drive around the car just to recharge the li-ion batteries from the generator, but with the panel's it's essentially self sustaining.

However, the difference between powering some random electronics and actually making any meaningful impact on EV power usage is two completely different beasts...