Solar panels provide very low voltage, you would either need a lot of them and I mean more than 100 or build some DC to DC voltage converter, either way definitely not worth it. On the other hand it would be easier, less expensive and beneficial to recharge 12 v battery, actually this would make a lot of sense if you don't drive your car for weeks at the time, since smart key and computers are constantly discharging 12 v battery, even when the car is shutdown. Another solar project you could try would be to have solar powered fan, keeping the car cool when parked in sun. This would have similar effect as charging traction battery: you don't need as much AC to keep temperature low and keeping inside temp of the car lower, would make traction battery being used more efficiently.