[jakobnev]

because the only scenario solar on a car makes sense is for those who don't have reasonable access to a petrol station or mains electricity

Even with access to petrol stations it makes sense if the price of gas is high enough, from post #12:

And assuming $0.13/kWh at home we could lose this much of the potential energy and still be better off with the panel on the car than at home (assuming we are unable to plug the car in):

Europe: 83%
Hawaii/California: 65%
Texas: 38%

Of course there are more costs than just the panel, but that is also true at home.

And there is another thing going on in Europe right now, a car that emits 10g/km less CO2 has €950 less penalty applied to it, that alone would pay for a significant solar system on a car.