Re: If you are going to describe a future, make it aspirational.
Solar cells on a car roof will make no significant contribution to the power. Physics is against you here. Wrong inclination, for a start. Plus you've got the extra weight to haul around. Far more efficient to put them beside the road.
The only use I can see for solar power on a car would be for camping. The car's huge battery would be great for running a caravan, with a solar panel to keep it topped up.