Back of the envelop calculation : A m² of solar panel receive about 1 kW (during the day). Efficiency of solar panel are around 10-20%, so basically you get ab

Back of the envelop calculation : A m² of solar panel receive about 1 kW (during the day). Efficiency of solar panel are around 10-20%, so basically you get about 150 W/m². Given than EV have motors with power in the range of 50 to 80kW. It is at least an order of magnitude bigger that what you could get from your solar panel. So a solar panel on the roof would be rather negligible. You will never ever power a car from mounted solar panel only. An electric bicycle with a 5m² roof maybe.