You may have seen news reports of cars powered by solar panels racing across the desert, showing that solar powered cars are possible. Possible but how practical?

On average about 100 Watts of power per square metre arrives at the Earths surface.
A car might be 1.6 metres wide by 5 metres long, and 1.5 metres high. These proportions are generous and the average car will be smaller than this.
The surface area of a car is then about
1.6*5+2*5*1.5=23m square metres.
The solar power incident on the car is then a maximum of 23*1.4=32.2 kW.
Not all of the Sun's radiation will be at right angles to the solar panel, because of cloud cover, time of day or because the solar panels present an angle to the sun, so the actual maximum power will be less than this.
The maximum efficiency of a solar panel is about 14% - far more efficient than photosynthesis at about 2 % - so the maximum power converted by the solar panels is 0.14*32.2-4.488KW.
A small car can develop about 50 KW.
It might seem then that solar powered cars are not practical, but is should be remembered that the figure of 50 horsepower is a maximum. With modification, 4.5 horsepower may well be able to power a small practical car at about 30mph - suitable for city driving.