????
By approximate you mean lose signifcant energy?
A car is a closed manifold. Take the area it casts a shadow on - that is the area a solar tracker would get ~100% of the sun's flux. A general closed manifold (which is prefect for a car since the car and sun will move) will get ~50% of that energy. That's pretty massive.
A simple way to compute exactly 50% loss is for the area of a shadow from a sphere - a tracking disk with that area would get pi * r^2 of the energy. A sphere with the same shadow would get 50% of that (set up, integrate).
Do you even check these claims?
Of course you'll fixate on a sphere vs a car, but make any closed manifold, let the sun move throughout the day, and you will end up with pretty much the same result (via theorems on total curvatures on closed manifolds stuff).
Solar options on EV’s will always be niche. Probably less than 20% of people would see significant benefits. However, as the percentage of EV owners increases that ratio should stay the same. 5% of EV buyers (themselves 5% of car buyers) the market isn’t very many people. However if EV’s made up 75% of new cars then 5% of that is a more significant market segment.
For now I suspect cars with an extreme focus on solar will flop. But, a base model with modest styling compromises and 2 levels of solar options roof vs every surface could be quite popular. In the short term a solar on a van seems to be the obvious option with the smallest compromise. It’s stick with large nearly flat surfaces to maximize internal volume, so why not toss in solar.