By the way, reading about the 2KW solar panel made me wonder just how short of a "solar powered" car that leaves us.
If you take the "Smart" car, which will actually seat two adults and a sack lunch (but has the lamest excuse for a transmission I have EVER seen), my best guess is that it would be usable at 60hp. That's what a British roadster had back in the 50s. That translates to about 44 KW. or TWENTY-TWO "Prius roofs." (Cover a flatbed trailer with cells, then see whether the car can pull it?)
Now, let's say we improve energy storage -- batteries, solar hydrogen for fuel cells, compressed air, high-speed flywheels; anything that can store juice and release it on demand. It makes marginal sense to cover the side of a building to get that 44 KW for "free" and store it somehow, maybe; but putting the cells on the car is a losing proposition for anything but accessories and ancillaries, such as the A/C.
Gasoline and diesel are damn hard to beat for high-density energy storage, especially if you prefer your fuel to remain conveniently liquid at room temperature and normal atmospheric pressure.