[ceequof]

  (But it would be nice if the next-gen solar panels 
  installed on a car would be efficient enough to provide 
  enough power for a car drive)

You only get about 1.5KW of light per square metre, on average. A car has maybe 4-8 square metres of usable solar panel space, so guess you could get 3-6KW of power using superexpensive cutting-edge 3-junction solar panels that manage 50% efficiency.

Model S has a 310KW motor. Assume you only run it at 10% of rated power when cruising, and that's 31KW of power draw. More than that, of course, since the motor controller won't be perfectly efficient.

No way you can run a consumer vehicle on solar panels built into the body.

[WalterBright]

It can work as a range extender, though, especially if factoring in charging while you stop for a bite to eat, shop, visit the office, etc. In addition, if you're an occasional driver, it can be charged and ready to go if you simply park it in a sunny spot.

I'd pay extra for such solar panels in the roof.