there are supplemental solar panels that are sold that can be roof mounted on a Prius, but those are simply to supplement the existing battery. They don't provide anywhere near the amount of energy that it would take to charge a plug-in hybrid battery. Here's an article on the technology and the company involved:
http://www.greencarcongress.com/2005...le_roofto.html
Furthermore, any of these kits, be they the solar panels or the full PHEV kits with added battery (that cost over $10k), violate the existing warranty of your vehicle's battery.
-Tim
2006 Mercury Mariner Hybrid AWD
Black with Pebble interior
Premium Package with Nav & Moonroof
Current ODO:
26,152
Typical Drive: 20 min crosstown in heavy traffic (3.5mi there and back twice a day)
532 Gallons of gas saved
That's 10,642 lbs less CO2 emitted