I've personally worked on a solar car. I've got friends and idols working with international companies to bring electric cars to consumers. My line of work is in doing standard regulatable Internet and finding ways to break it. I find this thread horribly offensive
Solar cars aren't really viable on a mass production scale, though. Silicon cells are good, cheap, and improving gradually. Gallium arsenide is the stuff used in solar races (by less ethical teams), but dear god.. gallium arsenide is a nasty compound and do more environmental damage than fossil fuels. Fricking expensive, and an even rarer resource too.
But I'm willing to believe that silicon cells are capable of becoming effective enough to power whole countries (at least the sunny ones). It's not going to be easy, but hey, if we went with everything that was easy, we wouldn't even have the Internet. I mean, c'mon, this thing has massive underwater cables, signal repeaters in
space, and quadrillions of bytes going around the world at half the speed of light. Half of it being porn and copyright infringements. If you told someone in the 50s that this would be possible, they'd think you were crazy. If you even told them that telephones wouldn't have wires or someone would have a computer in their city, they'd still think you were crazy, because computers were not economically viable.