Here's an interesting link regarding the topic:
With wind power I don't see one large site dominating but several smaller sites contributing that add up. The geothermal sites don't have to be everywhere but the good sites can produce allot of electricity for distribution.
One huge untapped source is the use of tides and ocean currents. The energy available from this source would probably supply all our electricity needs if it were developed properly.
Electric cars can reduce pollution if we utilize the proper sources for the production of electricity. It's also easier to remove the pollutants from one source like a power plant than several combustion engines. Just think of all the used motor oil, antifreeze, transmission fluid, gasoline additives etc. that aren't needed with electric cars. Batteries can be recycled but for electric cars to proliferate battery technology will need to take a quantum leap forward. Batteries that recharge in less than 5 minutes and give a 300+ mile range are needed to make electric cars practical for the general population, IMO.
The over population problem is really only a problem in the undeveloped portions of the world. It looks like humans do voluntarily control their numbers when they have a high standard of living. Look at Europe and the U.S. for example. European governments are trying to give financial incentives to get their citizens to reproduction at a rate to just keep the population from declining. It isn't working. The U.S. would have a stagnant population if it weren't for immigration.
I guess the key is to raise the standard of living for the rest of the world. Either that or nature always has a way to correct over population problems. Maybe we're overdue for another plague? ;)