Well, we are going to have to turn somewhere eventually when fossil fuels run out. We also have to evaluate which alternatives are better both for the short and the long term. If we pick the wrong thing, we might just dig ourselves into a bigger hole.
It won't just be one technology. It will have to be several. Solar only works well in some places. Wind only works well in some places. The same is true of hydro and geothermal.
My personal opinion is that algae will eventually be one of the biggest sources. Unused land like deserts with lots of sun would be great for growing algae. It's supposed to be very energy dense (it doesn't take a lot of land to grow a lot of algae under the right conditions; it would be much more efficient that growing corn or other crops for fuel), and you can feed it sewer waste. As the algae matures, you harvest it and squeeze the lipids out of it, and voila! You have oil. I think they're even trying to genetically engineer algae strains to produce end products like diesel fuel. Cost has been the biggest problem, but time and research keep bringing it down.
