From a technological point of view the answer is simple: fossil sources will run out in a few decades, so we need to start working now and build up reliance on those sources that will provide the largest amount possible, to be ready and replace oil.

Renewable sources - like solar, eolic, geothermic, hydroelectric and tidal - are clean but expensive, and have a negligible efficiency. We cannot depend on them simply because there's no way to generate enough and cover demand.

Therefore I foresee only one way declined in two solutions: thermonuclear power, using fission today and working to achieve fusion tomorrow.
The feasibility of any other option is purely delusional.