Ultimately, there are only a few types of energy available to us: Solar radiation (which in turn drives the wind), tidal forces, and nuclear reactions. Our future will have to depend on one or more of these.

Fossil fuels are essentially stored sunlight from millions of years ago and come at too high a cost to exploit fully, though it has been a cheap ride so far. Several on this thread seem to think that something equivalent -- or even better -- will somehow be discovered by someone and all of our problems will be solved. They are a little short on the specifics, though. Will we find rivers of pure hydrogen running beneath our feet? Not likely.

In the distant future all energy will have to come from a primary source. It may be converted to hydrogen or electricity for consumers to use -- but it isn't simply going to pop up out of nowhere. Thinking otherwise is equivalent to believing that food comes "from the grocery store." And, yes, it will cost a great deal more than we pay today. There is no free lunch.