Well, heres my thoughts on it.
1. Our energy demands have reached a point that no one energy source, renewable or not, will not sustain us. The obvious is that we either have to reduce consumption or find new sources. I do not buy into the global warming terror but it is obvious we do have an impact on the environment. But thats another issue altogether.
2. The major players out there now with regards to renewable sources is solar and wind. Neither of which is anywhere near being able to have an impact on a large scale. However, in rural areas I believe they can and probably will, particularly as investment and operating costs comes down. To see this, search on or check into wind farms. Solar farms are not as prevalent here in the US but they are to some degree in Europe and such.
I have seen technologies that generate electricity from ocean currents. I dont believe it generates as much as say a wind turbine, but it may be enough to supplement nicely coastal areas, where the majority of our populations are. It can also be out of sight so to speak so as to not offend those that are short sighted to such a point to be bothered by a a wind turbine or large solar array.
3. I do not think you will replace hydrocarbon based fuels. I just dont see it happening. When they run out, then maybe. I have seen fringe reports of work being done on synthetic fuels, much like synthetic motor oil. That could certainly put a dent in things if it can be done but still leaves us with burning hydrocarbon based fuels. But quite honestly dont look for them to go away any where in the near future.
4. Renewable sources, now, are only more economical because of the higher cost of hydrocarbon based energy sources. So with regards to economics, I dont see that it will be that economical if hydrocarbon based prices come down. That will take a change of mentality that this 'extra' cost is something we should do because its better overall in many facets, not solely because of economics.
5. Global conflict. Dont look for this to change either. If our cars, industrial centers, etc could all be powered by bubble gum, then conflicts would break out over that. Im not a pessimist, just being realistic about the human condition and approach to things. No matter what energy source prevails, there will be a top tier producer and everyone else and everyone else will be screaming subsidize us, its not fair, or want to start a conflict to in vain attempts to equalize things.
We can do more environmentally friendly, we can use energy sources that are less threatening to our health, and so on, but it will take a thinking process change to go there for the long term. The simple fact is that if we do not use renewable energy, it will not sustain us for 'future' generations as any energy source that is not renewable has a finite life span or useage. But our renewable sources are not yet at the point of being able have large scale impacts without people getting over themselves and being willing to put up with such things as wind turbines and solar arrays.