I think it does not matter which energy storage unit we consume right now. Eventually all of them will be consumed. Renewable energy? nope it is not really renewable, it is just another energy storage unit, just renews faster than oil, because it stores less energy. Ultimately the only energy source we have is the sun. What will happen when our daily consumption rate becomes larger than the amount sun can suppl?
To say that such levels of energy usage are "academic" and "purely hypothetical" is an understatement.
Total worldwide energy consumption (2008) 10^19
Total energy from the sun that strikes earth each year 10^24
Total energy output from the sun each year 10^34
I think we should be using each energy source to bootstrap toward this. By using wind, water, and burning trees, we were able to bootstrap technology to access and use fossil fuels. Using fossil fuels, we were able to bootstrap technology for nuclear fission, which converts a tiny amount of matter to energy. Using nuclear fission, we are working toward nuclear fusion, which would convert more matter to more energy. Using fusion we would work toward even more matter-energy conversion--through some yet-to-be-theorized process.
Yes, in the very long run, entropy will get all the energy sources, but that is a very long run to be worried about.