Nuclear Power Is The Way To GoOther than cooling the reactor which I assume still requires a fresh water source, uranium is very abundant. The power from nuclear reactors will be more plentiful and capable of producing the amount necessary to provide for large populations.
Once someone learns how to completely manipulate the human genome then power will not beso necessary. The ruling class will be able to manufacture enough perfect human slaves to provide for their needs, and the rest of humanity will be expendable.