That if you REALLY want to eliminate fossil fuel usage, the big spending is going to have to be on dams and nuclear reactors.
Hydro power won't do. The world technical potential for hydro power is about 16 PWh, while the world demand for energy is something like 500 PWh, so there is no way that those 16 PWh could ever make a significant contribution.
Nuclear power's technical potential is only limited by the effectiveness of the technology, so nuclear could be a viable replacement given the right advances in nuclear technology. It is unfortunately possible to rule out current nuclear technology because it simply takes too long and costs too much to build a power plant using that technology. If the US government or state governments began funneling money into current state of the art nuclear power now then the first new nuclear energy due to that investment would come online in the 2030's and it would probably take centuries to replace fossil fuel that way.
For nuclear to be a viable replacement for fossil fuels I think we would need to imagine a nuclear reactor the size of a shipping container that could be made in a factory, or at least a reactor that could be assembled on site from a small number of components all of which are small enough to fit inside shipping containers. This could probably lead to dramatic reductions in the time it takes to build a reactor, which I think would allow nuclear power to come online rapidly enough to match the depletion rates of dwindling fossil fuel reserves.