As is often the case, the language we use promotes confusion rather than understanding. To speak of “renewable energy” is absurd, as energy is not a material that can be renwed, rather it is a one-time flow from higher concentrations to lower concentrations. On Earth most of the energy we have access to is flowing from the sun (plus some from geothermal and nuclear forces), to ultimately be dissipated as heat at the background temperature of the surface. That flow can never be reversed or “renewed”.
The flow of energy can be delayed or diverted to different paths, which is chiefly done by life processes combining it with elements in the environment to build their physical structure. That usually involves molecular bonds with carbon atoms, and is true for wood as well as for fossil fuels. But it is still just a temporary delay in the flow.
Rather than “renewable”, the important difference is really whether the energy we are depending on is stored or the real-time flow. The energy we built our society on was abundant, dense, portable and easy to access stored energy in the form of fossil fuels. The economic part comes into play in the easy to access part – it did not take much energy input to get to the stored energy in fossil fuels, so it had a big return.
Now all we have left is much more expensive stored energy, plus of course the real time flow of energy we've always had.
Nuclear requires an enormously complex and expensive supporting infrastructure, from mining and concentration of the fuel, to construction, maintenance and operation of the plant. Most of that is is highly dependent on fossil fuel stored energy – and we totally ignored the energy required to deal with the waste, as we don't even know how to do that. Wind and solar connected to a centralized power grid also require a large fossil fuel dependent infrastructure, but are much less complex than nuclear.
Still, we cannot even afford to maintain the power grid we have now that our stored fossil fuel is more expensive, and we will not be able to operate it on the diffuse, distributed and intermittent real time energy flows – and we have not yet designed a power grid that can operate that way either. But wind and solar can be used directly at the point of use, as solar thermal heating sources and local mechanical energy, as they were for thousands of years. Nuclear cannot.
