I just assumed they mean clean energy.

Probably not the intention of parent, but if you could mine the uranium that is released on the oceans by the earth's crust each year you would have an effectively renewable energy source that is nuclear.

It’s a heckuva improvement on “clean” coal which produces the most greanhouse gases per BTU of any fuel. Nuclear still suffers from the distributed waste issue without a permanent storage facility or closed-loop reprocessing. Solar and wind are the ways to go long term. Solar especially, considering insolation gives a median daily recovery potential of about 1 kWh / m^2.

Solar and wind draw their energy from a nuclear reaction as well, albeit from a substantially greater distance.

On a long enough time scale, solar power isn't renewable either.