Nuclear is not renewable though, those isotopes were created when some past generation star collapsed as supernova.
> During the Carboniferous period, massive amounts of plant matter accumulated to form coal because microorganisms and fungi had not yet evolved the ability to break down lignin, a tough, aromatic polymer in woody plants.
Though it's close to useless because at that point they're too expensive to be worth it for anything else than very niche uses that absolutely require them.
IIRC, that's basically what charcoal is. Except charcoal is cleaner once made, because most of the nasty stuff happens while being made from the source plant material.