Comment by Mordisquitos
18 hours ago
No, not quite. Geothermal is powered by the accumulated heat stored in rocks from fission Uranium and other heavy atoms deep in the Earth (and other phenomena).
Geothermal hotspots do not reheat by fission or otherwise at the same speed that we extract their energy (if they did we'd be in trouble if we weren't extracting it!).
As I mentioned in another comment, build a Dyson sphere of solar panels around the Sun and it will last just as long. Build an all-Earth geothermal plant and the heat will be depleted.
By that definition, hydroelectric dams are not a renewable energy source for most of the year.
How long would it take for the heat to be depleted? Humans have only managed to drill something like 12km into the earth because it gets too hot to go further.
If it were possible to access all of the Earth's stored geothermal energy, probably a very, very, very long time.
But if we're open to applying a quantitative timescale threshold to the thought experiment, at which we can argue geothermal is renewable, that raises the question for nuclear. If we could access all fissile uranium and thorium on Earth, how long would it take for us to deplete its stored energy? Does that mean nuclear energy is renewable?