Comment by lxgr
15 hours ago
Yeah, "accumulate the heat over thousands of years" indeed sounds a bit misleading to me. The heat is largely already there (or is generated pretty uniformly through radioactive processes), it's just slowly transmitted outwards down a gradient.
No, the heat is not already there. The heat comes in and goes out; the heat energy initially in the crust decays away exponentially with time and has no effect on the steady stage temperature gradient.
What do you mean? It's already in the core and gradually reaches us through the crust. What's your point/distinction here, exactly?
It was not initially in the rocks that we are tapping for geothermal energy, which would be a few kilometers. I wasn't talking about the Earth as a whole. Remember, this is about why so much more thickness is needed for the rocks for ordinary geothermal energy systems, vs. artificial geothermal.