No, that is how natural geothermal energy works. Perhaps you mistakenly thought I was saying the heat comes from sunlight? I didn't. The heat comes from below (or, in some cases, from internal radioactive decay). And this delivery of heat from below (or from decay) is a slow process, taking a very long time, which is why geothermal resources have to be buried deeply (otherwise, that heat just leaks out and the temperature of the geothermal resource is too low).

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lxgr 2 days ago | parent [-]

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.

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pfdietz 2 days ago | parent [-]

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.

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lxgr 2 days ago | parent [-]

What do you mean? It's already in the core and gradually reaches us through the crust. What's your point/distinction here, exactly?

	▲	pfdietz 2 days ago \| parent [-]
		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.