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| ▲ | pfdietz 2 days ago | parent | next [-] | | This leads naturally to "artificial geothermal", where solar energy is used to heat rocks or soil, and the heat is later extracted. It doesn't have to be anywhere near as deep as ordinary geothermal, which had to accumulate that heat over many thousands of years. Just ~10 meters is about enough. | | |
| ▲ | lxgr 2 days ago | parent [-] | | That's not where natural geothermal energy is from. It's residual heat from planetary formation and some natural radioactivity. This form of storage also unfortunately only yields heat (via heat pumps or directly), not electricity, as the temperature difference is much too low in comparison to meaningfully run any heat engine from it. Great if you need to heat houses; not so great if you were hoping to store the solar energy for a rainy, or rather cloudy, day (or night). | | |
| ▲ | pfdietz 2 days ago | parent [-] | | 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). | | |
| ▲ | 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. | | |
| ▲ | 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. | | |
| ▲ | 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. |
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| ▲ | JoBrad 2 days ago | parent | prev [-] | | Thanks for that context. |
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