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The time has finally come for geothermal energy

(www.newyorker.com)
160 points riordan | 1 comments | 17 Nov 25 13:55 UTC | HN request time: 0s | source
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hodgehog11 ◴[17 Nov 25 15:21 UTC] No.45954362[source]▶
I've always been curious why a cost-effective widespread implementation of geothermal energy has never been considered a holy grail of energy production, at least not in the public debate. Much of the discussion is so focussed on nuclear fusion, which seems so much harder and less likely to be reliable.
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fuoqi ◴[17 Nov 25 15:41 UTC] No.45954566[source]▶
Because unless you sit on top of a volcano, amount of renewable geothermal energy is minuscule. In most places on Earth it's somewhere around 40 mW/m2 (i.e. accounting for conversion losses you need to capture heat from ~500 m2 to renewably power one LED light bulb!). In other words, in most places geothermal plant acts more like a limited battery powered by hot rock, so unless drilling is extremely cheap, it does not make economic sense compared to other energy sources.
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dns_snek ◴[17 Nov 25 16:20 UTC] No.45955026[source]▶
> In most places on Earth it's somewhere around 40 mW/m2 (i.e. accounting for conversion losses you need to capture heat from ~500 m2 to renewably power one LED light bulb!)

Ground-source heat pumps extract about 1000 times more power from ground loops, where does the difference come from?

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kragen ◴[18 Nov 25 03:06 UTC] No.45960955[source]▶
Ground-source heat pumps are irrelevant to geothermal energy sources, and it's unfortunate that the article mentioned them. Ground-source heat pumps are just storing heat from the air during the summer and retrieving it during the winter.
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adrianN ◴[18 Nov 25 11:11 UTC] No.45963665[source]▶
If it can be used to heat houses in winter it’s not irrelevant.
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kragen ◴[18 Nov 25 11:56 UTC] No.45964065[source]▶
Insulation, adobe construction, and vigorous exercise can all "heat houses in winter" in the same way as ground-source heat pumps, but none of them can be meaningfully compared with hydroelectric or nuclear power except in a specific situation. How much insulation is enough to charge your cellphone or run a load of laundry? The question is nonsense.
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adrianN ◴[18 Nov 25 18:43 UTC] No.45970261[source]▶
There are lots of houses getting the majority of their heat from ground source heat pumps. Not so many that are heated with vigorous exercise.
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kragen ◴[18 Nov 25 20:07 UTC] No.45971341[source]▶
Ground-source heat pumps (with a few exceptions and borderline cases like those mentioned in the article) are not sources of heat, so you can only "get heat from" them in the short term; as with a battery or an interest-free checking account, though you may be able to temporarily run a debit balance, in the long run you can only get out what you put in.

This is a fundamental difference from energy sources.

Energy storage is an important complement to energy sources, especially renewables, and can substitute for energy sources to a limited extent, but confusing them is a fatal error.

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adrianN ◴[19 Nov 25 03:55 UTC] No.45975686[source]▶
Ground source heat pumps as used for heating buildings source their energy from the sun and work very well. They are outcompeted by air source heat pumps despite better efficiency because digging is expensive.
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1. kragen ◴[20 Nov 25 16:39 UTC] No.45994571{3}[source]▶
As I understand it, no, they do not source their energy from the sun. You have to bury the pipes below the frost line. In temperate climates, the frost line is the place where the earth is so well insulated from the surface by the thickness of earth above it that heat conduction is insufficient to freeze it throughout the entire winter. The sun only heats that surface by radiation.

See for example https://igshpa.org/igshpa-blog/cold-climate-ground-source-he...:

> Unlike air-source heat pumps that struggle to extract heat from frigid air, ground source heat pumps tap into a remarkably stable heat source: the earth itself. Below the frost line, ground temperatures remain relatively constant year-round, typically between 50-60°F (10-15°C). This consistency makes ground source heat pumps highly efficient even during the coldest months.

If you were building a ground-source heat pump to heat your house in the summer, you could get away with burying the pipes at a much shallower depth and in effect converting the earth into a low-temperature passive solar collector. But generally people want to heat their houses in the winter instead.