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gorillapaws's avatar

Is a geothermal Sterling engine possible for utility-scale electricity production?

Asked by gorillapaws (30682points) June 10th, 2020

There are some very deep mines on the planet with constant high temperatures. Would it be possible to melt down a huge block of copper or aluminum to act as a heat-sink, connect it to well-insulated heat-pipes that transfer that heat to the surface, and use that heat differential with the ambient air temperature to power a huge, industrial Stirling engine for the purpose of electricity production?

I’ve never heard of anyone doing this, so I assume this idea has one or more fatal flaws (cost? low theoretical output? something else?).

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6 Answers

Call_Me_Jay's avatar

There is plenty of geothermal power generation. Looking at the Wikipedia page I see the US is the leader and the Philippines is second. It’s all located in areas with fault lines where the crust is thin.

Since drilling extremely deep wells for oil is routine, I would guess the math has been done many times to see if drilling down for a heat source is worthwhile.

I don’t know about Stirling engines, but again I would guess the math has been done there, too. If it was as efficient as turbines then nuclear and fuel-burning plants could use it.

In a similar vein, I have often wondered why geothermal heat pumps are not cost-effective for residential retrofits. New construction uses it up here in the Midwest with fluid in coils buried just a few feet deep.

So I wonder why 20 to 40 foot well for the hot end isn’t a good way to drastically reduce or even eliminate heating and cooling energy costs.

stanleybmanly's avatar

The drawback that occurs to me: The requirement of a huge temperature differential to produce sufficient surplus energy. As Jay has mentioned it is far more efficient to employ anything hotter than the boiling point of water to simply boil water. The boiling water will transfer the heat much more efficiently than the sterling engine, and is far less complex and expensive.

gorillapaws's avatar

Thanks for the great answers. I’m under the impression that the deep mines I’m referencing are still well below boiling temps. Also, would it require a huge temperature differential? If it’s a large scale with a moderate but consistent temperature differential (e.g. 40–60F), would that generate a meaningful output?

Not having to boil off large amounts of water, does have some advantages.

Tropical_Willie's avatar

Stirling Engine Forum They don’t do it in Iceland where boiling water is available.

Zaku's avatar

One great thing about geothermal energy in Iceland is that not only does it provide almost all of the electricity not already provided by hydroelectric power, but it also heats 87% of all buildings in Iceland without even using electricity.

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