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Comment by emtel | Hacker News Reader

As pointed out in the intro to the article, the total amount of power generated in the earth's center is ~50TW.

Global total energy (not just electricity) consumption is currently 180,000TWh/year, or about 20TW. So we would have to capture nearly half of all available geothermal energy to replace current energy usage.

Meanwhile, Solar PV covering (a favorably located) 1% of the earth's surface area would generate 20TW. (This is based on the estimate of 400kwh/year for a 1m^2 panel in a sunny area from https://en.wikipedia.org/wiki/Solar-cell_efficiency.

I don't expect geothermal to do well in this showdown.

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> So we would have to capture nearly half of all available geothermal energy to replace current energy usage.

No, you're completely misunderstanding the meaning of that number. 50TW is not the power generated in the earth's center, and definitely not the "available geothermal energy".

It's the heat flow that reaches the surface. The newly generated heat (from radioactive decay) is a fraction of that (estimates vary between 20% and 80%). The rest is a loss of the primordial heat that has been stored in those billions of cubic kilometers of magma for billions of years. And this loss has been happening for billions of years and there's plenty left.

So there are no physical reasons why we could not extract 500TW or 5000TW from geothermal energy. We'd be depleting the priomordial heat much faster than before, but it would still easily last for millions of years.

Of course, whether the engineering to do it on that scale would be feasible, let alone cost-effective, is a different question.

100 billion multiples of world energy use in 2010, according to an old IPCC estimate.

Ah, interesting. I had thought that any primordial heat would have long since cooled, with the remaining heat flux simply being the result of radioactive decay.

We also don't have to generate the entirety of our energy usage from one source.

Apparently it's currently around half of each (primordial heat vs. radioactive decay).

Kinda funny to think of geothermal energy as non-renewable.

Of course they all are in some sense…

But the energy released from the center is not GOING anywhere. so isn't it stored?

This whole discussion seems a bit confused. 50TW is the amount that does reach the surface naturally as far as I can see. The amount that escapes.

In the Earth itself there is some enormous amount, far far larger, with more energy being generated as well from radioactive decay

So it's not like some sort of oil situation where in 250 years we'll be at Peak Mantle, i.e. "The planet has spent millions of years generating this heat and we're draining it at an unsustainable rate!"

> favorably located

That's the problem, isn't it?

With enhanced geothermal, especially that being explored by Fervo, a massive fraction of locations on earth are opened up to favorable geothermal.

Fervo is actually drilling and producing energy today, and scaling the technology, using existing technologies. If Quaise is successful, it will only enhance what Fervo is already accomplishing, but we don't need the huge technical advance of Quaise to get a massive amount of geothermal energy on the grid.

The Volts podcast has been following Fervo over the past few years, and they have met and exceeded all their milestones so far. (Unlike, say, big fission or fusion startups)

https://www.volts.wtf/p/catching-up-with-enhanced-geothermal

Geothermal should be an obvious choice for new-build homes. Put a ground-source heat pump source in the ground, and build your home on top of it.

This works well only in a few cases. If you live in an area like Pennsylvania or New York, then you're far better off with an air-source heat pump. It's cheaper to install, and the average air temperatures are warm enough for the air source to work well.

If you live in a place like Minnesota, then the ground-source pump needs a water table. Or you'll just be freezing the water in the ground. And you'll likely still be better off with an air-source pump.

The ground loop just needs to be deep enough to be in a zone with relatively stable temperatures. Apparently 6 to 8 feet in Minnesota: https://www.minnesotageothermalheatpumpassociation.com/geoth...

(note, the 6 to 8 feet is for a closed loop, horizontal system)

The heat pump works by pumping the heat out of the ground. And the soil is a pretty good insulator, so you'll eventually just freeze the water in the soil around the pipes.

It looks like this: one day in winter, the temperature of the coolant in the loop outlet falls below 0C. And after that, it starts dropping down by about 1C a day, until the pump becomes a resistive heater. If you sized your loop correctly, it hopefully happens towards the end of the heating season.

If your ground heat system also provides cooling that's no longer a problem. I have that for my house. It's pretty great. You're basically time-shifting temperatures across the year. Cool temperatures get shifter to summer and warm to winter. The hole itself won't freeze, because you're not significantly pulling or pushing energy down it.

Even without running the AC, you generally will likely get enough heat flux from the surface and (hopefully) from the water table to thaw the ice during the summer for horizontal loops.

I don't have a personal experience with vertical loops.

This is very different from the sort of geothermal being discussed for power generation.

Residential geothermal for home heating and cooling could make a ton of sense, but more likely based on the scale of a residential natural gas network.

Drilling a hole per home is super expensive. Replacing gas pipes with moderate thermal pipes would be about the same cost as gas infrastructure but allow the massive efficiency gains of larger scale. Heat pumps operating on pumped water through these sorts of pipes doesn't need very high or low delivered temperatures to be effective, as long as it's somewhat above the -20C of the extremes of winter.

Thermal storage quantity scales roughly with volume (x^3) and storage costs roughly scale with surface area (x^2). Though I'm not sure if storage plays much into the gas -> thermal plans that have been explored.

We have that in the Netherlands in plenty of cities called “stadsverwarming”. It is hot water pumped around in a closed loop and residences take heat out of it with heat pump. The source is the cooling off industries, power plants, or dedicated heaters.

They currently are efficient but still expensive because of a law that the pricing has to be similar to heating with would have been.

Thanks for the extra context! Could you explain the law on pricing a bit more? What was the motivation, and what is the usual alternative heating source?

Natural gas, from the Slochteren gas field, was the cheapest way to heat a home for the past 60 years. It's probably not so anymore, considering the Slochteren field is mostly shut down.

The city heating network operator is a monopoly, that is why the price is capped.

Even though city heating networks utilize 'waste heat', the capital cost of the network is significant. The price cap and the capital costs (especially now with higher interest rates) led to many proposed projects being cancelled in recent years.

Actually the homes typically take heat out with a simple heat exchanger, not a heat pump. Projects previously could use the waste heat from electricity generation, but fewer of those sources are available with coal plants shutting down and gas plants only being run when there is no wind. Add to that the much higher cost of infrastructure compared to installing a heat pump in every home and it's not looking good for future projects. But inner cities that do not have room for that could still benefit.

The problem, as I understand it, is that one has to drill and hit the pocket where the geothermal power comes from. Now, here in Eifel, every drilling requires a permit (€€€), every drilling costs about €20k, you may have to drill more than once to hit the pocket. And Eifel sits on an old mega volcano.

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