General > General Technical Chat
What does drilling a Hole for Water cost here in Europe?
Someone:
--- Quote from: Lord of nothing on March 30, 2022, 06:52:34 pm ---
From my City I found that Information maybe someone can translate it:
<200m Berechnete konduktive Wärmeleitfähigkeit 0-200 m = 2 W/m/K (+/- 0,2 W/m/K)
<100m Berechnete konduktive Wärmeleitfähigkeit 0-100 m = 1,95 W/m/K (+/- 0,2 W/m/K)
<30m Berechnete konduktive Wärmeleitfähigkeit 0-30 m = 1,85 W/m/K (+/- 0,2 W/m/K)
Maybe someone can say something about the numbers. Maybe below 200m it get hotter? :-//
--- End quote ---
So 2W/m/K is close enough and within the error margin, next step is to find what the thermal gradient is. It varies wildly:
"Austria – Country Update" Proceedings World Geothermal Congress 2010
https://www.geothermal-energy.org/pdf/IGAstandard/WGC/2010/0134.pdf
But averages somewhere around 2-3 degrees per 100m, hence the 100mW/m2 figure.
https://en.wikipedia.org/wiki/Earth%27s_internal_heat_budget
Someone:
--- Quote from: Marco on March 30, 2022, 11:22:40 pm ---
--- Quote from: Someone on March 30, 2022, 11:10:24 pm ---there is a lot of energy there that can extracted but its not being replenished at the rates you claim are viable/sustainable.
--- End quote ---
I think the onus to prove that is on you.
There's decade level simulations which certainly seem to level off to an usable steady state from which I'm extrapolating ... I obviously haven't run the simulation to centuries, but still it's what I have to eyeball. In the absence of numbers I'll trust my eyeballs in this.
--- End quote ---
Claiming "infinite" energy But you won't quantify the input energy source and flux, sounds like you are the one out on a limb. The average flux is well agreed upon in the scientific community, and is not the same as the possible available flux when given some shorter lifetime. Which is what I already provided a citation for:
--- Quote from: Someone on March 29, 2022, 10:02:26 pm ---"Longevity and power density of intermediate-to-deep geothermal wells in district heating applications"
https://link.springer.com/article/10.1140/epjp/s13360-021-01094-8
Its still energy in < energy out or you're going to run out. Their simple explanation:
--- Quote ---One of the most important things to keep in mind is that, once the well has been depleted, its rather modest ability to recover leads effectively to a single-use solution unless additional charging is provided. This, however, would merely convert the well from a heat source into a heat storage, incurring additional, perhaps significant electricity costs. Hence, in sizing the well, one should consider choosing a configuration which guarantees a sustainable level of longevity and does not require re-drilling of the bore holes every few years.
--- End quote ---
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--- Quote from: Marco on March 30, 2022, 11:22:40 pm ---
--- Quote from: Someone on March 30, 2022, 11:10:24 pm ---Natural radiogenic resources are nifty too, and there are some exploitable resources scattered around the world. But as with thermal leakage from the earths core
--- End quote ---
That wasn't my point. The Moho heat flux is lower than upper crust heat flux for pretty much all continental crust. Thermal leakage from the core is not the main process heating up the crust, radiogenic heating is, everywhere on land.
--- End quote ---
You keep jumping to local/micro effects, and trying to connect them to global/macro effects. Yes, there are sites with highly localised natural radiogenic sources, but they are the exception and not the norm. Start with an average model...
several km boreholes are tiny compared to the 6000km radius of the earth, assuming the energy source is fairly distributed throughout that volume, then you can take a model that ignores the local sources and it becomes a simple infinite surface with energy coming in one side and going out the other. We know what this value is because it has been so carefully studied with both global averages, and extremely detailed local mappings.
A volume of rock has 2.5-3kWh/m3/k energy. For a 10km deep volume that is roughly 25-30MWh of energy per m2 for each degree of change, and its already hot! Yes, heaps of energy just sitting there, you could pull out 100W/m2 for a few decades (matching the above more rigorous model/evaluation). But its only being recharged slowly 100mW/m2 or so.
Have fun discharging your batteries and wondering why they dont refill.
Marco:
--- Quote from: Someone on March 30, 2022, 11:44:37 pm ---Claiming "infinite" energy But you won't quantify the input energy source and flux
--- End quote ---
~1 uW/m3 radiogenic heating throughout the entire crust.
But what's the point in knowing that unless you're some 160 IQ genius that you can intuitively use that together with thermal resistances to create a steady state 3D model heat flow model for a deep borehole? Even if you are that 160 IQ genius, I'm not going to just believe that you are on a random internet forum.
Power will flow preferentially to the lower temperature borehole, it does not go straight up as I said before. That's why you need FEM (or 160 IQ) you can't just use the steady state undisrupted straight up thermal flow to determine how much power flows to the borehole.
The borehole attracts power from a wide volume ... how much, hell if I know. The simulation suggests to me, enough.
--- Quote ---several km boreholes are tiny compared to the 6000km radius of the earth
--- End quote ---
But their size compares a lot better to the depth of the crust.
Someone:
--- Quote from: Marco on March 31, 2022, 12:05:10 am ---
--- Quote from: Someone on March 30, 2022, 11:44:37 pm ---Claiming "infinite" energy But you won't quantify the input energy source and flux
--- End quote ---
~1 uW/m3 radiogenic heating throughout the entire crust.
--- End quote ---
Which doesn't match the accepted numbers:
https://en.wikipedia.org/wiki/Earth%27s_internal_heat_budget
Total energy production
47±2 TW 47±2 (terawatts, 1012)
Earths volume
1.1 Zm3 (zetta, 1021)
Average volumetric power
50 nW/m3 (nano, 10-9)
Around half of that being from radiogenic sources:
https://en.wikipedia.org/wiki/Earth%27s_internal_heat_budget#Radiogenic_heat
roughly matching those figures for W/kg.
You keep throwing out figures without anything to back them up, you're starting with ideas (misapplied in their domain/scope) and coming up with incorrect inferences. Trying to just consider the crust (your framing) doesn't make sense when the flow from below dominates, calculate it yourself, even with your alleged much higher radiogenic heat in the crust (which is still much thicker than the practical/economic bore holes so you're back to an infinite plane model).
--- Quote from: Marco on March 31, 2022, 12:05:10 am ---But what's the point in knowing that unless you're some 160 IQ genius that you can intuitively use that together with thermal resistances to create a steady state 3D model heat flow model for a deep borehole? Even if you are that 160 IQ genius, I'm not going to just believe that you are on a random internet forum.
Power will flow preferentially to the lower temperature borehole, it does not go straight up as I said before. That's why you need FEM (or 160 IQ) you can't just use the steady state undisrupted straight up thermal flow to determine how much power flows to the borehole.
The borehole attracts power from a wide volume ... how much, hell if I know. The simulation suggests to me, enough.
--- End quote ---
Again you're comparing wildly different timeframes and physical scales.
I keep saying it, yes you can pull a whole shit-ton of power out of the earths rocks. But its stored energy that has been collected over geological timeframes. Small energy input over long time. It is possible to pull out a large amount of energy quickly, but thats not sustainable.
The sustainably available energy is well agreed upon, averaging around 100 mW/m2. A number that can be arrived at easily and intuitively from the thermal conductivity and temperature gradient/profile.
Marco:
--- Quote from: Someone on March 31, 2022, 01:30:10 am ---Which doesn't match the accepted numbers:
--- End quote ---
Because it's generated mostly in the crust and you're comparing it against the total volume of the planet.
--- Quote ---I keep saying it, yes you can pull a whole shit-ton of power out of the earths rocks. But its stored energy that has been collected over geological timeframes.
--- End quote ---
Prove it by modeling, to my eyeballs the steady state extraction for the borehole modelled and measured suggests stabilization in decades, not eons.
--- Quote ---The sustainably available energy is well agreed upon, averaging around 100 mW/m2. A number that can be arrived at easily and intuitively from the thermal conductivity and temperature gradient/profile.
--- End quote ---
Yes, if you put a ton of horizontal pipe near the surface that's the power you can extract from near the surface given the area covered by the horizontal pipeline field (though usually near the surface ground water will do a lot of the heavy lifting for you increasing the effective area). With deep boreholes you trade off area for depth though. It will pull in thermal power from a wide volume and create an expanding plume of lower temperature towards the surface. A single deep borehole is equivalent to a large horizontal pipeline field near the surface.
The steady state size and temperature of that plume near the surface relative to baseline would also let you calculate how much energy it extracts in steady state. But it would still take FEM or 160 IQ to determine exactly ... all I can say is that it almost certainly increases quadratically with depth.
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