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| What does drilling a Hole for Water cost here in Europe? |
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| nctnico:
This discussion is starting to run in circles :popcorn: |
| Someone:
--- Quote from: Marco on March 31, 2022, 01:51:24 am ---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. --- End quote --- Which is why its easiest to normalise everything to surface area, mW/m2 Yes, you can use a deep well to pull more power over a larger area and/or volume, but the incoming energy source is well known to be limited per uint of area as its almost entirely coming from below. --- Quote from: nctnico on March 31, 2022, 01:56:32 am ---This discussion is starting to run in circles :popcorn: --- End quote --- I just see someone coming back time and time again with outrageous/misleading/bonkers claims who won't even look at the established figures or simple models. If most of the geothermal energy sources were distributed through the crust then it wouldn't have a linear temperature vs depth profile, but almost everywhere does have a close to linear gradient. Using an electrical equivalent model its a classic transmission line, distributed resistance (thermal conductivity) and capacitance (thermal mass). When you run the numbers on such a model you see a tiny little current source at one end (the thermal energy coming up from deeper within the earth) and a huge amount of capacitance along the way to the surface. Like a railgun, massive short term power available, but recharging takes a long time. |
| Marco:
--- Quote from: Someone on March 31, 2022, 02:59:00 am ---Which is why its easiest to normalise everything to surface area, mW/m2 --- End quote --- Which requires quite complex FEM modelling or 160 IQ intuition to actually do. You don't currently have any real model either, just lots of talk and some intuition. --- Quote ---I just see someone coming back time and time again with outrageous/misleading/bonkers claims who won't even look at the established figures or simple models. If most of the geothermal energy sources were distributed through the crust then it wouldn't have a linear temperature vs depth profile, but almost everywhere does have a close to linear gradient. --- End quote --- It looks linear to the depth we can drill ... which isn't all that deep. With enough assumptions matching measurements with the accepted levels of radiogenic heating isn't a big problem. It's accepted science that radiogenic heating makes up a large part of the heat flux in the crust, the paper I linked has plenty of references if you want them. This isn't fringe science, it's just a corner of science which escaped your attention before. --- Quote ---Using an electrical equivalent model its a classic transmission line, distributed resistance (thermal conductivity) and capacitance (thermal mass). When you run the numbers on such a model you see a tiny little current source at one end (the thermal energy coming up from deeper within the earth) and a huge amount of capacitance along the way to the surface. --- End quote --- Talk and intuition. An excerpts from the above paper : --- Quote ---Therefore, in stable prov- inces, the crustal heat production can be calculated by subtracting the Moho heat flux from the surface heat flux averaged over a sufficiently wide area (relative to crustal thickness). Results from heat flow studies yield an average heat production of 0.77 ±0.08 μW m−3 for the Pre- cambrian crust and 1.08 ± 0.13 μW m−3 for the Phanerozoic with a range of 0.79–0.95 μW m−3 for the entire continental crust (Jaupart and Mareschal, 2012). --- End quote --- |
| Someone:
--- Quote from: Marco on March 31, 2022, 03:38:55 am --- --- Quote from: Someone on March 31, 2022, 02:59:00 am ---Which is why its easiest to normalise everything to surface area, mW/m2 --- End quote --- Which requires quite complex FEM modelling or 160 IQ intuition to actually do. You don't currently have any real model either, just lots of talk and some intuition. --- Quote ---I just see someone coming back time and time again with outrageous/misleading/bonkers claims who won't even look at the established figures or simple models. If most of the geothermal energy sources were distributed through the crust then it wouldn't have a linear temperature vs depth profile, but almost everywhere does have a close to linear gradient. --- End quote --- It looks linear to the depth we can drill ... which isn't all that deep. --- End quote --- But we're talking about geothermal energy extraction with wells we can drill, which as I said reach depths where approximations to the models are valid. I provided the links to the FEM modelling paper which does all the fancy stuff and still predicts close to a trivial model (one single storage with one input and output). --- Quote from: Marco on March 31, 2022, 03:38:55 am ---With enough assumptions matching measurements with the accepted levels of radiogenic heating isn't a big problem. It's accepted science that radiogenic heating makes up a large part of the heat flux in the crust, the paper I linked has plenty of references if you want them. This isn't fringe science, it's just a corner of science which escaped your attention before. --- End quote --- Even if half the energy comes from the crust (as example: "Controls of Radiogenic Heat and Moho Geometry on the Thermal Setting of the Marche Region (Central Italy): An Analytical 3D Geothermal Model" https://www.mdpi.com/1996-1073/14/20/6511) it doesn't change the fundamental limit of the surface flux. If you pull more than the surface flux out of the area, you are reducing the temperature of the thermal storage. Unless you want to argue that we have an imbalance of thermal flux and the earths core is currently increasing in temperature, then all (100%) of the thermal energy produced (from any depth) is released as the surface flux. Yes you can have a deep well and suck up heaps of power, but thats flux that doesn't come up where it used to. Hence sticking to mW/m2 as the measure of available sustainable resource. Which the paper you link to here leads with as Fig 1. Its not surprising they can point to locations with high crustal activity and low flux across the Moho discontinuity, such as the South Australian Heat Flow Anomaly. But the sustainable power production is still 100mW/m2 (even in that unusual and "highly active" [for the geological age] region) |
| Marco:
--- Quote from: Someone on March 31, 2022, 05:01:59 am ---If you pull more than the surface flux out of the area, you are reducing the temperature of the thermal storage. --- End quote --- Pulling less than the available surface area worth of flux in a region is good enough for lesser populated countries. In my country not so much, but all the large geothermal systems in my country have to operate at yearly net 0 extraction. --- Quote ---Yes you can have a deep well and suck up heaps of power, but thats flux that doesn't come up where it used to. --- End quote --- So the frost line goes a little deeper. For the theoretical 20 km deep boreholes, would it really matter if say 2000 km2 of desert soil gets its flux cut in half to run a 100 MW power plant |
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