General > General Technical Chat
What does drilling a Hole for Water cost here in Europe?
Someone:
--- Quote from: Marco on March 31, 2022, 05:33:29 am ---
--- Quote from: Someone on March 31, 2022, 05:01:59 am ---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
--- End quote ---
Probably wouldn't matter with the slow energy removal and ground cooling being barely noticeable on a human time scale. Even with the 2-3km as modelled above you can pull out 10-20x the surface flux and be out in the thousands of years timeframe for lifetime/side effects.
nctnico:
--- Quote from: Someone on March 31, 2022, 02:59:00 am ---
--- 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.
--- End quote ---
That doesn't really matter. You have to look at the practical side too. A well won't have an eternal lifetime due to material deterioration. As usual it is a cost versus benefit trade-off. That is what the reports are all about: providing information to assess energy production versus time so people can determine ROI. Having a well that produces for 30 to 50 years is more than long enough. By then technology will have advanced so much that the economics and technologies used are totally different.
Someone:
--- Quote from: nctnico on March 31, 2022, 12:56:46 pm ---
--- Quote from: Someone on March 31, 2022, 02:59:00 am ---
--- 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.
--- End quote ---
That doesn't really matter. You have to look at the practical side too. A well won't have an eternal lifetime due to material deterioration. As usual it is a cost versus benefit trade-off. That is what the reports are all about: providing information to assess energy production versus time so people can determine ROI. Having a well that produces for 30 to 50 years is more than long enough. By then technology will have advanced so much that the economics and technologies used are totally different.
--- End quote ---
Redrilling a well into a still productive resource is in no way equivalent to leaving an area denuded of thermal energy and going somewhere else. Current "shallow" geothermal plants are sometimes run in that regime, but being shallow they are leaving those areas to recover over human scale periods (hundreds of years) and:
long term extraction is still limited by the surface flux (where this keeps coming around and around to, fundamental energy in vs energy out).
When talking about deep/large volume extraction its leaving larger and longer lasting legacies. Major cities have histories of hundreds to thousands of years, but thermal energy distribution is more expensive and lossy than electricity (district heating) so it needs to be close to the consumer. Like rubbish dumps, thermal extraction leaves geological problems that need to be worked around. Feel free to pick a lifetime you think is reasonable, but I say anything less than 1000 years is short sighted given how cities tend to stay around longer than that. Intentionally going in with the plan to use all the stored resource in the material lifespan of the well/plant is roughly as sustainable as fossil fuels (completely not sustainable). You can promote selfish solutions all you like, and I'll keep pointing it out for what it is. The IPCC recognise this:
" Energy Systems. In: Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change"
--- Quote from: https://www.ipcc.ch/site/assets/uploads/2018/02/ipcc_wg3_ar5_chapter7.pdf ---Note that, in practice, the RE sources as defined here are sometimes extracted at a rate that exceeds the natural rate of replenishment (e. g., some forms of biomass and geothermal energy).
--- End quote ---
Geothermal energy can be sustainable, but much of it isnt, yet people get all warm and fuzzy about it being zero carbon and "green". There is a geological time scale store of energy that could be exploited for short term gain, just like fossil fuels, the rate of replenishment is very slow (replenishment rate of fossil fuels seems to be hard to find!).
CatalinaWOW:
While I agree philosophically about the concept of overusing a geothermal resource, rough numbers don't seem to make it a likely problem. The time constants required to make extraction workable seem to make recovery relatively short term. I haven't been able to come up with solid numbers, but they are definitely knowable. Deep diamond mines have been extracting heat for decades, not for use at the surface but to make the mines marginally habitable for the miners. The cost of such extraction should be well known and if there is significant depletion should show a distinct decline over time. There are other similar sources of hard data.
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