5 ms·

The cited value is the energy flow through the surface, which is about 0.1 W/m^2. But this is conducted through kilometers of rock and soil, which acts as insul

The cited value is the energy flow through the surface, which is about 0.1 W/m^2. But this is conducted through kilometers of rock and soil, which acts as insulation. Geothermal power works through convection instead of conduction. You inject cold water into a borehole, and hot water (steam) comes back, and spins a turbine. Convection can extract energy at a much higher rate than conduction through the crust. If you boil a pot of water, you can still comfortably hold the pot's handle if it's long enough, indefinitely. This is heat conduction. On the other hand, if you try drinking from the pot with a straw, you'll find it very painful. This is convection.

archon1410 2y ago
Perhaps a stupid question, but... what are the risks? Wolndn't extracting too much energy from the earth's core cool it down, at least a little bit? Or does it contain so much energy that extracting it to replace all of 'surface generation' won't make even a little difference?
- whatshisface 2y ago
  We can't drill anywhere near the mantle, geothermal extracts energy from the upper part of the crust.
  - archon1410 2y ago
    Wouldn't drawing energy from the crust cool it down, and wouldn't a cooler crust in turn 'draw' more heat from the lower layers? I guess the earth already radiates out a lot of energy, the process of extracting geothermal energy will presumably lead it to radiate more energy. I don't know by how much though, or if it will make any real difference, or if that's how it even works.
- __turbobrew__ 2y ago
  I guess if you could extract enough energy from the core it would reduce convection which would in turn reduce the strength of the earth’s magnetic field.
- numpad0 2y ago
  Earthquakes! There are couple comments mentioning "fracking" around, that's destabilizing the land by injecting acid to get energy out. The acid is dangerous, and so are breaking up soil deep down.
- tylerhou 2y ago
  > Wouldn't extracting too much energy from the earth's core cool it down, at least a little bit? The earth generates ~50 terawatts of energy through radiation/other processes, while global energy consumption over the last year was 0.003 terawatts. I think we're fine.
  - lurk2 2y ago
    Where are you getting 0.003 terawatts? Another user elsewhere in the thread[0] claimed "Global total energy (not just electricity) consumption is currently 180,000TWh/year, or about 20TW." Google is showing me other figures like 25,000 terawatt hours of electricity consumption annually. [0] - https://news.ycombinator.com/item?id=43234856 https://news.ycombinator.com/item?id=43234856
    - tylerhou 2y ago
      Oops, I missed the thousands. So 3 TW, which is larger, going by Google stats, and 20 TW by the other users. So that's not negligible.
    - boxed 2y ago
      One might also be careful to count energy properly. The fossil fuel industry has been counting "total energy" including losses to make fossil look bigger and harder to replace. But a gas car throws away like 70% of the energy, so going electric, you don't need the same energy to run the car. Not even close.
- renewiltord 2y ago
  Look at a cross section of the Earth: https://www.britannica.com/science/oceanic-crust https://www.britannica.com/science/oceanic-crust The deepest bore of all time was 12 km deep. The crust is between 5 km and 100 km and thinnest under the ocean. The numbers involved here are staggering. One might as well hope to stop the Earth's winds with a windmill.
- Paradigma11 2y ago
  I saw a documentary about some long running geothermal projects and basically the temperature in the well cooled down and made it uneconomical. They said they would have to wait, I think, 30 years for it to heat up again.
whatshisface 2y ago
What stops you from cooling down the area around the borehole to the point where you are conduction-limited again?
- jopsen 2y ago
  You probably do cool down the surrounding area. But my guess is that the 1w/m² quoted by GP is no where near the energy we get from the sun. Quick Google says sunlight in the order of 1kw/m² (sure that's dependent on where you are, it sun doesn't shine at night, but we're off by 3 orders of magnitude here). So probably it'll have no effect on surface temperature. Besides, the heat is mostly released anyways when driving a steam turbine, and the electricity also becomes heat, in your computer or whatever.
  - Retric 2y ago
    Pulling heat from km below the surface isn’t going to reduce surface temperature by 1w/m2, but ~0.001/m2 over thousands of years. Thus the issue is warming the area more so than cooling it. What matters here is the recharge rate, but all power plants have a finite lifespan. You can simply move somewhere else up to the point you run out of untapped geothermal energy across the surface of the earth which is a rather crazy number.
- Retric 2y ago
  On what timescale? Over even just a few second timescale you are cooling rock, but digging deeper gives higher starting temperatures and more volume to remove heat. So, dig far enough and you can get an above some temperature an arbitrary long period say 100 years. Given your geothermal power plant operates for 100 years and pulls from say 1w/m2. Then you move to a new location for 100 years, and then come back you’re limited to 1w/m2 + 1w/m2 = 2w/m2. Have not 2 locations but many and eventually you’re fully recharged.

archon1410 2y ago

Perhaps a stupid question, but... what are the risks? Wolndn't extracting too much energy from the earth's core cool it down, at least a little bit? Or does it contain so much energy that extracting it to replace all of 'surface generation' won't make even a little difference?

whatshisface 2y ago
We can't drill anywhere near the mantle, geothermal extracts energy from the upper part of the crust.
- archon1410 2y ago
  Wouldn't drawing energy from the crust cool it down, and wouldn't a cooler crust in turn 'draw' more heat from the lower layers? I guess the earth already radiates out a lot of energy, the process of extracting geothermal energy will presumably lead it to radiate more energy. I don't know by how much though, or if it will make any real difference, or if that's how it even works.
__turbobrew__ 2y ago
I guess if you could extract enough energy from the core it would reduce convection which would in turn reduce the strength of the earth’s magnetic field.
numpad0 2y ago
Earthquakes! There are couple comments mentioning "fracking" around, that's destabilizing the land by injecting acid to get energy out. The acid is dangerous, and so are breaking up soil deep down.
tylerhou 2y ago
> Wouldn't extracting too much energy from the earth's core cool it down, at least a little bit? The earth generates ~50 terawatts of energy through radiation/other processes, while global energy consumption over the last year was 0.003 terawatts. I think we're fine.
- lurk2 2y ago
  Where are you getting 0.003 terawatts? Another user elsewhere in the thread[0] claimed "Global total energy (not just electricity) consumption is currently 180,000TWh/year, or about 20TW." Google is showing me other figures like 25,000 terawatt hours of electricity consumption annually. [0] - https://news.ycombinator.com/item?id=43234856 https://news.ycombinator.com/item?id=43234856
  - tylerhou 2y ago
    Oops, I missed the thousands. So 3 TW, which is larger, going by Google stats, and 20 TW by the other users. So that's not negligible.
  - boxed 2y ago
    One might also be careful to count energy properly. The fossil fuel industry has been counting "total energy" including losses to make fossil look bigger and harder to replace. But a gas car throws away like 70% of the energy, so going electric, you don't need the same energy to run the car. Not even close.
renewiltord 2y ago
Look at a cross section of the Earth: https://www.britannica.com/science/oceanic-crust https://www.britannica.com/science/oceanic-crust The deepest bore of all time was 12 km deep. The crust is between 5 km and 100 km and thinnest under the ocean. The numbers involved here are staggering. One might as well hope to stop the Earth's winds with a windmill.
Paradigma11 2y ago
I saw a documentary about some long running geothermal projects and basically the temperature in the well cooled down and made it uneconomical. They said they would have to wait, I think, 30 years for it to heat up again.

whatshisface 2y ago

What stops you from cooling down the area around the borehole to the point where you are conduction-limited again?

jopsen 2y ago
You probably do cool down the surrounding area. But my guess is that the 1w/m² quoted by GP is no where near the energy we get from the sun. Quick Google says sunlight in the order of 1kw/m² (sure that's dependent on where you are, it sun doesn't shine at night, but we're off by 3 orders of magnitude here). So probably it'll have no effect on surface temperature. Besides, the heat is mostly released anyways when driving a steam turbine, and the electricity also becomes heat, in your computer or whatever.
- Retric 2y ago
  Pulling heat from km below the surface isn’t going to reduce surface temperature by 1w/m2, but ~0.001/m2 over thousands of years. Thus the issue is warming the area more so than cooling it. What matters here is the recharge rate, but all power plants have a finite lifespan. You can simply move somewhere else up to the point you run out of untapped geothermal energy across the surface of the earth which is a rather crazy number.
Retric 2y ago
On what timescale? Over even just a few second timescale you are cooling rock, but digging deeper gives higher starting temperatures and more volume to remove heat. So, dig far enough and you can get an above some temperature an arbitrary long period say 100 years. Given your geothermal power plant operates for 100 years and pulls from say 1w/m2. Then you move to a new location for 100 years, and then come back you’re limited to 1w/m2 + 1w/m2 = 2w/m2. Have not 2 locations but many and eventually you’re fully recharged.