Many thanks Hannah - that's a great summary and you've made the important distinction between the different types of "geothermal". NZ has a long history of generating electricity from geothermal - typically about 30% of our base load generation (25-30 GW). I would just make a couple of points: a) geothermal to electricity is best suited to base load usage as it doesn't lend itself to being ramped up and down to respond to a variable demand or peaks; and b) Emissions from geothermal fields vary widely - in NZ across 13 main generating stations the lowest is an impressive 21 gCO2e/kWh but the highest is 341 gCO2e/kWh, which is getting into the zone that can be compared with using natural gas for generation. Thanks again.
they are looking at geothermal as a battery as a well will build up heat naturally if not in use and added pressure can help store energy like excess solar
Geothermal desalination is an excellent add on for areas of differing energy demands
Geothermal heat to release in situ oil in oil shales and oil sands without the need for digging up and heat treating these resources as many areas in the western US one has to go through these formations to get to the hot rock granites.
Geothermal electricity also needs cooling. We can't directly convert heat to electricity, we can only tap the flow of heat energy from a hot source to a cool sink. A good heat sink would be ocean or river water. A cooling tower at a. nuclear power plants is an example of using the air as a (less efficient) heat sink. Here's a link to a pdf of the firsts chapter of my 2024 book, explaining this. https://hargraves.s3.amazonaws.com/Energy+for+Civilization.pdf
Hey Hannah! Just published a new piece on The Impact Report. A Princeton study says enhanced geothermal could supply up to 20% of U.S. electricity by 2050. So I profiled Tim Latimer, the founder turning that possibility into real, 24/7 clean power.
One aspect of geothermal energy that I often wonder about is how bringing heat up from the Earth’s core will impact on global heating. Not from carbon emissions, but from heat emissions.
How much savings would there be with using ground vs air sink for home heat pumps? I would speculate it’s low or it might be more commonly incorporated into new builds. With an insulation barrier could it not be put under the house?
Apologies - I need to eat a little humble pie: the units I gave missed an "h", and 25-35 GW should have read 25-35 GWh, being the daily output of the geothermal plants. The proportion of total generation remains valid. The real-time balance of grid generation and pricing in NZ can be seen at https://app.em6.co.nz/?stackedgwap.filter.gridZone=15&stackedgwap.filter.interval=30minute .
Keep in mind that natural dissipation of heat through the curst is only 40 TW, just about 4 times global energy demand. Safer to scale up wind (1000 TW natural dissipation) or, preferably, solar (100 PW).
I am puzzled by why geothermal electricity production cannot be readily ramped up and down. It seems like it would be easy to vary the flow of fluid though the system as required, though of course this would increase the cost of generated electricity due to large fixed initial investment, similar to curtailing renewables or nuclear w/o compensation
A technical question that has been bothering me for some time now about geothermal heat pumps, that maybe someone here can answer: Why does the fluid have to flow so far underground? The year-around soil temp here at only about one meter below the surface is around 11C. Both heating and cooling with a heat pump would be so much more efficient if the ambient temp it were drawing from were 11C than is it in the winter here (say, 0C air temp) or summer (say, 25-30C air temp), yet there is little geothermal heat pump usage. Why do GHP installations involve installing pipes several meters below the surface, hence at much higher cost than a shallower installation?
Not an expert here, but likely with quite correct answer. Heat pumps with ground source are relying more on the large mass of the ground and relatively stable temperature there rather heat than flow from the core- when demand temperature is close to hot/cold source heat pumps will get more efficient (high COP). Rocks and soil are insulators, so one needs very large surface area to get good heat transfer- otherwise little heat (total energy) will be transferred before temperature equilibrium. And then there is a risk of freezing the ground, where normally no frost ever happens- turning moisture into ice with its expansion- could be even dangerous for building, roads on top. Physical principles are well explained in free book by prof. David MacKay https://www.withouthotair.com
Hannah, thanks for the great article summarizing the details! I recently read another article about the Canadian company Eavor and what they had built in Germany - closed loop geothermal to provide heat to many homes. New technology again with high hopes to make it work.
I've been following Quaise energy, they have a technology they've been developing that can potentially reach significantly deeper drill depths than what's currently available. Hopefully they can successfully commercialize their tech in the next year or two and we will see geothermal become viable in many more regions shortly afterwards.
Good summary but the costs remain prohibitive for ESG and electicity generation. To move geothermal outside known areas of high heat flow, like Iceland or Nevada, you have to be able to drill deep, into the earth basement rocks. These rocks are hard to drill, literally, expensive, fracing is problematic and the heat avaible to the borehole depletes overtime. Regarding the last point of heat depletion, you state that the heat/energy is essentially free after the well is drilled, but to maintain the capacity to generate electricty from the geothermal plant, additional expensive wells would need to be drilled as the heat from the well bores is depleted. Not sure the LCOE takes that into account, by the way. Geothermal as a major source for electricit is decades away, as the drilling techonolgy is not there and the costs are very high. Conmpanies like Eavor advance the drilling technologies, but it is still a long way off. Even if costs come down, it is very hard to see how these projects become economic as the wells deplete overtime, like oil and gas wells and additional capital is needed. Geothermal is still a niche player, not a univeral energy solution
The heat underground is a combination of radioactive decay of the rocks and transfer of pressurized magma under the crust. For a deep geothermal well, it would be very difficult to extract heat from the rocks faster than new heat from the magma below to replenish it. Enhanced geothermal typically creates a broad reservoir at the base of a single well (with two conduits, one for cold fluid going down and the other for heated fluid coming up) or two wells. Drilling more holes would not increase the temperature at the base, and if heat is being extracted too quickly, the solution is to increase the size of the fracked reservoir at the base, or to drill deeper.
You are wrong on this. No geothermal wells drill into magma, it would melt the bits and destory the bore hole. Every geothermal well, that 12" diameter well bore depletes the heat around that bore hole over a relatively short time. You can't deplete the heat from the earth, but you can around the very small borehole. And the temperature around the borehole, and the fluids that come out need to be around 100C to drive turbines and make electricity. To drill and frac deep wells is very difficult and costly. Fracing cannot extend out far enough to stop heat depletion. Typical oil and gas well fracs might extend no more than 1000' laterally or vertically and fracs typically grow up, toward lower pressure.
Interesting writ up. Deserves follow up since sustainability of geothermal sources is more complex. Drilled place will "deplete the heat source", since hot rock is an insulator there is some sustainable rate to extract the heat. More and constant drilling will be needed to keep up with the demand(ground source heat pumps must pump heat in during summer, serving as AC, otherwise there is the risk of "freezing the ground in the winter"). If hot water is allowed to have direct contact with hot rock- it will carry corrosive salts(that is potential for some recovery of interesting elements), minerals, radon. If we imagine deep source of heat- under tremendous pressure, act of cooling it will increase density, and may cause earthquakes and land movements. Nothing comes for free.
Many thanks Hannah - that's a great summary and you've made the important distinction between the different types of "geothermal". NZ has a long history of generating electricity from geothermal - typically about 30% of our base load generation (25-30 GW). I would just make a couple of points: a) geothermal to electricity is best suited to base load usage as it doesn't lend itself to being ramped up and down to respond to a variable demand or peaks; and b) Emissions from geothermal fields vary widely - in NZ across 13 main generating stations the lowest is an impressive 21 gCO2e/kWh but the highest is 341 gCO2e/kWh, which is getting into the zone that can be compared with using natural gas for generation. Thanks again.
Thank you for an excellent piece. Another benefit of geothermal is that its per MWh critical mineral requirement is very low.
HI Hannah, a few other points of interest
they are looking at geothermal as a battery as a well will build up heat naturally if not in use and added pressure can help store energy like excess solar
Geothermal desalination is an excellent add on for areas of differing energy demands
Geothermal heat to release in situ oil in oil shales and oil sands without the need for digging up and heat treating these resources as many areas in the western US one has to go through these formations to get to the hot rock granites.
Geothermal electricity also needs cooling. We can't directly convert heat to electricity, we can only tap the flow of heat energy from a hot source to a cool sink. A good heat sink would be ocean or river water. A cooling tower at a. nuclear power plants is an example of using the air as a (less efficient) heat sink. Here's a link to a pdf of the firsts chapter of my 2024 book, explaining this. https://hargraves.s3.amazonaws.com/Energy+for+Civilization.pdf
I serialized NEW Nuclear is HOT starting at
https://hargraves.substack.com/p/serializing-new-nuclear-is-hot
Hey Hannah! Just published a new piece on The Impact Report. A Princeton study says enhanced geothermal could supply up to 20% of U.S. electricity by 2050. So I profiled Tim Latimer, the founder turning that possibility into real, 24/7 clean power.
Check it out and share if you’re interested!
https://impactbuilders.substack.com/p/the-most-overlooked-solution-to-ais
One aspect of geothermal energy that I often wonder about is how bringing heat up from the Earth’s core will impact on global heating. Not from carbon emissions, but from heat emissions.
How much savings would there be with using ground vs air sink for home heat pumps? I would speculate it’s low or it might be more commonly incorporated into new builds. With an insulation barrier could it not be put under the house?
Apologies - I need to eat a little humble pie: the units I gave missed an "h", and 25-35 GW should have read 25-35 GWh, being the daily output of the geothermal plants. The proportion of total generation remains valid. The real-time balance of grid generation and pricing in NZ can be seen at https://app.em6.co.nz/?stackedgwap.filter.gridZone=15&stackedgwap.filter.interval=30minute .
Keep in mind that natural dissipation of heat through the curst is only 40 TW, just about 4 times global energy demand. Safer to scale up wind (1000 TW natural dissipation) or, preferably, solar (100 PW).
https://royalsocietypublishing.org/doi/full/10.1098/rsta.2011.0316
I am puzzled by why geothermal electricity production cannot be readily ramped up and down. It seems like it would be easy to vary the flow of fluid though the system as required, though of course this would increase the cost of generated electricity due to large fixed initial investment, similar to curtailing renewables or nuclear w/o compensation
A technical question that has been bothering me for some time now about geothermal heat pumps, that maybe someone here can answer: Why does the fluid have to flow so far underground? The year-around soil temp here at only about one meter below the surface is around 11C. Both heating and cooling with a heat pump would be so much more efficient if the ambient temp it were drawing from were 11C than is it in the winter here (say, 0C air temp) or summer (say, 25-30C air temp), yet there is little geothermal heat pump usage. Why do GHP installations involve installing pipes several meters below the surface, hence at much higher cost than a shallower installation?
Not an expert here, but likely with quite correct answer. Heat pumps with ground source are relying more on the large mass of the ground and relatively stable temperature there rather heat than flow from the core- when demand temperature is close to hot/cold source heat pumps will get more efficient (high COP). Rocks and soil are insulators, so one needs very large surface area to get good heat transfer- otherwise little heat (total energy) will be transferred before temperature equilibrium. And then there is a risk of freezing the ground, where normally no frost ever happens- turning moisture into ice with its expansion- could be even dangerous for building, roads on top. Physical principles are well explained in free book by prof. David MacKay https://www.withouthotair.com
Thank you! I'll check out the book by MacKay.
Hannah, thanks for the great article summarizing the details! I recently read another article about the Canadian company Eavor and what they had built in Germany - closed loop geothermal to provide heat to many homes. New technology again with high hopes to make it work.
I've been following Quaise energy, they have a technology they've been developing that can potentially reach significantly deeper drill depths than what's currently available. Hopefully they can successfully commercialize their tech in the next year or two and we will see geothermal become viable in many more regions shortly afterwards.
https://www.linkedin.com/company/quaise-energy/
Good summary but the costs remain prohibitive for ESG and electicity generation. To move geothermal outside known areas of high heat flow, like Iceland or Nevada, you have to be able to drill deep, into the earth basement rocks. These rocks are hard to drill, literally, expensive, fracing is problematic and the heat avaible to the borehole depletes overtime. Regarding the last point of heat depletion, you state that the heat/energy is essentially free after the well is drilled, but to maintain the capacity to generate electricty from the geothermal plant, additional expensive wells would need to be drilled as the heat from the well bores is depleted. Not sure the LCOE takes that into account, by the way. Geothermal as a major source for electricit is decades away, as the drilling techonolgy is not there and the costs are very high. Conmpanies like Eavor advance the drilling technologies, but it is still a long way off. Even if costs come down, it is very hard to see how these projects become economic as the wells deplete overtime, like oil and gas wells and additional capital is needed. Geothermal is still a niche player, not a univeral energy solution
The heat underground is a combination of radioactive decay of the rocks and transfer of pressurized magma under the crust. For a deep geothermal well, it would be very difficult to extract heat from the rocks faster than new heat from the magma below to replenish it. Enhanced geothermal typically creates a broad reservoir at the base of a single well (with two conduits, one for cold fluid going down and the other for heated fluid coming up) or two wells. Drilling more holes would not increase the temperature at the base, and if heat is being extracted too quickly, the solution is to increase the size of the fracked reservoir at the base, or to drill deeper.
You are wrong on this. No geothermal wells drill into magma, it would melt the bits and destory the bore hole. Every geothermal well, that 12" diameter well bore depletes the heat around that bore hole over a relatively short time. You can't deplete the heat from the earth, but you can around the very small borehole. And the temperature around the borehole, and the fluids that come out need to be around 100C to drive turbines and make electricity. To drill and frac deep wells is very difficult and costly. Fracing cannot extend out far enough to stop heat depletion. Typical oil and gas well fracs might extend no more than 1000' laterally or vertically and fracs typically grow up, toward lower pressure.
Interesting writ up. Deserves follow up since sustainability of geothermal sources is more complex. Drilled place will "deplete the heat source", since hot rock is an insulator there is some sustainable rate to extract the heat. More and constant drilling will be needed to keep up with the demand(ground source heat pumps must pump heat in during summer, serving as AC, otherwise there is the risk of "freezing the ground in the winter"). If hot water is allowed to have direct contact with hot rock- it will carry corrosive salts(that is potential for some recovery of interesting elements), minerals, radon. If we imagine deep source of heat- under tremendous pressure, act of cooling it will increase density, and may cause earthquakes and land movements. Nothing comes for free.
I think the idea with fracking is that it opens a larger volume of hot rock for heat extraction.
Britain is converting to heat pumps search web.