5 ms·

I worked on geothermal control systems a decade or so back. There are some less obvious applications for geothermal that reduce electric use (as opposed to gene

I worked on geothermal control systems a decade or so back. There are some less obvious applications for geothermal that reduce electric use (as opposed to generating electricity). The systems I worked on were for cooling larger structures like commercial greenhouses, gov installations and mansions. 64° degree water would be pumped up from 400' down, run thru a series of chillers (for a/c) and then returned underground - about 20° or 25° warmer. I always thought this method could be used to provide a/c for neighborhoods, operated as a neighborhood utility. I've not seen it done tho. I've seen neighborhood owned water supplies and sewer systems; it tells me the ownership part seems feasible.

wood_spirit 6mo ago
In the nordics it is common to have ground source heat pumps (brine in closed circuit pipe or bore hole) that are run backwards in summer to cool the house while actually assisting in storing heat back in the ground to extract in the winter. It’s a bit like regenerative breaking on electric cars.
- jjtheblunt 6mo ago
  There was a new in 1988 house in Champaign, Illinois, USA that used the same system, and i mention that because it was a normal modern house, and it's the only one i've heard of with that system. It seems so smart.
  - maxerickson 6mo ago
    It's expensive. A relative has one in the northern Great Lakes, they wouldn't have installed it if their house had access to natural gas.
    - zrail 6mo ago
      Our house came with one and we upgraded the unit a few years ago. It's very efficient in terms of units of energy consumed, but in my area of the world gas is significantly cheaper than electricity so it ends up being expensive to run. That said, we will install solar at some point and then it'll be "free" HVAC.
  - zdragnar 6mo ago
    There's a pretty significant upfront cost in getting them drilled, and many homes need the vertical drilling if they don't have sufficient yard space for a horizontal system. It gets harder if you have your own septic drain field too, as that will complete for yard space. The cost difference is pretty massive- 3-10x for a vertical system. If you live in a city or a suburb with tiny lots, that's your only option though. Nat gas and central AC are way cheaper.
    - IncreasePosts 6mo ago
      Air source heat pumps are insanely more efficient and just plain better these days too. It used to be that if the air was below 40F you couldn't heat your house with a heat pump. Now, you can heat your house even when it's -10F
      - SR2Z 6mo ago
        If you can tolerate the price, I am _confident_ that you will pretty much always have better results using the Earth as your thermal exhaust, because you don't have to dig very far to find a large region that's pretty much always at 50 F.
      - wood_spirit 6mo ago
        The downvotes are unfair. The price of things - heat pumps and alternatives - in different regions - even different regions within the US - varies by what people are prepared to pay not what they cost to produce. The nordics have traditionally had cheap heat pumps whereas piped gas is only in the biggest cities and I’ve never seen bottled gas in the countryside. The competitor used to be cheap electricity and wood. Ground source heat pumps for rural install have been priced to compete with wood. In the US the market could be shaped by regulation and taxation etc. It’s the choice of the US to have cheap fossil fuels and not embrace tech instead.
      - hvb2 6mo ago
        > Air source heat pumps are insanely more efficient Citation needed? Efficient how? I'm sure a heat pump designed for a narrow range of input temperatures AND working with water which can transport a lot more heat should easily be more efficient. https://www.energysage.com/heat-pumps/compare-air-source-geothermal-heat-pumps/ https://www.energysage.com/heat-pumps/compare-air-source-geo... Seems to disagree
- ninalanyon 6mo ago
  No it's not. It exists but it's certainly not common for individual dwelling to use ground source heat pumps, at least in Norway. It is more common in Sweden[1] but still far less common than air source and over 90% of heat pump installations in Norway are air source[2]. The only ground source installations I can think of in Norway serve large office buildings and similar. The largest heat pump installation I know of in Norway is actually a third kind: water source[3]. It takes heat from the Drammen river to provide heat for a district heating system and for keeping the town centre clear of ice in the winter as well as supplying the new hospital with heat. I imagine that the rest of the Nordic region is similar. See: [1] http://publications.jrc.ec.europa.eu/repository/bitstream/JRC137131/JRC137131_026.pdf http://publications.jrc.ec.europa.eu/repository/bitstream/JR... [2] https://www.sciencedirect.com/science/article/pii/S2213138822008773 https://www.sciencedirect.com/science/article/pii/S221313882... [3] https://energiteknikk.net/2023/11/drammen-fjernvarme-storst-pa-sjovarme/ https://energiteknikk.net/2023/11/drammen-fjernvarme-storst-...
  - deliciousturkey 6mo ago
    In Finland around 50% of new single-family homes use ground source heat pumps. So it's definitely popular here.
  - emil-lp 6mo ago
    3 schools in my neighborhood (barneskole, ungdomsskole & videregående) all use ground source heat pumps.
  - deleted 6mo ago
    [deleted]
  - sumea 6mo ago
    If by Nordics you mean Norway, Sweden and Finland, then the most correct way to say would be that ground source heat pumps for redidential heating are (very) common in Sweden and Finland, especially in newer and larger buildings. Norway is somewhat different in energy and climate perspective than its eastern neighbours. The biggest reason to not install ground source heat pump is high installation cost. This means that it makes more sense for larger residential buildings. Also If you have district heating available then this might be more economical in the long run.
readthenotes1 6mo ago
Isn't that similar to how neighborhood heat pumps work? https://www.araner.com/blog/district-heating-in-sweden-efficiency-innovation https://www.araner.com/blog/district-heating-in-sweden-effic...
- hunterpayne 6mo ago
  Heat pumps require a specific temperate differential to work. So they work in zones with are a bit hotter or colder than you would like and so require moderate amounts of heating or cooling. They don't work in temperate zones nor in very hot or cold places. So Santa Fe or Minneapolis for example they work but Mexico City or San Francisco they don't. If you are in a place where they work and that isn't too dense or has earthquakes, go for it. If not, don't. There are businesses that will help you understand when they do and don't make sense. Those businesses don't sell heat pumps though (the businesses that sell things will almost always tell you it works, even when it doesn't, for example PV in the UK doesn't work).
  - adgjlsfhk1 6mo ago
    > pv in the UK doesn't work tell that to 6% of UK electric production https://www.bbc.com/news/articles/cz947djd3d3o https://www.bbc.com/news/articles/cz947djd3d3o (up from 5% in 2024
    - laurencerowe 6mo ago
      Solar is surprisingly useful in the UK since it is anti-correlated with wind power, the UK's largest electricity source. Solar peaked at 42% of UK electricity generation the other day: https://www.pv-magazine.com/2026/04/24/uk-solar-generation-hits-record-15-gw-as-gas-falls-to-historic-low/ https://www.pv-magazine.com/2026/04/24/uk-solar-generation-h...
  - sokoloff 6mo ago
    I’ve never heard a claim that heat pumps won’t work well in a climate like San Francisco and, from looking at the annual temperature patterns, it seems like both air source and ground source heat pumps should work extremely well as they do in the “shoulder seasons” here in New England.
Animats 6mo ago
Shallow geothermal works fine for heating. And you can use the ground as a heat sink. But if you want to generate power, you need to get down to where temperatures can boil water. That's deeper than most oil wells. Fervo Energy claims to have found 270C at 3350 meters well depth. That's progress.
- lostlogin 6mo ago
  > if you want to generate power, you need to get down to where temperatures can boil water. That's deeper than most oil wells. That’s going to be very dependant on location. Here in NZ there are regions where water is boiling at surface level. According to the below, 18% of our power is produced with it. https://www.eeca.govt.nz/insights/energy-in-new-zealand/renewable-energy/geothermal/ https://www.eeca.govt.nz/insights/energy-in-new-zealand/rene...
  - Animats 6mo ago
    "New Zealand has an abundant supply of geothermal energy because we are located on the boundary between two tectonic plates. ... Total geothermal electricity capacity in New Zealand stands at over 900 MW, making us the fifth largest generator of geothermal in the world. It has been estimated that there is sufficient geothermal resource for another 1,000 MW of electricity generation." That's not all that much. That total would be about equal to the 75th largest nuclear plant in the world. Good sites where high temperatures are near the surface are rare. California has a few, but no promising locations for more.
    - lostlogin 6mo ago
      > That's not all that much. We don’t have many people. It gets worse’s though, we burn coal and are looking to fund a gas terminal. We have abundant other ways of generating power and subsidise an aluminium smelter for some reason. Coming up next, data centres. ‘Clean, Green New Zealand.’
    - 0xDEAFBEAD 6mo ago
      Is there any earthquake risk from drilling near tectonic plates?
solarpunk 6mo ago
I think you're describing what is known as "district energy" systems.
quickthrowman 6mo ago
District heating and chilled water is uneconomical for single-family homes. It does work well in medium to high density areas.
- gambiting 6mo ago
  I don't know how economical that is, but just as an anecdote - the town I'm from in Poland has district heating to all single family homes, town of about 20k people. And coincidentally, I now live in the UK and a new estate near me has district heating to all the houses they are building, not apartment blocks. So it must make some sense to someone, or they wouldn't be outfitting 100+ houses this way.
  - hunterpayne 6mo ago
    "I don't know how economical that is" Sure you do. Think about it. Its just drilling a hole and making electricity from the heat. We have been able to do this for a very long time. So if people aren't really doing it much, its not economical. If it was now becoming economical, the article would describe some new way of doing it that makes it economical. The article doesn't, so you "know" it isn't. PS This has been tried many time, it only works in very specific situations, usually places where building a full PP doesn't make sense or where you are making a lot of electricity for some other purpose (mining usually).
    - LeFantome 6mo ago
      The “new” way is plasma drilling.
      - thinkcontext 6mo ago
        That's still a science project, they are piloting zapping a small hole to 100m. Very uncertain whether it will amount to anything.
    - thinkcontext 6mo ago
      > Its just drilling a hole and making electricity from the heat District heating does not involve making electricity.
mlwiese 6mo ago
Framingham, MA has a geothermal system using ground source heat pumps like what you are describing https://www.smartcitiesdive.com/news/first-networked-geothermal-utility-eversource-framingham-building-decarbonization/718015/ https://www.smartcitiesdive.com/news/first-networked-geother...
limagnolia 6mo ago
Whisper Valley in Austin Texas is one example of a neighborhood geothermal installation: https://www.canarymedia.com/articles/geothermal/texas-whisper-valley-neighborhood-homes https://www.canarymedia.com/articles/geothermal/texas-whispe... Maybe not quite exactly what you envision.
- WarOnPrivacy 6mo ago
  > Maybe not quite exactly what you envision. I'm too zonked to pick out the method from the article - but I'll offer that geo methods can be region specific. What I described fits the SE US, with our 13 month summers and abundant underground water.
  - limagnolia 6mo ago
    13 month summers lol :) Yeah, definitely if your interested neighborhood geothermal Whisper Valley seems to be the largest by far in the US, you might check it out.
wesapien 6mo ago
One of the problems with the data center boom is its use of fresh water. How does geo-thermal plants use water and how much?
- micro2588 6mo ago
  The water at these temperature / depths has a lot of dissolved salts and minerals so it's not (human / ag) usable. Modern designs are closed loop systems where production wells bringing the hot water to the surface go through a heat exchanger to a different working fluid to drive the turbine and then is re-injected back into the reservoir. There is consumptive water use for fracking the reservoirs in these types of enhanced geothermal systems, but beyond that it's more water redistribution in the area around the well systems where re-injection and production lead to different pressurization from pumping / natural ground water replenishment rates.
  - WarOnPrivacy 6mo ago
    > The water at these temperature / depths has a lot of dissolved salts and minerals so it's not (human / ag) usable. To clarify, our 400' water source is the same aquifer that supplies drinking water to the state. The water management districts will rubber-stamp permits for these wells. No one else gets off that easy.
- WarOnPrivacy 6mo ago
  > One of the problems with the data center boom is its use of fresh water. How does geo-thermal plants use water and how much? Baring leaks, ground source heat pump geo will consume no water at all. Water is pumped from one layer of the aquifer and is returned to a slightly higher layer.
- ksec 6mo ago
  I dont know why this keeps coming up? It is a closed loop system. The water aren't used at all.
  - justnoise 6mo ago
acdha 6mo ago
> I always thought this method could be used to provide a/c for neighborhoods, operated as a neighborhood utility. I've not seen it done tho. I've seen neighborhood owned water supplies and sewer systems; it tells me the ownership part seems feasible. I keep thinking this would be a great municipal code change: any time the roads are being built or ripped up for water/sewer maintenance, put in a ground loop and subsidize household connections for heat pumps so instead of having to deal with the marginal difference between 20℉ winter air you'd be working with 50-60℉ ground temperatures.
GJim 6mo ago
> The systems I worked on were for cooling larger structures like commercial greenhouses, gov installations and mansions. 64° degree water would be pumped up from 400' down, run thru a series of chillers (for a/c) and then returned underground - about 20° or 25° warmer. I read this several times in the context of _geothermal_ energy, and had no clue what you were talking about. Then I realised, you must be an American and use 'freedom units', coupled with a misunderstanding of what geothermal means.

wood_spirit 6mo ago

In the nordics it is common to have ground source heat pumps (brine in closed circuit pipe or bore hole) that are run backwards in summer to cool the house while actually assisting in storing heat back in the ground to extract in the winter. It’s a bit like regenerative breaking on electric cars.

jjtheblunt 6mo ago
There was a new in 1988 house in Champaign, Illinois, USA that used the same system, and i mention that because it was a normal modern house, and it's the only one i've heard of with that system. It seems so smart.
- maxerickson 6mo ago
  It's expensive. A relative has one in the northern Great Lakes, they wouldn't have installed it if their house had access to natural gas.
  - zrail 6mo ago
    Our house came with one and we upgraded the unit a few years ago. It's very efficient in terms of units of energy consumed, but in my area of the world gas is significantly cheaper than electricity so it ends up being expensive to run. That said, we will install solar at some point and then it'll be "free" HVAC.
- zdragnar 6mo ago
  There's a pretty significant upfront cost in getting them drilled, and many homes need the vertical drilling if they don't have sufficient yard space for a horizontal system. It gets harder if you have your own septic drain field too, as that will complete for yard space. The cost difference is pretty massive- 3-10x for a vertical system. If you live in a city or a suburb with tiny lots, that's your only option though. Nat gas and central AC are way cheaper.
  - IncreasePosts 6mo ago
    Air source heat pumps are insanely more efficient and just plain better these days too. It used to be that if the air was below 40F you couldn't heat your house with a heat pump. Now, you can heat your house even when it's -10F
    - SR2Z 6mo ago
      If you can tolerate the price, I am _confident_ that you will pretty much always have better results using the Earth as your thermal exhaust, because you don't have to dig very far to find a large region that's pretty much always at 50 F.
    - wood_spirit 6mo ago
      The downvotes are unfair. The price of things - heat pumps and alternatives - in different regions - even different regions within the US - varies by what people are prepared to pay not what they cost to produce. The nordics have traditionally had cheap heat pumps whereas piped gas is only in the biggest cities and I’ve never seen bottled gas in the countryside. The competitor used to be cheap electricity and wood. Ground source heat pumps for rural install have been priced to compete with wood. In the US the market could be shaped by regulation and taxation etc. It’s the choice of the US to have cheap fossil fuels and not embrace tech instead.
    - hvb2 6mo ago
      > Air source heat pumps are insanely more efficient Citation needed? Efficient how? I'm sure a heat pump designed for a narrow range of input temperatures AND working with water which can transport a lot more heat should easily be more efficient. https://www.energysage.com/heat-pumps/compare-air-source-geothermal-heat-pumps/ https://www.energysage.com/heat-pumps/compare-air-source-geo... Seems to disagree
ninalanyon 6mo ago
No it's not. It exists but it's certainly not common for individual dwelling to use ground source heat pumps, at least in Norway. It is more common in Sweden[1] but still far less common than air source and over 90% of heat pump installations in Norway are air source[2]. The only ground source installations I can think of in Norway serve large office buildings and similar. The largest heat pump installation I know of in Norway is actually a third kind: water source[3]. It takes heat from the Drammen river to provide heat for a district heating system and for keeping the town centre clear of ice in the winter as well as supplying the new hospital with heat. I imagine that the rest of the Nordic region is similar. See: [1] http://publications.jrc.ec.europa.eu/repository/bitstream/JRC137131/JRC137131_026.pdf http://publications.jrc.ec.europa.eu/repository/bitstream/JR... [2] https://www.sciencedirect.com/science/article/pii/S2213138822008773 https://www.sciencedirect.com/science/article/pii/S221313882... [3] https://energiteknikk.net/2023/11/drammen-fjernvarme-storst-pa-sjovarme/ https://energiteknikk.net/2023/11/drammen-fjernvarme-storst-...
- deliciousturkey 6mo ago
  In Finland around 50% of new single-family homes use ground source heat pumps. So it's definitely popular here.
- emil-lp 6mo ago
  3 schools in my neighborhood (barneskole, ungdomsskole & videregående) all use ground source heat pumps.
- deleted 6mo ago
  [deleted]
- sumea 6mo ago
  If by Nordics you mean Norway, Sweden and Finland, then the most correct way to say would be that ground source heat pumps for redidential heating are (very) common in Sweden and Finland, especially in newer and larger buildings. Norway is somewhat different in energy and climate perspective than its eastern neighbours. The biggest reason to not install ground source heat pump is high installation cost. This means that it makes more sense for larger residential buildings. Also If you have district heating available then this might be more economical in the long run.

readthenotes1 6mo ago

Isn't that similar to how neighborhood heat pumps work? https://www.araner.com/blog/district-heating-in-sweden-efficiency-innovation https://www.araner.com/blog/district-heating-in-sweden-effic...

hunterpayne 6mo ago
Heat pumps require a specific temperate differential to work. So they work in zones with are a bit hotter or colder than you would like and so require moderate amounts of heating or cooling. They don't work in temperate zones nor in very hot or cold places. So Santa Fe or Minneapolis for example they work but Mexico City or San Francisco they don't. If you are in a place where they work and that isn't too dense or has earthquakes, go for it. If not, don't. There are businesses that will help you understand when they do and don't make sense. Those businesses don't sell heat pumps though (the businesses that sell things will almost always tell you it works, even when it doesn't, for example PV in the UK doesn't work).
- adgjlsfhk1 6mo ago
  > pv in the UK doesn't work tell that to 6% of UK electric production https://www.bbc.com/news/articles/cz947djd3d3o https://www.bbc.com/news/articles/cz947djd3d3o (up from 5% in 2024
  - laurencerowe 6mo ago
    Solar is surprisingly useful in the UK since it is anti-correlated with wind power, the UK's largest electricity source. Solar peaked at 42% of UK electricity generation the other day: https://www.pv-magazine.com/2026/04/24/uk-solar-generation-hits-record-15-gw-as-gas-falls-to-historic-low/ https://www.pv-magazine.com/2026/04/24/uk-solar-generation-h...
- sokoloff 6mo ago
  I’ve never heard a claim that heat pumps won’t work well in a climate like San Francisco and, from looking at the annual temperature patterns, it seems like both air source and ground source heat pumps should work extremely well as they do in the “shoulder seasons” here in New England.

Animats 6mo ago

Shallow geothermal works fine for heating. And you can use the ground as a heat sink. But if you want to generate power, you need to get down to where temperatures can boil water. That's deeper than most oil wells. Fervo Energy claims to have found 270C at 3350 meters well depth. That's progress.

lostlogin 6mo ago
> if you want to generate power, you need to get down to where temperatures can boil water. That's deeper than most oil wells. That’s going to be very dependant on location. Here in NZ there are regions where water is boiling at surface level. According to the below, 18% of our power is produced with it. https://www.eeca.govt.nz/insights/energy-in-new-zealand/renewable-energy/geothermal/ https://www.eeca.govt.nz/insights/energy-in-new-zealand/rene...
- Animats 6mo ago
  "New Zealand has an abundant supply of geothermal energy because we are located on the boundary between two tectonic plates. ... Total geothermal electricity capacity in New Zealand stands at over 900 MW, making us the fifth largest generator of geothermal in the world. It has been estimated that there is sufficient geothermal resource for another 1,000 MW of electricity generation." That's not all that much. That total would be about equal to the 75th largest nuclear plant in the world. Good sites where high temperatures are near the surface are rare. California has a few, but no promising locations for more.
  - lostlogin 6mo ago
    > That's not all that much. We don’t have many people. It gets worse’s though, we burn coal and are looking to fund a gas terminal. We have abundant other ways of generating power and subsidise an aluminium smelter for some reason. Coming up next, data centres. ‘Clean, Green New Zealand.’
  - 0xDEAFBEAD 6mo ago
    Is there any earthquake risk from drilling near tectonic plates?

solarpunk 6mo ago

I think you're describing what is known as "district energy" systems.

quickthrowman 6mo ago

District heating and chilled water is uneconomical for single-family homes. It does work well in medium to high density areas.

gambiting 6mo ago
I don't know how economical that is, but just as an anecdote - the town I'm from in Poland has district heating to all single family homes, town of about 20k people. And coincidentally, I now live in the UK and a new estate near me has district heating to all the houses they are building, not apartment blocks. So it must make some sense to someone, or they wouldn't be outfitting 100+ houses this way.
- hunterpayne 6mo ago
  "I don't know how economical that is" Sure you do. Think about it. Its just drilling a hole and making electricity from the heat. We have been able to do this for a very long time. So if people aren't really doing it much, its not economical. If it was now becoming economical, the article would describe some new way of doing it that makes it economical. The article doesn't, so you "know" it isn't. PS This has been tried many time, it only works in very specific situations, usually places where building a full PP doesn't make sense or where you are making a lot of electricity for some other purpose (mining usually).
  - LeFantome 6mo ago
    The “new” way is plasma drilling.
    - thinkcontext 6mo ago
      That's still a science project, they are piloting zapping a small hole to 100m. Very uncertain whether it will amount to anything.
  - thinkcontext 6mo ago
    > Its just drilling a hole and making electricity from the heat District heating does not involve making electricity.

mlwiese 6mo ago

Framingham, MA has a geothermal system using ground source heat pumps like what you are describing https://www.smartcitiesdive.com/news/first-networked-geothermal-utility-eversource-framingham-building-decarbonization/718015/ https://www.smartcitiesdive.com/news/first-networked-geother...

limagnolia 6mo ago

Whisper Valley in Austin Texas is one example of a neighborhood geothermal installation: https://www.canarymedia.com/articles/geothermal/texas-whisper-valley-neighborhood-homes https://www.canarymedia.com/articles/geothermal/texas-whispe... Maybe not quite exactly what you envision.

WarOnPrivacy 6mo ago
> Maybe not quite exactly what you envision. I'm too zonked to pick out the method from the article - but I'll offer that geo methods can be region specific. What I described fits the SE US, with our 13 month summers and abundant underground water.
- limagnolia 6mo ago
  13 month summers lol :) Yeah, definitely if your interested neighborhood geothermal Whisper Valley seems to be the largest by far in the US, you might check it out.

wesapien 6mo ago

One of the problems with the data center boom is its use of fresh water. How does geo-thermal plants use water and how much?

micro2588 6mo ago
The water at these temperature / depths has a lot of dissolved salts and minerals so it's not (human / ag) usable. Modern designs are closed loop systems where production wells bringing the hot water to the surface go through a heat exchanger to a different working fluid to drive the turbine and then is re-injected back into the reservoir. There is consumptive water use for fracking the reservoirs in these types of enhanced geothermal systems, but beyond that it's more water redistribution in the area around the well systems where re-injection and production lead to different pressurization from pumping / natural ground water replenishment rates.
- WarOnPrivacy 6mo ago
  > The water at these temperature / depths has a lot of dissolved salts and minerals so it's not (human / ag) usable. To clarify, our 400' water source is the same aquifer that supplies drinking water to the state. The water management districts will rubber-stamp permits for these wells. No one else gets off that easy.
WarOnPrivacy 6mo ago
> One of the problems with the data center boom is its use of fresh water. How does geo-thermal plants use water and how much? Baring leaks, ground source heat pump geo will consume no water at all. Water is pumped from one layer of the aquifer and is returned to a slightly higher layer.
ksec 6mo ago
I dont know why this keeps coming up? It is a closed loop system. The water aren't used at all.
- justnoise 6mo ago

acdha 6mo ago

> I always thought this method could be used to provide a/c for neighborhoods, operated as a neighborhood utility. I've not seen it done tho. I've seen neighborhood owned water supplies and sewer systems; it tells me the ownership part seems feasible. I keep thinking this would be a great municipal code change: any time the roads are being built or ripped up for water/sewer maintenance, put in a ground loop and subsidize household connections for heat pumps so instead of having to deal with the marginal difference between 20℉ winter air you'd be working with 50-60℉ ground temperatures.

GJim 6mo ago

> The systems I worked on were for cooling larger structures like commercial greenhouses, gov installations and mansions. 64° degree water would be pumped up from 400' down, run thru a series of chillers (for a/c) and then returned underground - about 20° or 25° warmer. I read this several times in the context of _geothermal_ energy, and had no clue what you were talking about. Then I realised, you must be an American and use 'freedom units', coupled with a misunderstanding of what geothermal means.