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Croatia Wants To Turn Superhot Underground Lake Into a 16MW Geothermal Power Plant (thenextweb.com) 91

A Croatian energy company has discovered an underwater lake of superheated water that meets all the requirements for the construction of a 16MW geothermal power plant. The Next Web reports: The find was the result of a two-year study by state-run power company Bukotermal that sought to find suitable sites for the exploitation of the energy source, generated by heat from the Earth's core. The research verified the presence of a geothermal water source at Lunjkovec -- Kutnjak field, located in the Varazdin County, close to the border with Hungary. The underground lake, located at a depth of 2.4 kilometers, has an average temperature of 142.03 degrees Celsius.

To date, over 2.5 million euros has been invested in the project. However, according to Alen Pozgaj, CEO of Bukotermal, the total cost to build the plant would be around 50 million euros. The news comes just days after the Croatian Ministry of Economy and Sustainable Development awarded five licenses for the exploration of geothermal waters to firms from Croatia, the United Kingdom, and Turkey. [...] For now, Bukotermal has a six-month timeframe to propose how it will exploit the newly discovered geothermal pool. The company plans to construct one or more geothermal power plants and heat utilization facilities at the site, with construction expected to start within two years time.

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Croatia Wants To Turn Superhot Underground Lake Into a 16MW Geothermal Power Plant

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  • I wonder if we fully understand the impact of harvesting these sources. Do they add to anything like preventing the earth from cooling to much or is there an impact on the core should we all start getting heat from there? I guess there is plenty energy there, but i just wonder is any type of research was done in that area beforehand.
    • I call we will be much sooner be limited by dumping that heat into the atmosphere.
    • Re: (Score:1, Informative)

      by JBeretta ( 7487512 )

      Yes. We do understand. If the entirety of humanity ran on energy extracted from geothermal sources (natural or artificial) we wouldn't put a microscopic dent in the temperature of the core or mantle.

      The problem is that heat is much too far down for most places. The deepest hole humanity has ever drilled is a mere 12,000 meters. (Kola Superdeep Borehole SG-3). If your heat is 12,001 meters down, you're shit out of luck.

      Y'all really need to get over yourselves. Humanity isn't powerful in a planetary se

      • Hm interesting, I never thought of the megatonnage that way but yes. There are roughly 10,000 war heads on the planet averaging 5-10 megaton each which puts humanity's total max megatonnage at about 100,000 megatons. Which could certainly destroy civilization as we know it but unlikely wipe out human life much less all life.

        Sure, we'd be in caves and need Thundarr to rescue us from the evil wizard but we'd probably make it. :-)

        • by Rei ( 128717 ) on Thursday October 12, 2023 @06:22AM (#63920175) Homepage

          It doesn't work that way. Greenhouse gases change the radiative balance on the 175 petawatts of energy the Earth receives from the sun. All human global primary energy is under 20 terawatts. The heat output of all our industry combined is a speck of dust compared the energy of the sun. Even tiny changes to the radiative balance of the sun from greenhouse gases and aerosols utterly dwarf any direct heat outputs (which rebalance rapidly via radiative transfer... subject to the radiation balance set up by forcings of greenhosue gases like water vapour and CO2 - the former being a more major GHG, but one whose levels rapidly respond to whatever long-term forcings are present. You could remove every drop of water from the atmosphere and in about two weeks it'd be half back, and a couple months later essentially fully reverted)

          • I'm talking about post nuclear war and Thundarr saving us from wizardly science slavery with his sun sword and his companions Ariel the sorcerous and Ookla the mok.

            Did you post in reply to the right post? I'm not disagreeing with your scientific statement about the atmosphere but you don't seem to be a Thundarr fan. Are you saying Thundarr the barbarians isn't real future history? Shameful to suggest. The stories are obviously true and a warning sent back to us from the future by Ariel.

          • All human global primary energy is under 20 terawatts.

            Interestingly, all geothermal energy radiating from the surface to space is around 20 tetra watts as well. Some from the heat of formation of the earth and some from radioactive decay. All the impact is going to do is lower the underground reservoir temperature slightly and increase the amount radiated to space. Most people don’t understand how bad the heat trapping by CO2 is, far worse than heat emission by several times during use and lasting tens or hundreds of thousands of years longer for a to

        • I donâ(TM)t know where you got the figure of there be about 10,000 warheads on earth each averaging 5-10 megatons. I wrote all this before realizing someone else already commented on this but I think I can elaborate a lot more on it because I have watched lots of documentaries on the subject of nuclear weapons. Yes there are about 10k warheads but they are not 5-10 megatons on average. The correct range is approximately 1 to 1000 kilotons or .001 to 1 megaton. The biggest nuke in the US arsenal until
          • Sorry about all those stupid TM marks in my post I donâ(TM)t know why it does that the slashdot site should replace any apply specific characters with generic â characters automatically. I tend to write my replies in the notes app and then paste them in which must be why those characters appeared. Guess Iâ(TM)ll just remove all the apostrophes going forward
          • Oh one interesting thing about the 50 megaton Tsar Bomba test was that the airplane that dropped it lost like a kilometer of altitude after the bomb went off and the heat and shockwave hit them. The pilot of the aircraft was so pissed off that he quit the military (retired?) like a week or two after the test. Like I said had they gone with 100 megatons instead of changing it to 50 megatons at the last minute I think itâ(TM)s highly likely that the plane and crew would have been lost. Use the nuke map w
      • Humanity isn't powerful in a planetary sense. The only real impact humans can have on this planet is in regards to the biosphere and a few hundred meters of dirt. Nothing we can do now, or the foreseeable future, can have any impact on the natural processes of the Earth. Contrary to popular liberal belief, we do not have the power or technology to sterilize this planet. At best we can wipe ourselves and larger land animals out.

        This is correct. All of the people talking about how we need to "save the planet" are either exaggerating wildly, or clueless.

        We can and do have significant impacts on the biosphere, of course. We drive lots of other species to extinction all the time, and we are fully capable of changing the biosphere enough to make it a much less pleasant place for us to live... and possibly even changing it enough that it becomes downright inhospitable to us. We aren't actually capable (not yet, anyway) of changing it

        • by cusco ( 717999 )

          If we manage to somehow sterilize the surface there will still be life on (or rather in) Earth. Subterranean microbes may outmass everything that lives aboveground already, we're limited to a thin smear on the surface while they have multiple kilometers of depth and almost unlimited amounts of energy to work with. Several scientists who are investigating the origin of life propose that it originated underground, in part because of the enormous range of resources available in that much area.

    • Imagine the earth is a huuuuuge cup of McDonald's hot coffee.

      We live on the surface of the scummy layer that floats on top where some of the cream hasn't mixed in yet. When we dig a few km we're still so far from the actual coffee we don't even know what coffee tastes like.

      The crust of the planet is a micro thin layer of scum that's cooled off on the surface of a giant ball of molten iron and liquid rock almost 4000 miles deep.

      Don't worry about the earth cooling from geothermal projects. We are physically

      • Mostly iron and nickle in the core, they say
      • We are physically incapable of doing *anything* to the planets core or mantle.

        I dunno, I saw something about people accidentally stopping and having to restart The Core [wikipedia.org] ... :-)

        [Noting that this was a fun, but all around very bad-science movie.]

        • I liked "The Core", :) but yeah, lots of science issues. Then again, it is rare that a Hollywood file is both fun and has decent science. In fact, the only one that immediately comes to mind is "The Martian", who's book was written by an ex computer programmer.
      • by Rei ( 128717 )

        While I agree with the general sentiment, it should be pointed out that (for the most part), the mantle is not liquid. It's more something like taffy, if taffy were over a thousand degrees celsius at crushing pressures and loaded with olivine and pyroxene. It's solid rock, but more stretchable / pliable than rock on the surface.

      • ...of a giant ball of molten iron and liquid rock almost 4000 miles deep.

        If that's all it was, it would only take a few 10s of millions years to cool down, as Lord Kelvin calculated back in the day (well, in 1897). But, as it turns out, the Earth is actually a ball of radioactive molten iron and liquid rock almost 4000 miles deep. It's radioative decay that's kept the Earth hot for 4+ billion years.

      • Imagine the earth is a huuuuuge cup of McDonald's hot coffee.

        We live on the surface of the scummy layer that floats on top where some of the cream hasn't mixed in yet.

        So, you’re saying we live on a very deep, flat earth?

        Kidding aside, the concerns about cooling the core are spurious, as you said, but I sometimes wonder about the local systems when there are projects akin to this. If there’s a particular source of heat in the local system, removing that heat could in theory have local side effects, like the contraction of neighboring rock, right? Something like a thermal equivalent to fracking. Granted, in most/all cases we aren’t pulling anywhere close

        • Thermodynamics and conservation of energy still apply, but if the underlying source of thermal radiation is fairly constant over time, then it's going to have a very small effect.

        • Whoa, buddy, are you saying you don't believe the earth is flat?

          Good, because it's not. Everyone knows the earth is hollow, with an inner sun, to keep the dinosaurs and Nazis warm.

        • by cusco ( 717999 )

          Local earthquakes are a frequent result of tapping geothermal resources, to the point where several project have been abandoned because of them.

      • When I first learned how internal combustion engines worked, I wondered what happened to the air burned by the engine. I wondered if it mattered that we were dumping carbon dioxide into the atmosphere, but figured that the Earth and its atmosphere was so large that it would never matter.

        And yet, here we are. An atmospheric change in the parts per million is considered a climate emergency.

        What happens when something cools? It shrinks. Could we cool the planet enough that we increase the prevalence o

        • It is possible to cool a local area, maybe, if and only if the underlying heat source that made that region hot has shifted away and thus it is already undergoing natural cooling.

          For example, the Hawaiian island chain is the result of magma coming up at (roughly) the same spot in an absolute sense while the plate move and take the older islands away from the hot spot.

          But if we tapped that magma vent could we stop island formation or somehow fuck up the existing islands? Not with anything that doesn't look

      • by DarkOx ( 621550 )

        Don't worry about the earth cooling from geothermal projects. We are physically incapable of doing *anything* to the planets core or mantle.

        The same things were said about dumping trash into the ocean and carbon into the atmosphere, sucking water and oil out of the ground, and on and on.

        While I'll agree all the evidence suggests we'd be fly on the elephants back here. I don't think its unreasonable to wonder if for sufficiently large scale projects we could locally change cooling characteristics enough to cause heaves, fractures, small earth quakes etc, that were not anticipated.

        • There's a critical difference.

          When we fuck with the ocean or atmosphere we are not fundamentally changing the air or water. We are just adding shit to it that's bad for us and other life. They retain their fundamental wetness and airiness properties.

          The amount of energy we'd have to pull from the earth to have any impact could drive our civilization at full blast for so long we'd have a galactic civilization by then. The scale is vastly different and the energy draw is trivial compared to what's there.

          T

          • by cusco ( 717999 )

            When I took a meteorology class in the last century our instructor said, "Take a basketball, if the Earth were shrunk down to that size the bumps are larger than Everest and the cracks are deeper than the Marianas Trench. Now dip it in a bucket and take it out. That sheen of water on the surface for the first few seconds? That would be thicker than our breathable atmosphere."

      • You don't have to talk about the mantle or even the deeper parts of the crust. Things like fracking and coal mining show that just altering the first km or so can cause serious problems.

        • Yes, we can trigger quakes. Local quakes that aren't much on the quake scales (I'm from California and been through real ones).

          The original question was, "Do they add to anything like preventing the earth from cooling too much or is there an impact on the core should we all start getting heat from there?"

          And the answer is "No, it's ok, don't worry about it, there are lots of things to worry about but this isn't one of them and please be careful with your McDonald's coffee, it's fucking hot, almost as hot a

    • by Rei ( 128717 ) on Thursday October 12, 2023 @06:33AM (#63920191) Homepage

      The total internal heat of the Earth is about 2e31 joules. Using it all at our current rate of consumpion of all forms of energy combined would take 32 billion years.

      For comparison (barring megaengineering solutions):

        * In 600 million years, runaway greenhouse effects driven by the expansion of the sun will have caused silicate weathering to take up the CO2 from earth's atmosphere, preventing photosynthesis
        * In 1 billion years, said runaway greenhouse effects will have boiled off Earth's oceans
        * In 2-3 billion years, Earth's magnetic dynamo will shut down and the solar wind will strip the light elements from our atmosphere
        * In 1,5-4,5 billion years, Earth's axial tilt will become chaotic
        * 4 billion years from now, Earth will be hotter than Venus
        * 7,5 billion years for now, the Earth will be swallowed up entirely by the sun.

      Even with all our technology, we're ants on the surface of this ball compared to the energy within.

      • by Rei ( 128717 )

        This of course ignores the constant influx of heat from radioactive decay in the earth, FYI.

        • To be fair the amount radiated to space from the surface boundary is only 20 tetra watts, the vast vast majority of heat internal to the earth is inaccessible. But it’s interesting that it’s about the same as human consumption. On paper it looks like we could use the surface ambient temperature to create a 99% efficient heat engine for essentially unlimited power as we sit around 300K while space is but 3K, but the hang up is the high thermal resistance of the atmosphere. That said, you can g
      • by Pascoea ( 968200 )

        In 1 billion years, said runaway greenhouse effects will have boiled off Earth's oceans

        Great. That was the first opening my dentist had. Guess I can go ahead and cancel it.

      • I remember reading, years ago, in one of Azimov's many essays, about how tidal friction is gradually transferring angular momentum from the Earth to the Moon. This is causing the Moon's orbit to increase, and the Earth's rotation to slow. Eventually, this will reach equilibrium, with the Moon in what will then be a geosynchronous orbit. One of the effects of this will be that the Earth's surface temperature will be similar to what Venus' is now. Alas, I don't remember how the timing of that compares to
        • by dryeo ( 100693 )

          According to Wiki, at the current rate (which does change), it will take about 50 billion years to get to that point and the day/month will be 47 current days. https://en.wikipedia.org/wiki/... [wikipedia.org] under the tidal evolution section.
          Long before various other dooms will befall the Earth, with the expansion of the Sun in somewhere around 7 billion years likely to vaporize both Earth and Moon.

    • Earth's internal heat budget is 47 TW*. This plant of 16 MW, which amounts to 0.000034%, meaning we can build thousands of similar geothermal plants before any notable effect on heat budget will occur.

      * https://en.wikipedia.org/wiki/... [wikipedia.org]

    • I'd wonder if it would have the same issues with fracking and depleting underground aquifers where you get small earthquakes and/or subsidence. Either way you are altering the ground under you and there will be ramifications.

      • by cusco ( 717999 )

        Local small earthquakes are often the result of tapping geothermal resources, some projects have had to be abandoned because of them.

    • The risk is approximately the same is a naval base capsizing the island of Guam.
    • by smithmc ( 451373 )
      Lemme guess - you also wonder whether building wind turbines will slow down the earth's rotation.
  • Energy isn't created nor destroyed. It can be converted or moved and that's it.

    So there's this underground pool with energy. If we bring it up to the surface we do so through
    any number of methods but because it's an even trade when we move the energy out of that
    pool 2.4km down and to the surface, we cool that area. The effects of cooling the area underneath
    the earth's crust are unknown. I'm not trying to be scary, just saying it's unknown.

    Then we have brought the energy to the surface and we convert it,

    • by AmiMoJo ( 196126 )

      Fossil and nuclear electricity generation also produce massive amounts of waste heat. That's what cooling towers are for.

      The cost seems okay too, competitive with renewables.

    • the best place to transfer it to ... to maintain original equilibrium... is that 2.4km down pool from which we got it.

      Or we could just radiate it out into space, Like the Earth has been doing for the last 4+ billion years.

    • 140 C is s good temperate for a steam turbine.
      • Re:Steam tables (Score:5, Informative)

        by Rei ( 128717 ) on Thursday October 12, 2023 @06:12AM (#63920163) Homepage

        It really isn't. As far as geothermal resources go, 140C is definitely on the cool side. Here in Iceland I doubt we'd even use that for power generation, we'd probably just mix it with cold water and use it for municipal heating.

        Also, as for the article: "superhot underground lake" is a really weird way of saying "geothermal reservoir". Calling it an "underground lake" makes people think like there's some sort of cavern with a lake in it. It's just a hot aquifer.

        • Agreed. 140C is very cool when using it to turn a steam turbine, as the linked article suggests. We can only use steam down to about 75C before we have to condense it back to water. So the 140C - 75C = 65C temperature differential is minimal. My question would be whether the source can maintain a constant 48MWt loss (all thermal plants are approximately 1/3 efficient, so we need to extract the 48MWt to maintain the 16MWe). Is the hot water pool's linkage to the heat in the mantle sufficient to restore
          • by Rei ( 128717 )

            Geothermal resources vary. Some have almost no ongoing heat influx and can be thought of as basically fossil reservoirs, while some have significant influx, and you can basically treat them as fully renewable. Most are renewed, but much slower than you extract from them.

            BTW, the lower the temperature of the resource, not only do you drop the amount of heat available to do work, and the power density, and not only do you drop the maximum Carnot efficiency of the resource on top of that, but you *also* run i

            • Re:Steam tables (Score:5, Insightful)

              by Rei ( 128717 ) on Thursday October 12, 2023 @09:59AM (#63920521) Homepage

              BTW, my favourite almost-unused geothermal power mechanism is a bit... radical. Namely, drilling straight into volcanoes' magma chambers. It happened in Hawaii accidentally, and they capped it. When it happened accidentally in Iceland, we instead turned it into a production well. And it's produced spectacularly well, by far the most powerful well in Iceland (and obviously has a huge resource to tap).

              Contrary to what the popular misconception might be, you're not really at significant risk for triggering an eruption. Drilling wells are full of heavy mud, heavier than the surrounding ground, so you're not making a weak spot for a blowout (in ours at Krafla, the magma backed up a couple dozen meters into the well before the pressure neutralized). And by taking heat out of the magma chamber, you make the magma more viscous, easier to retain its gases, and harder to erupt. Take enough out and what you have is no longer a magma chamber, but what one might colloquially call "rock" ;)

              • Thanks for the information, Rei. Your knowledge is much deeper than mine. My knowledge comes from working with power plant instrumentation rather than the thermal properties of the heat sources.

                For your statement, "the issue that our low-temperature power generation cycles don't get as close to the theoretical Carnot maximum as higher-temperature cycles." Is that due to the the machinery we have being less efficient at recovering the energy available?

                I was mesmerized by the Iceland volcano at Litli Hr
        • Also, as for the article: "superhot underground lake" is a really weird way of saying "geothermal reservoir".

          See I was confused because they didn’t specify how big the underground lake was in swimming pools or how hot it was in terms of McDonald’s coffee. /s

    • Energy isn't created nor destroyed. It can be converted or moved and that's it.

      Kind of, not wrong but incomplete. You miss the principles of entropy and it’s cousin exergy [wikipedia.org] or energy available to do useful work because heat available to do work is precisely what this entire article and thread is about. Reframing the thermodynamic problem in terms of exergy greatly simplifies the many arcane explanations of things and reduces computational complexity in a manner similar to least action does for other physical phenomena.

    • A lot of heat is radiated out into space
  • by orzetto ( 545509 ) on Thursday October 12, 2023 @06:52AM (#63920219)

    The concept may be tantalising, but the price tag of 50 million euro is way out of proportion for a measly 16 MW plant. I mean, I have worked with air coolers that had that rating in a refinery.

    Assuming the plant lasts 50 years and has 8000 operating hours a year, that gives 40000 hours and 640 GWh through the lifetime, for a price of 78 €/MWh (not accounting for interest rate), or 291 €/kWh with a very favourable 4% interest rate, or 630 €/kWh with a commercial 10% interest rate.

    Considering that the current power price in Croatia usually are below 100 €/MWh (yes, they were higher in 2022), and that the assumptions I use are VERY generous in regard to lifetime and availability, and that I totally ignored operating costs, this looks like a horrible business case.

    • Re: (Score:3, Informative)

      by thegarbz ( 1787294 )

      I mean, I have worked with air coolers that had that rating in a refinery.

      That is quite an ignorant comment. Air cooling is to power generation like playing with lego is to building a house. Cooling something is trivial and cheap compared to heating something to a significant temperature. I have worked on 16MW power generation systems in a refinery (since you felt the need to point that out) and 50million is not that far off the price tag for building a small combined cycle gas generation system.

      Heck we're staring down the barrel of a 25MW retrofit for an old turbine, without eve

      • With a capacity factor of around 30% of nameplate in wind, that means to get the equivalent power for a windfarm you would be spending $66million for 16MW of actual generated power, and even then it's still intermittent and not baseload.

        Is there such a thing as baseload generation any more? Base load originally refered to load (obviously!) that was always required, and not power generation. Then it got applied to forms of power generation used to meet the base load. These were those that were cheap to run and / or had long startup times, so mostly thermal power plants like coal or nuclear that you didn't want to shut down. As these also had high capacity factors, that kind of got mixed in with the definition.

        With coal and oil fired thermal

        • there are only two types of base load:
          a) the german one, that does not exist anymore as renewables produce more power than "base load"
          b) the American one, where idiots on the internet mix up base load with load following and adjusting to demand

          All other kinds of baseload ceased to exist long ago, The only exception I'm aware of is France ...

          Yes, I know. 90% of the people on this site won't get it. As they do not know what base load means :P

      • It is most likely a typo anyway and it is a 160MW plant or bigger. No idea about the heat source, but if it is big enough it could be 16GW (8 nuclear reactors or big coal plants) ... but then the price would not fit.

        I mean 16GW as a typo of 16MW.

        So no. The business case is not horrible in the slightest.
        Correct. As if the builders never counted the money in the bank and calculated how much they would/could earn ... lolz

        • by Rei ( 128717 )

          16MW isn't abnormally low for a geo plant. It'd be larger than five US geothermal plants.

          Each well only produces a few MW of power, so you don't have to make geo plants very big to be viable.

      • 30% of nameplate would be quite low these days.
        • Actually, you might have been thinking of onshore. I'm in the UK so more used to thinking of offshore which has a much higher capacity factor for new installations.
        • 30% of nameplate would be quite low these days.

          Depends on where. But whatever bump the number up, it doesn't detract from the point in any way. 50million for 16MW for a geothermal powerplant is not expensive, and 16MW continuous generation for $50m investment is not unfundable.

          • by q_e_t ( 5104099 )
            Around 50% for offshore is possible but at higher cost, so agreed - much of a muchness.
    • Re: (Score:2, Insightful)

      by AmiMoJo ( 196126 )

      That cost is comparable to currently being constructed nuclear plants. Hinkley Point C is somewhere around the 150 Euro per MWh mark and rising with inflation.

      It really depends if that 50 million Euro price-tag includes technology development costs that lead to other plants being built more cheaply. Early wind and solar were expensive, now they are the cheapest.

    • by HiThere ( 15173 )

      My question would be "what's heating that water, and how fast does it reheat it?". And that may determine the effective lifetime of any plant, as if you start cooling the water by extracting heat faster than it is being added, the extraction becomes less efficient. Unless it's flowing (pools often aren't) you may also need to stir it periodically.

    • by ledow ( 319597 )

      I'd do it, if you gave me a 50-year exclusivity to the site.

      Because once you have that initial point proven (and that may be more expensive than optimal, but that barely matters), you'd be able to use the same bore or sink more bores and have an almost limitless energy source to sell on.

      So long as someone else can't plunk down another borehole down the road into the same source, I think that would be an attractive business/investment proposition.

    • by Rei ( 128717 )

      Check your math. You omitted a zero on your hours. Divide your calculated prices by 10.

      Also, you're comparing to fixed-rate power costs, but geo can provide baseload and peaking power, which goes for much higher rates.

    • ^ This is like ONE WIND TURBINE
      You should have some numbers memorized

      14-18 MW is what one wind turbine can produce with an average capacity factor of 36% for land https://css.umich.edu/publicat... [umich.edu]
      1.2 GW is what a typical nuclear plant produces at near 100% capacity factor
      Solar costs about $1billion per Gigawatt with 25% capacity depending on latitude https://coldwellsolar.com/comm... [coldwellsolar.com]
      • 14-18 MW is what one wind turbine can produce

        The world's largest commercially available turbines are 13MW. The largest currently in prototype phase is 16MW. 18MW turbines exist only as drawings and computer simulations so far.

      • Nukes do not have a nearly 100% capacity factor. The refueling alone drops it to 90%. Then they rarely run at max, they run around 90% - 95% capacity.

        Capacity factors are completely irrelevant. Except for reporting purpose and /. idiots: no one uses them to run a business.

    • 400000 hours, not 40000

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