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'A Very Finnish Thing': Huge Sand Battery Starts Storing Wind Energy In Soapstone (cleantechnica.com) 72

Posted by EditorDavid from the strong-Finnish dept.
This week Finland inaugurated the world's largest sand battery, according to the Independent, "capable of storing vast amounts of energy generated from renewable sources like solar and wind."

The battery "will enable residents to eliminate oil from their district heating network, thereby cutting emissions by nearly 70%," notes EuroNews: Euronews Green previously spoke to the young Finnish founders, Tommi Eronen and Markku Ylönen, who engineered the technology... Lithium batteries work well for specific applications, explains Markku, but aside from their environmental issues and expense, they cannot take in a huge amount of energy. Grains of sand, it turns out, are surprisingly roomy when it comes to energy storage... The sand can store heat at around 500C for several days to even months, providing a valuable store of cheaper energy during the winter... The battery's thermal energy storage capacity equates to almost one month's heat demand in summer and a one-week demand in winter in Pornainen, Polar Night Energy says...

Polar Night Energy has big ambitions to take its technology worldwide, and is currently in "active discussions" with both Finnish and international partners.
This project (in the Finnish city of Pornainen) "is really important for us because now we can show that this really works," a spokesperson for Polar Night told Clean Technica: The profitability of the sand battery is based on charging it according to electricity prices and Fingrid's reserve markets. Its large storage capacity enables balancing the electricity grid and optimizing consumption over several days or even weeks... "The Pornainen plant can be adjusted quickly and precisely," explained Jukka-Pekka Salmenkaita, vice president of AI and special projects at Elisa Industriq, "and it also has a remarkably long energy buffer, making it well suited for reserve market optimization. Our AI solution automatically identifies the best times to charge and discharge the Sand Battery and allocates flexibility capacity to the reserve products that need it most. Continuous optimization makes it a genuinely profitable investment."
Thanks to Slashdot reader AleRunner for sharing the news.

'A Very Finnish Thing': Huge Sand Battery Starts Storing Wind Energy In Soapstone More | Reply

'A Very Finnish Thing': Huge Sand Battery Starts Storing Wind Energy In Soapstone

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  • It rings a bell... (Score:3)

    by kackle ( 910159 ) on Saturday September 06, 2025 @10:10PM (#65644198)
    If I recall correctly, I read that London's "Big Ben" bell took an entire month to cool off after forging it.

    • Re:It rings a bell... (Score:4, Interesting)

      by serviscope_minor ( 664417 ) on Sunday September 07, 2025 @04:53AM (#65644452) Journal

      I haven't read that (or not read it), but it would not be quite reasonable. Probably you mean cast, though. Either way I gather that kind of thing (slow cooling) is important in large casts, since you want the stresses to equalize as it goes down to room temperature. That's probably more a case of insulating it very carefully so it cools slowly.

    • If I recall correctly, I read that London's "Big Ben" bell took an entire month to cool off after forging it.

      Cool story, but was there an explanation given as to why? Most forgers understand the advantages of quenching without delving into metallurgy hardending.

      Not sure why they needed to wait. That’s not exactly some knife-thin metal just begging to warp.

      • The bell they made on the first attempt cracked. So, the answer is they cooled it down as slow as possible.

      • Cool story, but was there an explanation given as to why? Most forgers understand the advantages of quenching without delving into metallurgy hardending.

        And most bell manufacturers understand you do *not* quench bells. A month isn't actually that exciting. Big Ben is a big arse bell, but even small bells often take several weeks to cool. The cooling process is done *in* their moulds. Not every forged item gets quenched. That is a function of what is being made and how it is being made.

        You don't want a bell to be hard. Hardened metals have a tendency to crack when you hit them with other hard metals. Additionally bells need to be tuned after casting, if you

    • The Hale telescope mirror was held at pouring temperature for a month, then cooled over 10 months.

  • Why don't you want to just convert Carbon and O2 into CO2? It seems to be more expensive now, but what the hell? It can't hurt. huh?

    • We no longer live in a world where this type of thing is obviously sarcasm; AI will parse this and feed parts of it back to idiots, and the context will be missed by both parties. You have got to tag it.

  • Heat is useful in Finland's metropolitan heating systems, no doubt, but I wonder how they convert that heat into electricity, which is something a chemical battery doesn't need to do. They clearly have chosen a solution,since there are surely many...I'm just too lazy to look it up.

    • Re:Heat? (Score:5, Informative)

      by jenningsthecat ( 1525947 ) on Saturday September 06, 2025 @10:47PM (#65644242)

      Heat is useful in Finland's metropolitan heating systems, no doubt, but I wonder how they convert that heat into electricity, which is something a chemical battery doesn't need to do. They clearly have chosen a solution,since there are surely many...I'm just too lazy to look it up.

      I RTFA, and I'm pretty sure that they don't convert the heat back to electricity. I think that they use it for home heating - including hot water for showers, laundry, etc. - and to provide some heat for industry.

      If I'm correct, the "optimizing consumption over several days or even weeks" is entirely about converting electricity to heat when supply is high and demand is otherwise low, allowing the stored heat to be used directly as needed rather than converting it back into electricity.

      So it works in a cold climate like Finland's, but probably wouldn't work so well in warmer places. Unless, of course, there's industry that could use that heat to reduce the percentage of heat generated using sources which emit CO2.

      • Hot water always has at least a little demand, but with heat pump systems, they could use excess power to produce cold water, to be used for cooling during high demand periods.
        Basically, imagine if for my house I had a X gallon insulated water tank. Rather than heating it, it's cooled using a heat pump when power is cheap and temperatures lower, such as at night, making the cooling more energy efficient.
        Then, during the day, rather than going through the high-power compressor for the cooling and the conden

      • Re:Heat? (Score:4, Informative)

        by AmiMoJo ( 196126 ) on Sunday September 07, 2025 @04:35AM (#65644440) Homepage Journal

        Indeed, MacMann will be getting a boner as he reads this because it makes inflexible nuclear plants a bit less redundant on a highly flexible grid, as when nobody wants their expensive energy they can dump it into heating sand.

      • So it works in a cold climate like Finland's, but probably wouldn't work so well in warmer places.

        It works wherever district heating is potentially a useful source of heating, that includes much of Europe and cities such as Paris where the average lows in the dead of winter are well above freezing point. If you need heaters in your house and you have relatively dense housing, this is a potentially good solution. No need for average highs below freezing like in the town where this is located.

    • They don't produce electricity, this is a heating solution.

      They keep and use what the Sun sent in last summer instead of burning the solar energy stored as gas hundreds of millions of years ago.

    • Re: (Score:2)

      by shilly ( 142940 )

      They're working through an electricity conversion process at the moment. Currently, the system can output hot water, hot air or steam, which is why it's useful for district heating and industrial applications. Obviously, being able to convert back into electricity substantially expands the use cases, but they're not there yet, and the current use cases are still pretty helpful

    • Given their location heat is the single largest use case for their entire system for at least half the year, and in many places entire towns rely on centralized systems for heating their homes and water. Coming up with a narrowly tailored optimisation like this for that specific need makes a lot of sense for them.

    • Fin like saunas though more of course in winter. Hot water common for dishes and bathing. Finland could get little chilly occasionally evenings.

    • As with 99% of all electricity generation, they use steam from a closed water loop that runs through the sand.

      https://polarnightenergy.com/s... [polarnightenergy.com]

  • Really. Rofl.

  • Facts behind it (Score:5, Informative)

    by Luckyo ( 1726890 ) on Saturday September 06, 2025 @10:38PM (#65644232)

    So I read the actual source, rather than all the silly editorials.

    https://www.loviisanlampo.fi/b... [loviisanlampo.fi]

    Then I followed up on some of the links in it leading to relevant companies.

    It's basically a sponsored grade local thing that seems to be done mostly for PR/environmental credits/environmental promises reasons for participants. 1MW hypothetical output, 100MWh potential storage. Thermal only, intended for remote heating. Blog breaks down project sponsors as follows:

    Municipal government has their own net zero project, so they chipped in. Most of their main buildings are remote heated, so they also have investment in this working.
    Region has a world's largest (according to them) manufacturing company for heat storing fireplaces (og. Finnish: varaava takka), and company that makes them has a lot of stone sand waste from making said fireplaces. They're providing the stone sand used plus some funding, and this gets them some "circular economy" certifications which makes their loans and credit lines cheaper in some cases.
    Heating company basically says that this will let them stop using some of their thermal peaking stations, so they're projecting total removal of oil based peaker and significant reduction in wood chip burning peaker. They're also owned by an environmental investment focused fund and that one is chipping in for the costs.
    Finally they're getting government subsidy from government's business fund.

    I also suspect this is about the fact that 2/5 Finnish nukes sit in the same municipality that this central heating company operates out of, which leads to complexities of running heat peakers because of how electric grid has to be set up. Many if not most of the heat peakers are dual use, and provide heat as a secondary function of electricity production (i.e.you just add an additional circuit in a typical power plant, where some of the steam is directed into a separate heat exchanger to heat remote heating circuit contents of which are then pumped across remote heating network).

    Overall, an interesting idea but seems like something that can be only really done on a very small level, and in very specific locations where they can easily source sand from that specific type of rock that is really good at reserving heat as some waste of a specific production line. Scaling is a very big question mark both in availability of this kind of sand, and in just how little heat you can actually get out of it (1MW maximum out of 100MWh capacity isn't great, and they're claiming very high efficiency (85-90% for smaller units) which seems rather high for what this is. I suspect they're only giving us efficiency of only some part of the system, rather than the whole thing.

    • Re:Facts behind it (Score:4, Informative)

      by Firethorn ( 177587 ) on Saturday September 06, 2025 @11:23PM (#65644264) Homepage Journal

      (i.e.you just add an additional circuit in a typical power plant, where some of the steam is directed into a separate heat exchanger to heat remote heating circuit contents of which are then pumped across remote heating network).

      Depending on how the heating system is set up, typically the steam is used for heating AFTER passing through the turbine. Basically, rather than going through a condensor that puts the heat into the air or a water source like a river, or even evaporating water, like nuclear power plant cooling towers, it's used for district heating.

      High grade dry steam is used for electricity generation, low grade wet steam for district heating. Done that way, it's practically free except for the infrastructure to utilize it. Basically, allows the plant to produce the electricity at the ~50-60% it can manage, but be effectively 90% efficient for how high efficiency furnaces for heat can be.

      Now, I was up in Alaska, heating demands often exceeded electricity production, so they did indeed have the ability to use the high grade steam for heating, but it's all about the ratios, I guess.

      • Re: (Score:2)

        by Luckyo ( 1726890 )

        It depends on specifics of the system, and expected loads, but yes, this is a common setup. Essentially when you don't need too much heating, you can just focus on keeping turbine in the optimal mode and dump whatever is left after steam has left low pressure stage of the turbine into the final heat exchanger before you cycle it back the boiler to be heated back up.

        But if it's cold outside and you need to get much more heating than electricity, you will want to have some kind of a partial bypass (or other w

        • I'm just confused at their efficiency numbers, because keeping this much of a surface at temperature sufficiently high to be able to effectively extract 1MW out of it into the heating circuit (needs high enough temperature differential between circuit taking heat out of the sand and sand itself) is going to be losing at least some heat just to the fact that no isolation is perfect.

          That would be getting into economies of scale and the square cube law.
          First, one doesn't need to heat "the surface" to temperature, one can run pipes through the sand even in the middle to deposit and extract heat.
          Next, it's like how a big office building or retail store can be heated/cooled more efficiently than a small house, even with less insulation (R-value). It's just so huge that there isn't as much surface area for the volume being conditioned. For that matter, any occupied building eventually swi

          • Re: (Score:1)

            by Luckyo ( 1726890 )

            All heat exchangers are fundamentally surface increase mechanisms. Because heat is transferred as a function of surface and thermal conductivity. You can see this in everything from tiny laptop CPU coolers to things we use to transfer heat in gigawatt grade power plants primary circuits. This is why exposed surface is one of the factors in the formula that determines R-value.

            As for volume, it is true that as volume increases, surface per volume ratio decreases. The issue remains in the thermal differential.

            • All heat exchangers are fundamentally surface increase mechanisms.

              Except this isn't a heat exchanger, this is a heat bunker, a storage system. It incorporates at least one heat exchanger in order to fulfill its function of actually storing and providing heat, but that can be buried more or less in the center of the thing. As such, other than the integrated heat exchangers that can have their interfaces insulted and not flow air or liquid when heat transfer isn't necessary, the goal is to minimize surface area, which one can by both making the shape closer to a sphere (a

              • Re: (Score:2)

                by Luckyo ( 1726890 )

                I don't think you understand what is being said, and end up arguing against wind mills as a result. This is what leads to these hilarious statements like "it's a heat bunker" (obviously, but the more surface, the more heat is exchanged, the more thermal difference, the more heat is exchanged) and "just heat pump it bro".

                It's also hilarious that you think cooling municipal buildings is of higher importance that heating them in Finland, and that you can heat pump things efficiently with this.

                Hint: it's really

      • Now, I was up in Alaska, heating demands often exceeded electricity production, so they did indeed have the ability to use the high grade steam for heating, but it's all about the ratios, I guess.

        I attended university in the Midwest and part of a thermodynamics class we got to tour the co-generation plant on campus that supplied heating, cooling, and electricity for the campus. Heating load often exceeded the electric production load, even in the warmer climate in the Midwest. They mentioned the steam was used for more than space heating, including in the cafeteria kitchens but they didn't specify what they used the steam for or how that worked.

        They had two different steam systems. There was the

        • I know trigeneration systems exist, was just focused on cogeneration. My other post mentioned using excess power to cool as well. They could even use a similar sand battery that is cooled to use as a heat sinkmto provide chilled water or even antifreeze.
          Using the steam to directly power a compressor is efficient, smart, over trying to generate electricity to then power it, at least as long as you already have a campus heat distribution system.
          There are other possible tricks with steam, of course.

        • Since you like this stuff, if you ever visit London, make sure you schedule time to visit HMS Belfast. It's all that, on the scale of a light cruiser (in WW2 terms). Tubes everywhere, vast amounts of steam for propulsion but also a huge number of ancillary systems, everything from electrical generation to heating the bread makers in the galleys.

        • they didn't specify what they used the steam for or how that worked,

          Definitely for humidifying dry air up to 50% relative.
          Possibly pre-heating water for cooking or dishwashing.
          Possibly an absorption refrigerator.

          • Assuming it's at 450F or so, it could even be heating ovens. A lot of stuff is baked at 350 - 450.

      • too bad the heating source is coal...

        • Re: (Score:2)

          by shilly ( 142940 )

          It's Finland, dummy. They were at 0.7% coal in 2024/25. They'll be at zero coal by 2029. They're 36% nuclear, 14% hydro, 26^ wind, and the rest a ragbag of other sources, and 89% total are low carbon.

    • Re: (Score:2)

      by AmiMoJo ( 196126 )

      This tech has been in use on a small scale for many years. Domestic heat storage is common in Europe, with everything from water tanks to special gels. They can be heated with gas or electricity, or even directly with solar by circulating water through concentrators on the roof (which work in winter).

      This is a nice scaling up of the idea. It could also be used to store electricity, which again has already been a thing for many years. Solar thermal generators have stored energy to use overnight for many year

    • Overall, an interesting idea but seems like something that can be only really done on a very small level

      This is a viable thermal storage solution to literally anywhere where district heating exists, and solves a problem that everyone has. Sure nukes need peakers, but you know what else does? Wind, and solar.

      This is energy storage. All grids regardless of makeup need either peaking or storage. While this doesn't directly store on the grid, it is a form of dispatchable demand allowing a district heating system to be electrified and run at a time when energy is plentiful. I.e. you don't need the wind to blow to

  • If they had spent all that money on subsidized drilling rigs for ground source heat pumps, those homes could have been heating at COP 5+.

    Sure, thermal storage is a form of seasonal storage too, but at COP 5+ the homes won't add a lot of electrical load in winter.

    • I'm sure there is a cigar box somewhere, with on its back an estimate of the costs of both systems.

      But i agree. I couldn't find anything of the source of their heat. Is it simple resistance heating (COP=1) or did they invest in some fancy heatpump system with an higher COP ??

      • District heating are the monorails of heating. When done as a private/public partnership it's almost always a disaster, a very profitable disaster. Businesses love the scam and politicians love getting scammed into it.

        Pumping to 500C might be COP 1.01 with an ideal heatpump, so yeah, it's resistive.

        PS. I think street level heating+cooling with ground source heatpumps could make economic sense though, the pipes needed are far smaller so it can go under the sidewalk.

        • Re: (Score:2)

          by shilly ( 142940 )

          In what way a disaster? Economic? User experience? Both? Something else like carbon intensity? And why are they always a disaster when set up as a PPP? What is it about that setup that makes them a disaster?

          • Because it's almost always more expensive for the consumer and losses get socialized and profits privatized. Electricity and gas hits all people, keeping the endless greed trying to corrupt PPPs somewhat in check. District heating only hits a couple rubes and requires convincing only local government, more room for monorails.

            In my country mandatory participation is no longer allowed though and now the schemes are completely falling apart, with local governments predictably getting fucked in the process.

    • Yeah but how does that help stabilise and electrical grid? I think you're trying to solve a different problem than they are. The point was not to heat homes, the point was to create an energy storage system.

      • Unfortunately, it's an energy storage system which makes even hydrogen look good efficiency wise (more than two times worse than electricity->hydrogen->electricity->ground-source-heatpump).

        Domestic heating is not a small consumer, to continue doing it at COP 1 is hard to justify.

    • Re: (Score:2)

      by chefren ( 17219 )

      There is no need to subsidise ground source heat pumps in Finland, 15% of single home houses and 9% of homes (which includes apartments) are using that already and the popularity is growing, because there is a clear ROI on switching from oil to heat pumps.

      • Most Fins just buy air to air though and just use more electricity when it gets really cold.

        If they could be convinced to go to ground source heat pumps when their system needs renewing, the worst case grid load will be reduced.

  • Of course it’s clean energy, they are using soapstone.
  • are cast in the lost wax method and cool in their sand molds for quite a while - i don't recall how long but quite a while

  • ... those sand batteries [wrestlinginc.com]!

  • ... through rock is slow. Very slow. This is why people can walk on Hawaiian lava fields while molten rock is some meters below them. It might be better to use molten salt for heat storage, aside from the costs. Rock/sand is cheap.

    I've often wondered about ground source heat pumps. Air condition your house for a few months and soon, the temperature of the earth around the heat exchange pipes warms up, decreasing the system efficiency. I suspect that these work in large part because the wells are often sun

  • Just wanted to point out that Pornainen is not a city. It's not even a town. It's a municipality of around 5 000 people, comprising eight villages.
    • Well, I know it varies quite a bit, but in New York State those eight villages incorporated as a single municipality would count as a town. New York's smallest town is about half that size.

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