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Power Earth

Could Sand Be the Next Lithium? Searching for Better Renewable Energy-Storing Batteries (msn.com) 135

"The green energy revolution still faces a huge obstacle: a lack of long-term, cost-efficient renewable storage," writes the Washington Post.

But then they check in on a Finnish start-up running the world's first commercial-scale sand battery, which uses solar panels and wind turbines to heat sand-filled vats (up to 1,000 degrees) to back up district heating networks: The sand can hold onto the power for weeks or months at a time — a clear advantage over the lithium ion battery, the giant of today's battery market, which usually can hold energy for only a number of hours.

Unlike fossil fuels, which can be easily transported and stored, solar and wind supplies fluctuate. Most of the renewable power that isn't used immediately is lost. The solution is storage innovation, many industry experts agree. In addition to their limited capacity, lithium ion batteries, which are used to power everything from mobile phones to laptops to electric vehicles, tend to fade with every recharge and are highly flammable, resulting in a growing number of deadly fires across the world. The extraction of cobalt, the lucrative raw material used in lithium ion batteries, also relies on child labor. U.N. agencies have estimated that 40,000 boys and girls work in the industry, with few safety measures and paltry compensation. These serious environmental and human rights challenges pose a problem for the electric vehicle industry, which requires a huge supply of critical minerals.

So investors are now pouring money into even bigger battery ventures. More than $900 million has been invested in clean storage technologies since 2021, up from $360 million the year before, according to the Long Duration Energy Storage Council, an organization launched after that year's U.N. climate conference to oversee the world's decarbonization. The group predicts that by 2040, large-scale, renewable energy storage investments could reach $3 trillion. That includes efforts to turn natural materials into batteries. Once-obscure start-ups, experimenting with once-humble commodities, are suddenly receiving millions in government and private funding. There's the multi-megawatt CO2 battery in Sardinia, a rock-based storage system in Tuscany, and a Swiss company that's moving massive bricks along a 230-foot tall building to store and generate renewable energy. One Danish battery start-up, which stores energy from molten salt, is sketching out plans to deploy power plants in decommissioned coal mines across three continents...

But in order to succeed, natural batteries will need to provide the same kind of steady power as fossil fuels, at scale. Whether that can be achieved remains to be seen, say energy experts. And the industry may be subject to the same pitfalls that loom over the renewables energy sector at large: Projects will need to be constructed from scratch, and they might only be adopted in developed countries that can afford such experimentation. Lovschall-Jensen, the CEO of a Danish molten salt-based storage start-up called Hyme, says the challenge will be maintaining the same standards to which the modern world has become accustomed: receiving power, on demand, with the flip of a switch.

He believes that natural batteries, though still in their infancy, can serve that goal.

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Could Sand Be the Next Lithium? Searching for Better Renewable Energy-Storing Batteries

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  • by Baron_Yam ( 643147 ) on Saturday August 26, 2023 @11:46AM (#63799078)

    He solved both the flammability and cathode degradation issues with a new solid-state battery.

    If I were looking to build a facility that stored electrical power that DIDN'T have to be converted into heat and back again, at much higher densities... I'd be funding the commercialization of the solid-state li-ion battery rather than trying out giant insulated vats of sand.

    • If I were looking to build a facility that stored electrical power that DIDN'T have to be converted into heat and back again, at much higher densities... I'd be funding the commercialization of the solid-state li-ion battery rather than trying out giant insulated vats of sand.

      Part of the point is that since this energy is going to be used for heat anyway, so you don't have to convert it back again. With that in mind, it's certainly possible that this is more efficient and cost-effective than a rack of Li-ion batteries.

      Although the author of the article presumably doesn't understand that, since while energy storage in sand makes sense in some circumstances, it certainly can't replace li-ion batteries for most uses.

    • by pixelpusher220 ( 529617 ) on Saturday August 26, 2023 @04:36PM (#63799754)
      Different use cases.

      Lithium is for density and quick discharge...mobile applications are it's bread n butter.

      This is more grid scale, you can mitigate a slower output with greater size.

      The real benefit is it doesn't degrade, has a very slow loss rate (with more insulation it gets even slower) AND it uses a *very* common natural material. Literally any grade sand, junk sand works just fine.
    • by dublin ( 31215 )

      Once again, ignorance of physics and engineering permeate an article rah-rah-ing for a scheme that can simply never work all that well.

      The ignorance is of the *quality* of heat - there's plenty of low-quality heat (and you'll lose a lot of that into sand before you can get to temps that provide high enough heat quality (delta-T) to be very useful for anything. And when you're done, you still don't have the advantages of latent heats of condensation vaporization. There's a reason phase changes rule in heat

  • Another article preaching a green agenda word soup without any interesting tech info.
    • Another article preaching a green agenda word soup without any interesting tech info.

      To paraphrase Crocodile Dundee, that's not word soup. That's word soup [imgur.com].

    • by StevenMaurer ( 115071 ) on Saturday August 26, 2023 @12:47PM (#63799234) Homepage

      Another article preaching a green agenda word soup without any interesting tech info.

      That's a fancy way of saying "I can't read"

      Let me break it down for you in simple terms: the technological idea is to create a "heat battery" consisting of several tons of sand, which is heated to 1000 degrees in the summer, and then keeps a building (commercial or residential) warm all throughout winter. Technically, the heat could be used to drive steam turbines as well, but the direct heat use is 95% efficient.

      This is important because just heating and lighting buildings account for 27% of all worldwide greenhouse gas emissions. It's not all cars.

      • Interesting tech info would be some calculations. How much heat can you store in several tons of sand ? How much heat do you need to warm a building throughout winter ?
        • Perhaps read/watch the numerous videos here [polarnightenergy.fi]

          They clearly explain their tech and specs.
        • For silica About 700 Joules per kilogram per degree Kelvin.

          For granite about 800.

          Water is 4184, but won't be a liquid anymore at 1000 C

          The data you are looking for is specific heat capacity. The rest of the math is up to you.

          The other information you need is this,

          "Most gravel and crushed stone products have similar weights per ton. Gravel and sand typically weighs 2,200-2,700 pounds per cubic yard. In addition, there are 2,000 pounds to a ton. Certain products, like washed gravel, weigh more like 2,835 poun

          • So, let's say I use 600 cubic meter of natural gas during a winter period, that's about 24 gigajoules. One ton of sand at 1000 degrees is good for 700 megajoules, so I need 34 tons of sand to keep my house warm. I don't think I have room for that.
      • by bn-7bc ( 909819 )
        Sems like a nice idea but you would need a small steam turbine to run everything that does requires electricity (Pc, tv fringe etc) obv, but for straight heating, absolutely run a heat carrier trough some pipes to a set of radiators an bingo stored solar het in the winter, for extra bonus you can have the heatsink of your air-conditioned dump het into the heat battery during summer (hey you.ve already paid for the energy to cool your house so why not store the output --- come toop think of it why not just
        • The tech you're describing is called a heat pump - and on simple inspection seems doable.

          One issue is just the temps of AC output aren't likely high enough to 'charge' this type of sand battery. With solar panels and electric heat generation you can easily get to 1000C. Your AC isn't putting out anywhere close to that...or at least I hope not! So you'd need some method of heat 'concentration' etc before it would be viable.
          • by bn-7bc ( 909819 )
            Thank you, yeas heat pump was the word i was searching for, but for some reason was unable to remembervat that moment oh well
    • What part of storing summer heat for winter is hard to understand?

      As anyone technical will happily tell you, simple is always better. And this is literally rock/sand simple.
  • by dfghjk ( 711126 ) on Saturday August 26, 2023 @12:00PM (#63799110)

    "The sand can hold onto the power for weeks or months at a time — a clear advantage over the lithium ion battery, the giant of today's battery market, which usually can hold energy for only a number of hours."

    Morons.

    Since this stores energy as heat and electricity is needed, what is the conversion efficiency? And what are the energy densities, including the entire assembly required?

    Seems like a mixture of LiIon demonization and deliberate lack of insight and information. Bad faith more than likely.

    • "The sand can hold onto the power for weeks or months at a time â" a clear advantage over the lithium ion battery, the giant of today's battery market, which usually can hold energy for only a number of hours."

      Morons.Doubly so, since that's flat-out wrong. Lithium Iron Phosphate batteries, for instance, only self-discharge 2% per MONTH. Charge 'em up, leave 'em for a year, and they still have over 78% charge. (They also don't contain cobalt.) Auto-type cells are similar. Can you imagine a car that

    • "The sand can hold onto the power for weeks or months at a time — a clear advantage over the lithium ion battery, the giant of today's battery market, which usually can hold energy for only a number of hours."

      Morons.

      Since this stores energy as heat and electricity is needed, what is the conversion efficiency? And what are the energy densities, including the entire assembly required?

      Seems like a mixture of LiIon demonization and deliberate lack of insight and information. Bad faith more than likely.

      Why morons?

      What do you use your electricity for? For most households and offices, the heating and/or cooling of the building and/or persons inside it is by far the largest chunk of the energy bill. So converting heat to electricity to heating or cooling, will indeed be terribly inefficient, as you correctly state. What you didn't read was the fact that these technologies skip the middleman, in this case electricity all together. And that is very interesting technically and financially.

      Now I live in Paraguay

      • Poster was apparently looking in a mirror when seeing 'morons' ;-)

        It does 'use' electricity...to create the heat it stores. But that can be from solar or whatever so it's generally not useful to worry about where it comes from. The 95% efficiency is the real killer metric here.
      • by tragedy ( 27079 )

        Why morons?

        I think they were referring to the statement that lithium-based batteries can only hold power for a few hours. This is self-evidently not true. There's basically a 100% chance that the author of the article has multiple electronic devices powered by lithium-based batteries, so it's practically inconceivable for them to think that.

    • maybe read their website. It's all laid out there.

      or hey, use Google if you're capable of that level of effort.

      But since you don't seem capable of that: it's efficiency is..... NINETY-FIVE PERCENT [polarnightenergy.fi]
      • by tragedy ( 27079 )

        95% should be impressive. However, a decent air-sourced heat pump is more like 400% efficient when it comes to heating applications. It seems like that should break some physical law, but it actually works. Storing heat in sand may still turn out to be more cost effective. As others have pointed out though, there's no phase change or chemical changes involved here. You can store orders of magnitude more energy in phase changes and chemical bonds than by merely heating a material. Batteries store power in ch

        • Industrial heat pumps go to about 200C...maybe. This is well outside those temps.

          Read their technical stuff - really is blatantly simple. No need to add a heat pump. Solar -> resistive heat -> air -> sand. That's it.
          • by tragedy ( 27079 )

            Industrial heat pumps go to about 200C...maybe. This is well outside those temps.

            I'm not sure what your point is. The purpose of this system is not to heat anything to more that 200C. In order to operate, the sand is heated to 1000C, but that's only so that there's enough heat to release a little at a time. If you were replacing this with an air source heat pump and batteries, there would be no need to heat anything to 1000C.

            Read their technical stuff - really is blatantly simple. No need to add a heat pump. Solar -> resistive heat -> air -> sand. That's it.

            I think you think I'm suggesting integrating a heat pump into their system? I'm not. I'm talking about the logistics and pros and cons of using batteries plus a hea

            • Lithium batteries don't have near the lifespan of this. Wildly more expensive in that you'll be replacing them multiple times during a single lifespan of this system.

              Lithium is best used for mobile applications. It's very dense / light per kwh and has high discharge rates. You don't need that for grid type stuff.
              • by tragedy ( 27079 )

                Lithium batteries don't have near the lifespan of this. Wildly more expensive in that you'll be replacing them multiple times during a single lifespan of this system.

                Not really relevant to the actual subject of discussion. If you recall, this thread started with criticism of the claim that lithium batteries only hold charge for a matter of hours, then you started talking about efficiency of the system. The only place cost has previously been mentioned in this thread is when I said that low cost is an advantage of the sand-based system. So, yes, overall expense of the system is a concern, but we're hardly in disagreement that, with current battery technology, the sand-ba

                • The cost of replacing expensive lithium batteries is not relevant to the discussion you started about the 'cost' of the systems?

                  Done with the troll.
                  • by tragedy ( 27079 )

                    You do realize that it is relatively simple to open up parent posts and see the entire thread, right? I'm not sure exactly what your deal is, you seem to just want to have a disagreement or tell people that they're wrong and it doesn't seem to bother you that you're not actually in disagreement. I did bring up cost at one point. However I was quite clear that, with current technology, sand is cheaper. Battery costs (which would include replacement costs over time) are higher. This was never in doubt.

    • Sure it does. It just does so at a rate much lower than other chemistries, somewhere like 2-3% per month.
    • by AmiMoJo ( 196126 )

      The heat issue can be mitigated, or just isn't that big of a deal for some applications.

      For example, say you want to extend solar power until after the sun goes down. With a well insulated battery the heat loss won't be an issue over the time-scales involved. You might even be able to heat it with waste heat from the solar array itself.

      You might similarly be able to use waste heat from nuclear too, but it's trickier because nuclear cooling loops have to be extremely safe, which makes adding secondary stuff

  • by Whateverthisis ( 7004192 ) on Saturday August 26, 2023 @12:01PM (#63799114)
    Comparing a Sand battery to lithium-ion is dumb. Lithium ion batteries are terrible batteries for all the reasons described; they're flammable, difficult to extract, and have poor reusability. The only reason they're used is that they are light; that one feature alone makes them great for phones and laptops.

    But a Sand battery is better compared to an Aluminum Ion battery or a molten salt storage system, which is not light but has way better properites for utility scale power storage. And Sand, exciting, fun story, but molten salt has been around and is already installed [energydigital.com] as a prototype, but functional, utility scale. Unfortunately the land required for solar thermal doesn't quite make the economics work for the amount of power generated unless you're competing with coyotes and scorpions for land, so a different generation method is probably better than solar thermal. Sand doesn't offer more over molten salt (it appears, could be wrong), but the issue is still economics and power generation scale of these things.

    • Sand should be less corrosive than molten salt, so it should require less service. Also, you can presumably use sea sand.

      While I still have fingers crossed for glass electrolyte batteries, Lithium will be the primary basis of high density batteries for the immediately foreseeable future. And while they do have a bit less energy density, lithium ferrous phosphate batteries have relatively few inherent ecological drawbacks. If we can continue to improve the cleanliness of lithium production, we can reduce the

      • yeah one of the really great things about sand batts is it's literally *any* sand. Junk sand works just as well.

        Lithium will always be for mobile scenarios where density and discharge rates are the important factors.

        Grid/house sized stuff can be big and slower.
    • Sand vs Molten Salt is different use cases I think. Both are great for what they do!

      Sand def isn't likely as good for 'power' storage - it's feature is heat storage.

      Another feature is it 'could' be scaled down to individual residential size at least in theory. One concept would be building the 'sand' battery into a building foundation.
  • Great! Bring them on. [imgflip.com]

  • Their cost is about a tenth of lithium ion per unit of storage and they last 17x the number of charge/discharge cycles. The technology has been developed and is being scaled up for commercial use and are expected to be on the market in the next couple of years.

    As would be expected from iron. they would be too heavy for mobile applications, but are perfect for stationary storage.

    • by dryeo ( 100693 )

      You still have the conversion from storage to electricity and then to heat. Sounds like this idea is directly using the heat for heating, run a bunch of pipes through the sand and then through radiators in a building.
      Going back and rereading as you broke your comment between the subject and your comment to make sure people have a hard time following your comment, there's a few technologies similar to iron/air batteries for grid scale electricity storage.

      • by tragedy ( 27079 )

        You still have the conversion from storage to electricity and then to heat.

        By the conversion from storage to electricity I assume you mean from the battery to electricity? Maybe you mean charging losses? In any case, round trip into batteries is generally very high. Above 90% typically. As far as conversion to heat, with resistive heating, that's basically 100% or as near it as makes little difference. Plus, for the kind of heating applications this is intended for, you can use electricity to power an air-source heat pump and apply an approximately 4-5X multiplier to the amount of

  • Because shitty round-trip efficiency.
    • Not if you are using them in a district heating system.

      We've doing variations on this theme for years -- they are called "storage heaters". Work well, but with some clear flaws and have largely ditched for central heating systems.

      But, years on, with a shift to renewables, scaled up for district rather than household heating, the old problems of storage heating may disappear. Sounds worth a try.

  • So a sand "battery" is simply using the thermal mass of sand to store heat. Great. I guess if I had a source of high-grade heat that I wanted to store and turn into low-grade heat, it's not a bad choice. But if all you want is thermal mass, why not use blocks of granite? You'd get roughly twice the mass density, which would give roughly twice the thermal density.

    The question really is, how big of a block of stone do I need to store enough heat in the summer to heat a neighborhood of homes in the winter?

    • From all that heating up/expanding and cooling down/contracting, wouldn't granite blocks crack up & turn into sand/rubble anyway?
    • by gweihir ( 88907 )

      This is not optimized for size. Also, granite blocks are a lot more expensive than sand, as this does not need sand fit to be used in concrete.

    • 23 ft tall cylinder of 100 tons of sand is currently providing 8MWh of heat energy to homes, buildings and a pool for 14,000 people.

      video explainer [youtube.com]
    • by tragedy ( 27079 )

      If all you want is thermal mass, why not use blocks of iron? Nearly 3 times as dense as granite and with about 60% of the specific heat value of granite, you could get more heat into a smaller area. The reason is because that's the goal. The goal is to be the cheapest possible storage system. Now, since the system will probably need a lot of insulation, a denser material might be better in that sense, but the bulk cost probably overrides other considerations. It may not do so at all scales though. Sand migh

  • The extraction of cobalt, the lucrative raw material used in lithium ion batteries, also relies on child labor. U.N. agencies have estimated that 40,000 boys and girls work in the industry, with few safety measures and paltry compensation. These serious environmental and human rights challenges pose a problem for the electric vehicle industry, which requires a huge supply of critical minerals.

    I missed the part where they explain why rich western countries can't compensate workers adequately & ensure that labour laws aren't flouted & human aren't rights abused. Could somebody please explain?

    • by ceoyoyo ( 59147 )

      Let's suppose you're going to give me ten times the normal price for a tonne of cobalt. I can dismiss my child workforce, hire adults, and give them nice safety equipment. Or I can continue as before with enormous profits. You could audit me regularly, but that's pretty failure prone, particularly with everything getting merged in commodity markets.

      What you *could* do is just buy cobalt from places that aren't the Congo.

      • It's not that easy. A lot of cobalt comes from politically unstable regions of Africa. At best you can refuse to do business with them, but your competition might not and now they're cheaper. Since the end consumer doesn't really see or understand this beyond some abstract idea of child-labor/slavery bad, there's not a lot of consumer pressure on companies to be ethical in this regard.

        Even if we banned it at a national level, there're plenty of countries that won't care as much and will buy what we don't
        • by ceoyoyo ( 59147 )

          Read the OP's post. "Rich western countries can't compensate workers adequately" in another country. They also can't "ensure that labour laws aren't flouted" when they don't exist, and they can't ensure human rights aren't abused in a foreign country, short of invading.

          The only possible interventions are economic. Individual companies really don't have the power to do much for the reasons that you mentioned. Entire countries could sanction the DRC, which is really the only significant exporter of cobalt tha

      • Cobalt is not available everywhere in the world. And most large enough deposits are in regions that are ruled/ruined by warlords and/or corrupt politicians. So you (as a company) either get your fill from those "institutions" or pay the same and get maybe 10% of your Cobalt needs, which will make your investors revolt. Rock, meet hard place. People have already been very busy working Cobalt completely out of the equation. Some more successful than others. Which is the best solution for everyone involved.

        • by ceoyoyo ( 59147 )

          This is a nice story, but it's not true. The Congo is the only major exporter of cobalt that's not a western nation. The DRC does have the largest reserves, but they're still a minority.

      • Well, if you believe in "the markets" & that conflict in developing countries "just happens" that could sound like feasible excuses. But we know that isn't true though, don't we. We know that the CIA, MI6, & every other countries' spy agencies are heavily involved in manipulating political, civil, & military conflict to their own advantages, don't we. You know, the countries that insist on "regime change" when a head of state doesn't do as he's told?

        This mostly happens without the press repor
        • by ceoyoyo ( 59147 )

          I can't really tell whether you've got a conspiracy theory that the CIA is responsible for the Congo being a basket case, or if you're suggesting that the CIA should just assassinate people until it's not any more.

          • Being a "basket case" today? I don't know. It got pretty f**ked up under despotic, brutal Belgian rule from the late C19th though. Western colonial powers haven't left it alone since. The DRC briefly achieved independence in the 1960s which was brought to a bloody end by the USA & Belgium. It's historical record. Is that what you mean by conspiracy theory?

            So what do you think contributed to the DRC being a "basket case", in your opinion?
            • by ceoyoyo ( 59147 )

              The Congo suffered quite a bit from the USA's foreign policy of installing "whoever, so long as they're not a communist" as leader, but I doubt they're running Congolese mines with child labour.

              I concur with your position that fewer CIA assassinations is the way to go though.

              • The CIA do the destabilisation & regime change. They don't care about how the minerals are extracted as long as the State Dept. & US corporations get a fire-sale deal. So yeah, child labour, human rights abuses, genocide, etc., it's all good as long as the money keeps flowing into the US.
                • BTW, one of the more recent outcomes of CIA interference & destabilisation is the Ukraine invasion: https://www.cato.org/commentar... [cato.org]

                  Just for the record, Russia invading Ukraine most likely qualifies as a war of aggression, which is officially defined as the worst crime that anyone can commit on the planet. There is nothing worse & it's inexcusable.
      • What you *could* do is just buy cobalt from places that aren't the Congo.

        Cobalt is just coal with two extra letters, so you can make it in a lot of different places.

  • Too lazy to read the article or do research, but does it matter what type of sand is used for this? Unlike glass making which requires a specific type of sand, as does concrete [bbc.com], both of which we are running low on (by previous standards), can you pull sand from the middle of the Saharan desert and be good to go?

    • by gweihir ( 88907 )

      The way I understand this, they heat resistively and that would work with any type of sand. For recovery, they probably use pipes or the storage walls, again should work with any type of sand.

      I know of an installation in Germany that uses volcanic rocks instead, but they blow air through the tank. Should give you faster storage and recovery, but whether you need that depends on usage scenario.

  • Supercapacitors could be the future, they are like regular capacitors but much smaller and highly efficient, they were once thought of as batteries for solar plants, but the development of these have leapt fast forward, still pricey so they need to come down in size and price, which means we need first time adopters.

    The problem with the "sand" concept is that it's not here yet, it's theoretical science and even if they have a working prototype there are tons of things that needs sorting out first as with ev

  • NREL looked at a concept using sand for thermal energy storage, called ENDURING. It uses sand at 1200 C stored in insulated silos, heated in resistive heaters. When dropped out the bottom of the silos, the sand passes into a fluidized bed heat exchanger, which compactly and efficiently transfers the heat to a compressed gas. The gas is then expanded through a commercially available turbine before being cooled for recompression. Round trip efficiency is around 52%, with levelized cost of storage estima
  • We don't need a way to store heat. We need a way to store cold.

    • Thermal storage like this can do both. The issue is range. You can't get that much colder than ambient compared to how much hotter than ambient you can get.

      And the differential between ambient and your storage is what gives the benefit.

      You can increase a temp 1000C easily. You can't decrease ambient temps more than 100C realisitically or so and if you can decrease ambient lower than 300C, call the Nobel Prize ;-)
    • YOU need to store cold, I need to store heat.

      The heat pump was in AC mode for part of 17 days for this summer, and summer is about done.

      The heat pump is in heat mode for all of October through March and intermittently in September and April and sometimes the first part of May.

  • See here: https://en.wikipedia.org/wiki/... [wikipedia.org]

    Still a good idea, there is room for improvement. From one installation that uses volcanic rocks, I remember efficiency not being so good for electricity (around 50 recovery, I think), and better for heating. Still, the idea is that when you have electricity in abundance you heat this up and then later use it. The advantage is that this is very cheap, very reliable, and scales well.

  • It's a fucking thermal battery. Why not use goat shit?
  • A battery that is good for a lot of deep (or shallow) cycles is a little trickier. A battery that doesn't take up a whole basement to power a single residential load...that's an even narrower set of possibilities.

    Or you could look forward, to the Year 2000, when Man finally tames the atom!

  • https://www.theintelligencer.n... [theintelligencer.net]

    The iron-air process, "power from rusting" takes 120 hours to chew through the little nurdles of iron they have in great amounts in a Form Energy system. The factory to build iron-air batteries at scale is now putting up walls, will be up in 2023, start production in late 2024. They already have orders based on their successful demonstrations.

    Their target (may not reach it) is storage for a CAPEX of less than $20/kWh of stored energy. Presumably, a $100M facility could

  • This is a very special-purpose form of storage, they get no electricity from it.

    They heat the sand up to 600C and "The heat storage is unloaded by blowing cool air through the pipes. It heats up as it passes through the storage, and it can be used for example to convert water into process steam or to heat district heating water in an air-to-water heat exchanger."

    https://polarnightenergy.fi/sa... [polarnightenergy.fi]

  • There are quite a number of "heated rock batteries" already built, here is an article on the projects of Siemens Gamesa for example: https://www.rechargenews.com/t... [rechargenews.com]
  • This is an edge case of what you might do if you have lots of excess power and you require heating for part of the year and you live close to somewhere that can have large thermal storage units and you can build and power them cost effectively.
    Compared to electricity it pretty inconvenient, inefficient, expensive and inflexible. Just look at the size of the prototype and image one of those in everyone's backyard. It heats resistively, resistance heating is 50% less efficient that a heat pump. Just because y

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