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Industrial-scale thermal storage unit in Pornainen, southern Finland, will be the world's biggest sand battery when it comes online within a couple of years
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- Title
- World's largest sand battery set to slash emissions in Finnish town
- Published
- Mar 10 2024
- Word count
- 1083 words
I've been actually considering doing a residential sand battery here at my house in the future. It seems rather simple compared to other energy storage solutions. What do I know, I'm sure I am oversimplifying this in my head haha. Has anyone else put in the research to build this on a small scale?
I follow Robert Murray Smith on YouTube, while he's quite quirky he does have some cool content:
DIY sand battery
It's certainly an interesting idea, however integrating it into the a house's existing HVAC system might be tricky. You could potentially just use a blower fan to circulate hot air through the battery to blow it into your house if you had a convinient place to pop the piping in an out. That's kind of the catch though with any storage idea: integration. He uses wood to heat his sand battery, did you have an idea of what you wanted to heat yours with? Electric resistance heating for example.
I'm a graduate student studying Mechanical Engineering with a focus on building energy, so if you had ideas and wanted to chat I'm all ears. These projects look really fun even and I like chatting about them since I don't have the resources to experiment with them now.
Sorry missed this comment. I honestly had been thinking about going from solar/wind to some sort of heating element to warm the sand, and basically reverse the process to gain the energy from the stored warm sand. So in my head the end result would be electricity not the warmth. My thought process was that this could be a better way to store energy to be later converted to electricity compared to traditional house batteries.
Now that I'm typing this it sounds like there could be a lot of energy loss between conversions.
Question I guess then, maybe I missed the point of the sand batteries that are popping up in the news, are these batteries mainly used as a heat source as the final energy product?
I think the answer to "are these batteries mainly used as a heat source as the final energy product," is no. The ones you're seeing in the news are massive projects with the goal of turning excess electricity into heat, then back to electricity. Some similar companies (using mediums other than sand) that jump to mind are Malta and Antora. There are quite a few losses in this process as you touched on, but at a big enough scale you can still get on ok (60%-80%) round trip efficiency. That comes down to having massive tanks, good insulation, and high quality turbo machinery. Now at least in the case of Antora, they are trying to design a system where you can discharge the heat, OR convert it back to electricity, or a mix of both depending on the customer's needs. For certain industries having high temperature heat stored to use directly may be more useful (and using the heat directly would be more efficient anyway).
A sand battery at the scale of your home would have a completly different meaning. The round trip efficiency would be abismal if your goal was to go from electricity, to heat, to electricity. You'd lose most of the stored heating wait to use it since the tanks would be so small. And you lose heat faster as the difference in temperature between something hot and it's surroundings increases (heat is a slippery bugger). So compared to electrochemical store where the round trip efficiency for a home battery system is pretty close to 90% I'm not sure thermal storage for electric power will ever be practical. Batteries have gotten really good and continue to make huge improvements every year.
However, in a cold climate there is certainly merit to storing heat when electricity is cheap, especially if you're relying on something like baseboard resistance heating to warm your home. Electric and heat pump water heaters are kind of where we already see this, though I'm not sure integrating them with a home's HVAC is very popular yet (though I think it's coming). You could potentially put a resistance element inside a sand tank, heat the sand up when energy is cheap and then blow air through it later when you need the heat back. Losing heat over time isn't that big a deal since the goal is to heat the home anyway.
Let me know if that all makes sense. It would be super cool to have an efficient way of going from electricity, to heat, to electricity with something like a sand battery at a home scale since the materials to make it are so abundant, but that's definitely a case where I don't think it'll ever practically compete with rechargable batteries.
Yeah very cool information, thanks for explaining. Do you think a very large storage container would get past some of the energy loss? Or is the scale not going to make a difference? I'm in a cold climate with a fully electric home, heat pumps for heat (single unit with forced hot air ducting in 3 zones) and heat pump hot water heater separate. However our electricity cost is usually double or triple the summer rate in the cold months.
Are you referring to a larger container under the idea of converting electricity to heat, and then back again? Or for storing the heat and using it later?
A bigger container will certainly help in either case, though I'm not sure it will practically help for the electricity to heat case at a residential scale. Because the other issue you run into is how to plan to turn the heat back into electricity. I think all the large grid storage systems being proposed plan to use a Brayton Power cycle (same cycle used for a natural gas power plant), and I'm not sure you could get something like a home generator that could use the heat from the sand to drive a cycle in the same way. Though that in itself is a very interesting idea. Still this assumes you're on a time of use rate and buying electricity cheap and then discharging your system when electricity is expensive.
Now if you just want the heat, there may be some potential to combine a solar collector with a heat pump system. If you took heat from a solar collector and used a heat pump to push the heat to a higher temperature in a storage device (hot water or sand), then you could potentially see cost savings on electricity as your storing solar heat for use later.
Honestly I'm interested in either perspective. Mainly for energy savings but I just find this stuff to be very interesting. Thanks for the chat, thank you.
Are there any resources you recommend to learn about the engineering behind these sorts of systems?
Well, it was going to be either them or Rondo Energy.
Not knowing anything about Finland's energy infrastructure, is this good or bad??
This seems good overall as it seems like pretty safe way to store a lot of energy, but probably only effectient in cold climates where the heat can be be used directly.
To my knowledge, Polar Night energy and Rondo energy are the only two big heat-battery companies (turns out I missed a couple though; there's Fourth Power and Antora; Antora has an interesting thermophotovoltaic electricity generation option so they're not just a heat battery, and Go Fourth is weird, they have an ultra-hot graphite pipe system and the whole apparatus is flooded with argon gas (airtight but not pressurized), presumably to prevent the graphite from burning when it's heated to 2400 degrees).
It's neither good nor bad which one they went with, although PNE is arguably the most boring option.
Resistive heating heats above ambient temperature. I don't think cold climates would be any more efficient, there would just be more demand for heating there in the first place.
This tech would be useful anywhere with district heating (or with a sufficiently large apartment block, just a single large building), not necessarily just cold climates. And given that sand isn't limited in the temperatures it can store. IIRC Polarnight energy is 600ish degrees and Rondo is aiming for 2000 degrees so they can target major industrial applications with a large delta (i.e. if you're targeting 1500 degrees and have a max temp of 1600 degrees then you can only store 100 degrees of heat spare, whereas if you can get to 2000 degrees then you'd have a delta of 500 degrees, 5x the usable energy).
In theory, Rondo could supplant gas entirely for most industrial heat-based applications, just because it can deliver the required temperatures, and because it can store enough energy to be heated directly off intermittent renewables.
Polarnight energy's main selling point seems to be purely cost - Rondo is doing their brick thing, which is more space-efficient but is almost certainly more expensive than just any old asbestos-riddled not-even-construction-grade sand.
The amazing thing about this tech is just how boring it is - sand, resistive heating, insulation. All dirt-cheap and very thoroughly understood. The most expensive part will likely be the land or underground excavation (due to the cube-square law these things become quadratically more efficient the larger they get, polarnight is aiming for 20m diameter IIRC, whereas Rondo is aiming for a shipping container).
Thanks for the explanation and the additional context. One thing I like about Tildes is learning things these little things from people who are in different places.
I think we are in agreement here, I meant (but didn't say explicitly) that it would be useful where the heat can be used directly, as opposed to turning it back into electricity. I imagine the net efficiency of doing so would be quite low, but maybe it's still worth it if you can even out the variability the renewable sources.
I think the efficiency might not matter if the solar gets widespread enough. And I'm not even talking about Swanson's law.
There's an aspect of solar that I think people miss: solar daytime generation is a bulk deal! Every solar panel that generates power will generate power during the whole day, even if your target is generating to meet supply at 6PM. This means that in order to match all 6PM demand, you must produce unneeded supply during midday!
Too-cheap-to-meter solar will probably never happen, but supply-outstripping-demand midday solar is IMO eventually inevitable once we roll out mass solar. And in such a world, the efficiency of storage is less important than simply having enough storage to catch all of that oversupply of energy.
Nice this is getting traction.
Then we could just ditch the dynamo in the windmill and make heat directly from wind
I'm not sure if this is practical or if this would rely on a magical heat pipe that transports the heat from the turbine to the battery. You certainly wouldn't want to have the battery of 100s of tons of glowing hot sand on top of a 100m tower. Ooooor you go for silly-geometry wind turbines - there's a reason these were never meaningfully adopted, and I'm not sure those disadvantages are outweighed by the allure of just continuing their shaft into a comically large brake in a comically large bed of glowing sand.
(Great, now I'm wondering about the potential of using a giant stirbar in a bed of sand as a means of (1) braking the shaft while (2) effectively distributing the heat in the sand.)
Of course we wouldn't be placing tonnes of hot sand up the tower... Just use a miter gear to transmit the rotation down 90°, and place the battery at the foot of the windmill. And don't use sand, just have a big insulated water tank. We know this would work because it allready has allready been done for 50 years.
Also, anecdotally, I knew fairly well an engineer working on designing on of those silly geometry wind turbine (for offshore). The way he said it, the real main disadvantage of those design was that current wind turbine maker would have to retool and redesign their production line, and they wouldn't use as much of their patent. So the wind turbine lobby ( nebulous, I know, but it was years ago so I don't remember exactly ) weren't interrested and ultimately got the project scrapped.
Sometime, it should come as no surprise, the reason we've always done things a certain way is because of entrenched interest... Even in "eco friendly" domain like renewable maker...
I appreciate the simplicity of the whole stirbar-in-a-tank system, but I think the flexibility afforded by electricity - and the scaling you unlock too - are worth the added complexity. Like, you can have the turbine located a fair way away from the battery. You can plug it into the grid and thus use the battery to load-balance not just this one turbine, but the entire renewable supply. You can sell excess electricity. You can reach much higher temperatures if the only hot components are sand and a resistive heating coil. So many nice things about it, plus the scaling laws unlocked by just building stupidly big wind turbines means the stirbar thing is not looking too great. If you want to attach this to a big turbine, it's going to be trouble finding heat customers that want to live that close to a big turbine and need that much heat.
That said, absolutely appreciate the stupefying simplicity of it. KISS at its best. Simple yet effective solutions like that always have a special place in my heart.
Oh, and as for your engineer friend: I don't doubt his story, but I think enough people have looked into VAWT by now that this idea would've had its breakthrough by now, surely. Maybe there's more disadvantages your friend doesn't know about or something, but I can't really believe that the entire industry, after having gone through countless retoolings to scale up the turbines again and again, and with multiple manufacturers being on the market, is collectively blind to the advantages of a design that a few blokes in a shed can prototype.
Well yes, all fair points ( about scaling up, transmitting easely , higher temp and the convenience of not living next to a massive turbine ) and I agree it's most of the time worth losing a third the energie to conversion loses.
But I love KISS too! ( sometime too much ) Maybe we should make a post to ask everyone all their best example of effective low tech solution. It's engineering katnip.
About the vertical windmill tangent, I don't think we'll reach consensus between us here, but it's nice talking about it. There are plenty of exemple where the industry has massively invested in inferior methods for a very long time just because the inferior method was the one that got adopted first... (x86 architecture, thorium vs uranium nuclear plant, DC vs AC in home's wall outlet)
And reasonable size (>5m span) wind turbine don't get built in a shed. ( I know you said prototype, but small wind turbine don't scale down well, and so make lousy prototype.)