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For reference, this city is about as north as Anchorage Alaska and today they got less than 7 hours of sunlight and it'll continue to decrease for the next 3 weeks.
The Nordic countries generally still wants to increase their wind and solar power, but the big issue during winters is when there's cold air high pressure systems we get neither sun nor wind, having an energy storage that can hold up to 5 days worth of energy should help us nudge past them.
Hydro-energy exist (mainly Sweden and Norway, but I think some in Finland as well), but it's fairly built out so stable non-fossil power needs to be nuclear, or wind/sun + storage (that hasn't been good enough so far).
> “Hydro-energy exist, but it's fairly built out so stable non-fossil power needs to be nuclear, or wind/sun + storage”
Interconnectors also exist (and more are planned), which means, for example, that Norway can buy wind energy from the UK when it’s cheap and abundant, in preference to using stored energy from their hydro lakes.
That way they effectively get more out of existing hydro lakes, which in Norway is already a very significant storage capacity.
Theres not going to be built any more interconnectors from Norway anytime soon.
Electricity became a lot more expensive in Norway after building several interconnectors to UK and mainland Europe. Importing high prices from the failed energy politics of UK and Germany which both have among the most expensive electricity in the world.
This has been a huge debate, and the general concensus seems to be that joining ACER and building inrerconnectors to mainland Europe was a big mistake.
Hydro energy generation is fairly built out, but the Nordics have lots of places suitable to build out hydro energy storage. Hydro generation requires a flow to dam, but storage doesn't.
We don't really. Hydro storage requires reservoirs where you can freely adjust the water level. Most of our lakes have shorelines that have been built out, and the property owners get really angry if you suggest frequently adjusting the water level significantly.
The largest planned hydro storage projects are using decommissioned mines, and those are going to run out quickly.
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You could use the ocean for the bottom level and an artificial reservoir for the top level. You're not going to noticeably affect ocean levels.
Or just use a large lake. You're not going to noticeably affect the water levels of a large lake. You might pump 10 billion litres of water, which is .02% of the volume of Mjøsa.
> You could use the ocean for the bottom level and an artificial reservoir for the top level. You're not going to noticeably affect ocean levels.
Then you have to deal with the problem of sea water corroding everything it touches.
> You might pump 10 billion litres of water, which is .02% of the volume of Mjøsa.
It's not the amount of water that you pump, it's the amount * the elevation delta. Where are you planning on getting the elevation delta from?
Neither of these challenges is technically insurmountable, but this is a field where capex + opex/KWH is everything.
> Where are you planning on getting the elevation delta from?
Elevation delta is not hard to find in Norway! A typical pumped storage facility uses 100m of delta; I imagine Norwegian ones would use more.
> but this is a field where capex + opex/KWH is everything.
And pumped storage is significantly cheaper for seasonal storage than any proposed alternatives.
The original post is efficient for heat storage, but converting low grade heat to electricity is not efficient.
> A typical pumped storage facility uses 100m of delta
Most projects seek 200-600m. This map doesn't even consider pumped hydro <200m: https://maps.nrel.gov/psh
> And pumped storage is significantly cheaper for seasonal storage than any proposed alternatives.
Based on what? Cost is particularly variable for pumped hydro. It can be one of the cheaper options when stars align. But you need 1) a suitable geography that minimizes the cost of damming or digging a resivoir with sufficient head 2) available for development without too much backlash 3) Near enough grid resources to minimize infrastructure and line losses. I'm surely leaving pieces out.
It can be cheap, but it has far more hoops to jump than alternatives like batteries, hot sand and other "storage-in-a-building" designs which can be built where needed and using fairly standard industrial construction.
For some applications, you don't actually convert the heat to electricity.
This sounds pretty cheap if it works out:
True, but that disrupts ecosystems. Or so the argument against go building storage dams go.
That said, there's been a fair bit of talk here in Norway recently about tax incentives blocking hydro owners from upgrading old generators, improving efficency. Apparently a lot of currently unused power available if they "just" did that.
I wonder if it's possible to also increase the amount of generation on existing dams? I could imagine there being situations where there's excess peak flow capacity but it isn't utilized because the flow rate would be unsustainable. But if we're looking for storage it could make sense.
I think hydro storage is a lot less disruptive because you don't need as much space. Traditional hydro reservoirs have to last all season.
Hydro doesn't work so well when things freeze over. Geothermal on the other hand...
It doesn't get cold enough for long enough for lakes to freeze solid.
I imagine the thaw/freeze cycle would be hell on the equipment to run pumped hydro storage.
Are there extant succesful examples of pumped hydro in cold regions?
You have Juktan in northern Sweden which was pumped hydro from 1978-1996, and now they want to re-build it back into pumped hydro again https://sv.wikipedia.org/wiki/Juktans_kraftstation
> Are there extant succesful examples of pumped hydro in cold regions?
There's some pumped hydro at Niagara falls in Canada, which is far enough North that it should see a bit of a that/freeze cycle but is still a relatively mild climate.
Don't know anything about what issues this does/doesn't present to them, just happen to know it exists.
For reference, Niagara Falls is at roughly the same latitude as Barcelona and Milan. Vääksy, Finland, is approximately 1,250 miles (2k km) north of there, slightly north of Anchorage, Alaska.
Latitude is a poor point of comparison here, North America tends to be substantially colder than Europe at the same latitude.
Or concretely Niagara Falls goes from an average low of -6.44 C in February to 21.0 C in July. Barcelona an average low of 4 C in January to 20.2 C in August (according to the internet).
But yes, it's warmer than Finland, just cold enough to see something of a freeze that cycle.
A reversable pump-turbine is not significantly different from a standard hydro generation turbine, and there are tons of examples of those operating in cold regions.
There's not much geothermal available when you are standing atop the baltic shield.
invest in saving/harvesting energy. Better than producing when solar is cheap as hell and you get no-solar-harvesting because of your location
Right, the worst case scenario is cold temperatures, transmission problems (say days after a storm), lull, and nuclear and hydro power malfunction. However, it should be pointed out that winters are usually quite windy and there are only a few days per year you get very cold temperatures coupled with nearly no wind at all.
"there are only a few days per year you get very cold temperatures coupled with nearly no wind at all"
This is a terrible handwave. How many days per year, in the middle of winter, in a cold country, are you OK with having no power?
This would be an argument for widespread backup power, actually. If every residence had enough backup power to get through 24 hours, it would be far easier to deal with these relatively rare doldrums.
The system in the article works alongside gas and wood chips heating, so there are other options in place if the sand battery cannot be "charged".
FTA:
> The project will cut fossil-based emissions in the Vääksy district heating network by around 60% each year, by reducing natural gas use bu 80% and also decreasing wood chip consumption.
I'm not ruling out Nuclear in general, but let's remember that:
* Energy can also be carried northward from other areas in the same country or neighboring countries, where there are more sunlight hours or more wind.
* Geothermal energy sources, e.g. https://www.rehva.eu/rehva-journal/chapter/geothermal-energy...
* Increase in solar panel farm area
* Improvements in panel efficiency (which continue)
* Improvement in energy use efficiency
... in some combination, and with decent storage, might get even the Nordic countries to cover their needs.
1. The southernmost spot in Finland is too far north, and the scramble that happened in EU at the loss of Russian energy supplies made it crystal clear that we can not trust any other country to help in times of need.
2. We have no geothermal sources sufficient for production of electricity, it can only be used to slightly reduce primary energy use during winter, but it will raise electricity use during winter.
3. Helps not at all, because 0 times however large number you like is still 0.
4. Likewise.
5. Improvements in efficiency do not help you stay alive when it's -30°C.
The option up here really truly is "do we use fossil fuels, or do we use nuclear". Renewables do not help. They are nice to have, and it makes sense to build them because they complement the reduced output of nuclear in summertime, and because the lower cost/kWh can help some industry, but that's all.
The difference between baseline and peak electricity consumption in Finland is >2x. That's mostly driven by heating. Because renewables make electricity cheap on the average, utility companies invest in cheap heat storage systems such as sand batteries. They use electricity when it's cheap, store the heat, and distribute it when it's needed.
As for nuclear, the challenge is finding companies that are able and willing to build it. Areva and Rosatom both failed at the "able" part. And a power company (I think it was Fortum) recently stated that they would consider building new nuclear reactors with German electric prices but not with Finnish prices.
There is more to that than a power company asking for subsidies. Finland is a small country. Olkiluoto 3 alone generates >10% of the electricity. Newer reactors would likely be smaller but still ~10% of the total. Finnish power companies are too small to take risks like that on their own. They can't build new reactors at their own risk, in order to sell the power in the market. Before a reactor gets built, the power company needs long-term commitments from industrial users and utility companies to buy power for a guaranteed price. Such commitments would make sense for the buyer with German electricity prices but not with Finnish prices.
I think this is exactly right, and people are focusing on the wrong risk with nuclear. It's financial risk, not safety risk, that is the biggest burden for more nuclear.
Finland was very very wise and savvy to get a fixed price contract for Olkiluoto 3. The final cost was far far far above its price, and France ended up paying that price. I'm not sure if you'll see a builder go down that route any time soon again.
> It's financial risk, not safety risk
If that's the case, then why does the indistry demand the repeated renewal of the Price-Anderson Nuclear Industries Indemnity Act?
Well that covers the financial risk from the safety risks... but even if it were purely about safety it's an act that's part of making the safety not be an issue. Unless it were not renewed, then it would be a problem agai.
> 3. Helps not at all, because 0 times however large number you like is still 0.
Show me your Monte Carlo simulation where wind (which is negatively correlated to solar) and 8 hours of battery storage are factored in, along with small amounts of gas peaking plants.
In case people want to play with a toy model: https://model.energy/
> The southernmost spot in Finland is too far north, and the scramble that happened in EU at the loss of Russian energy supplies made it crystal clear that we can not trust any other country to help in times of need.
That's the failure of European union
Note that even if Central Europe did have sufficient energy for export it wouldn't really help during crisis. To get the energy to Finland it would need to either go thru the Baltic Sea via undersea cables or via Northern Sweden. We have seen that it's not necessarily good idea to rely on the former during the crisis as those lines can easily be cut, they have been multiple times in just past year or so by certain commercial ships "accidentally" dropping their anchors.
As for latter Sweden, doesn't currently have capacity for it and I don't think they have been very interested in increasing it, currently Finland often benefits from the fact that there isn't enough transport capacity between Southern and Northern Sweden electric grids so Finland gets some cheap electricity from there.
I don't think it's necessarily a failure of the EU for member states to prioritize stability and independence of their electrical grid.
Texas having their own grid is not a failure of American federalism.
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> the big issue during winters is when there's cold air high pressure systems we get neither sun nor wind
Wind does better in the winter.
See eg here for Canada monthly stats: https://www150.statcan.gc.ca/t1/tbl1/en/tv.action?pid=251000...
Also, wind does better at night than day, which may be related or not.
There's an interesting property to thermal storage, as a consequence of simple geometry. Consider a cube. volume = n³ and surface area = 6*n². Surface area increases more slowly than volume. The ratio of surface to volume decreases with more size. Thus: a sufficiently large thermal reservoir becomes self-insulating with its own mass.
It's even better than that. In addition to the factor of n from ratio of volume to surface area, there's also a factor of n from the increased thermal resistance of the mass of the storage volume (the temperature gradient from the surface to the center goes as 1/n). So, the thermal time constant of the object scales as n^2.
This very favorable scaling is why natural geothermal retains heat even though the input energy was delivered gradually over as much as millions of years.
I've always wondered why we don't build homes with a buried tank of water used as heat storage. In the summer it can be heated with solar thermal to around 90c, and in the winter heat can be drawn out and go through radiators or underfloor heating, with a mixer valve. You just need a few pumps and valves, not even a heat pump is needed.
If you assume a modern house with a heat load of 1800kWh per year (fairly standard for a new build medium sized home where I live, in Northern Europe) that means you'd need a tank roughly 50m3, or 10,000 gallons for Americans. In terms of insulation you'd need around 50cm of XPS foam, and it would be buried a meter below ground.
It's nothing terribly complicated in terms of construction or engineering. Of course you'd pay more upfront, but then your heating bills would be practically zero. In warmer climates it would be much simpler, you could probably get away without burying it.
This is essentially what a ground source heat pump system is. Except instead of a sealed water tank you just make a tall hole that fills with water and the sun will warm it for you during the summer automatically.
1800 kWh is very little. We use around 12000 kWh and our neighbours' new house uses around 8000 kWh annually and most of that is heating. I'm not sure how many houses can hit 1800.
Yeah but if you transfer the energy as heat then you will end up with elongated structures (pipes).
Is that a problem? Pipes are not technically complicated. Is there something else I'm missing?
Larger storage structures are easier to (thermally) insulate. Because geometry.
But going with larger structures probably means aggregation (fewer of them are built, and further apart). Assuming homes to be heated are staying where they are, that requires longer pipes. Which are harder to insulate. Because geometry.
I can't help but wonder how the efficiency compares to generating electricity, running that over wires, and having that run heat pumps.
The conversion to electricity loses energy, but I assume the loss is negligible in transmission, and then modern heat pumps themselves are much more efficient.
And the average high and low in February in 26°F and 14°F according to Google, while modern heat pumps are more energy-efficient than resistive heating above around 0°F. So even around 14–26°F, the coefficient of performance should still be 2–3.
> heat pumps themselves are much more efficient.
For electricity-to-heat conversion, heap pumps are indeed much more efficient relative to resistive heating, yes. About 4 times more efficient.
In absolute terms, though - that is still only 50% of "Carnot cycle" efficiency.
https://en.wikipedia.org/wiki/Coefficient_of_performance
Similarly, heat-to-electricity conversion is about 50% efficient in best case:
https://en.wikipedia.org/wiki/Thermal_efficiency
So, in your scenario (heat->electricity conversion, then transmission, then electricity->heat conversion), overall efficiency is going to be 50% * 50% = 25%, assuming no transmission losses and state-of-art conversion on both ends.
25% efficiency (a.k.a. 75% losses) is pretty generous budget to work with. I guess one can cover a small town or a city's district with heat pipes and come on top in terms of efficiency.
We've got lots of heating districts around the world to use as examples. They only make sense in really dense areas. The thermal losses and expense of maintaining them make them economically impractical for most areas other than a few core districts in urban centers... Unless you have an excess of energy that you can't sell on the grid.
If the heat is stored at high temperature, but the demand (for heating buildings, say) is at lower temperature, it could make sense to generate power, then use that power to drive heat pumps. You could end up with more useful heat energy than you started with, possibly even if you didn't use the waste heat from the initial power generation cycle.
Alternately, if you are going to deliver the heat at low temperature to a district heating system, you might as use a topping cycle to extract some of the stored energy as work and use the waste heat, rather than taking the second law loss of just directly downgrading the high temperature heat to lower temperature.
High temperature storage increases the energy stored per unit of storage mass. If the heating is resistive, you might as well store at as high a temperature as is practical.
Gas-fired heat pumps have been investigated for heating buildings; they'd have a COP > 1.
I am interested if there are any cheap small scale external combustion engines available (steam? stirling? ORC?)
I think the big cost difference is the geothermal generators to convert the heat back into electricity. More of a cost issue versus efficiency.
That's a real issue, but this is for a district heating system which already exists and already faces this issue. And yet the district heating system is presumably practical.
Changing to a different central source of heating (i.e. storage) seems orthogonal.
From the article:
> [250MWh] held in a container 14m high and 15m wide
According to Gemini 3.0 Pro, lifepo4 is 1.5-3.5x more dense than this, which isn't bad. 250MWh is a lot of capacity for such a small land footprint. At 2MW it can power ~2000 homes for ~5 days while taking up the land footprint of ~1 home.
What's the price? And how does the price scale with capacity?
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I was interested in trying to make a DIY thermal battery as a hobby experiment. Other than using thermal energy directly, I couldn't find a way to effectively convert the heat energy to electrical energy.
Peltier modules can be used to generate electricity, but they are crazy inefficient.
An efficient steam turbine is largely inaccessible to hobbiests and I am scared of steam/pressure. Though I did look at repurposing a car turbo for this purpose. There were additional issues with regulating the amount of heat you wanted to extract (load matching) and recycling waste heat.
I wondered if it was possible to use a Sterling engine, but you can't buy anything other than very small toys online and I don't have the facilities to machine my own.
Haha, would love to get something working, but I suppose I'm not smart enough to figure out an effective way to get that heat back out as usable/controlled electricity.
In the articles case the end use of energy is household heating, so there is no need to convert back to electricity. The whole beauty of thermal energy storage that the end use of energy in many use cases is.. heat: heating buildings, cooking, industrial heating (from food processing to iron smelting), producing steam, etc.
The answer in almost all electrical production boils down to spinning a turbine with steam (or wind). Nuclear does it, all the fossil fuels do it and ultimately heat batteries do it too. The alternative is photovoltaic or directly nuclear to electron production and then storage with chemical batteries or massive capacitors.
Most of our electrical production is based on a solution found several hundred years ago, we just made it really big and worked out how to control the heating and pressure of the steam well.
You missed thermoelectric generators that uses the Seebeck effect to generate a current between two temperature differentials. It's terribly inefficient, unfortunately.
> An efficient steam turbine is largely inaccessible to hobbiests and I am scared of steam/pressure.
Thermal electricity generation really benefits from scale and extremes. The Carnot efficiency is proportional to the temperature differential between hot and cold. Even so-called "low quality" heat from a standard nuclear rector design is far hotter than anybody should deal with at home and it only gets ~1/3 efficiency. And dealing with small turbines is really inefficient too.
This is where batteries and solar really shine. They scale so well, and are extremely economical and electrically efficient.
Heat storage works well when you get beyond the scale of individual homes, but it's hard to make it work. I'd love to see something related to heat pumps in the future for homes, but district heating, such as could be accomplished by converting natural gas systems to heat delivery, are probably required for it to make sense.
Yeah, sadly, it seems almost impossible to get anything higher than 30% efficiency (theoretically with a Stirling engine, if you can find one, haha) out of a thermal battery without extreme pressures and temperatures.
Back-of-the-napkin math felt promising. A 1kg block of sand heated to 500 degrees Celsius should contain about 100Wh of electricity. Scaling that capacity up is easy, as it's just about adding sand or temperature (+ an effective method of transporting heat across the sand - maybe sand + used motor oil?).
Assuming 80% efficiency, tariff arbitrage (buy electricity during off-peak hours and use it during high-price hours) would pay off very quickly. In my area (Australia) it would be a matter of months - but the low real-world efficiency and lack of parts make it impossible.
It could work for heating during winter, though perhaps an AC/heatpump with the condenser a couple metres underground would be better value for money.
If you need to use heating in a cold climate, you could use your stored energy to heat the radiator of a heat pump, which would then be drastically more efficient than using normal air on the radiator.
There's a video of people doing this on YouTube. They use the ground as their heat source. https://youtu.be/s-41UF02vrU
Every couple of years I look around to see if anyone is selling sterling cycle engines in the 5-10 hp range, I always find a couple neat projects but nowhere can you just buy an engine.
I assume that because there is no current market for small sterling generators nobody wants invest in tooling to make one and because there are no small sterling generators there is no market for them.
In a cold climate, I would expect burying it to use the ground as a natural insulator. Why was an above ground design chosen?
Specifically, does the need for heavy insulation and the active heating of the sand make the ground a less effective or even problematic insulator? Could excavating and building a below-ground foundation for a high-temperature device like this be more complex and expensive than an above-ground silo? How would permafrost conditions affect this design?
These are interesting, but the cost per kWh of storage capacity is still probably too high for true seasonal storage. Short term storage runs into competition with batteries.
I point again to Standard Thermal for an idea tailored to true seasonal storage. I wait for more news from them, particularly on their very low cost resistive heater technology.
Doesn't need to be seasonal, we have enough energy in general to go through winter. This is to help through week long cold snaps, when Finland is short on energy. Week-long storage is still eyewateringly expensive with chemical batteries.
Also the capex from sand battery goes to (mostly) local construction, while when buying chemical batteries all the money goes to china.
But thermal storage doesn’t wear out, unlike batteries, right? So less future maintenance. Plus there is no danger of battery puncture.
More directly this is a very cold area. Enough it might effect battery storage enough to be a real problem.
I'm not sure why you think not wearing out would necessarily make up for the capex being too high. Interest rates aren't zero.
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Interesting. Does anyone know what source of electricity is going to be used for this ? Probably solar but it might be also useful with coal plants or wind farms that produce even when there is not enough demand. How are they moving the heat ?
It's a heat battery for district heating. Could be other sources than electricity, e.g. municipal garbage incineration plant.
See my other comment about Nordic power balancing.
Natural gas and wood chips,
> "The installation will supply heat to the Vääksy district heating network and is expected to lower fossil-based emissions by approximately 60% annually, primarily through an estimated 80% reduction in natural gas consumption and reduced reliance on wood chips."
https://www.pv-magazine.com/2025/11/25/finlands-polar-night-...
Those are the energy sources they're replacing with this tech - according to <https://reneweconomy.com.au/new-worlds-largest-sand-battery-...> it's surplus energy from renewables that will 'charge' the battery (so likely wind, hydro and solar that is produced but surplus to the grid's requirements)
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It's probably my ignorance about this sector, but I do find it impressive that they are getting that much storage capacity in a small area:
> "This latest project will use locally available natural sand, held in a container 14m high and 15m wide."
AI says this volume will hold about 4000 tonnes of sand. Hence the high capacity.
A website called energy-storage dot news should not be mixing up energy and power
I was surprised too at the 2nd sentence: "The project will have a heating power of 2MW and a thermal energy storage (TES) capacity of 250MW..."
and how a news outlet about energy could get such a fundamental unit wrong.
But given that later in the article it does revert to correct units (and the numbers are plausibly proportional), I assume it's just a typo. Strange that it hasn't been corrected even now.
"...It follows Polar Night Energy completing and putting a 1MW/100MWh Sand Battery TES project into commercial operations this summer..."
I like how sand batteries are the equivalent of sleeping on the ashes of your fire
I never see sand battery before
between this and salt battery which one is the future???
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EU is going to have to either
- embrace nuclear
- embrace North Africa, admitting them as member states, and doing massive solar there, and doing massive grid expansion to carry it north. And then in top of that, will their way to sufficient storage like the rest of us.
We'll see what they choose :D
EU does have trouble with solar seasonality, but wind is seasonally anti-correlated with solar, and the geospatial correlation between different wind turbines drops off more than linearly with distance, and the EU covers a very large land mass as-is. You can also over-build solar inside Europe to have reasonable collection during winter.
I also see no reason to admit North African states into the EU before an agreement can be reached about transporting solar. The geopolitical risks have always been about other states severing the link during a conflict with you, and less about the parties to the deal reneging. So whether Morocco or Algeria is part of the EU is quite immaterial to the risk profile.
This kind of thing really does need simulation modelling to be reasoned about properly. The one thing I am confident in saying is that these single sentence just-so stories about what is and isn't a good idea are going to be wrong, because the fundamental principle is statistical diversification, which needs to be approached through simulation rather than through words.
Here's your modeling site:
It's helpful to have two flavors of storage; one short term and efficient (batteries), one long term with low capex (hydrogen, thermal). The last is the most undeveloped but there are promising ideas.
Crafted by Rajat
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