Finnish City Inaugurates 1 MW/100 MWh Sand Battery

https://cleantechnica.com/2025/08/30/finnish-city-inaugurates-1-mw-100-mwh-sand-battery/

by erwinmatijsen • 11 months ago

193 178 11 months ago

cleantechnica.com

slumpvaldperson• 11 months ago

Very interesting. Did anyone find a ROI calculation?

theshrike79• 11 months ago

It's a prototype, so not really relevant.

flanked-evergl• 11 months ago

If they did, and it indicated that it's not just a money pit they would have shared it, so doubtful. As with most things in Europe it was likely done on the basis of a virtue signaling assessment alone. Europe's motto is going to keep saying "we have the resources" until it rapidly runs out of resources.

Norway's sovereign wealth fund will likely be completely gone in 20 years and will leave large swathes of the population without a pension because the Norwegian government works on the philosophy of "it's going to be okay, we have infinite money", already it's showing cracks as the only thing they actually have the money for is to make inflation skyrocket.

jonespen• 11 months ago

So, a gigantic sauna heater? Very on brand Tommi and Markku!

fulafel7• 11 months ago

It doesn't list the advantages over water, which seems the most common in https://en.wikipedia.org/wiki/Thermal_energy_storage systems.

You'd think water would be easier to exchange heat with since it can slosh around the heat exchanger elements in the tank more easily. Which should translate to lower costs since you don't need as many exchanger structures in the medium.

Any guesses for the motivation in using sand? Maybe it's that you can heat it over 100C? But then big heat differences to the environment mean high conductive/radiation losses or heavier insulation requirements.

isoprophlex3• 11 months ago

For this specific use case, you need to heat to far above the boiling point of water to retain some thermal efficiency. Sand/rock is better suited for storing the thermal energy at ~500 celcius.

vintermann• 11 months ago

I wonder if there are any chemical effects from heating the sand to 500 degrees Celsius. Finely roasted sand.

decimalenough• 11 months ago

The article mentions that they heat the sand to 500°C, which is not possible with water (well, at least not without turning into steam along the way).

Cthulhu_4• 11 months ago

To be pedantic, yes you can but you'd need to pressurize it to uuhh... According to this calculator [0], you can get water to 370 degrees C if the pressure is 207 atmospheres, which is about the pressure of the ocean two kilometers deep.

[0] https://www.engineeringtoolbox.com/water-vapor-saturation-pr...

chii• 11 months ago

perhaps sand is easier to heat to higher temps, and also it's less thermally conductive, so you'd lose less heat in storage for the same sized container.

tarvaina• 11 months ago

The Wikipedia article says:

"Rock, sand and concrete has a heat capacity about one third of water's. On the other hand, concrete can be heated to much higher temperatures (1200 °C) by for example electrical heating and therefore has a much higher overall volumetric capacity."

and

"Polar Night Energy installed a thermal battery in Finland that stores heat in a mass of sand. It was expected to reduce carbon emissions from the local heating network by as much as 70%. It is about 42 ft (13 m) tall and 50 ft (15 m) wide. It can store 100 MWh, with a round trip efficiency of 90%. Temperatures reach 1,112 ºF (600 ºC). The heat transfer medium is air, which can reach temperatures of 752 ºF (400 ºC) – can produce steam for industrial processes, or it can supply district heating using a heat exchanger."

fulafel7• 11 months ago

The higher temperature output is a good point, you can't get 400C output for industrial processes from a 100C water based heat battery.

internet_points2• 11 months ago

I learnt some new concepts here, specific heat capacity vs overall volumetric, things I kind of understood intuitively, but now much clearer:

If I add some fixed amount heat to some fixed volume of water, it might rise by 1℃, while the same volume of concrete rises by 3℃. And by the same logic, on release, that fixed volume of water dropping by 1℃ releases 3x as much heat as when that fixed volume of concrete drops by 1℃.

So if you can max heat water to 100℃, and max heat concrete to 1200℃, and on release you let it go to 10℃ (probably the range is less in practice), then the water can drop 90℃ and the concrete 1190℃, so even if the water releases 3x the amount of heat per ℃, the water just releases 270 (per volume) while the concrete releases 1190 (per volume)

d--b• 11 months ago

They probably use the trick where they blow air in the sand to give it "liquid" properties where they need the sand to flow.

For those who haven't seen it there is a famous Mark Rober video: https://www.youtube.com/watch?v=My4RA5I0FKs

grues-dinner9• 11 months ago

Sand also mostly stays where you put it. While obviously water can be put in tanks easily enough, there's still more maintenance and inspection required and a gigantic watertight tank that will last n decades is substantially more expensive then a steel sand box. Plus it only goes to 100C unless you pressurise it and that really gets hard. Unplanned release of that much water at 100C is also extremely dangerous. Whereas even 500C sand will mostly just sit there. Plus the usual corrosion and scaling effects water systems love to develop at high temperatures.

Insulation isn't such an issue with sand because sand itself is fairly good insulator and obviously doesn't convect. 1m of sand is about the same as 10cm of air. 500C through 1m of sand if roughly 125W/m². Which isn't nothing but it's also 7m from the center to the edge, and the efficiencies only improve the bigger you make the silo.

Presumably they have a double-skin gap and other external insulation too. As the Icelandic hot water pipe systems show, which drop only a few degrees C over hundreds of kilometres of pipe (and thus a gigantic surface area to volume ratio), you can have really quite good insulation if you have space to make it thick.

The hassle of handling hot water is also presumably why they use hot air rather than water as a working fluid for heating the sand in the first place. The worst case if you spring a leak in a heat-transfer tube inside the tank is that a bit of air escapes. Leaking super-heated high-pressure water or steam into the (unpressurised) tank would be a much larger problem, and unloading up to 2000 tonnes of hot, damp, sand to plug it would be operationally very annoying if nothing else.

Ekaros3• 11 months ago

District heating tends to operate at 50-70C at lowest. But more often up to 115C and in some case even 180C.

Even the lower range doesn't leave much delta in best case of boiling water. So you would need some type of heat pumps instead much simpler heat exchangers. So that is also one cost optimization.

fulafel7• 11 months ago

I think it's more like 90C in (winter), 40C out. The temps have been going down in newer infrastructure as it's more energy efficient. See eg https://www.shcbysweden.se/wp-content/uploads/2019/11/Best-P... p. 7

And of course it's still a win if you can heat the return water half of the way to spec with the battery, it's not necessary to have the battery heat it all the way to the plant outgoing temp.

District heating systems have been happily using ~90C water based heat batteries for a long time.

Tuna-Fish• 11 months ago

But then big heat differences to the environment mean high conductive/radiation losses or heavier insulation requirements.

Square cube scaling means that insulation becomes trivial in total costs as you scale the installation up. Something that's convenient for a single household would probably be too hard to insulate, but this thing holds 2000t of sand.

Puts• 11 months ago

Helsinki did the same thing but storing the energy in water instead of sand: https://helsinkismart.fi/worlds-largest-cavern-thermal-energ...

anttisalmela• 11 months ago

Several cities in Finland have water based thermal batteries already, connected to local district heating networks. They have been previously used to store energy from existing combined heat and power plants, but now that wind power build up has created a lot of excess cheap power period, have been modified to include electric boilers.

nabla92• 11 months ago

Helsinki has advanced integrated district heating and cooling. Over 300 MW of heat pumps by 2025.

Collecting heat from wast water is free energy. When you defecate, wash clothes or dishes, or take shower there is warm water and solids going down the pipes. That heat can be used. In the summer stored cold sea water can provide district cooling.

napoleoncomplex• 11 months ago

For anyone interested in a breakdown of the basic logic, this recent blogpost that trended on HN is probably the best: https://austinvernon.site/blog/standardthermal.html

Really interested in seeing how it fares in reality, almost sounds too good to be true.

jnsaff22• 11 months ago

Why too good to be true?

There are significant trade-offs with this technology.

It's storing heat, so if you need electricity then you eat a lot of efficiency. I think Vernon said ~45% round trip efficiency. Batteries are 90%+.

The storage is at a high temperature (500-600C) which means that you can't use heat-pumps to produce the heat to be stored. This means that you miss out on ~400% energy gains possible from converting electricity to heat.

So the efficiency is pretty low.

That said, solar PV is really cheap and moving large amounts of earth into a pile is also a very much solved problem so in some cases, notably higher latitudes which have very long days and low heat/electricity demand in the summer and the opposite in the winter, it could still be a very good solution.

HPsquared• 11 months ago

Yeah the efficiency is much less than 40% if you compare to heat pumps. It'll be something like 15% compared to those.

Sharlin3• 11 months ago

The whole point is that the thermal energy is used directly, via district heating. These are not meant to store energy for electricity production (though they could do that if really needed – emergency power for various facilities? Maybe not worth it compared to diesel.)

Heat from existing thermal power plants can be stored directly and later distributed with no conversion loss; excess electricity from renewables can be turned to heat at 100% efficiency, but the problem is that peak heat demand and peak electricity supply do not typically coincide. Heat batteries are meant to solve that problem.

kitd• 11 months ago

I like these technologies. They may not be as energy efficient as using more exotic materials, but what they do use is simple, cheap and often sourced locally. Such economic factors are often as important to the ROI as the purely scientific ones.

pilif• 11 months ago

They may not be as energy efficient as using more exotic materials

yes and given that the energy you put in is practically free, it doesn't matter if it's not as efficient.

looofooo0• 11 months ago

I think with enough renewable in the grid, there will always be times when the costs are 0 or negative, so you can help stabilize the grid by consuming.

yurishimo• 11 months ago

Are there downsides to "just" sending all of the extra energy to ground? I've often wondered why overpowering the grid has been talked about as this huge unsolvable problem.

I understand it's wasteful, of course, but waste in a ecosystem of vast abundance seems like a feature, not a bug.

petesergeant• 11 months ago

I live in a desert where we have district cooling (and no shortage of sand or solar power), instead of district heating. Wonder if they can pull off the same trick.

Cthulhu_4• 11 months ago

In theory, yeah, cooling the sand would work, and it wouldn't freeze / expand. You'd need to use a coolant that doesn't freeze though, and of course keep any liquid out of it.

phh• 11 months ago

Well you can't really do -600C sand (or anything), so the benefits of sand VS water largely diminished. "just" freezing water already gives you around 300C equivalent of sand (if my napkin is correct).

Also the point of this plant is to exploit the counter-correlation of cheap electricity and cold. Usually there is a bigger correlation between cheap electricity and heat.

dzhiurgis3• 11 months ago

you can't really do -600C sand (or anything)

You can if you stagger AC/HP or even peltier elements.

Gravityloss• 11 months ago

You can use heat to create cool by using absorption materials. It's of course way more complicated than with heat. But anyway with that, stored heat in sand could be used to create district cooling.

pintxo3• 11 months ago

Cooling needs tend to correlate with the availability of solar energy. While heating especially far north does not so much.

Havoc• 11 months ago

Interesting capacity vs discharge ratio. Way slower than battery but presumably sand scales well

Fwirt• 11 months ago

Interestingly this looks like the same principle as a rocket mass heater or masonry heater, but on a larger scale and powered by renewable energy. They say the system can retain heat for weeks whereas the smaller thermal battery in a masonry heater is exhausted in a matter of hours. I wonder if this is a function of size or if the tank is heavily insulated? It would be interesting if this same system could work at smaller scales for off-grid heating by harnessing excess solar capacity. There’s a lot of waste involved in going from solar to battery vs directly to thermal energy, as long as it doesn’t bleed off before you need to use it.

Cthulhu_4• 11 months ago

So why a surface sand silo instead of going down and using the soil/clay/bedrock/whatever is there? Ease of installation and maintenance?

whimsicalism3• 11 months ago

presumably you need the insulation from the air, otherwise it would just sort of dissipate through the ground

Findecanor• 11 months ago

I'm not a building engineer, but my impression is that it does not matter as much as we might think.

A housing complex near mine got a massive tank like this installed thirty years ago, and I think they put it underground to be able to build a house on top.

IshKebab4• 11 months ago

Open air is not a good insulator; that's why we wear coats! In contrast the ground is actually a pretty good insulator - that's why the London underground is so hot; the heat is all stuck in the ground.

It'll just be cheaper to build it on the ground than to dig a big hole and then build it in the hole.

shellfishgene2• 11 months ago

They heat it by blowing hot air through it, that needs loose, evenly sized material.

Cthulhu_4• 11 months ago

Related: in Sweden they filled a cave (an old mine?) with water and are using that as heat storage: https://www.youtube.com/watch?v=VSdKL0Nnk-k

pintxo3• 11 months ago

Really like the idea, but my house alone has roughly 16 MWh/a heat consumption. Of which half gets consumed November through January.

So this system could supply 12 houses? Shows the importance of proper insulation, which is still on our todo list.

diggan• 11 months ago

Sweden seems to have some of the highest "Electricity consumption per dwelling" (https://www.odyssee-mure.eu/publications/efficiency-by-secto...) in Europe, and sits at 10 MWh, which makes sense, it's a very cold country but with very well isolated houses in general :)

It sounds to me like you're likely an outlier here, for curiosities sake, where do you live?

lysace• 11 months ago

16 MWh of electricity/year isn’t really an outlier for an electrically heated (via efficient heat pumps) house in Sweden either.

Your number above probably includes apartments and houses heated using district heating, e.g. from incinerating forest industry waste products.

pintxo3• 11 months ago

Germany, and these are numbers from our gas heater. But the house is almost 50 years old and not insulated to current standards (yet).

We got a heatpump this year, going to be interesting to see how this changes things.

dzhiurgis3• 11 months ago

Wonder if one could use staggered heatpumps here - in summer there's quite a bit of heat out there (some of which needs to be removed) so you could get 3-6x more bang for your buck.

grues-dinner9• 11 months ago

Staggering heatpumps doesn't help except on a practical level, like how climbing a staircase in big or small steps is the same. The only thing that matters to overall efficiency limits is the temperature delta.

The coefficient of performance for a heat pump from with cold/hot of 10C/40C is about 10 - this is ballpark where a domestic heating heat pump sits - this is why a heat pump house needs to be well-insulated to work - the heating loop isn't actually hot-hot like with a boiler). From 10C to 500C, it's 1.5. That's 9/0.5 = 18 times less advantage.

At any delta, you can eke out a bit of advantage as COP is always over one, but at some point overheads in the system start to overwhelm your theoretical advantage and you might as well keep it simple and use a cheap and reliable resistor to heat things for dead-cert COP of 1.

You could use a heat pump with a higher COP if you have a really gigantic tank that you only heat to about 40-50C, but obviously the thermal transfer from that is pretty bad and getting it where it needs to go while still being hot enough to be useful is a problem.

bjoli• 11 months ago

90% roundtrip efficiency is pretty darn cool. I am not an engineer, but is it the high temperature difference that makes that possible?

smokel• 11 months ago

That's only in heat transfer, that does not include generating electricity from it.

IshKebab4• 11 months ago

I think they're talking about thermal efficiency (since this is a thermal battery, not an electrical battery). 90% of the heat they put in, they get out again. Probably all you need is good insulation.

arowthway• 11 months ago

This is super cool but the ending is bizarre.

A comment on the YouTube video below complained, “Not a word about return on investment in the presentation. That means it’ll never pay off” MAGAlomaniacs are everywhere these days.

Given the supposed 50+ year lifespan of such a battery, I find it hard to believe it doesn't turn a profit at some point. And I understand that debunking low-effort accusations is asymmetric warfare. But why cite a random YouTube comment if you have no intention of addressing its claims? A more charitable interpretation is that it's meant to ragebait the readers. But to me, it seems like trying to make people feel ashamed for having doubts, by making a public example of a skeptic.

ta12435• 11 months ago

People nowadays expect 10% return on their investment, so if you invest 1m you need to make 100k a year from it (120k to cover the deprecation over 50 years)

If you made 30k a year for 50 years you'd return 1.5m from your 1m investment, but you're only making 3%, which is a low return especially given the future risk (you'd have to run for 33 years just to get your initial investment back)

Either way it's worthwhile, because the reason people expect 10% is because the externalities are borne by others. Majority of people and countries in the world do not deem ROI to be the sole or even primary driver for investment, and judging investments only on the immediate financial reward already biases the conversation

testdelacc1• 11 months ago

I really like this comment. Concisely explains the points of view on an investment like this. There’s not much more to add.

This is why I open the comments before the link.

Avamander• 11 months ago

Majority of people and countries in the world do not deem ROI to be the sole or even primary driver for investment

It's partially that, other part is that we aren't really pricing in all the externalities of everything out there. So it's not that "there's no ROI", it's that "we aren't factoring things in the ROI calculation".

So while a heat battery might not make a huge profit, the ability to burn less fuel (less air pollution, less waste, etc), to offer redundancy and stability, the know-how and work it creates, that is all valuable as well.

kragen15• 11 months ago

Majority of people and countries in the world do not deem ROI to be the sole or even primary driver for investment

I think this is a little unfair. If it were true, it would be the reason for wealth inequality: you're saying that the majority of people and countries are so financially irresponsible that they consume any resources they get without investing any. But in fact everyone I have observed closely, in every socioeconomic group, tries to optimize ROI. Most of them aren't very good at it, but they do try.

On the other hand, people who expect a 10% risk-free return are just going to get scammed. There are 10% opportunities in most people's lives—weatherstripping, coupon clipping, bulk food buying, etc.—but you can run out pretty quickly.

anon191928• 11 months ago

they print more than %10 each year, LMAO. people are not smart. remember

lupusreal3• 11 months ago

And I understand that debunking low-effort accusations is asymmetric warfare

Is the comment even that unfair? Asserting that it will never pay off because the presentation avoided mentioning anything about the payoff might be a little bit cynical, but not terribly so. It could be fairly presumed that if the project is a clear economic win, they would be proudly bragging about it; and the opposite presumption is also reasonably fair, even if it turns out to be wrong.

And what does such cynicism have to do with "MAGA"? That asserted association seems much worse than the initial cynical assertion.

blueflow• 11 months ago

And what does such cynicism have to do with "MAGA"?

"Everyone i don't like is Hitler". It's a rather immature way of disagreeing.

There is a KYM page about this phenomenon: https://knowyourmeme.com/memes/everyone-i-dont-like-is-hitle...

csomar• 11 months ago

The battery (am assuming it's just sand and metal) should be very cheap compared to Lithium especially in the places where you generated solar energy (they are hot and have a lot of sand).

The problem is: is it profitable to even store energy there? There is no mention beyond "In operation, the sand battery has demonstrated a round trip efficiency of 90 percent.". That doesn't mean much if you do not compare it to Lithium and you don't give me a breakdown of the costs.

The other thing: Size. Is that big thing enough to store energy for a city? a neighborhood? A building? A house?

If it's enough just for a house, then I have trouble seeing this scale.

Sharlin3• 11 months ago

It's right in the title. 1 MW/100 MWh.

kragen15• 11 months ago

1 MW is enough to heat somewhere between 100 and 2000 houses, depending on other factors like insulation, climate, and house size.

rsynnott3• 11 months ago

If your house is consuming 100MWh in heating on any reasonable timescale, you, ah, have problems :)

kragen15• 11 months ago

If, say, further insulating your house or building a sand battery will pay for itself in 50 years, it's a bad investment, financially speaking, and probably environmentally speaking as well. You can deploy "the same amount" of resources in something else with a higher ROI, like maybe solar panels with a one-year payback, and get a much bigger benefit. This is an important consideration as long as you are constrained by some kind of resource limitation.

So I think ROI is a first-order consideration.

bryanlarsen5• 11 months ago

Finland is the only country in the world where solar isn't the cheapest form of electricity because they get so little sun and they have good alternatives.

danielfoster• 11 months ago

I agree with you, but one point I see everyone missing is the fact that this is a first-time installation of a new technology that hasn’t scaled. There needs to be a business plan of course. At the same time, no one would expect to see ROI figures for the first build of a concept car.

skrebbel2• 11 months ago

Does anyone understand why people do this? I mean, really why? It's similar to eg climate protestors quoting all kinds of outrageously incorrect statistics as fact, or saying that $TECH can supply "4% of all households" with electricity, fully knowing that households only consume a tiny % of total energy, and so on.

I simply don't get it! The political landscape across the west is that there's swaths of people who've simply stopped believing mainstream media when they're reporting things, and somehow our reaction is to just lie even more? Try to out-lie camp Trump? I mean I don't think it's even possible to lie more than Trump so wouldn't the honest, nuanced truth be a a much better antidote than global left's current strategy of "also lie, but a bit less"?

I simply don't understand where it comes from. Like in what bizarro world is this shit a smart strategy? Is it all just incompetence?

zahlman2• 11 months ago

It has nothing to do with political partisanship (except to the extent that false-flagging happens or that powerful individuals have bad ideas about how to propagandize for their cause). Most people are just terrible at critical thinking, and most of the interesting claims (especially statistical ones) are simply not verifiable by random individuals.

Plenty of leftists have their own reasons to distrust media. But scarcely anyone imagines reasons why someone else would lose trust. Not that they could do anything about it anyway.

The "global left" is not a real thing. I mean, of course you can draw lines around groups any way you like, but this one doesn't offer meaningful insight.

vjk800• 11 months ago

Given the supposed 50+ year lifespan of such a battery

Surely the lifespan is almost forever. It's just a tank full of sand and some heating pipes. Maybe the pipes and/or control electronics needs to be replaced occasionally, but nothing should happen to the sand inside - like ever.

idiotsecant• 11 months ago

'just' the piping, pumps, control systems, electrical system, valves, instruments...

The sand is the least complex part. Industrial facilities like this take a lot to keep running.

j45• 11 months ago

RoI is a fun one, anyone calling it out should be able to point out ROI as an example elsewhere that's accurate.

grues-dinner9• 11 months ago

There's also some long-term risk here. If we, humans, did massive amounts of dispatchable solar and wind, plus systems like this, static battery storage, other storage and things like widespread EV capacity arbitrage, it's not guaranteed that the negative or even low energy price events would even happen. The more people think they can store it and sell it later, the higher the demand for off-peak power. You could end up with op-ex exceeding revenue in the future.

Then again, the same also goes for the other storage methods as the spread compresses. Eventually, as always, it all comes down to who can do it on the thinnest shoestring. 1/4 the cost, but the thermodynamic efficiency is 1/3 (direct heat vs batteries + heat pump, say) is still a winner. Finns aren't going to stop needing heat in winter soon, and if you can provide it even a fraction under the cost of battery electricity and a heat pump, you get the customer. And the district heat infrastructure probably already exists.

moooo99• 11 months ago

Its of course true that this will somewhat even out once storage becomes more available. But there are still market forces at play. If the electricity prices are higher, operators have a renewed financial incentive to generate more power (more power = more revenue), for example by re-powering solar and wind farms.

Theoretically this would be an endless cycle, which is of course constrained by very practical needs of the electricity users.

echelon_musk• 11 months ago

What does MAGA have to do with Finland?

conception• 11 months ago

Authoritarian populism support is rising globally.

y-curious• 11 months ago

Unfortunately, people seem to see Boogeymen everywhere when they're terminally online. It's kind of like the mid-2010s where everything someone didn't like was "fascist" or "Nazi"

jagermo• 11 months ago

I find it fascinating that renewables always have to have a ROI.

nobody cares about his car loosing value as soon as you drive off the parking lot. Or any other appliance - a fridge will never have a ROI, a washing machine will not and neither will a stove, a macbook or a fancy smart home system. They are part of our live, loose value and we accept that.

But solar or batteries (granted, mostly with home-solutions)? Better make money, otherwise why even bother.

rogerrogerr• 11 months ago

ROI is implicitly against the alternative or status quo:

- Fridge: has ROI vs. going to the store more often or getting food poisoning.

- Washing machine: Has ROI measured in the value of your time spent not slapping clothes against a board to make them clean.

- Stove: ROI vs. using and maintaining a fire pit, with the risk of burning your house down factored in.

- MacBook: ROI is how much work you can get done vs. a Windows machine, or not having a laptop and doing math really fast by hand on paper.

Etc. It is suspicious that there isn’t a “this will pay for itself in N years vs. not having it” statement somewhere.

dguest4• 11 months ago

Finland is still 25% oil for electric generation [1] (and almost 40% fossil fuel). That means a lot of the electricity to heat the sand still comes from oil. It makes me wonder if this is more efficient than just using oil heating. Or some hybrid approach that uses oil to heat the sand.

Of course there are other benefits: it's still a good way to level electric generation, which is important for e.g. nuclear plants and wind power.

[1] https://ourworldindata.org/grapher/energy-consumption-by-sou...

Hikikomori• 11 months ago

Most of that is not for generating electricity as it includes transport and heat. Direct heating of homes traditionally used oil, wood and pellets, same as other Nordic countries. This is slowly being replaced with heat pumps that mainly use electricity from wind, water, nuclear or solar (not so much solar in Finland though).

myrmidon2• 11 months ago

Finland is still 25% oil for electric generation [1] (and almost 40% fossil fuel). That means a lot of the electricity to heat the sand still comes from oil.

This is not a valid conclusion. Battery projects like this are gonna charge/heat up when the electricity price is low, electricity price is low when supply/demand ratio is high and this often happens when renewable electricity is most available and makes up a disproportionate share of the electricity mix.

Edit: Your graph is not what you say it is, this shows primary energy (i.e. includes fuel/heating/...), not "electric generation". Electricity in Finland is mostly nuclear, wind, hydro and certainly not "40% fossil fuel".

dguest4• 11 months ago

I think the primary energy does include electric generation, but you're right, I posted the wrong chart. The correct one is here:

https://ourworldindata.org/grapher/electricity-prod-source-s...

and it backs up your point. Sorry to any Fins I might have offended with my lazy post.

nabla92• 11 months ago

95% of Finnish electricity is clean: nuclear, wind, hydro, renewable biomass. Oil 0.3%, coal 1.5%, net import of electricity 3.8% (most of it clean also).

Older private homes still use oil for heating. All new use electric, heat pumps, or geothermal heat pumps.

mzl• 11 months ago

The point of these types of systems is that you can store energy when it is cheap to do so (there is an abundance of wind and/or solar energy) and use it later.

happosai3• 11 months ago

It is amazing how internet commenters can see some data that appears insane and build an entire post around it. Instead of like, consider, that they have completely misunderstood the data. Confirmation bias much.

Eg that graph is not Finnish electricity usage. It's ALL energy, including cars and planes that still use oil...

dguest4• 11 months ago

Yeah I was wrong and completely misunderstood the data. I'd edit the post if I could but the timeout for that happened while I was editing. Not sure what confirmation bias I might have: I figured the Fins did their math correctly and was confused about why they were using electric heat.

Anyway, to explain my mistake, the data did not look "insane" to me, it's about right for most countries, and even if it had been correct for Finland the method they described might be favorable (some electric sources need leveling and using extra energy for heat is better than dumping it). Honest mistake, I'm not here with some agenda, and I learned of it by posting.

Anwyay, thanks for the correction! It's amazing (in a good way) that internet communicators can see something that looks plausible, but is wrong, and correct it! You've restored (some of) my faith in the internet.

phtrivier• 11 months ago

It seems to depend on having a network to distribute heat, which is something that you have to take into account... basically when you create your town ?

Or is there a way to "retrofit" district heating into houses with their own gas boiler or heat pump ?

lupusreal3• 11 months ago

They already have district heating.

jpalomaki• 11 months ago

Over half of Finland’s population lives in buildings connected to district heating.

Ekaros3• 11 months ago

Finland traditionally mostly used oil. If you have traditional water circulating radiators or underfloor water circuits it is pretty easy retrofit, just need to swap boiler with heat exchanger. Still, in many cases cost of infra is pretty high so heat pumps are often better options.

davedx• 11 months ago

Good idea but why is it being measured in MW/MWh when it’s not an electrical battery? I know they can be converted but maybe it should be measured in actual thermal units like Btu?

grues-dinner9• 11 months ago

Finland probably doesn't use US customary units like BTU (British Thermal Unit).

In fact even Britain doesn't often use such units - even gas boilers, heat pumps and some AC are specced in kW. You do see BTU (the /hr is often missing) sometimes on AC marketing. My theory is 18000 sounds big and impressive and 5.2kW sounds "meh". We definitely don't talk about "tons", and we buy gas in cubic metres or "units" (which is just kWh)

flowerthoughts2• 11 months ago

W and J are the SI units for power and energy. Those units make the most sense to use in Europe, regardless of the type of energy.

Wh is an abomination that has come about because professionals think consumer brains would expose if they ever saw the unit watt-seconds (J). No consumer had any preconceived notion of either Wh or J, so had we used J from the start, it wouldn't have been a problem...

(Yes, same with Ah vs C, though the battery pros also shot themselves in the foot by starting to use C (electrical charge) to mean "the capacity of this battery" when talking about charge rate, a.k.a. current.)

grues-dinner9• 11 months ago

I dunno, 1kWh seems quite natural as a unit of building-scale energy usage when you know a kettle or space heater is about 3kW. We think about energy usage much more in terms of kW and hours than in watts and seconds. And even in small devices like an LED bulb, 5W is more obviously 0.005kW than, say, 2 hours is 7200 seconds.

And in this context it's much more obvious that it can notionally deliver energy at a peak rate of about 1% capacity per hour. If you said 1MW/360GJ, I don't think that would be nearly as clear.

Same for batteries, which started with car batteries/deep cycle batteries, rather than AA batteries, which usual don't even say, and phones. A battery that provides 1 amp (at 12V, but that's already given in a system) for 50 hours. Makes immediate practical sense, especially when equipment is often labelled in current draw and you can measure amps with an ammeter. 2.16MJ far less so.

rsynnott3• 11 months ago

Watts and watt-hours are generally used internationally for heating; the Btu is largely a historical oddity in most places outside the US.

Also it is a mess, as is traditional for US customary units:

A Btu was originally defined as the amount of heat required to raise the temperature of one pound of liquid water by one degree Fahrenheit at a constant pressure of one atmospheric unit. There are several different definitions of the Btu that differ slightly.

(Best one is still the fluid oz, tho. A US customary fluid oz is about 29.6ml, a US food labelling fluid oz is exactly 30ml.)

anovikov• 11 months ago

Problem here is that if heating was done with electricity itself, it could have like 300% effective efficiency because of using heat pump, but a heat pump can't be used for 500C temperatures, it must be resistive heating. So even if no thermal loss occurs at all, we end up getting a lot, lot less heat than we could do otherwise. It's a lot better to use normal li-ion instead, surely 100 MWh means 500-ton battery and with longer life chemistries and thermal management, probably a 1000-ton one...

shellfishgene2• 11 months ago

In the end it may still make financial sense, the price for electricity often goes down to near zero or even below.

haspok• 11 months ago

This is not a battery, this is thermal storage. No electricity is stored or generated. (Unlike liquid-metal batteries, for example, which are actual battery storage.)

alkonaut• 11 months ago

No one is claiming it is storing electricity. I think people who use imperial (BTU) units for heat but SI units for electric power some times get confused by what power really is and what a battery is.

Something that stores _energy_ is a battery. Not necessarily electric energy. You can absolutely have a battery with mechanical energy (wound up springs), a battery with kinetic energy (a weight in a shaft) a battery with nuclear energy (Thermal reactor in a satellite), a battery with thermal energy (silo full of very hot sand) or a battery with chemical energy such as a Li-ion battery.

This stores 100 MWh heat energy, so it is a battery.

From wikipedia:

Energy storage is the capture of energy produced at one time for use at a later time to reduce imbalances between energy demand and energy production. A device that stores energy is generally called an accumulator or battery.

credit_guy• 11 months ago

It's not clear to me why you would hold 100 hours of energy, assuming you discharge at maximum power. If you want to store energy from summer to winter, then 4 days of energy is nothing. Even if your average discharge is only 30% of the maximum power, you still get only 2 weeks of energy. And if the use case is day to night, then 8 hours of storage is enough. Maybe the idea is that the houses in Finland are so well insulated that you need heating only in cases of extreme cold, and only during the night, 100 hours will do the job?

etrautmann• 11 months ago

4 days is often cited as a useful target for buffering power to backstop intermittent generation from renewable sources. You're never going to store a full winter's worth of power, and might want to be able to ride out a few days of weather.

rajnathani• 11 months ago

Previous discussion (104 points | 27 comments) from 79 days ago before the inauguration: https://news.ycombinator.com/item?id=44295132

Finnish City Inaugurates 1 MW/100 MWh Sand Battery

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