Gigantic heat caverns in Mustikkamaa have now been filled with water (2021) | Hacker News Reader

Gigantic heat caverns in Mustikkamaa have now been filled with water (2021)

helen.fi

174 pointsiljah103 comments

This energy storage system near Helsinki, Finland operated by Helen (https://en.wikipedia.org/wiki/Helen_Oy) might be interesting for HN readers. Some facts from previous article (https://www.helen.fi/en/news/2020/mustikkamaa), not sure which one would've been better in url field: District heat is stored in two rock caverns in Mustikkamaa. The temperature of the water in the caverns varies between 50 and 90 °C. The effective volume of the cavern storage facility is 260000 cubic metres and energy capacity about 11500 MWh. The charging and discharging capacity is 120 MW. The discharging or charging of the heat caverns at full power takes four days. The rock caverns will decrease Helen’s carbon dioxide emissions by 21000 tonnes per year. The stored heat can be used for balancing demand peaks and that way cutting fossil heat production, for example, in cold winter days.

This is a cool project, and I'm sure it has many benefits beyond just carbon savings. But 21,000 tonnes per year is surprisingly little in the scheme of things. Equivalent of about 150 or so long-haul 777 flights?

If I’m reading this report correctly:

https://julkaisut.hel.fi/en/reports/environmental-report-202...

It looks like the emissions for the Helsinki area are 2,345 kt per year, so I guess 21 kt is only a small part of that.

Of course, no one project should be expected to solve everything! But it is depressing to see the scale of the problem.

1% reduction from one project seems pretty decent to me. Especially when it's just from reusing pre-existing caverns from oil storage to decrease the district heat emissions.

Heating emissions for a city at 60° North are a big challenge to reduce, and combined heat and power is a huge efficiency gain - the heat is otherwise wasted, and thermal emissions are an environmental issue in their own right.

The emissions could be reduced much further if they decrease the 55% of their generation that comes from fossil fuel fired CHP plants[1], and increased their nuclear capacity from current 27% (unfortunately they had to cancel a plan to build another reactor because their partner was rosatom[2])

[1] https://fi.wikipedia.org/wiki/Helen

[2] https://en.wikipedia.org/wiki/Nuclear_power_in_Finland#React...

Heating is perhaps unsurprisingly a large part of overall energy consumption in the Northern hemisphere.

Helsinki shut down one coal plant used for district heating this spring and is shutting down the last remaining one next spring, well ahead of schedule.

https://www.hel.fi/en/news/helen-phases-out-coal-more-than-f...

I personally am bullish on deep geothermal - there was a pilot project near Helsinki which was unfortunately unsuccessful, but with cheaper new drilling tech (plasma etc) I think this can work out in the future. https://www.st1.com/st1s-otaniemi-geothermal-pilot-projects-...

There are also some startups looking to build small modular nuclear reactors for district heating - https://www.steadyenergy.com/

Yep, deep geothermal would be cool, but not as mature. Was specifically advocating nuclear as it is basically a drop in replacement for fossil fuel in existing CHP plants. SMRs might work, though I am somewhat skeptical of anyone proposing "this brand new nuclear tech!" as a solution to difficulties constructing proven nuclear tech - we have decades of examples showing they basically swap one issue for another

agree, I think it could take 7-10+ years for either (deep geothermal or SMRs) to be viable at scale. But once they are, it should hopefully solve carbon neutral heating for good - in areas with district heating at least.

Steady Energy is a spin-off from VTT (Finnish state technical research centre) - I haven't followed it too closely but they are legit. https://www.ldr-reactor.fi/en/development/

Can't be much worse than building another large scale nuclear plant with the French :D (which is what we did with the last one - https://en.wikipedia.org/wiki/Olkiluoto_Nuclear_Power_Plant#... - 4x over budget and 14 years behind schedule)

Yep, the EPR design has had major constructability issues with every site (except the one in China, but there may be a lack of transparency with any issues/solutions that were done with them). EPR2 looks specifically to address the issues they've faced at Hinkley, Olkiluoto, and Flamanville ... we'll see how it turns out, hopefully it isn't just another example of throwing out one set of issues for a different set.

Most large construction projects suffer when there is too great a separation between design and construction. There needs to be feedback from one to the other, and when it takes 30 years to go from conceptual design to operational reactor, that feedback loop just isn't there. One big promise of SMRs is for components to be prefabricated - if you're building multiple of an object, the connection between design and construction will be much closer.

Nuclear is often touted as a carbon solution (especially here on HN!) but the enormous cost and long construction times make it somewhat ineffective at reducing emissions compared to other technologies.

Given that governments and utilities operate with finite budgets, for each € invested in nuclear, we’re actually much better off investing in lower-cost, lower-risk projects and technologies (renewables, electrification, heat pumps, grid upgrades, insulation, storage, etc) that deliver more carbon savings per € spent much more quickly.

To put this in perspective: you could build on the order of 1000 Mustikkamaa heat caverns for the price of one nuclear plant!

> for each € invested in nuclear, we’re actually much better off investing in lower-cost, lower-risk projects and technologies (renewables, electrification, heat pumps, grid upgrades, insulation, storage, etc) that deliver more carbon savings per € spent much more quickly.

Don't get me wrong, I absolutely think all those are key, and need to be focused on immediately. Those help to reduce demand, but (with the exception of renewables) don't help improve supply. If we want to eliminate carbon emissions worldwide, nuclear will be a key component (along with massive renewables). For example, the Japanese grid has been developing various renewables on superdrive since 2011, yet they are only at 20% renewable, with national carbon emissions ~500gCO2/kWh - dramatically higher than when their nuclear fleet was operational. Germany has been pushing renewables for close to two decades, but they closed down their nuclear plants and are similarly at ~500gCO2/kWh. France has had a nuclear-based grid for a couple decades and while it has its own issues, their emissions intensity is ~50gCO2/kWh. Ontario is hydro and nuke, they're ~100gCO2/kWh (some storage and more renewables would help them dramatically reduce emissions from gas, but current conservative premier spent billions scrapping that plan)

> To put this in perspective: you could build on the order of 1000 Mustikkamaa heat caverns for the price of one nuclear plant!

Yes, all you need is 1000 old oil storage caverns already dug sitting there waiting to be filled with water...

The problem with this analysis is that existing renewable capacity was largely constructed during a time when renewables cost dramatically more than fossil energy and nuclear. We’re now moving into a period where they cost dramatically less, and the capacity to build them is vastly greater. We’ve already passed the tipping point for most types of generation, and the cost decreases don’t seem poised to stop. So it’s sort of like watching the first generation of inexpensive Intel PC CPUs roll out of the fab, while simultaneously pointing out that PCs were too expensive to get much adoption in the past. Technically a valid thing to observe, but also not really useful.

To give you some sense of the enormity of the change, China over the first 9 months of 2023 built 215 TWh of wind and PV (numbers already adjusted for capacity factor), which eclipses the combined 206 TWh of every single nuclear power plant they have under construction today (there are 26 of them.)

A reduction in foreign energy dependency is always nice to have. They can also use the geothermal to generate electricity. The carbon savings aren't that much but nearly free energy sources are nice to have.

That tells you how pointless all the at-home energy savings are when everyone and their dog flies to a weekend getaway every month

I know people who attend sit-in protests at Chase Bank locations over fossil fuel divestment who also fly internationally 3-4 times per year for pleasure. The cognitive dissonance and lack of engineering intuition among the general populace is staggering.

If there were less investment in fossil fuel exploration, prices for fossil fuels could rise and airfare might be priced more appropriately. They would fly less because it cost more, or trains and boats might become more competitive.

Moaning about individual "cognitive dissonance" is absolute nonsense when talking about global scale problems that require policy solutions. The activists' intuitions are more correct than yours, I'd wager. Climate change is not an engineering problem.

Protesting Chase doesn’t stop investments. It just pushes them elsewhere. Those activists are morons and stopping their flights would do far more to help than to protest a single bank.

If they were protesting the government to massively increase oil taxes then you might have a point. Alas, they don’t have any economic intuition.

They're not protesting Chase, they're protesting fuel investments. If government did its job, this wouldn't even be needed.

https://www.theatlantic.com/science/archive/2023/11/climate-...

> The international agency’s analysis, in contrast, assumes countries will follow through with more climate-friendly policies and renew the ones they already have on the books. “Look how different things could be,” Bowman said. The difference is night and day, despair and hope.

> Policy, and only policy, appears to make that difference. It represents the choices that our leaders make about when to finally change course. Naughten, the Antarctic-ice scientist, reminded me that “climate is a spectrum; it isn’t an on/off switch.” Whenever we do make a different set of decisions, ones that make the math properly compute, we will be saving what we have left, preventing some layer of livability from being irrecoverably sloughed off and swept away.

If those protestors did not have tickets on those flights, somebody else would be able to purchase them. It's not like the plane isn't going to fly that route because of this. So whether the protesters fly or somebody else, the plane is still make the emissions you're concerned about.

If enough people didn't buy tickets, then the airlines would have to reduce capacity on the routes, and that would reduce emissions.

what's more likely, people stop traveling by plane, or these seats will remain filled? I'm all for making changes, but let's make them realistic ones with actual chances of getting implemented. the world is a big place, and air travel is not going to be replaced by steamships. we've been there, done that, and tired of the slowness. progress, not regression. improve the engines for air travel. don't expect air travel to stop

“If I don’t rob this bank, someone else will!”

What do you think trains and ships are fueled with exactly?

This level of comment is honestly insulting on this site.

In case anyone needs it spelled out: train and boat travel are vastly more energy efficient than air travel.

If fossil fuels rise, the cost of transportation of EVERYTHING goes up and the entire economy explode. Do you want 50% annual inflation? What you saw during COVID would only be a taste.

Your comments are an insult to readers' intelligence. Efficiency is good. Cutting fossil fuel use ASAP is crucial for the future of humanity. Shifting demand from air travel to high speed rail and from air cargo to ocean freight are unalloyed goods.

If you want to bleat nonsense about imagined 50% inflation, please go do it on twitter.

I suggest you read the HN guidelines about personal attacks.

Or they want to look like they care, while having as much fun as possible?

there are other ways to look at it though

Is it more or less hypocritical than someone who pays lip service to climate change, flies 3-4 times a year and doesn't go to sit ins? Their total overall alignment of their actions and their words are probably greater than vast majority of people who also don't even consider emissions from flying but say they care about climate change.

It's legitimate to agitate for change at a higher level while maintaining individual behaviours that align with status quo.

No? They’re literally more hippocritical?

That’s like saying the catholic priest is more aligned with their sermons, even if they’re having random hookups too?

I thought pleasure is more important than business. The only reason I do business at all is to feed my interest in doing whatever I like.

Where’s the line between hypocrisy and an understanding of scale in your model?

You know, I'm not mad at them, and I don't think they're necessarily being hypocrites. I imagine that if they really understood the engineering and chemistry around oil, they would alter either their behavior or their politics.

I'm bothered that anti-oil westerners are unaware of how heavily their existence is subsidized by oil. Every part of life we take for granted exists because of readily available petroleum. Western students are taught the environmental consequences of fossil fuel burning without ever really learning the degree to which every first-world nation in the world relies on petroleum for plastic, fertilizer, fuel for shipping food/fuel/goods, etc. For the record, I would like to divest from oil wherever possible, but I am actually ready to give up many of the modern benefits of the oil-consuming first world. I don't think the people I know who sit in at the banks are.

Flying is only 1% of the total emissions

But "everyone and their dog" doesn't do that. About half of Americans never fly and a quarter fly once a year. Only 7% fly as much as you say or more

Aviation is 2-3% of global CO2 emissions, while not insignificant there are bigger fish to fry

Everyone's favorite thing is a small percentage. Frequent flyers need to sacrifice too.

It also benefits a tiny part of the global population so per user it's actually not that small of an impact.

That should tell you more about the energy intensity of a long-haul 777 flight.

Just for one city.

> The temperature of the water in the caverns varies between 50 and 90 °C.

Presumably 50 is in April or May and 90 is in August or September. Or are these swings shorter-term ?

Yea that is one thing missing. Is it seasonal heat storage, or for balancing wind power?

"Mustikkamaa" translates to "blueberry land" or "blueberry earth" (Mustikka|maa) in case anyone's interested.

Mustikamaa in Estonian :)

I've heard people joke that if a Finnish person just spends enough time in Estonia they start to understand it :)

Finns will say that Estonian sounds like some kind of really odd super-rural accent.

Estonians will say they wonder why the heck it takes a Finn twice as long as an Estonian to say the same thing.

Haha yeah definitely! I was watching the news where Estonian people were interviewed. While there were Finnish subtitles I could understand maybe half of the sentences without them, but the words would be "really odd super-rural", which I found funny.

Also, I'm not sure if it's a thing in Estonian, but I've heard in Lithuania or Latvian there's no distinction between spoken and written language.

Example from Finnish:

* Minä means I/me in written Finnish

* Mä/Mää/Mie/... is what people typically use in spoken language

Which is what some of my international friends have been complaining about the Finnish courses at my university -- that they learn the written Finnish from their 101 books, but it's not so useful since in daily interactions people just use spoken Finnish.

And well maybe the minä -> mä you can see the length difference. Maybe Estonian is just more advanced in the "spoken-ness", if you will, of the language.

Here you can see the different "minä"s by region in Finland: https://yle.fi/a/74-20010020. The article's in Finnish, but just scroll down and you can still very much understand the map.

Here's the article Google-translated to English, but I'm not sure if it would also translate the "minä"s: https://yle-fi.translate.goog/a/74-20010020?_x_tr_sl=auto&_x...

Same in Estonian.

Minä -> mä is Mina -> Ma (meaning "me")

Meie -> Me (meaning "us")

Tema -> ta (meaning "him/her")

I once did a duolingo course on Finnish and was surprised to find how much of it is almost literally the same, both in having almost the same amount of cases (we have 14, Finnish has 15), and that the overall structure is the same, meaning the biggest hurdle for me to learn Finnish is not so much the langauge, but the vocabulary. While a lot of Finnish words are almost identical in Estonian, there's also quite a few that actually mean things in Estonian, but totally different things than in Finnish.

A funny (or not funny?) example is "Raiska pappi", which in Estonian means "Spend/waste money", but in Finnish means "raping priest" or something like that.

Finna can kinda-sorta understand a lot of written Estonian with no training, because there's so much overlap in vocabulary. Spoken Estonian is basically incomprehensible though.

From my own experience as an Estonian, if we both get together in a pub and get drunk, even if neither of us speak each others languages, we'll have no problem communicating. Drunk spoken Estonian and Finnish sort of blend together and the use of vocabulary gets limited to the more common words.

Or even bilberry land?

Yeah bilberry land is the correct translation. The grocery store blueberry translates to pensasmustikka and the flavor is a lot less intense.

There is also one of these in Västerås, Sweden, about 100 km from Stockholm. 3 caverns 30 m below the surface that used to store oil during the Cold War in case shit would hit the fan. 300,000 cubic meters, 13 GWh. Basically identical. Not as far along as the Finnish site though; it'll start backing up the district heating plant in 2024.

One application of this technology is to economically harnessing fusion power. Sadly there are considerable engineering and political difficulties. https://en.wikipedia.org/wiki/Project_PACER

Not simply fusion power: exploding small fusion or fission bombs. I think some difficulties are to be expected with such a plan.

> the temperature of the water in the heat cavern will vary between +45 and +100 degrees

I'm not sure if I should be assuming Fahrenheit or Celsius? The article isn't clear on the units here.

If it isn't a story from the US, it will be Celsius.

That's what I would normally have assumed, but 100C seemed a little hot for water just sitting in a big cistern

I'm no physicist but I assume that you'd need to put a lot more energy into the system before the water starts boiling, so you wouldn't have to worry about it?

If the energy would just be lost otherwise, you might as well go all the way to 100℃?

That's at 1 atm, perhaps the water is a bit pressurized as well?

A bit further down there's this confusing quote though:

> District heat is stored in two rock caverns in Mustikkamaa. The temperature of the water in the caverns varies between 50 and 90 °C.

+100°C (relative to some other temperature not clearly explained, probably the rock) vs 90°C absolute temperature.

That would mean that the rock baseline would be 10 degrees below freezing, which seems improbable. I think it would be close to the yearly average temperature for Helsinki (6.5°C) that close to the surface. Maybe I'm missing your point?

6.5 sounds right. Average ground temperatures down where they are stable are under ten degrees C. So this project will definitely warm up the surrounding rock, which (I guess) will increase its effective heat capacity.

The heat store is used in the winter when it is cold.

> "perhaps the water is a bit pressurized as well?"

I suppose in such a large storage vessel, most of the water is naturally pressurised by its own weight. So most of it won't boil, even at 100°C, except right at the surface?

If the water is not being heated from the bottom then I'd expect all the hottest water at the top/and or at the point of entry to the system. Heat loss into the holding substrate will cause rather rapid convection and surface boiling.

I interpreted it as +100C compared to the temperature of the rock

That would be well above boiling.

Lol, you are right...

Great to see the perception of energy-waste leading to new ventures. In the past century wasted energy had become a blind-spot (except when it led to some environmental effects - killing fish for example).

Thought was seldom given to re-using heat (let alone storing it) after its primary purpose. (I don't recall ever seeing any meta-survey of the scope of this near-blindness ... but it has to have become enormous ...) Home-heating solutions have usually been limited to the cost for consumers rather than the environment. That will have to change drastically.

Mustikkamaa is a recreational island about 3 kilometres from Helsinki’s center. It’s really nice. It’s a gateway island to Korkeasaari, the city zoo island.

So there must be a maze of underground pipes westward to Helsinki peninsula and to points north of Mustikkamaa. In any case the ground under Helsinki must look like Swiss cheese - Finns are tunnelers. Thru granite.

Got to wonder if this kind of thing wouldn't be possible here in Canada on the Canadian Shield (half-a-continent-sized slab o' granite), especially in places in Northern Ontario where there's old nickel mines, etc.

Bonus points if one uses the waste heat from e.g. industrial plants to help heat up the water.

The municipal heating network consists of both cooling and warming networks. Excess heat from, for example, data centers will be used to heat the water. Newer apartments are cooled using cold water from the network in the summer and heated using hot water in the winter. There are also joint power-and-heat plants connected to the heating network which are quite efficient: first the generated heat is used to drive a generator turbine and the remaining waste heat is piped into the municipal heating network. Combined efficiency is way higher than with generator-only plants or heating-only plants.

We do have buildings here in Toronto that are cooled using pumped water from Lake Ontario, which is very close to the downtown. And I suspect a heat pump could be used to provide heat by the same process. But in general I don't think it's being done at scale.

The Toronto system uses heat exchangers on the incoming tap water supply. So everyone (close to that leg of the water treatment system) gets slightly warmer tap water in summer time.

I wonder why they used tap water instead of seawater

Seawater is a corrosion nightmare. Even tap water is going to soak up minerals from the rock eventually and be a problem, but it will still be less of a problem than seawater will from the very start.

The only advantage seawater usually has is it’s ’free’ if you’re on the coast. But in many habitable climates, freshwater is ‘free’ too. Like most of Finland.

Why they should use seawater? Fresh water is not in shortage in this region - yearly precipitation significantly exceeds evaporation.

To a first approximation, Finland is on average a swamp. Thousands and thousands of lakes everywhere.

The Finnish name for Finland, Suomi, literally means "Land of Swamps". And it is awesome here.

It makes sense that Finns love rally so much then, if all the roads are weaving around swamps!

That is one proposed etymology of "Suomi".

Slightly higher boiling point? Fewer antimicrobial additives required?

Please, take a look at the map. Even cursory inspection of it will reveal to you that Finland is the land of lakes.

Finland has vast stores of fresh water and annual precipitation has nothing to do with it.

They have a massive desalination and pipeline operation to create lakes throughout the country?

Or is it the the sun and rain that created the lakes?

https://www.geographyrealm.com/finland-many-lakes/

Thanks to the last ice age and retreating glaciers...

Ice age and retreating glaciers created holes. And those holes filled up by the melt water of the glaciers.

The fact that they are still full of water is due to them being replenished by precipitation more than they lose water. If they would lose more water then what flows into them we would be speaking about the "land of many bone dry holes" in the famous Finnish desert.

Seawater erodes everything it touches. It isn’t impossible to build hardware that touches it, but it’s more expensive and needs more maintenance.

Fresh water makes the entire project much cheaper.

(Edit: this is wrong – see comments)

And this water is supposed to be fed directly into the homes of hundreds of thousands of customers through the existing district heating network which obviously isn't built with seawater in mind. A seawater storage facility would at the very least require a heat exchanger which would decrease efficiency.

I don't think it is this water that is going to be fed directly to homes. More likely there is going to be systems of heat exchangers.

They mention they are recovering heat from waste water. Obviously, they aren't pumping waste water into the system but rather use heat exchange to extract energy.

I don't think they'll be pumping that water directly into the heat distribution system. My understanding is that it'll be used as a heat reservoir and there will be some sort of heat exchanger to get the heat out of it.

It would be more efficient without the heat exchanger, but you’re almost certainly right - the reservoir water would probably be too oxygenated/mineralized for direct use if being stored in contact with the rock, at least without a lot of additional treatment.

Don’t want to kill all those underground pipes with mineral buildup as things precipitate out as it cools.

Counterflow heat exchangers easily approach 100% efficiency. It needs to be large enough, and needs sensors to control the flow, but both of those are trivial at this scale.

They’ll need to move 2x the volume of water, and have more infrastructure to maintain - even if it was actually 100% thermally efficient. Not counting capital costs. Which I’d count as efficiency issues.

The water pumping and maintenance costs are likely going to be their largest ongoing costs, no?

> It would be more efficient without the heat exchanger,

No, the only cost really is the cost of heat exchanger and maybe energy to pump water through the heat exchanger. Heat exchange approaches 100% thermal efficiency with large enough heat exchanger.

> It would be more efficient without the heat exchanger

Not really, heat pumps as a transfer method can achieve better total efficiency and make distribution of the heat easier.

That is an interesting thought, but seems like the capex and ongoing electrical costs of the heat pump would be too high?

They’re looking to make cheap use of the existing waste heat, after all, which while ‘low quality’ is high enough quality for district heating already.

Ah, on second thought you're probably right.

There is a heat exchanger.

https://www.slideshare.net/HelsinginEnergia/innovation-and-s... (slide 21)

Sibling comments are on to this too, but I think an important detail here is that the water in lakes, river and ground in the nordics is so clean that the extra cleaning needed to make it "tap water" isn't really as big of a deal as it might be in other parts of the world.

The little town I live in (about 40 km south of Oslo) is supplied from a lake in the granite hills. They filter out the bugs and precipitate the solids with a little aluminium sulphate and that's it. It's above all the agriculture so no chlorine is needed and there is no chalk so no problems with deposits on the insides of kettles and water heaters.

Does it taste good?

My favorite so far has been Vienna - I would describe it as similar to Evian.

It has been crowned best water in the country. Yes it tastes good, I'm quite happy to put it in my Laphroiag.

Finland has a small number of lakes that are basically dead from pollution from pulp & paper plants. The rest are quite clean. Helsinki's tap water comes from Päijänne, the large lake that basically runs from Lahti northward to Jyväskylä.

Torilla tavataan!

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