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

[iljah]

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.

[Reason077]

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?

[euroderf]

> 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 ?

[anttiharju]

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

[askonomm]

Mustikamaa in Estonian :)

[leke]

Or even bilberry land?

[moogly]

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.

[wbl]

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

[switchbak]

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

[sdflhasjd]

> 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.

[Torkel]

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

[8bitsrule]

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.

[cromulent]

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.

[euroderf]

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.

[cmrdporcupine]

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.

[yason]

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.

[coffeebeqn]

I wonder why they used tap water instead of seawater

[lazide]

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.

[citrin_ru]

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

[Filligree]

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.

[Torkel]

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.

[wayvey]

Torilla tavataan!