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

helen.fi

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

#2

Post by 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.

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

#4

Post by Filligree »

coffeebeqn wrote: post #3

I wonder why they used tap water instead of seawater

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.

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

#5

Post by Sharlin »

Filligree wrote: post #4
coffeebeqn wrote: post #3

I wonder why they used tap water instead of seawater

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.

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

#7

Post by lazide »

coffeebeqn wrote: post #3

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.

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

#9

Post by michpoch »

Sharlin wrote: post #5
Filligree wrote: post #4

Earlier quoted context omitted.

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 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.
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