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Finnish City Inaugurates 1 MW/100 MWh Sand Battery

(cleantechnica.com)
190 points erwinmatijsen | 7 comments | 03 Sep 25 06:00 UTC | HN request time: 0.001s | source | bottom
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fulafel ◴[03 Sep 25 06:52 UTC] No.45112956[source]▶
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.

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1. decimalenough ◴[03 Sep 25 06:54 UTC] No.45112970[source]▶
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).
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2. Cthulhu_ ◴[03 Sep 25 08:00 UTC] No.45113324[source]▶
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...

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3. nick49488171 ◴[03 Sep 25 08:34 UTC] No.45113493[source]▶
How many kiloton of TNT equivalent?
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4. killingtime74 ◴[03 Sep 25 08:44 UTC] No.45113554[source]▶
Interestingly that's also about the pressure of gas in scuba tanks. Can't imagine how much energy to pressurize water to that
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5. grues-dinner ◴[03 Sep 25 08:46 UTC] No.45113560{3}[source]▶
Well, if you say the energy stored is the 100MWh from the headline figure, and say you can arrange release every joule of all at once by flashing high-pressure water to steam at 1 atm that's about 0.1kT.

So quite a bang - allegedly this is 200lb, so about the same: https://www.youtube.com/watch?v=ZDgvar7ON54

6. trhway ◴[03 Sep 25 09:36 UTC] No.45113855{3}[source]▶
Due to incompressibility of liquids, pressurizing a liquid is very cheap energy-wise - orders of magnitude cheaper than pressurizing a gas. The issue is that pressurized liquid also requires correspondingly strong and expensive vessels and pipes.
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7. sfn42 ◴[03 Sep 25 09:52 UTC] No.45113959{4}[source]▶
You don't need to pressurize it. You just put it in a tank and apply heat, the water evaporates and creates pressure. Like a pressure cooker.