π Finland's 'sand battery' survived its first brutal winter. But the viral story gets one big thing wrong.
What's real:
- Polar Night Energy built a commercial thermal battery in Pornainen, Finland (5,000 people)
- 2,000 tons of crushed soapstone heated to 500-600C
- 1 MW power, 100 MWh capacity
- 100% oil reduction (literally zero oil used now)
- 70% CO2 emissions cut, 60% less wood chip combustion
- Survived winter 2025-2026 without interruption
- 5 projects across Finland, 9M euros funding
What's misleading:
1) It stores HEAT, not electricity. The 100 MWh is thermal energy. It can't power your lights or EV - it heats buildings via district heating. 'Store electricity in sand' implies grid-scale electrical storage, which this isn't.
2) It's crushed soapstone, not ordinary quartz sand - but geologically, "sand" refers to grain size (0.0625-2mm), not composition. So crushed soapstone of the right size IS sand. Still, soapstone outperforms quartz sand in heat capacity (0.98 vs 0.83 kJ/kg/K) and density. 'Sand battery' is branding, but geologically accurate.
3) The 80-90% round-trip efficiency is company-claimed, not independently verified. And it's electricity-to-heat-to-heat, not electricity-to-electricity. Comparing it to lithium-ion (90-95%) is apples-to-oranges.
4) The underlying tech (packed-bed thermal storage) is decades old. What's new is the application, branding, and business model.
The sand battery isn't competing with your Powerwall. It's competing with oil boilers - and it's already winning.
Full writeup: hermez.prose.sh/finland-sand-bβ¦
#science #energy #renewable #Finland #engineering #CleanEnergy
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John Faithfull ππͺπΊπ΄σ §σ ’σ ³σ £σ ΄σ Ώπ§‘βπ»βπΏ
in reply to jcrabapple • • •Daniel AJ Sokolov
in reply to jcrabapple • • •And how many fireplaces could possibly be built to scale this business model?
And then how much CO2 would be released from the use of all these fireplaces?
I like the project, but I'm not sure it can reasonably scale.
Kathrin
in reply to jcrabapple • • •In everyday language, "sand" is obviously understood differently, but I think this should at least be noted in a fact-check. Giving physical properties for "sand" in a fact-check without specifying the material is not good, though "plain sand" probably means quartz.
bigblen
in reply to jcrabapple • • •I guess the district heating infrastructure was already there in Pornainen, powered by burning something.
I don't know how widespread this is in Finland?
e.g. I visited a friend in Oulu (pop. 200k) and was impressed by the district heat there, including keeping cycle paths free of snow. Powered by peat burning at the time, I think that is changing now. Info here oulunenergia.fi/en/heat-and-enβ¦
District heating
www.oulunenergia.fisortius
in reply to jcrabapple • • •sand is defined by grain size, not composition.
That said, awesome stuff
clew
Unknown parent • • •Explain more? If it makes sense for 50,000 people, why not build one in each neighborhood of 50,000?
District heat/cooling with ground loops moving heat around between seasons seems pretty hopeful, for example. Not free, but keeps people healthy using less than it takes now. No?
@jcrabapple @newstik
ohir
Unknown parent • • •> just don't make sense at scale.
Thermal batteries are way cheaper and better scaled up. The higher Volume / area ratio is the insulation costs per MWh are lower.
@newstik