Sand battery & development trend

Hello, Yesa, can you tell me what is sand battery in Finland? And how is its development trend? Can it replace lithium battery etc in future? Thanks

https://polarnightenergy.com/sand-battery/

OK, I am happy to answer your questions.

A sand battery (or sand-based thermal energy storage system) is a large-scale technology that stores excess renewable electricity as heat in sand or crushed rock (such as soapstone), then releases that heat on demand—primarily for district heating or industrial processes. It is not an electro-chemical battery like lithium-ion systems.

How it works?

Excess cheap electricity (from wind, solar, or low spot-market prices) powers resistive heaters that warm air. This hot air circulates through pipes in a closed loop inside a large insulated silo filled with sand or crushed stone, raising the material’s temperature to roughly 400–600°C (or higher in some designs). The solid medium retains the heat for days to weeks (or longer) with relatively low losses. When heat is needed, the system extracts it to produce hot water or steam for district heating networks, buildings, or industrial uses. Efficiency is typically around 85% or better for heat delivery (some reports note 10–15% losses overall).

Key advantages include:

• Abundant, low-cost, non-toxic materials (sand, crushed soapstone/byproducts, steel) with no rare-earth minerals or lithium/cobalt.
• No chemical degradation—long lifespan (decades, e.g., 20–30+ years design life).
• Safe (very low fire risk).
• Excellent for long-duration storage (hours to weeks/seasonal), which lithium-ion is less suited for economically at large scales.
• Ability to charge when electricity is cheapest and participate in grid reserve/balancing markets.

Finland is the leader via the company Polar Night Energy (founded 2018 by Tommi Eronen and Markku Ylönen). Their first commercial unit (about 0.1–0.2 MW / 8 MWh, 100 tons of sand) opened in Kankaanpää in 2022 for a local district heating network. The world’s largest commercial unit (1 MW thermal power / 100 MWh storage, ~2,000 tons of crushed soapstone, ~13 m tall × 15 m wide) went online in Pornainen in June 2025 for Loviisan Lämpö. It can cover roughly a month of the town’s (5,000 residents) summer heat demand or about a week in winter. After one year of operation, it reduced local district heating emissions by ~70%, eliminated oil use, and cut wood-chip/biomass use by ~60%, while exceeding efficiency targets and providing 100% supply reliability.

Development trend of the technology is scaling rapidly and attracting attention:

• From the small 2022 pilot to the 10× larger 2025 Pornainen unit.
• A larger project (~2 MW / 250 MWh) is planned/under construction for Lahti Energia in Vääksy (completion targeted for summer 2027), which would become the new largest.
• Additional Finnish projects (e.g., Valkeakoski pilot) and first international expansion (Latvia), with interest in northern Europe (Germany, Switzerland, etc.).
• Exploration of industrial applications (higher-temperature heat/steam) and power-to-heat-to-power conversion (using heat to generate electricity via turbines, still in earlier stages).
• Positive economics: charges at prices often 70–80%+ below average spot market; named among TIME’s best inventions; growing recognition as a low-cost, sustainable long-duration storage option.

Overall trend is strong commercial validation in district heating (especially in cold climates with existing networks), cost-effectiveness for long-duration needs, and gradual expansion beyond Finland as renewables penetration increases the need for storage that bridges intermittency without rare materials.

Can it replace lithium batteries in the future?

No—not as a direct replacement. They serve complementary roles rather than competing head-to-head in most applications.

• Lithium-ion (and similar electrochemical batteries)excel at high energy density, fast charge/discharge, compact size, and direct electricity storage/output. They dominate EVs, consumer electronics, short-duration grid storage (minutes to a few hours), and applications needing portable or high-power electrical response.
• Sand batteriesstore thermal energy at far lower cost per kWh for long durations, use abundant materials, last longer without degradation, and are ideal for heating-dominated uses or seasonal storage. Energy density is much lower (requiring large silos), round-trip efficiency is lower if converting back to electricity, and they are not practical for mobility or small-scale portable power.

Sand batteries can reduce reliance on lithium systems for certain grid-scale, long-duration, or heat-focused needs and help integrate more renewables by soaking up surplus power cheaply. In a future energy mix, both (plus other technologies like pumped hydro, gravity, hydrogen, etc.) will likely coexist: lithium for short/high-density electrical needs, sand/thermal for bulk heat and long-duration storage. Polar Night Energy and others explicitly position sand batteries as a materials-light complement rather than a lithium replacement.

In short, Finland’s sand batteries are a practical, proven success for clean district heating and long-duration thermal storage, with clear upward momentum in scale and applications. They strengthen the renewable energy toolkit but will not displace lithium batteries across the board.

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