The challenge of storing surplus power from intermittent sources like wind and solar has become a critical hurdle. Come in sand batteries, like those developed in Finland by Polar Night Energy.

The concept of using sand or similar materials to store heat is not entirely new – thermal energy storage has been explored for decades, with systems like molten salt used in concentrated solar power plants since the 1980s. However, the specific application of sand in a compact, low-cost, and scalable system for storing renewable energy as heat is a modern innovation.

In the below article I will give you a detailed overview on how they work, their sustainability potential, possible applications, limitations, and reasons for their limited adoption (so far).

How Do Sand Batteries Work?

Sand Batteries: A Game-Changing Energy Storage Solution?

Sand batteries store energy in the form of heat using sand or sand-like materials (e.g., crushed soapstone) as the storage medium.

Here’s a breakdown of their operation:

  • Charging: Electricity, typically from renewable sources like solar or wind, is used to heat air via resistive heating (similar to electric heaters). This hot air is circulated through pipes embedded in a large, insulated steel silo filled with sand or a similar material. The sand is heated to high temperatures, typically between 400–600°C, though some designs aim for up to 1,000°C.
  • Storage: Sand has a high heat capacity and low thermal conductivity, allowing it to retain heat for weeks or even months with minimal loss (around 10% heat loss over time). The silo is well-insulated to maintain the stored heat.
  • Discharging: When heat is needed, cool air is blown through the pipes in the silo, absorbing heat from the sand. This hot air can be used directly for space heating, to produce hot water or steam for district heating networks, or for industrial processes. Alternatively, the heat can be transferred via a heat exchanger to heat water for distribution.
  • Efficiency: The system achieves high efficiency (up to 99% for heat storage) when used directly for heating purposes. However, converting stored heat back to electricity is less efficient, with current technologies achieving only about 30% efficiency, though improvements are being explored, such as adding turbines for power generation.

The world’s first commercial sand battery, installed in 2022 in Kankaanpää, Finland, is a 7-meter-tall, 4-meter-wide silo with 100 tonnes of sand, delivering 100 kW of heating power and 8 MWh of storage capacity. A larger version in Pornainen, operational since 2025, is 13 meters tall, 15 meters wide, uses 2,000 tonnes of crushed soapstone, and can store 100 MWh of energy while delivering 1 MW of thermal power.

Are Sand Batteries A Sustainable Solution?

Sand batteries are highly sustainable for several reasons:

  • Material Availability: Sand is abundant and inexpensive. Polar Night Energy uses low-grade sand or industrial by-products like crushed soapstone, which are not in demand for construction, minimizing resource competition and environmental impact. For example, the Pornainen battery uses soapstone waste from a Finnish fireplace manufacturer.
  • Low Environmental Impact: The system avoids toxic materials, has no chemical degradation, and produces no harmful emissions. It uses standard steel and insulation materials, with sand itself acting as a natural insulator.
  • Carbon Emission Reduction: By storing renewable energy and replacing fossil fuels like oil and gas, sand batteries significantly reduce greenhouse gas emissions. The Pornainen battery is expected to cut district heating emissions by 70%, equivalent to 160 tonnes of CO2 per year.
  • Longevity: Sand batteries have a long lifespan with minimal maintenance, as the only moving part is a fan, and sand does not degrade like electrochemical batteries.
  • Circular Economy: The use of industrial by-products or mine waste as storage media promotes a circular economy, reducing waste and the need for new resource extraction.

Where Can Sand Batteries Be Used?

Sand batteries are versatile and can be applied in various contexts, particularly where heat is needed:

  • District Heating Networks: They are ideal for regions like Finland, where centralized district heating systems are common (70% of Finnish heating networks use renewables). They store excess summer solar energy to heat homes, offices, and facilities like swimming pools during winter.
  • Industrial Processes: Sand batteries can provide high-temperature heat (60–400°C, potentially up to 1,000°C) for industries such as food processing, cement, ceramics, or steel manufacturing. In countries like Australia, they could replace gas for industrial heating, which accounts for 16% of emissions.
  • Regions with Seasonal Energy Variability: They are particularly effective in areas with significant seasonal differences in renewable energy production, such as Northern Europe, where solar output drops in winter, or regions with long winters requiring consistent heating.
  • Grid Stabilization: Sand batteries can store surplus energy when renewable production is high and release it during peak demand, participating in electricity reserve markets to stabilize grids.
  • Alternative Materials: While sand is common, other materials like crushed brick or volcanic rock can be used, making the technology adaptable to local resources.

Where Are Sand Batteries Less Suitable?

Sand batteries do not offer a solution for every country or region. Let’s see the hurdles that inherent with the technology:

  • Areas Without District Heating: Sand batteries are less practical in regions lacking centralized heating infrastructure, as their primary output is heat rather than electricity. For example, in tropical climates or countries with decentralized heating (e.g., individual home systems), their application is limited unless adapted for industrial use.
  • Electricity-Centric Systems: Converting stored heat back to electricity is currently inefficient (30% efficiency), making sand batteries less viable for applications requiring electricity rather than heat. Other storage solutions like lithium-ion batteries or pumped hydro may be better suited for electricity storage.
  • High Land or Space Constraints: While compact compared to other storage systems, sand batteries still require significant space (e.g., a 13m x 15m silo for the Pornainen battery). Urban areas with limited space may face challenges.
  • Low Heat Demand: In regions with minimal heating needs (e.g., consistently warm climates), sand batteries lose their primary advantage unless paired with industrial processes requiring heat.

Why Haven’t Sand Batteries Been Used More?

Despite their promise, sand batteries have not yet seen widespread adoption for several reasons:

  1. Emerging Technology: Sand batteries are relatively new, with the first commercial unit launched in 2022. Scaling up and proving long-term reliability at industrial scales take time. The Pornainen battery, 10 times larger than the Kankaanpää prototype, is a recent step toward broader implementation (2025).
  2. Limited Application Scope: Their primary use is for heat storage, which is most relevant in regions with district heating or industrial heat needs. Many countries, especially in warmer climates or with decentralized heating, have less demand for such systems.
  3. Competition from Other Technologies: Lithium-ion batteries, pumped hydro, and other storage solutions are more established for electricity storage. For heat, alternatives like molten salt or water-based systems are already in use, and industries may be hesitant to adopt a new technology without extensive testing.
  4. Infrastructure Dependence: Sand batteries require integration with existing district heating or industrial systems, which may not be present or easily adaptable in many regions. Retrofitting or building new infrastructure is costly and complex.
  5. Investment and Awareness: While sand batteries are cost-effective (installation costs around $10/kWh for the Kankaanpää battery), scaling them requires significant upfront investment. Lack of awareness and limited international projects (though Polar Night Energy is in talks for global expansion) slow adoption.
  6. Electricity Conversion Challenges: The low efficiency of converting stored heat back to electricity (30%) limits their appeal in electricity-driven markets. Research into improving this, such as adding turbines, is ongoing but not yet commercially viable.
  7. Material Availability Concerns: While sand is abundant, high demand for construction-grade sand globally (expected to rise 45% in the next 40 years) could raise concerns about resource competition, though Polar Night Energy mitigates this by using low-grade or waste materials.

Scaling of Sand Batteries

Let’s compare the two Finnish installations to understand scaling, namely Kankaanpää’s 8 MWh vs. Pornainen’s 100 MWh. Based on the information provided about sand batteries, their specifications, and key characteristics we can already conclude the following.

Attribute Kankaanpää Battery (2022) Pornainen Battery (2025) General Sand Battery Characteristics
Location Kankaanpää, Finland Pornainen, Finland Varies (primarily suited for cold climates or industrial settings)
Operational Since 2022 2025 Recent innovation (first commercial use in 2022)
Storage Material Sand Crushed soapstone Sand, crushed soapstone, or other heat-retaining materials (e.g., brick, volcanic rock)
Storage Capacity 8 MWh 100 MWh Scalable, up to 1,000 MWh in future designs
Heating Power 100 kW 1 MW Varies by size (100 kW to multiple MW)
Dimensions 7m tall, 4m wide 13m tall, 15m wide Compact but requires significant space
Material Weight 100 tonnes 2,000 tonnes Depends on capacity (100–2,000+ tonnes)
Temperature Range 400–600°C 400–600°C Up to 1,000°C in advanced designs
Heat Storage Efficiency Up to 99% Up to 99% Up to 99% for direct heat use
Heat-to-Electricity Efficiency ~30% (if converted) ~30% (if converted) ~30% (ongoing research to improve)
Heat Loss ~10% over time ~10% over time Low (~10% over weeks/months)
CO2 Emissions Reduction Not specified 70% (160 tonnes/year) Significant when replacing fossil fuels
Applications District heating District heating District heating, industrial processes, grid stabilization
Sustainability High (uses waste materials) High (uses soapstone waste) High (abundant materials, no toxic emissions)
Cost ~$10/kWh (installation) Not specified Cost-effective compared to other storage
Limitations Heat-focused, space needs Heat-focused, space needs Less suitable for electricity-only or warm climates

Comparison of Sand Batteries vs. Other Energy Storage Technologies

In order to compare this new energy storage solution with existing energy storage solutions, we will base the sand battery costs on the Kankaanpää installation (~$10/kWh). For lithium-ion battery costs we will use 2025 market estimates for grid-scale systems. Pumped hydro costs do vary widely based on site-specific factors, while molten salt costs are derived from CSP plant storage systems.

You will see that sand batteries excel in direct heat applications (99%) but lag in electricity conversion (~30%). Lithium-ion and pumped hydro are optimized for electricity storage. Molten salt is just like sand batteries efficient for heat but less so for electricity conversion.

Sand batteries are niche for heat-focused applications, while lithium-ion and pumped hydro are electricity-focused. Molten salt is primarily used in CSP but can serve similar heat applications as sand batteries.

Here is a table comparing all 4 energy storage solutions.

Attribute Sand Batteries Lithium-Ion Batteries Pumped Hydro Storage Molten Salt Storage
Primary Energy Form Thermal (heat) Electrical Mechanical (potential energy) Thermal (heat)
Installation Cost ~$10/kWh (e.g., Kankaanpää battery) $300–$400/kWh $50–$200/kWh $30–$60/kWh
Operational Cost Low (minimal maintenance, no degradation) Moderate (battery degradation, replacement every 10–15 years) Low (long lifespan, minimal maintenance) Moderate (pumps, maintenance, corrosion management)
Storage Efficiency Up to 99% (for heat output); ~30% (heat-to-electricity) 85–95% (round-trip efficiency) 70–85% (round-trip efficiency) 80–90% (for heat); 40–50% (heat-to-electricity)
Lifespan Decades (sand does not degrade, minimal moving parts) 10–15 years (degrades with cycles) 50–100 years 20–30 years
Applications District heating, industrial heat (60–400°C, up to 1,000°C), grid stabilization Grid storage, electric vehicles, portable devices, backup power Large-scale grid storage, peak shaving, renewable integration Concentrated solar power (CSP), industrial heat, grid storage
Scalability High (modular, 8 MWh to 1,000 MWh potential) High (modular, kWh to GWh scale) Limited (requires specific geography, large scale only) Moderate (tied to CSP or large heat systems)
Environmental Impact Low (uses abundant/waste materials, no toxic emissions) Moderate (mining for lithium/cobalt, recycling challenges) Moderate (land use, ecosystem disruption) Low (non-toxic salts, but some mining and corrosion concerns)
Geographical Suitability Best in cold climates or industrial settings; less suited for warm climates Universal (compact, no geographical constraints) Limited to hilly/mountainous regions with water sources Best in sunny regions (for CSP) or industrial heat settings
Key Advantages Low cost, sustainable materials, long-term heat storage (weeks/months) High efficiency for electricity, fast response, compact Large-scale storage, long lifespan, cost-effective for grid-scale High heat storage efficiency, proven in CSP
Key Limitations Heat-focused, low heat-to-electricity efficiency, requires space High cost, degradation, environmental concerns Geography-dependent, high initial land impact Complex systems, corrosion risks, less versatile than sand batteries

Potential for Future Adoption

The sand batteries in Finland, particularly in Kankaanpää and Pornainen, have drawn global attention, with projects being considered internationally. Polar Night Energy is exploring larger systems (up to 1,000 MWh) and applications like converting heat back to electricity.

The technology’s low cost, sustainability, and ability to use waste materials make it a promising solution for decarbonizing heating, especially in cold climates or industrial settings. However, broader adoption will depend on overcoming infrastructure barriers, improving electricity conversion efficiency, and increasing investment in pilot projects worldwide.

Nevertheless, batteries are a sustainable, cost-effective solution for storing renewable energy as heat, particularly suited for district heating and industrial applications in regions with seasonal energy variability. Their limited adoption stems from their niche application, emerging status, and competition with established technologies, but their potential is significant.


I specialize in sustainability education, curriculum co-creation, and early-stage project strategy for schools and public bodies. When I am not writing, I enjoy hiking in the Black Forest and experimenting with plant-based recipes.