Sand energy storage explained for heat networks and long-duration storage
Sand energy storage is not a new battery chemistry. It is a form of thermal energy storage: electricity, usually low-cost renewable or off-peak power, heats sand, crushed stone, or another granular material inside an insulated vessel. The stored heat is then delivered to district heating, buildings, or industrial processes.
Its strongest current use case is heat, not round-trip electricity. That distinction matters. Using stored heat directly avoids the extra losses that come from converting heat back into power. Recent Finnish projects have moved the concept from a small commercial installation in 2022 to 100 MWh operation in 2025, with larger projects scheduled for 2027. That makes sand batteries a practical topic for energy storage planning, not just a laboratory concept.
What sand energy storage actually stores
A sand battery stores energy as sensible heat. In simple terms, the storage medium gets hotter, and that temperature difference represents the stored energy. The medium may be construction-grade sand, sand-like particles, crushed soapstone, mine waste rock, or another granular solid selected for density, cost, local availability, and thermal behavior.
Most commercial sand battery concepts use electric heaters and a closed-loop air system. Electricity heats air, the hot air circulates through pipes embedded in the storage medium, and the insulated container retains the heat. During discharge, air or another heat-transfer loop carries energy out through a heat exchanger. The output can be hot water, steam, or hot air, depending on the design and the customer’s heat demand.
This is where the word “battery” can be misleading. A lithium-ion battery stores electrochemical energy and discharges electricity. A sand battery primarily stores heat. It can support the power system by absorbing electricity when supply is abundant or prices are low, but its most efficient output is usually thermal energy.
Why interest is rising now
Interest in sand energy storage is rising because two energy-transition challenges are converging: more variable renewable electricity and persistent demand for heat. The International Energy Agency’s Renewables 2024 report said heat accounted for almost half of global final energy consumption and nearly 40% of energy-related CO2 emissions in 2023. Heat is therefore a major decarbonization target, not a secondary issue.
The IEA’s 2026 work on renewables in district energy also emphasized the value of flexible thermal storage. District heating and cooling networks can integrate electricity, heat pumps, waste heat, solar thermal, biomass, and stored heat at system scale. When a heat network or industrial steam demand is nearby, sand storage can convert cheap or surplus electricity into a useful product without first converting it back into electricity.
The U.S. Department of Energy has described thermal energy storage as a way to store heat or cold from hours to weeks and discharge it directly, avoiding inefficient thermal-to-electrical conversions when the end use is thermal. That principle is central to sand batteries: they are most compelling where the customer needs heat.
What verified projects show so far
The most visible commercial examples are in Finland, led by Polar Night Energy and local energy utilities. These projects do not prove that sand batteries fit every market, but they do provide operating reference points for capacity, application, and scale-up.
| Project | Status and date | Reported size | Main use | What it shows |
|---|---|---|---|---|
| Kankaanpää, Finland with Vatajankoski | In operation since 2022 | 200 kW thermal output and 8 MWh capacity | District heating and boosting data-center waste heat | A small commercial system can integrate with an existing heat network. |
| Pornainen, Finland with Loviisan Lämpö | Commissioned in June 2025; one-year results reported in June 2026 | 1 MW thermal output and 100 MWh capacity, using about 2,000 tonnes of crushed soapstone | Main heat production facility for the local district-heating network | Thermal storage can replace part of combustion-based heat and shift electricity use across days or weeks. |
| Vääksy, Finland with Lahti Energia | Under construction as of June 2026, with commissioning scheduled for 2027 | Planned 2 MW thermal output and 250 MWh capacity | District heating | Developers are scaling capacity and targeting reserve-market participation as well as heat supply. |
| Valkeakoski, Finland pilot | Announced in April 2025, planned to run through early 2027 | Pilot scale not positioned as a standard heat-only project | Power-to-heat-to-power testing plus heat recovery to district heating | Electricity output from stored heat is being tested, but it should be treated as a developing use case. |
The Pornainen project is the clearest recent operating example. Polar Night Energy reported in June 2026 that the installation had reduced climate emissions from the local district heating network by 70% during its first year, with 100% district-heating supply reliability, a 60% reduction in biomass consumption, and elimination of oil use in that network. Because these results are project-reported, they should be read as a developer and customer ecosystem claim, not as a universal performance guarantee.
Where sand batteries fit best
District heating and campus heat
District heating is the most natural fit because it already has pipes, customers, metering, and centralized heat production. A sand battery can charge when electricity is cheap or renewable output is abundant, then discharge heat into the network when demand rises. Similar logic can apply to university campuses, hospitals, industrial parks, and large mixed-use developments with central heat loops.
Industrial process heat
Many factories need hot water, steam, or hot air rather than electricity at the point of use. Food and beverage, pulp and paper, textiles, minerals, chemicals, and manufacturing are all potential categories. The exact fit depends on temperature, operating schedule, reliability requirements, and local electricity prices. Current commercial systems are most relevant where the required heat temperature is within the equipment’s output range and where the site can use stored heat for enough annual hours.
Grid flexibility
Sand storage can also act as a flexible electric load. When wind or solar output is high, or when wholesale prices are low, the system can charge. When the grid is tight, it can stop charging or discharge heat instead of running electric boilers or fossil-fuel boilers. This does not make it a direct substitute for battery energy storage systems that inject electricity into the grid. It can, however, reduce peak heating-related electricity demand and help use renewable generation that might otherwise be curtailed. See also: solar products.
Advantages and limits to consider
The advantages are straightforward. The storage medium can be abundant and locally sourced. Energy capacity can often be increased by adding more material and volume. The system can have a long service life because the storage medium is not a delicate electrochemical cell. It can also use materials that are unsuitable for construction, such as certain crushed stones or industrial by-products, if testing confirms they are thermally and environmentally appropriate.
The limits are just as important. Sand has lower energy density than many chemical fuels, so systems are physically large. The best economics require a steady thermal customer nearby. A sand battery does not automatically solve electricity storage, because converting heat back into electricity introduces thermodynamic losses and added equipment cost. Controls, insulation, heat exchangers, safety systems, foundations, grid connection, and market rules all affect the business case.
Terminology is another limitation. Public discussion often treats “sand battery” as if it describes one standard product. In practice, projects differ in temperature, storage medium, power rating, discharge duration, system integration, and revenue model. A 100 MWh district-heating asset and a pilot designed to regenerate electricity are not the same type of project.
How it compares with other storage options
| Technology | Best suited for | Main strength | Main limitation |
|---|---|---|---|
| Sand energy storage | District heating, industrial heat, long-duration thermal storage | Uses low-cost solid media and can store useful heat for long periods | Requires thermal demand and large insulated storage volume |
| Lithium-ion batteries | Short-duration electric storage, frequency response, solar shifting | High round-trip electrical efficiency and fast response | Cost rises with long duration, and it is not optimized for direct heat supply |
| Molten salt thermal storage | Concentrated solar power and high-temperature thermal systems | Commercially established in some power and heat applications | Salt freezing, corrosion, and system complexity must be managed |
| Hot water thermal storage | Low- and medium-temperature heat networks | Mature, simple, and widely understood | Lower temperature range and larger volumes for some applications |
The comparison shows why sand storage should not be framed as a winner-takes-all technology. It is not “better than lithium” in every context. It is suited to different energy flows. If a site needs electricity back at high efficiency within a few hours, lithium-ion or another electric storage technology may be more appropriate. If the site needs large amounts of heat over days or weeks, sand storage becomes more relevant.
What to watch next
The next phase will be defined by three questions. First, can larger projects such as Lahti Energia’s planned 250 MWh installation stay on schedule and meet performance expectations after commissioning? Second, can power-to-heat-to-power pilots demonstrate acceptable cost and efficiency for electricity markets, not only for heat networks? Third, can developers replicate Finnish success in markets with different electricity prices, permitting rules, heat-network infrastructure, and industrial load profiles?
For now, the evidence supports a measured conclusion: sand energy storage is a credible long-duration thermal storage option when there is a strong heat customer, a suitable site, and access to low-cost electricity. It is less proven as a general-purpose electricity battery. Its most valuable role may be bridging sectors by turning variable renewable electricity into dispatchable heat for places that still burn gas, oil, coal, or biomass for thermal demand.
Frequently asked questions
Is sand energy storage the same as a lithium battery?
No. A lithium battery stores and returns electricity through electrochemical reactions. Sand energy storage stores heat in a solid material and usually returns heat through a heat exchanger. It can support the electricity system by shifting electric load, but its current commercial strength is thermal output.
Can a sand battery generate electricity?
It can in principle, but that is not the main commercial use today. Converting stored heat back into electricity requires a heat engine or another conversion process, which lowers electrical efficiency. The Valkeakoski pilot in Finland is designed to test this power-to-heat-to-power pathway, with results expected after the pilot period.
Why use sand, crushed stone, or soapstone?
These materials can be abundant, inexpensive, stable at high temperatures, and available near the project site. The exact material must be tested for thermal performance, durability, environmental safety, and compatibility with the system design.
Where would this technology make the most sense?
The best candidates are district-heating networks, large campuses, and industrial facilities with steady heat demand. Sites with volatile electricity prices, high renewable penetration, or fossil-fuel boilers to displace may have a stronger case, but each project needs site-specific engineering and economic analysis.
