Electrochemical batteries, gravitational batteries and hydrogen storage tanks: the solutions for energy storage are plentiful. However, none of them appear to have gained widespread consensus, as some suffer from excessively high costs, while others possess inadequate power or storage duration capabilities.
Nowadays, there are already several types of energy storage batteries, which can be divided into two main categories: short-term storage systems, such as electrochemical batteries (lead, lithium, etc.), and long-term storage systems, such as hydrogen tanks, pumped-storage hydroelectricity also certain devices capable of storing heat (water, refractory bricks, etc.).
It has been 3 years since Polar Night Energy (a Finnish company) introduced the world’s first commercial high-temperature thermal storage system utilizing sand with a capacity of 100 kW and 8 MWh. As of 2024, Polar Night Energy has reported that the construction of its sand-based thermal energy storage system in Pornainen, southern Finland, is proceeding on schedule. This 1 MW system is designed to supply thermal energy to the Loviisan Lämpö district’s heating network.1
However, Finland is not the only country working on this concept. Latvia, Sweden, the United States, and other countries have various projects based on this idea.
Who conceived this idea?
The technology was developed by four young Finnish engineers and childhood friends: Tommi Eronen, Markku Ilionen, Liisa Naskali, and Ville Kivioja. According to Tommi Eronen, the idea for creating this system came to him after reading an article about traditional Finnish stoves made of stone and sand. This led him to consider that solid materials might be more suitable for storing solar and wind energy than water.
How does it work?
The battery, housed in a 7-meter-tall steel container, contains 100 tons of low-grade construction sand, two heating supply pipes, and a fan. The sand is converted into a battery after being heated to 600°C using electricity generated from wind turbines and solar panels. Renewable energy powers a heater that warms the air within the sand. Inside the battery, hot air circulates through heat exchanger pipes embedded in the sand.
Thick insulation surrounding the sand maintains the internal temperature of the battery at 600°C, even when outdoor temperatures are freezing. When fully charged, the battery stores 8 MWh of thermal energy. As energy demand rises, the battery releases approximately 200 kW of energy through the heat exchange pipes. This output is sufficient to provide heating and hot water for about 100 homes and a community swimming pool, supplementing electricity from the grid. The battery charges at night when electricity prices are lower.2
Figure 1 – Image representing how it works
Advantages of the system as an element of circular economy
The main advantage resides in the fact that it’s economically inexpensive. The company uses low-quality sand that has been rejected by builders so it’s easy to obtain. It is also environmentally friendly, and it is stable, quite stable, in a wide range of temperature.
The other advantages of the system itself are also noteworthy: the pipes and sand do not wear out. The fan is the only moving part and can be easily replaced if necessary. Sand, by nature, effectively retains heat for months and has a long lifespan; it can be heated and cooled as many times as needed.
How effective is the sand battery compared to other systems, particularly lithium-ion batteries?
A major issue with lithium-ion batteries, which we use to power our laptops, phones, and electric vehicles, is that they continually discharge even when not in use. Sand batteries, on the other hand, do not involve any chemical reaction, thus they do not experience the same aging process.
Lithium batteries are not suitable for large-scale storage and are inherently flammable.
Additionally, there are environmental concerns. The production of each ton of refined lithium results in emissions of three to nine tons of CO2. Also, lithium is a time limited resource as the quantity on our planet is limited.
What about similar projects in other countries?
As mentioned above, there are other companies working on similar concepts. For instance, Batsand (a company founded in Riga, Latvia) is developing household sand batteries for thermal energy storage. By charging during summer and providing both heating and cooling capabilities year-round, it addresses the challenge of balancing energy supply and demand across seasons. The offering of two system sizes (14KW and 25KW) allows for flexibility in meeting different household needs, potentially making this sustainable technology accessible to a wider range of consumers.
Another example, K-mit AB (a Swedish company) which is developing sand battery technology for energy storage. In 2023, K-mit AB constructed a prototype sand battery as part of the « Microgrid with sand battery » project, funded by the Swedish Energy Agency3. They were also working on optimizing heat input and output in the sand battery through a project called « High temperature heat pumps for thermo batteries ».
The sand batteries also have their limitations
The sand battery’s energy storage capacity per unit volume is five to ten times lower than that of traditional chemical batteries. Companies working in this field, including Polar Night Energy, acknowledge this limitation. However, they argue that the sand battery offers a significantly more cost-effective solution. Polar Night Energy’s calculations suggest that their battery is eight to ten times less expensive than a lithium battery storing an equivalent amount of energy. To illustrate, generating 8 MWh of energy using the sand battery in Kankaanpää costs approximately $200,000, whereas a lithium-ion battery with the same 8 MWh capacity would cost a minimum of $1,600,000.
According to one of the inventors, the efficiency of converting heat to electricity is currently only 30%. However, the next step to increase electricity generation from the battery will be to add a turbine that converts heat back into the grid. Moreover, the battery has much greater potential beyond heating homes. It can be utilized in all industrial processes that require high temperatures, such as bakeries, laundries, and metallurgical plants.
To know more:
Étudiante en M2 Droit et gestion des énergies et du développement durable
