A sand battery is a new technology that promises a cheap and sustainable solution for storing energy from renewable sources such as the sun or wind. A sand battery uses sand or other siliceous materials that are heated by electricity and store energy as heat. The heat can then be used for heating, industrial processes, or converted back into electricity. Sand batteries have several advantages, such as low cost, long life, high capacity, and minimal environmental impact. On the other hand, it also has some disadvantages, such as low efficiency, large dimensions, the need for insulation, and limited availability of siliceous resources. In this article, we will introduce the principle and properties of sand batteries and their first implementation in Finland.
Principle and properties of a sand battery
A sand battery is based on the principle of thermal energy storage, which involves storing energy in the form of heat in a material with high thermal capacity. Thermal capacity is the ability of a material to absorb and release heat when the temperature changes. The higher the thermal capacity, the more energy can be stored in the material. A sand battery uses sand or other siliceous materials, such as glass, ceramics, or quartz, which have high thermal capacity and are inexpensive and readily available. Sand or other siliceous material is placed in a container that is insulated from the environment. The container is then connected to a power source that heats the material using electrical resistance. This increases the temperature of the material to several hundred or thousand degrees Celsius. The heat is then stored in the material for several days, weeks, or months, depending on the quality of the insulation. When the energy is needed, the heat can be released from the material either directly, for example for heating, or indirectly, for example using a heat engine that converts heat into electricity.
- Přebytečná energie z obnovitelných zdrojů, jako je solární nebo větrná energie, se použije k ohřevu vzduchu pomocí odporového ohřívače.
- Ohřátý vzduch se přivádí do ocelového kontejneru naplněného pískem, kde se teplo přenáší na písek prostřednictvím výměníku tepla.
- Písek se zahřívá na teplotu až 1000 °C a uchovává teplo po dobu několika měsíců.
- Když je potřeba využít uloženou energii, vzduch se opět protlačí kontejnerem a získá teplo z písku.
- Tepelný vzduch se pak vede do topného systému nebo do elektrického generátoru.
Main advantages of sand batteries:
- Low cost: Sand or other siliceous materials are cheap and readily available, making sand batteries much cheaper than other types of batteries. For example, the cost of a sand battery is estimated at €0.5 to €2 per kWh, while the cost of a lithium-ion battery is around €100 to €200 per kWh.
- Long service life: Sand or other siliceous materials are resistant to wear and degradation, which is why sand batteries can operate for several decades without the need for maintenance or replacement. For example, the lifespan of a sand battery is estimated to be 40 to 50 years, while the lifespan of a lithium-ion battery is about 10 to 15 years.
- High capacity: Sand or other siliceous materials have high thermal capacity, and therefore a sand battery is capable of storing a large amount of energy in a small volume. For example, the capacity of a sand battery is estimated to be 1.5 to 2 kWh/kg, while the capacity of a lithium-ion battery is about 0.2 kWh/kg.
- Minimal environmental impact: Sand or other siliceous materials are harmless to the environment, and therefore sand batteries are environmentally friendly and recyclable. Sand batteries do not use any toxic or rare elements such as lithium, cobalt, or nickel, which are used in other types of batteries and whose mining and processing have a negative impact on the environment and human rights.
On the other hand, sand batteries also have some disadvantages that need to be overcome before they can become a widely used energy storage technology. These disadvantages include:
- Low efficiency: Sand batteries have low efficiency, which means that some energy is lost when converting from electricity to heat and back again. The efficiency of sand batteries is estimated at 25 to 50%, while the efficiency of lithium-ion batteries is around 80 to 90%. This means that sand batteries need more energy to charge and provide less energy when discharged than other types of batteries. According to information from Polar Night Energy, they are capable of achieving up to 95% efficiency in storing thermal energy.
- Large dimensions: Sand batteries are large, which means they require a lot of space for installation and operation. A sand battery consists of a container filled with sand or other siliceous material, which is insulated and connected to a power source and a heat utilization system. A sand battery is therefore similar in size to a container or small house, while other types of batteries are much smaller and more compact.
- Insulation requirements: Sand batteries require good insulation to prevent heat loss from the material to the surrounding environment. The insulation must be able to withstand high temperatures while also being lightweight and inexpensive.
The first sand battery was built in Finland in 2023 by Polar Night Energy in collaboration with a small power plant in the town of Kankaanpää. This battery is filled with about 100 tons of construction sand, which is heated to 500 °C and used to heat one of the city’s neighborhoods. This project is the first commercial test of this technology and demonstrates its potential applications and challenges.
Research into alternative materials for sand batteries, conducted by RWTH Aachen University in Germany. This research is investigating the possibility of using glass, ceramics, or quartz instead of sand, which could have higher thermal capacity, lower thermal conductivity, and better mechanical properties. This research could improve the performance and durability of sand batteries.
Real-life application of DIY sand batteries in the Czech Republic:
Sources:
https://www.comsol.com/story/heating-buildings-with-solar-energy-stored-in-sand-105101
