‘Sand Battery’ – Heat energy store that can be harnessed for later use

Polar Night Energy – Developer of heat storages designed to store renewable energy. The company designs and builds high temperature and zero-emission heat storage and enables the up-scaling of solar or wind energy to meet heating and electricity demand, thereby enabling customers to use heat storage facilities for housing and industrial applications.

They convert electricity to heat, and store it for later use. It uses sand as the storage medium, which leads to safe operation and a natural balance in the storage cycle. Additionally, sand is a cheap and abundant material, which can be heated up to 1000 °C and even higher.

The maximum temperature in the Kankaanpää heat storage is about 600 degrees Celsius. However, the temperature may even be higher depending on customer needs. In practice, the maximum temperature of a sand-based heat storage is not limited by the properties of the storage medium, but by the heat resistance of the materials used in the construction and control of the storage.

Inside the sand it has build heat transfer system that enables effective energy transportation to and from the storage. Proper insulation between the storage and environment ensures long storing period, up to months, with minimal heat losses.

Many solid materials, such as sand, can be heated to temperatures well above the boiling point of water. Sand-based heat storages can store several times the amount of energy that can be stored in a water tank of a similar size; this is thanks to the large temperature range allowed by the sand. So, it saves space and it allows versatile use in many industrial applications.

The size of the storages varies from tens to thousands of cubic meters. It is possible to locate the storage underground, reserving minimal space from the often highly valued square meters in construction sites.

It has designed and deployed commercial sand-based heat storage for Vatajankoski, an energy utility based in Western Finland. It will provide heat for Vatajankoski’s district heating network in Kankaanpää, Finland. The storage has 100 kW heating power and 8 MWh capacity.

It also have a 3 MWh running test pilot in Hiedanranta, Tampere. It is connected to a local district heating grid and it provides heat for a couple of buildings. The pilot enables testing, validation and optimization of the heat storage solution. In the pilot, the energy is partly from a 100 square meter solar panel array and partly from the electric grid.