Sand Batteries Heat Up Buildings in Finland Using Solar Energy

Polar Night Energy, an innovator of seasonal heat storage, brings sand batteries to warm buildings using solar energy, a cheap option for thermal storage.

Sand Battery For Cheap Power Storage

Chemical engineer Donald Sadoway said to make a dirt-cheap battery, one has to make one from dirt, and Polar Night Energy's system did that. The company believes that energy storage is as important as energy distribution.

Energy generated through renewable means like wind and solar is challenging to store. Even with new battery technology storing electric power remains expensive, especially for heating buildings.

The engineers thought of using a battery that could store heat instead of electricity, which could be expensive, and sand was the solution!

The storage and distribution of heat are already accomplished in many conventional heating systems thanks to the retention and circulation of warm water. Polar Night Energy founders Tommi Eronen and Markku Ylönen were aware of the advantages and disadvantages of using water as a medium for heat storage, Spectrum reported.

Eronen says there is a limit to the amount of heat that can be added to water before it becomes steam. Although steam can distribute heat effectively, using it as a large-scale storage medium is not cost-effective.

Instead of storing heat in water, which has several drawbacks, they used sand. They ended up using 42 tons of it! (Figure 3) When the Sun goes down, the heat stored in the sand is released gradually into the airflow to keep the temperature warm enough. Sand makes it possible for solar power to keep people warm, even during Finland's darkest and coldest nights. This is because sand is highly reflective. According to Eronen, the amount of energy stored in the sand is four times that of water. A sand battery is a practical, safe, portable and cheap alternative.

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What is a Sand Battery?

According to the company, a sand battery is a high-temperature thermal energy storage. It uses sand or sand-like materials as its storage medium.

It stores energy in the sand as heat, which can heat homes or provide hot steams and high-temperature process heat to industries that depend on fossil fuels.

Sand battery upgrades renewable energy by ensuring a way to benefit from clean energy.

What's Inside The Polar Night Energy System

Eronen said people think of electricity when asked about cleaner energy. However, he believed they also needed to cut the emissions from heating.

In Finland, 82 percent of energy-related emissions were from domestic heating buildings. So, they thought of a way to warm up buildings using only solar power. Their system started as a lighthearted student project that led to a 3 MWh/100 kW pilot plant in the Finnish city of Tampere, which began operation during the winter of 2020-2021.

The system uses electricity to heat the air, which is then routed through an exchanger, which heats the water, and then the water is distributed to a number of buildings in the Hiedanranta district.

Resistive heating elements powered by electricity warm the air inside the system to a temperature greater than 600 degrees Celsius. Inside a sand-filled heat storage vessel is hot air circulated through a network of pipes. The heated air is then expelled from the vessel and directed into a heat exchanger, where it is used to heat water that is subsequently distributed throughout the building's various heating systems. Because of the sand's ability to store heat, the circulating air will still be sufficiently warm to keep the water (and the buildings) at a comfortable temperature even when the resistive elements have cooled down.

The system only uses pipes, valves, a fan, and electric heating, according to Eronen.