Batteries made of sand could help provide clean and affordable energy to heat homes and businesses as well as for electricity grid balancing, according to a startup in Finland.
Polar Night Energy has sold a first working, commercial 'sand battery' that its founders say can store clean power for several months at a time.
The company has patented is a high-temperature large-scale heat storage, rather than an electrical battery, which uses sand as its medium to store heat.
Electricity from solar, wind or other power sources is converted to heat the sand when there is excess demand, then it can be used later, similar to a night storage heater.
Sand has been chosen as it is abundant, cheap and can be heated up to above 1000° celsius, plus provides four times the energy storage capacity of water.
The first device, where 100 tons of sand is held inside a 4m wide by 7m high steel container, has been installed in the power plant run by Vatajankoski, the company that provides the district heating system for the town of Kankaanpää in Western Finland (a similar district heating system that is used in New York).
Similar devices are unlikely to be of interest to other battery storage companies such as Gresham House Energy Storage Fund PLC (LSE:GRID), Gore Street Energy Storage Fund PLC (LSE:GSF) and Harmony Energy Income Trust PLC (LSE:HEIT).
"The construction of the storage went well, especially considering that the solution is completely new," said Polar Night co-founder and chief technology officer Markku Ylönen in a statement.
"We managed to get everything in order despite some challenges and a short delay."
He said the first installation has shown that the system "has even more potential than we initially calculated".
As a material, Ylönen said as well as being inexpensive sand is durable and can store a lot of heat in a small volume at a temperature of about 500-600 degrees Celsius.
The heat storage has 100 kW of heating power and 8 MWh of energy capacity.
"Heat storages can significantly help to increase intermittent renewables in the electrical grid. At the same time we can prime the waste heat to usable level to heat a city," says Ylönen.
"This is a logical step towards combustion-free heat production."
Vatajankoski, which has invested in the first sand battery, uses the heat provided by the storage to prime the waste heat recovered from their data servers which are intended for high-performance computing.
Depending on the season, Polar Night said the temperature of the 60-degree waste heat from the servers must be raised to 75–100 degrees before it is fed into the district heating network.
The idea came from a lighthearted student project examining whether it would be possible to build an "energy-sufficient and cost effective hippie commune for engineers using only solar power".
This led to a 3 MWh/100 kW pilot plant in the Finnish city of Tampere, which uses electricity to heat air, which is then circulated through a network of pipes inside of a sand-filled heat storage vessel. This pilot began operation during the winter of 2020-2021.