The idea of storing heat in sand to warm homes through winter may, on the face of it, seem too simple to work.
- The world’s first commercial “sand battery” stores heat at 500 degrees Celsius for months at a time
- It can be used to heat homes and offices and provide high-temperature heat for industrial processes
- Thermal storage could displace gas in industry and remove up to 16 per cent of Australia’s emissions, experts say
Drop a load of cheap builder’s sand in an insulated silo, heat the sand with renewable electricity, and then tap the stored thermal energy for months on end.
In an age of green hydrogen, lithium-ion batteries and other high-tech energy solutions, it can’t work, right?
Finland begs to differ. This month saw the Nordic nation launch the world’s first commercial “sand battery”.
About 230 kilometres north-west of Helsinki, in the town of Kankaanpää, homes, offices and the public swimming pool are being heated by thermal energy stored in a 7-metre steel container filled with 100 tonnes of sand.
So how does it work, what else can it be used for, and should we build them in Australia?
‘It’s really a typical silo’
The Kankaanpää sand battery is connected directly to the grid and runs when electricity is cheapest.
Hot air blown through pipes heats the sand in the steel container by resistive heating (this is how electric heaters work).
The sand is able to store heat at around 500–600 degrees Celsius for months, so solar power generated in the summer can be used to heat homes in the winter.
It can store up to 8 megawatt-hours of energy, which is the capacity of a large, grid-scale lithium battery.
The project was the work of Finnish startup Polar Night Energy and a local Finnish utility Vatajankoski.
Polar Night Energy’s chief executive officer Markku Ylönen said the entire battery could be built in “any steel workshop”.
“It’s really a typical silo with nothing that special,” he said.
To discharge the stored thermal energy, air is circulated through pipes in the sand where it’s heated, then directed, to wherever it’s needed.
Right now, that’s mostly heating homes, but it could also be used for high-temperature industrial processes, Mr Ylönen said.
Very little energy is lost in this process, so long as the heat is not being transported very far, he said.
In theory, the stored heat could be used to drive a steam turbine to generate electricity, but this is far less efficient.
“The efficiency will be something like 20–25 per cent,” Mr Ylönen said.
“Technologically speaking, there are no obstacles, but the economic case is harder to find than with heat-only projects.”
What can it be used for?
Australia doesn’t have the same domestic heating requirements as Finland, but there’s plenty of potential for using stored thermal for industrial processes, said Andrew Blakers, director of the ANU Centre for Sustainable Energy Systems.
“There’s an enormous storage market for these things and that is to replace gas in factories,” Professor Blakers said.
About 16 per cent of Australia’s emissions are due to burning of gas in industry for processes needing high temperatures (anything above 100C).
Heat pumps (the same technology used by reverse cycle air-conditioners), which can be powered by renewables, max out at about 100C, meaning they can’t replace gas for these industrial uses.
But thermal storage can deliver temperatures of more than 1,000C, depending on the storage medium.