The idea of storing heat in the sand to heat houses during the winter may seem too simple to operate.
Key points:
- 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
- Experts say thermal storage could displace gas in industry and eliminate up to 16 per cent of Australia’s emissions
Leave a load of cheap builder sand in an insulated silo, heat the sand with renewable electricity, and then harness the thermal energy stored for months and months.
In an age of green hydrogen, lithium-ion batteries and other high-tech energy solutions, it can’t work, right?
Finland intends to defer. This month, the Nordic nation launched the world’s first commercial “sand battery”.
About 230 kilometers northwest of Helsinki, in the city of Kankaanpää, homes, offices and the public swimming pool are heated with thermal energy stored in a 7-meter steel container filled with 100 tons of sand.
So how do they work, what else can they be used for and do we have to build them in Australia?
“It’s really a typical silo”
The Kankaanpää sand battery is connected directly to the grid and works when electricity is cheaper.
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 about 500-600 degrees Celsius for months, so solar energy generated in the summer can be used to heat homes in the winter.
It can store up to 8 megawatts-hours of power, which is the capacity of a large-scale lithium battery.
The project was the work of Finnish startup Polar Night Energy and a local Finnish company Vatajankoski.
Markku Ylönen and Tommi Eronen started working on the idea of drums when they were in college. (Supplied by: Polar Night Energy)
Polar Night Energy CEO Markku Ylönen said the entire battery could be built in “any steel workshop”.
“It’s really a typical silo with nothing so special,” he said.
To discharge the stored thermal energy, the air is circulated through pipes in the sand where it is heated, and then directed to where it is needed.
Right now, it’s mostly home heating, but it could also be used for high-temperature industrial processes, Ylönen said.
“Or it can be directed to a steam drum to generate industrial steam at 200ºC, which is quite common in industrial processes.”
In this process very little energy is lost, as long as the heat is not being transported very far, he said.
In theory, stored heat could be used to power a steam turbine to generate electricity, but this is much less efficient.
“Efficiency will be a bit like 20-25 percent,” 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 does not have the same domestic heating requirements as Finland, but there is a lot of potential to use stored thermal for industrial processes, said Andrew Blakers, director of the ANU Center for Sustainable Energy Systems.
“There’s a huge storage market for these things and it’s replacing gas in factories,” Professor Blakers said.
“[Stored thermal] it can be used for everything from food processing, to parts of the aluminum industry, to parts for the manufacture of cement, iron and steel, ceramics and plastics. “
About 16 per cent of Australia’s emissions are due to gas combustion in industry for processes that need high temperatures (anything above 100ºC).
Heat pumps (the same technology used by reverse cycle air conditioners), which can run on renewable energy, reach a maximum of about 100 ° C, which means they cannot replace gas for these industrial uses.
But thermal storage can offer temperatures of over 1,000ºC, depending on the storage medium.
A conceptual design for a storage of molten silicon thermal energy in South Australia, which could store heat at over 1,000 ° C. (Supplied: 1414 degrees)
“You choose the storage medium to adapt to the temperature of the process,” Professor Blakers said.
Sand is just one option. Others include crushed rock and molten salt.
“Cheaper storage than gas”
The idea of storing thermal energy, including the concept of sand battery, has been around for years.
So why are we just building these heat batteries now?
First, for many years it is cheaper to burn gas to generate high temperatures.
Second, due to heat loss, thermal energy cannot be transported as easily as pressurized gas, which can make it difficult to use.
But recently the economy has changed.
The Russian invasion of Ukraine has disrupted gas supplies to Europe and other markets.
During the first quarter of 2022, spot prices for European gas were five times higher than in the first quarter of 2021.
These high prices caused Australian gas producers to export their gas, rather than sell it nationally, raising prices in Australia.
Thermal storage has become cheaper than burning gas for high-temperature industrial processes, Professor Blakers said.
“In the last three years, the price of solar and wind energy has dropped so far and [in the past few months]the price of gas has gone up through the ceiling.
“Suddenly conditions have turned upside down completely and now I imagine most factories are looking at thermal storage.”
But factories that want to switch to thermal storage will not be able to simply channel heat, as they do with gas.
Instead, they will have to build their own thermal storage silos and heat them with cheap daytime solar electricity, from their own roof or grid systems.
“A few thousand cubic meters of storage would be enough to keep a factory running,” Professor Blakers said.
Or factories could expect gas prices to go down.
“I think they would be crazy if they waited,” Professor Blakers said.
“No one can predict where the price of gas will go, but all you know is that solar electricity during the day will be kept at a low price.”
What’s next?
Australian start-up 1414 Degrees has developed and patented a thermal storage system similar to the Finnish battery, but using molten silicon to store heat instead of sand.
He has recently partnered with another company, Vast Solar, to plan a solar thermal project in South Australia.
The proposed Vast Solar thermal solar project in South Australia. (Supplied by: Vast Solar)
Swedish public company Vattenfall is also building a 200 MW thermal energy storage facility in Berlin.
The heat storage tank can hold 56 million liters of water, which will be heated to 98ºC to heat homes.
The tank will take two months to fill and the system will start operating commercially in April 2023. (Supplied: Vattenfall)
Polar Night Energy has been very interested in building more sand batteries, with the Ukrainian war focusing on alternative energy sources and storage methods, Markku Ylönen said.
Moscow recently suspended the supply of gas and electricity to Finland due to its application for NATO membership.
The next battery will be 100 times larger, or about 20 meters in diameter and 10 meters high, with 1 GWh of power, Ylönen said.
“With economies of scale, if we go 100 times bigger, the price won’t be 100 times bigger. It will be 20-30 times bigger.
“It will be in Finland, but we are already negotiating several places internationally.”
Once the first of these larger designs was built and tested, others could be built quickly, he said.
“I would [eventually] I like to say we will build 10 next year. ”
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