Thermal batteries created from crushed soapstone or bricks are among the latest innovations entering the energy market, promising a revolution in energy storage, reports EuractivEurope has experienced a boom in wind and solar power in recent years, with new renewable energy projects popping up all the time. But the rise of renewables has created a problem few anticipated – sometimes there is simply too much electricity on the grid.
In search of solutions, companies are turning to a new version of an old technology. In Turkey, they have long known that sand can store and transfer heat, and they utilized it to build coffee. And no bourgeois central European home was complete in Mozart’s time without an ornate brick and tile stove that kept the living room warm long after the fire had gone out.
Centuries earlier, the Romans utilized wood-fired central heating systems and underfloor heating to heat homes and public baths where there were no hot springs. Now, these simple ideas and materials are building a comeback – offering a way to support save the world from climate alter and save Europeans from high energy bills.
Sand batteries
In Finland Startup Polar Night Energy wants to turn cheap soapstone scraps into massive sand batteries, which can store large amounts of green energy in the form of heat. They also offer it at a fraction of the cost of lithium-ion batteries.
The idea is simple – when renewable electricity is abundant and cheap, air is heated by electrical resistance, then pumped through sand into an insulated container, reaching temperatures of up to 600°C.
But unlike lithium-ion batteries, which discharge in a few hours, sand can store energy for days, for example ensuring that zero-emission steam is produced 24/7 for industrial applications or to power the district heating systems widely utilized in Northern and Central Europe.
Polar Night Energy has already demonstrated that its technology can keep compact towns warm in freezing Finland. The company is now developing a pilot project to convert the stored heat back into electricity.
However, the expected efficiency ratio is not impressive – about 30% of the electricity input is recovered, which is well below the 80% offered by utility-scale lithium-ion batteries.
The problem – free electricity
What the Finnish company and others are testing to do is turn the problem of green energy systems into a business opportunity. Europe has invested heavily in solar and wind power in recent years, but critics – from savvy local councillors to gas and nuclear lobbyists – never tire of pointing out that these inexhaustible renewable energy sources only produce electricity when the sun is shining or the wind is blowing.
They are right – but what if the solution is not to keep power plants on standby, build extremely expensive nuclear reactors, or even deploy millions of euros worth of expensive, hard-to-find lithium batteries on the grid?
When the sky is dark and the air is still, prices can skyrocket as traditional fossil-fuel plants ramp up production to fill the gap. But when renewable energy is abundant, the market price of electricity regularly drops below zero.
Counterintuitively, this is a huge problem. Negative prices slow down the return on investment in new power plants and incentivize power producers to build up for their losses by raising energy bills when there is no oversupply.
If negative prices affected only 0,3% of all hours in 2022, the figure increased to 3,6% in 2024 and is expected to increase even more in 2025 as more renewable energy is utilized in the EU.
The system is dysfunctional, and the lack of international power lines exacerbates the problem. Solar fields and wind turbines often shut down simply becautilize there is nowhere for the electricity to go.
Furthermore, the mass connection of new renewable energy power plants is being slowed down by connection queues to congested power lines, meaning the EU could delay large amounts of cheap, zero-emission renewable energy becautilize it is unable to obtain it up and running.
As technologies and utilize cases evolve, thermal storage is likely to play an increasingly important role in solving these problems.
EU electricity lobby group Eurelectric stated batteries created from sand and bricks could support tackle the problem of negative prices and the restriction of green energy.
“They have the potential to complement grid-scale batteries or pumped-storage hydroelectric plants by providing long-term heat storage. They can ease pressure on the energy system by creating new sources of flexible demand,” stated Eurelectric policy director Killian O’Donoghue.
Under development
Polar Night Energy is not the only European startup that wants to utilize sand to power batteries.
Batsand is doing the same in Latvia, offering compacter systems to individual homeowners.
In warm, sunny Portugal, Rondo recently installed a 100 MWh brick battery combined with a solar system to provide 24/7 steam for decarbonization at a brewery owned by Heineken.
Thermal and electrical storage can also complement each other. The price of lithium-ion batteries has fallen dramatically, but supplies are far from secure, and sand batteries can support ensure they are deployed where they are truly necessaryed. As they enter the market, the business case for solar and wind power is growing stronger by the day.
