The giant brick toaster is the brainchild of San Francisco-based Rondo Energy.
Speaking of Microsoft, Bill Gates Breakthrough Energy Ventures was Rondos first major investor.
And this week, the climate tech fund opened its coffers once more.
Rondo has secured 75mn from Breakthrough Energy Catalyst, and the European Investment Bank.
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Armed with the fresh funds, it looks to take on the European market.
In Denmark, the hot rock battery will be used to produce cleaner biogas.
In Germany, it will power a Covestro chemical plant that produces polymers.
In Portugal, it will power a yet-to-be-announced food and beverage facility.
How does the hot rock battery work?
Rondos hot rock battery uses renewable energy to power a internet of electrical resistance heaters.
These heat a stack of specially-designed bricks to a cosy 1,500C.
Rondo developed the rocks alongside the Siam Cement Group in Thailand.
This means the machine can store excess energy and release it on demand.
AI automates the exact temperature of the battery.
District heating, for example, will require much lower temperatures than a steel-making plant.
The machine delivers energy either as superheated steam or hot air.
Industrial manufacturing usesover a thirdof the worlds energy.
A lot of this power comes in the form of heat produced by fossil fuel-powered industrial boilers.
Rondo believes that its hot rock batteries can replace these boilers in 90% of applications.
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Europe urgently needs to replace imported gas with domestic renewable energy, she said.
Repowering our industries is a matter of climate security, economic security, and national security.
Rondo isnt the only company competing to solve the challenge of clean heat for heavy industry.
Some are working on using hydrogen or biogas to replace natural gas in boilers.
Others are using mega-scale heat pumps.
But these technologies all face the same problem: theyre more expensive than the status quo.
While Rondos idea is rather simple, that could be its greatest strength.
The battery doesnt require any technological breakthroughs or rare and expensive materials.
The system is modular, and factory operators can easily plug it into their existing energy system.
According to the startup, it also saves factories money.
But its most ambitious plan of all is to build theworlds biggest battery plantin Thailand for Siam Cement.
The factory would have a capacity of 90 GWh 2.5 times the size of Teslas largest gigafactory.
Antora Energy, a startup from California, is perhaps Rondos closest competitor.
Founded in 2017, the company has secured $200mn in funding.
Story bySion Geschwindt
Sion is a freelance science and technology reporter, specialising in climate and energy.
