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The Coolest Thing in Climate Tech Just Got More Buyers

Rondo Energy is taking its hot rock batteries on the road.

A Rondo heat battery.
Heatmap Illustration/Rondo

Rondo Energy, a Silicon Valley startup building “heat batteries” to replace fossil fuels in heavy industries, announced three new customers on Wednesday. In just a few months' time, the company has gone from serving a single industry — ethanol — at its pilot plant in California, to making deals around the globe that demonstrate the technology’s potential versatility.

With grant funding from Breakthrough Energy Catalyst, as well as the European Investment Bank, the company will install three commercial-scale batteries at factories in Denmark, Germany, and Portugal. Each one will prove Rondo's compatibility with a different industry: In Denmark, the battery will be used to produce low-carbon biogas. In Germany, it will power a Covestro chemical plant that produces polymers. In Portugal, it will power a to-be-announced food and beverage factory.

Rondo warms up literal tons of bricks to more than 1,000 degrees Celsius (more than 1,800 degrees Fahrenheit) using electric heaters powered by renewable energy. The bricks can retain the heat for up to 18 hours, my colleague Katie Brigham reported earlier this year. When the heat is needed, air flows through the system and releases energy as either hot air or steam. At the site in Denmark, for instance, the battery will generate high pressure steam to drive a turbine generator, delivering steady heat and power to the plant. Rondo sells the energy as a service, retaining ownership and control of the equipment.

The projects announced Wednesday follow a series of recent deals across a diverse list of industries: a cement plant in Thailand, a plastic recycling plant in Texas, and even whiskey — Diageo will use the tech to electrify its Bulleit Bourbon plant in Kentucky. The fast fashion giant H&M is exploring use of the tech, and the company has also announced partnerships with the renewable energy developer EDP as well as Saudi Aramco.

As Katie noted in her piece, there are a lot of technologies competing to solve the challenge of producing industrial-grade heat. Carbon capture and storage equipment can be added to existing fossil fuel boilers, or natural gas and coal can be replaced with clean hydrogen fuel. There are also industrial heat pumps that can produce lower-temperature heat. But all of these solutions have the same challenge — overcoming the “green premium” compared with the fossil fuel boilers and furnaces used today.

Just because Rondo has made inroads in some industries, doesn’t mean all its potential customers are ready or able to fork over that green premium today. That’s why, in addition to being an investor in Rondo, Breakthrough Energy Catalyst decided to provide grant funding to these three new deployments, said Mario Fernandez, the head of the Catalyst program. The hope is these projects will help bring down the cost and catalyze greater adoption.

Emily Pontecorvo profile image

Emily Pontecorvo

Emily is a founding staff writer at Heatmap. Previously she was a staff writer at the nonprofit climate journalism outlet Grist, where she covered all aspects of decarbonization, from clean energy to electrified buildings to carbon dioxide removal.


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