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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.

Emily Pontecorvo •
06/26/2024
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.

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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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Sparks

Don’t Look Now, But China Is Importing Less Coal

Add it to the evidence that China’s greenhouse gas emissions may be peaking, if they haven’t already.

Matthew Zeitlin •
05/09/2025
A Chinese coal worker.
Heatmap Illustration/Getty Images

Exactly where China is in its energy transition remains somewhat fuzzy. Has the world’s largest emitter of greenhouse gases already hit peak emissions? Will it in 2025? That remains to be seen. But its import data for this year suggests an economy that’s in a rapid transition.

According to government trade data, in the first fourth months of this year, China imported $12.1 billion of coal, $100.4 billion of crude oil, and $18 billion of natural gas. In terms of value, that’s a 27% year over year decline in coal, a 8.5% decline in oil, and a 15.7% decline in natural gas. In terms of volume, it was a 5.3% decline, a slight 0.5% increase, and a 9.2% decline, respectively.

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Blue
Sparks

Rewiring America Slashes Staff Due to Trump Funding Freeze

The nonprofit laid off 36 employees, or 28% of its headcount.

Katie Brigham •
05/08/2025
Surprised outlets.
Heatmap Illustration/Getty Images

The Trump administration’s funding freeze has hit the leading electrification nonprofit Rewiring America, which announced Thursday that it will be cutting its workforce by 28%, or 36 employees. In a letter to the team, the organization’s cofounder and CEO Ari Matusiak placed the blame squarely on the Trump administration’s attempts to claw back billions in funding allocated through the Greenhouse Gas Reduction Fund.

“The volatility we face is not something we created: it is being directed at us,” Matusiak wrote in his public letter to employees. Along with a group of four other housing, climate, and community organizations, collectively known as Power Forward Communities, Rewiring America was the recipient of a $2 billion GGRF grant last April to help decarbonize American homes.

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Yellow
Sparks

Sunrun Tells Investors That a Recession Could Be Just Fine, Actually

The company managed to put a positive spin on tariffs.

Matthew Zeitlin •
05/08/2025
A house with solar panels.
Heatmap Illustration/Sunrun, Getty Images

The residential solar company Sunrun is, like much of the rest of the clean energy business, getting hit by tariffs. The company told investors in its first quarter earnings report Tuesday that about half its supply of solar modules comes from overseas, and thus is subject to import taxes. It’s trying to secure more modules domestically “as availability increases,” Sunrun said, but “costs are higher and availability limited near-term.”

“We do not directly import any solar equipment from China, although producers in China are important for various upstream components used by our suppliers,” Sunrun chief executive Mary Powell said on the call, indicating that having an entirely-China-free supply chain is likely impossible in the renewable energy industry.

Hardware makes up about a third of the company’s costs, according to Powell. “This cost will increase from tariffs,” she said, although some advance purchasing done before the end of last year will help mitigate that. All told, tariffs could lower the company’s cash generation by $100 million to $200 million, chief financial officer Danny Abajian said.

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