Rondo Energy and Covestro broke ground on a new kind of industrial heat battery at Covestro’s Brunsbüttel chemical site in northern Germany, and it’s designed to do something industry desperately needs: make clean, reliable steam without burning fossil fuels.

Thanks to a surplus of renewable energy, Germany logged 573 hours of negative electricity prices in 2025, a 25% increase from 2024. Rondo’s Heat Battery charges up when there’s a surplus of cheap renewable electricity on the grid, stores that energy as heat in specially designed bricks (pictured), and then delivers steady, high‑temperature steam around the clock for industrial processes. It’s aimed squarely at replacing fossil‑fuel‑fired boilers in facilities that run 24/7.

At 100 megawatt‑hours (MWh), the Brunsbüttel system is scheduled to come online by the end of 2026. It will be tied with the 100 MWh Rondo heat battery that went into operation in California in October as the largest industrial heat battery in the world. Covestro’s project is backed by Breakthrough Energy Catalyst and the European Investment Bank.

Once operational, the battery is expected to supply about 10% of the steam needed at the Brunsbüttel site and cut carbon dioxide emissions by up to 13,000 metric tons per year. Steam production is a major energy demand for Covestro, and at the site, it’s currently still largely powered by natural gas.

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State officials see the project as a sign of what’s possible in a renewables‑heavy grid. Schleswig‑Holstein’s energy and climate minister, Tobias Goldschmidt, said at the groundbreaking that the state’s rapid build‑out of renewable energy is enabling industrial projects like this one, helping strengthen energy independence while supporting climate‑neutral goals.

The underlying technology is deceptively simple. Rondo’s heat battery uses bricks – a proven heat‑storage medium that’s been used in steelmaking for centuries – paired with modern automation and controls. Electricity heats the bricks; the stored heat runs a conventional boiler; and the system produces emission‑free steam using electricity from renewable sources.

Rondo Energy CEO Eric Trusiewicz said, “Together with Covestro, we are demonstrating that clean industrial heat can be both highly reliable and a powerful tool for balancing the grid – while building the energy infrastructure needed to strengthen Europe’s industrial base and energy security.”

If the Brunsbüttel project performs as expected, Covestro says it will decide whether to roll out the technology on a larger scale across its operations.

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