Covestro pioneers thermal storage with 100 MWh heat battery to cut industrial emissions

Covestro’s decision to install a 100 MWh “heat battery” from Rondo Energy at its Brunsbüttel chemical site crystallises a quietly powerful strategy for industrial decarbonisation: store low‑cost or surplus renewable electricity as high‑temperature heat in refractory bricks, then use that heat directly to generate steam on demand. According to Covestro, the unit is due to begin operations by the end of 2026 and will supply roughly 10% of the site’s steam demand, cutting up to 13,000 tonnes of CO2 a year. The project is supported by Breakthrough Energy Catalyst and the European Investment Bank.

The technology is deliberately simple. Excess wind and solar power heats thousands of tonnes of specialised refractory bricks to temperatures above 1,000°C via electrical heating elements. When steam is required, compressed air is run through the hot brick pack to transfer heat to water, producing high‑pressure steam for process use. Because the energy is delivered as heat rather than converted back into electricity, conversion losses are lower than in round‑trip electric storage: Rondo claims cycle efficiencies above 97% for the heat‑to‑steam cycle, a figure the industry has noted with interest because it sidesteps the rare‑earth and supply‑chain constraints associated with large chemical battery deployments.

The economic case is straightforward and timely for Germany’s energy mix. Industry data shows the country has seen a marked rise in hours with negative day‑ahead wholesale prices as renewable penetration has grown: research published for 2025 recorded approximately 573 hours of negative prices, driven by periods of high photovoltaic and wind output and low demand. That surplus – occasionally associated with prices below zero – creates opportunities for load‑shifting: buying power when it is cheapest, storing it as heat, and displacing gas‑fired boilers during peak or low‑renewables periods. Covestro’s rollout explicitly aims to exploit that volatility to achieve both emissions reductions and operating‑cost benefits.

For heavy industry, where continuous high‑temperature steam is a backbone requirement, the appeal of a modular, high‑temperature thermal store is pragmatic. Replacing a portion of fossil‑fuelled steam production without extensive process redesign reduces operational risk and preserves production continuity. In the case of Brunsbüttel, shifting about 10% of steam demand to stored renewable heat is positioned as a material first step: demonstrable emissions abatement at industrial scale while the wider electrification and hydrogen ecosystems continue to mature.

The deployment also speaks to broader system needs. Analysts and market reports have emphasised that rising shares of solar and wind increase instances of oversupply; Germany’s record quarterly solar output in 2025 and year‑on‑year increases in negative price hours underline the growing mismatch between generation patterns and industrial demand profiles. Thermal storage solutions plugged into that dynamic can play a balancing role on the demand side, complementing grid investments and other forms of storage.

Caveats remain. The 100 MWh unit at Brunsbüttel is significant but not a complete replacement for gas boilers; Covestro frames it as a partial decarbonisation lever rather than an immediate full‑system solution. Project economics depend on the persistence of price volatility, the relative cost of electricity versus gas, and the capital and operating costs of the heat battery system. Furthermore, independent verification of long‑term performance, including durability of refractory materials, degradation of thermal insulation, and actual day‑to‑day round‑trip efficiencies at industrial duty cycles, will be critical for other sites considering adoption.

Nevertheless, the Brunsbüttel project is illustrative of a pragmatic, technology‑neutral approach to industrial decarbonisation: where direct electrification or low‑carbon fuels are not yet fully viable at scale, high‑temperature thermal storage offers a route to reduce emissions, integrate renewables and lower fuel exposure. According to Covestro and Rondo, the system leverages well‑understood materials and established process‑heat practices in a new application, combining centuries‑old refractory technology with modern controls and grid integration to meet contemporary decarbonisation targets.

For companies managing large steam loads, the lesson is that a portfolio of options, electrification, thermal storage, hydrogen readiness and continued efficiency improvements, will be required. The Brunsbüttel installation, backed by institutional financiers and energy transition funds, will be watched closely as an early large‑scale demonstration of whether “hot bricks” can move from niche innovation to mainstream tool in the industrial decarbonisation toolbox.