French heat-battery start-up Epyr raises €15 million after paper mill debut

Epyr, a French start-up that stores electricity as heat in firebricks so factories can stop burning gas for steam, has raised a €15 million Series A round, the company's backers and French and European start-up media reported on Tuesday, October 13, 2026. The round is led by SlateVC. Existing investors AENU and Daphni put in more money, joined by WEPA Ventures, OVNI Capital and Aurum Impact. The raise comes after Epyr's first commercial unit, at paper maker WEPA's mill near Troyes in north-east France, began covering up to a quarter of that site's steam needs.

Heat is the hidden giant of industrial emissions. Factories making paper, food, chemicals and textiles need large amounts of steam, and most of it is still made by burning natural gas, coal or oil. Electrifying that heat is hard because factories run around the clock while cheap renewable electricity comes and goes. Thermal batteries like Epyr's try to bridge that gap: they soak up power when it is cheap and plentiful, store it as heat in a simple material, and give it back steadily.

The approach is attracting investors because it relies on cheap, well-understood materials such as firebricks rather than expensive battery chemistry, and because it lets a factory keep its existing steam network. The hard part is proving it works inside a real plant, at a cost that beats gas. Epyr's paper-mill unit gives it that first commercial reference, which is usually what start-ups in industrial technology need before larger customers will sign.

For readers following global climate-tech capital, the round shows where early-stage money in Europe is going: into hardware that cuts fuel bills and emissions for heavy users, backed by both specialist impact funds and a customer's own venture arm. WEPA Ventures, the investment arm of the paper group hosting the first unit, is among the backers, a sign that the customer is willing to bet on the technology as well as buy from it. Steam-hungry sectors in India, such as paper and textiles, face the same fuel-cost and emissions questions, which is why thermal storage is a field Indian manufacturers and founders watch.

Short-term: Epyr has the money to build more units for industrial customers and to grow its team beyond the first deployment.

Long-term: If the technology proves cheaper than gas boilers at scale, thermal storage could become a standard way for factories to use renewable power for process heat.

Who is affected: Paper, food, chemical and other steam-using manufacturers, European clean-energy investors, grid operators looking for flexible demand, and rival thermal-storage start-ups.

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