Storing energy when the sun shines or the wind blows, to reuse it later, remains a puzzle. What if the solution came from... salt? This is the bet of Hyme Energy, a Danish start-up, which has partnered with Sulzer, a Swiss fluid pumping specialist. Together, they are developing a thermal storage system based on molten hydroxide salt, a cheap residue from the chlorine industry.
A thermal battery that retains heat for two weeks
Concretely, the system stores electricity from renewable sources and transforms it into heat, which raises the temperature of the salt to 600°C. This heat can be stored for up to two weeks in large reservoirs. When energy is needed, the heated salt is used to produce steam, which is used to power electric turbines or directly to heat industrial facilities.
Hyme announces up to 90% efficiency for thermal uses, between 80 and 90% for cogeneration, and around 40% for electricity production alone. All this with a capacity planned capacity of 1 GWh, enough to power 100,000 homes for 10 hours. Not bad for a product that is recovered cheaply from the chemical industry.
The project is no longer at the PowerPoint stage. In April 2024, Hyme and Sulzer commissioned a pilot site called MOSS, in Esbjerg, Denmark. This demonstrator validated the feasibility of storage in molten salt at very high temperatures. As a result, the two partners are moving on to the next stage, with a 200 MWh project in Holstebro, also in Denmark.
This new facility will be used by Arla Foods, a Danish-Swedish dairy group, which could save around €3 million per year on its industrial heating costs.
Sulzer, for its part, is leveraging its experience in developing molten salt pumps, already tested in solar power plants in China. "We are now working on optimizing the system and setting up a real supply chain," explains Benoît Martin, an engineer at Sulzer. For Ask Emil Löslash;vschall-Jensen, CEO and co-founder of Hyme, the partnership is obvious: "Working with established companies like Sulzer helps us move faster and get the technology out of the lab."
A simple, rather rustic system, but potentially very useful for stabilizing the electricity grid. And above all, a solution that does not require rare materials or complex batteries. Salt, heat, and a little ingenuity.
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