Wind and sun now supply more than half of Germany's electricity – topping 50 percent for the first time in the first half of 2026, according to a projection by the ZSW research centre and the industry association BDEW. But their output rises and falls with the weather. To bridge the calm, cloudy stretches, researchers at the Karlsruhe Institute of Technology (KIT) have examined a surprisingly down-to-earth idea: iron powder.
In a new study in the journal Chem Circularity, the team shows that existing coal-fired power stations could be converted into "iron-powder plants" – and become an important building block of a climate-neutral European energy system.
"Iron powder behaves very much like coal when it is burned," explains KIT researcher Julia Schuler. Burning it produces iron oxide – ordinary rust. Using hydrogen from renewable sources, that rust can be reduced back to iron carbon-neutrally and burned again. "It works in a cycle without carbon dioxide emissions or environmentally harmful substances," Schuler says. Converting a coal plant mainly means adapting its heat generator; the steam cycle, turbines and generator can stay in place.
A store that is easy to move
For their analysis, the researchers in the "Clean Circles" project extended the PERSEUS energy-system model and pitted the iron cycle against batteries, hydrogen storage and hydrogen power plants, looking ahead to an optimised European energy system in 2050. The result: iron cannot replace hydrogen-based power generation, but it can usefully complement it.
The big advantage lies in handling. Unlike volatile hydrogen, which demands elaborate infrastructure, iron powder is easy to store and to transport over long distances. Solar power from deserts or wind power from the coast could, for instance, be carried to industrial hubs with high demand.
According to the model, the technology is especially attractive for countries with little hydrogen-storage capacity and limited hydropower, where iron powder could close supply gaps. In Germany, the potential is high thanks to the many coal plants that could be converted with relative ease. Whether such plants are built at industrial scale still depends on the cost of conversion and on how efficiently iron oxide can be turned back into iron. The authors argue for developing the technology further.
"Iron could in future play a specific but economically sensible role in achieving climate neutrality and making renewable energy reliably available," Schuler says.