KIT Study Highlights Potential of Iron Powder for Long-Term Energy Storage

Iron could serve as a chemical energy storage medium in the future, making large quantities of renewable energy available long-term. In this process, iron powder is burned in a carbon-neutral cycle and then converted back to its original state using energy. Researchers at the Karlsruhe Institute of Technology (KIT), Germany, have, for the first time, comprehensively investigated the potential of this technology in power generation. Their findings show that iron does not replace hydrogen but can usefully complement it in a climate-neutral energy system. 

Whether wind energy from coastal regions or solar power from desert areas, iron could act as a transportable energy carrier to make these renewable energies usable worldwide. "This works in a cycle without carbon dioxide emissions or environmentally harmful substances," says Julia Schuler from KIT’s Institute for Industrial Production (IIP). To generate energy, iron powder is burned, leaving behind iron oxide – rust. This is then reduced back into iron using renewable hydrogen, removing the oxygen in the process. The iron powder can be reused. "Iron powder behaves very similarly to coal in combustion. This raises the question in research of whether existing coal-fired power plants can be retrofitted for iron combustion," Schuler explains. Adaptations would primarily be necessary in the heat generator, while other power plant components such as the steam cycle, turbines, generator, and grid connection could continue to be used in this concept.

Iron cycle complements the hydrogen economy

Building on findings from the "Clean Circles" research project on the iron cycle, KIT researchers – funded by the Baden-Württemberg Foundation for Energy Research – examined how the iron cycle could be used for power generation in a climate-neutral European energy system. To do this, they expanded an established energy system model (PERSEUS) to include options for retrofitting coal-fired power plants, reduction plants, and storage and transport routes. Using the enhanced model, they then optimized the development of the European energy system up to 2050. In this process the iron cycle competed with other technologies such as batteries, hydrogen storage and hydrogen power plants.

The results show that iron does not replace hydrogen-based power generation but can meaningfully complement it in a climate-neutral energy system. Iron offers particular advantages as a long-term storage medium. The powder is relatively easy to store and transport, whereas hydrogen requires an extensive network of pipelines, import terminals, and underground storage facilities. Iron powder could also enable the global transport of renewable energy with lower infrastructural effort. At the same time, local reduction plants could convert excess electricity in Europe into iron powder via hydrogen production, creating a storable energy carrier.

In simulations, iron-fueled power plants proved particularly attractive in countries with limited hydropower or underground hydrogen storage capabilities. In such regions, iron could help bridge supply gaps during prolonged periods of low power generation from wind and solar plants. It could also relieve pressure on hydrogen infrastructure, for example, when import capacities or transport lines reach their limits. Given its many coal-fired power plants, Germany also has particularly high potential. Turbines, grid connections, heating networks and other infrastructure components could remain in use.

Reducing costs with the iron cycle

The researchers viewed it as an encouraging sign for the further development of the technology that iron-fueled power plants were part of a cost-minimal energy system across all scenarios considered. "In the future, iron could play a specific but economically viable role in achieving climate neutrality and ensuring the reliable availability of renewable energies," says Schuler. Whether a new "Iron Age" will indeed dawn depends largely on how complex the retrofitting of existing power plants is and how efficiently iron oxide can be reduced back into iron in the future.

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