How can renewable energy surpluses from summer be stored in the long term and used in winter? While hydrogen is seen as a beacon of hope, iron could fill a crucial gap – as the new E+E Insight Paper from the Energy and Environment research field at TU Darmstadt shows.

The concept is as simple as it is innovative: iron powder is burned, releasing energy in the form of heat – without CO₂ emissions. This produces iron oxide, which can be converted back into iron using green hydrogen or electrolysis. This cycle can be repeated as often as required and enables long-term energy storage which, unlike batteries, does not self-discharge.

Iron powder could complement hydrogen technology in a targeted manner, especially in areas where the infrastructure for hydrogen has not yet been developed. The paper makes it clear that iron is not a substitute for but rather a useful extension of hydrogen technology. While hydrogen is suitable for the chemical industry and long-distance mobility, iron offers advantages for decentralized applications and regions without a hydrogen infrastructure. Iron powder can be stored at room temperature and transported using existing logistics systems – a cost-effective solution for the “last mile”.

The E+E Insight Paper outlines a scenario in which surplus solar power from southern Europe or wind energy from northern Europe is used to convert iron oxide into iron. This iron powder could then be transported to central Europe by ship, rail or truck and used to generate heat and electricity.

This concept opens up new energy partnerships: regions with high potential for renewable energies could export iron fuel and thus create economic value, while Europe reduces its dependence on fossil fuels.

The concept is already being tested in pilot projects at TU Darmstadt. A first demonstration plant of the E+E profile topic Carbon-Neutral Circles is intended to show that iron works as a seasonal energy storage system and can also be used on an industrial scale. The aim is to convert existing coal-fired power plants into iron-fired power plants without expensive infrastructure modifications.

The scientists in the research field E+E are pursuing a vision with this technology: an energy market in which green powerfuels such as hydrogen and iron jointly replace fossil fuels, showing that the vision of a climate-neutral energy future can be thought through, networked and consistently implemented.