Iron is best known as the metal used to make buildings, bridges and cars.
But in the future, it could also become an important way to store renewable energy for weeks or even months.
Scientists believe that a simple cycle involving iron and rust could help make clean energy more reliable while reducing dependence on fossil fuels.
Researchers at the Karlsruhe Institute of Technology (KIT) in Germany have carried out the first major study to examine how iron could be used to generate electricity on a large scale.
Their findings, published in Chem Circularity, suggest that iron is unlikely to replace hydrogen, but it could become a valuable partner in a future climate-friendly energy system.
Renewable energy from wind and solar power is growing rapidly around the world.
However, one of its biggest challenges is storage. Wind does not always blow, and the sun does not always shine. Large amounts of energy need to be stored so they can be used later when demand is high or renewable energy production is low.
The researchers say iron powder could offer a solution.
The idea is surprisingly simple. Iron powder is burned to produce heat that can generate electricity. During this process, the iron combines with oxygen and becomes iron oxide, better known as rust. Unlike burning coal, this reaction does not release carbon dioxide or other harmful pollutants.
The rust is then turned back into iron by removing the oxygen. This step uses hydrogen made from renewable electricity. Once the iron is restored, it can be used again, creating a repeating cycle that stores and releases energy without producing carbon emissions.
According to the researchers, burning iron powder behaves much like burning coal. This means many existing coal-fired power plants might be converted to use iron instead of coal. While the heat-producing equipment would need to be changed, much of the expensive infrastructure, including turbines, generators, steam systems and power grid connections, could remain in place.
Using computer models, the research team explored how this technology could fit into Europe’s energy system through 2050. They compared the iron cycle with batteries, hydrogen storage and hydrogen-powered electricity generation.
The results showed that hydrogen will continue to play the leading role in storing renewable energy. However, iron has important advantages. Iron powder is much easier and cheaper to store and transport than hydrogen, which often requires special pipelines, import terminals and underground storage facilities.
Iron could also make it easier to move renewable energy around the world. For example, countries with abundant wind or solar power could use extra electricity to convert rust back into iron. The iron powder could then be shipped to other countries and used later to produce electricity when needed.
The study found that iron-based power plants could be especially useful in countries with limited hydropower resources or few places to store hydrogen underground. Germany, with its large number of coal power plants, could particularly benefit because much of the existing infrastructure could be reused.
The researchers believe the technology still needs further development, especially to make converting rust back into iron more efficient.
Even so, their study suggests that iron could become an important part of a reliable, affordable and carbon-neutral energy system, helping the world make better use of renewable energy for many years to come.
