Updated 5 October 2023 to make several corrections as stated at the bottom of the post.
By the end of June, a large 1-megawatt plant that burns iron fuel will fire up, producing the heat needed to brew beer at the Swinkels brewery near Eindhoven, Netherlands, in a test lasting for several months. Startup IRON+ is a joint venture between three companies and built on technology first demonstrated as a 100-kilowatt system in 2020 by the Metal Power Consortium, which includes the Eindhoven University of Technology and innovation center Metalot, which was spun out of the university.
The high melting points of metals make them useful components for machinery, electronics, and furnaces. But even metals can burn if you grind them into fine powders. What’s more, metals can burn without emitting toxic or planet-warming emissions, making them a potentially attractive fuel for producing clean power—one that can be easily stored and transported.
RIFT (Renewable Iron Fuel Technology), another spinoff out of Eindhoven, recently demonstrated that it could heat 500 homes using its iron fuel technology. In Canada, meanwhile, startup Altiro Energy, launched by McGill University researchers, has run a prototype 10-kW iron fuel plant that they now plan to scale up.
Demonstration plants like this one are showing the possibility of iron as a fuel. European Space Agency
Iron powder is an ideal alternative to carbon fuels, says Jeff Bergthorson, a mechanical engineering professor at McGill and the chief scientific advisor for Altiro. Bergthorson and colleagues at the European Space Agency and the Canadian Space Agency developed the metal fuel concept and published their report in the journal Applied Energy in 2015.
Iron is one of the most abundant metals on Earth, and the most produced. It has an energy density of about 11.3 kilowatt-hours per liter—better than gasoline. Burning iron powder produces heat that can be used directly or converted into electricity by a steam turbine, leaving behind iron oxide, or rust. This can later be reduced—that is, the oxygen can be stripped away—back into iron powder. “You can think of iron fuel as a clean, recyclable coal,” says Bergthorson.
Iron oxide can also be reduced to iron using hydrogen. Hydrogen is already a carbon-free green fuel if produced by splitting water using renewable electricity. But it is also an ultralight, voluminous gas, so it must be converted using high pressures and extreme cold into liquid, which then has to be stored and transported in special containers. Iron, by contrast, is already moved in dry containers for a lower cost.
So while both hydrogen and metals are essentially a way to store energy, using metals makes more sense, Bergthorson says. Technical assessments by Metalot and the Technical University of Darmstadt suggest that “it’s more efficient to produce iron from hydrogen gas than to produce liquid hydrogen. So iron powder as fuel is more expensive than gaseous hydrogen but cheaper to produce and move across the oceans than liquid hydrogen.”
That’s not to say iron fuel doesn’t come with its own challenges. It does not ignite as easily as hydrocarbon fuels, and the flame speed is slower, which makes it unstable and more prone to extinguishing. Altiro gets around this problem by adding a little natural gas to ignite the iron powder when the boiler first starts up. They have also come up with a technology to stabilize the flame so that it burns for long periods of time without extinguishing, Bergthorson says.
Collecting the resulting iron oxide is also tricky. Altiro’s technology ensures the formation of iron oxide particles that are large enough to easily capture “using cyclones and other methods without needing high-tech or costly equipment,” Bergthorson says.
Some of the iron powder inevitably evaporates to form iron-oxide nanoparticles that cannot be collected and turned back to iron. Both Altira and IRON+ have worked out ways to minimize this nanoparticle formation to reduce metal loss. “We improved the boiler by increasing the efficiency of heat transfer,” says Philip de Goey, a mechanical engineering professor at Eindhoven and cofounder of Metalot. “The evaporation of iron powder leading to nanoparticle emissions has been decreased by a factor of 10, so it is smaller than 0.3 percent. The nanoparticles are not emitted in the atmosphere but captured in a HEPA filter.”
RIFT generates heat through the combustion of iron powder.Krols Media
The next step for iron fuel is further increasing the conversion efficiency of iron to iron oxide since some of the iron does not get completely converted, de Goey says. Then there are market hurdles to jump, such as increasing iron powder production and lowering the cost of producing green hydrogen.
If these problems can be overcome, you could use renewable electricity to produce iron, store it as long as necessary, transport it there and then burn it for power when needed, says Bergthorson. “Places that have excess energy could make iron, and others can buy it. This way, you could commodify renewable energy so it can be globally distributed without the need for transmission lines. Metals can solve a big problem in the renewable energy transition: long-duration energy storage.”
This article appears in the October 2023 print issue.
Editor’s note on corrections to this article: In the second sentence, “The plant, IRON+” was changed to “Startup IRON+” and “startup Metalot” was changed to “innovation center Metalot.” The first sentence of the third paragraph was corrected to state that Metalot could heat 500 homes using its iron fuel technology, not five as originally stated. Finally, in the third-to-last paragraph we incorrectly stated that Philip de Goey, was a cofounder of RIFT; he is not. IEEE Spectrum regrets these errors.
