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More flexible power grids thanks to iron-air batteries

More flexible power grids thanks to iron-air batteries

The story begins at the end of the 19th century. Back then, MIT engineers figured out how to reverse the corrosion process - a discovery that can be used to make batteries. Unlike the rare and expensive material lithium, iron is cheap because it occurs often. And so estimates for iron-air batteries are around 20 US dollars per kilowatt hour, while lithium-ion batteries cost about ten times that.

Maximum storage at a low price

This information comes from Form Energy, a Virginia spin-off from the Massachusetts Institute of Technology (MIT), which plans to enter mass production of iron-air batteries soon. To this end, Form Energy has acquired a 223,000-square-foot property located in Wierton, West Virginia. In addition to the significantly lower manufacturing costs, there is another advantage, according to the manufacturer: the long storage time of iron-air batteries - 100 hours is how the new types of batteries are supposed to store energy.

Mateo Jaramillo, CEO of Form Energy and until 2016 energy storage manager at Tesla Energy, says the company has been working on scaling production in 2021 and could soon enter mass production. Jaramillo is convinced that the process could represent a breakthrough towards the desired decarbonisation. Even in extreme weather or grid failures, renewable energy can be stored for a longer period of time and thus made available.

Once rust in iron and back

The way the batteries work is very simple: energy is stored by converting rust into elemental iron. When the battery is discharged, oxygen from the air reacts with the iron to form iron oxide: Rust. MIT calls this process "reverse rusting" and now wants to go into series production with the iron-air batteries.

Limited applicability

As advantageous as the new technology may seem, lithium-ion batteries have not yet been phased out. Not only because of the slow charging and discharging process are the batteries not suitable for electric cars; but also because of their size and high weight. For comparison: each battery module is the size of a washing machine. Inside them are about 50 cells with iron and air electrodes through which the electrochemical reaction takes place. There is also a non-flammable water-based electrolyte in each cell.

Great expanses

Several hundred of these battery cells, housed in robust enclosures, are combined into power blocks, several of which are in turn connected to the power grid. To get an idea of the necessary expansion, one must bear in mind that an area of half a hectare is needed for a system with a storage capacity of 1 megawatt. And depending on the demand, several such energy blocks in the megawatt range are connected to the power grid - the space required is correspondingly large.

Ideal for mains operation

Iron-air batteries will probably find their ideal application in grid operation. There, they could store electricity that is produced during strong winds or strong solar radiation and is not immediately taken up, until it finds its consumers. According to Autoevolution, a capacity of 7.5 megawatts per hectare can be assumed.

Sources:, Raimund Schesswendter, 25.01.2023;, Werner Pluta, 23.01.2023;, Wolfgang Kempkens, 20.01.2023;
Image Form Energy