Hydrogen stored in iron: A cheap, scalable grid battery

Good news! However, I think, it sounds a bit too good to be true (400 degrees °C, water storage in a tank)

"While hydrogen's high energy per mass makes it an excellent fuel, it's awfully hard and expensive to store long-term. ...

Surplus solar power is used to split water to produce hydrogen in the summer; it's then streamed into stainless steel reactors filled with iron ore at 752 °F (400 °C). The hydrogen extracts oxygen from the iron oxide, so you're left with iron and water in the reactor, ready to store without expending a lot of energy. ..."

"In brief

• Storing hydrogen is expensive and inefficient. In a pilot plant  ... researchers are showing how this could soon change.
• The researchers react the hydrogen with iron oxide in three reactors. The resulting iron is easy to store and convert back into hydrogen and iron oxide.
• The pilot plant is to be expanded such that by 2026, one-fifth of the ... campus’s winter electricity requirements can be met with solar power.

... To store hydrogen better ... team are relying on the steam-iron process, which has been understood since the 19th century. If there is a surplus of solar power available in the summer months, it can be used to split water to produce hydrogen. This hydrogen is then fed into a stainless steel reactor filled with natural iron ore at 400 degrees Celsius. There, the hydrogen extracts the oxygen from the iron ore – which in chemical terms is simply iron oxide – resulting in elemental iron and water. ..."

From the abstract:

"Our society is gradually moving from traditional energy sources to renewables. Due to the temporal mismatch between the production and demand of renewables, seasonal energy storage is proposed as a way to bridge the gap and ensure reliable power supply throughout the year. In this article, we demonstrate a seasonal energy storage process based on the redox pair iron/iron oxide, where energy is stored in the form of fine iron powder produced on-site by reducing iron oxide with electrolytic hydrogen, and released by oxidizing iron with steam. We prove its feasibility at a technically relevant scale, in a 1 : 10 scaled-down pilot reactor representing the electricity need of a typical European household. The operating data of the reactor, together with physico-chemical analysis of the iron/iron oxide during this process, and calculated estimation of its investment cost, provide a solid foundation for its future application in the field of energy storage."

Hydrogen stored in iron: A cheap, scalable grid battery for the winter

Iron as an inexpensive storage medium for hydrogen (original news release) "Researchers at ETH Zurich are using iron to store hydrogen safely and for long periods. In the future, this technology could be used for seasonal energy storage."

Safe seasonal energy and hydrogen storage in a 1 : 10 single-household-sized pilot reactor based on the steam-iron process (open access)

The charging and discharging process for the storage technology