Presume that a wide range of metals can be used in the same way. We all know magnesium burns nicely and the navy can tell you about burning aluminium. As they can be re-used the value of the metal is not critical. So the nub point will be which metal can be recycled and burned with the highest efficiency ?

Yes interesting idea but science without number is not science. Without the TU Eindhoven team can quantify the efficiency (energy produced/energie (renewable) input )it cannot be compared with other "high density storage" methods such as hydrogen. Hydrogen fuel cell is under 70% and modern batteries are over 85% when assuming renewable generation. Numbers please someone?

"It might seem a little odd"... bl**dy stupid would be my thoughts; like using renewable energy (or any energy, for that matter) to harness hydrogen in the same way. Just put it in a battery, FCOL! No need to re-invent the wheel (and waste $$$/€€€ in the process) and 90% efficiency. Utterly bonkers! And no mention of the energy (probably electrical... and I'm guessing *a lot*) used to grind the iron to a power in the first place. It won't do it itself! Whilst I'm in rant-mode, I can't help thinking a bucketful of iron powder at a time won't get them very far, either...!

But wait ...... the iron oxide requires more energy to reduce it back to iron metal than it's oxidation yielded in it's burning. (That's elementary thermodynamics). And using electricity to do it by electricity makes no sense. You would be better off just using the electricity to heat your process in the first place. Am I missing something?

What an interesting idea! And far more usable than batteries, which have dirty manufacturing processes and fall apart eventually.

What temperature does the iron burn at? Does that have implications for the efficiency of the steam production? Also, it does seem that a lot of what people are talking about for green energy innovation is not so much the generation but the issues of moving energy from place to place.

What’s required for the ignition? Will a lit match ignite the iron powder? Will the iron powder sustain ignition, or do you need a constant heat source to maintain combustion? Lots of questions. I don’t think we’re getting the whole story here.

Exactly correct, GRG!! It seems like we have a never ending parade of idiots coming up with totally stupid ideas on how to "save the environment" by one bogus scheme or another! When I see words like "theoretical" or "might", "maybe", "perhaps" or some other vagueness being used to sell me on some point, I instantly smell the stink of it. How much energy is involved if getting the Iron in the first place? It doesn't grow on trees, and even if it did, it would still have to be processed into a usable form. Is just plain air being used to oxidize it into rust? Our air is only about 21% Oxygen, the rest is Nitrogen and a handful of other gasses, so to get the thermal efficiency up we need to use pure Oxygen, and how do we get that, outside of using a very expensive process?
There are NO perfectly closed loop systems, that I know of. If someone can point one out to me, I'd love to know what it is! And if this system was perfectly closed, then there would be no need for it, because you wouldn't be getting anything out of it! They should just use the electricity coming from their solar panels or such directly, and forget about all of the rest. Just think of all the money they would save by being smart, instead of stupid!!

Someone who knows chemistry better than I - Would it be feasible to add aluminum to the iron oxide to make thermite for a second exothermic reaction (thus turning the iron oxide back to elemental iron for the next burn) and selling off the aluminum oxide product to the many industries that need/use it? This would be instead of burning solar/wind energy on reversing the oxidization of the iron. If that is stupid, please tell me why - I want to learn.

Sounds interesting, however, iron is already a pretty high demand material, just how much would it take to meet demands? Would we have to start strip mining the crap out of places and removing whole mountains? And when they say it's recyclable, what percentage comes out after burning? i.e. is there 10% left over, 40%?? And what about initial processing to get it into a burnable state? That sounds rather energy intensive. Are there any issues with impurities? i.e. Either having to remove them before hand and or if some gets burned? Somehow this feels like an idea the coal and mining industries would come up with. When factoring *everything* in, end to end, what is they total cost and environmental impact with large scale implementation?