Like in an energy plant. That during the day when there Is surpluses they generate iron powder from ironoxide and cheap electricity. And when there is no surplus they burn the iron powder to irononoxid. And they can both be stored at unlimited scale on a heap.
So in other words, this is a really crappy version of something that already exists. I guess there are three takeaways to be had:
1) We still need large scale energy storage and it simply cannot just be a pile of batteries. It really needs to be a chemical system and it really has to be able to burn.
2) But that always takes you down one road: Hydrogen or something made from hydrogen. That's the only class of chemicals that really works and doesn't involve carbon. This causes a lot of conflict since it is definitely not many people's favored energy storage idea. And since so much FUD has been flung around for so long because of that, many people have become convinced that this inevitability is actually impossible.
3) So you usually end up with two alternative ideas: Something crazy like burning metals. I've heard of burning boron too BTW. This particular proposal is a continuation of that way of thinking. Probably they are all DOA ideas. And the other is something akin to linking all of the grids across world together with vast numbers of HVDC lines. But this too is crazy, especially once you realize the sheer cost and complexity of it all. Not to mention you are still wasting oodles of energy since you have minimal energy storage.
So eventually we end up in this cycle of one crazy idea being proposed after another, and nothing of importance actually being achieved.