[tim333]

I don't think anyone's cracked that yet. There was a YC startup trying to do stuff with iron oxide. (https://www.canarymedia.com/articles/batteries/gigantic-form...)

And proposals using aluminium but again not in action.

Also zinc air https://inc42.com/startups/sthyr-energy-aims-to-tame-169-bn-...

the trouble is it's easy enough to propose such things but hard to be economically competitive with existing solutions. My guess is sodium ion will get cheap because the ingredients are cheap and there's a lot of money going into mass production which will bring the cost of that down over time.

There's an ancient non electrical seasonal solar storage practiced in Austria and such places where they grow tree and then chop them into logs for the winter but it's a bit labour intensive.

[hgomersall]

I've been thinking about Polysulphide-Air for this. There are certainly engineering questions, but on the face of it it looks like it might be tractable. I think the trick is to view it like a winter base-supply, and treat it like a power station that runs when solar is less.