Sure you could use renewables to make iron. But that thought process also extends to other methods too. You could use renewables to make other non renewable fuels.
Why not just skip the middleman? Use renewables?
Why not just skip the middleman? Use renewables?
At grid-level, battery tech is challenging, requiring technologies like pumped storage that require particular environments (e.g. damming a river) and can't really be transported.
If this works out you could use excess solar during the day to deoxidize the rust produced, and then run the iron reactor overnight, or on cloudy, windless days.
and then put back energy in the spent fuel to make new fuel again
then you have really a battery. That's how li-ion batteries work. The issue is the efficiency: how much of the energy you used to recharge the "battery" (iron) is going to be available when you discharge (burn) it
It is a bit of a fuzzy distinction. Batteries are typically simple chemical reactions that cause electrons to move around. But viewed from the outside a hydrogen fuel cell behaves the same; so why not call this one a battery too (especially since the process is reversible).
I think the one thing is that iron storage would be a potential long term form of storage, while all those other methods that you mentioned are really short term, designed primarily just to deal with the daily peaks and troughs of renewable production, but not as much the "it's been completely overcast for 3 weeks" problem. The only other form of storage I'm aware of that is also long term like that is pumped water storage, and that is obviously very geographically limited.
There could be a space for it. Or maybe batteries will just always be better. Depends on the full costs of each and the use case. Burning fuel to make electricity is pretty inefficient, but burning fuel for heat compares better.