If the amount of space used is absolutely no concern at all, what are the cheapest options out there right now for solar battery storage? I’ve read a lot about iron/air/rust batteries, but haven’t really found anything commercially available yet.
From my direct experience, and from what I have seen and read, Lithium iron phosphate (LFP) batteries are still the cheapest option available. This is especially true when considering round-trip efficiency, performance and lifespan.
Most new battery technologies still seem to be in the development phase, except for redox flow batteries which are quite economical on a large scale (500kWh or more).