Blueprint: Iron-Air Long-Duration Battery (from DOI 10.5281/zenodo.24108666)

Design blueprint for the 48-hour configuration of the iron-air stationary battery designed in the source paper (DOI 10.5281/zenodo.24108666): 1 kilowatt for 48 hours (48 kilowatt-hours delivered) from one 40-cell string at 42.0 volts discharge and 66.0 volts charge, built from iron, air, water and 30 percent potassium hydroxide. DESIGN BLUEPRINT - SIMULATED, NOT MEASURED - NOT BUILT. Round-trip efficiency is 58.6 percent; the blueprint prints at full size that this makes the design the wrong choice for daily cycling on priced energy, and specifies it for long-duration, low-to-moderate cycle duty on surplus solar, where the source paper prices delivered energy at $0.104 per kilowatt-hour at 150 cycles per year against $0.387 for lithium iron phosphate and $0.701 for lead-acid, with a build cost of $4,766. Full build specification: cell and stack geometry, iron and electrolyte quantities, air management with carbon dioxide scrubber and hydrogen venting, assembly sequence, failure modes, tolerances as given in the source, and maintenance schedule including the year-10 refurbishment. Every quantity is from the source paper or derived from its parameters by the accompanying compute.py (derived items marked). Civilian energy storage only. AI use disclosed: this blueprint was drafted and its calculations scripted with the assistance of Dave, an artificial intelligence assistant; the named author is responsible for the design choices and for publishing the efficiency limit at full size. No hardware was built or tested.