An Iron-Air Store for Multi-Day Village Supply: Iron Mass, Air-Electrode Area, Rusting Round-Trip Loss and Seasonal Throughput for Two Hundred Usable Kilowatt-Hours

This paper sizes a iron-air storage system for a village microgrid requiring two overcast days of autonomy. The duty calls for 200 usable electrical kilowatt-hours delivered at a rated power of 20 kilowatts. Working from a stated specific energy of 55 watt-hours per kilogram, an energy density of 90 watt-hours per litre, a usable depth-of-discharge fraction of 0.85, and a round-trip efficiency of 55 percent, the calculation gives a gross stored energy of 235 kilowatt-hours, an active-store mass of 4.28e+03 kilograms, a complete system mass of 6.42e+03 kilograms, and a complete system volume of 3.92e+03 litres (3.92 cubic metres). Full discharge at rated power lasts 10 hours, and a full recharge takes 15.9 hours at the stated charge power. Losses amount to 143 kilowatt-hours per complete cycle, appearing as heat at average rates of 4.5 kilowatts during charging and 7.14 kilowatts during discharge. Standing loss is 0.02 percent of the stored energy per day. Life is limited by the cycle limit, giving 5e+03 effective full cycles, about 16.7 years at the assumed cycling rate, and a lifetime delivered throughput of 1e+03 megawatt-hours. All values are computed from the stated assumptions; the system is a design study and has not been built or measured. Status: SIMULATED, NOT MEASURED.