A Vanadium Redox Flow Store for a Rural Clinic: Tank Volume, Stack Power, Pumping Loss and Decoupled Energy Scaling for Forty Usable Kilowatt-Hours

This paper sizes a vanadium redox flow storage system for a rural clinic requiring overnight refrigeration, lighting and instrument supply. The duty calls for 40 usable electrical kilowatt-hours delivered at a rated power of 8 kilowatts. Working from a stated specific energy of 22 watt-hours per kilogram, an energy density of 25 watt-hours per litre, a usable depth-of-discharge fraction of 0.8, and a round-trip efficiency of 75 percent, the calculation gives a gross stored energy of 50 kilowatt-hours, an active-store mass of 2.27e+03 kilograms, a complete system mass of 3.64e+03 kilograms, and a complete system volume of 3.2e+03 litres (3.2 cubic metres). Full discharge at rated power lasts 5 hours, and a full recharge takes 7.22 hours at the stated charge power. Losses amount to 14.4 kilowatt-hours per complete cycle, appearing as heat at average rates of 1 kilowatts during charging and 1.44 kilowatts during discharge. Standing loss is 0.1 percent of the stored energy per day. Life is limited by the calendar limit, giving 6e+03 effective full cycles, about 20 years at the assumed cycling rate, and a lifetime delivered throughput of 240 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.