A Molten-Salt Sensible-Heat Store for Process Steam: Salt Mass, Tank Volume, Freezing Margin and Overnight Heat Loss for Eight Thousand Usable Thermal Kilowatt-Hours

This paper sizes a molten-salt sensible-heat storage system for an industrial site requiring process steam through the night from daytime heat collection. The duty calls for 8e+03 usable thermal kilowatt-hours delivered at a rated power of 1e+03 kilowatts. Working from a stated specific energy of 42 watt-hours per kilogram, an energy density of 95 watt-hours per litre, a usable depth-of-discharge fraction of 0.9, and a round-trip efficiency of 93 percent, the calculation gives a gross stored energy of 8.89e+03 kilowatt-hours, an active-store mass of 2.12e+05 kilograms, a complete system mass of 2.75e+05 kilograms, and a complete system volume of 1.22e+05 litres (122 cubic metres). Full discharge at rated power lasts 8 hours, and a full recharge takes 10.2 hours at the stated charge power. Losses amount to 645 kilowatt-hours per complete cycle, appearing as heat at average rates of 31.5 kilowatts during charging and 40.3 kilowatts during discharge. Standing loss is 0.35 percent of the stored energy per day. Life is limited by the calendar limit, giving 7.5e+03 effective full cycles, about 30 years at the assumed cycling rate, and a lifetime delivered throughput of 6e+04 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.