A Solid-Gravity Store of Lifted Composite Blocks: Block Mass, Lift Height, Motor-Generator Sizing and Round-Trip Loss for Eight Hundred Usable Kilowatt-Hours

This paper sizes a solid-gravity storage system for a solar farm requiring daily shifting without any electrochemical consumable. The duty calls for 800 usable electrical kilowatt-hours delivered at a rated power of 150 kilowatts. Working from a stated specific energy of 1.8 watt-hours per kilogram, an energy density of 3.5 watt-hours per litre, a usable depth-of-discharge fraction of 0.98, and a round-trip efficiency of 82 percent, the calculation gives a gross stored energy of 816 kilowatt-hours, an active-store mass of 4.54e+05 kilograms, a complete system mass of 5.67e+05 kilograms, and a complete system volume of 2.92e+05 litres (292 cubic metres). Full discharge at rated power lasts 5.33 hours, and a full recharge takes 6.44 hours at the stated charge power. Losses amount to 162 kilowatt-hours per complete cycle, appearing as heat at average rates of 12.6 kilowatts during charging and 15.2 kilowatts during discharge. Standing loss is 0 percent of the stored energy per day. Life is limited by the calendar limit, giving 1.2e+04 effective full cycles, about 40 years at the assumed cycling rate, and a lifetime delivered throughput of 9.6e+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.