Figure 3- Diagram for the one-factor sensitivity analysis for the CB-GES output power. Based on the sensitivity findings, an optimized configuration was defined by selecting the parameter combination that maximizes regenerated output while maintaining high round trip efficiency: H=300m, v=4m/s, q=660kg/m, electrical efficiency nel=0.95, handling loss factor nmat= 0.03, and mechanical efficiency nmech= 0.91. Under this optimized case, the system reaches an electrical charging requirement of approximately 9.2 MW, with regenerated discharge power near 6.5 MW, and an improved round-trip efficiency of ~0.71. This optimized performance is directly in line with the improvement pathway noted by Jennings (2020), where reduced resistances and highefficiency drives shift conveyor-based storage from ~60% toward ~70% round-trip efficiency. Overall, the combined sensitivity and optimization results demonstrate that CB-GES performance is primarily a site-and-design coupled problem since favourable mine geometry (large H) sets the fundamental efficiency upper limit, while throughput by means of q and v determines output capability. Consequently, the most efficient engineering strategy for performance enhancement should entail the selection of sites exhibiting favourable topography and the implementation of conveyor technology choices that minimize resistive losses. 4. TECHNO-ECONOMIC ASSESSMENT The techno-economic assessment of the CB-GES concept was based on the estimation of the Levelized Cost of Storage (LCOS), a metric widely used to compare energy storage technologies with different lifetimes, cycling characteristics, and efficiency levels. LCOS expresses the discounted lifetime cost of the storage plant per unit of electricity delivered from the system, typically in €/MWh or $/MWh of discharged energy (Schmidt, 2018). This approach is particularly appropriate for CB-GES because it includes the combined influence of fixed investment costs, operational expenditures, round-trip efficiency, and annual throughput. These factors jointly determine whether a site-specific mechanical storage project can compete with electrochemical or hydropower-based options (U.S. DOE, 2024). 100 230 2 2.3 0.9 0.07 1000 300 660 4 1.6 0.95 0.03 500 1000 1500 2000 2500 3000 Vertical Drop (m) Material Load (kg/m) Belt Speed (m/s) Mechanical loss coefficient Motor/generator efficiency (90-95%) Loss factor due to material handling Conveyor Length (m) Power regenerated (kW), Pout
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