Operational assessment of hybrid energy storage systems integrated with post-mining infrastructure under day-ahead market conditions

Hybrid energy storage systems (HESS) integrated with post-mining infrastructure represent a promising pathway for enhancing flexibility in centralized energy systems. Their effective deployment requires simultaneous consideration of market-driven operation and system-level performance constraints. This study investigates the operational and economic performance of selected hybrid energy storage configurations under day-ahead market (DAM) conditions, using the Budryk coal mine in Ornontowice (Poland) as a representative case study. Particular attention is given to operational cycling characteristics associated with pumped storage hydroelectric (PSH) systems. Three storage technologies were evaluated: CO₂-based energy storage, compressed air energy storage (CAES), and conventional PSH. The analysis incorporates DAM price signals derived from publicly available data published by the Polish Energy Regulatory Office (URE), together with operational constraints, to assess system profitability and utilization patterns across different storage capacities. The results indicate a strong dependence of system performance on both technology selection and storage capacity. Among the analyzed configurations, the CO₂-based system achieved the highest unit profit of 298 PLN/MWh for a medium-capacity system (42 MWh). These findings demonstrate the importance of aligning storage design with market conditions and operational dynamics. The proposed approach supports the evaluation of hybrid energy storage deployment in repurposed mining assets and contributes to the development of economically viable energy transition strategies.