Screening Post-Mining Shafts in Poland for Adiabatic CAES with Integrated Thermal Storage: A Multi-Criteria Method and National-Scale Potential Assessment

Achieving high shares of variable renewable energy in coal transition regions requires large-scale energy storage solutions that can be deployed rapidly and cost-effectively. This study addresses the pressing need to identify underground infrastructure by developing a national-scale screening framework for adiabatic compressed air energy storage (A-CAES) integrated with thermal energy storage (TES) in post-mining shafts. A multi-criteria decision analysis (MCDA) tool is constructed to rank active and non-decommissioned shafts using eight engineering-relevant parameters grouped into geometry, casing condition, and hydrogeology, enabling transparent down-selection under limited and heterogeneous data. Applied to the Polish shaft inventory (228 shafts), the approach identifies 52 priority candidates and estimates a total storage potential of approximately 4100 MWh for systems with a maximum air storage pressure of 5 MPa and a round-trip efficiency of about 67%, demonstrating the value of a rapid decision filter before resource-intensive geomechanical modeling and site-specific design. The results support a shift in decommissioning practice from irreversible backfilling toward targeted conservation of high-value shafts for energy-storage reuse, strengthening the circular-economy rationale and contributing to just-transition pathways in coal basins. The proposed screening tool provides a practical, reproducible basis for investors and public authorities to prioritize assets and accelerate early project development for shaft-based A-CAES systems.