1 3 % of final energy consumption by 2030 [4]. Wind and solar energy have become the dominant sources of new generation capacity, reflecting rapid technological development and declining costs [5]. However, wind and solar power are inherently variable and only partially predictable, resulting in temporal imbalances between electricity generation and demand. As highlighted by recent system analyses, the demand for energy storage is strongly correlated with the share of renewable energy in the power system, which currently stands at approximately 25 % globally [6]. Increasing the share of renewable energy sources, therefore, requires a substantial expansion of energy storage capacity to maintain system reliability and operational flexibility. According to European studies, installed storage capacity must increase from approximately 89 GW in 2025 to around 200 GW by 2030 and to approximately 600 GW by 2050 to support a highly renewable European electricity system [6, 7]. At the same time, the energy capacity of storage systems is projected to grow significantly, reaching up to 30% of total electricity demand in the EU by 2050 (approximately 2,189 TWh), up from around 11% in 2021 [6]. These numbers underline the critical role of energy storage as an enabling technology for deep decarbonisation. At present, large-scale electricity storage is dominated by pumped-hydroelectric storage (PHS), which accounts for approximately 96–98% of global installed storage capacity, corresponding to roughly 200 GW worldwide [8, 9]. All other commercial and emerging storage technologies together account for only 2–4% of installed capacity [10]. Battery energy storage systems, particularly lithium-ion technology, are the fastest-growing segment, with installed battery capacity in the EU reaching approximately 36 GWh and round-trip efficiencies of 85– 95 % [11, 12]. Nevertheless, challenges related to material availability, lifecycle sustainability, and long-term storage duration motivate the development of other energy storage solutions. In this context, gravity-based energy storage systems are receiving increasing attention as a mechanical storage option capable of medium-scale, long-duration operation. These systems store energy as gravitational potential energy by lifting solid masses with electrical power and recover it during controlled descent [13]. A potentially long service life characterises gravity-based storage concepts, negligible performance degradation, and the use of low-cost, widely available materials [13, 14]. 1.2 Possible use of post-mining areas for energy storage Post-mining areas constitute a significant and largely underutilised resource for deploying energy storage technologies. Across the European Union, more than 3,200 open-pit mines with surface areas exceeding 0.5 km² have been identified, offering substantial topographical and geotechnical potential for energy storage applications. These areas provide opportunities for technical reuse while supporting regional redevelopment. Gravity energy storage (GES) systems are particularly well-suited to post-mining sites. The GES installations are expected to operate at approximately 0.5-100 MW, with response times of a few seconds and round-trip efficiencies of 70%-85 %. Unlike electrochemical batteries, gravity storage systems do not suffer capacity degradation and can enable long-term energy storage without significant energy loss [13]. In addition to technical advantages, reusing post-mining areas for energy storage aligns
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