1 9 If the factor of safety (FS) of the slope with the load from the gravitational energy storage system is unsatisfactory (less than 1.5), the possible solutions of subsoil reinforcement should be considered. The final decision on the location of the gravitational energy storage system shall take into account economic and safety factors. As a result, a method for assessing the potential of mass energy storage technology in specific locations within post-mining areas will be developed. The 2D & 3D numerical models will be validated to account for static and dynamic loads from the gravitational energy storage system. Infrastructural factors Gravity energy storage systems based on the cyclic transport of rock masses on slopes can be successfully used in lignite open pits that already have several types of infrastructure and provide relatively large elevation differences. Fundamentally, the efficient operation of these energy storage systems depends on two components: the transport and electrical infrastructures. Their influence is equally evident in the system's storage capacity, installed power, and overall efficiency. The existing transport infrastructure in an open pit is, in most cases, represented by railway lines or conveyor belt systems. The use of these infrastructures reduces investment costs and accelerates the implementation of energy storage systems [16]. The storage capacity of a gravity system is directly proportional to the transported mass and the available elevation difference. Both transport systems encountered in the open pits analysed in the project (conveyor belts and rail transport) are highly energy-efficient, offer automation possibilities, and thus represent solutions for cyclic transport in such applications. The technical condition of the transport infrastructure is a major factor that can limit the application of GES systems, as wear of the rails, rollers, or foundations reduces the maximum allowable load and the operating cycle frequency. In these cases, it is necessary to adapt and reinforce them for operation in an intense cyclic regime, specific to energy storage. The presence of electrical networks near open lignite deposits is an important factor for the applicability of gravitational energy storage systems, since they provide essential infrastructure for energy exchange, system stability, and economic efficiency. The mining areas considered in the project are generally characterised by well-developed electrical infrastructure, a significant advantage for integrating energy storage systems. There is also the possibility of reusing existing electrical equipment, such as drive motors and transformers. Additionally, electric motors can be adapted for reversible operation in motor-generator mode, thereby reducing initial investment [17]. In conclusion, the existing transport infrastructure and the electricity grid significantly affect the applicability of GES systems. Transport infrastructure influences storage capacity and mechanical efficiency, whereas the electricity grid determines installed power and integration into the energy system. The advantages of these infrastructure facilities associated with lignite quarries primarily involve cost reduction and increased sustainability of mining activities. Social factors The assessment of the suitability of post-mining areas for siting gravitational energy storage systems should account for social conditions, as these may influence investment acceptance [18, 19]. Key aspects include the level of public acceptance, the perception of technological risk, and the expected local benefits, such as the development of services and new technical competencies, job creation, the possibility of utilising the existing human capital of
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