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The world is undergoing an energy transition with the inclusion of intermittent sources of energy in the grid. These variable renewable energy sources require energy storage solutions to be integrated smoothly over different time steps. In the near future, batteries can provide short-term storage solutions and pumped-hydro storage can provide long-term energy storage with large generation capacities. However, none of these technologies can provide long-term energy storage in grids with small demand. This paper proposes a new storage concept called Mountain Gravity Energy Storage (MGES) that could fill this gap in storage services.MGES systems move sand or gravel from a lower storage site to an upper elevation. The higher the height difference the greater the amount of stored energy in a given installed capacity, as this technology is constrained to the topography of the location. MGES cost varies from 50 to 100 $/MWh of stored energy and 1 to 2 M$/MW of installed capacity. MGES could be a feasible option for micro-grids, for example, small islands and isolated areas, and power systems where electricity costs are high, demand for energy storage is smaller than 20 MW with monthly or seasonal storage requirements.