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The conversion of the energy supply system towards renewable technologies is indispensable for climate and environmental protection. With the predominant use of inexhaustible but fluctuating renewable energy sources, energy storage capacities and physical networks are key infrastructure for sustainable functionality. Efficient pumped‐storage hydropower can meet these demands. However, suitable sites for conventional surface reservoirs are facing natural limits, and new storage capacities in ecologically sensitive mountainous valleys are increasingly difficult to license. To gap these aspects this article reflects the construction of fully underground pumped‐storage hydropower plants to cover multipurpose energy storage requirements. Thus, the surface reservoirs are substituted by underground storage caverns with less water volume required by equivalent energy storage capacity since high heads are utilized. Proximity to urban areas improves the construction and operation through various infrastructure and close connection to existing power grids, power plants and consumers. Valuable surface resources remain untouched and the closed water cycle ensures a constant storage volume and independent operation against external influences. Furthermore pumped‐storage is combined with seasonal underground thermal energy storage. This system leads the well‐proven hydraulic energy storage technology into a new energetic age and ensures the demand‐based and cross‐sectoral renewable energy supply. [ABSTRACT FROM AUTHOR]

Water power is the oldest and most-used energy source for provision of mechanical work and electricity generation. Furthermore pumped storage hydropower is ranked as the most reliable and efficient storage technology for electricity. The energy carrier water is also the most commonly-used thermal storage medium due to its high specific heat capacity. In a study, the combination of electrical and thermal energy storage in a pumped storage power station is investigated in order to cover two energy-intensive sectors with the economical double use of water as an energy medium. With this double application the energy output compared to separate storage usage can be considerably increased. Underground power stations are independent of topography, so this storage concept can be used for district heating supply. One possible vision is to stor solar energy into the water reservoir of a pumped storage power station in the summer months and transfer it in the high-demand winter months. In order that pumped storage power stations can keep functioning at high and seasonally fluctuating water temperatures and simultaneously store thermal energy efficiently, some adaptations of the structures and the pressure tunnel layout are necessary. [ABSTRACT FROM AUTHOR]