Water and energy storage in the European Union: current situation and future challenges

Water storage is a key element in the Water-Energy-Food-Ecosystem Nexus (WEFE Nexus). Water storage systems can be designed in different ways and for serving several purposes. Water storage is also associated to energy storage, when there are turbines that can produce energy (hydropower) from the stored water. More than 95% of the current energy storage in the European Union (EU), and worldwide, is stored in artificial reservoirs behind dams. In the EU there are 4491 large dams according to the ICOLD 2023 register of dams and 40% are for multiple uses. Overall, 48% of EU’s large dams are powered. The theoretical potential of energy storage E_s in hydropower reservoirs (E_s = k·h·V, V=reservoir volume in m³, h=head in m, k=coefficient for the units) is some tens of TWh in the EU. The theoretical potential so calculated is 9 TWh for pumped-hydropower storage (PHS) plants. However, the real technical storage capacity is much less than the theoretical one (1200 GWh in PHSs).

As the impacts of climate change have considerable effects on people and ecosystems, which are exacerbated by a rising demand for water due to population and economic growth, higher temperatures and decrease in precipitation in certain regions, water&energy storage capacity needs to increase in the future, and should consider the interdependence of water, energy and food security and ecosystems – water, soil, and land. In this contribution, the current state-of-the art of PHSs in the EU is discussed and the challenges are presented considering the recent developments at the European Commission and the results of the Clean Energy Technology Observatory. The sustainable development opportunities for PHS are discussed also considering the recent Horizon calls for projects launched by the European Commission and the ongoing discussions on water and energy storage needs, with focus on emerging technologies and strategies, e.g. sustainable refurbishment, digitalization, new electro-mechanical equipment and reservoir interconnection.