Background: The share of renewable energy feeding the European grid has been growing over the years, even though the intermittency of some renewable energy sources can induce electric grid instability. Energy storage has proven to be an effective way of reducing grid instability. Various solutions for large-scale energy storage are being researched nowadays. This study focusses on the innovative low-head pumped hydro storage (LH PHS) technology, a large-scale energy storage scheme suitable for shallow seas (5 – 30 m depth). Implementation of renewable energy technologies, such as wind farms in Europe, Asia and North America, has faced public opposition which has delayed or even cancelled the implementation of renewable energy projects. Literature about public perception of projects highlights the importance of involving stakeholders from the early stages of project planning. Considering this, the present study aims to collect stakeholder opinions (via an online survey) to determine what is necessary for a smooth implementation of LH PHS in the North Sea, both from technical and policy points of view. Results: Stakeholders from commercial parties, government authorities and local groups recognized the potential of LH PHS as a means to increase the share of renewable energies within the European power grid. Economics, bureaucratic burden, and structural safety have emerged as primary aspects of concern respecting the implementation of LH PHS. The impression of the respondents is that a low-head pumped hydro station would not have negative effects on their organizations. Furthermore, most of the engineering firms participating in the study communicated that their knowledge and resources could be involved in the construction of such an energy storage facility. Conclusion: As identified stakeholder concerns such as economics and structural safety are currently being researched, effective communication of the findings of this research is paramount to keep stakeholders informed of the ongoing progress. Two-way communication between researchers and stakeholders is recommended to enhance public acceptance of future technologies. Furthermore, is it advisable to undertake an examination of the available energy policies relevant to LH PHS.

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To provide large-scale energy balancing and ancillary services to grids experiencing rapidly increasing shares of inverter coupled renewable generators, the ALPHEUS project proposes a novel low-head pumped storage system. Aimed at regions where traditional high-head pumped storage systems are not feasible due to topographic constraints, the system consists of a newly designed reversible pump-turbine (RPT), axial-flux motor-generators and a dedicated control and grid coupling. The main aims of ALPHEUS include increased round-trip efficiencies, reduced switching times between pump and turbine mode as well as faster power ramp rates. These directly aid its capability to contribute to grid stability. Aiming to validate simulation results investigating the hydrodynamic performance of the two novel contra-rotating runners making up the RPT as well as the axial-flux motor-generators, an experimental series is planned as part of ALPHEUS. For this, a scaled down version of the RPTs and motor-generators are assembled and connected to two open tanks serving as the upper and lower reservoir. Before the experiments are conducted, preparatory tests are performed to characterise Coulomb and viscous friction in the drivetrain, hydraulic losses in the conduit and other system components. This paper introduces the proposed low-head pumped storage system before presenting the developed experimental setup, approach and the aforementioned characterisation tests.@en