The electric grid is transitioning from fossil fuels to renewable energies. However, this transition requires upgrading the energy storage capacity and transmission infrastructure to ensure a reliable energy supply. Pumped Hydro Storage (PHS) is currently the most mature large-scale energy storage technology, but it is limited to mountainous areas, not being suitable for flat land locations such as those south of the North Sea coast. The concept of Low-Head Pumped Hydro Storage (LH PHS) has emerged as a possible solution for enabling large-scale storage of renewable energy in flat topographical regions. This thesis aims to advance both the technical and social feasibility of LH PHS by experimentally investigating the hydraulic efficiency of a novel pump-turbine as well as the stakeholder perceptions on LH PHS technology. A 1:22 scale novel variable-speed contra-rotating pump-turbine (impeller diameter: 276 mm) was tested in test rig in the hydraulics laboratory of the Leichtweiß- Institut für Wasserbau (LWI) (Braunschweig, Germany). The test rig provided head by two open water surface tanks and worked with discharges of up to 380 l/s. Discharge, static water pressures, rotational speed of the impellers, and impeller torque data were recorded to evaluate the efficiency of the machine across variable operating conditions representing a LH PHS system. The machine performed at efficiencies over 80% for a wide range of operating conditions while at its Best Efficiency Point (BEP) the roundtrip efficiency is 76%. Comparison with other types of machine revealed that the tested unit had the largest power density, being beneficial for both the mechanical and civil engineering requirements associated with its manufacture and integration in LH PHS systems. From a social perspective, an online questionnaire was designed and distributed to stakeholders from local communities, governmental authorities and commercial parties. The respondents showed interest in LH PHS as a technology to increase energy storage and did not mention any red-lines for its development. Furthermore, all groups expect no negative affection from a LH PHS to their activities and the commercial parties expressed having both the expertise and technologies to make a LH PHS system feasible. This thesis concludes that LH PHS systems are feasible from a hydraulic and social perspective. The contra-rotating pump-turbine machine seems the best for efficient operation in the variable conditions required in a LH PHS system, while the respondents seem to support LH PHS development at this research stage. Future work should address scaling up and marine testing of the machine as well as continuation of stakeholder engagement at key milestones, such as at each Technology Readiness Level (TRL) stage. The current work advanced LH PHS systems from TRL 2 to TRL 4.
Ruben Ansorena Ruiz (Thu,) studied this question.