With a growing share of intermittent renewable energy sources, the grid stability can be maintained, and flexibility enhanced, by applying pumped hydropower energy storage. ALPHEUS will improve reversible pump/turbine (RPT) technology and adjacent civil structures needed to make pumped hydro storage economically viable in shallow seas and coastal environments with a flat topography. Three promising technologies will be considered:

• Shaft-driven variable-speed contra-rotating propeller RPT– avoiding guide vanes in a two-way device improves overall efficiency
• Rim-driven variable-speed contra-rotating propeller RPT – rim driven configuration avoids the complexity of a shaft assembly, decreasing noise, vibrations, switching time, and maintenance costs
• Positive displacement RPT – fish friendly and seawater-robust, low cost technology. ALPHEUS plans stepwise development, starting by validating current assumptions in the lab and optimizing efficiency with numerical simulations

Based on the results, two of these technologies will be chosen and their functionality will be demonstrated for working models under realistic circumstances. Finally, a reasoned and quantified assessment of these two technologies will be delivered for further development into full scale and a prototype. Combining the current state-of-the-art and expertise of the partners, ALPHEUS expects to reach a round-trip RPT efficiency of 0.7 to 0.8. Fatigue resistance of mechanical and civil installations will be addressed, which occurs with switching between pumping and turbining modes within 90-120 seconds. ALPHEUS will address environmental aspects, including fish friendliness, scenery and land use, juxtaposed with the ability of decentralized pumped hydro storage to stabilize the grid over a range of timescales and therefore allow higher penetration of intermittent renewable energy supplies. This will result in a methodology for assessing potential sites for pumped low-head and ultra-low head energy storage.

The activities of UGent in this project are related to the PTO. More specifically, an advanced high-efficient axial flux permanent magnet synchronous generator will be developed and a scale-model will be constructed for lab testing. A full multi-dimensional model-based predictive control system for the machine-side will be developed which is capable of controlling the turbine and PTO to track the power reference as desired by the grid-side control.