A NEW SEAWATER LOW-HEAD TURBINE FOR THE OBREC

Abstract

The OBREC (Overtopping Breakwater for wave Energy Conversion) is based on the overtopping phenomenon [1] where incoming waves run over an overtopping ramp and fall into a reservoir located above the sea level inside a conventional rubble mound breakwater, or into a vertical caisson breakwater. The wave energy is transformed into potential energy, with some contribution of kinetic energy. Then, the flow is driven through a turbine addressing the final transformation into electrical energy. The OBREC prototype is located in the middle of the San Vincenzo breakwater, in Naples harbour (Italy). The key target of the whole pilot project was to demonstrate the high capacity factor of the system (expressed as the ratio of the electrical energy produced to the electrical energy that could have been produced at continuous full power operation), even in a low-energy wave climate. At the study site, in fact, the yearly average wave power was found to be 1.8 kW/m over the last 42 years [2]. However, during last 5 years, a maximum wave height of over 5 m has been registered, confirming the high reliability under severe wave conditions.

Due to the short monitoring period and to the undersize of the previous power take-off (PTO) systems, no definitive power matrix is available for OBREC [3]. The energy conversion efficiency of OBREC has been deeply investigated over the last years through both physical and numerical model tests. Within the ongoing full-scale monitoring activities in real environments, a new set of power take-off was installed. A propeller-type pico-turbine equipment was in 2021, and its final setting was completed in 2022. Performance and reliability of the entire structure were closely monitored under different “stress tests”, i.e. start & stop cycle in marine environment with a high variable combination of flow rate/hydraulic head.

This paper presents the design stage for the new equipment and preliminary results from these tests numerical and field tests.

1. Contestabile, P., Crispino, G., Di Lauro, E., Ferrante, V., Gisonni, C., & Vicinanza, D. (2020). Overtopping breakwater for wave Energy Conversion: Review of state of art, recent advancements and what lies ahead. Renewable Energy, 147, 705-718.
2. Contestabile, P., Russo, S., Azzellino, A., Cascetta, F., Vicinanza, D. (2022). "Combination of local sea winds/land breezes and nearshore wave energy resource: Case study at MaRELab (Naples, Italy)", Energy Conversion and Management, ISSN 0196-8904, 257, 115356, https://doi.org/10.1016/j.enconman.2022.115356    
3. Mariani, A., Crispino, G., Contestabile, P., Cascetta, F., Gisonni, C., Vicinanza, D., & Unich, A. (2021). Optimization of Low Head Axial-Flow Turbines for an Overtopping BReakwater for Energy Conversion: A Case Study. Energies, 14(15), 4618.