Renewable Energy

The aim of this research study is to perform experimental tests on a new morphable mini Wells turbine designed to operate in presence of waves with limited energy content which presents a high frequency of occurrence along the Mediterranean coasts. The small size and low investment costs of the turbine make it particularly suitable to be installed either in existing structures, such as anti-reflective perforated caissons, or in devices for the coastal defense from erosive phenomena located on shallow water conditions. The need to carry out experimental tests derives from the difficulty of handling in a virtual Computational Fluid Dynamics environment the huge difference in the time scale of the turbine, which spins at 1500-3000 rpm, and the wave periods, in the order of some seconds. Properly designed lab tests are mandatory to characterize the behavior of Wells turbines to be employed in the Mediterranean Sea. 

Point absorber wave energy converters (WECs) closely placed in array hydrodynamically interact through wave radiation and diffraction. The power absorption by these WECs is optimised by altering the WEC dynamics through the control of the Power Take-Off (PTO). As the WEC dynamics are changed, the hydrodynamic interactions change as well. Therefore, the PTO control should be optimized taking all these interactions into account, referred to as centralized control. This work discusses the experimental design, implementation and testing of centralized controlled arrays of up to five 'WECfarm' heaving point absorber WECs, tested at the Coastal and Ocean Basin Ostend. A causal impedance matching Proportional (P) controller is used, approximating the complex conjugate of the intrinsic impedance of the WEC array in the peak wave frequency of the design sea state. Short-crested and long-crested irregular waves are used to obtain realistic operational and extreme sea conditions.

This study presents an experimental proof-of-concept for an innovative floating system designed to harness solar energy in coastal regions. The concept leverages the combination of two distinct elements: a double-axis solar tracker, maximizing solar energy generation, and a tension-leg platform (TLP), ensuring structural performance and stability. Tests on a 1:30 reduced scale model of the preliminary prototype were conducted in a wave tank, initially focusing on regular wave conditions. The outcomes are highly encouraging, with the motions of the platform remaining remarkably stable even during large amplitude waves. This stability is crucial, as it enables floating solar systems to minimize electricity generation losses caused by panel misalignments and ensures their resilience during extreme events.

Wave Energy Converters (WECs) placed in an array configuration change the incident wave field due to radiation and diffraction. These are the so-called near- and far-field effects of WEC farms. This study investigates these effects for an array of up to five heaving point absorber WECs, that was tested at the Coastal & Ocean Basin Ostend.
To optimize the absorbed power of the array, the Power Take-Off (PTO) devices are controlled using a centralized control algorithm, influencing the hydrodynamics of the WECs and hence the wave field. Wave elevations around the WEC array are recorded using an array of up to 17 wave gauges to characterize the wave field. Wave directionality is measured in the wake zone of the WEC array using a CERC 5 wave gauge array. Multiple wave conditions are examined including irregular long-crested and short-crested waves, resembling both operational and extreme conditions.