A Novel Hybrid Floating Breakwater- Wave Energy Converter Device: Preliminary Experimental Investigations

Abstract

The marine space is increasingly gaining ground as the ideal candidate to drive the energy economic sector as it hosts a huge amount of natural resources to be exploited, such as waves, wind, and solar irradiation. Innovative devices harnessing these marine renewable resources have been thought to be assembled in a new concept of an energy hub for the Mediterranean Sea, recently proposed by the National Research Council of Italy.

The feasibility of this floating energy archipelago is strongly dependent on the creation of a protected sea area with reduced wave heights, where to safely install new types of floating devices for energy harvesting from the sea, like solar islands.

For this purpose, a floating breakwater module has been specifically designed to surround the archipelago with one or more rows. Moreover, investigating the possibility to implement a dual and alternative use of this floating module, as a traditional dissipative system and wave energy converter has resulted in an extremely challenging task. With respect to the existing hybrid floating breakwater-Wave Energy Converters in fact, the novelty of this device is the optimization of both functionalities by varying its draft.

In extremely rough seas, the hybrid module should only serve as a passive breakwater, soaking up incoming waves and safeguarding the equipment installed inside the archipelago. Otherwise, the floating module should operate as a WEC in more frequent mild sea states, assisting the archipelago's energy output. The whole produced energy can be stored and used to supply the development of new productive activities, such as aquaculture, the expensive process of seawater desalination, as well as the production of low environmental impact fuels like methanol or hydrogen.

The model's dual functionality is accomplished by different draft values. This parameter is directly influenced by the volume of water pumped into the module, which raises the floater's displacement. The module is almost completely immersed in the first scenario, which simulates breakwater functioning, increasing the device's stability and the amount of reflected and dissipated waves. On the other hand, when the module exhibits WEC behavior, a lower displacement is necessary, allowing greater device motions, able to better exploit the energy of the waves.

In this study, preliminary results obtained from an experimental campaign carried out on a 1:10 Froude-scaled model are reported. In particular, the dynamic behaviour of the hybrid device is evaluated in terms of response amplitude operators, while the attenuation performances are condensed in the transmission coefficient which indicates the reduction of the wave height inside the archipelago.