Introduction

Design of a new point absorber device, equipped with a fully submerged toroidal shape, capable of harnessing the wave energy and increasing the power production as regards a conventional Wave Energy Converter (WEC) device, having the same dimensions of the floating buoy and nominal power of the Power Take Off (PTO) unit. The WEC device allows properly tuning the heave natural period of the floating buoy, so as it reaches the resonance condition with the prevailing sea states at the deployment site. The invention can be applied to increase the power production and make the marine renewable energy sector more competitive on the international market

Technical features

The point absorber technology is based on the transmission of the heave motion of a floating buoy, with small dimensions as regards the incoming wavelength, to a PTO unit, but it presents some issues concerning the overall efficiency of the plant, provided that the heave natural period of the WEC device is generally lower than the wave one, with a consistent drop-off of power production. The patented WEC device allows solving this issue by properly tuning the heave natural period of the floating buoy, depending on the prevailing sea state conditions at the deployment site. The point absorber has a spar-type configuration, consisting of a floating buoy, connected by a means of a tapered vertical cylinder, to a fully submerged toroidal shape. By properly selecting the main dimensions of the fully submerged mass, it is possible to suitably tune the frequency-dependent added mass of the WEC device and, consequently, the relevant heave natural period, so as the point absorber operates at near-resonance conditions with the prevailing sea states at the deployment site, with a very appreciable increase of the power production harnessed from sea waves. The patent has a stage of development TRL 2.

Possible Applications

• Power production from marine renewables energies.

Advantages

• Increase of power production from marine renewables;
• Tuning of the heave natural period of the floating buoy depending on the prevailing sea state conditions at the deployment site;
• Building easiness, scalability of the WEC device and simplicity of maintenance activities;
• Wave farms in restricted areas, on deep water depth and far from the coastline, with a positive impact also in terms of visual restraints.