Abstract
Sea wave energy is one of the most promising renewable sources, even if relevant technology is not mature enough for the global energy market and is not yet competitive if compared with solar, wind and tidal current devices. Particularly, among the variety of wave energy converters developed in the last decade, heaving point absorbers represent one of the most feasible and studied technologies, as shown by the small-scale testing and full-scale prototypes, deployed in the last years throughout the world. Nevertheless, the need for further reduction of the energy production costs requires a specialized design of wave energy converters, accounting for the restraints provided by the power take-off unit and the device operational profile. Hence, actual analysis focuses on a new cost-based design procedure for heaving point absorbers. The device is equipped with a floating buoy with an optional fully submerged mass connected, by means of a tensioned line, to the power take-off unit. It consists of a permanent magnet linear generator, lying on the seabed and equipped with a gravity-based foundation. The proposed procedure is applied to several candidate deployment sites located in the Mediterranean Sea; the incidence of the power take-off restraint and the converter operational profile is fully investigated and some recommendations for preliminary design of wave energy converter devices are provided. Current results show that there is wide scope to make the wave energy sector more competitive on the international market, by properly selecting the main design parameters of point absorbers, on the basis of met-ocean conditions at the deployment site.
Highlights
Following the variety of attempts, devoted to making the wave energy sector competitive on the international market, a new cost-based design procedure of wave energy converter (WEC) devices, consisting of heaving point absorbers with an optional fully submerged mass and connected to a permanent magnet linear generator lying on the seabed, is outlined and investigated, focusing on the following main subjects: (i)
A new-cost based design procedure for point absorbers, equipped with an optional fully submerged mass and connected to a permanent magnet linear generator lying on the seabed, was developed to minimize the levelised cost of energy (LCoE)
A new hydrodynamic model for point absorbers with a fully submerged mass was developed. It accounts for the WEC operational profile, in terms of “cut-out” sea state, and the heave motion restraint provided by the permanent magnet linear generator when the translator mass hits the upper/lower end-stop springs, as detailed in the Appendix A
Summary
The wave energy sector experiences a moderate slow-down in the rate of progress, mainly due to the high investment needs, combined with challenging environmental conditions and technical risks [7] In this respect, it is quite challenging to achieve the 7/8 Technology Readiness Level [8], with reference to system prototype demonstration in the operational environment, and move the sector towards competitive manufacturing systems, at least in the case of key enabling technologies. It is predictable that in the future the wave energy sector will reach competitive LCoE levels, with the increase of the total installed capacity that will help to reduce uncertainties and costs, as well as improve system reliability and availability [7,9] These targets comply with the EU Strategic Energy Technology Plan, according to which the LCoE of wave energy devices is expected to decrease up to 0.15 €/kWh by 2030 and 0.10 €/kWh by 2035
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