Assessment of a novel PTO system for swell energy convertors using digital twin modelling

Abstract

There is no lack of ideas and prototypes for wave energy converters (WECs). However, existing WECs are designed to extract energy from waves at normal to high frequencies and typically focus on close-to-shore steep waves and short wavelengths to gain a frequent movement of interactive components. This limits the size of the buoyancy structure and results in the need to use many generating units to achieve a high-power output. We reverse this focus in small and coastal WECs mentioned above by harvesting swell energy through the Swell Energy Convertor (SWC). SWC uses an innovative power take-off (PTO) system, which Ocean Energies AS invented. This patented crankshaft mechanism transforms the linear motion from ocean waves into rotation for rotating a generator. When combined with a large buoy structure, this PTO system allows the SWC to focus on the swells (large wavelengths and low to high wave heights) further offshore and reduce/remove the drawbacks associated with the abovementioned coastal areas. The SWC (i) focuses on the high energy swells offshore, (ii) uses large buoy structures in combination with slight vertical movement, and (iii) can optimally extract energy in any direction. This results in SWC being a far less complex system with a much higher power output than existing WECs, which will significantly lower the cost of WECs. The SWC will target the area between Greenland and Scotland, with significantly high wave energy above 60 kW/m. This paper will present the design and analysis of the proposed PTO system in the SWC. First, the PTO model and working mechanism will be described. Second, a digital model of the PTO system will also be introduced. Third, three optimal design candidates are selected and analysed further to provide a deeper insight into the PTO design. Last, discussions and planned future works are presented.