EPECentre Seminar Series

Wave Energy Potential with Magnetic Thread Power Take-Off


Dr John Outram, Bathwick Electrical Design Limited and Dr Josh Schipper, Research Engineer, EPECentre, University of Canterbury


A novel magnetic thread power take-off (PTO) that converts slow linear motion, first to fast rotary motion and then to electricity, is introduced here. The proposed PTO can be used with any wave energy converter (WEC) type that has a reciprocating linear motion. Here it is deployed in one of floating-structure, direct-extraction type WEC. The magnetic thread is unique in that the components of the PTO can slip harmlessly when overloaded, thereby overcoming a significant disadvantage of direct-extraction technologies that are susceptible to higher stresses. In the chosen floating-structure WEC, the PTO is driven by a point absorber: a buoy working against a reaction plate. A dynamic model representing the control and behavior (mechanical and electrical) of the WEC is developed to accept wave data as an input resulting in an effective output power. A stochastic model that generates a spatial and temporal wave characteristic data set for Banks Peninsula, New Zealand, is developed using available measurements. Different configurations of wave farm are assessed under a condition typical to this location, well suited for such an energy harvesting device. The variability of the aggregate farm output, compared to that of a single buoy, is examined. Reduction in variability is maximized when the outputs of individual buoys are uncorrelated. A criterion that determines the extent of correlation is derived