Step-WEC: STEP CHANGE FOR WAVE ENERGY CONVERSION THROUGH FLOATING MULTI-BODY MULTI-MODE SYSTEMS IN SWELL

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Marine energy should make a substantial contribution to the UK renewable energy target of 30% electricity by 2020 and the potential of wave energy is high. However wave energy conversion requires a step change in power output per unit cost to be readily commercially viable. Here we address the question 'what is the maximum power which can be converted if structure size is no object and if several modes of motion are exploited for power conversion?' We further know that the system must be floating to avoid the high costs of fixed, bed-mounted structures. The intention here is to investigate multi (initially two) body systems with multiple mode motion providing superposition of energy output from the different modes of motion. A particular form of two-body device with heave and pitch has in fact been devised (and patented) and high efficiency has been demonstrated in the lab, showing the potential. We are particularly interested in ever-present, predominantly regular, swell waves providing a base load. For small swell around the west of UK periods are predominantly in the 9-11 s range and a system would be tuned to exploit these waves, knowing that for larger waves substantial generation is straightforward. However the interaction of swell and random (wind) waves is an important but unexplored consideration in this context. Generic methodologies need to be applied for operational testing and large-scale deployment. To investigate complex multi-body multi-mode response methodologies need to be developed. Mooring loads also need to be evaluated for intermediate-to-deep water. The important aspect of extreme loading and survivability will not be specifically covered in this project but links will be made with the on-going Supergen Marine Challenge projects X-MED and SMARTY. The overall aim is thus to design, analyse and optimise floating systems for wave energy conversion of approximately 10 MW capacity in swell and mixed swell/wind waves based on two or more dynamically connected bodies with multi-mode response and to assess their interaction, particularly power generation, within an array.