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

Lead Research Organisation: University of Manchester
Department Name: Mechanical Aerospace and Civil Eng

Abstract

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.

Planned Impact

Marine energy should make a substantial contribution to the UK renewable energy target of 30% electricity by 2020 and, while the potential of wave energy is high, commercially attractive systems for conversion have remained elusive. The aim here is to develop floating systems with high power output that are commercially attractive with simple deployment and maintenance. To achieve this we need intellectual innovation coupled with the practical knowledge of shipbuilders and power system suppliers integrated with the commercial requirements of utilities. This project is fortunate to be closely involved with Cammell Laird, Bosch Rexroth and EDF who will provide these inputs. The project will also benefit considerably from being part of the UKCMER programme. The work will be exposed to further commercial interests and will be scrutinised by all the academics directly involved and by international experts joining the annual assemblies for example. The exposure could hardly be higher.
The call is for technology for 2050. Fundamental understanding of swell and random (wind) wave interaction is of direct relevance to all wave energy technology and project developers. Development of multi-mode concepts provides the potential for a step-change of economic viability that is needed prior to large-scale wave energy deployment. If the project is successful, full-scale prototypes of a multi-mode wave energy converter should be tested and generating electricity by 2020. Optimising and tooling for manufacture of a complex novel system may be expected to take another decade, by 2030. Large-scale UK deployment with associated infrastructure, maintenance and grid integration would be expected to take at least a decade. As a mainstay of renewable electricity supply this technology should be possible by 2050. However speed of deployment will be affected by cost. If cost, reliability and survivability are shown to be comparable with onshore wind then large scale deployment could be much quicker. These systems have little visual impact and will meet with less resistance than onshore and offshore wind. Within an international context the demand for such a system exploiting swell waves could be very hig

Publications

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Eatock Taylor R (2016) A coupled hydrodynamic-structural model of the M4 wave energy converter in Journal of Fluids and Structures

 
Description A moored, three-float, multi-mode wave energy converter has been developed and optimised to give high capture widths across a broad band of wave periods. The float sizes increase from bow to stern; the bow and mid float are rigidly connected by a beam and the stern float is connected by a beam to a hinge above the mid float where the rotational relative motion is damped to absorb power. The floats are approximately half a wavelength apart so the float forces and motion in antiphase generate a relative rotation. The maximum capture width ratio is close to the theoretical maximum for a single multi-mode device in resonance. This performance is substantially superior to that of other devices (based on information in the public domain). Patent 2872772 has been awarded to M4 WavePower Ltd for on the device known as M4.Linear diffraction modelling accounting for all interactions has been developed and shown to give good predictions of power and motion in operational conditions in random and regular waves. Linear diffraction modelling has been extended to multiple devices to determine energy capture in arrays.Experiments at two scales, differing by a factor of 5, have been shown to give very similar results based on Froude scaling, lending confidence to extrapolation to full scale. The modelling has been extended to multiple floats, up to 8, showing high capacity, similar to wind, and competitive LCOE. This has now been backed by wave basin testing through Marinet2.
Exploitation Route Further testing of a 6 float system has been undertaken in the ocean basin at MaREI, Cork, through EU Marinet2 funding, validating linear diffraction modelling. To further reduce LCOE a grant developing PTO control will be submitted. The modelling methods are being applied to floating wind platforms and hybrid wind/wave platforms. The intention is to demonstrate the cost effectiveness of offshore renewable energy for industry to exploit.
Sectors Construction,Energy,Manufacturing, including Industrial Biotechology

URL http://www.mace.manchester.ac.uk/media/eps/schoolofmechanicalaerospaceandcivilengineering/research/specialisms/waveenergy/Offshore-Web.pdf
 
Description Energy Sustainability Conacyt-SENER fund
Amount £160,000 (GBP)
Organisation Government of Mexico 
Sector Public
Country Mexico
Start 01/2017 
End 12/2021
 
Description Marinet2 transnational access
Amount € 3,000 (EUR)
Funding ID M4WW 
Organisation European Union 
Sector Public
Country European Union (EU)
Start 01/2018 
End 02/2018
 
Title Surge based wave energy converter 
Description multi-body multi-mode wave energy converter 
IP Reference WO2013182837 
Protection Patent application published
Year Protection Granted 2013
Licensed No
Impact nothing commercial as yet but sea trials planned in China
 
Company Name M4 WavePower 
Description Owner of IP on surge based wave energy converter 
Year Established 2013 
Impact none as yet