The capability of the WITT wave energy converter to generate megawatts of offshore power at a competitive LCOE

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The potential for harnessing significant amounts of clean renewable energy from ocean waves is vast. Commitments madeby the UK government and others to tackle climate change require an expansion in development and deployment ofrenewable technologies and it is widely recognised that ocean wave energy will play an important role in meeting futuretargets for the reduction of carbon emissions. Whilst significant advances have been made over the last 35 years indeveloping new ideas aimed towards producing robust and economically viable wave energy converters (WECs) thereremains no clear consensus on future direction of design and operation of WECs. In addition to supporting existingconcepts, it is important that promising new ideas for wave energy conversion continue to be explored. It is widelyaccepted that there are two key elements to a successful WEC design.First, the design should be driven by fundamental theoretical principles of wave energy absorption as these ultimatelydetermine the capacity for power conversion. Second, prospective designs must take account of the significantengineering challenges that arise when operating in harsh marine environments.In a recent paper "A submerged cylinder wave energy converter" Crowley, Porter & Evans, Journal of Fluid Mechanics,2013, vol 716, (hereafter CPE) advocated a WEC design which sought to address these two demands. In particular, thedesign was assumed to use an internal power take-off system consisting of a pendulum rotating on a horizontal axis whoserotation was damped to produce power.Such a design benefits by its isolation from the marine environment, mechanically robust by relying on few moving partsand free from end-stop problems associated with over-excitation of the device. A combination of theoretical and numericalresults demonstrated that the device of CPE extracts significant power over a broad range of energy-dense wave periods.Indeed, a mean capture factor more than double any existing WEC of its type was predicted.The WITT developed by WITT Limited under whom this TSB grant is being led is closely related to the device conceived inthe work of CPE. Instead of a linear device working in surge/pitch modes of motion enclosed within a long cylinder, theWITT is a device designed for use in buoys. It not only converts power in surge and pitch modes but also in sway and roll.The WITT has been developed by specialists in gear transmission systems and has been shown to have high efficiency inconversion of kinetic to electric power. It is scalable and robust. The project being led by WITT includes partnersspecialising in mooring systems and marine deployment, power take-off design and manufacture and experimentalmethods including wave tank testing. In Bristol, the project will develop a theoretical model for the operation of the WITTWEC device as a spherical buoy either floating or submerged, to include effect of the mooring lines, the device and itsinteraction with a model sea state and the internal power take-off system. The work will be based on the earlier work ofCPE, with changes implemented to account for the revised converter geometry, mooring line configuration and power take-off system.After verification tests have been completed, an optimisation method will be applied to determine parameters for optimalpower conversion for WITT WEC devices over a range of physical scales. The work will develop in tandem with otherpartners on the project, in particular in developing the optimal mooring system and through the validation of theoreticalpredictions by the experimental work performed in Southampton. The successful completion of this project will result in aset of experimentally-validated theoretical results for a WEC design with the potential to be developed a larger scale andeventually to full scale commercialisation.