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

50ec7f59-e843-45f6-90c0-4837626f08a5

Closed

EPSRC
EPSRC
EPSRC
EPSRC
EPSRC

£240,880

June 30, 2015

Nov. 30, 2016

The potential for harnessing significant amounts of clean renewable energy from ocean waves is vast. Commitments made
by the UK government and others to tackle climate change require an expansion in development and deployment of
renewable technologies and it is widely recognised that ocean wave energy will play an important role in meeting future
targets for the reduction of carbon emissions. Whilst significant advances have been made over the last 35 years in
developing new ideas aimed towards producing robust and economically viable wave energy converters (WECs) there
remains no clear consensus on future direction of design and operation of WECs. In addition to supporting existing
concepts, it is important that promising new ideas for wave energy conversion continue to be explored. It is widely
accepted 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 ultimately
determine the capacity for power conversion. Second, prospective designs must take account of the significant
engineering 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, the
design was assumed to use an internal power take-off system consisting of a pendulum rotating on a horizontal axis whose
rotation was damped to produce power.
Such a design benefits by its isolation from the marine environment, mechanically robust by relying on few moving parts
and free from end-stop problems associated with over-excitation of the device. A combination of theoretical and numerical
results 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 in
the work of CPE. Instead of a linear device working in surge/pitch modes of motion enclosed within a long cylinder, the
WITT 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 in
conversion of kinetic to electric power. It is scalable and robust. The project being led by WITT includes partners
specialising in mooring systems and marine deployment, power take-off design and manufacture and experimental
methods including wave tank testing. In Bristol, the project will develop a theoretical model for the operation of the WITT
WEC device as a spherical buoy either floating or submerged, to include effect of the mooring lines, the device and its
interaction with a model sea state and the internal power take-off system. The work will be based on the earlier work of
CPE, 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 optimal
power conversion for WITT WEC devices over a range of physical scales. The work will develop in tandem with other
partners on the project, in particular in developing the optimal mooring system and through the validation of theoretical
predictions by the experimental work performed in Southampton. The successful completion of this project will result in a
set of experimentally-validated theoretical results for a WEC design with the potential to be developed a larger scale and
eventually to full scale commercialisation.

Potential Impact:
The academic aspect of this work is in developing a greater understanding of the system dynamics (mechanical and
hydrodynamic) and performance optimisation of a wave energy converter design which incorporates the disruptive,
patented and internationally awarded technology - The WITT. This work is vital in designing and operating the technology
to its full potential, yielding the greatest operational performance and supporting the consortium in order for them to achieve
their commercial aspirations.
Who will benefit from the research?
1. The work will be of key interest to (theoretical and experimental) researchers in engineering (mechanical, naval
architecture, renewable energy and dynamics).
2. Equipment suppliers to the maritime sector.
3. The wider engineering sector, who may benefit from such a device.
How will they benefit from this research?
1. The lead company, project partners and their suppliers will potentially benefit from increased sales and increased added
value to their products.
2. Policy makers, through the development of quantitative results on the
performance of wave energy conversion systems.
3. The broad thrust of new knowledge and academic thinking will also increase the two Universities relevance to a greater
number of businesses focused on energy harvesting. This in turn will potentially
increase its volume of consultancy and applied research interactions not only in the UK, but also across the EU and
beyond. Increased interaction with a greater number of industry players also continues to increase the attractiveness of the
Universities in this proposal (Southampton and Bristol) for future students, which is now a critical driver in an increasingly
competitive market place resulting from increased tuition fees.