David Sudall

PhD Student in Offshore Renewables with specific focus on “Combined systems of wind and tidal stream turbines: Hybrid floating structures.”


This role was jointly proposed between my supervisors and me. I originally suggested pursuing research into combined systems of wind turbines and wave energy convertors, providing a method of both increasing the capacity of the wind turbines and also potentially smoothing the variation of power supply. However, after some discussion it was felt that a more promising and novel area of research would be to combine wind turbines with tidal current turbines. I find the opportunity to be embarking upon a project of such a new idea, with very little prior research, extremely exciting and it is this which really attracted me to the role.

For me, the project was the deciding factor when choosing my institution. Having already studied my undergraduate degree in Mechanical Engineering with Industrial Experience at Manchester I was a little wary of staying at the same institution for my doctorate. However my supervisors, Peter Stansby and Tim Stallard, are leaders in the field of marine energy devices. The chance to pursue such an innovative project, under the supervision of the best academics in the field, was incomparable to any of the offers posed from other institutions, and to my mind could not be missed.


In order to meet the UK’s offshore wind energy targets, turbines must be deployed in deeper waters (30-60m). Tidal turbines are in earlier stages of development, yet have potential to provide around 20TWh/yr. Neither system is currently commercially viable without subsidy. A major driver towards commercialisation is the capital cost per MW capacity installed. The aim of this project is to investigate potential cost advantages by collocating wind and tidal turbines on the same structure, sharing common electrical substations. The work is multi-disciplinary, combining atmospheric modelling for estimating combined resource, with numerical models for array wake and blockage effects, and hydrodynamic/aerodynamic theory to evaluate structural loads.

The first year of this PhD requires assessing the combined energy yield from collocated devices and determining the implication this has on both, the combined system’s operating loads and also the cost of energy produced. To do this, I am developing a numerical model of both tidal and wind energy resource, which looks at the energy extractable from arrays of wind and tidal turbines. This work requires knowledge of a broad range of subjects, including atmospheric modelling for wind and tidal conditions, hydrodynamic and aerodynamic theory for wake interactions and tidal blockage effects, and the understanding of a number of computer programs and systems. Day to day, this means a lot of reading around all of these subjects, critically assessing suitability of various methods and then coding developments and improvements into the numerical computer model.

I particularly enjoy the fact that the work is always very varied and never dull. Combining two complementary technologies means that the focus remains quite broad and there is much scope to take the project. This feeds into the day to day problem solving nature of the research, which at the same time as often being frustrating, it is incredibly rewarding to overcome challenges. This sense of reward helps fuel the enthusiasm to keep progressing the project forward and tackling the next obstacle.

In these first 6-7months of my PhD, I have been involved with a number of cross-university departments. I have been working with the Energy Systems and Climate Change research group to provide predicted tidal energy data as input into a model on electricity network resilience. I have also been part of establishing a university WRF users group with participants from across the university, to whom I gave a presentation about my work. Further afield, I have attended workshops as part of the SuperGen UK Centre for Marine Energy Research (UKCMER) and meetings with the Extreme loading of Marine Energy Devices (X-MED) partners, whereby networking with other participants and industry personnel has helped to raise the awareness of my research.


I hope by successfully completing this research, I will be able to demonstrate that collocating wind and tidal stream turbines on the same structure allows these technologies to become much more financially attractive options in the near future. If this is the case, offshore renewable energy will be able to provide a significantly greater contribution to the UK energy production portfolio, requiring little government subsidy and energy suppliers pushing for their installation. This would help significantly reduce our reliance on fossil fuels and ultimately, help reduce our country’s CO2 emissions.

2015 will see the installation of the MeyGen demonstration tidal turbine array off the north coast of Scotland; this will surely be a significant ‘game changer’ in tidal stream energy. Up until now, array interaction and blockage effects of tidal turbines have only been studied at experimental scale with no robust theoretical models yet verified. The impacts of blockage and the support structure to the tidal flow regime will all come to the fore when this array comes online and real site data can start to be collected. I think this will be when the feasibility of tidal energy as a significant source of renewable energy is truly demonstrated and will really help start to accelerate its development.

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