Tidal Stream Energy - Designing for Performance

The fellowship will provide leadership in tidal stream energy research that will promote cost and risk reduction, through design for increased performance, maintainability and reliability, thus accelerating the realization of commercial energy supply from tidal streams.
Tidal stream energy can make a substantial contribution to UK and worldwide renewable energy targets, helping to achieve emissions reductions and climate change objectives. The potential for energy generation by hydrokinetic tidal stream turbines is well accepted and the predictability of the resource is a significant benefit that will facilitate integration into the wider electricity system. Tidal stream energy offers an as yet largely untapped source of renewable energy; global resources are estimated at 100 to 500 TWh/yr, with around 20 TWh/yr estimated to be within the UK's waters. Various commercial tidal stream systems are under development with most emphasis on design and control of individual turbines. There has been some cascade of knowledge and technology from the wind energy industry. Turbines are typically 15-20 m in diameter, rated capacity 1-2 MW at flow speeds of around 2-3 m/s, and designed to be deployed in flows of up to 40 m depth. Over the next few years the first small scale tidal stream turbine arrays, 5-20 MW each, are planned to be deployed in France and the UK.
However, significant improvements in performance, reliability, deployability, maintainability and thus economic viability are needed if tidal stream energy is to be deployed at a sufficiently large scale to contribute to commercial electricity markets. This requires that power output per MW installed is increased, expenditure per MW installed and the risk of cost variations are reduced. Installation costs are both high and extremely variable, with current cost estimated at £200/MWh reducing to £120/MWh accounting for future economies in scale production and deployment.
The, sometimes implicit, assumption, and basis for current tidal farm proposals, is that turbines will be installed on individual seabed mountings in an underwater wind turbine style farm with turbines positioned to minimally interact with each other. Motivated by the necessity to dramatically improve the economic viability of tidal installations, this proposal will challenge these assumptions and seek revolutionary new solutions in the form of closely coupled turbine arrays using constructive interference effects to enhance array performance. It is known that there is a potential uplift in performance of up to 35% available through arraying turbines in a multi-rotor fence that partially spans the width of a much wider channel (Nishino & Willden 2012). This fellowship will seek to develop the underlying science, engineering tools and rotor designs required to deliver this significant performance uplift and the inferred expected reduction in cost of energy of circa 10-20%. A combination of analytic, numerical and experimental activities will be used to deliver the understanding, engineering tools and design guidelines for turbines designed to operate in confined tidal channels, multi-rotor tidal fences incorporating mutual constructive interference effects, high speed rotors, design against cavitation, and flow and pitch control strategies.
This fellowship will involve close and sustained engagement with both the academic and industrial marine energy communities, internationally as well as within the UK. Academic engagement will be achieved through traditional publication means, journal articles, international conferences and workshops, as well as active participation in the UK academic marine energy network UKCMER, and in international academic collaborations. The resulting turbine technologies, engineering models and design guidelines will be developed in close cooperation with the tidal energy industry in order to maximise impact and accelerate the realization of commercial energy supply from tidal streams.

The UK Government has made energy security and emissions reduction through clean energy key priorities. The UK, which has one of the largest marine energy resources in the world, is at the forefront of marine energy research and engineering innovation, and this fellowship will help enhance the UK's leadership in this field. The overall aim of the fellowship is to provide leadership in tidal stream energy research that will direct the research landscape to promote cost and risk reduction, through design for increased performance, maintainability and reliability, and thus accelerate the realization of commercial energy supply from tidal streams. The fellowship will deliver next generation tidal stream turbine technologies that will yield a step change reduction in the cost of energy through increased performance per MW installed, increased reliability and maintainability, and increased confidence in design models and solutions.
The research areas of this fellowship, which include turbine design for operation in confined tidal channels, multi-rotor tidal fences incorporating mutual constructive interference effects, high speed rotors, cavitation design guidelines, and flow and pitch control strategies, seek to address some of the key challenges that the tidal stream industry faces in reducing energy costs, and delivering predictable, renewable power. Conservative design practices, largely based on knowledge transfer from the wind industry, have led to sub-optimal design, such that tidal stream resources are not being harnessed as effectively as they could be. The fellowship will develop reduced-order engineering models, appropriate for use in industrial design processes, that capture the performance of tidal stream turbines in a range of conditions specifically required to meet the objectives of reduced costs and project risk associated with tidal energy deployment. The design models and associated guidelines, to account for the effects of constructive interference and blockage, will be directly useful to turbine developers, such as Atlantis, to engineering tool software developers, DNV GL (Garrad Hassan), to project developers, such as Meygen, and to agencies such as the ETI, EMEC and The Crown Estate in assessing the effects of flow constraints on the extractable tidal energy resource. The design guidelines for operating turbines at higher rotational speeds whilst safely guarding against cavitation inception, and for using individual blade pitch control to reduce fatigue damage rates arising from flow unsteadiness, will be disseminated across the tidal industry; turbine, project and software developers, and importantly with relevant engineering standards bodies, e.g. DNV GL.
This fellowship will involve close and sustained engagement with both the academic and industrial marine energy communities, internationally as well as within the UK. Academic engagement will be achieved through traditional publication means, journal articles, international conferences and workshops, as well as active participation in academic networks in the UK, such as UKCMER, and in international academic collaborations such as existing Oxford-China connections with Harbin Engineering and Shanghai Jiaotong Universities, as well as new international partnerships. The PI and the Oxford group have strong relationships, through on-going joint projects, with some of the leading tidal energy manufacturers, e.g. Atlantis, as well as with utility companies E.On and EdF. These collaborators will be invited to form a project advisory panel that will meet biannually. The role of the advisory panel will be to help inform future project directions to ensure industrial relevance, and also to act as an additional dissemination route for project outputs.