Tidal Stream Energy - Designing for Performance

Lead Research Organisation: University of Oxford
Department Name: Engineering Science

Abstract

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.

Planned Impact

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.

Publications

10 25 50
 
Description Using this award we have developed design methods for high performance tidal stream rotors for renewable energy generation. We have used these methods to develop tidal rotor designs that we have then tested both computationally and experimentally at large scale (1/7th) in large facilities. The results indicate that we have designed significant performance advantages into our rotors through the use of our multi-rotor constructive interference design techniques, which are a design method pioneered by the Oxford Tidal Energy group. The significant performance advantages that we have demonstrated will have an impact on reducing the Levelized Cost of Energy of future tidal energy systems.
Exploitation Route The design methods and rotor designs that we have developed will be of significant use to the tidal energy industry as they seek to reduce the Levelized Cost of Energy (LCoE) of future tidal energy systems. Significant reductions in LCoE are required to make tidal energy commercially viable. Using the techniques we have developed LCoE of future systems can be reduced both through improved design leading to greater energy yield, and also through improved modelling techniques with improved prediction fidelity that will lead to better and thus cheaper engineering design. The outputs of the research will be of benefit to the wider academic community through the development, presentation and demonstration of new physics.
Sectors Energy

 
Description EPSRC Centre for Doctoral Training in Wind and Marine Energy Systems and Structures
Amount £6,423,728 (GBP)
Funding ID EP/S023801/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 04/2019 
End 09/2027
 
Description Supergen ORE hub 2018
Amount £5,097,482 (GBP)
Funding ID EP/S000747/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 07/2018 
End 06/2022
 
Description Atlantis Resources - Tidal environment guidance 
Organisation Atlantis Resources Ltd
Country United Kingdom 
Sector Private 
PI Contribution We have discussed tidal rotor performance outputs and their relevance to proposed tidal installation environments with Atlantis Resources.
Collaborator Contribution Atlantis resources have discussed aspects of tidal turbine siting and in-situ operating conditions with us. This has provided background information that has informed our on-going research.
Impact On-going collaboration, with first results from collaboration submitted for publication.
Start Year 2017
 
Description Harbin Collaboration 
Organisation College of Shipbuilding Engineering
Country China 
Sector Academic/University 
PI Contribution Provision of loading data for tidal turbines operating in sheared currents with and without free surface waves
Collaborator Contribution Development of floating platform systems to support the tidal rotor designs provided by Oxford.
Impact Floating multi-rotor turbine system design
Start Year 2014
 
Description Oxford Tidal Energy Workshop 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact This is an annual workshop that has been running since 2012, although only part supported by EPSRC from 2018 (for 5 years until 2022). The workshop is open access and attracts between 60-90 researchers each year, postgraduates, academics and industrial participants, from around the UK and from further afield; past international attendees have included from France, Italy, USA, Canada, Australia, China. The purpose of the workshop is to provide a technical forum in which to discuss cutting edge research and to support post graduate students in making early career presentations. The workshop is enthusiastically supported and has rapidly become the UK's leading technical meeting in this area of research.
Year(s) Of Engagement Activity 2018,2019
URL https://www.eng.ox.ac.uk/events/7th-oxford-tidal-energy-workshop/
 
Description Public Lecture on Tidal Stream Energy 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Talk on Tidal Stream Energy and research developments for the "Offshore Engineering Society" (society within the Institute of Civil Engineers).
Year(s) Of Engagement Activity 2021