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.
 
Description This award has led to some significant outputs:

1) Proven methods for the design of high performance tidal stream rotors with demonstrated performance increases of around 10% with commensurate reductions in resulting device Levelized Cost of Energy. Higher turbine performance can be achieved by operating turbines in side-by-side configurations in co-planar arrays. This utilises constructive interference effects between the turbines so that they can operate at higher thrust and power levels. Whilst theoretical models for this effect have existed for some time (developed by the Oxford Tidal Energy group), design tools and turbine designs were yet to be developed. Within this grant we have developed the design tools, developed a range of rotor designs of different scale, demonstrated the performance of these devices through numerical simulation, and then built and tested candidate rotor designs at large laboratory scale across a range of testing facilities. The experimental demonstration has been highly successful and shown that power per turbine area can be increased for practical engineering design. The largest experiments conducted were of a closely spaced array of four 1.2m diameter 3-bladed axial flow turbines.

2) The project has developed significant data volumes and analysis for turbines operating in hostile environments. In particular the influence of free stream turbulence, head waves and platform motions on the unsteady loading of turbines has been investigated both numerically and through physical experiments. Understanding unsteady loading is extremely important for the design and safe operation of turbines and this data, together with understanding of how wave and platform motion conditions effect loads, will be invaluable in the development of future turbine designs, and in future turbine modelling and design research.

3) The project has, jointly with the Supergen ORE Hub, delivered the Tidal Turbine Benchmarking Project. This is a community engagement project which has engaged many engineering teams from 12 participant organisations from 6 different countries to date. The project seeks to validate, quantify uncertainty in and develop best practice in the use of engineering models for the analysis of the hydrodynamic loads experienced by tidal turbines. The project conducting large-scale model experiments on a highly instrumented 1.6m diameter tidal rotor. The turbine was tested in well-defined flow conditions, including wave-generated unsteadiness and grid-generated free-stream turbulence, and was towed through the 12.2m wide, 5.4m deep long towing tank at QinetiQ's Haslar facility. These experiments are unprecedented in their scale and available measurement data. The second stage of the project involved a community wide blind exercise to predict the performance and loads of the turbine. This attracted 26 blind predictions of the turbine's loading in a variety of flow conditions from across the 12 participant organisations. The project has delivered a trusted high-quality data set, that will be used in future model validation, to the quantification of model error for a range of different engineering and research modelling techniques, and to improvements in those techniques and their use that has already led to a significant reduction in modelling uncertainty. The data generated in the Tidal Turbine Benchmarking Project is being made open access to facilitate future model validation and development across the community.
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 improved and more reliable engineering design.

The outputs of the research will be of benefit to the wider academic community through the development, presentation and demonstration of data sets and new understanding relating to turbine loads and performance in hostile environments, including the influence of free stream turbulence, waves and platform motions.

The open access data set developed through the Tidal Turbine Benchmarking exercise is a trusted high-quality data set that will be of use to future researchers and engineers in validating, improving and developing new modelling techniques. This data set, the physical and numerical model turbine will become a reference turbine to be used widely across the research and engineering communities.

The next step in delivering the largely hydrodynamic outputs of this project is to integrate the results, methods, understanding and design with structures and materials so that high-performance hydro-structural coupled designs can be developed. This is the focus of the CoTide Programme Grant which will build significantly on the outputs of this project.
Sectors Energy

 
Description The developers of tidal turbine devices have started to recognise the need and potential benefits of understanding the interference of turbines on each other and with their support structures. Several developers have started to consider and use optimal inter-turbine spacing developed through our research. The data and blind-prediction exercise followed in the Tidal Turbine Benchmarking Project engaged a number of commercial engineering consultancy companies as well as research institutes. In particular the project has provided the validation dataset that the community requires for those engineering consultancies to validate and quantify error in their engineering models. This in-turn supports the wider commercial tidal sector community through delivery of improved, more robust and reliable engineering design and consultancy services. The potential for performance increases for tidal turbines through constructive interference between rotors resulting from this work has been cited by both US and UK agencies (ARPA-E Submarine Hydrokinetic and Riverine Kilo-Megawatt Systems (SHARKS) programme FOA, 2020; and UK Parliament POST Note, number 625, 2020) as a route to achieving significant cost reduction for this emerging technology sector.
First Year Of Impact 2021
Sector Energy
Impact Types Economic

 
Description CoTide - Co-design to deliver Scalable Tidal Stream Energy
Amount £7,363,043 (GBP)
Funding ID EP/X03903X/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 06/2023 
End 06/2028
 
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 03/2019 
End 09/2027
 
Description Supergen ORE Impact Hub 2023
Amount £7,965,317 (GBP)
Funding ID EP/Y016297/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 06/2023 
End 06/2027
 
Description Supergen ORE hub 2018
Amount £9,193,414 (GBP)
Funding ID EP/S000747/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 06/2018 
End 06/2023
 
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 publication from collaboration, results submitted for publication.
Start Year 2017
 
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
 
Description Tidal Turbine Benchmarking Project 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Study participants or study members
Results and Impact The Tidal Turbine Benchmarking Project is a community engagement project which seeks to develop best practice in the use of engineering models for the analysis of the hydrodynamic loads experienced by tidal turbines. The Project has been jointly funded by the EPSRC Fellowship grant EP/R007322/1 (Tidal Stream Energy - Designing for Performance) and the EPSRC Supergen ORE Hub EP/S000747/1.The Project seeks to improve engineering models for tidal rotors through highly instrumented controlled experiments, followed by model blind-prediction and evaluation across an international industry and academic community.

The rationale for the project is that uncertainty in the prediction of the steady and unsteady loading of tidal turbines, especially in hostile unsteady environments dominated by waves, shear and turbulence, leads to conservatism in design. Uncertainties can stem from difficult-to-measure field conditions, uncertainty in physical process that generate fluid loads, and associated modelling errors. In order to reduce this conservatism, the limitations and errors associated with the mathematical and engineering models used in turbine design must be understood and improved. This requires large-scale experimental data for model assessment and validation.

The project has conducting large-scale model experiments on a highly instrumented 1.6m diameter tidal rotor. The turbine is instrumented for the measurement of spanwise distributions of flapwise and edgewise bending moments using one hundred strain gauges and a fibre Bragg optical system, as well as overall rotor torque and thrust. The turbine has been tested in well-defined flow conditions, including wave-generated unsteadiness and grid-generated freestream turbulence, and was towed through the 12.2m wide, 5.4m deep long towing tank at QinetiQ's Haslar facility. These experiments are unprecedented in their scale and available measurement data (Tucker Harvey et al. 2023).

The second stage of the project has run a community wide blind exercise to predict the performance and loads of the turbine and its spanwise load distributions. This attracted 12 research groups from 6 countries who submitted 26 blind predictions of the turbine's loading in a variety of flow conditions, with prediction methods ranged from engineering Blade Element Momentum models to blade-resolved CFD simulations. Importantly this exercise has cut across both academic and industry research teams with good engagement from engineering consultancies servicing the tidal stream sector. The benchmarking exercise has been extremely successful and well received by all participants and the wider community. The turbine experimental data and vast array of computational modelling data have cross-validated each other providing a go-to dataset for testing and benchmarking numerical models for tidal turbines.

The first stage of the benchmarking project, steady flow results, has been reported in Willden et al. (2023) as well as other related papers. The second stage, relating to the turbine in combined current and waves, is ongoing with further experiments planned for 2024 and supported through on-going funding through the renewed Supergen ORE Impact Hub.

The Benchmarking project has not just produced engineering model improvement and related analyses, but has brought the community of engineers and researchers working on tidal turbine loading together. This has been extremely positive and has led to a number of very cooperative and community supporting developments.

The project has run around 10 workshops; physical workshops engaging a wide participant base at the EWTEC conferences in Plymouth (2021) and in Bilbao (2023), and virtual workshops engaging with participants in the benchmarking exercise, device developers and engineering consultancies.

The data generated in the Tidal Turbine Benchmarking Project is being made open access to facilitate future model validation and development across the community.
Year(s) Of Engagement Activity 2021,2022,2023,2024
URL https://www.supergen-ore.net/projects/tidal-turbine-benchmarking