Testing Tidal Energy Systems

1. Testing Tidal Energy Systems Professor Ian Bryden The University of Edinburgh

2. Contents • Part 1 • Consideration of testing in laboratory facilities • Part 2 • Testing prototype devices at sea

3. Tank Testing • Test in still water or moving water? • Large test tanks designed for testing resistance of model vessels are common in many maritime nations

4. Problems with towing tanks • They cannot replicate the turbulent structure of genuine environmental flows • It is not simply a matter of ensuring turbulent intensity is correct but the spatial distribution if turbulence is also a major issue • The flow profile of tidal currents will also not be effectively replicated

5. Progress in Resolving the Quandary! • A numerical model of energy extraction in turbulence flows has been constructed and used to further understand the limitations of tow tank testing • Experimental tests have been conducted in moving and still water in order to quantify the limitations • Tests in still water can be useful, although post processing for the influence of profile is required and • It is vital that turbulence is effectively modelled and this is not a trivial task

6. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. • Scope: • Aim is to provide insight into the rationale and methodology proposed by the University of Edinburgh focussing on device performance. • The Protocol proposed is to be evolved to fit the requirements of the UK DTI MRDF program.

7. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. • Existing performance testing landscape: • No significant history of full-scale grid-connected device operation. • Very limited history of rigorous performance testing of scaled prototype devices • Limited underlying understanding of extreme tidal currents that are of interest to device developers. • BUT: analogy with more mature technologies can provide a kick-start to development of performance testing strategies.

8. Long term industry goals: Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G.

9. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. Short – medium term practical solution:

10. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. • Overarching rationale: • Performance characteristics are defined by a measured power curve, and comparison of estimated and observed annual energy production. • The measured power curve is determined by collecting simultaneous measurements of tidal velocities and power output at the test site at a period long enough to establish a statistically significant database over a wide range of tidal velocities and under varying sea conditions.

11. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. • Procedure to characterise the local resource: • Conducted prior to site development • Rationale. • Site survey. • Resource measurement. • Data analysis.

12. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. • Rationale: • Device performance is fundamentally limited by the magnitude of the resource available for harvesting. • The tidal current resource at a particular location can be reliably predicted based upon harmonic analysis of a suitable in-situ measurement record over a defined period. • The theoretical, technical and practically extractable resource can then be quantified for the location.

13. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. • Site survey (i): • Adequate understanding is required of the site bathymetry and topography to determine the available technical resource. • The International Hydrographic Organisation (IHO) Standards for Hydrographic Surveys have been adopted as a normative reference.

14. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. Resource measurement: Acoustic Doppler device Minimum of three acoustic beams Defined accuracy Binning and record Restrictions on Minimum length guidance siting of device 30-day record

15. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. • Data analysis: • Determine the principal-axis. • Using a recognised method of harmonic analysis determine a minimum resolution of tidal constituents. • Use the determined constituents to produce a tidal and kinetic energy flux prediction spanning • the lifetime of the intended deployment

16. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. • Procedure to characterise device performance envelope: • Rationale. • Resource measurement. • Power production measurement. • Data analysis. • Production of a device specific power curve

17. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. • Rationale: • The performance of an individual device is characterised using a measured power curve. • The power curve relates the variation of electrical power produced by a particular device to the variation in the magnitude of the incident resource.

18. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. Tidal rise and fall: Minas Basin, Canada Source: http://en.wikipedia.org/wiki/Tide • Resource measurement: • Resource and power production data collection must be conducted simultaneously with a synchronised time-stamped record. • Incident resource measurement repeats process adopted for pre-deployment stage (15-day period).

19. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. • Power production measurement: • Electrical power produced is measured using the same approach and standards adopted by the wind industry. • Only net power produced from the device is considered. • To facilitate auditing an independent power measurement provided by a third-party is required.

20. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. • Data analysis: • Each continuous 10 minute piece of recorded data binned in 0.05 m/s discrete current resource bins. • Velocity record integrated across the performance surface area of the device. • Different procedures for fixed and self-orientating devices.

21. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. • Production of a device specific power curve: • Adopting a similar approach to the wind industry, mean values of current resource acting across the performance surface are plotted against device power output for each discrete 0.05 m/s current resource bin.

22. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. • Procedure for monitoring operational status and annual energy production: • Rationale • Measuring operational status • Annual facility power production. • Device availability and downtime. • Attributable external downtime • factors.

23. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. • Rationale: • Longer term performance data is required to fully prescribe both the characteristics of a device and an energy harvesting location. • Understanding of the reliability of design concepts is vital in informing the economics of the emerging sector. • Annual statements of relevant identified parameters provides the necessary data.

24. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. Measuring operational status: (i) Annual facility electrical power production: • Provide copies of statements received from the accredited meter operator detailing energy production by the eligible facility. • Comparisons between the above and the technically extractable resource informed by preceding resource and power curve analysis.

25. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. • Measuring operational status: • (ii) Device availability and downtime: • Number of hours each device in facility available. • Number of hours lost due to: • a device fault. • planned maintenance (program submitted in advance). • (iii) Attributable external downtime factors: • e.g. grid fault (constrained off).

26. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. • Significant knowledge gaps identified: • Large scale impact of harvesting on the resource. • The larger scale impact on the underlying resource of operation is an ongoing research question. • Data from the field is required to validate existing and ongoing modelling and analysis. • An all encompassing answer to the existing research questions has yet to be produced.

27. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. • Significant knowledge gaps identified: • Wave-current interaction. • Whether or not combined wave-current interaction will have significant impact on device performance remains unknown. • Fundamental understanding of wave-current interaction is itself a growing area of research in the oceanographic community. • The underlying science is not ready to be applied to the emerging field of marine renewables.

28. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. • Significant knowledge gaps identified: • AD device sampling and recording periods. • The recording and sampling period of AD devices and the impact they may have on biasing the Protocol results is not fully understood. • The experience of the developer community and survey companies was sought without producing a definitive answer–consensus on initial parameters. • Calibration of AD devices also an ongoing issue.

29. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. • Significant knowledge gaps identified: • The impact of turbulence on device performance. • It remains unclear whether turbulence will have a significant impact on device performance. • Turbulence is not in itself a fully understood concept, and therefore what exactly to measure is also unclear. • What scale of ‘turbulence’ will be of most significance?

30. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. • Summary: • A Protocol for performance testing of operational full-scale devices has been presented. • The Protocol relies on existing knowledge and techniques and is therefore ready to roll out. • Significant knowledge gaps which need to be overcome before a credible international standard can be prescribed or enacted have been identified.

31. Proposed Methodology for the Performance Testing of Tidal Current Energy Devices Couch, S.J., Jeffrey, H.F. & Bryden, I.G. • Discussion points: • Where are we on the timeline towards a credible internationally accepted standard? • Where can we best target research effort to assist in the process of development of a credible internationally accepted standard? • Current level of knowledge, experience and understanding points towards initial adoption of a Protocol to inform the points above on the road to putting a ‘quality’ standard in place.