Tidal Energy Extraction Environmental Response to Large Scale Tidal Energy Extraction Alice J. Goward Brown*, Simon P. Neill and Matt J. Lewis School of Ocean Sciences, Bangor University *a.j.gowardbrown@bangor.ac.uk INTRODUCTION Tidal streams offer a highly predictable and reliable energy resource The Pentland Firth is a world leading tidal energy resource which is home to four development sites leased by the Crown Estate For a practical resource assessment, tidal resource models require 3-D tidal energy extraction to be implemented. Modelling tidal energy extraction enables the quantification of hydrodynamic interactions with tidal energy arrays Previous research uses depth-averaged tidal extraction techniques which will not accurately represent the vertical profile around the array. METHOD A high resolution (1/600° x 1/600°) Regional Ocean Modeling System (ROMS) model was set-up for the Pentland Firth A force term was added to the 3-D momentum equations at each grid cell within each of the four Crown Estate leased sites Each array was rated to the maximum capacity allowed by the lease Tidal streams in the Pentland Firth - control Schematic of impact of turbine on the velocity profile RESULTS Prior to tidal energy extraction the resource is characterised at each of the leased tidal stream sites : Asymmetry, flood and ebb current misalignment and power density is calculated (Theoretical Resource). After implementing tidal energy extraction the resource is characterised at the same locations (Practical Resource). Control Tidal Energy Extraction Mean velocity difference between control case and tidal energy extraction case – whole model domain Current misalignment at most energetic grid square within each leased site before and after tidal energy extraction CONCLUSIONS 3-D tidal energy extraction is implemented in a ROMS model of the Pentland Firth. Tidal arrays are implemented at each of the four leased sites within the Pentland Firth. The largest effects of tidal energy extraction are localised to the tidal energy arrays. In some cases areas of the arrays see an enhanced velocity on either the flood or the ebb tide Changes to the nearshore hydrodynamics in the Inner Sound region could be a cause for concern and is a topic for further research, Mean velocity difference between control case and tidal energy extraction case – Pentland Firth Spatial mean time series of 3-D velocities at each leased site REFERENCES ACKNOWLEDGEMENTS Baston, S. and Harris, R. E. (2011). Modelling the hydrodynamic characteristics of tidal flow in the Pentland Firth, Proceedings European Wave and Tidal Energy Conference, p. 7. Draper, S., Adcock, T. A., Borthwick, A. G. and Houlsby, G. T. (2014). Estimate of the tidal stream power resource of the Pentland Firth, Renewable Energy 63: 650–657. Lewis, M., Neill, S. P., Robins, P. E., & Hashemi, M. R. (2015). Resource assessment for future generations of tidal-stream energy arrays. Energy, 83, 403-415. Neill, S. P., Hashemi, M. R., & Lewis, M. J. (2014). The role of tidal asymmetry in characterizing the tidal energy resource of Orkney. Renewable Energy, 68, 337-350. Robins, P.E., Neill, S.P., Lewis, M.J. and Ward, S.L., 2015. Characterising the spatial and temporal variability of the tidal-stream energy resource over the northwest European shelf seas. Applied Energy, 147, pp.510-522. Roc, T., Conley, D. C., & Greaves, D. (2013). Methodology for tidal turbine representation in ocean circulation model. Renewable Energy, 51, 448-464. Johnson, K., Kerr, S. and Side, J., 2012. Accommodating wave and tidal energy–Control and decision in Scotland. Ocean & coastal management, 65, pp.26-33. I would like to thank my supervisor Dr. Simon Neill and Dr Matt Lewis for their help and direction. Thanks also goes to Fujitsu who in partnership with HPC wales funded this PhD work.