Tidal resource and environmental effects of energy extraction in the Pentland Firth: sensitivity to array layouts and turbulence changes

The Pentland Firth (UK) is a channel between Scotland’s mainland and the Orkney Islands which has high-speed currents. This high tidal stream resource has encouraged the development of a tidal stream energy sector in Scotland, motivated to develop commercial scale tidal farms. It is important to consider how such developments may affect physical processes in the region, and how the layout of arrays could influence this. Tidal dynamics in the Pentland Firth and Orkney Waters (PFOW) have been reproduced by a high spatial resolution, unstructured grid, three-dimensional FVCOM model implementation [4]. The tidal stream turbines were then represented in the model as sub grid scale objects by using two different parameterizations: (1) a momentum sink approach [4]; (2) a momentum sink approach plus changes in turbulence generation and dissipation [5]. The practical resource available from the Pentland Firth, which includes feedbacks of the turbine realistic operations on the flow, has been estimated. In particular, this work explored how different tidal stream turbine arrays can interact in terms of both power resource availability and environmental effects. It has been found that different array layouts (location, number of turbines, spacing between turbines) can allow achieving very different amount of power resource, as well as degree of change to flow velocities. It has also been verified that turbulence changes can lead to an increase in bottom currents in the vicinity of the tidal turbines, which were not detectable using a simple momentum sink approach.