Misha D. Patel

The development of tidal stream energy sites is constrained by numerous practical, technical, and accessible constraints, including changes in the flow caused by the presence of the tidal farm. Large and complex sites are typically developed incrementally and may involve multiple developers. This regional modelling case study of the Pentland Firth, widely regarded as one of the most significant global locations for tidal energy extraction, investigates these dynamics. This study examines scenarios for the incremental development of the Pentland Firth, incorporating assumptions regarding tidal farm design. The analysis considers a range of configurations, including variations in turbine density and the incorporation of shipping lanes within designated lease areas. The study finds that there are interactions between individually developed tidal farms of the site, but they are moderate with the power in a given farm unlikely to vary by more than 20% (based on a positive interaction), as a result of the development of other farms in other parts of the Pentland Firth. To minimise such array interactions, it is recommended that site leasing be based on the allowable thrust applied to the flow rather than on projected power generation. Furthermore, the findings suggest that the maximum power generated from turbines in the Pentland Firth, averaged over time, is unlikely to exceed approximately 1 GW, broadly consistent with most estimates in the literature.

The effective development of tidal stream energy sites requires an understanding of constraints limiting extraction of the resource. This study considers the implications of certain spatial constraints on the practical tidal stream energy resource. Specifically, we investigate how bathymetry influences array design and how much energy is obtained when heterogeneous arrays (comprising of turbine devices with varying specifications) are deployed at a site compared to homogeneous arrays. A novel framework for designing arrays of homogeneous and heterogeneous turbine specifications is set out and applied to the Inner Sound of the Pentland Firth as a case study. The array that delivers the most energy yield consists of 5 m diameter turbines with homogeneous diameter and control. However, this case achieves the lowest capacity factor due to the assignment of a homogeneous rated speed across the entire site, which does not account for the spatial variability of the resource. A 6% increase in capacity factor is achieved when turbines of heterogeneous control (rated speed = 1.5–2.5 m/s) are deployed across the site, producing a similar amount of power. The power per turbine can be increased if a heterogeneous diameter and control array design is adopted because 69% fewer turbines can be deployed with only a 5% decrease in average power. Heterogeneous array design maximises usage of a site, whilst allowing the maximum allowable diameter of turbine to be deployed in areas, and to exploit the spatial variation of the resource across a site by tailoring turbines to operate at appropriate rated speeds.