Tidal stream power in the Pentland Firth – long-term variability, multiple constituents and capacity factor

The Pentland Firth, Scotland, is one of the World’s prime locations for the eventual installation of large farms of tidal stream turbines. This paper seeks to improve the upper bound estimate of available power output obtained by Adcock et al. (2013) who used a depth-integrated numerical model of the region containing the Pentland Firth with the outer boundary forced solely by M2 and S2 tidal constituents. Herein, the analysis is extended to include six additional tidal constituents and the model run for 11.5 years, more than half of the 18.6-year lunar nodal cycle, to allow variations over this to be analysed. The consequent increase in available power is estimated, and the variation in power output over an 11-year period is examined. Although further power could theoretically be extracted from the additional six tidal constituents, this would require the tidal turbine farm to have such a low capacity factor that it would probably be economically unfeasible.