Unidirectional power extraction from a channel connecting a bay to the open ocean

Bays connected to the open ocean by a channel can give rise to large tidal currents which might be suitable for tidalz stream turbines. The maximum power extractable from such a geometry was found by Blanchfield et al. (The extractable power from a channel linking a bay to the open ocean. Proc IMechE, Part A: J Power and Energy 222(3): 289-297) to be given to within approximately 15%, as 0.22 rho gaQ(0), where a is the water level amplitude of the dominant tidal constituent in the open ocean and Q(0) is the maximum volumetric flow rate in the undisturbed state. This analysis is based on turbines operating on both flood and ebb tides. In the present paper, we show that for sites with relatively small bays greater power can be extracted by only operating the turbines in one direction. The pros and cons of this alternative strategy are briefly discussed.