Power peaks against installed capacity in tidal stream energy

Owing to the natural variability of tidal flow, the curve of available power against time at the site of a tidal stream plant is typically spiky. This means that, for the power peaks to be fully exploited, the installed capacity of the plant would have to be large relative to its mean power output. In practice, a balance should be struck between the percentage of the total resource that is exploited and the installed power (and installation cost) of the plant. The purpose of this study is to examine this problematic through a case study: a tidal stream plant proposed for Ria de Ortigueira, a large estuary in north-west Spain with a tidal range of 4.5 m. A numerical model of the estuary hydrodynamics is implemented, calibrated and successfully validated using field data. The model is used to determine the tidal flow patterns. The question of the installed capacity is examined for the two areas with the greatest potential as tidal stream sites. It is shown that the nominal power that is required can be greatly reduced by relinquishing the peaks of the power curve, with only a slight reduction in the energy output.