Quantification of tidal power in a highly dynamic estuary.

Stephen Nash, Anna Phoenix

Tuesday 30 june 2015

9:00 - 9:15h at Antarctica (level 0)

Themes: (T) Special session, (ST) Marine renewable energy

Parallel session: 4D. Special session: Marine Renewable Energy

The Shannon River and its estuary is one of the largest such systems in the British Isles. The tidal range at the mouth and head of the estuary is over 5m and 6.5m, respectively, during normal spring tides, inducing peak currents of up to 3m/s in water depths of 35m. The estuary has been rightly identified as a potential location for tidal energy extraction; however, little detailed analysis has been carried out to determine accurate potential. This research presents a methodology for accurately determining the tidal stream resource in an estuary. Traditional methods for calculating the power that is available from tidal currents involve using either the peak or time-varying current velocities. In either case, the total velocity vector is employed. However, tidal turbines cannot rotate into the tidal stream as it changes direction during different stages of the tide. In this research, tidal ellipses are constructed and used to determine the primary direction of flow and only those velocity components aligned with the primary direction of flow are used to calculate available power. It is shown that using the total velocity vector for power availability calculations can significantly over-predict the tidal energy potential. Tidal harmonic analysis is also employed to facilitate long-term forecasts of current velocities and the resulting available power. The model results are used to determine the frequency of occurrence of particular current speeds and power availabilities which can then be used to determine the most suitable turbine to be deployed at a site.