The talk started with a brief summary of the potential for tidal power in the UK: EU Commission figures from the 1990s estimate that it could provide 5% (18 TWh/yr) of the UK's requirement, although Dr Willden believes it could be closer to 10% - the EU figures are quite old. Tidal power is therefore of considerable interest to the UK in particular.
Although they might at first sight appear similar, tidal power is not quite like wind power: the environment is harsher, with heavier loadings, and of course tidal power is predictable - the time, volume and direction of flow are known in advance - which enables different strategies to be employed.
There is a balance to be found between power coefficient (ratio of power obtained to power available in the stream) and efficiency when extracting energy from tidal flow: developers want maximum power coefficient, while regulators want maximally efficient use of the water resource. Predictably, these two goals cannot be met simultaneously!
The speaker's speciality is device modelling, using numerical modelling and simulation tools: as well as discussing the performance of various different device types, he also laid to rest some basic misconceptions, chief among which is that no device can out-perform simple momentum theory (which sounds obvious, but apparently some people claim otherwise).
During a wide-ranging overview of the field, four different types of turbine were discussed in particular:
Common problems of tidal stream turbines were also discussed:
Comparing the various types, Dr Willden observed that axial-flow rotors are very hard to beat (while engaging in some good-natured banter with the Head of Department, who is currently involved in an attempt to develop a commercial cross-flow turbine!)
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