The turbines in operation float submerged in the tidal stream, free to swing and heave in the turbulent water flow. Shown above is an artist’s impression of part of a 7 x 4 array (ie 4 diameters - 200m across the stream, and 7D - 350m downstream) of 10 MW Triton 6’s in the Pentland Firth. This amounts to 14 turbines, ie 22 turbines providing 140 MW per square kilometre. So 120 tidal turbines of capacity equivalent to a 1200 MW nuclear power station would occupy a sea area of 8.4 square km. In contrast, a 140 MW wind farm would occupy roughly 4 times as much upland or sea area.
The Triton platform system is designed to minimise the impact it will have on the environment:
Full environment studies would be carried out for specific site locations to ensure any impact on mammals, diving birds, migratory routes, plants or other site specific features are fully understood and mitigated. Tidal turbines are quieter and far less obtrusive than wind turbines. Typically, as the rotors turn so slowly (12 m/s or so tip speed compared to 70 m/s or more for a wind turbine) they are likely to present less of a danger to sea fauna than the keel of a yacht (and much less than the danger of propeller impact from ships). Evidence to support the minimal impact on mammals and other sea life is being gained by first generation tidal turbines. The Siemens MCT SeaGen in Strangford Lough has been operating for over three years and has had very close monitoring of any environmental issues so far without any detrimental impact.
Whatever type of tidal turbine is deployed, existing stakeholders will be affected in some way. Sea traffic, apart from maintenance workboats, will need to avoid tidal turbine areas. This is true even if the turbines were fully submerged, as they would require bringing to the surface at regular intervals for both unplanned and planned maintenance such as the removal of performance-degrading marine fouling on the blades. With a tidal farm of say 50 units, each requiring two ‘retrievals’ per year for routine maintenance and de-fouling, that would mean 100 occurrences per year where shipping would need to be re-routed to avoid the obstruction. In reality, exclusion zones are required that are then well marked.
Fishing in the immediate vicinity of any installation would need to be controlled to prevent fouling with nets or anchors with resulting damage on both sides.
Renewable Tidal Energy - current and stream - TidalStream development
Halving the cost of tidal energy