The turbines in operation float submerged in the tidal stream, free to swing and heave in the turbulent water flow. Loads are several times those on a wind turbine, and the sheer size of the turbine, combined with the 60m water depth, makes any kind of fixed structure almost unthinkable. But with a simple seabed anchorage, and with cable connection achieved from the surface, a semi-submersible concept such as this is entirely plausible.

Shown below is a part view of a 7 x 4 array (ie 4 diameters - 200m across the stream, and 7D - 350m downstream) of 10 MW Triton 10’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.

In operation, these turbines will be silent and unobtrusive compared to wind turbines. They will produce energy  predictably, enabling premium pricing from forward contracting of electricity supply to a pre-set date and time.

Because 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 no more danger to sea fauna than the keel of a yacht (and much less than the danger of propeller impact from ships). If anything, the bases may provide shelter for seabed creatures that would otherwise be swept away by the tidal flow.

The turbines would be free to swing round to follow the flood and ebb tides, see below. There are various options to ensure that this is done reversibly, to avoid excess cable wind-up.

Whatever type of tidal turbine is deployed, existing shipping movements will inevitably be affected and sea traffic, apart from maintenance workboats, will need to be kept clear of 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 routine or unplanned maintenance such as the removal of performance-destroying 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 where shipping would need to be re-routed to avoid the obstruction. In reality, it would be far safer to simply provide exclusion zones that are then well marked.  In the Pentland Firth shipping goes both along the channel and across it with little constraint in passage routing.  The adoption of marked navigation channels similar to the English Channel would be required.

 

Operation

TidalStream TRITON

The enabling technology for tidal turbine deployment

Provides the most cost effective and  efficient turbine deployment system

Up to 10MW from a single installation

Did you see TidalStream?