Tidal energy from deep and slow waters

The turbine complements the first full-scale Deep Green device. The underwater power plant will be deployed in 2017 at the Holyhead Deep site off the coast of Anglesey, Wales. During the coming three years, 19 more devices will follow and eventually form an array with an overall capacity of 10 MW.  
Current velocities multiplied by underwater kite
Deep Green is the first device that allows the harvesting of tidal energy in slower waters that have been thought unproductive so far – with low current velocity of 2m per second and in depth of 60 to 120m.
It resembles an underwater kite and consists of a wing and a turbine. The kite has a wingspan of 12m and is attached by a tether to the seabed. It moves along a preprogrammed eight-shaped trajectory and thus increases the water current velocity around the kite by its own speedy movements. The attached turbine therefore works with an up to ten times’ higher current velocity than originally available, Schottel said. The obtained energy is transferred onshore via a cable connection on the seabed.
Customised turbine components
For Minesto, Schottel Hydro is developing a new turbine variant, which is said to optimally fit the requirements of Deep Green: The light weight nacelle power-take-off system includes turbine, drive train, power electrics and auxiliary devices. The drive train concept is based on the proven concept of the Schottel Instream Turbine (SIT) with its inline arrangement of open rotor, rotor shaft including sealing and bearing, planetary gearbox and generator. In contrast to this readily available device with rotor diameters between 3m and 5m, the Deep Green turbine will be significantly smaller and operate at higher rpms. In addition to the turbine engineering and manufacturing, Schottel Hydro will also carry out a full-load test series on a specially built test stand prior to installing the turbine in the third quarter of 2016.   
Power for 8,000 homes
Holyhead Deep provides low flow tidal velocities (1.5m/s – 2m/s mean peak flow) at a depth of 80m to 100m. Twenty devices with a capacity of 500 kW each will be installed in an array until 2019 and reach an overall capacity of 10 MW – enough energy to power 8,000 homes. The project is supported by the European Regional Development Fund through the Welsh Government.