A semi-submersible tidal power generator based on wind energy technology could allow the UK to meet a significant chunk of its electricity needs from deep coastal waters, according to engineers working on the project.
The TidalStream system, which has already been tested in the Thames, would harness power from the fast-flowing waters found at depths of 40m or more, where an estimated 63 per cent of the UK’s tidal energy resource is estimated to be.
Most tidal energy initiatives focus on shallow waters, which are technically less challenging to tap into, but yield far less power. Tides in the 60m-deep Pentland Firth off the northern tip of Scotland, for example, generate water flows of up to three million tonnes/sec, and tidal speeds averaging 1.5 to 2.2m/sec — some of the fastest in the world. By harnessing this, TidalStream believes this single location could supply five per cent of the UK’s electricity demands.
The system was designed by Dr. John Armstrong, former technical director of Taylor Woodrow’s Wind Energy Group. It consists of turbines mounted on semi-submersible spar buoys tethered to sea bed anchors by swing-arms.
If maintenance is required, water used as ballast is pumped out of the spar, allowing the turbine to roll over and swing up to the surface. It is then accessible in the same way as a fixed platform such as an oil rig.
‘An operational system should be up and running by 2010, subject to funding,’ said company director Michael Todman, a former Rolls- Royce chief engineer.
‘One of the biggest advantages of this is that maintenance does not involve anyone having to get into the water.’
The turbines consist of four 20m rotors. Each four-rotor turbine is rated at 4MW. They operate while floating submerged in the middle of the tidal stream. A swing-arm allows the turbine to follow the water’s flow direction as the tides change to generate the maximum power. They can be floated into place before their ballast tanks are flooded to submerge them, removing the need for the use of cranes and barges.
According to TidalStream’s calculations, turbines with a capacity equivalent to a 1200MW nuclear power station would take a sea area of 14km2.
The cost of the turbines and their electricity should be comparable to that of offshore wind farms, but with the advantage of 100 per cent predictability of output, claim the developers.
A model of the concept has been successfully tested in the Thames at Chiswick, and TidalStream is now seeking funding to take the project further.
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