Tidal turbines

Two British engineers have developed a marine energy device design that they claim could generate substantial amounts of cheap electricity from deepwater tidal flows within five years.

TidalStream recently reported that its turbine platform design - nicknamed Triton - has successfully undergone validation testing at the deep-water test basin at Ifremer in Brittany, France.

The developers believe the model-scale device demonstrates the design is practical for tidal stream capture with major advantages over other renewable energy systems. They point out the UK has half the tidal stream resource of the whole of Europe - the equivalent of several nuclear power stations in energy terms - with no CO₂ emissions, fewer concerns over safety and at a potentially lower cost.

The developers explained a tidal stream turbine works like a wind turbine underwater, adapted to deal with the density and flow rates of water, and would be located in the highly energetic channels close to shore around the north of Scotland, Ireland and England. TidalStream stated its design differs from other attempts to capture power from the sea in that it can generate a large amount of power, 10MW, from a single installation. It was claimed a tidal farm of just 50 Triton turbines could supply the needs of more than 250,000 homes

Triton can be operated in two distinct modes. The first mode is a catamaran, which can be floated out to site and deployed and maintained without the use of cranes or divers. The other is a vertical submerged spar supporting up to six turbines across the flow.

The model tested in France was 3m in size. It is hoped a full-scale version could be installed in selected places around the UK. Once in position, it would reportedly have the potential to span a water depth of more than 60m, but with only a small amount of the structure showing above water. When floating it becomes a 1,200 tonne catamaran.

‘Up to now no one has managed to create a practical tidal stream system that is also at an economically large size with simple access for maintenance,’ explained John Armstrong, one of the partners in the project. ‘Triton also has twice the output of the largest wind turbine yet installed offshore, so has a huge generating capacity.

‘A key feature of the design, and a likely shortcut to success, is to have turbines which use technology and components developed from the wind industry that already exist and have been developed over the last 30 years,’ Armstrong added. ‘It is only the support structure that is truly new and innovative.’

The TidalStream partnership was founded in 2005 by John Armstrong and Michael Todman, who have backgrounds in the wind, marine and power industries.

John Armstrong was technical director of the Wind Energy Group. Michael Todman was chief engineer at Rolls-Royce, specialising in marine propulsion turbines and power generation systems from concept designs to in-service support.