Seaworthy power

Turbines using existing designs could be placed inside large-bore underwater pipes to produce a reliable, clean and cost-effective source of tidal power, a Dorset engineer claims.

Don Cutler, founder of the Weymouth, UK-based engineering firm Tekflo, which developed equipment for water systems and North Sea oil rigs, produced his design after hearing that Portland Harbour was being investigated as the possible site for a wind farm. He has now set up a company, SusGen, to develop his system in collaboration with Southampton University. A working model generating around 100kW should soon be tested offshore, he said.

In the Channel, tides flow in relatively straight lines, varying from a maximum of five knots to zero before the process reverses as the sea flows back. In Cutler’s design a simple framework is attached to a reinforced-concrete base consisting of a hollow box with open ends which is fixed to the seabed by anchors or screws.

The turbine and generator are positioned in the mid-section of the box, and are fitted as a module so they can easily be removed for maintenance. Each end of the box is slightly flared to act as a funnel for the water, gathering it into a narrower section that forms the entrance to the turbine. This also extends the useful energy capture when the tide’s direction changes.

The design uses multi-bladed turbines driving electric generators, all of which are positioned under the sea to minimise their environmental impact. In tests, simple six-blade turbines have achieved an efficiency of 50 per cent, but Cutler is working to develop a more efficient system, likely to be made from carbon fibre or reinforced glass fibre and featuring a twisted design where the angle of attack changes along the blade length.

The generators would be located along the south coast and connected to power cables linked to a shoreside converter. By transmitting the power at a high voltage and low current, power loss would be minimised. Conversion of energy into a form suitable for the national grid would take place onshore.