Humber rides the wave

A full-scale demonstrator of what is claimed to be the first tidal-stream-energy device for estuaries is to be deployed in the Humber Estuary.

The £1m Neptune Proteus NP1000, from East Yorkshire-based Neptune Renewable Energy, will be completely constructed this month and commissioned shortly afterwards.

Jack Hardisty, technical director of Neptune, said that, once fully commercialised, there will no devices like it on the market.

‘We are not aware of any other device designed to capture the shallow-water resource,’ he said. ‘Proteus has a lightweight, exoskeletal structure designed to optimise estuarine locations where there are not the problems and stresses associated with wave activity but where, nevertheless, strong tidal regimes can be found. This produces very considerable build-cost benefits.’

The turbine is built with a distinctive square-turbine cross section, which Hardisty said generates 30 per cent more electricity per unit channel width compared to circular turbines.

‘The capture area of a square is about 30 per cent greater than the capture area of a circle that has the same diameter as the side length of the square -technically it is 4/pi,’ he said.

The Proteus is also designed with patented flow-control shutters to maximise the area of water hitting the turbines, thus increasing torque and power output.

Hardisty said the flow-control shutters help maintain tip-speed ratio -the ratio of the tip speed to the fluid speed – and that effects the turbine’s overall efficiency.

‘For the vertical axis, crossflow rotors on Proteus maximum efficiencies are achieved at a tip-speed ratio of 0.35,’ he said. ‘The computer-controlled shutters direct the flow at variable angles onto the blades in order to maintain this optimum tip-speed ratio, regardless of flow speed, and thus maximise the electrical output.’

Neptune Renewable Energy stated that the Humber Estuary was selected for the first deployment of Proteus as, given its depth and tidal flow, it is considered one of the best locations in the British Isles for tidal-stream power.

It is estimated that, once in situ, the Proteus should generate at least 1,000MWh/year.

Neptune Renewable Energy claims that the Proteus will have minimal impact on the environment because it is a moored system. Also, the bulk of its mainly steel construction can be recycled once decommissioned.