Turbine to produce electricity from river or tidal streams

A UK clean-tech start-up is designing a new turbine for generating electricity from river or tidal streams.

The device, from Cambridge-based Green-Tide Turbines (G-TT), works by causing the flow of water to rotate before capturing the rotational kinetic energy with a reaction turbine.

This differs from current technologies that use bladed fans or oscillating hydrofoils to convert kinetic energy in a flowing current of water into rotary motion driving a generator.

With the G-TT device, the water first flows through a duct, where it meets a series of stator blades that cause the water to rotate and form a vortex. The water then flows through a series of channels that are angled in a way that makes the fluid travel in the shape of a helix. The channels dogleg, causing the water to change direction and lose momentum.

The changing direction creates equal and opposite forces that act tangentially to the axis of the turbine rotor. This creates the torque needed to power a generator. 

Michael Evans, the inventor and chief executive of G-TT, said that his company’s design puts less strain on the turbine and reduces failures that would be a result of fatigue. He pointed out that this greatly reduces operation and maintenance costs.

Evans is finalising the design of the device with the help of researchers in the fluid and jet engine laboratories at Cambridge University and computational fluid dynamics (CFD) modellers at Cambridge Consultants.

The ultimate goal will be to develop a 2MW tidal turbine device measuring 15m in diameter. Currently, the team is testing a device a fortieth of that size.

Evans expects to produce a prototype device by 2012 that measures 1m in diameter. At that scale, the turbine would be ideal for generating electricity from rivers. He estimated that a 1m-diameter river turbine could produce about 25kW.  

Once the river turbine is developed and proven, Evans plans to split his company so it has a wholly owned subsidiary for promoting the device to the developing world. ‘We will be forming partnerships with manufacturing companies in Brazil, India and China to manufacture our devices for us and then we will be in those markets,’ he said.

Evans expects that it will take a longer timeframe of possibly four to five years to test a full-scale prototype of the tidal turbine. He hopes that the commercial success of the river turbine will help his company leverage more funding.

‘Tidal turbines are going to cost in the region of £20m to get to market,’ added Evans.

He said that he only needs another £500,000 to prepare his turbine for river applications. G-TT is receiving support from angel investors and it has been promised further funding from the Carbon Trust, although the fate of that grant rests in the hands of the coalition government, which has announced that it is restructuring public funding for ’green’ energy programmes.  

‘One of the anxieties we have is there is going to be a transition period and that is going to create a lot of uncertainty in the investor community,’ added Evans. ‘That’s going to have a knock-on effect on our ability to raise future funding. I think the government should recognise that and put something in as a temporary fix to give our investors some confidence that there will be continued support.

‘We’re a long way from market and the technology is really expensive to develop. There is a very large onus on us to give operational data over a significant period of time before the power generation industries will even consider new technologies.’