Turning the tide

A renewable tidal energy technology which eliminates the need for moving parts and could prove more competitive than fossil fuel power has been developed at Imperial College London spin-out HydroVenturi.

A submarine venturi — a funnel- shaped tube originally used to measure flow rate — is placed in a primary flow (tidal or non-tidal) to accelerate the water and create a subsequent pressure drop which can be used to drive a turbine. Relying on Bernoulli’s theory, which stipulates that an increase in fluid rate produces a reduction in pressure, the device generates a reduction at the point where the flow is most constricted. This pressure drop is used to suck air from another location into the primary flow. It is this suction — which can be moved through a pipe to the shore up to 50m away — that drives an air turbine. These are significantly smaller than water turbines and can be driven at a very high speed. Removing the need for complex mechanical and electrical parts not only avoids expensive maintenance issues through corrosion of engineering materials and replacement of parts, but also enables the system to be located in differing bodies of water and depth than conventional technology. This allows electricity to be generated at costs competitive with fossil fuels, with low recurring maintenance or fuel costs, its developer claims. HydroVenturi chairman Dr John Hassard explained that the versatility of the technology gives it a number of advantages over conventional methods. ’Our approach is much more widely applicable. We can operate in far slower waters than conventional systems and at different depths. The system can go from two to 30m easily, whereas conventional systems are constrained to depths of between 30m and 50m in locations such as in tidal inlets. ’ The technology also benefits from water being denser than air. Water weighs 1,000kg/m3 while air is 1kg/m3, explained Hassard, so water has a thousand times more mass density — and it is this greater kinetic energy potential that underpins the technology. ’What we realised was, water can be induced to create power without moving parts,’ he said. The technology has so far attracted a £2.5m development grant from Porton Capital and £200,000 from the Carbon Trust. Imperial Innovations — the commercialisation arm of Imperial College — has the right to invest a further £900,000. Despite this, Hassard is frustrated over the UK’s tardy approach to research development. Consequently, the next installation will be in New Zealand, where he claims: ’We will be undercutting gas turbines very shortly. ’We have talked to many UK groups, but because of the legislation you have to go through it is easier to make progress outside the country. The UK probably has the best resource and leads the way in tidal development but this approach is killing it,’ he said.