Snake Power

Anyone who’s ever tried to defend a sand castle against the onslaught of a rising tide will have some notion of the enormous energy carried by the waves crashing onto our shores. It has been estimated that wave power could supply a quarter of UK energy demand, yet converting it into electricity is more difficult than it looks.

Current research efforts have branched out into many directions, each seeking to tame the ocean into an efficient commercially viable energy source. One such approach is Anaconda, an innovative wave power system invented by physicist Francis Farley and engineer Rod Rainey.

As its name suggests, Anaconda’s shape is reminiscent of a giant snake, consisting of a rubber tube 200 m long and 7 m across, filled with water and tethered below the ocean surface. Unlike its reptilian cousin however, its habitat is not the Amazon river but the UK coastline.

‘As a wave goes by and passes over the tube, it instigates another wave inside the tube, called a bulge wave,’ explains Professor Grant Hearn, who has been entrusted with the development of Anaconda along with fellow University of Southampton researcher John Chaplin.

The bulge wave stretches out the elastic walls of the tube and, as the rubber regains it shape, is pushed along its length, exactly like the pulses of blood travelling down your arteries. The energy from this wave could then be converted into electricity, for example by using a water turbine at the far end of the tube.

Thinking outside the box

‘You’re essentially using the natural resonance of fluid to transport energy,’ comments Hearn. In this way, Anaconda offers a startingly fresh approach. ‘All the other structures tend to use articulations of some sort, and you exploit the relative motion due to that articulation,’ he adds. The Salter duck for example, invented in the 1970s, uses the motion of ‘ducks’ bobbing up and down on the surface of the water.

Despite highly efficient conversion rates, other hurdles have kept the Salter duck out of water. Constantly buffeted by waves and immersed in salty water, wave power devices tend to suffer from short life spans. Anaconda neatly sidesteps this issue by having no articulations to wear down or parts to fail. ‘Rubber is a very resilient material, so it’s not likely to suffer fatigue in the same way that concrete or metal might, ’ says Hearn.

Soaring costs are also a major headache for engineers, but Anaconda’s simple rubber structure has the additional advantage of making it relatively cheap to produce.

In many ways Anaconda seems to outsmart rival technologies, but Hearn remains pragmatic about its merits, seeing it instead as just one of many innovations that will be necessary to build the perfect wave power system. ‘Each exploits a different technique, but eventually a mixture of these things will come together,’ he says.

Hearn and his team still have a lot of fine tuning to do to maximise Anaconda’s efficiency, but if all goes to plan the sea serpent might be rearing its head on the English or Scottish coast in five years' time. Looks like Nessie too might be facing some tough competition.

www.physics.org