Tube test

Snake-like rubber devices being developed and tested in the UK could provide wave power technology with a difference within five years. Siobhan Wagner reports


Giant rubber tubes anchored below the sea’s surface could each produce 1MW of power for use in homes in the UK and around the world, according to the technology’s developers.

Called the Anaconda because of its long, snake-like shape, the device is being developed and tested at Southampton University and could be commercially available in the next five years.

The tube is filled with water and closed at both ends, with one end facing the oncoming waves. A wave hitting the Anaconda’s end squeezes it and causes a ‘bulge wave’ to form inside.

John Chaplin, one of the Southampton engineers testing the device, said it works the same way a pulse is measured.

‘It’s the same mechanism by which you feel your pulse in your arteries,’ he said. ‘What happens there is your heart gives a thump and basically a bulge travels down your arteries at a certain speed.’

As the bulge wave runs through the Anaconda, the initial sea wave that caused it runs along the outside of the tube at the same speed, squeezing the tube more and causing the bulge wave to get bigger. This then turns a turbine fitted at the far end of the device, and the power produced is fed to shore via a cable.

Chaplin said the Anaconda is a better option than other wave energy devices because it is made of rubber. This makes it much lighter than other devices, which are primarily made of metal and need hydraulic rams, hinges and articulated joints.

‘As far as we can make out it is much simpler than those devices,’ he said. ‘And I think it has a good chance of surviving the extreme conditions that failed many past technologies.’

Yet the Anaconda is still in its early stage of development — the idea for the device was only thought up a few years ago by retired physicist Francis Farley and Rod Rainey of technology-based consultant Atkins Global.

Rainey had asked Chaplin and his colleague Grant Hearn at Southampton to test the devices in their laboratory two years ago.

The Southampton team is currently testing small tubes with diameters of 250mm and 500mm in its tanks to assess the Anaconda’s behaviour in regular, irregular and extreme waves. Chaplin and Hearn, meanwhile, are measuring parameters such as internal pressures, changes in tube shape and the forces to which mooring cables would be subjected.

As well as providing insights into the device’s hydrodynamic behaviour, the data will form the basis of a mathematical model that can estimate exactly how much power a full-scale Anaconda would produce.

Chaplin said a full-size Anaconda — designed to be deployed in depths between 40m and 100m — would measure 200m long x 7m in diameter. ‘That’s a very big rubber tube,’ he said. ‘No-one has built one that big.’

Initial assessments indicate that the Anaconda would be rated at a power output of 1MW (approximately the electricity consumption of 2,000 houses) and might be able to generate power at a cost of 6p/kWh or less.

While this is almost twice as much as the cost of electricity generated from traditional coal-fired power stations, the researchers said this is much better than the generation costs for other leading wave energy concepts.

‘The Anaconda could make a valuable contribution to environmental protection by encouraging the use of wave power,’ said Chaplin. ‘A one-third scale model of the device could be built next year for sea testing, and we could see the first full-size device deployed off the UK coast in around five years’ time.’