Anaconda Advances Wave Power

Could an Anaconda be the best way to extract power from waves?  Possibly not the snake itself, but it's namesake - a rubber tube capable of harvesting wave power...

Chris - Scientists have been exploring how they can use a giant rubber tube which has been called the Anaconda to generate electricity from the sea. Professor Grant Hearn is from the University  of Southampton. Hello, Grant.

Grant - Hey.

Chris - Welcome to the Naked Scientists. What actually is your device?

Grant - The device was really invented by Francis Farley and Rod Rainey. Essentially it's a long rubber tube and it's closed off at one end and moored. At the other end you have a power take-off system. Essentially you keep the rubber tube close to the free surface. It's actually facing the on-coming wave. It's like it's at right-angles to the wave-front. As the waves come past the tube then they set off what is called a bulge wave inside the tube. As this bulge wave travels along the tube it gradually gathers more and more energy. One power take-off system we've tried is that as the wave travels along the tube essentially you can convert that energy into potential energy by allowing the water, which is being pumped to go through a valve system, and you generate a high pressure level. Then,  you have a low level and you pass the water from one to the other through a turbine. Hopefully you can take the energy out of the bulge wave.

Chris - How much energy do you think you could make this way?

Grant - What they're thinking about is devices which will generate of the order on average one megawatt which may have a peak of three megawatts and an average over a year of one megawatt. If you assume that you have essentially half a kilowatt per person then that's one device that will provide energy for around 2000 homes.

Chris - Would you just have one tube in isolation or would you have rafts of these out at sea somewhere?

Grant - You would probably have a farm and at the moment what we're trying to do is understand how best to operate the tube in terms of things such as the pressure in it. The question would be, would you have tubes which are all identical or would you have tubes with different properties? If you put a tube with a different pressure in then you can take energy from a different wave frequency. So what you might then do is use a range of devices such that they're all taking power from a mixed sea state.

Dave - There's been lots of other ideas of getting energy out of waves. What's the advantage of the Anaconda over them?

Grant - If we look back in the mid 70s-early 80s most of them were mechanical devices. Salter's Duck was essentially a set of segmented sections which rotated around the cylinder and you essentially used the relative pitch of the ducks as they're called and the back spine to actually take the energy out. Cockerell Rafts were simply using the relative motion of the rigid structure. You have to have squash plates. Then you have things like oscillating water columns. In this case the only movable part is the rubber so you're actually using the stored elastic energy in the walls of the tube to actually convert the energy external into the energy which flows internally.

Chris - So it should be a lot more robust. Finally, what stage of development is this at and when can we see it in the North Sea?

Grant - I can't answer when it will be. Rod Rainey and Francis think that once we've finished the work it'll be possibly five years. At the moment myself, with John Chaplain, are entering a two year research programme sponsored by the Engineering and Physical Sciences Research Council in the UK. There we're doing both experiments at different scales and we're also developing mathematical models because the difficulty with this structure is that we know the physical boundary conditions but we can't actually put numbers on them. We have an interesting mathematical problem which is: how do you solve the problem and determine the boundary conditions at the same time?