An Ocean Teeming with Opportunity

January 2011The World Energy Council estimates the global potential of wave energy at one terawatt – equal to the output of 1,000 power plants. The Pelamis wave power station points the way to the promising future of this climate-friendly form of energy. As development partner, ContiTech is also on board the floating power pack.

How will we sate the constantly growing hunger for energy in the future? On the one hand, we consume more energy all the time, while, on the other hand, producing it raises a number of questions. Reserves of fossil fuels like oil, gas and coal are dwindling away. Other energy carriers are controversial or are still in the developmental phase. So it comes as no surprise that eyes are all directed to renewable energies, which use natural resources like sun, water, wind and other free possibilities to generate energy.

ContiTech's Air Spring Systems business unit makes a contribution to the Pelamis wave energy power plant. Air, fire and the sun is used elsewhere. What is more logical, then, than to also generate energy from water – explicitly from the force of ocean waves.

Together with development partners like ContiTech, Pelamis has created a world-renowned product. Unlike many others of its kind, it has long since passed beyond the trial stage. The first Pelamis prototype was already put into operation in 2004 – off the coast of Scotland.

Anyone who has ever been mowed down by the immense power of a wave while surf swimming will intuitively understand that there can be a huge amount of force in ocean waves. But how can wave power be transformed into electricity?

Pelamis consists of five gigantic steel tubes, positioned one behind the other and all connected by hinges. The 180-meter-long and 1,300-tonne system floats on the surface of the water at some distance from the coast. It is moored at cross angles to the waves by means of anchors. The steel tubes adhere to the constant rise and fall of the waves.

“Via a hydraulic device, the bobbing force drives generators, producing in this way the coveted current,” explains the Pelamis management. “A unit can generate up to 750 kilowatts and thus convert up to 80 percent of the wave energy absorbed. Ocean depths of around 50 meters are optimum locations for the latest generation of power stations, because the waves generated there are normally three to six meters high.” This is true, in any case, where the project partners operate such converters – preferably along coastlines with regularly high waves. Orkney, off the Scottish mainland, is pounded by four-meter high waves from the Atlantic nearly twenty-four hours a day. When turbulent autumn storms are raging, the sea can be extremely rough, with waves up to 25 meters high. To deal with this, Pelamis is constructed in such a way that it simply ducks through the highest waves, thereby solving one of the biggest technical problems.

Coping with the problems of durability and constant exposure to stress in aggressive salt water was a whole lot more challenging. Where adjacent tubes meet, enormous hydraulic rams positioned between them pump high-pressure fluid through hydraulic motors. Permanently protecting their pistons from corrosion and vegetal growth was a conundrum until ContiTech Air Spring Systems got into the picture. Now gaiters specially reengineered for this task do the trick. “Combining our product know-how for rubber expansion joints and air springs, we developed a pressure resistant sealing element which exhibits outstanding resistance to oil and salt water and at the same time can withstand high dynamic stress,” says Dr. Olaf Kluth, head of the Industry segment at ContiTech Air Spring Systems, explaining the key functions of the gaiters. Fabric reinforcement of the gaiter walls enables them to even withstand high water pressure and the still greater force of collisions with flotsam. Once again rubber has proven to provide very effective resistance to salt, sun and ozone, as well as mussel and other organic growth.

With the E.ON energy supplier now on board, Pelamis, originally a university project, has already come very close to commercial exploitation. At present power stations are planned off the coasts of Portugal and Scotland. “Marine technology for the purpose of generating electricity is still new terrain for industry. Pelamis marks our first major investment in a wave power station. We ascribe enormous renewable-energy-generating potential to this project,” explains Dr. Paul Golby, general manager of E.ON UK, the British subsidiary of E.ON.

The domestic energy utility Scottish Power Renewables also plans to anchor wave power stations off the coast of Orkney, contingent on successful testing of the second-generation Pelamis, the P2. The planned power stations with a total output of around 50 megawatts, could then supply enough power for up to 33,000 homes. The World Energy Council has determined that wave power stations could theoretically cover 15 percent of the worldwide demand for electricity.