Wave Power – Air Spring Bellows for Pelamis

The power of oceanic waves

According to estimates of the World Energy Council (WEC), wave power stations could satisfy about fifteen per cent of global energy demands. Europe's coastline alone is pounded each year by waves with an aggregate energy quantity of about a billion megawatt hours. This energy could cover 5 to 10% of the power consumption in the EU countries. This renewable, non-polluting and climatically compatible energy source is sure to trigger growing interest in harnessing water power in years ahead.

The Scottish company Pelamis Wave Power Ltd. (PWP) has developed a solution for gaining electricity from wave power. Four gigantic steel cylindrical sections are linked together by means of hinged joints. This unit floats snakelike on the surface of the water. It is moored to the seabed in such a way that it is always positioned head on to oncoming waves. The rise and fall of the waves causes the cylindrical sections to articulate, causing resisting motion between the sections. Hydraulic cylinders in three power modules between the floating sections absorb the movement, causing their pistons to pump six hydraulic generators which generate 750 kilowatts of electricity. A seabed cable links the offshore power station to the power grid on land.

Pelamis converts up to 80% of the absorbed wave energy into electric energy. The offshore power station operates most efficiently at a distance of five to ten kilometers from the coast. The sea there is about fifty to one hundred meters deep and the waves three to six meters high, which are optimum conditions for this kind of energy generation. At the same time, the costs for the seabed cable are lower here than they would be if the station were positioned further out.

At the Pelamis ocean power station, innovative ContiTech air spring bellows ensure ultra-flexible, hard-wearing seals between the steel sections and hydraulic cylinders. The experience gained and the material range used for the product range of expansion joints were able to be drawn on for the development of these new types of oil proof and sea water proof special bellows with connectors of stainless steel.

PELAMIS in operation

• A 120 meter long Pelamis ocean power station off the coast of the Orkney Islands at the northern tip of Scotland, where the North Sea meets the Atlantic, has been demonstrating high performance and endurance since 2004. And next year Scottish Power will be setting up the world's biggest wave farm off the coast of Orkney.
• At the moment, three sea snakes – each about 140 meters long and weighing 750 tons – are installed off the coast of Povoa de Varzim in northern Portugal; it marks the first instance of commercial use of the energy generation system. If Pelamis lives up to expectations, 28 additional machines will be joining those already in service.