Tuesday, July 17, 2012

Pelamis Wave Power

Ocean waves represent a considerable renewable energy resource. Waves are generated by the wind as it blows across the ocean surface. They travel great distances without significant losses and so act as an efficient energy transport mechanism. Waves generated by a storm in mid-Atlantic will travel all the way to the coast of Europe without significant loss of energy.

All of the energy is concentrated near the water surface. This makes wave power a highly concentrated energy source with much smaller hourly and day-to-day variations than other renewable resources such as wind or solar. Conveniently, the seasonal variation of wave power closely follows the trend for electricity consumption in Western Europe.

The western seaboard of Europe offers an enormous number of potential sites. The most promising sites are off the UK, Ireland, France, Spain, Portugal and Norway. There is sufficient energy breaking on the UK shoreline to power the country three times over.  However, it is not practical to recover all of this energy. The economically recoverable resource for the UK alone has been estimated to be 87TWh (terawatt hours) per year, or about 25% of current UK demand.

OPD was established at the beginning of 1998 by Dr Richard Yemm to develop the Pelamis Wave Energy Converter. This device is known as a 'point absorber' and can effectively focus energy from a wide area by interacting with an area of waves much larger than its physical size. As it is flexibly moored it swings head-on to the incoming waves and can therefore span successive wave crests.

The Pelamis is a semi-submerged, articulated structure composed of cylindrical sections linked by hinged joints. The wave-induced motion of these joints is resisted by hydraulic rams, which pump high-pressure oil through hydraulic motors via smoothing accumulators. The hydraulic motors drive electrical generators to produce electricity. Power from all the joints is fed down a single umbilical cable to a junction on the sea bed. Several devices can be connected together and linked to shore through a single seabed cable.

Following six years of detailed design and development, OPD has completed the build of the first full-scale Pelamis Wave Energy Converter. The 750kW machine measures 120m long by 3.5m wide (about the size of four train carriages) and weighs 750 tonnes fully ballasted. In August 2004 Pelamis was connected to the UK gird at the European Marine Energy Centre (EMEC) in Orkney to be tested. This is the first offshore wave energy to be exported into the UK electricity system.

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