Wave energy converters
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Contents
Introduction
Vast and reliable, wave power has long been considered as one of the most promising renewable energy sources. Wave Energy Converters (WECs) convert wave power into electricity. Although attempts to utilize this resource date back to at least 1890, wave power is currently not widely employed (Miller,2004[1]). The plethora of innovational ideas for wave power conversion have been invented in the last three decades, resulting in thousands of patents over recent years. At present, a number of different wave energy concepts are being investigated by companies and academic research groups around the world. Although many working designs have been developed and tested through modelling and wave tank-tests, only a few concepts have progressed to sea testing. Rapidly decreasing costs however, should enable wave plants to compete favorably with conventional power plants in the near future (Pelc and Fujita,2002[2]).
Classifications
Wave Activated Body
Wave activated bodies (WABs) are devices with moving elements that are directly activated by the cyclic oscillation of the waves. Power is extracted by converting the kinetic energy of these displacing parts into electric current. One example of such a WAB, is made by a single floater connected to a linear magnetic generator fixed to the seafloor. In other cases, only parts of the body are fully immersed and dragged by the orbital movements of the water. In order to maximally exploit this resource, the moving compounds need to be small in comparison to the wave length and preferably they are placed half a wavelength apart. For these reasons, wave activated bodies are usually very compact and light. The main disadvantage of this type of wave energy converters is the high cost of the power generator needed to convert the irregular oscillatory flux into electricity.
The "DEXA", developed and patented by DEXA Wave Energy ApS, is an illustrative example of a WAB. The device consists of two hinged catamarans that pivot relative to the other. The resulting oscillatory flux at the hinge, is harnessed by means of a water-based low pressure power transmission that restrains angular oscillations. Flux generation is optimized by placing the floaters of each catamaran half a wavelength apart. A scaled prototype (dimensions 44x16.2m) placed in the Danish part of the North Sea should generate 160 kW (Kofoed,2009<ref>Kofoed, J.P., 2009. Hydraulic evaluation of the DEXA wave energy converter. DCE Technical Report No. 57. Dep. of
Civil Eng., Aalborg University, 23 pp.Cite error: The opening <ref> tag is malformed or has a bad name;Martinelli et al.,2009<ref>Martinelli L., Zanuttigh,B., Kofoed, J.P., 2009. Statistical analysis of power production from OWC type wave energy converters. EWTEC Conference, Uppsala, 7-11 Sept 2009, electronic format, 9 pp.Cite error: The opening <ref> tag is malformed or has a bad name). Full-scale models are thought to be able to generate up to 250 kW.
Overtopping Devices
Point absorbers, Terminators and Attenuators
Wave energy converters as a coastal defense technique
See also
References
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