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Preliminary Design of a Floating Wind Turbine Support Structure and Relevant System Cost Assessment

pubblicazioni - Articolo

Preliminary Design of a Floating Wind Turbine Support Structure and Relevant System Cost Assessment

and Relevant System Cost Assessment Claudio Andrea Casale*, Ettore Lembo*, Laura Serri*, Silvano Viani* OWEMES 2009-Offshore Wind and Other Marine Renewable Energies in Mediterranean and European Seas Brindisi, 21-23 Maggio 2009 * CESI RICERCA This paper describes the preliminary project of a floating support structure for offshore wind turbines that has been developed by CESI RICERCA, in consideration of the prospects that this kind of structure could hold with regard to its possible use for exploiting wind resources in the windiest sea areas along the coasts of Italy (Sardinia, Sicily, Apulia). A review of the various types of floating structure that have been devised worldwide for wind turbines has made it possibile to single out the floating structure that looks most interesting from the technical and economic standpoint. Specifically, the selected structure is of the Tension Leg Platform (TLP) type. It consists of a nearly fully submerged hexagonal platform, which carries a 6 MW wind turbine and is linked to the sea bottom by 6 ties which assure stability and limited tilting, even under the worst loads induced by wind and sea. The phases of construction and installation of this structure have been analysed, and the most effective and economically viable techniques chosen. Particularly, with a view to avoiding the use of expensive sea craft, the floating structure has been designed in such a way that it can be towed to site with the wind turbine already standing on it. A preliminary dimensioning of the floating structure has been carried out, along with verification of the main structural members. This work has been performed in co-operation with the engineering company TECON, which used, among others, the MOSES computation code by Ultramarine. Attention has also been devoted to the most suitable options for mooring the floating structure to the sea bottom. Specifically to assess the behaviour of the floating system under the action of wind and waves, the BM computation code has been developed by CESI RICERCA. This code takes into account the whole “wind turbine + floating platform” system, represented by a scheme featuring 8 degrees of freedom. No anomalous or unexpected behaviours have been observed. The costs of building and installing floating systems like that described above have been calculated, also drawing on experience gained with similar offshore structures in the oil and gas fields. The peculiar conditions of Italy as regards shipyards, harbours, electrical grid layout etc. have been taken into account. Along with estimates of operation and maintenance costs, and annual energy yields, these results have allowed to figure out the likely unit energy production costs of floating wind farms in deep-water coastal areas of Italy

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