Use of a Vertical Wind Turbine in an Offshore Floating Wind Farm
Authors: Cahay Marc , Luquiau Eric , Smadja Charles , Silvert Frederic 
Published: May 2011

With 2.0 Giga watt (GW) already installed and more than 50.0 GW planned in Europe by 2020 as reported by the European Wind Energy Association, the installation of bottom mounted offshore wind turbine in very shallow water (less than 40 m / 120 ft) is now well established. The foundation and the offshore installation costs represent approximately 50% of the total development cost of an offshore wind farm and this proportion increases with the water depth. Hence, floating wind turbine is the solution for deep offshore, which does not mean far from the coast.

In summer 2009, the world's first full scale offshore floating wind turbine, has been installed in Norway in 220 m water depth. The offshore floating wind turbine is now becoming a reality considering the following advantages:Offshore floating wind farms offer a more constant and predictable wind resource.Location of wind farms in areas or countries with no shallow water is made possible.When necessary, the location of wind farms far from the coast greatly reduces the visual impact.Wind farms can be developed in areas subject to earthquake.The floating substructure design can be used for projects in various site locations.Integration and installation procedures are simplified.Anchoring installation does not require sophisticated vessels.

This paper will focus on the ongoing development of a breakthrough solution with the goal to reduce the cost for offshore floating wind applications. The overall concept is based on the use of a vertical axis wind turbine that offers a much lower centre of gravity than the more standard horizontal axis wind turbine concepts. Combined to an effective mooring system, this new floating wind turbine can economically compete with bottom mounted solutions in shallow water, bearing in mind that integration of the turbine in the floater and installation of the floating wind turbine must remain as simple and as safe as possible.

Further more, in order to reduce as much as possible the cost of the electricity generated, a wind turbine dedicated to the offshore environment is actually designed with a reduced number of parts and auxiliaries assuring low maintenance (no pitch, no yaw, and no gearbox). The test results of a vertical axis wind turbine onshore prototype which has been running for several months will be presented as well as the development plan for a 2 Mega watt (MW) onshore prototype and a full scale 2 MW floating prototype to be installed in France in 2012.

Introduction

Oil & Gas industry has a vast experience in floating production units. Starting more than 35 years ago, there is to date around 540 floating units on all seven seas. These floating units can be classified into four major families: tension leg platform (TLP), semi submersible, spar and ship shape. The distribution of such units is as follows:25 TLP the first one was Conoco Hutton, installed in 1984.84 Semi the first one was BHP Argyll, installed in 1975.17 Spar the first one was Anadarco Neptune, installed in 1996.414 ship shapes: 149 Floating Production Storage and Offloading (FPSO), the first one was Cities Service Indonesia Inc's Poleng PB FPSO barge installed in 1975 and 265 Floating Storage Units (FSU), Sevans and other mobile (early) production units.