Floating Offshore Wind Turbines in Goto Islands, Nagasaki, Japan

Abstract – Offshore wind energy resources in Japanese EEZ (Exclusive Economic Zone) are now considered to be huge. In order to utilize the huge amount of energy located in relatively deep water areas (water depth range: 50 – 300m), Ministry of the Environment, Japan funded a demonstration project on floating offshore wind turbine (FOWT). The project continued for six years beginning from 2010 to 2015. In the project, two FOWTs have been installed. The first FOWT mounted a 100kW wind turbine of downwind type, and the length dimensions are almost half of the second FOWT (so it was called as half scale model). The second FOWT mounted a 2MW wind turbine of downwind type, and was referred to as the full scale model. The FOWTs consist of PC-steel hybrid spar which is cost-effective and are moored by three mooring chains. The half scale model was installed at the site (Kabashima, Goto Islands, Nagasaki prefecture, Japan) on 11th June, 2012 as the first grid-connected FOWT in Asia-Pacific, and also as the third grid-connected FOWT in the world, following Hywind in Norway and Windfloat in Portugal. The half scale model was attacked by a very severe typhoon Sanba (1216), the greatest tropical typhoon in 2012 in the world. The behavior of the half-scale model during the typhoon attack was recorded, and compared with the computer simulations, indicating the validity of the design method. After a successful demonstration test of the half-scale model, the full-scale model was designed, constructed and installed at the same site. The demonstration test for the full-scale model was also successful. After completion of the demonstration project, the full-scale model was moved to a different site off Fukue island, where future expansion as a floating wind farm is planned. There, the full scale model is operating as a commercial floating wind turbine, providing valuable data and experience for operation and maintenance toward commercial-scale floating wind farms.