The challenge to the world's first floating wind farm
Takeshi ISHIHARA, Atsushi YAMAGUCHI and Shigeru TAKI
Department of Civil Engineering, School of Engineering, The University of Tokyo

Project overview

Compact semi-sub floater for 2MW turbine

Fukushima offshore wind consortium, which consists ofMarubeni Corporation (Project integrator), the University ofTokyo(Technical advisor), Mitsubishi Corporation, Mitsubishi
Heavy Industries, Japan Marine United Corporation, Mitsui
Shipbuilding & Engineering, Nippon Steel & Sumitomo Metal
Corporation, Ltd., Hitachi Ltd., Furukawa Electric Co., Ltd.,
Shimizu Corporation and Mizuho information & Research, isproceeding with Fukushima floating offshore wind farmdemonstration project (Fukushima FORWARD) funded by
the Ministry of Economy, Trade and Industry.

The construction of compact semi-sub floater for 2MW
downwind turbine was completed in May 2013. This floater
consists of one center column, three side columns andthree braces, and the main deck beams and the pontoon
beams support the wind turbine. The compact semi-sub
floater has advantages for construction and installation due
to its shallow draft. The draft of the floater can be controlled
by using the ballast tank located at the bottom of the sidecolumns.

In this project, three floating wind turbines and one floating
power sub-station will be installed off the coast of Fukushima.
The first phase of the project consists of world first 2MW
downwind floating wind turbine, the world first 25MVA
floating substation and submarine cable, and werecompleted on 11th of November, 2013. In the second phase,
two world largest 7MW wind turbines will be installed before
2015. The detailed information is available in the projectbrochure [1]Installation and grid connection
The compact semisub floater with2MW
downwindturbine left Chiba
dockofMitsuiShipbuidling&Engineeringon
27th of June, 2013.
After testing atOnahama Port, it
was towed to thesite.
Theadvanced
spar floater for
floating substation
left Isogo dock ofJMU and towed tothe installation site
directly. From the16thofJune,
2013,
theanchoring began.

World first 2MW downwind offshore wind turbine wasinstalled on the compact semi-sub floater in June, 2013. The
55m tower was divided into three sections and after theinstallation of the nacelle, 40m blades were installed .

In May, 2013, the anchor and mooring chain for both floaters
were installed. In June, at the coast of Hirono, whereonshore substation is located, the construction of thesubmarine cable began. The grid connection of the floating
offshore wind turbine and substation was completed on 31stof October.

Advanced spar floater for substation

Research and development
Water tank test
By using a scaled model of 2MW compact semi-sub floater,water tank test was carried to clarify the response of thefloater under design wind, wave and current conditions. The
optimum control method during power production for floating
wind turbine was also investigated.

Metocean Measurements
The floating substation is equipped with met-ocean
measurement devices. Wind velocities are measured byusing
cup anemometers, wind vanes and sonicanemometers on the met mast, and the doppler ridar on themain deck. The wave and current are measured by using thewave meter and ADCP on the middle hull. The floater motion
is also measured with accelerometers, GPS and gyros on themain deck, and a floater motion compensation algorithm isalso developed.

Construction of the floating substations on the advanced spar
floater was completed in June, 2013. On the main deck of theupper hull, a met mast and a helicopter deck are installed.
Inside the upper hull, the world first floating substation islocated. The bottom hull is filled with concrete to lower thecenter of gravity, which enabled the construction and towing invertical position. The floater motion is controlled by using thecob under the upper hull, and the middle hull.

Conclusions
The first phase of the Fukushima FORWARD project
has started power generation on November 2013.
The first phase of the project can be summarized asfollows.

Floating grid integration system
An offshore floating transformer system which is both durableand unsusceptible to floater motion is developed and theperformance against vibration and inclination was evaluatedthrough shaking table tests. Furthermore, a large capacity
water proof riser cable superior to fatigue is developed andoptimized by motion analysis. Based on these technology,
the world first floating offshore transformer system wasestablished against severe metocean conditions.

1.Although several typhoons were observed aroundthe project site during construction, all the technicalproblems were solved and the installation has
finished on schedule successfully.
2.Eight months have passed since the installationand the world first floating substation and 2MW
down wind turbine have been operating without any
problems. The capacity factor of 43.5% wereachieved in December 2014, which is higher thanthe estimated 35%.
3.Metocean and floater motion measurement on thesubstation and compact semi-sub with 2 MW
turbine started. All the collected data are underanalysis.

Acknowledgement
This project is funded by Ministry of Economy, Trade andIndustry, Japan. The authors wish to express their deepest
gratitude to the concerned parties for their assistance andcontribution in this project.

Reference[1] Fukushima FORWARD English brochure,
http://www.fukushima-forward.jp/pdf/pamphlet3.pdf