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NREL/DOE Develop Collaboration with Japan’s Offshore Wind Programs

November 3, 2014

A delegation from the offshore wind technical teams of the Energy Department (DOE) and its National Renewable Energy Laboratory (NREL) recently traveled to Japan to develop a collaborative relationship between U.S. and Japanese offshore wind programs.

In the aftermath of the Fukushima nuclear disaster in 2011, Japan re-scoped its national energy strategy to include the development of floating offshore wind turbines. This policy shift has resulted in accelerated technology development,including the full-scale deployment of three prototype turbine designs, representing half of the worldwide floating offshore wind turbine deployment to date. This milestone was achieved in a short 2-year time frame as a result of the financial and regulatory support provided by the Japanese government. including both financial and regulatory backing.

DOE and NREL can learn from the example of these Japanese projects and use that knowledge to build success in their offshore wind program as they move forward to support the development of floating wind turbines for deployment in the U.S.. The U.S. and Japan share many common challenges in the deployment of offshore wind energy, including an abundance of deep water and the need to design floating turbines capable of withstanding tropical weather conditions. The Japanese demonstration systems have been impacted by three typhoons since their deployment, resulting in valuable data that characterize how the floating systems respond to tropical weather disturbances.

The first project that the U.S. team visited with was the Kabashima spar. The Kabashima spar is a 2-MW demonstration project using a Hitachi downwind turbine on a floating deepwater spar developed by Kyushu University, TODA Corporation, and Hitachi. The project was funded after the Fukushima disaster by the Japanese Ministry of the Environment. The U.S. delegation spent one day visiting the demonstration system, and a second day meeting with the Kabashima project team, giving presentations and discussing potential areas for collaboration.

A second site visited by the delegation was the Fukushima Forward project, which is managed by Marubeni and includes Mitsubishi, Japan Marine United, the University of Tokyo, Mitsui Engineering and Ship Building, and Shimizu. They have also installed a 2-MW semisubmersible system supporting the same Hitachi wind turbine and a floating advanced spar substation. The project was funded by the Japanese Ministry of International Trade and Industry. The advanced spar floating substation is the world's first floating substation designed by Japan Marine United. The spar design is novel because of its shallow draft with three wider sections at different levels to concentrate the ballast and the buoyancy at levels to maintain good stability while allowing the structure to be towed to sea in an upright position. While visiting the site, they were able to visit the control room for the turbine and spend a full-day meeting with the Fukushima project team.

The U.S. delegation also visited the offices of MODEC, a Japanese ship-building company, where engineers presented details of their SKWID (Savonius Keel and Wind Turbine Darrieus) project. Their design is a hybrid device that produces 1 MW of power from the combination of a tidal turbine and vertical-axis wind turbine. They built a demonstration system in 2013, but the tidal device sank during deployment. This portion of the structure was rebuilt, and the entire system is being redeployed. The unique qualities of the project include a large buoyancy member at the waterline that rotates with the waves independent of the rest of the project through a unique gimbal joint, keeping the remainder of the device vertical during wave loading. MODEC has also developed an innovative tow-out and construction method for a new offshore spar system that does not require a crane or other expensive equipment. Another innovation MODEC has developed is an approach to reduce the number of anchors needed in an offshore wind farm.

As a result of their visit, the DOE and NREL delegation gained valuable information about the methods used to design and deploy these early floating wind turbine prototype systems. In addition, the delegation returns with valuable information about Japanese regulatory processes, certification procedures, design and deployment costs as well as challenges encountered along the way. Relationships were established that will form the basis for data sharing between the United States and Japan, with informal agreements made to exchange data on mooring load measurements and metocean conditions during tropical weather disturbances at turbine level.

—Kelly Yaker