Approval gained for next-generation offshore wind power generation facility with TLP hybrid floating structure

The New Energy and Industrial Technology Development Organization (NEDO) announced on May 25 that Obayashi Corporation has obtained an Approval in Principle (AiP) from ClassNK (General Incorporated Foundation Nippon Kaiji Kyokai) for a floating offshore wind power generation facility. The facility utilizes a TLP (Tension Leg Platform) floating offshore wind turbine support structure that adopts a steel-concrete hybrid design under a NEDO-commissioned project. This marks the world's first instance where ClassNK has issued an AiP for a TLP hybrid floating offshore wind power generation facility.

Floating offshore wind power technology remains a developing field globally, leaving many challenges to be addressed regarding reliability enhancement and cost reduction. Under its project for next generation floating offshore wind power generation system demonstration research, NEDO is driving the development of various elemental technologies, feasibility studies (FS), design based on these findings, and planning for open-sea demonstrations. These efforts aim to significantly reduce costs and strengthen the supply chain from 2030 onward.

The TLP system is being spearheaded by Obayashi Corporation as part of its commissioned project, "Development of a TLP Hybrid Floating Offshore Wind Turbine Support Structure" (fiscal 2024-2025), under the aforementioned NEDO project (Development of next-generation technologies to promote introduction of floating offshore wind power generation). In this configuration, a buoyant body is forced to semi-submerge and is anchored to the seabed via tensioned mooring lines. The system anchors the buoyant body by utilizing the high tension generated by this forced buoyancy.

Since 2012, Obayashi Corporation has independently engaged in the research and development of floating offshore wind turbine structures utilizing this TLP design. It has repeatedly verified structural safety and motion characteristics through wave tank model experiments, numerical analyses, and open-sea demonstration tests using the floating body alone.

Under the NEDO project, the company advanced this research further by validating the feasibility of the joints connecting the steel and concrete components and developing precast construction methods.

Leveraging these achievements, Obayashi Corporation combined steel and concrete components in an optimized, right-material-for-the-right-place design to develop the floating offshore wind power generation facility with a TLP floating offshore wind turbine support structure. For this facility, it has now achieved the world's first AiP from ClassNK.

For this approval, ClassNK evaluated the safety and structural strength of the facility's support structure against the requirements of its technical guidelines, confirming that the design is viable. Capitalizing on the results of this FS project, Obayashi Corporation plans to further accelerate its research and development toward commercialization.

Features of the TLP hybrid floating offshore wind power generation facility

1. Floating foundation capable of cost reductions:
   By adopting a hybrid structure for the TLP floating body, the steel and concrete components can be manufactured separately, transported, and then joined at an on-site assembly yard.

   This broadens the selection of manufacturing of components and construction methods. According to Obayashi Corporation's estimates, this method is projected to cut floating structure construction costs by 25% compared to other floating configurations, such as steel semi-submersible models. Furthermore, because components can be manufactured in parallel, establishing a production system optimized for mass production becomes easier.

2. Stable power generation performance:
   TLP mooring systems suppress the vertical motion of the floating body by maintaining constant tension on the mooring lines. Obayashi Corporation estimates that wind turbine power generation efficiency will improve by approximately 8% compared to semi-submersible models, ensuring steady power generation performance.

3. Minimizing impacts on fishing activities:
   Catenary mooring systems typically require to occupy a width roughly 10 times the water depth. In contrast, TLP mooring lines exhibit minimal spread, confining the occupied sea area to a bare minimum. Consequently, the system is drawing attention as a design that easily mitigates interference with local fishing activities.