The Ministry of Land, Infrastructure, Transport and Tourism (MLIT) has simulated the port scale required to construct a 1GW-class floating offshore wind farm using detailed Gantt charts.
What emerges clearly from this data is the overwhelming disparity in infrastructure scale required for ports in the supply chain between the “Pacific Ocean side, where year-round offshore construction is possible,” and the “Sea of Japan side, where offshore construction is limited to May–October due to rough winter seas”.
This article details the reality of building 1GW looking ahead to commercialization after 2030, and the massive infrastructure requirements demanded on the Sea of Japan side.
DeepWind Key Takeaways
- Premise: “15MW x 60 units = 1GW”. Construction paces tested were “20 units/year (3-year completion)” and “30 units/year (2-year completion)”.
- Quay Requirement Disparity: The Pacific side can manage with 2 quays, but aiming for 30 units/year on the Sea of Japan requires “a total of 3 quays” (2 for turbine integration, 1 for load-in).
- Manufacturing Yard Disparity: Floater foundation manufacturing lines require 5 lines on the Pacific side, compared to an estimated “12 lines” on the Sea of Japan side, where winter stockpiling is necessary.
- Vast Storage Area: The Sea of Japan side requires enormous water and land areas to store mooring equipment and completed floater foundations prior to the construction season.
The topics covered in this article are part of a broader analysis examining floating offshore wind from a structural perspective — spanning technology, costs, regulations, and project viability. For a comprehensive overview, see the full guide below.
👉 Floating Offshore Wind in Japan｜A Structural Guide to Markets, Costs & Policy
1. Two Scenarios Defining the Study
In MLIT’s simulation, to capture the entire floating offshore wind supply chain, two cases were established based on where the floater foundations (steel semi-submersible) are assembled.
- Case 1: Assembling floater foundations at existing large docks in Western Japan and towing them to the installation area.
- Case 2: Assembling floater foundations at an onshore yard near the base port.
Based on these, detailed schedules were created by applying the sea conditions of the Sea of Japan and the Pacific Ocean, respectively, to determine the number of vessel deployments and working days per month.
2. Base Port Scale Requirements: Quays and Yards
The scale of the base port for turbine assembly and load-out varies greatly depending on the construction pace. Let’s look at the disparity when assuming a fast pace of “30 units/year (2-year completion)”.
① Pacific Ocean Case (Year-round Construction)
Because work can proceed evenly throughout the year, the process can be managed with “a total of 2 quays”: 1 for material load-in and 1 for turbine integration. Work vessels can also be managed with 1 fleet or sporadically 2 fleets. The equipment storage yard area is estimated at up to approximately 11.6ha to 14.0ha.
② Sea of Japan Case (Concentrated Summer Construction)
Conversely, the Sea of Japan side must execute integration and load-out all at once during the six months from May to October. Therefore, 2 integration quays are needed to run parallel operations, requiring “a total of 3 quays” including the load-in quay. Furthermore, 2 fleets of work vessels must operate simultaneously. A vast site of approximately 14.0ha to 20.8ha is required for the equipment storage yard.
3. Floater Manufacturing Yards: The Wall of Production Lines
In the scenario where floater foundations are manufactured at an onshore yard near the base port (Case 2), the bottleneck in production capacity becomes even more pronounced. Manufacturing (assembly) of one steel semi-submersible floater foundation takes about 2 months.
- Pacific Ocean (30 units/year): To meet the weekly installation pace, “5 lines” must operate in parallel.
- Sea of Japan (30 units/year): Because it is necessary to “stockpile” during the winter for the offshore construction season starting in spring, a staggering “12 lines” of manufacturing lines are needed simultaneously.
Handling a 15MW-class floater requires a 110m x 110m (approx. 1.2ha) section per line. 12 lines would require developing a dedicated new facility of massive area, including yards, access roads, and ground reinforcement areas (10t/m² to 25t/m²).
4. Winter Storage and Mooring Equipment Stock: The Wall of Area
The “time lag” between component delivery/manufacturing and actual offshore construction demands even vaster storage spaces.
Mooring Equipment (Chain & Anchor) Storage: While a stock of up to 3 to 6 units is sufficient on the Pacific side, the Sea of Japan side (30 units/year) experiences a delivery backlog during winter, requiring a stock of mooring equipment for up to 20 units, with the facility area estimated to reach up to 5.7ha.
In-Port/Off-Port Floater Storage Water Area: The Sea of Japan side requires a vast water area to temporarily store floaters manufactured during the winter until the construction season. According to MLIT’s estimates, even for short-term in-port storage (using fixed anchors, etc.), approximately 1.7 to 4.1ha of water area is required per unit. Furthermore, if floaters are wintered off-port using catenary mooring—such as in the scenario where they are manufactured in Western Japan and towed to the Sea of Japan (Case 1)—a vast footprint of approximately 17.5 to 35.9ha per unit is required. If attempting to store 10 units together over the winter, the estimated water area reaches a staggering 175 to 359 hectares, making securing such expansive and tranquil water areas an extremely difficult challenge.
【DeepWind Insight】
This detailed simulation by MLIT substantiates with data the harsh reality that “aiming to complete 1GW on the Sea of Japan in the same timeframe (2 years) as the Pacific side will require 1.5 to over 2 times the number of quays and yard area (= necessitating unrealistic infrastructure expansion).”
The Sea of Japan side is a prime project formation area blessed with good wind conditions, but the meteorological constraint of a “short construction window” translates directly into increased infrastructure investment costs. Developing a massive facility with “3 quays and 12 lines” at a single port is unrealistic. Overcoming this constraint will inevitably require the following approaches:
- Promoting Broad Regional Cooperation: Introducing a “Port Integrator” system that distributes roles (manufacturing, assembly, storage) across multiple ports and operates them as a single entity.
- Making Rules Flexible: Hacking the rules, such as “equalizing lease fees when using multiple ports” and “relaxing restoration obligations,” as MLIT presented at the previous study group.
- Optimizing Construction Schedules: Flexible setting of Commercial Operation Date (COD) deadlines under the FIT/FIP schemes, predicated on regional constraints.
A 1GW floating offshore wind project has grown beyond a scale that can be completed through the efforts of a single developer. The true value of optimal port infrastructure allocation and rule-making by the public and private sectors acting as one is now being put to the test.
[References]
This article was created based on the following materials submitted at the “3rd Study Group on Port Infrastructure for Offshore Wind Power” held on March 4, 2026:
・MLIT Document 1 “Study of Port Facility Scale”
The topics covered in this article are part of a broader analysis examining floating offshore wind from a structural perspective — spanning technology, costs, regulations, and project viability. For a comprehensive overview, see the full guide below.
👉 Floating Offshore Wind in Japan｜A Structural Guide to Markets, Costs & Policy
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