Offshore Wind Disadvantages in Japan: Costs 38% Above Plan (2026)

The usual list of offshore wind disadvantages covers variable output, high cost, and effects on wildlife and views. In Japan, the problem that is breaking project economics is narrower and easier to measure. Government data published in September 2026 show capex for commercial offshore wind units running 38% above the assumption used to set prices. Operations and maintenance (O&M) costs are 60% above. Prices, meanwhile, are fixed at auction, years before construction. This article sets out the four disadvantages that show up in Japan’s numbers.

Policy design→Execution reality→Bankability test

Key Takeaways

1. Actual costs are running well above the pricing assumption
Four commercial units reported average capex of JPY 779,000/kW against an assumed JPY 565,000/kW. O&M averaged JPY 36,000/kW a year against JPY 22,500. Capacity factor came in at 27.7% against 30.0%.

2. Fixed prices turn cost overruns into developer losses
Round 1 lost about 1,742 MW when the winning consortium withdrew in August 2025. Japan’s port-area auctions have drawn no winner three times in a row. Both show the gap between a fixed price and rising cost.

3. Grid and ports are part of the cost problem
In the FY2031 outlook, grid-congestion curtailment of wind appears only in Hokkaido and Tohoku, the regions with the most offshore zones. Base ports are still being sized for larger and floating turbines.

👉 Background: how to read Japan’s offshore wind market

Contents

The Standard List: Variability, Cost, Wildlife and Views

Five disadvantages appear in most general guides to wind power.

Variable output. Generation falls when the wind drops, so the grid needs other plants or storage to fill the gap.
High upfront cost. Offshore, foundations, subsea cables and specialised vessels add cost.
Noise and visual impact. These matter most onshore and shrink with distance from the coast.
Wildlife. Bird collisions and construction noise affecting marine life are the main concerns.
Fisheries. Offshore, sharing sea space with fishing is a condition of any project.

Developers can price most of these in at the planning stage. Japan’s difficulty is the gap between what was assumed at planning and what construction and operation actually cost. The four disadvantages below are the ones where that gap is visible in public data.

1. Actual Costs Exceed the Assumption: Capex +38%, O&M +60%

On 25 September 2026, METI’s Procurement Price Calculation Committee, which advises on renewable power prices, published periodic cost reports from Japan’s operating offshore wind plants. The “assumed” values are the levels the committee has used when setting prices.

Item	Assumed	Reported	Gap
Capex (4 commercial units)	JPY 565,000/kW	JPY 779,000/kW	+38%
O&M (4 commercial units)	JPY 22,500/kW/yr	JPY 36,000/kW/yr	+60%
Capacity factor (all 6 units)	30.0%	27.7%	-2.3 points

Source: METI Procurement Price Calculation Committee, 116th meeting, Material 1, p.13 (25 September 2026); DeepWind analysis. The two demonstration units averaged JPY 2,056,000/kW capex and JPY 50,000/kW/yr O&M.

Capacity factor is the share of maximum possible output a plant actually generates over a year. It sets how much power, and therefore revenue, a project earns. All three numbers moved the wrong way at once: costs up, output down.

The sample has limits. There are only six reports, two from demonstration units. All are smaller, closer to shore and older than the projects now being tendered. The gap will not transfer one-for-one to a new 400 MW project. It is, however, the government’s own measure of how far reality has drifted from its pricing assumptions.

👉 Offshore Wind Cost Structure and Economics: A Structural Guide for Japan

2. Prices Are Fixed First: Round 1 Withdrawal and Auctions With No Winner

Japanese offshore wind prices are set at auction. Construction comes several years later, and operation lasts more than 20 years. If materials or interest rates rise in between, the power price does not follow, so the developer absorbs the overrun.

Round 1 is the largest example. In August 2025, a Mitsubishi Corporation-led consortium withdrew from three zones off Akita and Chiba, about 1,742 MW in total. The zones are waiting for a re-tender.

👉 Why Japan’s Offshore Wind Round 1 Ended in Withdrawal

The same gap shows up in a different way elsewhere. Japan’s auctions for fixed-bottom projects in port areas, which sit outside the Renewable Sea Area Act, have produced no winner in three rounds since FY2020. When developers judge the ceiling price too low, they simply do not bid. The fourth round opens for applications on 13 October 2026.

👉 Japan Offshore Wind Auction Outside the Sea Area Act: A Secret Ceiling After Three Rounds With No Winner

Revenue from outside the auction price is still thin. The Long-Term Decarbonization Auction (LTDA), which funds the fixed costs of new low-carbon plants over long periods, awarded no offshore wind capacity in its third round.

3. The Grid: FY2031 Curtailment Concentrates in Hokkaido and Tohoku

Transmission lines can carry only so much power. When more generation wants to flow than the lines can take, plants are told to cut output. This is curtailment, and curtailed power earns nothing.

The Organization for Cross-regional Coordination of Transmission Operators (OCCTO) plans Japan’s national grid. Its FY2031 outlook shows grid-congestion curtailment of wind in only two areas: Hokkaido and Tohoku. These are also where most of Japan’s promotion and promising zones sit. The best wind is far from the biggest demand, so grid reinforcement timing feeds straight into output.

👉 Where Japan’s Offshore Wind Faces Curtailment: Two Grid Areas Carry the FY2031 Congestion Outlook

4. Ports, Vessels and Maintenance: Keeping Up With Larger Turbines

Offshore turbine parts are too large for ordinary harbours, so they are stored and pre-assembled at dedicated base ports. Japan had seven designated base ports as of April 2026. MLIT is now working out how large a port must be to serve floating wind, with a draft due within FY2026.

Maintenance is the other half. In May 2025, a blade broke at the Arayahama wind farm in Akita, an onshore site. In August 2026, METI revised its technical standard interpretation so that operators must always be able to tell whether a turbine has been struck by lightning. Offshore, every inspection needs a vessel and a weather window, so maintenance requirements feed directly into O&M cost.

👉 Japan Rewrites Its Wind Turbine Lightning Rule: Operators Must Now Know a Strike Happened, or Borescope the Blade

Fisheries coordination runs through the law itself. Councils of national and local government, fishers and other users meet before a zone is designated. Since April 2026, the Environment Minister also surveys the marine environment before designation.

👉 Japan’s Offshore Wind Law Explained (2026): 12 Promotion Zones, One Operating Project, and a New EEZ Permit Route

Bankability Note

Lenders size debt on the debt service coverage ratio (DSCR): cash available for debt service divided by debt service, in the tightest year. A capacity factor of 27.7% against an assumed 30.0% cuts output and revenue by about 8% (simple proportional DeepWind estimate). O&M rising from JPY 22,500 to JPY 36,000/kW a year takes another slice of the same cash flow. With the power price fixed, the two together push minimum DSCR toward or below 1.35x, the level DeepWind treats as bankable.

DeepWind View

Japan’s biggest offshore wind disadvantage is the sequence: prices are fixed first, and costs move afterwards.

Variability and visual impact can be planned for. What cannot be planned for is how far costs move in the years between auction and construction. The 116th committee paper puts the gap between assumption and reality in the government’s own numbers. The next signal is the ceiling price for the fourth port-area auction, which will be published after bids are opened.

Policy can soften this. Japan already adjusts prices for future inflation, and the LTDA is opening to some offshore projects. How much each tool helps depends on project terms. Consider entering if an auction makes clear who bears cost movements before construction starts. Exercise caution if that risk sits entirely with the developer.

Frequently Asked Questions

Q: What are the main disadvantages of offshore wind?

Variable output, high upfront cost, effects on wildlife and fisheries, and visual impact near shore. In Japan, the most material issue is that actual costs are running above the assumptions used to set prices.

Q: How much more does offshore wind cost in Japan than planned?

Government data from September 2026 show average capex of JPY 779,000/kW for four commercial units, 38% above the assumed JPY 565,000/kW. O&M averaged JPY 36,000/kW a year, 60% above assumption. The sample is six reports, two from demonstration units.

Q: What are the advantages of offshore wind?

Stronger and steadier wind than onshore, room for very large turbines, and less noise and visual impact further from shore. Japan targets 10 GW of offshore wind project formation by 2030 and 30 to 45 GW by 2040.

Offshore Wind Disadvantages in Japan: Costs 38% Above Plan and Three Other Risks (2026)