Published: April 24, 2026
Last updated: April 29, 2026
On 22 April 2026, Japan’s Organization for Cross-regional Coordination of Transmission Operators (OCCTO) convened the 100th meeting of its Transmission Planning Committee to frame the scenario design and regional demand–supply allocation for reviewing its long-term grid outlook for 2050 — the so-called Grid Master Plan. The current outlook (the Second-Generation Master Plan) was adopted in March 2023, and since then the Seventh Strategic Energy Plan (cabinet-approved February 2025) and the FY2025 Supply Plan have materially shifted the underlying assumptions. This review exists to quantify how much those shifts change the plan.
For offshore wind, the structural choice is straightforward. Generation-side capacities — including offshore wind at 45 GW — are held at current Master Plan levels. What moves across scenarios is the demand-side regional allocation, specifically for data centers, semiconductors, hydrogen production, and DAC (direct air capture). Where demand locates determines interconnector flows and reinforcement scale; where generation locates does not change between scenarios.
While this article focuses on a specific topic, those looking to understand Japan’s overall offshore wind policy and regulatory framework should also read our comprehensive summary here:
👉 Japan’s Offshore Wind Policy & Regulatory Framework Explained
Overview
The committee paper boils down to five points.
- Demand baseline: The 2050 1,250 TWh model from OCCTO’s Future Power Demand–Supply Scenario Committee is adopted as the base case.
- Scenario set: Three scenarios — a base case, a “demand-induced to generation sites” case, and a “demand-induction limited” case — are evaluated in parallel. Generation-side allocation is held common across all three; only demand-side allocation varies.
- Variable demand elements: Four demand elements vary across scenarios — data centers, semiconductors, hydrogen production, and DAC. These account for most of the future demand increase, and their siting has the largest impact on transmission flows.
- Generation capacities: Solar PV 260 GW, onshore wind 41 GW, offshore wind 45 GW, nuclear 37 GW, and battery storage 24 GW, reflecting the Seventh Strategic Energy Plan and related policy discussions.
- Sensitivity analyses: One case distributes a portion of renewable capacity (solar, onshore wind, offshore wind) according to demand share, and another varies battery storage capacity. Separately, results using the Future Demand–Supply Scenario’s renewable values (offshore wind 28 GW, etc.) will be presented as a reference.
Scenario design: widening the range through demand, not generation
Both the current Master Plan and this review rest on a single premise: the scale of grid reinforcement is driven by the imbalance between where demand sits and where generation sits. The further apart they are geographically, the more interconnector and backbone reinforcement is required. Scenario width therefore reflects how much that imbalance narrows or persists.
The three scenarios are positioned as follows.
- Base scenario: Policy-led siting resolves the imbalance to a limited degree. Directly adopts the Future Demand–Supply Scenario’s regional allocation.
- Demand-induced scenario: Drawing on the GX Strategic Regions framework, data centers and similar loads are channeled toward regions where generation (renewables in particular) is expanding. Imbalance narrows further than in the base case.
- Demand-induction limited scenario: Policy-led siting is limited, and demand growth tracks historical regional demand shares. Imbalance is sustained.
The decision to keep generation allocation common across scenarios is deliberate. The current Master Plan did the same, and the logic is clear. To isolate the effect of demand-siting policy on reinforcement scale, generation must be held fixed — moving both sides simultaneously would blur attribution.
Base scenario: Tokyo concentration persists to 2050
The 2050 1,250 TWh base allocation loads heavily toward the three major urban corridors. Tokyo at 435 TWh, Kansai at 193 TWh, and Chubu at 185 TWh together account for 65% of national demand. Hokkaido (61 TWh), Shikoku (31 TWh), and Hokuriku (33 TWh) combined sit at just 10%. The pattern reflects current demand shares projected forward, and the 2050 picture does not, by itself, dissolve the Tokyo-centered structure of Japanese electricity consumption.
Data centers are the clearest illustration. Of the 140 TWh allocated to data centers, 85 TWh (61%) lands in Tokyo, followed by 23 TWh in Kansai and 14 TWh in Chubu. The three major metropolitan regions capture the overwhelming majority. The allocation is derived from FY2035 individual supply-plan entries and therefore reflects the current trajectory before regional dispersal policies (such as the Watt-Bit Linkage demonstration programs) take effect. Semiconductors, in contrast, are allocated toward generation-friendly regions — Hokkaido 9 TWh, Kyushu 10 TWh, Chugoku 8 TWh — reflecting announced investments such as TSMC in Kumamoto and Rapidus in Hokkaido.
Hydrogen production (10 TWh) and DAC (10 TWh) are allocated entirely to Hokkaido and Tohoku, the regions with the largest expected renewable expansion. This already mirrors the “demand-induced” logic of the current Master Plan and is carried into the base case.
Interconnector flow simulation: flows tilt further toward Tokyo
The committee paper also presents a pre-reinforcement interconnector flow simulation for the base scenario. The shift from the current Master Plan is decomposed into two layers.
The first layer is the merit-order change driven by fuel costs and CO2 compliance costs. In the review, coal’s total fuel-plus-carbon cost now exceeds that of LNG (both MACC and ACC classes). LNG generation in the Chubu and Kansai areas is traded more widely across regions, pushing flows toward Tokyo and, separately, toward Chugoku–Kyushu.
The second layer adds the updated demand and generation assumptions. Tokyo’s allocated demand increases by roughly 40 TWh, lifting eastward (Tokyo-bound) flows further. The structural message is clear: the economic and physical value of large-capacity lines feeding Tokyo — particularly the Tohoku–Tokyo interconnector — remains elevated across scenarios.
What it means for offshore wind: 45 GW held, but the 28 GW reference matters
The most important point for offshore wind stakeholders is that the 45 GW installed capacity assumption carries over unchanged from the current Master Plan. That figure tracks the Public–Private Council targets (10 GW by 2030, 30–45 GW by 2040, of which 15 GW+ floating) and remains consistent with the Seventh Strategic Energy Plan. Holding 45 GW as a planning input provides a meaningful level of predictability for developers, EPC contractors, and lenders.
At the same time, OCCTO has decided to present results derived from the Future Demand–Supply Scenario’s renewable figures (solar 180 GW, onshore wind 14.5 GW, offshore wind 28 GW) as a reference. The paper is explicit on the distinction. The Future Demand–Supply Scenario is designed as a reference for long-term decarbonized capacity auctions and orderly generation planning, and is not required to align with the Strategic Energy Plan. The long-term grid outlook, by contrast, represents the transmission architecture consistent with national energy policy.
The distinction matters. Reinforcement scale, cost, and congestion all look different at 45 GW versus 28 GW of offshore wind, even on the same transmission topology. Presenting both in parallel surfaces — in the specific context of reinforcement decisions — the gap between the policy target (45 GW) and a cost-optimized market-equilibrium estimate (28 GW) produced by the technical consultancy. For developers and investors, this is the most concrete framing to date of how much transmission investment is implied by pursuing the policy target rather than the market-optimum case.
A further note on the sensitivity analysis. The case that distributes a portion of renewable capacity by demand share is, for offshore wind, a thought experiment — Japan’s maritime geography does not permit relocating offshore projects toward Tokyo Bay or Osaka Bay. But the exercise quantifies the transmission burden created by the physical reality that the best offshore wind resources sit in Hokkaido, Tohoku, and Kyushu while the loads sit in Tokyo and Kansai. That burden is, in effect, a cost of pursuing offshore wind at policy-target scale.
What comes next
OCCTO will run the transmission simulations on the assumptions settled here and present results — the effects of the changed environment on the current Master Plan — at subsequent committee meetings. Findings feed directly into the identification of issues for the Third-Generation Grid Master Plan. The paper explicitly reserves flexibility to reflect further policy developments, meaning the scenarios may be re-calibrated as the GX Strategic Regions framework and Watt-Bit Linkage initiatives mature.
The structural message of the review
Three messages emerge from the scenario design.
First, the axis of grid planning is shifting from “where to place generation” to “where to place demand.” Holding generation allocation constant across all scenarios and varying only the four demand elements — data centers, semiconductors, hydrogen production, and DAC — tells us that the lead actor in 2050 transmission planning is demand-siting policy.
Second, offshore wind’s 45 GW is clearly maintained as a policy target, while the Future Demand–Supply Scenario’s 28 GW figure now sits alongside it as a reference. The gap between the two offers a new lens on the transmission cost required to deliver the policy target.
Third, the eastward flow structure toward Tokyo persists to 2050. Data center concentration in the capital region, an additional 40 TWh of Tokyo demand, and the merit-order change combine to keep the value of north-to-Tokyo transmission elevated — important background for offshore wind grid-value assessment and PPA design. Subsequent committee meetings will present concrete interconnector flow and reinforcement-scale results built on these assumptions, and DeepWind will continue to track them.
Source
100th Transmission Planning Committee (22 April 2026), Document 2: “Review of the Long-Term Outlook for Cross-regional Transmission Planning — Scenario Design and Regional Allocation of Demand and Generation.” Organization for Cross-regional Coordination of Transmission Operators (OCCTO).
For a broader understanding of Japan’s offshore wind legal system, policy structure, and support measures, be sure to check out our pillar article:
🌊 Japan’s Offshore Wind Policy & Regulatory Framework Explained