Published: August 25, 2026 | Updated: August 25, 2026
TECHNOLOGY & SYSTEMS
On 6 August 2026 Japan’s Ministry of Economy, Trade and Industry revised its interpretation of the technical standard for wind power generation equipment. An interpretation of this kind sets out, in concrete terms, what an operator must do to meet the safety level the law requires. This revision swapped one kind of obligation for another. The old text required installing a lightning detection device. The new text requires being able to know at all times whether a strike has occurred, using detection devices, monitoring cameras, weather information or other measures of the operator’s choosing. If those measures fail to establish whether a strike occurred, the operator must inspect inside the blade with a borescope to confirm whether damage exists. Detection failure now has a price, and it is paid in inspection. Forty-four comments were filed, and the final wording differs from the draft.
👉 Japan’s Offshore Wind Technology Roadmap 2026
→
Execution Reality
→
Bankability Test
Installing a device used to satisfy the rule. Now the operator has to be able to say whether a strike happened. The choice of method opened up, and the cost of not knowing landed on the operator as a mandatory internal inspection.
METI states that on the turbine involved in the April 2026 blade failure, the lightning detection device was inactive for a period while the turbine was stopped, and strikes during that period could not be identified. What the revision closes is the window when monitoring stops, not the performance of the monitor.
METI published no threshold for what counts as a strike worth acting on, and no transition period for existing assets. Operators set their own thresholds and record them in their safety regulations. Flexibility stayed with industry, and so did the burden of justifying it.
From installing a device to knowing what happened
Two provisions changed, sub-items (ha) and (ni) of Article 7, paragraph 6, item 1(a). Placing the old and new text side by side shows what kind of change this is.
| Provision | Before | After (6 August 2026) |
|---|---|---|
| (ha) Down conductor | Install a down conductor, the cable that carries strike current from the blade tip safely to ground | As before, plus: where conductive materials such as carbon fibre reinforced plastic are used in the blade, that material must be properly electrically bonded to the down conductor |
| (ni) Knowing about strikes | Install a lightning detection device so the turbine can be stopped immediately when a strike occurs | Take measures so the presence or absence of a strike can be known at all times, through detection devices, monitoring cameras, use of weather information or other means. Where those measures fail to establish whether a strike occurred, confirm whether damage exists by inspecting inside the blade with a borescope or equivalent. While the turbine is operating, a detection device must still be installed so it can be stopped immediately |
The (ni) rewrite is the substance. The old provision was satisfied by the presence of hardware. Whether that hardware was actually working at a given moment was a separate question the rule did not reach. The new provision is satisfied by knowledge. It does not care which method produced the knowledge, but it does care about periods when no method produced any, and it prices those periods at one internal inspection each.
The final sentence deserves attention because it was not in the draft. Several commenters asked whether knowing “at all times” implied that two or more independent measures were mandatory. METI responded by adding the clause requiring a detection device during operation. Read together, the new latitude applies mainly to periods when the turbine is stopped or without power, while operating turbines keep the old hardware duty.
The April 2026 failure: detection was off while the turbine sat stopped
METI explains why stopped periods became the issue. In its response to comments it states that on the turbine involved in the April 2026 blade failure, there was a period during which the lightning detection device was not operating while the turbine was stopped, and that strikes during that period could not be identified.
The sensor had not failed. While the turbine was idle, the detection system was idle with it. A strike in that window leaves no record, and when the machine returns to service nothing triggers an inspection. That silence is what the revision is written against.
The event was the second such failure in Akita, following one in May 2025, with the same turbine model and the same maintenance provider. We covered those overlapping conditions when the second failure was reported.
On the May 2025 case, METI is explicit that removal of a receptor, the metal fitting set into the blade surface to take the strike, has not been reported as the direct cause. What was reported, it says, is that the blade structure allows damage to arise from discharge caused by potential difference during a strike, and that inspection failed to find the discharge marks. The two failures should not be collapsed into a single cause.
What METI declined to define: thresholds, existing assets, and who pays for weather data
Forty-four comments were submitted. Reading the responses, the questions METI settled and the questions it deliberately left open separate cleanly.
| Issue | What operators asked for | What METI answered |
|---|---|---|
| Definition of a strike | Detectable strikes can occur dozens of times a day. Publish a coulomb threshold | No threshold. Operators may set their own, based on equipment structure and lightning characteristics, and record the resulting inspection scope in their safety regulations, the self-imposed rulebook each operator files with the ministry, provided the basis is reasonable |
| Existing assets | State whether the revision applies, and any transition or grace period | The interpretation has no concept of retroactive application, but each operator is expected to take measures sufficient to meet the ministerial ordinance. No grace period was specified |
| Weather data | Release JMA lightning data free of charge. Nowcast is image data without an API | Operators should obtain weather information themselves if they need it |
| Scope | Limit the rule by turbine rating or proximity to inhabited areas | No limitation applied |
The first row carries the most weight. Until it is settled what counts as a strike, it is not settled when the inspection duty is triggered. Operators now set that line themselves and must be able to defend it. Method flexibility came with an accountability transfer.
Some comments were blunt. One noted that the operator in the reference case was already inspecting monthly, so changing inspection cycles could not be expected to prevent recurrence. METI answered that the revision is intended to improve the effectiveness of lightning protection measures in light of recent blade failures, and that it will act further as investigations and other cases yield findings. That exchange is not closed.
A rule can create an inspection trigger. This one did not decide when the trigger fires. With thresholds delegated to operators, practice will vary according to how each company writes its safety regulations. The treatment of existing assets sits in the same open space: no retroactive application, and an expectation of compliance with the ordinance, stated together. Both readings remain available, and for now each operator closes the gap on its own judgment.
Scoring our January read: bonding yes, drones no
In January 2026, analysing the Arayahama failure, DeepWind made two predictions about how regulation would move. Both can now be checked.
The first was right. We wrote that requirements for electrical bonding between the down conductor and the CFRP would be clarified, and the revised (ha) now requires exactly that connection.
The second was half right. Inspection scope did extend into areas that are hard to access, as we expected, but the means we named, drones and robotic cameras becoming a de facto obligation, is not what the text adopted. The rule specifies borescope inspection inside the blade. Both reach confined internal spaces, but the regulator chose looking in through an opening rather than surveying remotely.
👉 Case Study Deep Dive: The Arayahama Blade Failure Analysis
Why this reads differently offshore
Neither the revision documents nor the comment responses use the words offshore or at sea. The discussion proceeded on onshore turbines. The interpretation nonetheless applies to wind power generation equipment as a category, and offshore projects sit inside it.
Onshore, a fallback borescope inspection means moving people and equipment to a site. Offshore it means a vessel and a weather window. The same sentence describes an added task in one setting and an access plan in the other. Japan’s offshore fleet is only now beginning to accumulate operating hours, and O&M structures are still being set, so the asymmetry is something that can still be designed around rather than absorbed later.
Offshore, the cost driver sits in the design choices that avoid triggering an inspection at all. If strike data keeps being recorded while a turbine is stopped or without power, borescope inspection stays exceptional. If the record breaks, every break becomes a vessel and crew mobilisation. Where the detection device draws its power, and how records survive a grid outage, are unglamorous specification questions that translate directly into annual O&M cost.
The revision did not change how often blades are inspected. It changed which side has to prove what.
Under the old provision, an operator satisfied the rule by installing equipment. The obligation attached to the presence of a device, not to the hours during which that device was actually watching. The new provision asks whether the operator can say a strike did or did not occur. Where that cannot be said, the operator must demonstrate through inspection that nothing happened in the unmonitored window. What the rule demands has moved from a device to a record.
Read alongside METI’s refusal to set a threshold, the design becomes clearer. The state declined to specify how to measure and required only the state of knowing. How much counts as a strike, at what fidelity it is logged, and how interrupted periods are handled will be written into each operator’s safety regulations. Practice will therefore diverge under identical text. For operators the working question is no longer how many inspections to add, but how far to go in building a record that does not break. Offshore, that difference shows up directly as the number of vessel mobilisations in a year.
Related DeepWind Articles
- Case Study Deep Dive: The Arayahama Blade Failure Analysis
- Japan’s First Offshore Wind Tower Factory, Akita Blade Failure, and MLIT’s Floating Wind Installation R&D Program
- Japan’s First Fatal Wind Turbine Accident: Causes and Safety Measures
- Japan’s Offshore Wind Technology Roadmap 2026
DeepWind Weekly tracks Japan’s offshore wind market beyond headline announcements, focusing on execution risk, cost structure, project viability, supply-chain constraints, and policy implications.
Subscribe to receive weekly intelligence on Japan’s offshore wind market.
Why Isn't Floating Wind Bankable in Japan Yet?
The synchronized supply-chain bottleneck, quantified node by node, with a full sensitivity ranking and a bankability ladder of scaling conditions. Includes Simulator Professional (β) access to reproduce every figure on your own assumptions.
See the full analysis →