Wind turbine inspection: seeing blades a hundred metres up, with less downtime

Turbine deterioration splits into blades, tower and foundation, and the nacelle (the housing for the generator and drivetrain). Blades take the most punishment — tips moving at high speed through rain and sand, serving as the lightning path, flexing tens of millions of times. That is why blades are the main subject of inspection.

In Japan, since April 2017 wind facilities of 500 kW or more have been subject to periodic safety management inspection under the Electricity Business Act. Drawing on the periodic inspection guideline (JEAG 5005) and the industry association’s blade inspection and repair guidance, operators check blade and tower condition, bolt tension, lightning protection and more, and keep records. Abroad too, periodic inspection is commonly required by permits, insurers or manufacturer warranties.

The means of getting close becomes the downtime and the risk. Blade tips often sit more than a hundred metres above ground. Rope-access technicians hanging from the nacelle have long been the standard, but they cannot work in strong wind and each turbine takes a long time.

Offshore, the pain multiplies: send a vessel, wait for the sea to settle, transfer to the turbine. Japan’s offshore wind pipeline is growing, and since O&M is widely cited as a large share of lifetime cost, inspection efficiency goes straight to project economics.

The drone replaces ropes and gondolas by carrying a camera along each blade surface. Once the turbine is stopped and the rotor locked in a set position, the drone automatically captures the four faces — leading edge, trailing edge, pressure side and suction side. Finishing a turbine within a short stop is its biggest strength.

In Japan, a NEDO-funded project validated drones that detect the nacelle direction and blade position by themselves and track swaying blades while imaging. How to capture turbines that keep moving even when stopped, such as floating offshore units, is one of the big challenges ahead.

Turbines are built precisely where the wind is strongest — which makes them among the hardest places for a drone to fly. They are also tall. Offshore adds salt and spray, northern sites add icing, and blade and tower interiors are cramped and dark. Wind inspection is a showcase of environmental barriers.

• Wind & turbulence: air wraps around the nacelle and tower, and disturbed flow trails behind the blades. Keep wind-tolerance margin, approach from upwind and leave an escape path. Wind & turbulence
• Height: blade tips often exceed 100 m above ground. Check altitude limits and how exceptions near structures apply, and plan to return with battery to spare. Height
• Offshore salt & spray: launching from a vessel is a fight with motion. Salt attacks the aircraft, so post-flight cleaning matters. Water, spray & humidity
• Cold & icing: in cold months batteries lose power and ice can form on propellers and sensors. Warm packs before flight and do not fly in icing conditions. Cold & icing
• Confined spaces: inspecting inside blades or towers needs collision-tolerant aircraft and lighting. Confined spaces

For a general guide to how much wind is too much for a drone, read how strong a wind a drone can fly in (Airffic World).

One turbine yields hundreds of high-resolution images. From them you find damage, locate it on the blade (distance from root and which face), grade its severity, compare with last time and decide when to repair. AI is strong at finding, locating and comparing; deciding whether to repair now or wait belongs to the person responsible for the turbine.

In Japan, wind facilities must meet technical standards under the Electricity Business Act, and those of 500 kW or more are subject to periodic safety management inspection. Offshore wind proceeds through zone designation and developer selection under the Act on Promoting the Utilisation of Sea Areas for Renewable Energy, where long-term O&M plans weigh heavily. Using drones within the inspection depends on the operator being able to justify them as an inspection method.

Abroad, the IEC 61400 series and certification-body standards (e.g. DNV) are the common language for design and certification. In some countries, periodic inspection by qualified experts is a permit condition.

For flight rules, height is the key issue. In Japan, airspace 150 m or more above the surface generally requires permission, although exceptions exist close to tall structures. Blade tips on large turbines can exceed that height, so check the current rules. Offshore, coordination with maritime traffic and port authorities is also needed. Compare countries in world regulations.

• Internal defects: delamination and bond-line failure often do not show from outside. Tapping, ultrasonics or other NDT are needed; drone-based tapping is still in trials.
• The repair itself: re-applying leading-edge protection is work for people or robots.
• Bolt torque: checking bolt tension is done by people inside the tower.
• Windy days: the turbines you most want to inspect are in the windiest places. Some days you cannot fly; schedule inspections toward calmer seasons.
• Rating and accountability: reading damage severity and deciding whether to keep running remains a human job.

At the base of an offshore turbine sits a drone box. At a calm dawn the drone launches by itself, images all three blades of the stopped turbine and returns. Even as the floating foundation moves, it tracks the blades and captures from the same pose as before. Onshore, only the blades that changed after the winter storms appear on screen. That is the picture our editors expect.

Nobody needs to cross the waves for every inspection. People decide repair order, line up parts, vessels and weather windows, and work out how to extend blade life. Inspection shifts from hanging off tall structures to caring for the whole life of the turbine.