Better damage prediction for wind turbine blades through unique weather measurements at sea

Surprising research results

For a year, TNO’s senior consultant Wind Energy Harald van der Mijle Meijer and Wind Energy researcher Marco Caboni conducted detailed precipitation measurements in the North Sea. When they analyzed the data, they saw something interesting: most damage occurs at very selective moments. In fact, 30% of the annual erosion damage to offshore wind turbine blades occurs within just 12 hours of the year. This happens during specific moments when strong winds and intense rainfall coincide. The damage in question is erosion on the leading edge of the rotor blades, known as Leading Edge Erosion (LEE).

"We already knew that heavy rain significantly affects the rotating turbine blades, but the fact that 30% of the erosion damage occurs in such a short time was a new insight," says Harald.

When the tip speed reaches the maximum of 325 km/h (90 m/s) and wind speeds exceed 63 km/h (10 m/s) and rainfall exceeds 7.5 millimetres per hour, damage occurs to the rapidly rotating blades. The analysis also showed that offshore damage occurs twice as fast as onshore.

With this knowledge, wind farm operators can now proactively reduce turbine speeds at the right moments to prevent severe damage.

Regional differences in the North Sea

Another notable finding, thanks to the Whiffle simulations, is that there are significant differences within the North Sea region. In the northeastern part, the protective coatings on the blades last about 20% less time than in the southwestern part."

This is because there is not only more wind in the northeast, but also more rain," explains Marco. "This combination leads to accelerated erosion." New wind farms are planned for this part of the North Sea starting in 2030.

Collaboration with experts

The researchers worked in the PROWESS project (PRecipitation atlas for Offshore Wind blade Erosion Support System) in collaboration with wind farm operators such as Eneco, Shell, and Equinor. By incorporating their maintenance experiences with wind turbines into the research, data could be collected very specifically. Conversely, the new insights are invaluable for the wind farm operators."

Unexpected maintenance can shut down a wind turbine for weeks," says Harald. "Especially in winter, technicians often have to wait a long time for suitable weather conditions to carry out repairs."

More targeted preventive maintenance

Usually, operators plan their maintenance in the summer when there is less wind. The production loss from shutting down the wind turbines is then minimal, and the conditions for technicians are better.

But now, even more maintenance costs can be saved. On the one hand, preventive maintenance can be better scheduled with the new weather data. On the other hand, operators can now better predict when to proactively reduce the speed of the wind turbines to prevent extreme damage as much as possible.

Innovative measurement methods

What exactly leads to these new insights? To get a better, more detailed picture of wind and rain, we developed a new measurement method. "Until now, detailed rain measurements at sea were lacking, even in the data from the KNMI," says Marco. "We also wanted to know the size of the raindrops, as this determines the erosion damage to the rotor blades." Therefore, new sensors, called disdrometers, were placed at various locations in the North Sea.

These measurements were used to analyze potential erosion at those specific locations. The existing current and historical radar data were validated, including that from SKYECHO, one of the technical partners in the project.

Lessons for the future

The project also provided immediate lessons for the future. "The available sensors were actually not well suited to the aggressive conditions at sea," says Marco. "We faced severe corrosion problems." In follow-up projects, the researchers want to work with the manufacturer of the disdrometers to develop sensors better suited to the conditions at sea.

Global interest

The researchers hope for an international follow-up to the study. "Interest is being shown in various parts of the world," says Harald. Because there is also interest in areas with even more extreme weather conditions than the North Sea, research here can provide new data. Harald: "UV radiation, for example, also affects the protective coatings. It is interesting to see what those conditions do to the turbine blades."

"Especially the impact of this project, when we share our findings, has positively surprised me," says Harald. "There is a lot of interest in our approach at conferences." He also sees opportunities for the future: " Translating the rain atlas info into an erosion assessment tool to be used by operators, could be an important next step.”