TNO research leads to better damage prediction for offshore wind turbine blades

Weather Measurements in the North Sea

TNO conducted detailed measurements of precipitation in the North Sea for a year. Analysis of this data (pdf) revealed that about 30% of the annual erosion damage to wind turbine blades occurs within just 12 hours of the year. This happens when strong winds and intense rainfall coincide.

The damage, known as Leading Edge Erosion (LEE), occurs when the tip speed reaches the maximum of 325 km/h (90 m/s) at wind speeds exceed 63 km/h (10 m/s) and rainfall exceeds 7.5 millimetres per hour. The analysis also showed that offshore damage occurs twice as fast as onshore.

"We already knew that heavy rain significantly affects the rotating turbine blades, but the fact that nearly one-third of the erosion damage occurs in such a short time was a new insight," said Harald van der Mijle Meijer, wind energy researcher at TNO. "With this knowledge, wind farm operators can now proactively reduce turbine speeds to prevent severe damage, thereby lowering maintenance costs. By better predicting when turbine speeds need to be reduced, damage can be prevented more effectively."

Erosion radar based on innovative measurement methods

To obtain detailed data on wind and rain, TNO used new measurement methods. "We also wanted to know the size of the raindrops, as this determines the erosion damage to the rotor blades," says Van der Mijle Meijer. Disdrometers, sensors that measure raindrop size, were placed at various locations in the North Sea.

These measurements were used to analyze potential erosion and validate existing radar data. Based on the research and weather simulations with a model developed by the company Whiffle, TNO and partners developed an 'erosion atlas' that predicts where and when wind turbine blades will suffer damage from rain. With the erosion atlas, wind farm operators can better predict when to take preventive measures.

Regional differences

Another notable finding 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. The combination of more wind and rain in the northeast leads to accelerated erosion. New wind farms are planned for this part of the North Sea starting in 2030.

Collaboration with experts

The PROWESS (PRecipitation atlas for Offshore Wind blade Erosion Support System project) research was conducted in collaboration with wind farm operators such as Eneco, Shell, and Equinor. Their maintenance experiences with wind turbines were valuable for the research. "Unexpected maintenance can shut down a wind turbine for weeks," says Harald van der Mijle Meijer. "Especially in winter, technicians often have to wait a long time for suitable weather conditions to carry out repairs."