Wind turbines in the North Sea face extreme weather conditions that cause erosion to the turbine blades. The PROWESS research, led by TNO, shows that a substantial part of the damage to offshore wind turbines occurs within just twelve hours of the year under specific weather conditions.
Source article: TNO
With these new insights, the wind energy sector can save millions of euros in maintenance through preventive measures.
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Weather measurements in the North Sea
TNO conducted detailed measurements of precipitation in the North Sea for a year. Analysis of this data revealed that about thirty per cent of the annual erosion damage to wind turbine blades occurs within just twelve 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 that exceed 63 km/h (10 m/s) and rainfall that 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,’ says 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.’
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Erosion radar
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,’ explains Van der Mijle Meijer. Disdrometers, sensors that measure raindrop size, were placed at various locations in the North Sea.
These measurements were used to analyse 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.
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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 twenty per cent shorter 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.
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 Van der Mijle Meijer. ‘Especially in winter, technicians often have to wait a long time for suitable weather conditions to carry out repairs.’
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