Bird Collision Monitoring System WT-Bird®

Background
The effects of wind turbines on birds have been studied extensively, mainly by means of visual observation and radar. This has provided a good knowledge of disturbances and collision risks for birds in onshore wind farms.
The application of the current methods is limited to small non-remote sites. The methods are labour intensive, so that long campaigns are expensive.
To assess the collision risks at a broader geographical scale and particularly offshore there is a great need for validated collision risk models. This requires additional and more reliable data of actual collision rates.

Description
ECN has developed and tested a new method to monitor bird collisions that is suitable for large-scale application in both onshore and offshore wind farms. The monitoring system, named WT-Bird®, detects vibrations in the rotor blades due to a collision and then triggers video cameras to store selected video fragments. It operates continuously and is completely independent from the turbine operation.

Overview of WT-Bird^® prototype instrumentation and operation

Whenever a collision is detected the WT-Bird system sends a detailed alert message to the operator, who can access the sound and image recordings remotely to verify that a collision took place and to identify the species.

Test results (click here to view video)
A prototype has been tested successfully on a Nordex N80/2.5MW turbine. Functional tests with bird dummies of only 50 grams and 7 centimetres in diameter - which represent the smallest abundant bird species along the Dutch coastal region - hitting the rotating blades, showed that the majority of impacts were detected. Turbine noises under varying operating conditions are suppressed effectively by means of real-time digital signal processing, leading to about 5 to 10 false trigger events a day. The flight track of the dummies and the collision events were clearly visible on the recordings. The silhouette and flap movements of a passing bird at high altitude can also be distinguished. The image quality at night is still insufficient for species recognition, however camera and infrared lighting technology show rapid improvements.

Application
Compared to other methods this monitoring system can be applied on a large scale and at any location. It will reduce the uncertainty of the number of birds killed by collisions with wind turbines. Experience in the field showed that the system is also suitable for other monitoring tasks, such as the assessment of visual blade damage after thunderstorms, which could save time and costs for inspection and repair.

Developments
ECN is preparing campaigns on wind farm scale for ornithological verification of the measurements and reliability testing under harsh climatic conditions. Other developments consist of tuning the system to different turbine types and making the design suitable for series production.

References
Wiggelinkhuizen, E.J., Rademakers, L.W.M.M., Barhorst, S.A.M., den Boon, H.J.: "Bird collision monitoring for multi-megawatt wind turbines WT-Bird®, prototype development and testing", ECN-E--06-027, ECN-E--06-028, Oct. '06.