Evaluation of the Application of Warning and Discouraging Sounds Automatically Emitted from Wind Turbines on Bird Collision Risk: Case Studies in Sweden and Switzerland

Wind energy is expanding worldwide, and there is an increasing demand to reduce the collision risk of birds with wind turbines (WTG, hereinafter). Methods commonly proposed include: - “Deter” birds flying in the proximity... [ view full abstract ]

Wind energy is expanding worldwide, and there is an increasing demand to reduce the collision risk of birds with wind turbines (WTG, hereinafter). Methods commonly proposed include:
- “Deter” birds flying in the proximity of WTG.
- Stop the WTG before birds fly across the rotor swept area.
Useful technologies applying these methods should be able to efficiently detect bird flights in real-time, and to take the proposed actions on time to reduce the collision risk.
The aim of this research is to evaluate the effect on bird collision risk of warning and discouraging sounds emitted automatically from WTGs, to birds detected in real-time flying in the WTG vicinity.

The evaluation has been performed by DTBird® Team using DTBird® System:
- Detection Module surveys the airspace around WTGs detecting bird flights in real-time.
- Collision Avoidance Module emits warning and discouraging sounds from the WTG to birds flying in collision risk.
- Collision Control Module records bird flights in collision risk and potential collisions.

DTBird® System produces video and sound records of every detected flight, and stores them in a Data Center.
The evaluation has included 2 WTGs:
- Switzerland. WTG: Vestas 3MW, tower height of 119 m, rotor diameter 112 m. Testing period: Autumn 2014.
- Detection Module recorded bird activity: 4.2 flights/day (274 flights, 423 birds): Corvids 15%, Raptors 3%, Medium size birds 61%, others 21%.
- Sweden. WTG: Vestas 850 KW, tower height of 74 m, rotor diameter 52 m. Testing period: Summer 2015.
- Detection Module recorded bird activity: 5.8 flights/day (285 flights, 604 birds): Seabirds, 27%, Corvids 19%, Raptors 10%, Geese 4%, Cranes 4%, others 36%.

The research has been focused in bird flights detected at the rotor swept area (RSA, hereinafter) height, <100 m to the blades, and with the rotor running. It has considered High Collision Risk Flights (HCR) those detected at <1 blade length to the RSA.

The evaluation methodology consisted of the activation/deactivation of sound emission on a weekly basis, and the comparison of collision risk variables determined from the video records.

The results have been:

- Nº HCR Flights reduction with sound activated:
• 100% in Switzerland (at 1/2 HCR area)
• 31% in Sweden.

- % HCR Flight Pattern Changes with sound emitted compared with sound deactivated:
• 60% to 0% in Switzerland.
• 82% to 44% in Sweden.

- Flight duration reduction with sound activated:
• >50% in Switzerland
• >50% in Sweden.

- % Collision Avoidance Flights with sound emitted compared with sound deactivated:
• 100% to 0% in Switzerland.
• 87% to 33% in Sweden.

- Nº RSA crosses: No crosses with sound emitted on both sites, and 1 cross with sound deactivated in Switzerland.

- Nº Collisions: No collision observed in flight video records (DTBird Collision Control) on both sites and treatments.

The research points out that the automatic emission of warning and discouraging sounds from the operating WTG, to birds detected in real-time flying in their proximity, has reduced the bird collision risk.