1. www.hoarelea.com Wind Farm Noise Impact Assessment NOISE PREDICTIONS – SOURCE DATA AND PROPAGATION

2. www.hoarelea.com Source Propagation Receiver The situation to be assessed ….

3. www.hoarelea.com VHVH V 10 SWL v = SPL v + 10 x log ( 4 x p x r 2 ) – 6dB Source Sound Power (IEC 61400-11) r H

4. www.hoarelea.com ISO 61400-11: Frequency based data Third octave SWL Narrow band tonal assessment

5. www.hoarelea.com Sound power values? Tested sound power (IEC 61400-11) with reported test uncertainty σ Warranted values: includes “safety margin” of typically up to 2dB(A) …… but sometimes not (commercial considerations) Turbine specification: additional uncertainty in warranty? Declared values: procedure of IEC 61400-14 for adding uncertainties (1.654 σ) N.B: test results are L Aeq data, so L A90 prediction is obtained by subtraction of 2dB

6. www.hoarelea.com Source Propagation Receiver The situation to be assessed ….

7. www.hoarelea.com Propagation models ‘Exact’ numerical methods (e.g. parabolic equation, fast field program) Approximate semi-analytical methods (e.g. ray tracing) Empirical ‘engineering’ methods (e.g. ISO 9613-2, Concawe) Input data Calculation implementation Output results

8. www.hoarelea.com Factors affecting sound propagation

9. www.hoarelea.com Factors affecting sound propagation - 1 Spherical spreading of noise Atmospheric attenuation

10. www.hoarelea.com Factors affecting sound propagation - 1

11. www.hoarelea.com Factors affecting sound propagation - 1

12. www.hoarelea.com Factors affecting sound propagation - 2

13. www.hoarelea.com Factors affecting sound propagation - 2 In ISO 9613-2: modelled by ground factor coefficient G (0 to 1)

14. www.hoarelea.com Factors affecting sound propagation - 2 G = 1 : soft, porous ground ground covered by grass or trees cultivated farming land  Not used as it will often under-predict G= 0: hard ground paving, water ice, concrete, etc. Industrial ground  Robust but can over-predict, particularly with warranted source data G= 0.5: mixed ground  Used with warranted source data or tested data + uncertainty

15. www.hoarelea.com Factors affecting sound propagation - 3 Refraction effects…

16. www.hoarelea.com Factors affecting sound propagation - 3 Hot Cold Temperature lapse Upwind

17. www.hoarelea.com Factors affecting sound propagation - 3 Hot Cold Temperature inversion Downwind

18. www.hoarelea.com Factors affecting sound propagation - 4

19. www.hoarelea.com Factors affecting sound propagation - 4 Sound energy enters ‘shadow region’ via turbulent scattering

20. www.hoarelea.com Factors affecting sound propagation – 3 + 4

21. www.hoarelea.com Comparison of PE and ISO 9613 results 20m 200m 1000m Harmonoise PE model (based on annual measured meteorological conditions [Salomons]) ISO 9613 (based on typical downwind propagation conditions) Percentage of time below stated noise level, % Calculated noise level, dB

22. www.hoarelea.com Factors affecting sound propagation - 6

23. www.hoarelea.com Factors affecting sound propagation - 6 In downwind conditions: limited to no more than 2 to 3 dB Terrain = noise barrier?

24. www.hoarelea.com Factors affecting sound propagation - 6 “Valley effect”: +3 dB h m ≥1.5 abs(h s -h r )/2

25. www.hoarelea.com Measurement studies 3 Separate wind farm sites, both located in rural environments and each comprising more than 20 turbines Two-speed turbines rated at over 2MW peak generating capacity, 60 to 70m hub height Type 1 sound meters continuously sampling statistical and equivalent data at varying distances, with double wind-shield arrangements Published 2007-2009

26. www.hoarelea.com Measurement locations: from approximately 100m to 750 m from nearest turbine Very flat terrain Minimal vegetation Propagation path covered by peat bog Ground prone to flooding – saturated for duration of survey Wind Farm Envelope N Site B

27. www.hoarelea.com Site B Single site wind speed (G = 0 / 754m)

28. www.hoarelea.com Turbine specific wind speed (G = 0 / 754m) Site B

29. www.hoarelea.com Turbine specific wind speed (G = 0 / 754m) Site B

30. www.hoarelea.com Turbine specific wind speed (G = 0 / 754m) Site B

31. www.hoarelea.com Turbine specific wind speed (G = 0 / 754m) +2dB(A) “warranty” margin added ~5dB Site B

32. www.hoarelea.com Main measurement locations: from approximately 100m to 820 m from nearest turbine Lightly undulating but acoustically flat terrain Minimal vegetation surrounding turbines, forestry close to locations Ground cover of mixed soft ground and flooded areas N Wind Farm Envelope P1 P2 P3 P4 P5 Predictions are made for: high speed mode only G=0.5 tested sound power data + 1dB (Stated test uncertainty) Site C

33. www.hoarelea.com Location P4: 700 m distance Turbine only (predicted) Turbine + background Site C

34. www.hoarelea.com Additional research Evans and Cooper Comparison of predicted and measured wind farm noise levels and implications for assessments of new wind farms Paper Number 30, Proceedings of ACOUSTICS 2011 2-4 November 2011, Gold Coast, Australia “Steady slope”“Concave”

35. www.hoarelea.com Recommendations For use and application of ISO 9613-2 to WTN L A90 = L Aeq – 2 dB Use spectrum data if available 4m receiver height 10 degrees / 70% humidity Do not use G=1 G=0.5 recommended, with source levels which incorporate test uncertainties (as in most warranties or “declared“ values as per IEC 61400-14) For propagation across a valley add +3dB Terrain screening: no more than -2dB State all assumption and input data

36. www.hoarelea.com Thank you