Wind turbine noise
Jeroen van Dam 14 December 2004
Contents
Brief terminology Measurement techniques and results Examples of allowable levels
Sound power vs. sound pressure
Sound power level is a measure of the source strength; typical values 90-105 dB(A) Sound pressure level is a measure of the level at a receptor (neighbor, microphone); typically <45 dB(A)
Information taken from The Scottish Office, Environment Department, Planning Advice Note, PAN 45, Annex A: Wind Power, A.27. Renewable Energy Technologies, August 1994
dB scale
dB scale is a logarithmic scale:
Doubling distance to turbine reduces sound pressure level 6dB Two turbines produce 3dB more then one turbine. Examples:
40dB(A) + 40dB(A) = 43dB(A) 40dB(A) + 45dB(A) = 46dB(A)
A-weighting compensates for sensitivity of human ear
Source: Acoustic noise measurements, Bruel & Kjaer
Measurement techniques
IEC 61400-11, 2nd edition. Wind turbine noise measurement techniques IEA recommended practices for wind turbine testing, part 10 Measurement of noise immission from wind turbines at noise receptor locations Measuring the source and calculating immission is typically preferred. IEC method used for certification of a turbine type
IEA method
or
IEC 61400-11 method
H+D/2
Results
sound pressure level [dB(A)] 2
8 Measured wind speed @10 m
10
12
14
Sound power level
Background correction
Ls = 10 log 100.1Ls+n 100.1Ln
Obtain apparent sound power level from background corrected sound pressure level
LWA = LAeq ,c 6 + 10 log
[ ]
4R12 S0
Results
For wind speed range 6-10 m/s:
Apparent sound power level 1/3rd octave spectra Directivity (optional) Tonality
Tonality
55
50
sound pressure level [dB]
45
40
90
35
80
70
30 432 436 440 444 448 452 456 460 464 468 472 476 480 484 488 492 496 500 504 508 512 516 520 524 528 532 536 540 544 548 Frequency [Hz]
Sound Pressure Level (dB)
60
50
40
30
20
10
0 0 500 1000 1500 2000 2500 Frequency (Hz) 3000 3500 4000 4500 5000
Noise propagation
Simple models, spherical or semispherical spreading, input: sound power level Semi complex, frequency dependence, input: octave or 3rd octave spectrum Complex, includes wind shear, input: 3rd octave spectrum
90 Sound Pressure Level [dB(A)]
Shortcomings: Turbulence Country dependent
80 70 60 50 40 30 20 10 0 0 50 100 150 Distance to turbine [m]
Examples of allowable noise regulations
Denmark:
45 dB(A) for single residence, 40 dB(A) for groups of residences, 5 dB(A) penalty for prominent tones
Germany:
Commercial: 65 dB(A), 50 dB(A) (day, night) Mixed: 60 dB(A), 45 dB(A) Residential: 55 dB(A), 40 dB(A) Rural: 50 dB(A), 35 dB(A) penalty for tones industrial\commercial 60, 55, 50 (day, evening, night). Residential: 50, 45, 40 recreational: 40, 35, 35 5dB(A) penalty for tones
Sweden:
Examples of allowable noise regulations contd
Netherlands, guideline:
Background noise dependent, base line 40dB(A) at 1m/s, 50dB(A) at 12m/s
France:
5dB increase of background noise (3dB(A) at night)
UK, guideline:
Maximum of (background noise + 5dB(A)) or 35-40 dB(A) day Maximum of (background noise + 5 dB(A)) or 43dB(A) at night 2-5dB(A) penalty for tones
Greece, law nr 2280:
industrial: 70 dB(A), mainly industrial 65dB(A) mixed industrial and residential: 55dB(A) mainly residential: 50dB(A) inside dwelling with open windows: 45 dB(A), Penalties for tonality up to 6 dB(A)
Examples of allowable noise regulations contd
USA:
Varies state by state, county by county, California Assembly Bill 1207: SWT shall not exceed 60dB(A) at
nearest dwelling except for short term events
Perception
Sound quality:
Amplitude variations Intermittent noises (yaw actions, stops, starts) Tonality
Psycho-acoustics
Ownership Control Human ear smarter then microphone Psycho-acoustics, facts and models E. Zwicker, H. Fastl
Background noise
Back ground noise increases with wind speed Typical levels 30-45dB(A)
65 60
55 sound pressure level [dB(A)]
50
45
40
35
30 0 2 4 6 8 10 Wind speed [m/s] 12 14 16 18 20
Background noise
Noise sources
Gearbox Cooling fans Generator Power converter Hydraulic pumps Yaw motors Bearings Blades
Source: Wind turbine noise Wagner, Barei, Guidati
Development
130
120
80's 90's Multi MW sound power level = 22 LOG(D) + 72
sound power level dB[A]
110
SWT's Log. (80's) Log. (90's)
100
90
sound power level = 11 LOG (D) + 82
80
70 1 10 Diameter [m] 100 1000
SWTs
High rpm with more variation Less sophisticated controls Flutter Closer to dwellings, sometimes on houses No cut out wind speed References:
P. Migliore, J. van Dam, A. Huskey Acoustic tests of small wind turbines, January 2004, NREL CP-500-34662 Paul Gipe, www.wind-works.org
Conclusions
Turbines make noise
Typically both turbine noise and background noise increase with wind speed
Noise level is not the only important measure
Sound quality Psychological effects
Planning is key
