Academic
Wind Turbine Noise Ordinances in the US
Energy generated from winds has been one of the favorites of those advocating for the environment. In
fact, wind power is among America’s fastest-growing renewable energy sources. This is energy without
any carbon emission, and where the free resource is utilized, but never in the least depleted. As against
power generated from a centralized power plant, wind power comes from distributed sources. For a
long time, wind energy seemed like the panacea for all the power-generation problems plaguing our
dreams of the future in clean energy.
The wind turbine has come a long way from the kit designs of the 1970's. Today's turbines are hundreds
of feet in height and massive in structure. They are constructed in large farms in rural landscapes, in the
rangelands of Texas, along the grassy hills of California, over the ridgelines of the Appalachians, and
the commons in England. As installations of wind farms increase all over the world and energy
production from the wind steps up, the returns on investments are certainly tilting towards the positive.
However, as the break-even is crossed, the downsides are also becoming more apparent. Resistance to
wind farms has been increasing.
The trouble is the noise generated by the wind farms. This is reported by The US National Wind
Coordinating Collaborative. This is a multi-stakeholder group that aims to facilitate wind development,
and the situation is summarized in fairly straightforward terms: “By and large, those affected by the
noise generated by wind turbines live within a few miles of a large wind power plant or within several
hundred feet of a small plant or individual turbine. Although the noise at these distances is not great, it,
nevertheless, is sufficient to be heard indoors and may be especially disturbing in the middle of the
night when traffic and household sounds are diminished.”
As found by the AEI Wind Turbine Noise Factsheet, “The bottom line is that most modern industrial
wind turbines are designed to keep noise levels at or below 45dB at 1000 feet (350 meters), which
should drop to 35-40dB at a bit over a half mile (1000m); commercial turbines are quite often built this
close to homes. Some are rated at lower sound levels.”
The AEI factsheet continues, “...atmospheric conditions can wreak havoc with nice clean sound
propagation models, especially at night. And, as turbines get bigger, their noise can be deceptively hard
to predict; certainly, they can be quieter at their bases than some distance away, and temperature
inversions, wind layers, and other atmospheric effects can lead to surprisingly distant sound impacts. ”
Tranquil night atmospheric conditions seem to cause the turbine noise to travel across greater distances.
A study by Van den Berg has found that at specific night conditions, the noise levels were perceived to
be higher than that predicted. In some cases, the noise levels were found to be louder by as much as 15
dB. The study also found that people living as far as 1900m away were disturbed by the noise from the
turbines. Predictably, in a majority of the cases, those downwind had to withstand the worst of the
sound; living upwind of a wind farm, noise problems are likely to be far less severe.
As wind farms are situated in rural areas, where the ambient noise levels can fall up to 35dB lower in
night conditions, the noise from the wind farms could very well become the new and predominant
acoustical presence. In most cases, the gentle whooshing noise from the wind farm is easily drowned
out by the natural wind noise. However, certain wind conditions may give rise to pulsating noise that
people find hard to be acclimatized to, or even ignore totally.
Other issues with the wind turbines are often the low-frequency sounds generated. These travel through
the ground and although inaudible to the human ear, create a physiological response in humans and
animals. Such low-frequency sounds often travel further through the ground with less loss of intensity
as compared to the high-frequency sounds. As found by Christopher Bajdek’s research paper, presented
at the NOISECON 2007, a noise control industry conference, “...the irregularity of turbine noise may
be a more important factor in making wind farms more annoying than other industrial sounds.” All this
has led to the conclusion that noise standards must be part of any set of wind turbine siting regulations.
Several countries, such as the UK and Denmark, have quantitative national noise standard or such
guidelines for wind turbines. In the US, few of the states have some regulations in place and, they vary
significantly. Wind turbine noise regulations of Iowa, Texas, Washington, Pennsylvania, and Michigan
are examined for their noise ordinances.
According to the Wind Energy Update, 17 Mar, 2011, from the National Renewable Energy Laboratory
of the US Dept. of Energy, Iowa has the second highest installed wind power capacity. Even though the
state generates over 15% of its energy from wind, practically no regulations exist statewide for the
commercially generated wind power. Approvals are required for projects, which will generate more
than 25 MW. However, the Iowa Utilities Board, which approves such projects, does not have any
specific regulations governing the generation of power from wind. Likewise, there are no regulations
for Noise from wind farms and this is relegated to the discretion of the local governments and counties.
Although Texas has the highest installed wind power capacity in the entire United States, regulations
for the installations of wind power generation are mostly silent on the subject of Noise generation from
such sources. The concern is almost entirely focused on land use, while noise generation or any limits
thereof do not get any mention.
Washington started statewide noise legislation in 1975, through the Washington Administration Code
(WAC) 173-60-030 and 173-60-040. According to the code, noise sources and receivers are categorized
into industrial, commercial and residential. Different sound limits are set depending on the involvement
of the receiver and sources. Wind turbines are treated as industrial noise sources and have to limit the
noise production levels below 55 dBA during the day and below 45 dBA during the night times. These
levels are set for the property lines of lands not belonging to or leased by the wind farm developer.
Although not declaring the intent of the code, the rationale behind the decision, and not citing any
background references, the standard levels provide protection against health effects such as sleep
deprivation. Additionally, the code encourages local ordinances for abatement and control of noise, as it
considers the role of the local government as primary in this function. However, very few counties in
Washington have developed local guidelines specific to noise from wind turbines.
Whatcom County in Washington is one such county to have come up with a noise ordinance, which
they have recently amended in 2008. According to the ordinance, the maximum outside noise level is
limited to 30 dBA or five dBA above ambient, whichever was lower. Their rationale in downsizing the
earlier limit of 55 dBA is stated thus, “does not adequately protect rural residents from adverse health
effects associated with large wind turbine noise.” However, the 30 dBA limit is at the lowest absolute
limit of audibility. This will require the wind turbines to be almost whisper-quiet at the property lines,
and may bar them from the county altogether. If the ambient noise levels themselves are higher than
this limit, as can happen, in reality, the 30 dBA limit could pose to be impossible to meet.
Pennsylvania and Michigan have a sample set of guidelines. However, they have left it to the local
governments to choose to adopt it verbatim or modify as they see fit. Pennsylvania sets the noise levels
at the exterior of homes on non-leased property to a 55 dBA limit. The 2007 guideline from Michigan
defines that the maximum sound generated by a utility-scale wind energy system shall not exceed 55
dBA on the properties of non-leased lands. In cases of background sound levels exceeding 55 dBA, the
wind-energy system sound shall not generate more than 3 dBA above the ambient sound level.
Most of the wind-turbine noise ordinances are deficient to the understanding of acoustics and the limits
are either set arbitrarily high, or exceedingly low. However, some counties have done well-researched
jobs of producing ordinances. Centerville Township, Michigan, formed a subcommittee and took four
years of protracted discussions, meetings, interviews, studying and traveling to form a 19-page
ordinance. This is one of the most comprehensive and complete noise standards.
According to the Centerville standard, the sound levels generated by the wind turbines during the
daytime between 6 A.M. to 10 P.M., must not exceed 35 dBA or ambient plus 5dBA, whichever is
higher. During the night, the sound is expected to remain lower than the background level plus 5 dBA.
This standard is applicable on closest property lines and at locations within one-mile distance from the
turbines. Additionally, the standard defines the low-frequency noise levels must not exceed specific 1/3
octave band levels inside the project area and within a one-mile radius of the project.
The specialty of the Centerville standard is that although it is conservative in its approach, and
restrictive to wind energy developers for their generating potential, it is protective of the residents'
health concerns, annoyance and perceptibility related to noise generated from wind farms.
The Wind Energy Conversion System (WECS) Ordinance of Shawano County, has now brought
“small” electrical generating facilities less than 100 MW, under the purview of the local governments.
The WECS Ordinance defines several types of noise such as aerodynamic noise, ambient noise,
background noise, broadband noise, impulsive noise, low frequency noise, mechanical noise, and
includes a detailed measurement method for measuring and reporting such noise parameters.
According to the WECS Ordinance of Shawano County, the noise due to Wind Energy Commercial
Unit (WECU) operations shall not be greater than 5 dBA above the established background noise level,
for more than five 5 minutes, out of any one hour time period. WECU operations will not be permitted
if low frequency impulsive noises, below 20Hz, are emitted.
According to the WECS Ordinance of Shawano County, sound pressures for low frequency or
infrasound noise, within the project boundary, including a 1-mile radius beyond the project boundary,
are acceptable, if they are below the levels given in Table 1:
1/3 Octave Band
Center
frequency (Hz)
Sound Pressure
level (dB)
2 to 1
16
20
25
31.5
40
50
63
80
100
125
250
500
1000
2000
4000
8000
70 (each band)
68
68
67
65
62
60
57
55
52
50
47
45
42
40
37
35
Table1: Acceptable sound pressure levels for infrasound noise, WECS Ordinance of Shawano
County.
LOCATION
ACCEPTABLE COMMERCIAL WIND
TURBINE NOISE LEVELS
DAY
NIGHT
IOWA
---
---
TEXAS
---
---
WASHINGTON
55dBA
45dBA
WHATCOM
Lower of 30dBA or (Ambient +5dBA)
PENNSYLVANIA
55dBA / (Ambient+3dBA), if
Ambient>55dBA
MICHIGAN
55dBA / (Ambient+3dBA), if
Ambient>55dBA
CENTERVILLE
Higher of 35dBA or
(Ambient+5dBA)
Ambient+5dBA
SHAWANO
Background + 5dBA (for general noise)
Background + 5dBA (- 5dBA if pure /
repetitive / impulsive tones are present)
Table2: Permissible Noise Levels applicable to wind turbines in the USA
References:
AEI Wind Turbine Noise Factsheet. Available at: http://acousticecology.org/srwind.html
Wind Turbine Noise Regulations at State and Local Levels - Acoustical Society of America - 161st
Meeting Lay Language Papers. Available at:
www.aip.org/asa_laypapers2011/Old.html
National Renewable Energy Laboratory, “Wind Energy Update: April 2011”. Available at:
www.windpoweringamerica.gov/pdfs/wpa/wpa_update.pdf
Washington Administration Code (WAC) 173-60-030 and 173-60-040. Available at:
www.mrsc.org/wa/rcwwac/index_dtSearch.html