Wind Turbine Noise
Wind turbine noise is covered here with discussion of the Northwind 100 wind turbine as well as various factors that influence noise output and noise impacts.
Research the last five years on wind turbine noise complaints has showed the following:
- Wind turbine noise (for the tall three blade turbine of the kind considered by Monhegan) has a unique sound character that varies over time due to blade rotation up and then down through the air. It has been described as a repetitive "swishing" sound,. Because of its unique noise character, wind turbine noise is easily detectable by humans who have evolved with very complex and sensitive sensory systems.
- Noise induced annoyance and sleep disturbance at night has been found near wind turbine facilities sited in rural areas. After sunset air turbulence goes away and there can be very still wind conditions on the ground while there are strong winds aloft. This means there is no sound to obscure noise arriving from a wind turbine turning at speed some distance away- the turbine noise dominates the acoustic environment. Atmospheric conditions at night can include acoustic reflections from temperature gradients or "atmospherics", meaning the wind turbine noise can travel farther than they would during the day and noise energy emitted upward from the turbine (that would not otherwise be heard on the ground) can be reflected back down, increasing the apparent noise level on the ground at distance.
- There is no effective means of noise control except using sufficient distance as a buffer between the wind turbine and the nearest noise sensitive receptors.
NOISE INDUCED ANNOYANCE
- Noise induced annoyance from wind turbine noise rises faster than for transportation noise and starts at levels far below typical lowest regulatory limits (figure from Pedersen 2004).
The onset of high annoyance is some 10 to 15 dB lower than for transportation. Wind turbines are a new industrial noise source. From what I have seen in testimony and project data, manufacturers and noise consultants working for power companies tend to focus on promises to meet regulatory limits rather than siting to prevent complaints and sleep disturbance.
There seems to consensus emerging among researchers that wind turbine installations may produce annoyance at lower levels and at faster rates because of their swishing, time-varying noise character and when sited in quiet rural areas. They are more audible as a result compared to noise sources in urban areas and possibly more prone to disrupt the resident who is accustomed to natural rural quiet at night. Wind turbine noise intruding into that very quiet rural setting may possibly disrupt the perception that the environment is a restful place. It may possibly disrupt the ability to come home and relax if the wind turbine noise is audible indoors and outdoors. It may be possible that although the wind turbine noise level is lower than the noise regulation limit, the fact that it is audible day and night and has an unnatural swishing sound may possibly be experienced as a "taking" of the natural environment.
Would complying with a 45 dBA regulation limit work to protect the population's health and well being on Monhegan at night? That is not at all clear at this time. On the contrary, it appears from published research that one of three people are highly annoyed at 45 dBA wind turbine noise, and high annoyance can occur at levels more than 10 dB below that.
People respond to changes in sound level.
People are sensitive to sound character.
This new range of human response to a noise source is anathema to an engineering effort. Engineers want clear, concise standards and can possibly have great difficulty accomodating this degree of real potential impact and annoyance so far below the existing regulatory limits. The project has an opportunity to be a good neighbor by addressing and designing to meet this documented gap between the regulations and the onset of annoyance and sleep disturbance from wind turbine noise in the rural setting.
At the currently proposed location, the turbine will likely be audible throughout the village and exceed Maine regulatory statutes at one or more residences depending on wind and atmospheric conditions. The only way to reduce wind turbine noise in the Monhegan homes and inns would be to site the turbine farther away. It is not clear yet what site location would reduce the wind turbine noise sufficiently to prevent annoyance and sleep disturbance. Several hundred more feet of distance from the community could be required to be "a good neighbor".
SLEEP DISTURBANCE
In Pedersen's studies, 16 percent (20) of the 128 respondents living at sound exposure above 35.0 dBA stated that they were disturbed in their sleep by wind turbine noise (Pedersen 2004). The project quoted preliminary sound levels (to Working Waterfront in July 2009) as ranging from 37 to 45 dBA in the village, and the manufacturer has indicated the new design is up to 5 dBA noisier than projected levels used by the project so far.
Is Monhegan willing to risk having a substantial portion of its residents and visitors subjected to sleep disturbance and the health risks associated with sleep loss?
SWISHING NOISES
Wind turbines make a swishing noise when they rotate. The noise is from turbulence off the trailing edge of the blades as they rotate up and down. Differences in noise output through the rotational arc may be related to different wind speeds and turbulence between the lower portions and upper portions of the blade arc. Noise from wind turbines comprises modulations with a frequency that corresponds to the blade passage frequency (Hubbard et al., 1983) and is
usually poorly masked by ambient noise in rural areas (Arlinger
and Gustafsson, 1988).
Among those who noticed noise from wind turbines, swishing, whistling, pulsating/throbbing, and resounding were the most common sources of annoyance according to verbal descriptors of sound characteristics... These descriptors were all highly correlated to noise annoyance (Pederen 2004).
Noise Criteria
Noise criteria are thresholds or limits noise consultants use to evaluate the extent of environmental impact at a location or noise exposure for an individual or set as a limit for a noise source or facility.
You may have seen references to the Maine DEP noise limit of 45 dBA for night. Let's cover some history here to see what's going on.
The DEP regulation is some twenty years old and was based on research done in the early 1970s by the EPA. The EPA research was valuable and provided basic criteria which was adopted in regulations and ordinances for traffic, aircraft and industrial noise during the 1970s and 1980s. Separately, studies were done for traffic and aircraft to determine how annoyance is related to noise level.
The Maine DEP regulation stemmed from a lawsuit related to an industrial noise issue on the west end of Portland (an urban residential area)/ There was annoyance and sleep interference due to noise from a nearby industrial metal handling facility owned by Merrill Transport. A 45 dBA night limit was applied to that problem (along with some constraints for banging sounds); a reasonable limit given the urban locale and situation. The noise consultant's work was extended into a very detailed State regulation which was oriented to permitting new development.
At the time, little study had been done of appropriate criteria for rural areas. The federal noise programs had been focused on researching noise related health impacts from traffic, aircraft and industry in the noisy urban areas. When the Reagan administration shut down the federal noise office in the early 1980s, that stopped any adoption of a comprehensive federal standard as well as further research to cover the rural areas. The US is now covered by a patchwork of regulations on the state and local municipal levels. Each one is different and many contain poorly written or obsolete language. A few recognize the background level as an important pre-existing condition. Most do not, setting a fixed A-weighted sound level as a regulatory limit.
The emergence of the large industrial wind turbine has introduced a new kind of industrial noise impact.
Most industrial noise sources are continuous sources which do not vary audibly from second to second, and are at ground level where noise controls can be applied. Wind turbines are different:
- Wind turbines are constructed tall (or elevated) by necessity to capture the strongest winds and require unobstructed access to the winds, making the use of barriers or silencing impossible.
- Wind turbines tend to be erected in rural areas where there is the right topography and wind conditions as well as the lowest background sound levels.
- Wind turbine noise can be louder and more audible at night than predicted by manufacturers and proponents, due to overly simple modeling and not factoring in the effects of complex atmospheric conditions and low noise levels at ground level.
- Wind turbines produce a unique low-frequency, time-varying sound that "swishes" and is easily detectable by humans.
- Wind turbine noise is apparently more annoying at significantly lower sound levels than transportation noise.
Manufacturers and power companies may possibly tend to orient their analysis and permitting simply towards "meeting all applicable regulations"- naturally, they want to sell the system and make a profit. While it is important to meet regulations, those regulations at the State level are based on EPA data from the 1970s which were focused to a large extent on speech interference. Given the number of sleep disturbance complaints around wind turbine sites, despite prior assurances from power company consultants and engineers (who are paid to ensure the project goes forward), it is possible that the old single-number limits may not adequately protect the population and the environment from the new and more noticeable wind turbine noise in quiet rural areas. It may be appropriate to utilize a lower noise limit as well as a threshold above background to account for the apparent higher sensitivity to wind turbine noise in rural areas.
This is all by way of saying, when a manufacturer or power company says they pledge to "meet all applicable regulations" (those are regulatory noise criteria)- it may not mean all that much later to people who can't sleep or are trying to move away from a neighborhood near a wind turbine site but can't sell their home. People are sensitive to industrial wind turbine noise in quiet rural areas. The old noise standards need revision.
----
Kemperman et al proposed in 2008 a wind turbine siting outdoor immissions (received) outdoor noise level limit of 35 dBA or 5 dBA above the lowest 10-minute nighttime background sound level, whichever is lower. Power company consultants have pushed back hard on Kemperman's assertions. However, it is difficult to tell why power company noise consultants as INCE members (who have sworn to a code of professional ethics) would be so adamantly opposed to these noise limits that may actually protect against sleep disturbance- unless they were working simply to ensure the project was not derailed or sued.
The Town of Union looked closely at using Kemperman's draft ordinance in August 2008, thought they could "err on the side of caution and support 35 dB" and the town attorney preferred Kemperman's draft language to the Town's draft ordinance. (See notes of meeting.)
Sound Levels
Sound power levels are like the wattage rating on a light bulb. In fact they are referenced to the acoustic watt using decibel notation such as "101 dBA re 1 picowatt". Sound pressure levels are what we measure with a sound level meter. Sound pressure levels are referenced to pascals, as in "45 dBA re 20 microPascals". The "A" in dBA or db(A) refers to a filter applied to the microphone signal that matches how the human ear responds to sound. We're sensitive to speech frequencies but not so sensitive to low frequencies (like rumble or bass) or very high frequencies. We describe the limits of our hearing using terms like "infrasound" and "ultrasonic".
Preliminary data published in the Working Waterfront July 2009 indicate that wind turbine noise levels will be about 45 dBA at the nearest home and around 37 dBA in the vllage. Those noise levels likely would be highly audible to audible and, based on Pedersen's research might possibly induce annoyance for a sizeable portion of the village and visitors (who come to Monhegan to get rest and be in the natural environment, to get away from industrial noise). Northern Power indicated that the Northwind 100 design has changed and now it will be 3-5 dB louder than initial projected levels. (They expect to conduct more testing some time in the fall of 2009.) Therefore noise levels could be 50 dBA at the nearest homes. However those levels are not neessarily at full wind speeds available at Monhegan. Under worst case conditions (full wind speeds aloft, night, still wind conditions on the ground) the wind turbine could be well above MEDEP limits (which at that may be overly lenient for wind turbine noise) at a number of homes and, highly audible througout the village with increased potential for sleep disturbance.
In other words, it appears premature to say that the project would have "modest impacts" simply because levels at nearby homes could be a little below the DEP regulatory limits, as suggested in the Working Waterfront July 2009. On the contrary, it appears that there is a very real possibility of significant impacts. The DEP regulatory limit created twenty years ago now appears outdated relative to the sound character and annoyance potential of the new industrial wind turbines when sited in rural areas.
Blade Icing Noise
Blade icing can increase wind turbine noise levels as much as 5 dB (decibels) over quoted operating noise levels. This should be factored into and discussed in noise modeling. Manufacturers may insist that their wind turbines don't ice up. I notice I would be very careful taking that kind of assertion at face value.. I've lived in Maine most of my life. I like to be a skeptical consumer (how many Enrons do we need to experience?). The one thing we can count on here in Maine in the winter is ice. Right out of the crate, wind turbines blades might be resistant to ice from manufacturer-applied coating. Give anything a year or two exposure to the elements, dust, bugs, hail, salt, rime, and then see what happens.
Background: "In cold climates, with sustained temperatures below 32○ F., atmospheric icing conditions are common. The northeast U. S. has the highest incidence of icing in North America. Due to their aerodynamic shape significant rime ice buildup can occur on turbine blades in cold weather and high humidity conditions. This effect is similar to the rime icing of airplane wings. The ice can build symmetrically and then be extremely difficult to detect. Even a low buildup of ice can disturb the aerodynamics of air passage over the blades and create higher noise emission due to increased turbulence. Generally blade noise is the predominant noise source and can be increased 3-5 dBA due to this rime ice, or other changes to the airfoil surface as due to insect accretion or dirt accumulation." (Seifert, Henry, Technical Requirements for Rotor Blades Operating in Cold Climate, Deutsches Windenergie-Institut, 2003). - from Assessment of the Sound Level Study for the Mars Hill Wind Farm, Bolton, 2007.
Ice Removal Noise
Wind turbine manufacturers assert that their turbines don't throw ice, that they have ice detectors and ice removal mechanisms. The Northwind 100 is shipped with an anti-ice coating. However there must be an ice removal mechanism that's activated when needed once the anti-ice coating has deteriorated. Ice removal noises should be properly quantified and presented to the township so that all parties can be fully informed prior to voting.
Sleep Disturbance
In Pedersen's studies, 16 percent (20) of the 128 respondents living at sound exposure above 35.0 dBA stated that they were disturbed in their sleep by wind turbine noise (Pedersen 2004). The project quoted preliminary sound levels (to Working Waterfront in July 2009) as ranging from 37 to 45 dBA in the village, and the manufacturer has indicated the new design is up to 5 dBA noisier than projected levels used by the project so far.
Is Monhegan willing to risk having a substantial portion of its residents and visitors subjected to sleep disturbance and the health risks associated with sleep loss?
Research the last five years on wind turbine noise complaints has showed the following:
- Wind turbine noise (for the tall three blade turbine of the kind considered by Monhegan) has a unique sound character that varies over time due to blade rotation up and then down through the air. It has been described as a repetitive "swishing" sound,. Because of its unique noise character, wind turbine noise is easily detectable by humans who have evolved with very complex and sensitive sensory systems.
- Noise induced annoyance and sleep disturbance at night has been found near wind turbine facilities sited in rural areas. After sunset air turbulence goes away and there can be very still wind conditions on the ground while there are strong winds aloft. This means there is no sound to obscure noise arriving from a wind turbine turning at speed some distance away- the turbine noise dominates the acoustic environment. Atmospheric conditions at night can include acoustic reflections from temperature gradients or "atmospherics", meaning the wind turbine noise can travel farther than they would during the day and noise energy emitted upward from the turbine (that would not otherwise be heard on the ground) can be reflected back down, increasing the apparent noise level on the ground at distance.
- There is no effective means of noise control except using sufficient distance as a buffer between the wind turbine and the nearest noise sensitive receptors.
NOISE INDUCED ANNOYANCE
- Noise induced annoyance from wind turbine noise rises faster than for transportation noise and starts at levels far below typical lowest regulatory limits (figure from Pedersen 2004).
The onset of high annoyance is some 10 to 15 dB lower than for transportation. Wind turbines are a new industrial noise source. From what I have seen in testimony and project data, manufacturers and noise consultants working for power companies tend to focus on promises to meet regulatory limits rather than siting to prevent complaints and sleep disturbance.
There seems to consensus emerging among researchers that wind turbine installations may produce annoyance at lower levels and at faster rates because of their swishing, time-varying noise character and when sited in quiet rural areas. They are more audible as a result compared to noise sources in urban areas and possibly more prone to disrupt the resident who is accustomed to natural rural quiet at night. Wind turbine noise intruding into that very quiet rural setting may possibly disrupt the perception that the environment is a restful place. It may possibly disrupt the ability to come home and relax if the wind turbine noise is audible indoors and outdoors. It may be possible that although the wind turbine noise level is lower than the noise regulation limit, the fact that it is audible day and night and has an unnatural swishing sound may possibly be experienced as a "taking" of the natural environment.
Would complying with a 45 dBA regulation limit work to protect the population's health and well being on Monhegan at night? That is not at all clear at this time. On the contrary, it appears from published research that one of three people are highly annoyed at 45 dBA wind turbine noise, and high annoyance can occur at levels more than 10 dB below that.
People respond to changes in sound level.
People are sensitive to sound character.
This new range of human response to a noise source is anathema to an engineering effort. Engineers want clear, concise standards and can possibly have great difficulty accomodating this degree of real potential impact and annoyance so far below the existing regulatory limits. The project has an opportunity to be a good neighbor by addressing and designing to meet this documented gap between the regulations and the onset of annoyance and sleep disturbance from wind turbine noise in the rural setting.
At the currently proposed location, the turbine will likely be audible throughout the village and exceed Maine regulatory statutes at one or more residences depending on wind and atmospheric conditions. The only way to reduce wind turbine noise in the Monhegan homes and inns would be to site the turbine farther away. It is not clear yet what site location would reduce the wind turbine noise sufficiently to prevent annoyance and sleep disturbance. Several hundred more feet of distance from the community could be required to be "a good neighbor".
SLEEP DISTURBANCE
In Pedersen's studies, 16 percent (20) of the 128 respondents living at sound exposure above 35.0 dBA stated that they were disturbed in their sleep by wind turbine noise (Pedersen 2004). The project quoted preliminary sound levels (to Working Waterfront in July 2009) as ranging from 37 to 45 dBA in the village, and the manufacturer has indicated the new design is up to 5 dBA noisier than projected levels used by the project so far.
Is Monhegan willing to risk having a substantial portion of its residents and visitors subjected to sleep disturbance and the health risks associated with sleep loss?
SWISHING NOISES
Wind turbines make a swishing noise when they rotate. The noise is from turbulence off the trailing edge of the blades as they rotate up and down. Differences in noise output through the rotational arc may be related to different wind speeds and turbulence between the lower portions and upper portions of the blade arc. Noise from wind turbines comprises modulations with a frequency that corresponds to the blade passage frequency (Hubbard et al., 1983) and is
usually poorly masked by ambient noise in rural areas (Arlinger
and Gustafsson, 1988).
Among those who noticed noise from wind turbines, swishing, whistling, pulsating/throbbing, and resounding were the most common sources of annoyance according to verbal descriptors of sound characteristics... These descriptors were all highly correlated to noise annoyance (Pederen 2004).
Noise Criteria
Noise criteria are thresholds or limits noise consultants use to evaluate the extent of environmental impact at a location or noise exposure for an individual or set as a limit for a noise source or facility.
You may have seen references to the Maine DEP noise limit of 45 dBA for night. Let's cover some history here to see what's going on.
The DEP regulation is some twenty years old and was based on research done in the early 1970s by the EPA. The EPA research was valuable and provided basic criteria which was adopted in regulations and ordinances for traffic, aircraft and industrial noise during the 1970s and 1980s. Separately, studies were done for traffic and aircraft to determine how annoyance is related to noise level.
The Maine DEP regulation stemmed from a lawsuit related to an industrial noise issue on the west end of Portland (an urban residential area)/ There was annoyance and sleep interference due to noise from a nearby industrial metal handling facility owned by Merrill Transport. A 45 dBA night limit was applied to that problem (along with some constraints for banging sounds); a reasonable limit given the urban locale and situation. The noise consultant's work was extended into a very detailed State regulation which was oriented to permitting new development.
At the time, little study had been done of appropriate criteria for rural areas. The federal noise programs had been focused on researching noise related health impacts from traffic, aircraft and industry in the noisy urban areas. When the Reagan administration shut down the federal noise office in the early 1980s, that stopped any adoption of a comprehensive federal standard as well as further research to cover the rural areas. The US is now covered by a patchwork of regulations on the state and local municipal levels. Each one is different and many contain poorly written or obsolete language. A few recognize the background level as an important pre-existing condition. Most do not, setting a fixed A-weighted sound level as a regulatory limit.
The emergence of the large industrial wind turbine has introduced a new kind of industrial noise impact.
Most industrial noise sources are continuous sources which do not vary audibly from second to second, and are at ground level where noise controls can be applied. Wind turbines are different:
- Wind turbines are constructed tall (or elevated) by necessity to capture the strongest winds and require unobstructed access to the winds, making the use of barriers or silencing impossible.
- Wind turbines tend to be erected in rural areas where there is the right topography and wind conditions as well as the lowest background sound levels.
- Wind turbine noise can be louder and more audible at night than predicted by manufacturers and proponents, due to overly simple modeling and not factoring in the effects of complex atmospheric conditions and low noise levels at ground level.
- Wind turbines produce a unique low-frequency, time-varying sound that "swishes" and is easily detectable by humans.
- Wind turbine noise is apparently more annoying at significantly lower sound levels than transportation noise.
Manufacturers and power companies may possibly tend to orient their analysis and permitting simply towards "meeting all applicable regulations"- naturally, they want to sell the system and make a profit. While it is important to meet regulations, those regulations at the State level are based on EPA data from the 1970s which were focused to a large extent on speech interference. Given the number of sleep disturbance complaints around wind turbine sites, despite prior assurances from power company consultants and engineers (who are paid to ensure the project goes forward), it is possible that the old single-number limits may not adequately protect the population and the environment from the new and more noticeable wind turbine noise in quiet rural areas. It may be appropriate to utilize a lower noise limit as well as a threshold above background to account for the apparent higher sensitivity to wind turbine noise in rural areas.
This is all by way of saying, when a manufacturer or power company says they pledge to "meet all applicable regulations" (those are regulatory noise criteria)- it may not mean all that much later to people who can't sleep or are trying to move away from a neighborhood near a wind turbine site but can't sell their home. People are sensitive to industrial wind turbine noise in quiet rural areas. The old noise standards need revision.
----
Kemperman et al proposed in 2008 a wind turbine siting outdoor immissions (received) outdoor noise level limit of 35 dBA or 5 dBA above the lowest 10-minute nighttime background sound level, whichever is lower. Power company consultants have pushed back hard on Kemperman's assertions. However, it is difficult to tell why power company noise consultants as INCE members (who have sworn to a code of professional ethics) would be so adamantly opposed to these noise limits that may actually protect against sleep disturbance- unless they were working simply to ensure the project was not derailed or sued.
The Town of Union looked closely at using Kemperman's draft ordinance in August 2008, thought they could "err on the side of caution and support 35 dB" and the town attorney preferred Kemperman's draft language to the Town's draft ordinance. (See notes of meeting.)
Sound Levels
Sound power levels are like the wattage rating on a light bulb. In fact they are referenced to the acoustic watt using decibel notation such as "101 dBA re 1 picowatt". Sound pressure levels are what we measure with a sound level meter. Sound pressure levels are referenced to pascals, as in "45 dBA re 20 microPascals". The "A" in dBA or db(A) refers to a filter applied to the microphone signal that matches how the human ear responds to sound. We're sensitive to speech frequencies but not so sensitive to low frequencies (like rumble or bass) or very high frequencies. We describe the limits of our hearing using terms like "infrasound" and "ultrasonic".
Preliminary data published in the Working Waterfront July 2009 indicate that wind turbine noise levels will be about 45 dBA at the nearest home and around 37 dBA in the vllage. Those noise levels likely would be highly audible to audible and, based on Pedersen's research might possibly induce annoyance for a sizeable portion of the village and visitors (who come to Monhegan to get rest and be in the natural environment, to get away from industrial noise). Northern Power indicated that the Northwind 100 design has changed and now it will be 3-5 dB louder than initial projected levels. (They expect to conduct more testing some time in the fall of 2009.) Therefore noise levels could be 50 dBA at the nearest homes. However those levels are not neessarily at full wind speeds available at Monhegan. Under worst case conditions (full wind speeds aloft, night, still wind conditions on the ground) the wind turbine could be well above MEDEP limits (which at that may be overly lenient for wind turbine noise) at a number of homes and, highly audible througout the village with increased potential for sleep disturbance.
In other words, it appears premature to say that the project would have "modest impacts" simply because levels at nearby homes could be a little below the DEP regulatory limits, as suggested in the Working Waterfront July 2009. On the contrary, it appears that there is a very real possibility of significant impacts. The DEP regulatory limit created twenty years ago now appears outdated relative to the sound character and annoyance potential of the new industrial wind turbines when sited in rural areas.
Blade Icing Noise
Blade icing can increase wind turbine noise levels as much as 5 dB (decibels) over quoted operating noise levels. This should be factored into and discussed in noise modeling. Manufacturers may insist that their wind turbines don't ice up. I notice I would be very careful taking that kind of assertion at face value.. I've lived in Maine most of my life. I like to be a skeptical consumer (how many Enrons do we need to experience?). The one thing we can count on here in Maine in the winter is ice. Right out of the crate, wind turbines blades might be resistant to ice from manufacturer-applied coating. Give anything a year or two exposure to the elements, dust, bugs, hail, salt, rime, and then see what happens.
Background: "In cold climates, with sustained temperatures below 32○ F., atmospheric icing conditions are common. The northeast U. S. has the highest incidence of icing in North America. Due to their aerodynamic shape significant rime ice buildup can occur on turbine blades in cold weather and high humidity conditions. This effect is similar to the rime icing of airplane wings. The ice can build symmetrically and then be extremely difficult to detect. Even a low buildup of ice can disturb the aerodynamics of air passage over the blades and create higher noise emission due to increased turbulence. Generally blade noise is the predominant noise source and can be increased 3-5 dBA due to this rime ice, or other changes to the airfoil surface as due to insect accretion or dirt accumulation." (Seifert, Henry, Technical Requirements for Rotor Blades Operating in Cold Climate, Deutsches Windenergie-Institut, 2003). - from Assessment of the Sound Level Study for the Mars Hill Wind Farm, Bolton, 2007.
Ice Removal Noise
Wind turbine manufacturers assert that their turbines don't throw ice, that they have ice detectors and ice removal mechanisms. The Northwind 100 is shipped with an anti-ice coating. However there must be an ice removal mechanism that's activated when needed once the anti-ice coating has deteriorated. Ice removal noises should be properly quantified and presented to the township so that all parties can be fully informed prior to voting.
Sleep Disturbance
In Pedersen's studies, 16 percent (20) of the 128 respondents living at sound exposure above 35.0 dBA stated that they were disturbed in their sleep by wind turbine noise (Pedersen 2004). The project quoted preliminary sound levels (to Working Waterfront in July 2009) as ranging from 37 to 45 dBA in the village, and the manufacturer has indicated the new design is up to 5 dBA noisier than projected levels used by the project so far.
Is Monhegan willing to risk having a substantial portion of its residents and visitors subjected to sleep disturbance and the health risks associated with sleep loss?
Ice Throw
Wind turbines throw ice that accumulates on blades. The distance can be significant. According to GE Energy's Wind Application Engineering Group "wind energy production in cold climate provides the following formula for calculating a safe distance: 1.5 * (hub height + rotor diameter)".
The Northwind 100 hub height is 121 feet. The rotor diameter is 69 feet. The safe distance for ice throw is therefore 285 feet (87 meters). Locations inside the circle shown below are closer than the safe distance. (Turbine location assumed from telephone discussions with the project.)
The Northwind 100 hub height is 121 feet. The rotor diameter is 69 feet. The safe distance for ice throw is therefore 285 feet (87 meters). Locations inside the circle shown below are closer than the safe distance. (Turbine location assumed from telephone discussions with the project.)
Flicker
Wind turbines create visual "flicker" when sunlight or other light is momentarily blocked by the turbine blades. Flicker occurs at up to about three times per second for a three-bladed turbine rotating at about 1 rotation per second.
Modeling conducted by the Minnesota Department of Health suggests that a receptor 300 meters perpendicular to, and in the shadow of the blades of a wind turbine, can be in the flicker shadow of the rotating blade for almost 1½ hour a day. At this distance a blade may completely obscure the sun each time it passes between the receptor and the sun.
With current wind turbine designs, flicker should not be an issue at distances over 10 rotational diameters (...). This distance has been recommended by the Wind Energy Handbook (Burton et al., 2001) as a minimum setback distance in directions that flicker may occur (..).
Wind Turbine Acoustic Noise, Renewable Energy Research Laboratory, 2002
The Northwind 100 rotor diameter is 69 feet, making the recommended minimum setback for flicker avoidance 690 feet. The figure below shows the recommended minimum setback distance from the proposed site in orange. Excessive flicker appears definite at the Lighthouse and Museum buildings, possible in nearby westerly residential areas and, flicker appears possible for periods of time all the way to the Island Inn and surrounding village on certain summer mornings. Total flicker avoidance may be possible by using a more remote site farther north on the Island. (Turbine location assumed from telephone discussions with the project.)
Modeling conducted by the Minnesota Department of Health suggests that a receptor 300 meters perpendicular to, and in the shadow of the blades of a wind turbine, can be in the flicker shadow of the rotating blade for almost 1½ hour a day. At this distance a blade may completely obscure the sun each time it passes between the receptor and the sun.
With current wind turbine designs, flicker should not be an issue at distances over 10 rotational diameters (...). This distance has been recommended by the Wind Energy Handbook (Burton et al., 2001) as a minimum setback distance in directions that flicker may occur (..).
Wind Turbine Acoustic Noise, Renewable Energy Research Laboratory, 2002
The Northwind 100 rotor diameter is 69 feet, making the recommended minimum setback for flicker avoidance 690 feet. The figure below shows the recommended minimum setback distance from the proposed site in orange. Excessive flicker appears definite at the Lighthouse and Museum buildings, possible in nearby westerly residential areas and, flicker appears possible for periods of time all the way to the Island Inn and surrounding village on certain summer mornings. Total flicker avoidance may be possible by using a more remote site farther north on the Island. (Turbine location assumed from telephone discussions with the project.)
Fire
Wind turbines catch on fire. This happens despite fire suppression systems. Would Monhegan residents be willing to risk industrial fire 121 feet aloft with burning embers falling off in the wind to nearby tinder?
Wind Turbine on Fire in Palm Springs, CA"
A wind turbine on fire in Germany:
Wind Turbine on Fire in Palm Springs, CA"
A wind turbine on fire in Germany:
