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3. P
OTENTIAL
E
FFECTS OF
W
IND
E
NERGY
D
EVELOPMENT
The development of wind energy projects in Rhode Island is a novel enterprise, and it has the potential to impact surrounding natural resources and nearby residents in novel ways. While
some of these potential impacts are common to the development of any large structure, others are unique to wind turbines, and present challenges previously unknown in Rhode Island. The type
and magnitude of an individual project’s effects vary based on the technology used and the characteristics of the turbine site. This section discusses those concerns, and presents mitigation
measures available to eliminate or reduce their potential impact. 3.1 Structural Failures and Blade Throw Considerations
S
ECTION
S
UMMARY
Structural failure of wind turbines is rare but not impossible. Publically available data on wind turbine failure rates is very limited. Therefore,
calculating failure rates for current wind turbines technology can be difficult, as not all incidents are reported, and there is no centralized regulatory body charged
with compiling and verifying failure incidents in the United States. If a blade fragment detaches from a turbine, the location of landfall is controlled
by the angular velocity of the rotor, the position of the breaking point on the blade, and the size of the thrown piece. This relationship can be used to identify
an appropriate setback from homes and other populated sites given different risk tolerances.
Similar to other structures icing may occur on wind turbines. When ice falls or is flung from a moving blade, it can potentially become dangerous.
Rhode Island experiences weather conditions conducive to icing of turbine blades about 0-2 times annually. During those times, there is a risk of ice throw,
particularly if a turbine continues to operate.
The potential risk associated with ice throw can be minimized through setbacks, shutdown procedures, and ice detection mechanisms.
As with any technology involving moving parts and operational components under stress, wind turbines present a risk of structural failure. Turbines can fail in a number of different ways:
towers can bend or collapse, nacelles can topple, anemometers and bolts can fall, and blades can break or be thrown. Structural failures in turbines may result from extreme environmental events,
improper design or manufacturing, failures in turbine controlsafety system, and human error. Nonetheless, while structural failures are possible, they are rare. As of March 2012, the
only fatal injuries known to occur worldwide due to structural failure of wind turbines have been experienced by turbine technicians or associated personnel Caithness Wind Information Forum,
2012. However, it should be noted that calculating failure rates for wind turbines is difficult, as not all incidents are reported, and there is no centralized regulatory body charged with compiling
and verifying failure incidents in the United States. One of the most robust resources detailing cases of structural failure in wind turbines is provided by the Caithness Wind Information Forum
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CWIF, which records information worldwide on turbine accidents and failures reported between 1970 and 2012 see
http:www.caithnesswindfarms.co.ukpage4.htm . The Caithness
Wind Information Forum data is not comprehensive, as it only documents those failures that are voluntarily reported. In addition, the accident summary reports provided in this database should
be used with caution as some incidents classified as wind turbine accidents may be misleading.
3
One highly cited study examining the failure frequency of blades, towers, and other parts of a particular wind turbine was conducted by Rademaker and Bramm 2005 at the Energy
Research Center of the Netherlands ECN. This study examined data collected in Germany and Denmark by the ISET Institut für Solare Energieversorgungstechnik and the EMD Energie-og
Miljødata. The study reviewed failure information from 4,400 turbines, with over 43,000 years of operation among them, operating from 1984 to 2001. Ch. 1 Table 2 summarizes the results of
this study. Analysis of this dataset calculated that the probability of detachment for a whole blade and blade fragment within a 95 confidence interval equal 8.4 in 10,000 and 2.6 in 10,000,
respectively. It should be stressed that the findings presented in Rademaker and Bramm 2005 are
based on turbine models installed from 1984 to 2001, and reflect the general probability and risk based on machinery from that time period. As with any technology, the past decade of
advancement has led to improvements that will likely make turbines safer. For example, remote monitoring, automatic shutdown capabilities or blade feathering, more efficient turbines that
operate at lower RPMs rotations per minute, and improved blade composite materials are all advances in technology that are aimed at improving turbine performance, as well as lowering
risk and safety concerns.
3
For one example, on its accident summary report, Caithnesswindfarms.co.uk refers to an accident in which 17 bus passengers were killed in one single incident in Brazil in March 2012. The report fails to mention that the Wind Turbine Accident to
which it refers involved a bus crossing lanes and hitting a truck carrying wind turbine parts. The accident was found to be the fault of the bus driver, and as such should not be labeled a fatal wind turbine accident without qualification.
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While the longest distance reported for the throw of a broken blade or blade fragment in Rademaker and Bramm’s 2005 dataset were 150 meters 492 feet and 500 meters 1640 feet,
respectively, blades and blade fragments tend to fall closer to the turbine base California Energy Commission 2006. Where tower collapses and nacelle failures occurred within Rademaker and
Bramm’s 2005 dataset, the parts were recorded as falling within a radius less than or equal to the height of the turbine.
Rogers et al. 2011 further examined blade throw distances using the same dataset compiled by Rademaker and Bramm 2005. Their analysis concluded that the probability of a
part falling within a certain distance from a turbine is driven less by the size of the turbine and more by the release velocity of the blade fragment and, in turn, by the angular velocity of the
rotor, the position of the breaking point on the blade, and the size of the thrown piece Rogers et al.
2011; see Ch. 1 Figure 17.
Ch. 1 Table 2. Assessment of Wind Turbine Failures using Danish and German Data from 1984-2001 as Reported in Rademaker and Bramm 2005.
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Ch. 1 Figure 17. Rogers et al. 2011 Analysis of Blade Throw Dynamics.
Setback distances for public safety reasons have traditionally been based on the height of the turbine e.g. 1.5 times the total turbine height. However, the analysis performed by Rogers et
al. 2011, combined with incidents reported in Rademaker and Bramm 2005 and in the CWIF
database, illustrate that it is possible for blade fragments to be thrown greater distances than those estimated using turbine height alone. A more mathematical approach to determining
appropriate setbacks performed by Rogers et al. 2011 took into account variables related to the turbine height, blade fragment size, and probability of occurrence, to calculate the specific radius
of risk corresponding with a particular project. However, a key challenge with the Rogers et al. 2011 analysis is defining a risk level that can be agreed upon by all those involved in siting
decisions. In addition, in order to obtain realistic results from this analysis that applies to the turbine technology being used today, accurate blade failure statistics should be used.
Unfortunately, the best available structural failure data is presented in Rademaker and Bramm 2005 covering turbines operating between 1984 and 2001 and therefore may not be
representative of the technology used today. If the Rogers et al. 2011 methodology were to be applied in order to establish a setback distance, it is recommended that more recent failure data
be used in the analysis.
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3.2 Icing Considerations S
ECTION
S
UMMARY
Similar to other structures icing may occur on wind turbines. When ice falls or is flung from a moving blade, it can potentially become dangerous.
Rhode Island experiences weather conditions conducive to icing of turbine blades about 0-2 times annually. During those times, there is a risk of ice throw,
particularly if a turbine continues to operate.
The potential risk associated with ice throw can be minimized through setbacks, shutdown procedures, and ice detection mechanisms.
Wind turbines may accumulate a surface coating of ice during certain atmospheric and meteorological circumstances, such as ambient temperatures near freezing 0°C 32°F
combined with high relative humidity, freezing rain, or sleet. Under such icing-prone climatic conditions, two types of risks may occur. If a wind turbine continues to operate, ice fragments
clinging to turbine blades may be thrown outward due to aerodynamic and centrifugal forces. When a turbine is shut down or idling, ice fragments may fall downward from the blades or other
parts of the turbine as they may from other structures that experience icing. A first question to consider when evaluating the potential occurrence of ice fall and ice
throw incidents at a loc ation is how frequently icing conditions occur. Although Rhode Island’s
low topography and temperate latitude are not highly conducive to conditions in which ice can accrete to rotor blades, these conditions do occur in Rhode Island about 0-2 times annually
University of Massachusetts Amherst, 2000; NCDC, 2008. The University of Massachusetts at Amherst calculated a 0.88 annual probability of occurrence of an ice storm capable of producing
ice thicker than 0.63cm 0.25in or almost once per year, in New England Lacroix 2000. However, local icing conditions may vary considerably over short distances due to elevation. It is
recommended that data at a specific location be used to determine incidences of icing if possible Baring-Gould, 2006.
A second question to consider is how far ice fragments are likely to fall or be thrown in the event that icing conditions do occur. Surveys and modeling suggest that in extremely rare
instances, ice fragments may be thrown as far as hundreds of meters from the base of a turbine Seifert et al. 2003; Cattin et al. 2005. However, if a turbine is shut down during icing
conditions, the ice throw zone is much smaller. An assessment of icing risk performed for the Canadian Wind Energy Association estimates that only very high winds can cause fragments of
significant mass to be blown more than 50m 164ft from the base of a modern 2MW turbine while the turbine is stationary LeBlanc 2007. There have been zero 0 reported fatalities to the
public resulting from ice thrown from wind turbines Morgan et al. 1998; this fact, however, does not imply no risk to public safety.
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Icing of turbines and the impacts of icing can be managed through ice detection mechanisms, signage and visible warnings, setbacks, and most importantly, proper operating and
shutdown procedures during icing events. In order to ensure that a turbine does not operate during icing conditions, the turbine must
have an adequate icing detection system. Icing detection technology is a relatively new area of research, but detection systems are already in use commercially LeBlanc 2007. These systems
can be set up to trigger automatic or manual shutdown of a turbine or to activate blade heating systems that inhibit icing LeBlanc 2007. The most widely available type of icing detection
systems is mounted to the nacelle of a turbine and utilizes an ultrasonic vibrating probe; when the probe becomes coated with ice, its vibration slows, signaling to the instrument that icing has
occurred LeBlanc 2007. Other forms of ice detection system include the installation of cold- tolerant anemometers to measure variances in the relationship between detected wind speed
versus power generation and vibration sensors to detect rotor imbalances General Electric 2000.
3.3 Acoustic Impacts S
ECTION
S
UMMARY
Wind turbines produce noise through the rotation of blades and operation of the generator.
Turbines can produce white noise broadband noise, tonal noise, impulsive noise “swishing”, low-frequency noise, and infrasound.
Turbine noise dissipates with distance from the turbine, but is also affected by the physical conditions of a project location including topography, ground cover,
wind speed and direction. As a result, noise impacts may vary in a given location and over time. This can make setting noise standards or regulatory thresholds
difficult.
Low frequency noise 100Hz-20Hz and infrasound below 20Hz emitted from wind turbines are becoming an increasingly studied topic. Within the scientific
community, there is not yet complete consensus on the impact of infrasound from wind turbines on humans. Many researchers state that infrasound in the areas
surrounding wind turbines are at levels inaudible to humans, and that there a lack of medical evidence to suggest any health effect associated with wind turbine
infrasound, while others suggest that even at inaudible levels infrasound may have an effect on the human ear.
Background noise is an important factor to consider when predicting the acoustic impacts of wind turbines. Where ambient noise levels are high, as in densely
populations or industrial zones, turbine noise is less audible. Furthermore, during times of the day when ambient noise levels are lowest e.g. at night between
midnight and dawn turbine noise may be most noticeable.
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Wind turbine noise can be considered annoying. This is a highly subjective and individualized impact, and can be a significant nuisance to those people bothered
by it. The level of annoyance experienced by people living in proximity to a wind
turbine varies widely, and is often correlated with general attitudes towards the turbine in question, visibility of the turbine, and experience of shadow flicker
effects caused by the turbine.
Of the issues raised by community members when utility-scale wind turbines are proposed or installed in residential or rural areas, noise is a primary concern, especially for
residents whose homes are closest to the turbines AEI, 2012. This section describes the potential sources of noise from a wind turbine, the types of noise produced, and what is currently
known about potential health impacts to surrounding residents. Generalizing noise impacts is difficult as site-specific conditions that vary by project location and time of day or year greatly
influence the acoustic impacts experienced. While the noise produced by a wind energy project will vary based on the size and specifications of the turbines, the impacts to the surrounding
area will also vary based on site-specific conditions including the ambient noise levels, the topography, wind speed and direction, etc. Therefore, the noise impacts of two identical turbines
installed in two different locations will vary based on the physical conditions of the area. Wind turbine noise can result from both mechanical and aerodynamic operation of a turbine.
Mechanical noise can be caused by the gear box, generator, yaw drives, cooling fan, hydraulics, or other parts of the wind turbine. Aerodynamic noise is caused by interaction of the turbine
blades and the wind see Ch. 1 Table 3. Several different types of sound can result from wind turbine operation. Broadband noise, also called “white noise,” is composed of many frequencies
in the audio spectrum greater than 100Hz. Wind turbines produce broadband noise as blades
interact with the air, and such noise is experienced as a “whooshing” sound when the wind is
blowing. Tonal noise, also called pure tones, is a constant hum occurring at a distinct frequency. Turbines produce tonal noise
or “pure tones”, a constant hum occurring at a distinct frequency. Tonal noise may result from the mechanical operations of wind turbine components, such as
meshing gears RERL 2006. Pure tones are more noticeable when wind speeds are low, since high wind speeds lead to high aerodynamic turbine noise and ambient noise that obscures them.
Low-frequency noise measuring between 20 and 100Hz is produced by the aerodynamic operation of wind turbines, and measures 20-100Hz. Infrasound is a type of low-frequency noise
produced by wind turbine operation, and is below 20Hz. Infrasound is generally inaudible to humans, but can cause a sensation of pressure in the eardrums Møller and Pedersen, 2011. .
However, if the level is sufficiently high above 90dB humans may perceive infrasound. Infrasound is discussed in more detail later in this section. Finally, turbines produce impulsive
noise, which is characterized as “short acoustic impulses or thumping sounds that vary in amplitude with time” and “is caused by the interaction of wind turbine blades with disturbed air
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flow around the tower of a downwind machine” RERL 2006. Ch. 1 Table 3 presents a synopsis of the types of noise typically produced by wind turbines. The nature of the sound
produced by a turbine is to some degree influenced by the design of the turbine MA DEP and MA DPH 2012.
Ch. 1 Table 3. Sources and Types of Noise Potential Produced by a Wind Turbine Potty and Miller, 2012; Rogers, 2006.
Possible Sources of
Noise from a Wind Turbine
Mechanical Noise: caused by the gear box, generator, yaw drives, cooling fan,
hydraulics, etc.
Aerodynamic Noise: caused by the interaction of the turbine blades with the wind
and therefore is dependent on wind and rotor speed
Possible Types of Noise
Produced by a Wind Turbine
1. Broadband Noise: This is sound characterized by a continuous distribution of sound
Kategori