Environmental impact of wind energy

Abstract

Since the beginning of industrialization, energy consumption has increased far more rapidly than the number of people on the planet. It is known that the consumption of energy is amazingly high and the fossil based resources may not be able to provide energy for the whole world as these resources will be used up in the near future. Hence, renewable energy expected to play an important role in handling the demand of the energy required along with environmental pollution prevention. The impacts of the wind energy on the environment are important to be studied before any wind firm construction or a decision is made. Although many countries showing great interest towards renewable or green energy generation, negative perception of wind energy is increasingly evident that may prevent the installation of the wind energy in some countries. This paper compiled latest literatures in terms of thesis (MS and PhD), journal articles, conference proceedings, reports, books, and web materials about the environmental impacts of wind energy. This paper also includes the comparative study of wind energy, problems, solutions and suggestion as a result of the implementation of wind turbine. Positive and negative impacts of wind energy have been broadly explained as well. It has been found that this source of energy will reduce environmental pollution and water consumption. However, it has noise pollution, visual interference and negative impacts on wildlife.

Full text

Renewable and Sustainable Energy Reviews 15 (2011) 2423–2430
Contents lists available at ScienceDirect
Renewable and Sustainable Energy Reviews
journal homepage: www.elsevier.com/locate/rser
Environmental impact of wind energy
R. Saidur∗, N.A. Rahim, M.R. Islam, K.H. Solangi
Centre of Research UMPEDAC, Level 4, Engineering Tower, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia
article info
Article history:
Keywords:
Wind energy
Environmental aspect
Conventional energy
abstract
Since the beginning of industrialization, energy consumption has increased far more rapidly than the
number of people on the planet. It is known that the consumption of energy is amazingly high and the
fossil based resources may not be able to provide energy for the whole world as these resources will be
used up in the near future. Hence, renewable energy expected to play an important role in handling the
demand of the energy required along with environmental pollution prevention.
The impacts of the wind energy on the environment are important to be studied before any wind firm
construction or a decision is made. Although many countries showing great interest towards renewable
or green energy generation, negative perception of wind energy is increasingly evident that may prevent
the installation of the wind energy in some countries. This paper compiled latest literatures in terms of
thesis (MS and PhD), journal articles, conference proceedings, reports, books, and web materials about
the environmental impacts of wind energy. This paper also includes the comparative study of wind
energy, problems, solutions and suggestion as a result of the implementation of wind turbine. Positive
and negative impacts of wind energy have been broadly explained as well. It has been found that this
source of energy will reduce environmental pollution and water consumption. However, it has noise
pollution, visual interference and negative impacts on wildlife.
© 2011 Elsevier Ltd. All rights reserved.
Contents
1. Introduction ..........................................................................................................................................2424
1.1. Comparison of habitat impact with other energy sources...................................................................................2425
2. Positive impact of wind turbine ..................................................................................................................... 2425
2.1. Reduction of water consumption ............................................................................................................ 2425
2.2. Reduction of carbon dioxide emission .......................................................................................................2425
3. Negative impact of wind turbine ....................................................................................................................2426
3.1. Impacts on wildlife ...........................................................................................................................2426
3.1.1. Current figure on the accident for wildlife .........................................................................................2426
3.1.2. Factors affecting avian mortality ...................................................................................................2426
3.1.3. Prevention and protection..........................................................................................................2427
3.2. Noise impact..................................................................................................................................2428
3.2.1. Relationship between noise and wind .............................................................................................2428
3.3. Visual impact .................................................................................................................................2428
3.3.1. Color and contrast of wind turbine.................................................................................................2428
3.3.2. Distance of wind turbine with residential area ....................................................................................2428
3.3.3. Moving or stationary blades of wind turbine ......................................................................................2429
3.3.4. Shadow flickering...................................................................................................................2429
4. Conclusion............................................................................................................................................2429
Acknowledgement ...................................................................................................................................2429
References ........................................................................................................................................... 2429
∗Corresponding author. Tel.: +60 3 79674462; fax: +60 3 79675317.
E-mail address: saidur@um.edu.my (R. Saidur).
1364-0321/$ – see front matter © 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.rser.2011.02.024

2424 R. Saidur et al. / Renewable and Sustainable Energy Reviews 15 (2011) 2423–2430
1. Introduction
Due to the economical and technological developments around
the world, demand for energy is increasing significantly [1]. The
global economy grew 3.3% per year over the past 30 years and
energy demand increased 3.6% [2]. World energy production was
17,450 TWh [3] in 2004 and it is estimated that the world will con-
sume about 31,657 TWh in 2030 [4]. According to international
energy outlook 2009, world energy consumption will increase from
472 quadrillion Btu in 2006 to 552 quadrillion Btu in 2015 and 678
quadrillion Btu in 2030 – a total increase of 44% over the projected
period 2006–2030 as shown in Figs. 1 and 2 [5,6]. Various industries
and machineries/appliances used in different energy consuming
sectors are releasing contaminated gases to pollute the environ-
ment. Global warming and the associated changes in the world
climate pattern have been accepted world wide as the gravest
threat to humanity in the 21st century [7,8].
It is observed that there are growing concerns about future
global energy demand and environmental pollution. To reduce
these concerns to some extent, global communities are trying to
find and implement different energy saving strategies, technology,
and alternative sources of energy for different sectors that rely on
energy produced from different sources. In that regard wind energy
development will play a significant role to meet future energy
demand and reduce environmental pollution to a certain extent. For
the wind energy development, the United States passed Germany to
become world number one in wind power installations, and China’s
total capacity doubled for the fourth year in a row. Total worldwide
installations in 2008 were more than 27,000 MW, dominated by the
three main markets in Europe, North America and Asia. Global wind
energy capacity grew by 28.8% last year, even higher than the aver-
age over the past decade, to reach total global installations of more
than 120.8 GW at the end of 2008. Based on available figures from
11 of the top 15 countries representing over 80% of the world mar-
ket, WWEA recorded 5374 MW new installed capacity in the first
Fig. 1. World energy demand growth [5].
Fig. 2. Rate of world energy usage in terawatts (TW), 1965–2005 [6].
Fig. 3. Total world installed capacity [10].
quarter of 2009, equaling an increase of 23% compared with last
year in the same countries. Fig. 3 shows a total installed capacity of
152,000 MW worldwide at the end of 2009 [9,10].
Wind energy does not pollute the air like thermal power plants
that rely on combustion of fossil fuels such as coal or natural gas.
Wind turbines do not produce atmospheric emissions that cause
acid rain or greenhouse gases (GHGs). Wind turbines can be built
on farms or ranches, thus benefiting the economy in rural areas,
where most of the best wind sites are found [11,12].
Wind energy is considered as a green power technology because
it has only minor negative impacts on the environment. The energy
consumed to manufacture and transport the materials used to build
a wind power plant is equal to the new energy produced by the
plant within a few months of operation. Garrett Gross, a scientist
from UMKC in Kansas City, Missouri, states, “The impact made on
the environment is very little when compared to what is gained”
[13].
A few concerns associated with wind turbines are potential
interference with radar and telecommunication facilities. And like
all electric power generating facilities, wind generators produce
electric and magnetic fields. Although wind power plants have rel-
atively little impact on the environment compared to fossil fuel
power plants, concerns have been raised over the noise produced
by the rotor blades, visual impacts, and deaths of birds and bats
that fly into the rotors [14,15]. However, wind may play a role in
regional carbon dioxide emission control programs, such as those
being developed in New England and California. Fig. 4 shows that
wind energy has a low carbon footprint compared to biomass, PV
and marine [14].
It may be mentioned that there are number of works on the wind
energy development, design, performance, economics, and policy.
However, there is no comprehensive work on the environmental
impact of wind energy development. It is expected that this paper
may fill that gap.
Fig. 4. Range of carbon footprints for UK & European ‘low carbon’ technologies [14].

R. Saidur et al. / Renewable and Sustainable Energy Reviews 15 (2011) 2423–2430 2425
Table 1
Comparison of habitat impacts of wind energy to other energy sources [17].
Habitat impacts Coal Natural gas Oil Nuclear Hydropower Wind
Air and water pollution √√ √
Global warming √√ √
Thermal pollution of water √
Flooding of land √
Waste disposal √√
Mining and drilling √√ √√
Construction of plants √√ √√ √ √
1.1. Comparison of habitat impact with other energy sources
Table 1 shows the comparison of habitat impacts of wind energy
with other energy sources. It has been observed that wind energy
has the less habitat impacts compared to others sources of energy.
It can be stated that wind energy is the most environmental friendly
and the healthiest one compared to other energy sources [16].
2. Positive impact of wind turbine
Energy produced by wind turbines does not produce pollu-
tants like other sources of energy (i.e. coal, gas, and petroleum
based fuel). Wind energy may help to reduce the air pollutions by
replacing the current sources of conventional energy. As a result,
emissions especially carbon dioxide, nitrogen oxide and sulfur
dioxide can be reduced. It has been found in the literatures that
the emission of these gases is responsible for acid rain and global
warming which causes greenhouse gas effect, rise in sea-level, and
fluctuating weather conditions. Wind energy is an infinite type of
energy that can be harvested either in the mainland or on the ocean.
It was estimated that a 2.5 kW system can save 1–2 tonnes of CO2
and a 6 kW system can save 2.5–5tonnes CO2[18].
In a suitable site, wind turbines represent a relatively low-cost
method of micro-renewable electricity generation. They can bring
increased security for electricity supply to non-grid connected
locations and give some protection against electricity price rises.
Renewable Obligations Certificates (ROCs) can be received by gen-
erating electricity. These can then be sold to electricity generators
to allow them to meet their targets to derive a specified proportion
of the electricity they supply to their customers from renewable
energy sources [19]. A consumer can benefit from onsite genera-
tion of power by qualifying for exemption from the Climate Change
Levy. One can also be paid for any surplus of electricity to supply
to the grid. According to the fourth assessment report released by
the Intergovernmental Panel on Climate Change (IPCC), the warm-
ing of the earth over the past half century has been caused by
human activities. The main culprits are the greenhouse gases emit-
ted by burning of fossil fuels, in particular carbon dioxide (CO2).
Wind power can provide energy while reducing the emission of
CO2. According to the World Energy Commission, use of one million
kWh of wind power can save 600 tonnes of CO2emission. Therefore,
massive use of wind power will help mitigate climate change. The
use of wind power can also avoid regional environmental problems
brought about by burning coal [20].
2.1. Reduction of water consumption
In an increasingly water stressed world, water consumption is
vital and is a great concern especially for countries like Singapore
where clean water is highly valuable and scarce. It may be men-
tioned that conventional power plants use large amounts of water
for the condensing portion of the thermodynamic cycle. For coal
power plants, water is also used to clean and process fuel. Amount
of water used can be millions of liters per day. By reducing the
usage of water, water can be preserved and used for other purposes.
Table 2
Water consumption of conventional power plant and renewable energy based
sources [21,22].
Technology gal/kWh l/kWh
Nuclear 0.62 2.30
Coal 0.49 1.90
Oil 0.43 1.60
Combined cycle gas 0.25 0.95
Wind 0.001 0.004
Solar 0.030 0.110
Table 3
Reduction of different pollutants [24].
Gases CO2NOxSO2
Reduction on emission per year (short-tonnes) 3251 20 421
California energy commission [21] estimated the amount of water
consumption for conventional power plants as shown in Table 2.
From Table 2, it has been found that water usage for wind turbine is
lower than the conventional power plants and solar energy system.
It was reported that the average amount of water consump-
tion in Malaysia for conventional power plant was about 1.48 l/kWh
while wind energy operated power sources used only 0.004 l/kWh
for the year 2007[20].
2.2. Reduction of carbon dioxide emission
Generally, wind energy has zero direct air pollution. A small
amount of CO2emissions is released by the wind energy during
its construction and maintenance phases. However, this amount
of CO2is much less than other fossil-fuel based power plants. This
amount of CO2produced can actually be absorbed by the tree by the
process of photosynthesis. Every unit (KWh) of electricity produced
by the wind displaces a unit of electricity which would otherwise
have been produced by a power station by burning fossil fuel [17].
It does not produce carbon dioxide, sulfur dioxide, mercury, par-
ticulates, or any other type of air pollution, as do fossil fuel power
sources [23].
A study by the Irish national grid stated that “Producing elec-
tricity from wind reduces the consumption of fossil fuels and
therefore leads to emissions savings”, and estimated reductions in
CO2emissions ranging from 0.33 to 0.59 tonnes of CO2per MWh
[13]. Amount of pollutants that can be reduced is shown in Table 3.
According to data from the German Federal Ministry for the
Environment, Nature Conservation and Nuclear Safety, approxi-
mately 67 million tonnes of CO2was avoided in 2006 by generating
electricity through wind, biomass, photovoltaics and hydropower.
Among these few types of electricity generation systems, wind
energy plays the most important role [25]. Emission reductions
can be calculated using carbon emission factor 640 gCO2/kWh and
following equation [26]:
CO2(in tonnes) =
A×0.3×8760 ×640
1000 (1)

2426 R. Saidur et al. / Renewable and Sustainable Energy Reviews 15 (2011) 2423–2430
Table 4
Regional and overall birds fatality rates in United States [27].
Region Studies MW Rotor diameter (m) Birds/turbine/year Birds/MW/year
Min Max Avg. Min Max Avg. Min Max
Northwest 4 397 47 65 1.9 0.6 3.6 2.7 0.9 2.9
Rocky Mts. 2 68 41 44 1.5 1.5 1.5 2.3 2.0 2.5
U. Midwest 4 254 33 48 2.7 1.0 4.5 4.2 2.0 5.9
East 2 68 47 72 4.3 0 7.7 3.0 2.7 11.7
Overall 12 787 33 72 2.3 0.6 7.7 3.1 0.9 11.7
where Ais the rated capacity of the wind energy development in
MW; 0.3 is a constant, the capacity factor, which takes into account
the intermittent nature of the wind, the availability of the wind
turbines and array losses; 8760 is the number of hours in a year.
A typical turbine was installed in the Perhentian Island currently
with a rated capacity of 100 kW and estimated that 168 tonnes of
CO2can be reduced annually. According to ecological footprint, a
forest absorbs approximately 3 tonnes of CO2per acre of trees per
year [17]. Hence, a 100 kW wind turbine will prevent as much CO2
from being emitted each year as could be absorbed by 24 acres of
forest. While saving about 168 tonnes of CO2each year, a 12.5 kW
wind turbine still can produce a significant amount of electricity.
3. Negative impact of wind turbine
Besides the positive impact, it is important to study the negative
impact of a wind turbine technology. Before any decision is made,
the worst condition has to be determined and predicted. By doing
this, the damage can be reduced to minimum. The most significant
negative impact of a wind turbine technology is the wildlife, noise
and visual impact which will be discussed in the following sections.
Some other impacts include the distraction of radar or television
reception due to magnetic forces generated by the wind turbine,
and the increased possibility of being struck by lightning.
3.1. Impacts on wildlife
Many researchers found that wind energy is one of the healthiest
and environmental friendly options among all the energy sources
available today. Wind energy is the energy source that is most com-
patible with animals and human beings in the world. However,
there are some minor wildlife impacts reported by few researchers.
The wildlife impacts can be categorized into direct and indirect
impacts. The direct impact is the mortality from collisions with
wind energy plant while the indirect impacts are avoidance, habi-
tat disruption and displacement. However, the impacts are smaller
compared to other sources of energy [27]. Furthermore, researchers
and industries are trying to find protections and preventions for the
wildlife impacts of wind energy. Through researches and based on
the available evidences, many found that the appropriate position
of wind plants do not contribute to a significant number in reduc-
tion of birds’ mortality. Studies also show that climate changes have
much more significant threat to wildlife [28].
3.1.1. Current figure on the accident for wildlife
3.1.1.1. Birds. It is found that birds are one of the largest victim
groups in mortality collision of wind turbines around the world
[29]. Regional and overall birds’ fatality rates in United States are
shown in Table 4.
On the other hand, Sovacool and Benjamin stated that wind
energy killed about twenty times fewer birds than fossil fuels. The
number of birds killed by wind turbines can be negligible compared
to other human activities [30].
It was found that out of the total number of birds killed in a year,
only 20 deaths were due to wind turbines (for an installed capacity
Table 5
Leading human-related causes of bird kills in United States [24].
Human-related causes Number of birds kill per year (million)
Cats 1000
Buildings 100
Hunters 100
Vehicles 60–80
Communication towers 10–40
Pesticides 67
Power lines 0.01–174
Wind turbines 0.15
of 1000 MW), while 1500 deaths were caused by hunters and 2000
caused by the collisions with vehicles and electricity transmission
lines (they are almost “invisible” for birds [31]).
Summing up, it is important to understand that whatever
impacts wind turbines have, on the one hand they are very obvi-
ous, and on the other hand, it is possible to minimize them through
proper design and planning. In contrast, the impacts of thermal or
nuclear energy production are slow to appear, are long term and
no matter how much effort and money are spent, it is impossible
to minimize them. In conclusion, we must decide that if we have
to produce electricity, it is certainly preferable to produce it in a
way which has the smallest possible impact on the environment.
From a technical and economic standpoint, the most mature form
of renewable and “clean” energy is wind energy. It can effectively
contribute to combating climate change while at the same time pro-
viding various environmental, social and economic benefits [31].
Table 5 shows the leading human-related causes of bird kills in
United States [32]. AWEA calculates that if wind energy were used
to generate 100% of U.S. electricity needs, wind energy would only
cause one bird death for every 250 human-related bird deaths with
reference to the current rate of bird kills as described in Table 5
[24].
3.1.1.2. Bats. Bats’ mortality contributes a significant number due
to wind turbine installation around the world [33]. Regional and
overall bats’ fatality rates in United States are shown in Table 6.
3.1.1.3. Raptors. Table 7 shows the regional and overall raptors’
fatality rates in United States. A significantly low number of rap-
tors’ fatality compared to birds and bats’ fatality in United States is
found.
3.1.2. Factors affecting avian mortality
In the installation of a wind turbine, danger to avian is often the
main complaint against it. In order to reduce the numbers of avian
mortality, we must find out the main reason of the avian mortality
caused by the collision of wind turbines [34].
3.1.2.1. Impact of lighting. Studies show that birds may become dis-
oriented in poor weather or foggy night. Subsequently, the avian
are attracted to light emitted from wind energy plants which leads
to the increasing number of avian fly through the wind plants and
their vulnerability from collision with wind turbine blades [35].

R. Saidur et al. / Renewable and Sustainable Energy Reviews 15 (2011) 2423–2430 2427
Table 6
Regional and overall bats’ fatality rates in United States [27].
Region Studies MW Rotor diameter (m) Bats/turbine/year Bats/MW/year
Min Max Avg Min Max Avg Min Max
Northwest 4 397 47 65 1.2 0.7 3.2 1.7 0.8 2.5
Rocky Mts. 2 68 41 44 1.2 1.0 1.3 1.9 1.3 2.2
U. Midwest 4 254 33 48 1.7 0.1 4.3 2.7 0.2 6.5
East 2 68 47 72 46.3 28.5 47.5 32.0 31.7 43.2
Overall 12 787 33 72 3.4 0.1 47.5 4.6 0.9 43.2
Table 7
Regional and overall raptors fatality rates in United States [27].
Region Studies MW Rotor diameter (m) Raptors/turbine/year Raptors/MW/year
Min Max Avg. Min Max Avg. Min Max
Northwest 4 397 47 65 0.05 0.00 0.07 0.07 0.00 0.09
Rocky Mts. 2 68 42 44 0.03 0.03 0.04 0.05 0.05 0.06
U. Midwest 4 254 33 48 0.00 0.00 0.01 0.00 0.00 0.04
East 2 68 47 72 0.02 0.00 0.02 0.01 0.00 0.02
Overall 12 787 33 72 0.03 0.00 0.07 0.04 0.00 0.09
California 3 ∼878 13 33 0.15 0.01 0.24 1.37 <0.1 2.24
Table 8
The percentage of birds at different heights of flight [37].
Percentage of birds Height of flight (m) Percentage of birds Distance from turbine (m)
70–75% <21 74.8–80% >31
16–17.5% 21–51 5–14.1% <16
3.1.2.2. Impact of weather. In a study of Gregory et al. [36] it was
found that only 3 out of 48 fatalities occur when the weather is
not a factor. Although migrating birds generally fly at altitudes
higher than 150 m, migrants tend to fly lower during heavy over-
cast weather such as high winds, low clouds, and rain. This increases
the birds’ potential of flying through the wind turbines, especially
when light attraction may be an issue [36].
3.1.2.3. Tower design. A study [27] found that the relatively high
bird mortality at Altamont Pass is due to the large numbers of older
wind turbines located there. The design of the majority of these
older turbines has lower hub heights, shorter rotor diameters which
caused the blades to spin at high RPM, and tighter turbine spacing
compared to typical newer wind turbines. Older turbines often have
the lattice towers which attract nesting of birds.
3.1.2.4. Height of flight. Sarah and Ellen [37] stated that fewer birds
that flew near sites with turbine strings compared to reference
sites. Authors found that the birds flying through turbine strings
will adjust their flight patterns when turbine blades are rotated.
Table 8 shows the percentage of birds at different heights of flight
and different distances from wind turbines.
The rotor blade height is normally 21 m and 16–17.5% of birds
that flew at this range of height have risks in collision with rotors.
About 5–14.1% of birds that flew within 16 m from turbines put
themselves in risk of collision with rotors.
3.1.3. Prevention and protection
To reduce the number of avian mortality, prevention and pro-
tection must be carried out. If negative impacts of wind energy on
wildlife are reduced, wind energy will become more environmen-
tal friendly and can be used widely all around the world. New wind
projects should be carefully planned to minimize the environmen-
tal impact [27].
3.1.3.1. Formation of society to protect bird. In United Kingdom, a
society (Royal Society for the Protection of Birds, RSPB) is formed
to protect the bird mortality due to wind turbine installment. In
California, the wind energy industry joined with other stakehold-
ers such as government officials and environmental groups to form
the National Wind Coordinating Committee [27]. These societies
are engaged in resolving problems and issues on wildlife associ-
ated with wind energy development. They also give funding for
researches on wind energy and wildlife issues.
3.1.3.2. Guidelines and consultancy for industry. In United States,
the U.S. Fish and Wildlife Service developed voluntary guidelines
for the sitting of wind energy facilities. These guidelines make rec-
ommendations regarding sitting of the wind plants. However, the
wind industries are resisting such guidelines. A wildlife consultant
may identify any issues of possible concern. The consultant exam-
ines the proposed site and prepares a detailed report on impacts for
review for the developer. These surveys reduce the threat to avian
to minimal levels [38].
3.1.3.3. Radar technologies. Avian radar was developed for NASA
and United States to detect birds as far as four miles away. The
system will determine whether the birds are in danger or in
safe. If the system detects that a bird is in danger, it will shut
down the wind turbines automatically. Once a bird crossed the
turbine safely, the system will automatically restart the turbine
[39].
3.1.3.4. Improvement of tower design. A new tubular steel tower can
be used to substitute the existence of the lattice tower in older wind
turbines. The new turbines with tubular steel towers which have
smooth exteriors prevent the nesting of birds [39].
3.1.3.5. Researches on turbine lighting. The wind industries are cur-
rently consulting with the Federal Aviation Agency (FAA) to reduce
the aviation safety lighting on wind projects. The main purpose
of this discussion was to ensure that the lighting of the wind tur-
bines do not attract the migrating birds in poor weather or on foggy
nights. The minimum lighting is necessary for safety and security

2428 R. Saidur et al. / Renewable and Sustainable Energy Reviews 15 (2011) 2423–2430
purposes and techniques should be used to prevent casting glare
from the site [39].
3.1.3.6. Vertical shaft turbines. Study of Cathy [40] showed that
vertical shaft turbines are safer and produce twice the energy of
prop-style turbine. In addition, their slow turning blades gently
generate clean, abundant energy for a revitalized, green Earth. Its
design can decrease a bird’s mortality from collision of the wind
turbine [40].
3.2. Noise impact
The most critical environmental impact of wind turbine is the
noise pollution. The effect of noise pollution has the potential to
lower property values within a varying radius of the construction.
As a result, turbines should be set back from residences and prop-
erty lines to insulate participating and neighboring landowners
from noise and safety concerns. Before building a wind turbine,
engineers must be familiar with the types of noise a wind turbine
produce.
Noise emitted by a wind turbine can be divided into mechani-
cal and aerodynamic types. Mechanical noise is produced by the
moving components such as gear box, electrical generator, and
bearings. Normal wear and tear, poor component designs or lack of
preventative maintenance may all be factors affecting the amount
of mechanical noise produced [41]. Aerodynamic noise is devel-
oped by the flow of air over and past the blades of a turbine. Such a
noise tends to increase with the speed of the rotor. For blade noise,
lower blade tip speed results in lower noise levels. Of particular
concern is the interaction of wind turbine blades with atmospheric
turbulence, which results in a characteristic “whooshing” sound
[42].
Mechanical noise can be minimized at the design stage (side
toothed gear wheels), or by acoustic insulation on the inside of
the turbine housing. Mechanical noise can also be reduced during
operation by acoustic insulation curtains and anti vibration sup-
port footings. Aerodynamic noise can be reduced by careful design
of the blades by the manufacturers who can minimize this type of
noise [43].
3.2.1. Relationship between noise and wind
Wind direction has the tendency to increase noise level rel-
ative to the turbine and the receiving point. The highest noise
level can be found at the bottom of wind turbine situated with
the wind direction from the plant towards the receiving point
[44].
Fig. 5 shows the relationship between noise level and wind
speed from a wind turbine. The sound level is represented with the
L90 metric, which is the best descriptor for the continuous sound
from the wind turbine. This example is taken from a site relatively
far from the wind turbine, 300 m. The measuring time in the dia-
gram is 2 weeks with varying wind speed levels from 1 to 9 m/s. It
can be seen that the correlation between the sound level and the
wind speed at this particular site was relatively low. From this fig-
ure, it can be seen that wind turbine noise is independent of wind
speed for the distance higher than 300 m which also recommended
for guideline [44].
A small amount of noise is generated by the mechanical compo-
nents of the turbine. To imagine clearly, a wind turbine 350 m from
Fig. 5. Wind speed and noise level in dBA L90 versus time [44].
a residence is not even noisier than a kitchen refrigerator which is
clearly shown in Table 9.
3.3. Visual impact
Visual impact assessment has been carried out by Ian [46] to
evaluate the negative effect of wind turbine. Authors [47] reported
that the visual impact varies according to the wind energy tech-
nology such as color or contrast, size, distance from the residences,
shadow flickering, the time when the turbine is moving or station-
ary and local turbine history.
It may be mentioned that most of the visual impact assessment
was based on the geographical information system (GIS). When a
particular site is proposed, GIS and visibility assessment can help
determine the affected areas and the likely degree of the visual
impact [48]. The affected areas are called zones of visual influences
(ZVIs) under the planning guidelines used in the UK [49]. Levels of
impact can potentially be mapped by also taking account of distance
and setting as has been used for transmission lines [50].
3.3.1. Color and contrast of wind turbine
Bernd [51] stated that when wind turbines are painted in white
(or any grey tone), this will be a minor issue, as lightness will tend
to dominate color differences. Basically wind turbines are painted
in light grey color to make the turbine blades like skyline. In addi-
tion, the color of turbine is made green at the base and gradually
changed to grey at top to reduce the contrast levels. This conse-
quently will reduce the visual impact [52]. There is an argument
that if the turbine is blended with the skyline color, it may be a
cause of killing more birds. Since the effect of the wildlife impact is
not evident as compared to the visual impact, it is recommended
to choose a color of turbine blended with skyline.
In the paper written by Ian and David [53] it was reported that
that the impact level of contrast caused by wind turbine increases
with the increase of contrast with the surroundings. Authors also
mentioned that the contrast level declines with distance. Certainly,
the designer will tend to blend the turbine pixels with the back-
ground pixels at the turbine’s edges. At larger distances this effect
is greater as a higher proportion of pixels are at the edge. The per-
centage contrast in different conditions is shown in Table 10.
3.3.2. Distance of wind turbine with residential area
Fig. 6 shows the visual impact decreases with the increase of
distance of turbine from the residential area.
Table 9
Summary of sound level limits for wind turbines [45].
Wind speed at 10 m height (m/s) 45678910
Wind turbine sound level limits class 3 area (dBA) 40 40 40 43 45 49 51
Wind turbine sound level limits class 1 and 2 area (dBA) 45 45 45 45 45 49 51

R. Saidur et al. / Renewable and Sustainable Energy Reviews 15 (2011) 2423–2430 2429
Table 10
Calculated contrast levels under the different conditions [53].
Condition (increasing contrast) % contrast at 4km
Deep haze/fog nearly hiding turbines 1.9
Clear air, lighting from behind turbines 9.5
Mid-level haze/fog 7.4
Clear air, lighting from the front 20.5
Clear air, dark clouds behind 27.9
Fig. 6. Graph of visual impact versus distance. The value 3.0 is a neutral response.
The five lines represent the different atmospheric conditions as shown in table [53].
Table 11
Intensity of shadow flickering with its occurrence condition [52].
Intensity of shadow
flickering
Condition
Higher shadow
flickering intensity •Sunrise or sunset where the cast shadows are
sufficiently long
•Wind turbine rotor plane is perpendicular to
the sun-receptor (rotor diameter)
•Larger wind turbine
•Smaller distance with resident
Lower shadow flickering
intensity •Wind turbine rotor plane is in plane with the
sun (blade thickness)
3.3.3. Moving or stationary blades of wind turbine
The visual impact is influenced by the movement of wind tur-
bine or when it is stationary as discussed by Jaskelevicius and
Uzpelkiene [31]. It was found that turbine will create more visual
impact compared to stationary condition. Authors concluded that
the negative visual effect during the moving condition is lower than
that when the blades are stationary. It may be mentioned that when
the turbine is moving, the blades can be quite hard to see.
3.3.4. Shadow flickering
In general shadow flickering is produced in two ways: shadow
flicker caused by moving blade and the reflection of sun ray on
the wind turbine body or so called ‘disco effect’. Shadow flicker-
ing caused by the wind turbine is changed with the light intensity
caused by the moving blade casting shadows on the ground and
stationary objects, such as a house. This will cause the disturbance
for residents living in the surrounding area of the turbine. In addi-
tion, the reflection of the sun ray shining on the turbine is caused
by the periodic flashes of light. This can be minimized by optimiz-
ing the rotor blade surface smoothness as well as by coating the
turbine with a material having less reflection properties as shown
in Table 11.
3.3.4.1. Problems caused by shadow flickering. The problem of shad-
ows caused by wind turbine is not a serious issue because the
turbines are relatively small and therefore did not result in long
shadows. As the hub-height of the turbine increases, the impact of
their shadows increases with it. This leads to significant visual pol-
lution from which the surrounding residents must be protected.
This moving shadow, at a frequency of three times of the rotor
speeds (where the turbine has three blades), can lead to a pulsating
light level especially in rooms which are naturally lit.
3.3.4.2. Solution to overcome shadow flickering. There is a need to
minimize the shadow flickering in order to widen the use of wind
energy in future. If the shadow at certain area is more than the
allowable guideline, one should shut down the wind turbine. This
can be done by using a module especially designed for this pur-
pose. Simple module of this type carries out their turbine switching
according to a calculated shadow calendar, without taking into
account if shadows are really possible at the theoretical times of
shadow [54].
On the other hand, modules which use a light sensor would
allow the wind turbine which can automatically cause shadow to
stay in service on cloudy days but it is only allowed not more than
8 h per year. In addition, turbines can be made to operate in a low
noise mode, and a special device can be fitted to switch off the
machine for a short period when a shadow flickering may occur.
4. Conclusion
Following conclusions can be drawn from this study:
It has been found that wind energy is clean, environmental
friendly, and cheaper compared to other sources of renewable
energy. As such this source of energy will protect the earth from
the atmospheric contamination. It was also found that water con-
sumption can be reduced with the usage of wind energy compared
to petroleum based power plants that produce energy. It was also
found that wind energy has minimal impacts on the habitat com-
pared to other sources of energy.
However, energy produced by wind turbine is not free from neg-
ative impacts. It has been found that wildlife is killed with the
collision of wind turbines in many cases. This source of energy
also creates sound noise which is annoying to the vicinity of wind
turbine installation project. Visual performance is also interfered
by the wind turbine. If wind turbines are designed and planned
carefully, many of these negative impacts can be minimized.
Acknowledgement
The authors would like to acknowledge the University of Malaya
for funding the project. The research has been carried out under the
Project no. RG056/AET09.
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