Wind Power System

8/10/2019 Wind Power System

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The University of Jordan

Electrical Engineering Department

The Wind Power System

(Physical, Offshore and Noise)

Prof. Mohammed zaki khader

The Physical By : Yousuf Al-Khateeb 0090550

The offshore By : Anas Mahmoud Al-Najdawi 009537

The Noise By : Anas Mahmoud Kataa 0115115


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The Physics of the Wind Power System

Done by : Yousuf Al-Khateeb 0090550

Overview:

What is wind?

Wind is the flow of gases on a large scale. On the surface of the Earth, wind consists o

the bulk movement of air.

How to classify?

Winds are commonly classified by:

1) Theirspatial scale.

2) Theirspeed.

3) The types of forces that cause them.

3) The regions in which they occur.

4) Their effect.

Winds have various aspect, one important aspect is its velocity; another the density of

gas involved; another is the energy content orwind energyof a wind.

Inmeteorology,winds are often referred to according to their strength, and the direction

from which the wind is blowing. Short bursts of high speed wind are termed gusts. Stron

winds of intermediate duration (around one minute) are termedsqualls.

Long-duration winds have various names associated with their average strength, such

asbreeze,gale,storm,hurricane,andtyphoon.Wind occurs on a range of scales, from

thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land

surfaces and lasting a few hours.
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What causes wind?

toglobalwinds resulting from the difference in absorption ofsolar energybetween

theclimate zoneson Earth.

The two main causes of large-scaleatmospheric circulationare the differential heating

between the equator and the poles, and the rotation of the planet (Coriolis effect).

Within the tropics,thermal lowcirculations over terrain and high plateaus can

drivemonsooncirculations. In coastal areas thesea breeze/land breeze cycle can defin

local winds; in areas that have variable terrain, mountain and valley breezes can domina

local winds.

Air pressure

Wind is caused by air flowing fromhigh pressure tolow pressure.Since the Earth isrotating, the air does not flow directly from high to low pressure, but it is deflected to theright (in the Northern Hemisphere; to the left in the Southern Hemisphere), so that thewind flows mostly aroundthe high and low pressure areas.

This effect of the wind "feeling the Earth turn underneath it" is important for very largeand long-lived pressure systems. For small, short-lived systems (such as in the coldoutflow of a thunderstorm) the wind will flow directly from high pressure to low pressure
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The closer the high and low pressure areas are together, the stronger the "pressuregradient", and the stronger the winds, and the higher difference in pressure the strongethe wind. On weather maps, lines of constant pressure are drawn (as in the example,above) which are called "isobars". These isobars are usually labeled with their pressurevalue in millibars (mb). The closer these lines are together, the stronger the wind.

The curvature of the isobars is also important to the wind speed. Given the samepressure gradient (isobar spacing), if the isobars are curved anticyclonically (around thehigh pressure in the above example) the wind will be stronger. If the isobars are curvedcyclonically (around the low pressure in the example above) the wind will be weaker.

Near the surface of the Earth, friction from the ground slows the wind down. During tday, whenconvective mixing is stirring up the lower atmosphere, this effect is minimized

At night, however, when convective mixing has stopped, the surface wind can slowconsiderably, or even stop altogether.

Wind can be thought of one way that the atmosphere moves excess heat around.
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Directly or indirectly, wind forms for the promary purpose of helping to transport excessheat either away from the surface of the Earth, where sunlight causes an excess ofenergy buildup, or from warm regions (usually the tropics) to cooler regions (usually thehigher latitudes).

Extra tropical cyclones accomplish much of this heat transport outside of the tropics,

while in the tropics thetrade winds,monsoons,andhurricanes transport much of the he

Interesting facts:

WORLD RECORD WIND SPEED The highest wind speed ever recorded on thesurface of the Earth was 231 mph on April 12 1934, atop Mt. Washington, NewHampshire. This high-elevation weather station experienced the winds of an extremelystrongjet stream that had descended unusually low in the atmosphere.

THE WIND AFFECTS THE EARTH'S ROTATION During the northern hemispherewinter, the stronger westerly winds that build up in the Northern Hemisphere, combinedwith frictional drag at the Earth's surface, actually produce a very small, but measurable

increase in the speed of rotation of the Earth.

Global wind patterns

Global wind patterns:Winds are named by the direction from which they blow. The glo

is encircled by six major wind belts, three in each hemisphere. From pole to equator they

are the polar easterlies, the westerlies and the trade winds. All six belts move north in th

northern summer and south in the northern winter.

Polar Easterlies:At about the latitude of Norway and northward (60-90 degrees) thePoeasterlies blow irregularly from the east and north.

Polar Front:Between the polar easterlies and the westerlies is thepolar front.

Westerlies:At about the latitude of Western Europe and the United States (30-60 degre

theWesterlies blow from the west, tending somewhat toward the north. This causes mo

weather in the United States to move from west to east.

Horse Latitudes:Where the Westerlies meet the trade winds at about 30 degrees

(Jacksonville, Florida) is theHorse latitudes,also Variables of Cancer, Subtropical High

orSubtropical ridge.This is a region of high pressure, dry air and variable winds and isassociated with deserts over land.

Trade Winds:South of about 30 degrees the northern or northeasttrade winds blow

mostly from the northeast toward the equator. These were the sailor's favorite winds sinc

the weather was warm and the winds usually blew steadily in an advantageous direction

Columbus used these to sail to the Caribbean.
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Doldrums:At about the equator is Intertropical Convergence Zone ordoldrums,a region

light and irregular wind broken by occasional thunderstorms and squalls. The width and

exact location of the doldrums is hard to predict. Sailing ships are sometimes becalmed

here for many days waiting for a proper wind.

Southern hemisphere:In the southern hemisphere the belts are reversed. The southea

trade winds blow from the southeast toward the equator. The southern equivalent of thehorse latitudes (or Variables of Cancer) is called the Variables of Capricorn. The southe

westerlies start somewhat south of South Africa. They tend to be stronger than the north

westerlies because they are mostly over water (roaring forties). The southern polar

easterlies are mostly over Antarctica.

The six major wind belts .

Seasonal shifts:All of the belts move north during the northern summer and south duri

the northern winter. Because global heating and cooling lags behind the position of the s

they reach their northernmost latitude at or after the end of the northern summer. This

brought the trade winds within reach of the Spain and Portugal and determined the sailin

time of theSpanish treasure fleet.The northernmost position of the wind belts correspon

to the Atlantichurricane season.

Land and sea breezes:Land gains and loses heat more rapidly than water. During the

the land warms more rapidly than the water. The air above land warms, becomes thinne

and rises drawing cooler air landward from the sea. At night the process reverses and co

heavy air from the land flows out to sea. Theseland and sea breezes are important alon

the coast.Monsoon:The annual equivalent of the daily land and sea breezes is the yearlymonso

During summer the continents heat more rapidly than the oceans. Air over the continent

warms, thins and rises drawing cooler moist ocean air landward, producing awet seaso

During winter the process reverses and cold, dry heavy air flows outward from the

continents, producing adry season.The monsoon is most striking in south Asia because

the size of the Eurasian landmass and because the Himalayas tend to bottle up the air
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above the continent. Approximations of the Indian monsoon exist in other places but the

are poorly developed.

Ocean Gyre:The fact that the westerlies and trade winds blow in opposite directions an

that the continents prevent water from circling the globe contributes to the formation of

circularocean currents,clockwise in the northern hemisphere and counterclockwise in th

southern hemisphere. The Coriolis force also plays a part. The trade winds push waterwest. At the doldrums it flows back east producing theequatorial countercurrent.

The five major ocean gyres .

Coriolis force, Hadley cell and other things:In the northern hemisphere theCoriolis

effect causes wind and water currents to bend to the right (clockwise). Cold heavy air flo

south from the north pole and is bent west, forming the polar easterlies. Warm air rises a

the equator drawing air from the north which bends to the west, contributing to the trade

winds. The Coriolis effect bends the westerlies and trade winds slightly clockwise in the

northern hemisphere.

Hot air rises at the doldrums. As it rises it cools producing thunderstorms. The dry air flow

north at a high altitude and descends at the horse latitudes and flows back to the equato

with the trade winds. This is called theHadley cell.There is also aFerrel cell over the

westerlies and a polar cell over the pole. There are other complexities, not all of which a

properly understood.
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The offshore of The Wind Power System

Done by : Anas Al-Najdawi 0095370

UK Green Investment Bank to Raise 1 Billion for Offshore Wind

At the time of announcing its performance for the financial year, the UK GreenInvestment Bank also announced plans to raise 1 billion for a new fund to acquireequity stakes in operational offshore wind projects in the UK. The move is expected

boost the offshore wind sectors rapid growth.

The Green Investment Bank (GIB) has already invested in 5 large offshore wind farmsince its inception in November of 2012, including the majestic London Arraythelargest offshore wind farm in the world. The group have already committed 668 millto 18 green energy projects over the past financial year, more than doubling the numbof projects it backed in its first year, making them the most active investor in the UK

green industry economy.

GIBs plans for a dedicated offshore wind fund are a real boost for our industrialstrategy in a sector where we have a strong competitive advantage compared to othercountries, said Vince Cable, the British Business Secretary. There are great

opportunities for British companies and the industry has the potential to create 30,000

jobs for the UK.

The move has also been greeted with enthusiasm from others in the renewable industr

The GIBs offshore wind fund will provide a significant boost to the UKs offshore

wind industry, at a time when its expanding by leaps and bounds, saidRenewableUDirector of External Affairs, Jennifer Webber.

It will create a virtuous cycle by encouraging more private investors to come forward

this will in turn enable offshore wind farm developers to invest in further projects. Mothan 13,000 people are already employed full time in the UKs world-leading offshorwind industryand thats set to grow to 45,000 jobs by 2023. The establishment of thfund by the GIB helps to secure those jobs for the future.


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Offshore wind powerrefers to the construction ofwind farmsin bodies of water togenerateelectricity from wind.Better wind speeds are available offshore compared toland, so offshore wind powers contributionin terms of electricity supplied is higherandNIMBYopposition to construction is usually much weaker. However, offshore wfarms are relatively expensive. At the end of 2012, 1,662 turbines at 55 offshore wind

farms across 10 European countries are generating electricity enough to power almostfive million households. At the end of June 2013 total European combined offshore wenergy capacity was 6,040 MW.

As of 2010SiemensandVestaswere turbine suppliers for 90% of offshore wind powwhileDong Energy,VattenfallandE.onwere the leading offshore operators. As ofOctober 2010, 3.16 GW of offshore wind power capacity was operational, mainly inNorthern Europe. According toBTM Consult,more than 16 GW of additional capacitwill be installed before the end of 2014 and the United Kingdom and Germany willbecome the two leading markets. Offshore wind power capacity is expected to reach atotal of 75 GW worldwide by 2020, with significant contributions from China and theUnited States.

As of 2013 the 630 MWLondon Arrayis the largest offshore wind farm in the world,with the 504 MWGreater Gabbard wind farmas the second largest, followed by the 3MWWalney Wind Farm.All are off the coast of the UK. These projects will be dwarby subsequent wind farms that are in the pipeline, includingDogger Bankat 9,000 M

Norfolk Bank (7,200 MW), and Irish Sea (4,200 MW). In the end of June 2013 totalEuropean combined offshore wind energy capacity was 6,040 MW. UK installed 513MW offshore windpower in the first half year of 2013.

Definition

Offshore wind power refers to the construction ofwind farmsin bodies of water togenerateelectricity from wind.Unlike the typical usage of the term "offshore" in themarine industry, offshore wind power includes inshore water areas such as lakes, fjord

and sheltered coastal areas, utilizingtraditional fixed-bottom wind turbine technologias well as deep-water areas utilizingfloating wind turbines.

A subcategory within offshore wind power can benearshore wind power.
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Economics and benefits

Offshore wind power can help to reduce energy imports, reduce air pollution andgreenhouse gases (by displacing fossil-fuel power generation), meet renewableelectricity standards, and create jobs and local business opportunities. However,

according to the US Energy Information Agency, offshore wind power is the mostexpensive energy generating technology being considered for large scale deployment"The advantage is that the wind is much stronger off the coasts, and unlike wind over tcontinent, offshore breezes can be strong in the afternoon, matching the time whenpeople are using the most electricity. Offshore turbines can also be "located close to thpower-hungry populations along the coasts, eliminating the need for new overlandtransmission lines".

Most entities and individuals active in offshore wind power believe that prices of

electricity will grow significantly from 2009, as global efforts to reducecarbonemissionscome into effect.BTMexpects cost per kWh to fall from 2014, and that theresource will always be more than adequate in the three areasEurope,United StatesaChina.

The current state of offshore wind power presents economic challenges significantlygreater than onshore systems - prices can be in the range of 2.5-3.0 million Euro/MWThe turbine represents just one third to one half of costs in offshore projects today, the

rest comes from infrastructure, maintenance, and oversight. Larger turbines withincreased energy capture make more economic sense due to the extra infrastructure inoffshore systems. Additionally, there are currently no rigorous simulation models ofexternal effects on offshore wind farms, such as boundary layer stability effects andwake effects. This causes difficulties in predicting performance accurately, a criticalshortcoming in financing billion-dollar offshore facilities. A report from a coalition ofresearchers from universities, industry, and government, lays out several things needein order to bring the costs down and make offshore wind more economically viable:

Improving wind performance models, including how design conditions and the winresource are influenced by the presence of other wind farms. Reducing the weight of turbine materials Eliminating problematic gearboxes Turbine load-mitigation controls and strategies Turbine and rotor designs to minimize hurricane and typhoon damage
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Economic modeling and optimization of costs of the overall wind farm system,including installation, operations, and maintenance. Service methodologies, remote monitoring, and diagnostics.

In 2011, aDanish energy companyclaimed that offshore wind turbines are not yet

competitive with fossil fuels, but estimates that they will be in 15 years. Until then, stfunding and pension funds will be needed.Bloombergestimates that energy fromoffshore wind turbines cost 161 euros ($208) per MegaWattHour.

In Belfast, the harbour industry is being redeveloped as a hub for offshore windfarmconstruction, at a cost of about 50m. The work will create 150 jobs in construction, awell as requiring about 1m tonnes of stone from local quarries, which will createhundreds more jobs. "It is the first dedicated harbour upgrade for offshore wind".

As the first Offshore Windfarms move beyond their initial Warranty periods with theTurbine Equipment Manufacturer an increase in alternative Operations and Maintenansupport options is evident. Alternative suppliers of spare parts are entering the marketand others are offering niche products and services many of which are focused onimproving the power production volumes from these large renewable energy powerplants.

Technical details

In 2009, the average nameplate capacity of an offshore wind turbine in Europe wasabout 3 MW, and the capacity of future turbines is expected to increase to 5 MW.

Offshore turbines require different types of bases for stability, according to the depth water. To date a number of different solutions exist:

A monopile (single column) base, six meters in diameter, is used in waters up to 30meters deep. Gravity Base Structures, for use at exposed sites in water 2080 m deep. Tripod piled structures, in water 2080 metres deep. Tripod suction caisson structures, in water 20-80m deep. Conventional steel jacket structures, as used in the oil and gas industry, in water 20-80m deep. Floating wind turbinesare being developed for deeper water.
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Turbines are much less accessible when offshore (requiring the use of a service vesselfor routine access, and ajackup rigfor heavy service such as gearbox replacement), athusreliabilityis more important than for an onshore turbine. A maintenanceorganization performs maintenance and repairs of the components, spending almost aits resources on the turbines. Access to turbines is byhelicopteror service access vess

Some wind farms located far from possible onshore bases have service teams living osite inoffshore accommodation units.

Because of their remote nature, prognosis and health-monitoring systems on offshorewind turbines will become much more necessary. They would enable better planningjust-in-time maintenance, thereby reducing the operations and maintenance costs.According to a report from a coalition of researchers from universities, industry, andgovernment (supported by theAtkinson Center for a Sustainable Future), making fieldata from these turbines available would be invaluable in validating complex analysiscodes used for turbine design. Reducing this barrier would contribute to the educationengineers specializing in wind energy.

The planning and permitting phase can cost more than $10 million, take 57 years andhave an uncertain outcome. The industry puts pressure on the governments to improvethe processes. InDenmark,many of these phases have been deliberately streamlined bauthorities in order to minimize hurdles, and this policy has been extended for coastalwind farms with a concept called one-stop-shop. USA introduced a similar model

called"Smart from the Start"in 2012.

Some of the guidelines for designing offshore wind farms areIEC 61400-3, but in theUS several other standards are necessary. The standards requires that a loads analysis based on site-specific external conditions such as wind, wave and currents.

Design environment

Offshore wind resource characteristics span a range of spatial and temporal scales and

field data on external conditions. Necessary data includes water depth, currents, seabemigration, and wave action, all of which drive mechanical and structural loading onpotential turbine configurations. Other factors include marine growth, salinity, icing, the geotechnical characteristics of the sea or lake bed. A number of things are necessain order to attain the necessary information on these subjects. Existing hardware forthese measurements includes Light Detection and Ranging (LIDAR), Sonic Detectionand Ranging (SODAR), radar, autonomous underwater vehicles (AUV), and remote
http://en.wikipedia.org/wiki/Jackup_righttp://en.wikipedia.org/wiki/Jackup_righttp://en.wikipedia.org/wiki/Jackup_righttp://en.wikipedia.org/wiki/Reliability_engineeringhttp://en.wikipedia.org/wiki/Reliability_engineeringhttp://en.wikipedia.org/wiki/Reliability_engineeringhttp://en.wikipedia.org/wiki/Helicopterhttp://en.wikipedia.org/wiki/Helicopterhttp://en.wikipedia.org/wiki/Helicopterhttp://en.wikipedia.org/wiki/Accommodation_platformhttp://en.wikipedia.org/wiki/Accommodation_platformhttp://en.wikipedia.org/wiki/Accommodation_platformhttp://en.wikipedia.org/wiki/Atkinson_Center_for_a_Sustainable_Futurehttp://en.wikipedia.org/wiki/Atkinson_Center_for_a_Sustainable_Futurehttp://en.wikipedia.org/wiki/Atkinson_Center_for_a_Sustainable_Futurehttp://en.wikipedia.org/wiki/Denmarkhttp://en.wikipedia.org/wiki/Denmarkhttp://en.wikipedia.org/wiki/Denmarkhttp://en.wikipedia.org/wiki/Offshore_wind_power#Offshore_wind_farmshttp://en.wikipedia.org/wiki/Offshore_wind_power#Offshore_wind_farmshttp://en.wikipedia.org/wiki/Offshore_wind_power#Offshore_wind_farmshttp://en.wikipedia.org/wiki/IEC_61400http://en.wikipedia.org/wiki/IEC_61400http://en.wikipedia.org/wiki/IEC_61400http://en.wikipedia.org/wiki/Offshore_wind_power#Offshore_wind_farmshttp://en.wikipedia.org/wiki/Denmarkhttp://en.wikipedia.org/wiki/Atkinson_Center_for_a_Sustainable_Futurehttp://en.wikipedia.org/wiki/Accommodation_platformhttp://en.wikipedia.org/wiki/Helicopterhttp://en.wikipedia.org/wiki/Reliability_engineeringhttp://en.wikipedia.org/wiki/Jackup_rig


13/29

satellite sensing, although these technologies should be assessed and refined, accordinto a report from a coalition of researchers from universities, industry, and governmentsupported by theAtkinson Center for a Sustainable Future.

Because of the previous factors, one of the biggest difficulties with offshore wind farm

is the ability to predict loads. Analysis must account for the dynamic coupling betweetranslational (surge, sway, and heave) and rotational (roll, pitch, and yaw) platformmotions and turbine motions, as well as the dynamic characterization of mooring linefor floating systems. Foundations and substructures make up a large fraction of offshowind systems, and must take into account every single one of these factors.

Corrosion is also a serious problem and requires detailed design considerations. Theaspect of remote monitoring of corrosion looks very promising using expertise utiliseby the offshore oil/gas industry and other large industrial plants.

Common environmental concerns associated with offshore wind developments

include:

The risk of seabirds being struck by wind turbine blades or being displaced fromcritical habitats; The underwater noise associated with the installation process ofdriving monopoleturbines into the seabed; The physical presence of offshore wind farms altering the behavior of marine

mammals, fish, and seabirds with attraction or avoidance; The potential disruption of the nearfield and farfield marine environment from largeoffshore wind projects.

TheTethysdatabase seeks to gather, organize and make available information onpotential environmental effects of offshore wind energy development.
http://en.wikipedia.org/wiki/Atkinson_Center_for_a_Sustainable_Futurehttp://en.wikipedia.org/wiki/Atkinson_Center_for_a_Sustainable_Futurehttp://en.wikipedia.org/wiki/Atkinson_Center_for_a_Sustainable_Futurehttp://en.wikipedia.org/wiki/Pile_driverhttp://en.wikipedia.org/wiki/Pile_driverhttp://en.wikipedia.org/wiki/Pile_driverhttp://en.wikipedia.org/w/index.php?title=Tethys_%28database%29&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Tethys_%28database%29&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Tethys_%28database%29&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Tethys_%28database%29&action=edit&redlink=1http://en.wikipedia.org/wiki/Pile_driverhttp://en.wikipedia.org/wiki/Atkinson_Center_for_a_Sustainable_Future


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The Noise From Wind Power System

Done by : Anas Kata 0115115

Introduction

Wind turbines generate sound via various routes, both mechanical and aerodynamic. As the

technology has advanced, wind turbines have gotten much quieter, but sound from wind turbin

still an important siting criterion. Sound emissions from wind turbine have been one of the more

studied environmental impact areas in wind energy engineering. Sound levels can be measured,

similar to other environmental concerns, the publics perceptionof the acoustic impact of wind

turbines is, in part, a subjective determination.

Noise is defined as any unwanted sound. Concerns about noise depend on:

1. The level of intensity, frequency, frequency distribution and patterns of the noise source

2. Background sound levels

3. The terrain between the emitter and receptor

4. The nature of the receptor

5. The attitude of the receptor about the emitter.


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In general, the effects of noise on people can be classified into three

general categories:

1. Subjective effects including annoyance, nuisance, dissatisfaction

2. Interference with activities such as speech, sleep, and learning

3. Physiological effects such as anxiety, tinnitus, or hearing loss

In almost all cases, the sound levels associated with wind turbines large & small produce

effects only in the first two categories, with modern turbines typically producing only the first. T

third category includes such situations as work inside industrial plants and around aircraft. Whe

a sound is objectionable will depend on the type of sound (tonal, broadband, low frequency, or

impulsive) and the circumstances and sensitivity of the person (or receptor) who hears it. Becau

of the wide variation in the levels of individual tolerance for noise, there is no completely

satisfactory way to measure the subjective effects of noise or of the corresponding reactions of

annoyance and dissatisfaction.

Operating sound produced from wind turbines is considerably different in level and nature

than most large scale power plants, which can be classified as industrial sources. Wind turbines

often sited in rural or remote areas that have a corresponding ambient sound character.

Furthermore, while noise may be a concern to the public living near wind turbines, much of the

sound emitted from the turbines is masked by ambient or the background sounds of the wind it

The sound produced by wind turbines has diminished as the technology has improved. As

blade airfoils have become more efficient, more of the wind energy is converted into rotational

energy, and less into acoustic energy. Vibration damping and improved mechanical design have

significantly reduced noise from mechanical sources. The significant factors relevant to the pote

environmental impact of wind turbine noise are shown in Figure 1 [Hubbard and Shepherd, 199

Note that all acoustic technology is based on the following primary elements:Sound sources,

propagation paths, and receivers.In the following actions, after a short summary of the basic

principles of sound and its measurement, a review of sound generation from wind turbines, sopropagation, as well as sound prediction methods is given.


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Noise and Sound Fundamentals

Sound and Noise

Sounds are characterized by their magnitude (loudness) and frequency. There can be loud lo

frequency sounds, soft high frequency sounds and loud sounds that include a range of frequenc

The human ear can detect a very wide range of both sound levels and frequencies, but it is more

sensitive to some frequencies than others. Sound is generated by numerous mechanisms and is

always associated with rapid small scale pressure fluctuations, which produce sensations in the

human ear. Sound waves are characterized in terms of their amplitude or magnitude (see below

wavelength (), frequency (f) and velocity (v), where v is found from:

V = f.

The velocity of sound is a function of the medium through which it travels, and it generally

travels faster in more dense mediums. The velocity of sound is about 340 m/s or (1115 ft/s) in a

at standard pressures. Sound frequency denotes the pitch of the sound and, in many cases,

corresponds to notes on the musical scale (Middle C is 262 Hz). An octave is a frequency range

between a sound with one frequency and one with twice that frequency, a concept often used t

define ranges of sound frequency values. The frequency range of human hearing is quite wide,

generally ranging from about 20 to 20 kHz (about 10 octaves). Finally, sounds experienced in dai

life are usually not a single frequency, but are formed from mixture of numerous frequencies, fr

numerous sources.


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Sound turns into noise when it is unwanted. Whether sound is perceived as a noise depends

subjective factors such as the amplitude and duration of the sound. There are numerous physica

quantities that have been defined which enable sounds to be compared and classified, and whic

also give indications for the human perception of sound. They are discussed in numerous texts o

the subject (e.g., for wind turbine sound see Wagner, et al., 1996) and are reviewed in the follow

sections.

Measurement of Sound or Noise

Sound pressure levels are measured via the use of sound level meters. These devices make use of a

microphone that converts pressure variations into a voltage signal which is then recorded on a meter

(calibrated in decibels). As described above, the decibel scale is logarithmic. A sound level measurement

that combines all frequencies into a single weighted reading is defined as a broadband sound level. For t

determination of the human ears response to changes in sound, sound level meters are generally equip

with filters that give less weight to the lower frequencies. As shown in Figure 3, there are a number of fi

that accomplish this:

A-Weighting: This is the most common scale for assessing environmental and Occupational noise. I

approximates the response of the human ear to sounds of Medium intensity.

B-Weighting: this weighting is not commonly used. It approximates the ear for Medium-loud soun

around 70 dB

C-Weighting: Approximates response of human ear to loud sounds. It can be used for low-frequen

sound.

G-Weighting: Designed for infrasound

The weighting is indicated in the unit, e.g. measurements made using A-weighting are Expressed in un

of dB (A).Details of these scales are discussed by Breakneck and Ver [1992].


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Once the A-weighted sound pressure is measured over a period of time, it is possible to

determine a number of statistical descriptions of time-varying sound and to account for the grea

community sensitivity to nighttime sound levels. Terms commonly used in describing environme

sound include:

L10, L50, and L90: The A-weighted sound levels that are exceeded 10%, 50%, and 90% of the ti

respectively. During the measurement period L90 is generally taken as the background sound lev

Leq: Equivalent Sound Level: The average A-weighted sound pressure level which gives the sam

total energy as the varying sound level during the measurement period of time. Also referred to

LA eq .

Ldn: Day-Night Level: The average A-weighted sound level during a 24 hour day, obtained afte

addition of 10 dB to levels measured in the night between 10 p.m.and 7 a.m.

Infrasound & Low Frequency Sound

Terminology: Low frequency pressure vibrations are typically categorized as low freque

sound when they can be heard near the bottom of human perception (10-200 Hz), and infrasou

when they are below the common limit of human perception. Sound below 20 Hz is generally

considered infrasound, even though there may be some human perception in that range. Becau

these ranges overlap in these ranges, it is important to understand how the terms are intended

given context.

Infrasound is always present in the environment and stems from many sources includin

ambient air turbulence, ventilation units, waves on the seashore, distant explosions, traffic, airc

and other machinery. Infrasound propagates farther (i.e. with lower levels of dissipation) than

higher frequencies.

Some characteristics of the human perception of infrasound and low frequency sound are:

Low frequency sound and infrasound (2-100 Hz) are perceived as a mixture of auditory and tac

sensations.

Lower frequencies must be of a higher magnitude (dB) to be perceived, e.g. the threshold of

hearing at 10 Hz is around 100 dB; see Figure 5

Tonality cannot be perceived below around 18 Hz

Infrasound may not appear to be coming from specific location, because of its long wavelengths.


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The primary human response to perceived infrasound is annoyance, with resulting secondary

effects. Annoyance levels typically depend on other characteristics of the infrasound, including

intensity, variations with time, such as impulses, loudest sound, periodicity, etc. Infrasound has

three annoyance mechanisms:

A feeling of static pressure

Periodic masking effects in medium and higher frequencies

Rattling of doors, windows, etc. from strong low frequency components

Human effects vary by the intensity of the perceived infrasound, which can be grouped into

these approximate ranges:

90 dB and below: No evidence of adverse effects

115 dB: Fatigue, apathy, abdominal symptoms, hypertension in some humans

120 dB: Approximate threshold of pain at 10 Hz

120 130 dB and above: Exposure for 24 hours causes physiological damage.

There is no reliable evidence that infrasound below the perception threshold produces

physiological or psychological effects.


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Sound from Wind Turbines

Sources of Wind Turbine Sound

There are four types of sound that can be generated by wind turbine operation: tonal,

broadband, low frequency, and impulsive:

1. Tonal: Tonal sound is defined as sound at discrete frequencies. It is caused by components su

as meshing gears, non-aerodynamic instabilities interacting with a rotor blade surface, or unstab

flows over holes or slits or a blunt trailing edge.

2. Broadband: This is sound characterized by a continuous distribution of sound pressure with

frequencies greater than 100 Hz. It is often caused by the interaction of wind turbine blades wit

atmospheric turbulence, and also described as a characteristic "swishing" or "whooshing" sound

3. Low frequency: Sound with frequencies in the range of 20 to 100 Hz is mostly associated with

downwind rotors (turbines with the rotor on the downwind side of the tower). It is caused whenturbine blade encounters localized flow deficiencies due to the flow around a tower.

4. Impulsive: This sound is described by short acoustic impulses or thumping sounds that vary in

amplitude with time. It is caused by the interaction of wind turbine blades with disturbed air flo

around the tower of a downwind machine. The sources of sounds emitted from operating wind

turbines can be divided into two categories:

1) Mechanical sounds, from theinteraction of turbine components.

2) Aerodynamic sounds, produced by the flow of air over the blades. A summary of each of thessound generation mechanisms follows, and a more detailed review is included in the text of

Wagner, et al. [1996].

Mechanical Sounds

Mechanical sounds originates from the relative motion of mechanical components and the

dynamic response among them. Sources of such sounds include:

1. Gearbox

2. Generator

3. Yaw Drives

4. Cooling Fans

5. Auxiliary Equipment (e.g., hydraulics)


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Since the emitted sound is associated with the rotation of mechanical and electrical equipme

tends to be tonal (of a common frequency), although it may have a broadband component. For

example, pure tones can be emitted at the rotational frequencies of shafts and generators, and

meshing frequencies of the gears.

In addition, the hub, rotor, and tower may act as loudspeakers, transmitting the mechanical

sound and radiating it. The transmission path of the sound can be air-borne or structure-borne.

borne means that the sound is directly propagated from the component surface or interior into

air. Structure-borne sound is transmitted along other structural components before it is radiated

into the air. For example, Figure 6 shows the type of transmission path and the sound power lev

for the individual components for a 2 MW wind turbine [Wagner, et al., 1996]. Note that the ma

source of mechanical sounds in this example is the gearbox, which radiates sounds from the nac

surfaces and the machinery enclosure.

Infrasound from Wind Turbines

When discussing infrasound from wind turbines, it is particularly important to distinguish

between turbines with downwind rotors and turbines with upwind rotors. Some early wind turbdid produce significant levels of infrasound; these were all turbines with downwind rotors. The

downwind design is rarely used in modern utility-scale wind power turbines.

Upwind rotors emit broad band sound emissions, which include low frequency sound and som

infrasound. Note that the swish-swish sound is amplitude modulation at blade passing

frequencies of higher frequency blade tip turbulence and does NOT contain low frequencies.


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One example of low frequency sound and infrasound from modern turbine is shown in Figure

The magnitudes of these are below the perception limits of humans, which are shown in Figure

Sound Reduction Methods for Wind TurbinesTurbines can be designed or retrofitted to minimize mechanical sound. This can include specia

finishing of gear teeth, using low-speed cooling fans and mounting components in the nacelle

instead of at ground level, adding baffles and acoustic insulation to the nacelle, using vibration

isolators and soft mounts for major components, and designing the turbine to prevent sounds fr

being transmitted into the overall structure. Efforts to reduce aerodynamic sounds have include


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[Wagner, et al., 1996] the use of lower tip speed ratios, lower blade angles of attack, upwind rot

designs, variable speed operation and most recently, the use of specially modified blade trailing

edges.

Recent improvements in mechanical design of large wind turbines have resulted in significant

reduced mechanical sounds from both broadband and pure tones. Today, the sound emission f

modern wind turbines is dominated by broadband aerodynamic sounds .

Factors that Affect Wind Turbine Sound

Wind turbine generated sound that is perceived at any given location is a function of wind spe

as well as turbine design, distance, ambient sound levels and various other factors, which are

explored below.

Wind Turbine Design and Sound Emissions

All large, modern wind turbines available commercially today in the US are upwind, horizonta

axis, variable pitch, and many have some variability of rotational speed. There are, however, oth

designs that have been used historically and may appear again in some form.

Several basic design characteristics can influence sound emissions. Wind turbines may have

blades which are rigidly attached to the hub and thence to the rotor shaft. Other designs may ha

blades that can be pitched (rotated around their long axis). Some have rotors that always turn a

constant or near-constant speed while other designs might change the rotor speed as the wind

changes. Wind turbine rotors may be upwind or downwind of the tower. Other things being equ

each of these designs might have different sound emissions because of the way in which they

operate. In general, upwind rotors as opposed to downwind rotors, lower rotational speeds and

pitch control result in lower sound generation.

Aerodynamic sound generation is very sensitive to speed at the very tip of the blade. To limit

generation of aerodynamic sounds, large modern wind turbines may limit the rotor rotation spe

to reduce the tip speeds. Large variable speed wind turbines often rotate at slower speeds in low

winds, increasing in higher winds until the limiting rotor speed is reached. This results in much

quieter operation in low winds than a comparable constant speed wind turbine.

Small wind turbines (under 30 kW) are also often variable-speed wind turbines. These smaller

wind turbine designs may even have higher tip speeds in high winds than large wind turbines. T

can result in greater sound generation than would be expected, compared to larger machines. T

is also perhaps due to the lower investment in sound reduction technologies in these designs. So

smaller wind turbines regulate power in high winds by turning out of the wind or fluttering the


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blades. These modes of operation can affect the nature of the sound generation from the wind

turbine during power regulation.

Noise Standards and Regulations

There are standards for measuring sound power levels from utility -scale wind turbines, as we

local or national standards for acceptable noise power levels. Each of these is reviewed here. As this writing (February 2005), there are no sound measurement standards for small wind turbine

but both the American Wind Energy Association and the International Electro technical Commis

(IEC) are working on future standards.

Turbine Sound Power Measurement Standards

The internationally accepted standard to ensure consistent and comparable measurements o

utility-scale wind turbine sound power levels is the International Electro technical Commission IE

61400-11 Standard: Wind turbine generator systemsPart 11: Acoustic noise measurement

techniques [IEC, 2002]. All utility-scale wind turbines available today in the US comply with IEC

61400-11. It defines:

The quality, type and calibration of instrumentation to be used for sound and wind speed

measurements.

Locations and types of measurements to be made.

Data reduction and reporting requirements.

The standard requires measurements of broad-band sound, sound levels in one-third octavebands and tonality. These measurements are all used to determine the sound power level of the

wind turbine at the nacelle, and the existence of any specific dominant sound frequencies.

Measurements are to be made when the wind speeds at a height of 10 m (30 ft) are 6, 7, 8, 9 an

m/s (13-22 mph). Manufacturers of IEC-compliant wind turbines can provide sound power level

measurements at these wind speeds as measured by certified testing agencies.

Measurements of noise directivity, infrasound (< 20 Hz), low-frequency noise (20-100 Hz) and

impulsivity (a measure of the magnitude of thumping sounds) are optional.

Measured sound power levels for a sampling of wind turbines are presented in Figure 13 as a

function of rated electrical power. The data illustrate that sound emissions from wind turbines

generally increases with turbine size. The graph also shows that wind turbine designers efforts t

address noise issues in the 1990s and later have resulted in significantly quieter wind turbines th

the initial designs of the 1980s.


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Community Standards for Determining Acceptable Sound Pressure Levels

At the present time, there are no common international noise standards or regulations for so

pressure levels. In most countries, however, noise regulations define upper bounds for the noise

which people may be exposed. These limits depend on the country and may be different for

daytime and nighttime.

For example, in Europe, as shown in Table 2, fixed noise limits have been the standard [Gipe, 1995].


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In the U.S., although no federal noise regulations exist, the U.S. Environmental Protection Age

(EPA) has established noise guidelines. Most states do not have noise regulations, but many loca

governments have enacted noise ordinances to manage community noise levels. Examples of su

ordinances for wind turbines are given in the latest Permitting of Wind Energy Facilities Handbo

[NWCC, 2002].

The Massachusetts Department of Environmental Protection (DEP) regulates noise emissions

form of air pollution under 310 CMR 7.00, Air Pollution Control. These can be found at

http://www.mass.gov/dep/air/laws/7a.htm.The application of these regulations to noise is deta

in the DEPs DAQC Policy Statement 90-001 (February 1, 1990). The regulation includes two

requirements. First, any new broadband sound source is limited to raising noise levels no more t

10 dB(A) over the ambient baseline sound level. The ambient baseline is defined as the sound le

that is exceeded 90% of the time, the L90 level. Second, pure tones, defined here as an octave

band, may be no greater than 3 dB(A) over the two adjacent octave bands. All these readings are

measured at the property line or at any inhabited buildings located within the property.

It should be pointed out that imposing a fixed noise level standard may not prevent noise

complaints. This is due to the changing of the relative level of broadband background turbine no

with changes in background noise levels [NWCC, 2002]. That is, if tonal noises are present, highe

levels of broadband background noise are needed to effectively mask the tone(s). In this respect

is common for community noise standards to incorporate a penalty for pure tones, typically5 dB

Therefore, if a wind turbine meets a sound pressure level standard of 45 dB(A), but produces a

strong whistling, 5dB(A) are subtracted from the standard. This forces the wind turbine to meet

standard of 40 dB(A).

A discussion of noise measurement techniques that are specific to wind turbine standards or

regulations is beyond the scope of this paper. A review of such techniques is given in Hubbard a

Shepherd [1990], Germanize Lloyd [1994], and Wagner, et al. [1996].

Conclusions and Recommendations

Modern, utility-scale wind turbines are relatively quiet; still, when sited within residential areanoise is a primary siting constraint. The following are recommendations for standards, regulatio

and siting practices:


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Turbine Standards:

Utility-scale turbines: Any incentives to promote wind energy should be provided only to turbin

for which the manufacturer can provide noise data based on IEC standards or for turbines w

are to be located at sites where there will clearly be no problem.

) Small turbines: national standards for small wind turbine technology in general are needed. Fo

noise in particular, sound levels should be measured at lower and higher wind speeds, in additio

those measured under the IEC standard. Any operation-mode-dependent, time-dependent and

frequency-dependent components also need to be described. These standards need to provide

sound measures that provide an accurate representation of issues of interest to potential listene

Noise Regulations:

Community noise standards are important to ensure livable communities. Wind turbines must b

held to comply with these regulations. Wind turbines need not be held to additional levels ofregulations.

For small wind turbines: Because of the wide variety of sound levels from small wind turbines,

blanket setback limits should not be set a priori. However, they should be examined carefully ba

on the technology proposed.

Wind turbine siting practice:

a) In order to comply with state noise regulations and to fit within community land use, the sitin

wind turbines must take sound levels into consideration.

b) If a wind turbine is proposed within a distance equivalent to three times the blade-tip height

residences or other noise-sensitive receptors, a noise study should be performed and publicized


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References:

- AWEA (American Wind Energy Association), Procedure for Measurement of Acoustic Emissio

from Wind Turbine Generator Systems, Tier IStandard 2.1 (1989), American Wind Energy

Association, Washington, DC, 1989

- Beranek, L. L. and Ver, I. L., Noise and Vibration Control Engineering: Principles and Applicatio

Wiley, New York, 1992.

- Danish Wind turbine Manufacturers Association, www.windpower.dk, 2002.Germanisher Llo

Regulation for the Certification of Wind Energy Conversion Systems, Supplement to the 1993

Edition, Hamburg, March, 1994.

- International Energy Agency: Expert Group Study on Recommended Practices for Wind Turbi

Testing and Evaluation, 4. Acoustics Measurements of Noise Emission from Wind Turbines, 3

Edition 1994.

- International Organization for Standardization, ISO:7196, Frequency weighting characteristic

infrasound measurements, 1995

- Leventhall G, Notes on Low Frequency Noise from Wind Turbines with special reference to th

Genesis Power Ltd Proposal, near Waiuku NZ Prepared for Genesis Power/ Hegley Acoustic

Consultants, 4th June 2004, Surry UK. Available at:

http://www.windenergy.org.nz/documents/2004/040604-LeventhallReportLowFrequency.p

Documents

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