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Discover the unique power of the windDiscover the unique power of the wind

Wind through the ages

How do windturbines work?

Windturbine projects

Where are windturbines erected?

How does wind arise?

Printversion of www.vestas.com/dupowDK/

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Discover the unique power of the wind

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Windthroughthe ages

The entrancing power o the wind has always had a captivating eect

on man. For thousands o years, people have been particularly ascinated

by the possibility o capturing the wind and harnessing its power. This

section explains how they have been utilising the power o the wind down

through the ages.

Wind in the sailsThe technique o using a sail to capture the wind and utilising its

power or propulsion is, in principle, the same today as it was 6,000

years ago, when the rst sailing vessels appeared.

Sailing vessels are propelled by the dierential orces created on

each side o a sail when the wind blows across it. The underpres-

sure on the rear side o the sail interacts with the overpressure on

the ront side to drive the vessel orwards.

Today, it is believed that people had learned to tame the wind as

early as in 4000 BC. At around that time, the Chinese became the

rst people to attach sails to their primitive rats. Approximately

600 years later, the Egyptians launched their rst sailing vessels,initially to sail the waters o the Nile. Later on, they used sailing ves-

sels to trade along the coasts o the Mediterranean. In addition, the

Viking conquests were largely attributable to their ability to build

and sail their ast ships more-or-less all over the world.

Since the invention o the steamship around 150 years ago, the

sailing ship has largely been replaced by more ecient, machine

powered vessels, particularly in the industrialised countries. Today,

sailing vessels are primarily used as a popular leisure pursuit, or

races and or schooling. However, in less developed countries, sail-

ing ships still play an important role in trade, shing and transport.

Here, the wind remains a crucial resource.

Conquering the skiesIt seems that man has always dreamed o using the power o the

wind to fy. Indeed, ancient Greek mythology eatures stories o

people who attempted to fy like birds.

In the teenth century, the genius Leonardo da Vinci devoted

much time and energy to studying the same eld. Through a series

o impressive sketches and complex wing designs, he attempted

to copy the wing movements o the birds. His wing designs would

never have helped man to fy, but today da Vincis work is consid-

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ered the rst scientic attempt to create a fying machine.

Up and away in a balloonFor centuries, it was considered an almost irreutable act that in

order to fy, man would have to imitate the wings o the birds. How-

ever, it was actually a bubble o air that rst helped man to break

the hold o gravity and ascend into the clouds. The rst passen-

ger-carrying balloon lited o in 1783. The primitive balloon was

made o canvas and powered by the smoke rom a bonre.

Since this early experiment, balloon design has been developed

and rened. Both the technology and the materials involved have

developed appreciably and today, ballooning is a hobby enjoyed by

people over much o the world.

From the very rst balloon fight, it became clear that ballooning

was linked to some element o risk. Not long ater the rst balloon

fights were completed, the parachute was invented. Quite simply,

parachutes were designed to save balloon pilots who ound them-

selves in diculty. However, they were also used or entertainmentin connection with balloon displays. Today, parachutes are still

used to save lives, but parachuting has also become a popular high-

adrenaline hobby.

The ships o the airAlthough ballooning had been popular or a couple o centuries,

even the most enthusiastic balloon pilots could become a little rus-

trated at having the wind decide the direction they were to ollow.

Henri Giard took a good look at this problem, and in 1852 intro-

duced the rst airship in the world. The airship was shaped like a

cigar and tted with a small steam engine that made actual naviga-tion possible. Airships soon became popular air liners, and in the

1920s they few people back and orth across the Atlantic. However,

a number o atal crashes including the Hindenburg disaster, in

which the airship exploded, killing 35 passengers heralded the

end o the age o airships.

Gliding planesIt was not until the end o the 1800s that da Vincis ideas about

using wings to fy were made real. It was at that time that George

Cayley, the British engineer, drew inspiration rom a simple toy: the

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kite. His observations o kites in fight convinced him that wings

could carry a human being to the skies.

He made his dream come true by building the rst simple glider

in the world. Since then, gliders have become more and more

advanced, and it is now possible to complete controlled fights.

Gliding is a popular hobby today, but there can be no doubt that

motorised aircrat dominate air trac.

A ying machineThe rst motorised fight in the world took place in the United

States in 1903. Two brothers, Orville and Wilbur Wright had spent

years working to develop both their aircrat and, in particular, their

skills as pilots. Their aircrat Flyer was powered by a petrol en-

gine and on its virgin fight managed to cover just 40 metres beore

landing saely on the ground.

The years that ollowed the fight o Flyer saw new types o

aircrat being developed at a dizzying pace, and just a ew years

later, longer fights had already become common. For example,the rst fight rom France to Britain across the English Channel

was completed by an elegant little plane built in 1909. At the same

time, experiments were carried out with new, more creative aircrat

designs involving two sets o wings (biplanes) or even three sets o

wings (triplanes).

As early as the end o the 1920s, aircrats had become appreci-

ably more streamlined. The machines were already being made o

metal and few at higher speeds, which naturally opened up a host

o new opportunities. Just a ew years later, the Boeing 247 was in-

troduced; the rst modern passenger aircrat in the world. The

development o new and improved types o aircrat has ascinated

fying enthusiasts ever since the rst plane took to the skies. And

everything suggests that people will carry on developing the aero-

plane to create bigger, aster models.

The helicopterThe most advanced and versatile orm o aircrat is the helicopter.

The rst primitive version o a helicopter was developed by Juan

de la Cierva, the Spanish aircrat engineer, at the start o the 1920s.

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He discovered that a rotating wing could cut through the air just

like a propeller, thus pulling the helicopter upwards. The advan-

tages o the helicopter are that it can rise vertically through the

air and hover in the same place or long periods. In addition, it

requires very little space to land.

Wind becomes electricityThe word windmill makes it plain that wind power was used to

mill grain. The word mill itsel stems rom the Latin word or a

machine that grinds grain: molina. Many European languages con-

tain closely related words that all have the same meaning: French

moulin; English: mill; German: Mhle; and Danish: mlle. The

interpretation o the word is thus closely linked to the primary task

o the mill or centuries.

Persian inventors drew inspiration or the windmill rom looking

at the water mill. They took the mill wheel as their starting point

and attached 612 sails made o hide or reeds to an axle. They

then attached a millstone to the other end o the axle and erected

the mill on a hill, surrounding it with unnel-shaped walls to ensurethat the wind was channelled towards the mill sails. This primitive

yet ecient windmill model spread to other countries including

China, where it is still used today.

The frst windmills in EuropeThe rst European windmills were built around 1100 and were

used both to grind grain and to pump water. For the agricultural

community, windmills provided invaluable assistance in grinding

grain, and in the low-lying armland o the Netherlands, mills were

used to pump water away rom the elds.The rst windmills were erected in Denmark around the middle o

the 1200s. These mills were what are known as post mills. They

typically eatured our sails consisting o a wooden rame covered

with canvas. The mill house itsel was placed on a rotating base,

which made it possible or a group o strong men to turn the entire

mill construction into the wind.

The Dutch millLater on, people discovered that a better approach was to build

mills in which only the top o the mill tower (the mill cap) could

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be turned. This type o mill known as a Dutch mill reached

Denmark at the start o the 1700s, and in 1870 there were more

than 6,000 Dutch mills operating in Denmark. The advantage o

this type o mill was that it allowed the construction o much big-

ger mills than the old post mills, and they could also provide more

power.

The popularity o the Dutch mills was largely attributable to An-

drew Meikle, the Scottish inventor, who developed a range o tech-nical improvements including one that ensured that the mill cap

automatically turned to ace into the wind. In addition, his devel-

opment o moveable wooden slats to replace the xed construction

sails made it much easier to operate these mills. Today, one o the

best-preserved examples o a Dutch mill in Denmark is to be ound

at Dybbl Mlle in Southern Jutland. Damgrd Mlle, which is also

in Southern Jutland, is another ne example o a Dutch mill.

Mills on Danish armsOriginally, the large commercial mills had the exclusive right to

grind grain or the armers o the region, but in 1862, this mo-nopoly was revoked. Farm owners were subsequently allowed to set

up independent mills on their own arms. The mill quickly became

a popular tool on Danish arms. Farm mills were not only used to

grind grain; a simple system involving a perpendicular drive linked

to a horizontal axle with a drive belt made it possible to use the

mill to power other arm machinery such as threshing machines.

On some arms, the mill was even used to pump water rom the

well to a container, which ensured a supply o running water to the

taps. Mills thus took over a lot o the hard work o the arm, so it is

no surprise that they became so popular. It is not known preciselyhow many mills were built in Denmark, but it is likely that in 1920,

there were between 20,000 and 30,000 mills on Danish arms.

A mill to generate electricityIn the winter o 188788, the visionary American inventor Charles

F. Brush built the rst windmill intended to generate electricity. It

was erected in Cleveland, Ohio. This windmill was not just the rst

automatically operating mill that generated electricity it was also

o a truly impressive size or the time. The rotor had a diameter o

17 metres and eatured 144 cedar rotor blades.

The mill was located in the garden behind the Brush amily man-

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sion, and, via a dynamo, generated power or the 12 batteries that

supplied current to no ewer than 350 incandescent lamps, two arc

lamps and three motors. This giant windmill was a peculiarity o its

age and remained in operation or 20 years. However, slow wind-

mills o this kind were gradually overtaken by the ast mills with

rotor blades, which the Danish inventor Poul la Cour discovered

were better or generating energy than the slow models.

Denmarks windmill inventorTowards the end o the 1800s, Denmark joined the leading coun-

tries in windmill development or the rst time. It was at this time

that Poul la Cour, the greatest gure in the history o the Danish

windmill industry, started to develop a range o inventions that

attracted considerable international attention. Beore turning his

attention to windmills, Poul la Cour had already proved his skill as

an inventor by developing patented solutions in the elds o teleg-

raphy and radio.

In 1878, he was given a position at Askov College o Further Educa-

tion, and in 1891, he was awarded a grant to build his rst experi-mental mill in the school grounds. With the construction o this

mill, he aimed to prove his theory that wind energy could be stored

by using it to separate water into hydrogen and oxygen and then

using the resultant gases to power lights and motors. In the wind-

mill itsel, the motion o the sails was to be used to power a dynamo

to generate electricity. This electricity was to be led into a tank o

water, which it would then separate into hydrogen and oxygen.

Each o these gases was to be stored in a separate gas tank, rom

where the two gases were led in separate lead pipes rom the mill

to the college lamps.

Poul la Cours workshopWithin a year o completing the rst windmill, Poul la Cour had a

new invention ready or patenting. He had developed an intricate

system o weights and pulleys that could be used to even out the

gusts o the wind to provide an even, uniorm level o pressure or

transerring to the dynamo.

In 1896, Poul la Cour was awarded a grant to build an even bigger

windmill in which he could continue with his experiments and

inventions. In the spacious machine room o the giant mill, he con-structed two wind tunnels. Here, he carried out experiments on as-

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pects such as the number o sails, speed o revolution and capacity.

He then collated the results o his wind tunnel research in a book

entitled Forsgsmllen (The Experimental Mill). It was this book

that cemented his international reputation as a windmill inventor.

Poul la Cours experimental mill at Askov, Denmark, still exists

and is a building with a long and ascinating history. In 1902, it was

made the power station or the entire town o Askov, and in 1904

it was converted into a research centre or the use o electricity inrural areas. In this capacity, it was used as a venue or courses or

rural electricians. One o the teachers was, o course, Poul la Cour

himsel. The centre was used to teach everything rom practical in-

stallation work, geometry and physics, to bookkeeping, Danish and

German. Today, the experimental mill at Askov College houses the

Poul la Cour Museum and stands as a maniestation o Denmarks

trail-blazing inventions in the eld o windmills.

Windmill renaissance during the warDuring the rst hal o the 1900s, windmills were gradually meeting

greater and greater competition rom coal-red power stations andthe nationwide high-voltage grid, and many people predicted the

complete disappearance o the windmill. However, the two World

Wars resulted in shortages o coal and oil, so wind power ound it-

sel back on the agenda. Danish pioneering spirit and inventiveness

helped the windmill to develop into an even more ecient source

o energy.

The Agricco turbineIn 1918, inspired by developments within the aeronautical industry,

two Danish engineers Poul Vinding and Johannes Jensen de-veloped a completely new type o windmill, or turbine, with blades

designed on the basis o aerodynamic principles. The new turbine,

the Agricco, which was immediately patented, eatured rotating

blades that resembled an aircrat propeller. In addition, the blades

could be regulated to suit the wind speed and the turbine itsel ea-

tured an automatic yaw system, which meant that it automatically

aced into the wind.

The aeromotorDuring World War II, the cement group F.L. Smidth joined orces

with the aircrat company Kramme & Zeuthen to develop another

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remarkable, direct current-generating wind turbine: the Aeromo-

tor. This turbine greatly resembled the turbines we know today and

was one o the models developed as a result o the increase in inter-

est in turbines attributable to the war. The turbine tower was made

o solid concrete, while the turbine blades were slim and aerody-

namic.

Yet another Danish wind turbine geniusWhen, at the start o the 1900s, Poul la Cour was teaching wind-

mill/turbine technology at Askov College, one o his students was a

young man named Johannes Juul. Around 50 years later, his inter-

est in wind turbines and exciting inventions resulted in a turbine

that would prove to be the blueprint or the wind turbines o today.

Its introduction was preceded by a painstaking research project

completed by the talented inventor.

Johannes Juul did not limit himsel to taking systematic measure-

ments o the wind; he also built his own wind tunnel, which he

used to test his theories and no ewer than around 25 dierent

blade designs. His ambition was to produce a turbine that gener-ated alternating current and he wanted to connect an asynchro-

nous generator. However, he was well aware that this would make

completely new demands on generator size, blade dimensions and

the speed o revolution. In return, the turbine would be auto-regu-

lating and would stop automatically in high winds.

Johannes Juuls remarkably thorough preliminary work paid o,

and when the rst turbine was erected in South Zealand in 1950, it

lived up to all his expectations. For nancial reasons, the turbine

had only two blades, but a year later, Johannes Juul added an extra

blade to a similar turbine to stabilise the construction. This newturbine made it possible to utilise a much higher proportion o the

energy o the wind than had been possible previously.

The blueprint or the turbines o todayFinally, in 1957, Johannes Juul aged 70 could unveil the Gedser

turbine, which became the blueprint or the turbines o today. Just

north o Gedser, Denmark, a 200 kW trial turbine was installed on

top o a 25-metre-high concrete tower. The turbine eatured a gen-

erator and three xed blades stabilised with bracing wire with

rotating tips. These three principles used on the visionary Gedserturbine became the cornerstones or Danish turbines rom the

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middle o the 1970s onwards.

In 1962, long ater Johannes Juul had retired, he presented a range

o visionary ideas about the wind turbine o the uture. He was con-

vinced that the turbine o the uture would be based on the Gedser

turbine, but that it would be improved by the use o new materi-

als such as plastic and breglass. In addition, he was sure that the

Danish wind turbine sector would take a dominant position on the

global market.

Large and small successesIn the years ater the age o wind turbine geniuses such as Poul

la Cour and Johannes Juul, Danish pioneering spirit and interest

in wind energy have ound expression in a range o wind turbine

inventions o various types.

For example, in 1975 a group o teachers and pupils at the Tvind

schools in West Jutland started work on the biggest wind turbine

in the world a project they took on without having any proes-

sional knowledge o the area. Through working relationships withengineers centred on areas such as the blade prole, this ambitious

wind turbine project was completed three years later. The turbine

had a blade diameter o 54 metres and the concrete tower was 53

metres high. The turbine blades were replaced in 1993, and the

Tvind turbine is still operating in windswept West Jutland.

It was also in the middle o the 1970s that master carpenter Chris-

tian Riisager built a very ecient three-blade turbine with a blade

diameter o just 6.5 metres and a tower height o 12 metres. The

design was inspired by the old Gedser turbine, and Christian Riis-

ager applied or and received permission to connect his turbine

to the municipal grid. A ew years later, Christian Riisager started

to sell his turbines, and a number o manuacturers started to de-

sign turbines inspired by the Riisager model.

Towards the end o the 1970s, the working relationship involving

Henrik Stiesdal, the engineer, and Karl Erik Jrgensen, the smith,

resulted in the development o the HVK pioneering turbine. This

ecient turbine eatured a generator output o 22 kW as well as

a number o the properties that were subsequently to distinguish

Danish wind turbines: three ree-standing breglass-reinorced

blades with rotating tip brakes, an electric yaw system and two

generators connected to the grid one each or high and low wind

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speeds.

The turbines developed by the two mid-Jutland pioneers Karl

Erik Jrgensen and Christian Riisager on the basis o research

carried out earlier by the sector visionaries later became known

as The Danish Concept. The distinguishing eatures o turbines

built according to The Danish Concept were a high, slim design

with three ast-turning blades acing into the wind. The qualities o

this model were soon recognised, and this type o turbine was thenexported to most parts o the world, where it outperormed wind

turbines made by some o the largest and most advanced industrial

companies in the world. The Danish Concept became the corner-

stone o Denmarks international wind turbine success.

The Darrieus turbineAround the end o the 1970s, a West Jutland machine actory

Vestas which, among other things, had previously concentrated

on the production o agricultural trailers and machinery, started

to investigate the potential o the wind turbine as an alternative

source o energy. Among the early experiments at Vestas was LeonBjernvigs vertical wind turbine. This was a variation on the Dar-

rieus turbine and resembled an upright egg whisk. However, the

Darrieus turbine never became a success.

The strong Danish oursomeAt the end o the 1970s, ater only limited success with the Darrieus

turbine (the egg whisk turbine), Vestas was on the lookout or a

new, ecient turbine. They ound it in Henrik Stiesdals and Karl

Erik Jrgensens HVK turbine, and ater months o thorough test-

ing, Vestas purchased the rights to this turbine model in 1979. TheHVK turbine thus became the oreather o the Vestas turbine

range.

In the meantime, the oil crisis was also having an eect on the East

Jutland company Nordtank, which had previously built tankers

or the oil industry. As a result, this company started looking or a

new business area and decided to start developing wind turbines.

At the end o 1980, Nordtanks rst wind turbine was ready, and

it was unveiled at the Ungskuet air in Herning, Denmark, that

same year. It was a robust, well-unctioning turbine and eatured an

innovation in that it was designed with a closed tubular tower thatmade it possible to position the control and electrical installations

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in the tower itsel. This simultaneously improved saety conditions

or the service technicians, who no longer had to climb up a lattice-

work tower to work on the turbine. Instead, they could use ladders

inside the tower.

In 1980, another new wind turbine manuacturer appeared on

the scene. This company, Danregn, was actually a specialist in the

area o irrigation systems, but the agricultural crisis had orced it

to seek out new business areas. At the Ungskuet air in Herning in1980, the Danregn management dropped by the Nordtank stand

and were inspired by what they saw. Later that same year, Dan-

regn Vindkrat launched its rst wind turbine. Danregn Vindkrat,

which was based in Brande, Denmark, later changed its name to

Bonus Energy A/S.

Finally, in 1983, Micon the ourth company in the oursome o

successul Danish wind turbine manuacturers was ounded in

Randers, Denmark. Behind this company were two brothers, Erling

and Peder Mrup, who drew inspiration or their rst turbine at

the Agromek trade air in Herning.

In the period leading up to the new millennium, these our wind

turbine manuacturers Vestas, Nordtank, Bonus and Micon

were recognised internationally as the Danish oursome o suc-

cessul wind turbine companies.

Danish turbines in CaliorniaIn 1980, the state o Caliornia decreed that 10 per cent o its

energy in 2000 was to stem rom wind power. At the same time, the

power stations oered to purchase electricity or a xed price or

ten years. These initiatives triggered wind-turbine ever in the

sunshine state.

However, the Caliornian wind power airytale did not get o to a

good start. The rst years were distinguished by damaged turbines,

dubious investments and ast money. The American turbines were

o suspect quality, and the wind power airytale soon spun out o

control as investors proved more interested in tax deductions than

alternative energy.

In 1982, three Danish wind turbine manuacturers Vestas, Nor-

dtank and Bonus noticed the great potential o the American

market or wind turbines, so they all sent teams to Caliornia to sellturbines. On account o the increase in demand rom the United

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States, Danregn changed its name to Bonus in 1983 out o consid-

eration the Americans, who had diculty pronouncing Danregn

Vindkrat.

During the wind turbine boom in Caliornia, Vestas made contact

with Zond Systems, a Caliornian wind power company. This re-

sulted in a working relationship between the American and Danish

companies along with contracts or Vestas to deliver turbines. Lots

o turbines.

Ups and downsIn the middle o the 1980s, Danish wind turbine exports to the

United States received a severe blow, the result o a combination

o aspects including alling oil prices, an unavourable exchange

rate and a decline in energy policy interest in wind turbines. The

collapse o the American wind power boom had serious eects on

the Danish wind turbine manuacturers which all, with the excep-

tion o Bonus Energy, either had to suspend payments or le or

bankruptcy.

Towards the end o the 1980s, the Danish wind turbine companies

began to see light in the darkness again. New people joined the

Boards and management teams, and this was one o the reasons

why Vestas, Nordtank and Micon all got back on their eet again.

At the same time, it transpired that the American market was not

quite as dead as it seemed, and new markets also started showing

interest in Danish turbines.

In act, the United States turned out still to be an exciting and

attractive market or wind turbines. Around 1990, Vestas re-estab-

lished its working relationship with Zond Systems and began to

export large numbers o wind turbines to the United States once

more. In 1988, Micon managed to nd its eet again ater several

years on the verge o total collapse. This turnaround was largely at-

tributable to two orders or turbines or a Danida project in India.

Nordtank managed to recover, too. In 1987 and 1988, this compa-

ny succeeded in ramping up turbine production or both domestic

and overseas markets.

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The golden decade o wind turbinesThe 1990s turned out to be a golden decade or the wind turbine

industry. The big our Danish wind turbine companies enjoyed

almost explosive growth in both turnover and employment, and

wind turbines became one o the leading Danish exports. In act,

the Danish companies held an impressive 45 per cent share o the

global market.

The success o the Danish wind turbine sector also resulted inincreasing proessionalisation o the companies themselves. This

took the orm o stock exchange fotations and numerous mergers

within the sector. Nordtank became the rst Danish wind turbine

company to foat its operations in autumn 1995. Vestas preerred

to wait a little longer, beore ollowing suit in May 1998.

In July 1997, Nordtank merged with Micon to create the wind tur-

bine specialist NEG Micon.

A new millennium

At the start o the new millennium, the lines were drawn or anoth-er exciting period or the Danish wind turbine industry. In 2002,

the American giant GE Enron purchased Wind Corp. to create a

new company, GE Wind Energy. In spring 2004, the undisputed

world leader o the wind power industry was ormed when Vestas

joined orces with NEG Micon. Later that year, the German com-

pany Siemens purchased the Danish company Bonus to become a

major player on the growing market or wind turbines under the

name o Siemens Wind Power.

SourcesThe text is based on the ollowing sources:

Christopher Chant, Sejlskibe (Sailing Ships), 1992.

www.experimentarium.dk

Andrew Nahum, Flyvemaskiner (Flying Machines), 1991.

Bjarne Chr. Jensen, Ballonfyvning, historie og historier,

(Ballooning, history and stories) 1994.

Per Dannemand Andersen, Ris Publications: Review o

Historical and Modern Utilization o Wind Power.

www.dkvind.dk/akta/akta_pd/M5.pd

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Benny Christensen (Danmarks Vindkrathistoriske Samling

The Danish Wind Power History Collection): Mindre

danske vindmller 18601980, (Small Danish Wind

Turbines, 18601980) 2001.

www.windpower.org

www.laavre.us/brush/mansion.htm

Jytte Thorndahl, Fra stemmegafer til knaldgas (From

tuning orks to oxyhydrogen), rom Elektrikeren

www.poullacour.dk

Ib Konrad Jensen, Mnd i modvind (Men acing a

headwind), 2003.

Pictures:Pictures o RA II by kind permission o the Kon-tiki

Museum, Oslo, Norway.

Picture o glider by kind permission o K. Krjgaard.

Pictures o biplanes and the Ciervo C.30 (autogiro) by kindpermission o the Danish Air Force History Collection,

Karup Aireld, Denmark.

Picture o the Dutch mill (Damgrd mill) by kind permis

sion o Christen Poder.

Picture o Brundby Post Mill on Sams by kind permission

o www.moellearkivet.dk

Picture o Charles Brush with the kind permission o

Westers Reserve Historical Society, Cleveland, Ohio, USA.

Pictures o Poul la Cour and the experimental turbines bykind permission o the La Cour Museum.

Pictures o Johannes Juul and the experimental turbine at

Gedser by kind permission o the Electricity Museum,

Bjerringbro, Denmark.

Pictures o the arm mill (Heeager), the Agricco turbine,

the Aeromotor and the Darrieus turbine by kind permis

sion o the Danish Wind History Collection.

Picture o the Tirstrup turbine by kind permission o the

Tistrup-Hodde Parish Archives.Pictures o the Tvind turbine and the HVK turbine by kind

permission o Benny Christensen, the Danish Wind History

Collection.

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How does

wind arise?

This section explains how the wind arises and describes the weather condi-

tions suited to the erection o wind turbines.

Meteorological rulesIn order to understand how the wind arises, it is important to know

some rules o physics that apply to the eld o meteorology:

1. Cold air is heavier than warm air

2. The wind blows rom areas o high pressure to areas o low pres-sure

3. High pressure is ormed when the air is cooled and sinks down

through the atmosphere (c. rule 1)

4. Low pressure is ormed when the air is heated and rises up

through the atmosphere (c. rule 1)

5. The rotation o the Earth defects the wind to the right in the

northern hemisphere and to the let in the southern hemisphere

(known as the Coriolis eect).

The sun generates windImagine that an area o the Earth is heated by the sun. On account

o the non-uniorm nature o the Earth, this area will be heated

more than the areas surrounding it, so the air immediately above it

will start to rise. When air rises in this manner, a vacuum-like state

is created close to the surace o the Earth, because the pressure

in this area starts to all. The surrounding area will, however, try

to balance out the dierence in pressure between the heated and

non-heated areas by moving cooler air into the vacuum. I the sun

is strong enough to maintain its heating eect and thus to con-

tinue the rising o the air wind will be generated.

The ability o wind turbines to generate energy is naturally depend-

ent on wind. The ollowing sections explain which weather condi-

tions are avourable or wind turbines, and describe how these

weather conditions arise.

Weather conditions or wind turbinesWhen erecting wind turbines, it is important to be ully amiliar

with the local weather conditions to ensure that the turbines in-

stalled generate as much energy as possible. Normally, wind tur-

bines are installed:

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in places where a local wind blows requently,

in zones where extratropical lows oten pass, or

in zones where trade or monsoon winds blow.

Local windsWind is created through pressure dierences in the atmosphere.

The greater the dierence in pressure, the stronger the wind can

become.

Local weather systems are oten caused by dierences in the heat-

ing o the Earths surace by the sun. One example o this is sea

breezes which, in the summer months, can arise over land close to

the sea or a large lake when the weather is clear and calm. When

the sun heats the Earths surace, the air close to the surace is

heated and rises and the wind starts to blow in rom the sea or

the lake. I the air rises high enough, it will be cooled to such an

extent that it may orm clouds or even rain showers. Towards the

end o the aternoon, when the heating by the sun decreases, the

wind stops blowing and the clouds disappear.

At night, the wind can turn so that it fows rom the land towards

the sea (land breeze). This oten occurs on still, clear nights when

the heat radiated by the Earth can pass almost unhindered through

the atmosphere to space. When the Earth radiates heat, the surace

cools down, rather like a patch o exposed skin in a cold room, or

a wood-burning stove when the re has gone out. The air closest

to the surace is also cooled, as it transers some o its heat to the

soil. I the process continues long enough, the air above the land

will nally become colder than the air above the sea and a land

breeze will set in. (The sea also radiates heat into the atmosphere,but here, the mixing o the waters almost completely negates the

all in temperature near the surace).

Mountain and valley winds are other examples o local wind sys-

tems created by solar heating. These winds arise in mountainous

regions in clear weather. When the sun heats up the slopes o the

mountains during the day, the wind begins to fow up the slopes

and up through the valleys as hot air naturally rises. At night, when

the mountains are cooled by the radiation o heat into the atmos-

phere, the wind changes direction and fows down the slopes and

down through the valleys.

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How does

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Winds that arise locally because o solar heating are known as ther-

mal winds. Local winds attributable to the shape o the landscape

(orography) are known as orographic winds. Mountain and valley

winds are both thermal and orographic.

Areas subject to local wind systems make good sites or erecting

turbines. When planning wind arms, a lot o work is done to nd

precisely the places where the wind blows most strongly on moun-

tain peaks and crests, or example. However, places where the windgusts can be so strong that they can actually damage the turbines

are naturally to be avoided. For more inormation about where it is

most protable to install turbines, see the section entitled Where

are wind turbines erected?, which you can access via the main

menu.

Extratropical low pressure systemsThe generation o wind energy is not exclusively limited to areas

with local wind systems. Most o the wind turbines in the world are

sited in what are known as the westerlies the broad zones north

and south o the tropics where the wind typically blows rom thewest and large passing lows and storms (also called extratropical

cyclones) determine wind and weather conditions. Around such

low pressure systems there is plenty o energy or wind turbines to

exploit. In the southern hemisphere, the zone o the westerlies has

been named The roaring orties on account o the very strong

winds that blow here.

Westerly winds and extratropical lows occur because the sun heats

the Earth dierently at dierent latitudes. In the low latitudes,

solar heating is generally stronger than the cooling attributable to

the radiation o heat to space. In higher latitudes, the reverse ap-plies. Extratropical lows occur as waves in the zone known as the

polar ront that separates hot and cold air. Due to the rotation o

the Earth, winds do not blow directly towards areas o low pressure,

but are defected so that they blow around these areas anticlock-

wise in the northern hemisphere and clockwise in the southern

hemisphere. This is known as the Coriolis eect (c. rule no. 5).

Trade winds and monsoonsCloser to the equator, tropical and subtropical wind systems the

trades and the monsoons dominate. The trade winds blow acrossthe sea rom the subtropical areas o high pressure to be ound

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around latitudes 30 north and south o the equator, and in to-

wards the area o low pressure in what is known as the intertropical

convergence zone close to the equator. The rotation o the Earth

defects the wind to the right in the northern hemisphere (the

north-east trades) and to the let in the southern hemisphere (the

southeast trades), c. rule no. 5.

The monsoons are thermal winds on a large scale. They blow in

rom the sea across the subtropical continents in the summer, andin the other direction in the winter. The countries o South-east

Asia and those around the Indian Ocean are particularly aected

by the monsoons the south-west monsoon in the summer and the

north-east monsoon in the winter.

The shape o the landscapeThe shape o the landscape has a signicant eect on the strength

and stability o the wind. The more uneven the landscape, the

more unstable the wind. In this context, we are reerring not only

to the large-scale ormation o the landscape with mountains and

valleys (the orography), but also to the small-scale unevennesso the surace (the roughness). An area o woodland or a built-

up area will be rougher than an open eld, which, in turn, will

be rougher than the surace o the sea or a lake. The rougher a

surace, the more it will hinder the wind by creating more ric-

tion. Thereore, the wind blows more strongly over the sea than

across the land; and more strongly over open land than in wooded

or built-up areas. For additional inormation about orography

and roughness, see the section entitled Where are wind turbines

erected?, which you can access rom the main menu.

When erecting wind turbines, it is best to choose a site where thewind can blow reely over the turbines rom all directions. That is

why turbines are typically erected away rom towns. To generate the

most energy, it is best to erect the turbines at oshore sites but

this is a more complicated and costly process.

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How dowindturbines

work?

Wind turbines use the energy in the wind to generate electricity. This

section traces the route energy ollows rom the wind itsel, through the

turbine and out into the grid and then on to households in the orm o

electrical current. It also describes how turbines regulate their output to

prevent overloading in high winds.

The main components o a wind turbineWind turbines consist o our large main components: a ounda-

tion unit, a tower, a nacelle (turbine housing) and a rotor. In

principle, the oundation unit takes the orm o a giant concrete

block buried in the earth. The nacelle is positioned at the top o

the tower, and the rotor is attached to the ront o the nacelle.

Click the picture to the right to build your own wind turbine. Click

the turbine oundation to call up the various components.

The principal task o the tower is to raise the nacelle high into the

air because the wind speed and thus the power o the wind is

much greater 50100 metres above the ground. The tower is also

used to guide the cables rom the nacelle down to the electricalgrid in the ground. The nacelle contains the large primary com-

ponents such as the main axle, gearbox, generator, transormer,

control system and electrical cabinet. The rotor consists o a hub to

which three blades are attached.

From wind to currentWind turbines use the power o the wind to generate energy. This

happens when the blades on the rotor capture the wind, which

makes them turn. When no wind is blowing, the turbine will adjust

the blades to an angle o 45, which is the position in which the

turbine can draw as much energy as possible rom gentle winds.The blades begin to turn very slowly, without generating any en-

ergy. This is known as idling. When there is sucient wind or

the turbine to start generating energy normally at wind speeds o

around 4 metres per second, the blades will gradually start to rotate

longitudinally towards an angle o 0, which means that the broad

surace o the blade is acing into the wind. When the wind then

strikes the blade, it generates overpressure on the ront surace o

the blade and underpressure on the reverse. In other words, the

wind pushes onto the ront surace and simultaneously generates

a suction eect across the rear surace and it is this dierence inpressure that makes the rotor turn. Wind turbines typically gener-

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ate energy at wind speeds o 425 metres per second. When tur-

bines are generating electricity, the rotor speed will be 919 revolu-

tions per minute, depending on the wind speed and the turbine

type. At the maximum speed o revolution, the blade tips reach a

speed o 250 km/h.

Blades and wind speedClick the picture to the right to see the relationship between wind

speed and the position o the blades.

The nacelle componentsThe wind thus causes the rotor to turn, converting the energy in

the wind into rotating, mechanical energy. This rotating, mechani-

cal energy is channelled to a gearbox in the nacelle. From there,

the energy fows to a generator, where it is converted into electri-

cal energy. The purpose o the gearbox is thus to convert the slow

speed o rotation o the blades into the high speed o revolution

o the generator. This conversion is perormed at a ratio o 1:100,

which means that i the blades are rotating at a speed o 15 revolu-tions per minute, the generator will rotate at 1500 revolutions per

minute (depending on the type o turbine). Through this process,

the generator converts mechanical energy into electrical energy.

Connection to the gridThe electrical control system in the turbine links up the genera-

tor, leading the electrical output generated through a high voltage

transormer to the grid, which supplies current to households. In

just 23 hours, a V90-3.0 MW turbine can generate enough electric-

ity to cover the annual consumption o an average Danish house-hold. This means that in a year, a turbine o this type can cover the

electricity requirements o around 3,400 Danish households.

YawWind turbines are designed to ensure that their rotors always ace

into the wind. This process is controlled by a wind vane positioned

on the top o the nacelle. This instrument determines the direc-

tion o the wind just like a weather vane. When the wind changes

direction, a contact is activated in the wind vane, initiating the

motors that turn the turbine into the wind. This is known as yaw.

Turbine blades can also pitch i.e. turn on their longitudinal

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axes so as to adjust to the wind speed. This ensures that the blades

always capture as much o the power o the wind as possible, thus

generating as much energy as possible.

Wind turbines are designed to unction optimally in wind speeds o

425 metres per second. In other words, turbines will always reap

the maximum amount o energy rom the wind at wind speeds

within this range. The volume o energy a wind turbine can gener-

ate depends on actors such as the size o the generator, the dimen-sions o the rotor and the strength o the wind. For example, a V90-

3.0 MW turbine, which has a rotor diameter o 90 metres, starts

to generate power in wind speeds as low as 4 metres per second,

and achieves its maximum power output (3 MW) at 15 metres per

second. When the wind speed reaches 4 metres per second, the

angle o the blades will be 0 so as to ensure that the turbine draws

as much energy as possible rom the wind. When the wind speed

reaches 1012 metres per second, the blades will rotate longitudi-

nally away rom the wind slightly to prevent the turbine generat-

ing more energy than its components are dimensioned or. This is

known as output regulation.

Output regulationThere are three ways to regulate output:

1) Passive stall: The turbine operates with a constant speed o

revolution and has non-adjustable blades. In this case, aerodynam-

ics will orce the blade prole to stall, i.e. to generate turbulence

which limits uplit and thus stops the turbine drawing energy rom

the wind. This will occur at wind speeds in excess o 1215 m/s,

depending on the turbine type.

2) Active stall: The turbine operates with a constant speed o revo-

lution but has adjustable blades. In this case, the turbine regulates

output by turning the rear edge o the blades into the wind to pro-

duce a stall eect at wind speeds in excess o 1215 m/s.

3) Pitch: There are two types o pitch-based output regulation:

- Pitch: The turbine operates with a constant speed o revolu-

tion and has adjustable blades. In this case, the leading edge o the

blade is turned into the wind to reduce uplit.

- Variable speed pitch: The turbine operates with a variable

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speed o revolution and has adjustable blades. In this case, the

leading edge o the blade is turned into the wind to reduce uplit.

The turbines in the Vestas range use only variable speed pitch and

active stall to regulate output.

Shut-down in high windsI the wind reaches speeds in excess o 25 metres per second,

the turbine stops because such speeds place too much strain onturbine components. At the same time, wind speeds only rarely

exceed the stop limit, so there is little need to generate energy

rom winds blowing at higher speeds. It would thereore be pro-

hibitively expensive to design a model that could handle such high

wind speeds. When wind speeds exceed 25 metres per second, the

blades pitch to 90, which means that the leading or rear edges o

the blades (depending on the output regulation principle applied)

point directly into the wind. This makes the blades unction as gi-

ant air brakes, slowing the turbine down until it comes to a com-

plete stop.

Vestas technologiesThe technologies Vestas uses or output and generator regulation

are:

Active Stall: a hydraulic active stall technology that ensures that

the rotor captures the maximum amount o energy rom the wind

while simultaneously minimising load on the turbine design and

controlling turbine production. This technology is used in the V82-

1.65 MW turbine.

OptiTip: a microprocessor-controlled pitch regulation systemthat constantly adjusts the angle o the blades to the optimal posi-

tion in relation to the prevalent wind. This technology is used in

all the turbines rom the Vestas range other than the V82-1.65 MW

model.

OptiSlip: a generator system that makes possible a variation o up

to 10 per cent between the speeds o revolution o the blades and

generator in the event o powerul gusts o wind. In addition to

minimising load on the turbine components, OptiSlip also con-

tributes to a signicant improvement in power quality. OptiSlip

turbines are also tted with OptiTip. The V80-1.8 MW turbine is

the only model in the current Vestas range to use OptiSlip.

OptiSpeed: a development o the OptiSlip technology. OptiS-

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peed allows the rotation speed o turbine blades to vary by up

to 60 per cent, thus optimising energy generation especially at

modest wind speeds. In addition, OptiSpeed makes it possible

to adjust noise levels to match local requirements. As the variable

speed o revolution reduces load, the OptiSpeed system minimis-

es strain on the gearbox, blades and tower. OptiSpeed turbines

are also tted with OptiTip. OptiSpeed technology is used in all

turbines in the Vestas range except the V82-1.65 MW and V80-1.8

MW models.

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Windturbineprojects

From start to fnish, wind turbine projects can be divided into three main

phases: a sales phase, a project phase and a service phase. This section

presents an overview o some o the activities that take place in each o

these three phases.

The sales phaseIn the context o the sale o a wind turbine project, the initial

contact between the customer and Vestas may be established in di-

erent ways. For example, the customer may contact Vestas directly,

or the project may be put out to tender. However, beore any wind

turbine project can be implemented, the authorities must grant

approval.

Direct contactSome customers preer to work with specic manuacturers and

thereore contact them directly. This preerence may be based on

actors such as the manuacturer operating local production, being

a leading player within the sector, or simply because the customer

enjoyed a good working relationship with the manuacturer duringprevious wind turbine projects.

TendersWhen a wind turbine project is put out to tender, the customer

wishes to receive tenders or the execution o the project rom

several dierent manuacturers. There are two types o tendering:

open and closed.

In open tendering also known as public tendering manuactur-

ers contact the customer who has put the wind turbine project out

to tender. In contrast, the closed tendering approach involves thecustomer inviting selected manuacturers to bid or the wind tur-

bine project. This approach may, or example, be chosen because

only the selected manuacturers have the necessary technological

competence, or because the turbines must be o a given size due

to the conditions at the site in question. It may also be chosen

because there is no direct requirement or open tendering, which

generally costs more than a closed process.

When putting a project out to tender, the customer prepares a

set o material, which contains the inormation the manuacturer

needs to prepare a tender or the project. This inormation may,

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or example, comprise technological requirements, a description

o the conditions at the site where the turbines are to be installed,

delivery schedules and the like.

Tendering processes are run according to xed procedures. For

example, all the tenders rom the various manuacturers have to be

delivered to a specic address by a specic time on a specic day.

Once all the tenders have been submitted, the customer chooses

a supplier. In the same way as the xed procedure or submit-ting tenders, there are rules governing the deadline by which the

customer is to make the choice and inorm the preerred supplier.

Once the supplier who has won the tender and thus the contract

has been inormed, the actual contract negotiations can begin.

Negotiating the contractWhen negotiating a contract, Vestas and the customer lay down the

conditions that are to be included in it. For example, these may in-

clude the project price, terms o payment and delivery, as well as a

range o technological conditions such as tower type, tower height,monitoring system and so on.

Contact negotiations are oten protracted and can sometimes take

several years to conclude. The duration o the negotiations de-

pends on actors such as the size o the project, whether the cus-

tomer is a new or existing customer (who will already be amiliar

with the process), and the options or nancing the project.

Choosing the type o turbineIt is crucial to the protability o the wind turbine project that the

customer choose the type o turbine best suited to installation atthe site in question. In order to establish what type o turbine is

best suited to the site, it is necessary to study inormation about the

wind conditions and the eatures o the landscape at the site. For

additional inormation about choosing the type o turbine, see the

section entitled Where are wind turbines erected?, which you can

access rom the main menu.

Permission rom the authoritiesNational authorities have a lot o infuence on the implementation

o wind turbine projects. Beore the project can be implemented,

the customer bears the responsibility or applying or and receiv-

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ing all the necessary permits rom the authorities.

The authorities lay down requirements concerning aspects such as

the height o the turbines and their positioning in the landscape.

The authorities also issue construction permits to the customer,

dene the criteria or connecting the wind turbines to the national

grid, and lay down the saety requirements. For example, all the

oundations or turbines erected in Taiwan and Japan have to be

designed according to the legislation pertaining to earthquakes.

Close collaboration with the customerThroughout the sales process, Vestas works closely with the cus-

tomer so closely, in act, that the working relationship can best

be described as a partnership. Vestas has a network o agents, sales

companies and oces that covers the entire globe. This helps en-

sure that Vestas has in-depth knowledge o local conditions on the

various markets and, in particular, is ully amiliar with the culture

in the customers country. For this reason, sales sta are always

rmly linked to a limited number o markets to help them build up

the best possible knowledge o the local conditions and culture.

In the sales phase, the sales sta naturally play a central role. Their

task is to help the customer with, or example, inormation about

the product and the site, and to inorm the customer about nanc-

ing options. The intention here is to boost condence in Vestas

and Vestas products and, at the same time, to assist the customer

in collecting the required approvals and nding the necessary

nancing. The overall aim is to ensure that the customers project

can be implemented as eciently as possible.

The project phaseOnce the contract has been negotiated and signed, the sales phase

draws to a close. The project then moves into the actual project

phase, which comprises everything rom logistics and transport to

the erection and commissioning o the turbines. The project phase

is distinguished by stringent requirements or planning and fex-

ibility.

Transer to the project managerThe transer rom the sales phase to the project phase is marked

by a hand-over meeting and a kick-o meeting. The sales team and

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the project manager participate in the hand-over meeting. Very

oten, the project manager will have been involved in the nal

stages o the sales phase, and at the hand-over meeting, the project

is ormally transerred to the project manager. The purpose o this

meeting is to examine all the signicant, practical details concern-

ing the project. These typically include:

nances

schedule

division o responsibility (or what areas are the customer

and Vestas each responsible?)

subcontractors

logistics

transport

special agreements, i any

Ater the hand-over meeting, the project manager is equipped to

take control o the project and can start to collect inormation andinitiate assignments.

The kick-o meeting involves the sales team, the project manager

and the customer. At this meeting, the customer and project man-

ager are ormally introduced. The meeting also marks the start o

the planning or the subsequent stages o the project phase, and is

used to dene the practical acilities that need to be established or

the service technicians who are to work at the site. This involves,

or example, setting up the site oce, telephone lines, ADSL con-

nection, toilet acilities and, possibly, a canteen.

Ater the kick-o meeting, the work on the project phase begins inearnest.

TransportThe rst period o the project phase ocuses largely on aspects

such as logistics and transport. Vestas logistic department is re-

sponsible or ensuring that all the turbine components (nacelles,

blades, hubs and towers) are ready or transportation to the site

on time. Vestas transport department has ultimate responsibility

or organising and co-ordinating the transportation o the turbine

components rom Vestas production acilities to the site.

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The entire process is monitored by the project manager, who co-

ordinates input on the basis o reports rom the logistic and trans-

port departments. The project manager will oten be present at the

dispatch o a large number o wind turbines to make sure that the

components are loaded properly to prevent damage in transit.

As a general rule, Vestas is responsible or the transportation o the

wind turbines rom the production acilities all the way to the site.

Depending on the location o the site, the components are typical-ly transported by lorry, ship or train. Visit the Vestas Cinema, which

you can access rom the main menu, to see a lm about how wind

turbines are transported.

Preparing the siteBeore the turbines arrive, the site is prepared to receive the vari-

ous components so that the work to erect the turbines can start

as quickly as possible. The cranes and liting equipment must be

in position, and the oundations which were laid at the site in

advance must have hardened.

I the project is what is known as a turnkey project i.e. a project

in which Vestas is also responsible or establishing the inrastruc-

ture at the site Vestas subcontractors will have started work at the

site many months beore the turbines arrive. The reason or this

is that it is oten necessary to make comprehensive changes at the

site. For example, transormer stations have to be installed, new

roads have to be laid, and cable connections have to be established.

It is essential that the large, heavy lorries that transport the turbine

components can access the site via a solid road network. In addi-

tion, the electricity cables have to be buried and led up through

the oundations.

The site itsel is not the only thing that has to be prepared or the

arrival o the turbines. The site personnel have to get ready, too.

They must be thoroughly prepared or the task and inormed o all

the signicant details o the project. Preparation o the site person-

nel is quite simply crucial to the success o the project.

Erecting the turbines

When the turbine components arrive at the site, the erection work

itsel can begin. It is not a good idea to wait until all the turbine

components have arrived beore starting the erection work. Onthe contrary, the various turbines are erected as soon as the rel-

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evant components arrive. It is essential to ensure that the work is

perormed as eciently as possible, as there are appreciable costs

linked to having cranes and other liting equipment at the site.

Firstly, the tower, which consists o several sections, is installed on

top o the oundations. Then the nacelle is hoisted to the top o

the tower, and nally, the hub and blades are tted to the nacelle.

The rotor (the hub and blades) can be lited into position as a

complete unit, or the hub can rst be tted to the nacelle, with theblades subsequently being hoisted one at a time and connected

to the hub. When a turbine has been erected, the work is ar rom

nished, as the cable work still has to be completed.

Visit the Vestas Cinema, which you can access rom the main menu,

to see a lm about how wind turbines are erected.

Connection to the gridAs the turbines are erected, they are consecutively commissioned

and made ready or connection to the grid. Beore the turbines are

handed over to the customer and ocially connected to the grid,they are subjected to a thorough test phase which involves operat-

ing without error or a set number o hours and then being con-

nected to the grid or a specic period (the number o hours may

vary according to the terms o the contract).

Once all the turbine tests have been completed successully, what is

known as a Take Over Certicate (TOC) is issued and the project

can be handed over to the customer. The TOC serves as documen-

tation that the customer has received the project as agreed in the

contract.

ChallengesVarious challenges can arise during the project phase. That is why

the key concepts o any wind turbine project are planning and fex-

ibility. A great many actors are involved, and they must all com-

bine to create a coherent whole. Unortunately, not everything can

be controlled.

For example, the weather plays a signicant role. I the wind tur-

bines are to be transported by ship, the weather largely determines

whether the turbines arrive on time. The weather also exerts its

infuence during the erection phase: i the wind is too strong, it is

not possible to raise the components, and work has to be stopped

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or a while. This means that it is essential to remain fexible and to

go the extra mile while the weather is good.

Other actors that can delay projects include applying or driving

permits or the heavy transport vehicles, and clearing customs at

the border which sometimes takes a long time.

Thereore it is essential always to think ahead and to be ready to

change plans to avoid major delays in the work.

The service phaseThe service phase begins when the wind turbine project has been

handed over to the customer. During this phase, the service de-

partment makes sure to monitor the wind turbines and maintain

contact with the customer. Beore the service department ormally

takes over responsibility or the wind turbine project, a meeting is

held between the project manager and a service manager. At this

meeting, the wind turbine project is examined in detail so that

the service manager is thoroughly brieed on the progress o the

project to date and on all the signicant details o the project.

Service visitsA number o service visits are perormed at regular intervals during

the 2-year warranty period that applies to Vestas turbine models.

During each visit, the service technicians ollow a set procedure. In

act, they have a checklist to ollow. During service visits, the techni-

cians tighten all the bolts, lubricate the rotating parts (the genera-

tor and blade bearings, or example) and check to see whether any

parts need replacing.

As a part o all service visits, the technicians check the wind turbineblades and take an oil sample rom the gearbox or subsequent

analysis. Technicians conclude all their service visits by cleaning

the wind turbines internally. During nal service visit, th e

service technician perorms a complete examination o all the

wind turbines in the project to make sure that none o the turbines

contains any deects when the warranty period expires.

Training service techniciansVestas trains its own service technicians, all whom have to complete

a comprehensive training course beore being allowed to workon installed turbines. All technicians receive the same training to

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Windturbineprojects

ensure that the service visits are always perormed in the same way

and always meet Vestas standards no matter where in the world

the turbines may be located.

During the training course, technicians acquire in-depth knowl-

edge not only o wind turbine technology, but also o saety regu-

lations. The technicians have to pass a course which involves, or

example, learning how to climb around in turbines in a sae and

responsible manner. Saety is extremely important particularlywhen a service technician is working on top o an installed nacelle.

As all Vestas service technicians have completed the same training

course, they can all work on any site. Very large sites will oten have

a group o technicians permanently attached. The number o asso-

ciated service technicians depends on the size o the site, and some

sites have teams o up to 20 technicians. The advantage o having

technicians permanently linked to large sites is that it allows these

technicians to build up in-depth knowledge o both the turbines at

the site and the site itsel.

In addition to the technicians who live and work on individualmarkets, Vestas employs a number o travelling service technicians.

These technicians travel around to work on sites all over the world.

Travelling service technicians spend much o their time working

away rom home. Some can spend up to 250 days a year abroad.

The advantage o employing travelling service technicians is that

it improves fexibility. As a general rule, travelling service techni-

cians work on small sites that do not have a permanent team o

technicians. They can also travel to sites where extra manpower is

required or a set period o time.

Even though travelling service technicians are always on the move,great emphasis is placed on close contact with the Vestas service

department.

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Where arewind turbines

erected?

The implementation o a wind turbine project is always preceded by

months o measurement o actors such as wind speed and wind direction

at the intended site. This section explains the actors used to determine

whether a site is suitable or wind turbines, and those that defne the type

o turbine used.

Measuring wind resourcesWhen establishing whether an area is suitable or installing wind

turbines, it is naturally essential to make sure that there is su-

cient wind. The rst step is to nd out whether there are any data

available rom previous studies o the wind in the area, or whether

there are any existing wind reports including maps o the wind re-

sources at the site. It is also a good idea to speak to local residents,

who oten have a good sense o the wind conditions in the region.

Once it has been established that an area has reasonable wind

potential, one or more measuring masts are erected, depending

on the size o the planned project. These masts are typically 4080

metres high, with measuring equipment installed at 35 dierent

heights. As a general rule, to obtain the best results the measuringmasts should be as high as the turbines are expected to be.

The actual measurement o the wind resources is carried out by

several wind meters (cup anemometers), which are attached to the

measuring masts at dierent heights. The primary intention here

is to measure the wind shear at the site. Wind shear is an expres-

sion or the ratio between the increase in wind speed and the

increase in height. It is important to measure wind speed at various

heights to make it possible to calculate how much it increases. This

measurement is used not only to calculate how much energy the

turbines will generate, but also to establish the loads to which theturbines will be subjected.

Measuring wind directionIn addition to measuring the wind speed, it is also essential to es-

tablish the direction rom which the wind typically blows. What are

known as wind vanes are used or this purpose. These are instru-

ments that unction according to the same principles as a weather

vane.

The anemometers and wind vanes are connected to a battery-pow-

ered data logger that processes the data and stores them on a mini-

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hard disk. Wind data are measured at regular intervals, typically o

10 minutes. It is recommended to take measurements or at least a

year in order to collate sucient inormation to make it possible to

calculate the mean annual wind speed. The wind speed measured

is presented as a unction o the wind direction in a circular graph

(a pie chart) divided into twelve sections o equal size. This dia-

gram is also called a wind rose and illustrates the wind speed, the

directions rom which the wind blows, and the dominant direction.

The wind direction is principally used to determine how the tur-

bines are to be positioned in relation to each other. The necessary

distance between the turbines and rows is, in act, heavily depend-

ent on not only the wind speed, but also the wind direction as it is

important to ensure that the turbines do not generate turbulence

or block the wind or each other.

Ensuring proftabilityMeasuring the wind or a year thus helps dene the annual mean

wind. This is the value that primarily provides the basis or calcu-

lating how much power a wind turbine will be able to generate.However, the annual mean wind can vary greatly rom year to year

by up to 20 per cent which translates, as a rule o thumb, into

variation in energy generation o approximately double that gure,

i.e. 40 per cent.

Such a large margin o uncertainty would result in serious prob-

lems in calculating the protability o the project. This, in turn,

would make it very dicult to nd the nancing required. There-

ore, it is common to use long-term data rom a reerence mast,

which measures wind conditions over a 20-year period. Using data

rom such a reerence mast, it is possible to calculate the averagewind speed or the entire 20-year period. When data rom the

measuring masts overlap those rom the reerence mast, the annual

mean wind or the specic year is corrected to the average wind

speed so as to make it possible to orecast the mean wind or the

coming 20 years. This is known as long-term correlation.

In Denmark, a reerence mast could be one o the DMI (Dan-

ish Meteorological Institute) weather stations that have been set

up all over the country. In other countries it could be one o the

measurement masts set up by the public authorities or installed

in connection with an airport. Wherever such masts are available,

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attempts are made to access the relevant data so as to minimise the

risk o incorrectly orecasting the production o a uture wind arm

or, as a worst-case scenario, installing the wrong type o turbine or

the site resources. Data rom a reerence mast oten reduce the

level o uncertainty linked to calculations based on inormation

rom just one year o measurements.

Wind conditions or each turbineIt is important to establish the wind conditions not only around the

measuring mast itsel, but also in every single place where a wind

turbine is to be erected. In order to determine the areas richest

in energy at the projected site, it is necessary to draw up a wind-

stream eld, otherwise known as a wind resource map. To do

this, the WAsP calculation tool can be used. This tool not only uses

inormation rom the measuring mast, but also takes into account

actors that aect the wind such as the roughness o the terrain

(plants, trees, buildings, etc.) and the orography o the region

(the contours o the landscape in the orm o hills and/or moun-

tains). The dierence between orography and roughness is thatorography ocuses on the contours o the landscape, whereas

roughness is centred on everything that is built on or grows on

the landscape. Together, roughness and orography produce what is

known as the topography (the surace shape) o the area.

RoughnessAs rom a height o around 1,000 metres above ground level, the

wind is not aected by the conditions on the ground, but the closer

to the earth the wind comes, the more it is aected and slowed

by uneven eatures o the landscape such as buildings and trees.

Roughness is dened according to what are known as roughness

categories that run rom Class 0 (sea surace) to Class 4 (high,

dense woodland or large cities with skyscrapers). For additional

inormation about roughness, click the ollowing link: www.wind-

power.org/en/tour/wres/shear.htm

OrographyThe wind is also aected by the orography (contours) o the land-

scape. Generally speaking, the wind blows more strongly at higher

altitudes, so it is oten best to position wind turbines on the peak or

crest o a mountain. When the wind blows over a mountain crest,

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the wind is oten subject to compression. This compression triggers

a speed-up eect also called an acceleration which means that

even a wind that is gentle at the oot o a mountain can become

very strong at the peak. However, it is important to remember that

the energy in the wind is also dependent on the density o the air

and that density decreases as altitude increases. When the den-

sity drops, so does the amount o energy in the wind, which is a

actor that is mainly a problem in high mountains. In Denmark,

the National Survey and Cadastre publishes a contour map o thelandscape which the WAsP calculation program converts into a 3D

fow domain.

The WAsP calculation program thus uses inormation rom three

sources to predict wind speeds at a given site data rom the

measuring mast, inormation about the roughness o the area and

a contour map converted into a 3D model. Using this inormation,

the program can simulate wind conditions at every single spot on

the site, making it possible to calculate the energy production o

each turbine.

In parallel with the measurement o wind conditions at the site,

work is also done to answer the ollowing questions:

1. What are the options or grid connection? Will it actually be

possible to deliver the power? Are there any connection options

relatively nearby? (As a rough rule o thumb, a project can accom-

modate the construction o one kilometre o grid connection cable

per installed MW. However, this depends to a great extent on the

area, the project itsel, etc.)

2. Is the project protable, and are there enough investors?

3. Will the local and national authorities issue the permits neces-sary to install turbines in the area?

Choosing the type o turbineNumerous parameters come into play when choosing the optimal

type o turbine or a specic site. The most common are listed

below:

1. Are there any local restrictions regarding turbine height, noise

levels, nature conservation and the like?

2. Does the turbine meet requirements rom the authorities (IEC,

or example)?

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3. Is there any risk o earthquakes, typhoons or other extreme,

external infuences?

4. Is it physically possible to transport the turbine components to

the site, or does the inrastructure place limits on turbine size?

5. Is it possible to access the required crane capacity locally, or will

cranes also have to be transported long distances to the site?

The turbines have been designed in accordance with international

wind turbine standards to ensure that they are products o inter-

national quality. In act, the turbines have been designed accord-

ing to standards laid down by GL (Germanischer Lloyd) and IEC

(International Energy Center) two almost identical approval

authorities.

The IEC standard comprises our categories that divide the tur-

bines into dierent levels which refect the design loads o the

turbines or, in other words, how much the turbines can withstand

during their 20-year service lietimes. The table below lists some o

the principal parameters that apply to turbine design. Please note

that there are many other parameters o signicance to the overallload calculation.

IEC Cat-

egory

Expected

mean wind

(20 years)

(m/s)

Expected

50-year wind

gusts

(m/s)

Expected

50-year wind

10-minute av-

erage

(m/s)IEC S According to manu-

facturers design

parameters

According to manu-

facturers design

parameters

According to manu-

facturers design

parametersIEC1

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Discover the unique power of the windDiscover the unique power of the windDiscover the unique power of the wind


erected?

The principal reason why IEC 1 turbines are not simply used or all

sites is that they are over-dimensioned or many sites, which, or ex-

ample, means more expensive components. Using IEC 1 turbines

or projects involving sites with less strong winds would, or exam-

ple, result in the projects being less protable or even unprot-

able. Using the right type o turbine or each site makes it possible

not only to reduce costs or the project but also to cut noise levels

and improve production rom the turbines.

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