1- BRIEF HISTORY OF WIND POWER

1.1 WIND ENERGY

Wind energy is a converted form of solar energy which is produced by the nuclear fusion

of hydrogen (H) into helium (He) in its core. The H → He fusion process creates heat and

electromagnetic radiation streams out from the sun into space in all directions. Though

only a small portion of solar radiation is intercepted by the earth, it provides almost all of

earth’s energy needs. Wind energy represents a mainstream energy source of new power

generation and an important player in the world's energy market. As a leading energy

technology, wind power’s technical maturity and speed of deployment is acknowledged,

along with the fact that there is no practical upper limit to the percentage of wind that can

be integrated into the electricity system.

It has been estimated that the total solar power received by the earth is approximately 1.8

× 10 11 MW. Of this solar input, only 2% (i.e. 3.6 × 10 9 MW) is converted into wind

energy and about 35% of wind energy is dissipated within 1000 m of the earth’s surface.

Therefore, the available wind power that can be converted into other forms of energy is

approximately 1.26 × 10 9 MW. Because this value represents 20 times the rate of

the present global energy consumption, wind energy in principle could meet entire energy

needs of the world.

Compared with traditional energy sources, wind energy has a number of benefits and

advantages. Unlike fossil fuels that emit harmful gases and nuclear power that generates

radioactive wastes, wind power is a clean and environmentally friendly energy source. As

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an inexhaustible and free energy source, it is available and plentiful in most regions of the

earth. In addition, more extensive use of wind power would help reduce the demands for

fossil fuels, which may run out sometime in this century, according to their present

consumptions. Furthermore, the cost per kWh of wind power is much lower than that of

solar power. Thus, as the most promising energy source, wind energy is believed to play

a critical role in global power supply in the 21st century.

1.2 WIND GENERATION

Wind results from the movement of air due to atmospheric pressure gradients. Wind

flows from regions of higher pressure to regions of lower pressure. The larger the

atmospheric pressure gradient, the higher the wind speed and thus, the greater the wind

power that can be captured from the wind by means of wind energy-converting

machinery. The generation and movement of wind are complicated due to a number of

factors. Among them, the most important factors are uneven solar heating, the Coriolis

Effect due to the earth’s self-rotation, and local geographical conditions.

1.2.1 UNEVEN SOLAR HEATING

Among all factors affecting the wind generation, the uneven solar radiation on the earth’s

surface is the most important and critical one. The unevenness of the solar radiation can

be attributed to four reasons. First, the earth is a sphere revolving around the sun in the

same plane as its equator. Because the surface of the earth is perpendicular to the path of

the sunrays at the equator but parallel to the sunrays at the poles, the equator receives the

greatest amount of energy per unit area, with energy dropping off toward the poles. Due

to the spatial uneven heating on the earth, it forms a temperature gradient from the

equator to the poles and a pressure gradient from the poles to the equator. Thus, hot air

with lower air density at the equator rises up to the high atmosphere and moves towards

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the poles and cold air with higher density flows from the poles towards the equator along

the earth’s surface. Without considering the earth’s self-rotation and the rotation-induced

Coriolis force, the air circulation at each hemisphere forms a single cell, defined as the

Meridional Circulation.

Second, the earth’s self-rotating axis has a tilt of about 23.5° with respect to its ecliptic

plane. It is the tilt of the earth’s axis during the revolution around the sun that results in

cyclic uneven heating, causing the yearly cycle of seasonal weather changes.

Third, the earth’s surface is covered with different types of materials such as vegetation,

rock, sand, water, ice/snow, etc. Each of these materials has different reflecting and

absorbing rates to solar radiation, leading to high temperature on some areas (e.g. deserts)

and low temperature on others (e.g. iced lakes), even at the same latitudes. The fourth

reason for uneven heating of solar radiation is due to the earth’s topographic surface.

There are a large number of mountains, valleys, hills, etc. on the earth, resulting in

different solar radiation on the sunny and shady sides

1.2.2 CORIOLIS FORCE

The earth’s self-rotation is another important factor to affect wind direction and speed.

The Coriolis force, which is generated from the earth's self-rotation, deflects the direction

of atmospheric movements. In the north atmosphere wind is deflected to the right and in

the south atmosphere to the left. The Coriolis force depends on the earth’s latitude; it is

zero at the equator and reaches maximum values at the poles. In addition, the amount of

deflection of wind also depends on the wind speed; slowly blowing wind is deflected

only a small amount, while stronger wind deflected more.

In large-scale atmospheric movements, the combination of the pressure gradient due to

the uneven solar radiation and the Coriolis force due to the earth’s self-rotation causes the

single Meridional Cell to break up into three convectional cells in each hemisphere: the 3

Hadley cell, the Ferrel cell, and the Polar cell. Each cell has its own characteristic

circulation pattern. In the Northern Hemisphere, the Hadley cell circulation lies between

the equator and north latitude 30°, dominating tropical and sub-tropical climates. The hot

air rises at the equator and flows toward the North Pole in the upper atmosphere. This

moving air is deflected by Coriolis force to create the northeast trade winds. At

approximately north latitude 30°, Coriolis force becomes so strong to balance the

pressure gradient force. As a result, the winds are defected to the west. The air

accumulated at the upper atmosphere forms the subtropical high-pressure belt and thus

sinks back to the earth’s surface, splitting into two components: one returns to the equator

to close the loop of the Hadley cell another moves along the earth’s surface toward North

Pole to form the Ferrel Cell circulation, which lies between north latitude 30° and 60°.

The air circulates toward the North Pole along the earth’s surface until it collides with the

cold air flowing from the North Pole at approximately north latitude 60°. Under the

influence of Coriolis force, the moving air in this zone is deflected to produce westerlies.

The Polar cell circulation lies between the North Pole and north latitude 60°. The cold air

sinks down at the North Pole and flows along the earth’s surface toward the equator. Near

north latitude 60°, the Coriolis Effect becomes significant to force the air flow to

southwest.

1.2.3 LOCAL GEOGRAPHY

The roughness on the earth’s surface is a result of both natural geography and manmade

structures. Frictional drag and obstructions near the earth’s surface generally retard with

wind speed and induce a phenomenon known as wind shear. The rate at which wind

speed increases with height varies on the basis of local conditions of the topography,

terrain, and climate, with the greatest rates of increases observed over the roughest

terrain. A reliable approximation is that wind speed increases about 10% with each

doubling of height. In addition, some special geographic structures can strongly enhance

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the wind intensity. For instance, wind that blows through mountain passes can form

mountain jets with high speeds.

1.3 HISTORY OF WIND ENERGY APPLICATIONS

The use of wind energy can be traced back thousands of years to many ancient

civilizations. The ancient human histories have revealed that wind energy was discovered

and used independently at several sites of the earth.

1.3.1 SAILING

As early as about 4000 B.C., the ancient Chinese were the first to attach sails to their

primitive rafts. From the oracle bone inscription, the ancient Chinese scripted on turtle

shells in Shang Dynasty (1600 B.C.–1046 B.C.), the ancient Chinese character sail - in

ancient Chinese) often appeared. In Han Dynasty (220 B.C.–200 A.D.), Chinese junks

were developed and used as ocean-going vessels. As recorded in a book wrote in the

third century there were multi-mast, multi-sail junks sailing in the South Sea, capable of

carrying 700 people with 260 tons of cargo. Two ancient Chinese junks are shown in

Figure. Fig (a) is a two-mast Chinese junk ship for shipping grain, quoted from the

famous encyclopedic science and technology book Exploitation of the works of nature.

Figure (b) illustrates a wheel boat in Song Dynasty (960–1279). It is mentioned in books

that this type of wheel boats was used during the war between Song and Jin Dynasty

(1115–1234). Approximately at 3400 BC, the ancient Egyptians launched their first

sailing vessels initially to sail on the Nile River, and later along the coasts of the. Around

1250 BC, Egyptians built fairly sophisticated ships to sail on the Red Sea. The wind-

powered ships had dominated water transport.5

Figure: Ancient Chinese junks (ships): (a) two-mast junk ship; (b) wheel boat

1.3.2 WIND IN METAL SMELTING PROCESSES

About 300 BC, ancient Sinhalese had taken advantage of the strong monsoon winds to

provide furnaces with sufficient air for raising the temperatures inside furnaces in excess

of 1100°C in iron smelting processes. This technique was capable of producing high-

carbon steel.

The double acting piston bellows was invented in China and was widely used in

metallurgy in the fourth century BC. It was the capacity of this type of bellows to deliver

continuous blasts of air into furnaces to raise high enough temperatures for smelting iron.

In such a way, ancient Chinese could once cast several tons of iron.

1.3.3 WINDMILLS

China has long history of using windmills. The unearthed mural paintings from the tombs

of the late Eastern Han Dynasty (25–220 AD) at Sandaohao, Liaoyang City, have shown

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the exquisite images of windmills, evidencing the use of windmills in China for at least

approximately 1800 years. The practical vertical axis windmills were built in Sistan

(eastern Persia) for grain grinding and water pumping, as recorded by a Persian

geographer in the ninth century. The horizontal axis windmills were invented in

northwestern Europe in 1180s. The earlier windmills typically featured four blades and

mounted on central posts – known as Post mill. Later, several types of windmills, e.g.

Smock mill, Dutch mill, and Fan mill, had been developed in the Netherlands and

Denmark, based on the improvements on Post mill. The horizontal axis windmills have

become dominant in Europe and North America for many centuries due to their higher

operation efficiency and technical advantages over vertical axis windmills.

1.3.4 WIND TURBINES

Unlike windmills which are used directly to do work such as water pumping or grain

grinding, wind turbines are used to convert wind energy to electricity. The first

automatically operated wind turbine in the world was designed and built by Charles

Brush in 1888. This wind turbine was equipped with 144 cedar blades having a rotating

diameter of 17 m. It generated a peak power of 12 kW to charge batteries that supply DC

current to lamps and electric motors. As a pioneering design for modern wind turbines,

the Gedser wind turbine was built in Denmark in the mid-1950s. Today, modern wind

turbines in wind farms have typically three blades, operating at relative high wind speeds

for the power output up to several megawatts.

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1.4 HISTORY OF WIND TURBINES

The first known use of wind power are placed, according to various

sources, in the area between today’s Iran and Afghanistan in the period from 7th to

10th century. These windmills were mainly used to pump water or to grind wheat. They

had vertical axis and used the drag component of wind power: this is one of the reason

for their low efficiency. Moreover, to work properly, the part rotating in opposite

direction compared to the wind had to be protected by a wall.

Figure: Persian Windmill

Obviously, devices of this type can be used only in places with a main wind direction,

because there is no way to follow the variations.

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The first windmills built in Europe and inspired by the Middle East ones had the same

problem, but they used a horizontal axis. So they substitute the drag with the lift force,

making their inventors also the unaware discoverer of aerodynamics.

During the following centuries many modifies were applied for the use in areas

where the wind direction varies a lot: the best examples are of course the Dutch

windmills, used to drain the water in the lands taken from the sea with the dams,

could be oriented in wind direction in order to increase the efficiency.

Figure: Dutch Windmill

The wind turbines used in the USA during the 19th century and until the

’30 of 20th century were mainly used for irrigation. They had a high number of steel-

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made blades and represented a huge economic potential because of their large quantity:

about 8 million were built all over the country.

Figure: American Multi Blade Windmill

The first attempt to generate electricity were made at the end of 19th century, and

they become more and more frequent in the first half of the following century.

Almost all those models had an horizontal axis, but in the same period (1931)

Georges Jean Marie Darrieus designed one of the most famous and common type of

VAWT, that still bears his name.

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Figure: Eole Darrius wind turbine

The recent development led to the realization of a great variety of types

and models, both with vertical and horizontal axis, with rated power from the few kW

of the beginning to the 6 MW and more for the latest constructions. In the electricity

generation market the HAWT type has currently a large predominance.

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1.5 TYPES OF WIND TURBINES

Wind turbines can be separated into two types based by the axis in which the

turbine rotates. Turbines that rotate around a horizontal axis are more common. A wind

turbine applicable for urban settings was also studied. All three types of wind turbines

have varying designs, and different advantages and disadvantages.

1.5.1 HORIZONTAL AXIS WIND TURBINE

Horizontal axis wind turbines, also shortened to HAWT are the most common type used.

A HAWT has a similar design to a windmill; it has blades that look like a propeller that

spin on the horizontal axis. All of the components (blades, shaft and generator) are on top

of a tall tower, and the blades face into the wind. The shaft is horizontal to the ground.

The wind hits the blades of the turbine that are connected to a shaft causing rotation. The

shaft has a gear on the end which turns a generator. The generator produces electricity

and sends the electricity into the power grid. The wind turbine also has some key

elements that add to efficiency. Inside the Nacelle (or head) are an anemometer, wind

vane, and controller that read the speed and direction of the wind. As the wind changes

direction, a motor (yaw motor) turns the nacelle so the blades are always facing the wind.

The power source also comes with a safety feature. In case of extreme winds the turbine

has a break that can slow the shaft speed. This is to inhibit any damage to the turbine in

extreme conditions. These are identified by the fact that the axis of rotation of the blades

are in a fixed horizontal position therefore the unit must be placed in the direction of the

wind, these are most popular in rural areas. Downwind machines have been built, despite

the problem of turbulence, because they don't need an additional mechanism for keeping

them in line with the wind, and because in high winds, the blades can be allowed to bend

which reduces their swept area and thus their wind resistance. Since turbulence leads to

fatigue failures, and reliability is so important, most HAWTs are upwind machines.

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Currently Horizontal Axis Wind Turbines (HAWT or propellers) cover more than 90% of

wind turbine World Park. About 100 companies produce these machines.

HAWT ADVANTAGES:

The tall tower base allows access to stronger wind in sites with wind

shear. In some wind shear sites, every ten meters up the wind speed can

increase by 20% and the power output by 34%.

Variable blade pitch, which gives the turbine blades the optimum angle of

attack.

Blades are to the side of the turbines center of gravity, helping stability.

Tall tower allows placement on uneven land or in offshore locations can

be sited in forest above tree-line.

Most are self-starting.

Accept wind from any angle

HAWT DISADVANTAGES:

Massive tower construction is required to support the heavy blades,

gearbox, and generator.

Components of a horizontal axis wind turbine (gearbox, rotor shaft and

brake assembly) being lifted into position.

Their height makes them obtrusively visible across large areas, disrupting

the appearance of the landscape and sometimes creating local opposition.

HAWTs generally require a braking or yawing device in high winds to

stop the turbine from spinning and destroying or damaging itself.

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The tall towers and blades up to 90 meters long are difficult to transport.

Transportation can reach 20% of equipment costs.

Tall HAWTs are difficult to install, needing very tall and expensive cranes

and skilled operators.

Reflections from tall HAWTs may affect side lobes of radar installations

creating signal clutter, although filtering can suppress it.

1.5.2 VERTICAL AXIS WIND TURBINE

Vertical-axis wind turbines (or VAWTs) have the main rotor shaft arranged vertically.

Key advantages of this arrangement are that the turbine does not need to be pointed into

the wind to be effective. This is an advantage on sites where the wind direction is highly

variable. VAWTs can utilize winds from varying directions.

It is difficult to mount vertical-axis turbines on towers, meaning they are often installed

nearer to the base on which they rest, such as the ground or a building rooftop. This can

provide the advantage of easy accessibility to mechanical components. However, wind

speed is slower at a lower altitude, so less wind energy is available for a given size

turbine. Air flow near the ground and other objects can create turbulent flow, which can

introduce issues of vibration, including noise and bearing wear which may increase the

maintenance or shorten the service life. In designs that do not have helical rotors

significant torque variation will occur.

VAWT ADVANTAGES:

A VAWT can be located nearer the ground, making it easier to maintain

the moving parts.

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VAWTs have lower wind startup speeds than the typical the HAWTs.

VAWTs may be built at locations where taller structures are prohibited.

A massive tower structure is less frequently used, as they are more

frequently mounted with the lower bearing mounted near the ground,

making it easier to maintain the moving parts.

VAWTs situated close to the ground can take advantage of locations

where mesas, hilltops, ridgelines, and passes funnel the wind and increase

wind velocity.

VAWT DISADVANTAGES:

Most VAWTs have an average decreased efficiency from a common

HAWT, mainly because of the additional drag that they have as their

blades rotate into the wind. Versions that reduce drag produce more

energy, especially those that funnel wind into the collector area.

Having rotors located close to the grounds where wind speeds are lower

due and do not take advantage of higher wind speeds above.

While the parts are located on the ground, they are also located under the

weight of the structure above it, which can make changing out parts nearly

impossible without dismantling the structure if not designed properly.

Having rotors located close to the ground where wind speeds are lower

due to wind shear, they may not produce as much energy at a given site as

a HAWT with the same footprint or height.

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1.5.3 EARLY VAWT DESIGNS

VAWTs appear to have been developed long before their horizontal axis cousins. One of

the reasons for this is that the VAWT has a number of inherent advantages including the

fact that a drive shaft may be connected directly from the rotor to a mechanical load at

ground level, eliminating the need for a gearbox. The early pioneers involved in the

development of wind turbines many centuries ago applied VAWTs to the milling of

grain, an application where the vertical axis of the millstone could be easily connected to

the VAWT rotor. Quite a number of excellent review articles have been published in the

past detailing the historical development of wind turbines of all types Virtually all of

these reviews suggest that the very earliest wind turbines were indeed VAWTs and it is

thought that these were first used in Persia for milling grain more than 2000 years ago.

These early wind turbines were essentially drag devices with a rotor comprising a number

of bundles of reeds, or other simple blades, on a timber framework. The rotor was housed

within a walled enclosure that channeled the flow of wind preferentially to one side of the

rotor thereby generating the torque necessary to rotate the millstone. This type of device

was still in use during the latter half of the 20th century and an example located in the

border region of Afghanistan and Iran. The Persian and Sistan VAWTs had rigid vanes

to generate torque whereas other designs have used sails that can effectively pitch with

respect to their alignment on the rotor and thus can potentially increase efficiency. An

example of a Chinese VAWT of the type used for many years for pumping applications,

and which was described by King for pumping brine for salt production, is illustrated in

Figs below.

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Figure 1: An example of VAWTs in the Sistan Basin in the border region of Iran and

Afghanistan. Note in the right hand image how the upstream wall is used to expose only

one half of the rotor to the wind (photographs taken in 1971 near Herat, Afghanistan,

copyright: Alan Cookson).

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Figure 2: A Chinese VAWT used for pumping brine (photo taken in early 20th

Century) from King

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2- TYPES OF VERTICAL AXIS WIND TURBINES

A wide variety of VAWTs have been proposed over the past few decades and a number

of excellent bibliographies on VAWTs have been published that summarize research and

development of these devices. Some of the more important types of rotor design are

highlighted in the following sections.

2.1 DARRIEUS

2.1.1 HISTORICAL BACKGROUND

French aeronautical engineer Georges Jean Marie Darrieus patented in 1931 a “Turbine

having its shaft transverse to the flow of the current”, and his previous patent (1927)

covered practically any possible arrangement using vertical airfoils.

It’s one of the most common VAWT, and there was also an attempt to implement the

Darrieus wind turbine on a large scale effort in California by the FloWind

Corporation; however, the company went bankrupt in 1997. Actually this turbine

has been the starting point for further studies on VAWT, to improve efficiency.

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2.1.2 USE AND OPERATION

The fundamental step forward made by Darrieus was to provide a means of raising the

velocity of the VAWT blades significantly above the free stream wind velocity so that lift

forces could be used to significantly improve the coefficient of performance of VAWTs

over previous designs based primarily on drag. Darrieus also foresaw a number of

embodiments of his fundamental idea that would be trialed at large scale many decades

later. These included use of both curved-blade (Fig. a) and straight blade versions of his

rotor. He also proposed options for active control of the pitch of the blades relative to the

rotor as a whole, so as to optimize the angle of attack of the wind on each blade

throughout its travel around the rotor circumference (as shown in Fig. b ).

Figure: Images from the Darrieus VAWT patent: (a) curved-blade rotor

embodiment; (b) plan view of straight-blade rotor showing an optional active

blade pitching mechanism

The Darrieus turbine can take a number of forms but is most well known in the geometry

sometimes called the “egg-beater” shown in Fig. a , where the two or three blades are

curved so as to minimize the bending moments due to centrifugal forces acting on the

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blade. The shape of the curved blade is close to that taken by a skipping rope in the

absence of gravity and is known as the Troposkein (“spinning rope”).

One of the characteristics of the Darrieus family of turbines is that they have a limited

self-starting capacity because there is often insufficient torque to overcome friction at

start-up. This is largely because lift forces on the blades are small at low rotational speeds

and for two-bladed machines in particular the torque generated is virtually the same for

each of the stationary blades at start-up.

The swept area on a Darrieus turbine is A=23

. D 2, a narrow range of tip speed ratios

around 6 and power coefficient Cp just above 0.3.

Figure: Cp- λ diagram for different types of wind turbines

Each blade sees maximum lift (torque) only twice per revolution, making for a

huge torque (and power) sinusoidal output that is not present in HAWTs. And the

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long VAWT blades have many natural frequencies of vibration which must be avoided

during operation.

Figure: Forces that act on the turbines.

One problem with the design is that the angle of attack changes as the turbine spins, so

each blade generates its maximum torque at two points on its cycle (front and back of the

turbine). This leads to a sinusoidal power cycle that complicates design.

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Another problem arises because the majority of the mass of the rotating

mechanism is at the periphery rather than at the hub, as it is with a propeller. This leads

to very high centrifugal stresses on the mechanism, which must be stronger and heavier

than otherwise to withstand them. The most common shape is the one similar to an egg-

beater that can avoid in part this problem, having most of the rotating mass not far from

the axis. Usually it has 2 or 3 blades, but some studies during the ’80 demonstrate that the

2 bladed configurations have a higher efficiency.

Figure: Three bladed Derrius wind turbine

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2.1.3 EXAMPLES

The biggest example of this type of turbine was the EOLE, built in Quebec

Canada in 1986. Its height is about 100 m, the diameter is 60 m and the rated

power was about 4 MW, but due to mechanical problems and to ensure longevity the

output was reduced to 2.5 MW. It was shut down in 1993.

2.2 SAVONIUS

2.2.1 HISTORICAL BACKGROUND

Savonius wind turbines were invented by the Finnish engineer Sigurd J. Savonius

in 1922, but Johann Ernst Elias Bessler (born 1680) was the first to attempt to build a

horizontal windmill of the Savonius type in the town of Furstenburg in Germany in 1745.

2.2.2 USE AND OPERATION

The Savonius is a drag-type VAWT, so it cannot rotate faster than the wind speed. This

means that the tip speed ratio is equal to 1 or smaller, making this turbine not

very suitable for electricity generation. Moreover, the efficiency is very low compared

to other types, so it can be employed for other uses, such as pumping water or grinding

grain. Much of the swept area of a Savonius rotor is near the ground, making the

overall energy extraction less effective due to lower wind speed at lower heights.

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Figure: Savonius Rotor

Its best qualities are the simplicity, the reliability and the very low noise production. It

can operate well also at low wind speed because the torque is very high especially in

these conditions. However the torque is not constant, so often some improvements like

helical shape are used.

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2.2.3 EXAMPLES

The Savonius can be used where reliability is more important than efficiency:

• Small application such as deep-water buoys

• Most of the anemometers are Savonius-type

• Used as advertising signs where the rotation helps to draw attention

2.3 GIROMILL

2.3.1 HISTORICAL BACKGROUND

The straight-bladed wind turbine, also named Giromill or H-rotor, is a type of

vertical axis wind turbine developed by Georges Darrieus in 1927.

This kind of VAWT has been studied by the Musgrove’s research team in the

United Kingdom during the ’80.

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In these turbines the “egg beater” blades of the common Darrieus are replaced with

straight vertical blade sections attached to the central tower with horizontal supports.

These turbines usually have 2 or 3 vertical airfoils. The Giromill blade design is much

simpler to build, but results in a more massive structure than the traditional

arrangement and requires stronger blades. In these turbines the generator is located at

the bottom of the tower and so it can be heavier and bigger than a common

generator of a HAWT and the tower can have a lighter structure. While it is cheaper and

easier to build than a standard Darrieus turbine, the Giromill is less efficient and requires

motors to start. However these turbines work well in turbulent wind conditions and

represent a good option in those area where a HAWT is unsuitable.

2.3.2 USE AND OPERATION

The operation way of a Giromill VAWT is not different from that of a common

Darrieus turbine. The wind hits the blades and its velocity is split in lift and drag

component. The resultant vector sum of these two components of the velocity makes the

turbine rotate.

The swept area of a Giromill wind turbine is given by the length of the blades

multiplied for the rotor diameter. The aerodynamics of the Giromill is like the one of the

common Darrieus turbine.

Kirke conducted an in-depth study of a number of three-bladed Giromill with

aerodynamic/mechanical activation of the blade pitch mechanism. These devices were

referred to as “self-acting variable pitch VAWTs” with straight blades. Each blade was

mounted at its mid-span on the end of the rotor radial arm and counterweighted so the

mass center coincided with the pivot axis, located forward of the aerodynamic center.

The pitch mechanism was activated by the moment of the aerodynamic force about a

pivot, opposed by centripetal force acting on a “stabilizer mass” attached to the radial

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arm, such that the aerodynamic force overcomes the stabilizer moment and permits

pitching before stall occurs.

Figure: Three blade variable pitch VAWT developed by Kirke clearly

showing the counterweights incorporated in the blade pitch mechanism

(photograph − copyright Brian Kirke).

2.3.3 EXAMPLES

The VAWT-850 was the biggest H-rotor in Europe when it was built in UK in

the 1989. It had a height of 45m and a rotor diameter of 38m. This turbine had a gearbox

and an induction generator inside the top of the tower. It was installed at the Carmarthen

test site during the 1990 and operated until the month of February of 1991, when one

of the blades broke, due to an error in the manufacture of the fiberglass blades.

In the 90’s the German company Heidelberg Motor GmbH developed and built

several 300 kW prototypes, with direct driven generators with large diameter. In

some turbines the generator was placed on the top of the tower while in others turbines it

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was located on the ground. In 2010 the VerticalWind AB, after a 12 kW prototype

developed in Uppsala, Sweden, has developed and built in Falkenberg the biggest

VAWT in Sweden: it’s a 3 blades Giromill with rated power of 200 kW, with a tower

built in with a wood composite material that make the turbine cheaper than other

similar structure made by steel.

Figure: VerticalWind Giromill wind turbine (3 blades, 200 kW, Falkenberg,

Sweden)

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2.4 CYCLOTURBINES

A variant of the Giromill is the Cycloturbine, which uses a vane to mechanically orient

the pitch of the blades for the maximum efficiency. In the Cycloturbines the blades

are mounted so they can rotate around their vertical axis. This allows the blades to be

pitched so that they always have some angle of attack relative to the wind.

Figure: Cycloturbine Rotor

The main advantage of this design is that the torque generated remains almost constant

over a wide angle and so the Cycloturbines with 3 or 4 blades have a fairly constant

torque. Over this range of angles the torque is near the maximum possible and so the

system can generated more power. Compared with the other Darrieus wind turbines,

these kind of VAWT shows the advantage of a self-starting: in low wind conditions,

the blades are pitched flat against the wind direction and they generated the drag forces

that let the turbine start turning. As the rotational speed increases, the blades are

pitched so that the wind flows across the airfoils generating the lift forces and

accelerating the turbine.

The blade pitching mechanism is complex and usually heavy, and the

Cycloturbines need some wind direction sensors to pitch the blades properly.30

REFERENCES

http://www.energybeta.com

http://www.energybeta.com/windpower/windmill/wind-power-from-the-darrieus-

wind-turbine/

http://www.windturbine-analysis.netfirms.com/

http://www.awea.org

http://www.awea.org/faq/vawt.html

http://telosnet.com/wind/govprog.html

http://en.wikipedia.org/

http://www.reuk.co.uk/Giromill-Darrieus-Wind-Turbines.htm

http://dspace1.isd.glam.ac.uk

http://www.reuk.co.uk/OtherImages/cycloturbine-vawt.jpg

31

3- THEORY OF AERODYNAMICS

3.1 INTRODUCTION

From an aerodynamic point of view, the different VAWT, have a number of

aspects in common that distinguish them from the HAWT.

The blades of a VAWT rotate on a rotational surface whose axis is at right angle

to the wind direction. The aerodynamic angle of attack of the blades varies

constantly during the rotation. Moreover, one blade moves on the downwind side of the

other blade in the range of 180° to 360° of rotational angle so that the wind speed in this

area is already reduced due to the energy extracted by the upwind blades. Hence, power

generation is less in the downwind sector of rotation. Consideration of the flow

velocities and aerodynamic forces shows that, nevertheless, a torque is produced in

this way which is caused by the lift forces. The breaking torque of the drag forces in

much lower, by comparison.

In one revolution, a single rotor blade generates a mean positive torque but there

are also short sections with negative torque. The calculated variation of the total torque

also shows the reduction in positive torque on the downwind side.

The alternation of the torque with the revolution can be balanced with three rotor blades,

to such an extent that the alternating variation becomes an increasing and decreasing

torque which is positive throughout. However, torque can only develop in a vertical

axis rotor if there is circumferential speed: the vertical axis rotor is usually not self-

starting.

32

The qualitative discussion of the flow conditions at the vertical axis rotor shows

that the mathematical treatment must be more complex than with propeller type. This

means that the range of physical and mathematical models for calculating the generation

of power and the loading is also wider.

Various approaches, with a variety of weightings of the parameters involved have been

published in the literature. Most authors specify values of 0.40 to 0.42 for the maximum

Cp for the Darrieus type wind turbine.

In order to analyze the aerodynamics of a rotor and to get information about its power

generation, it’s necessary to start by considering that a wind turbine works

converting the kinetic energy of a wind flow in electricity, following several steps:

From the wind flow the turbine gets the energy to rotate the blades. The energy

produced by this rotations is given to the main shaft (or to a gearbox, if it is present) and

from here to the electrical generator, that provide the electricity to the grid.

3.2 POWER IN THE WIND

The power of the wind is described by:

Pkin=12∗¿V 2

33

Where:

Pkin = kinetics power [W]

= mass flow = ρ*A*v [kg/s];

ρ = density [kg/m3];

A = area [m2];

v = speed [m/s];

The frequency distribution if the wind speed differs at different sites, but it fits quite well

with the Weibull distribution. An example of how measured data fit the Weibull

distribution is shown in the picture below (source: www. re.emsd.gov.hk).

Example of Weibull distribution

The wind turbine swept area is calculated in different way, according to the geometry of

the rotor.

For a HAWT, the swept area is described by:

A=π∗r2

34

Where the parameter r is the radius in [m] of the rotor.

HAWT Swept Area

For a Giromill VAWT, also named H-rotor, the swept area is:

A=d∗h

Where:

d = diameter of the rotor [m];

h = length of the blades [m];

35

VAWT Swept Area

The formula of the power in the wind can be written also as:

Pkin=12∗ρ∗A∗v3

The density of the air varies with the height above sea level and temperature.

The maximum mechanical power that can be got from a wind turbine depends on

both the rotational speed and on the undisturbed wind speed, as shown in the picture

below.

36

Mechanical Power and Rotational Speed for different wind speeds.

3.3 POWER IN THE WIND

When a wind turbine is crossed by a flow of air, it can get the energy of the mass flow

and convert it in rotating energy. This conversion presents some limits, due to the Betz’

law. This law mathematically shows that there is a limit, during this kind of

energy conversion, that cannot be passed.

In order to explain this limit, a power coefficient Cp and it is given by:

Cp= P12∗ρ∗A∗v3

The coefficient Cp represents the amount of energy that a specific turbine can

absorb from the wind. Numerically the Betz’ limit, for a HAWT, is 16/27 equal

37

to 59,3%. It means that, when a wind turbine operates in the best condition, the wind

speed after the rotor is 1/3 of the wind speed before, as shown in the picture below.

Figure: Airflow, pressure and speed before and after the turbine

The value of the coefficient Cp is affected by the type of wind turbine and the

value of the parameter λ, which is named tip speed ratio and is described by:

38

λ=ω∗rv

Where:

ω = rotational speed of the turbine [rpm];

r = radius of the rotor [m];

v = undisturbed wind speed [m/s];

The relation between Cp and tip speed ratio is shown in the picture below (source:

Developing wind power projects”, T. Wizelius)

Figure: Cp curves for different types of turbines

39

The different types of wind turbine have various value of optimal wind speed

ratio and optimal coefficient of power.

Savonius rotor, not shown in the picture above, usually presents an optimal λ

value around 1, as shown in the picture (source: Claesson, 1989)

Figure: Cp curve, Savonius rotor

3.4 WIND GRADIENT

To calculate the wind speed at the height of the hub, it is necessary to take care that the

wind speed varies with height due to the friction against the structure of the ground,

which slows the wind. This phenomenon is named wind gradient or wind profile and it is

shown in Figure.

40

Figure: Wind speed profile for various locations

If a “z” height is considered, the average of the wind speed at this height is described by:

vz=vz 0∗( zz0

)α

Where:

vz0 = wind speed at the reference height z0 [m/s];

z0 = reference height [m];

α = value depending on the roughness class of the terrain, as shown in the following

table;

41

Table: Roughness Classes

3.5 LIFT AND DRAG FORCE

When the air flow acts on the blade, it generates two kinds of forces, named lift and drag,

which are responsible for the rotating of the blades.

An analysis of these forces, acting on a 3 blades HAWT, shown in the following

picture, can be done:

Figure: Torque Generation in Wind Turbine

42

Figure: Aerodynamic Forces on the blade

Where:

U = undisturbed wind speed;

Wx = component of wind speed that interacts with the blade;

Vx = rotational speed of the rotor;

α = angle of attack;

The undisturbed wind speed hits the blades with a certain angle chord line of the blade.

The relationship between the rotational speed of the turbine and the undisturbed

wind speed is related to the angle φ:

λ=tan−1(ϕ )=V x

U=ω∗R

U

In a HAWT with variable speed this angle is used to control the rotational speed,

with the stall control or pitch control: a variation of this angle is used to increase

43

the turbine rotational speed when the wind speed is under the rated one and to stop the

increasing of the rotational speed when the wind speed gets a value higher than the rated

one.

Looking at the previous figure, the lift and the drag force can be described by:

FL ~ CL (α) * Wx2

FD ~ CD (α) * Wx2

CL and CD are the lift coefficient and the drag coefficient and they depend on the value of

angle α. The lift coefficient is higher than the drag one and it increases with the

increasing of α until the value of 15°, where it shows a value of about 1,2. After this

value it decreased strongly due to the stall effect. Instead the value of CD increases with

the increasing of the angle of attack, passing the value of 0.3 just for α > 20°.

Figure: Lift Co-efficient

44

In a VAWT the angle of attack changes during the rotation and the direction from which

the wind invests the rotor is not so important like in the HAWT, where a yaw system is

necessary to rotate the wind turbine in front of the direction of the wind speed.

The resultant force Fris of the vector sum of FL and FD can be divided in two components:

Fc: on the direction of the rotation of the wind turbine; it’s the force that makes the

turbine rotate;

Fs: releases its energy on the structure of the tower, flexing it.

3.6 CONTROL OF THE BLADE

Usually a wind turbine operates in a range of wind speed form 4 m/s to 25 m/s.

In this range the generated power increases to the rated power, usually located between

11 m/s and 15 m/s.

After the value of rated power, a control system is necessary to avoid that too

much high wind speed causes a too high rotational speed that can create strong stress on

the tower and damage it.

By changing the angle attack and the pitch angle, the power of the turbine can be

controlled and there are passive control and active control.

The passive control, for a wind turbine with fixed rotational speed, takes

advantage from the fact that, when the wind speed increases, α increases and the

blade goes towards the stall situation, decreasing the value of the lift force and of the

coefficient of power Cp: this is a cheap technique that doesn’t need any special

equipment, but creates strong stress on the tower structure.

The active control, for wind turbine with variable rotational speed, uses some electronic

equipment to rotate the blade around their own axis in order to reach the stall or to reach

the feather of the blades.

45

REFERENCES:

Theory of wind machines, Betz equation; M. Ragheb, 2010

http://re.emsd.gov.hk/wind2006/Wind_Resource_Information.html

http://discoverthewind.com/images/vertical-wind-turbines-o-04.jpg

http://en.wikipedia.org/wiki/Lift_coefficient

http://adamone.rchomepage.com/profile_raf32.gif

Developing wind power projects (Tore Wizelius)

46

4- MAGNETIC LEVITATION

Use of Neodymium Magnets in place of bearings for supporting the shaft in our VAWT

design required us to study the concept of Magnetic Levitation.

4.1 INTRODUCTION

Magnetic levitation or magnetic suspension is a method by which an object is suspended

with no support other than magnetic fields. Magnetic pressure is used to counteract the

effects of the gravitational and any other accelerations.

Earnshaw's theorem proves that using only ferromagnetic or paramagnetic materials it is

impossible to stably levitate against gravity, but servomechanisms, the use of

diamagnetic materials, superconduction, or systems involving eddy currents permit this to

occur.

In some cases the lifting force is provided by magnetic levitation, but there is a

mechanical support bearing little load that provides stability. This is termed pseudo-

levitation.

4.2 LIFT

Magnetic materials and systems are able to attract or press each other apart or together

with a force dependent on the magnetic field and the area of the magnets, and a magnetic

pressure can then be defined.

The magnetic pressure of a magnetic field on a superconductor can be calculated by:

Pmag=B2

2 μ0

Where:

47

Pmag = Force per unit area in Pascal.

B = Magnetic Field just above the superconductor in teslas.

µ0 = 4π x 10-7 N.A-2, it is the permeability of the vacuum.

Figure: A Magnetic Levitation Sculpture that levitates a small magnetic cube

4.3 STABILITY

Static stability means that any small displacement away from a stable equilibrium causes

a net force to push it back to the equilibrium point.

Earnshaw's theorem proved conclusively that it is not possible to levitate stably using

only static, macroscopic, paramagnetic fields. The forces acting on any paramagnetic

object in any combinations of gravitational, electrostatic, and magneto static fields will

make the object's position, at best, unstable along at least one axis, and it can be unstable

equilibrium along all axes. However, several possibilities exist to make levitation viable,

48

for example, the use of electronic stabilization or diamagnetic; it can be shown that

diamagnetic materials are stable along at least one axis, and can be stable along all axes.

Dynamic stability occurs when the levitation system is able to damp out any vibration-

like motion that may occur.

4.4 METHODS

For successful levitation and control of all 6 axes (3 spatial and 3 rotational) a

combination of permanent magnets and electromagnets or diamagnets or superconductors

as well as attractive and repulsive fields can be used. From Earnshaw's theorem at least

one stable axis must be present for the system to levitate successfully, but the other axes

can be stabilized using ferromagnetism.

4.4.1 MECHANICAL CONSTRAINT (PSEUDO-LEVITATION)

With a small amount of mechanical constraint for stability, pseudo-levitation is relatively

straightforwardly achieved.

If two magnets are mechanically constrained along a single vertical axis, for example,

and arranged to repel each other strongly, this will act to levitate one of the magnets

above the other.

Another geometry is where the magnets are attracted, but constrained from touching by a

tensile member, such as a string or cable.

49

Figure: Mechanical Constraint

4.4.2 DIAMAGNETISM

Diamagnetism is the property of an object which causes it to create a magnetic field in

opposition to an externally applied magnetic field, thus causing a repulsive effect.

Diamagnetism is a form of magnetism that is only exhibited by a substance in the

presence of an externally applied magnetic field. It is generally quite a weak effect in

most materials, although superconductors exhibit a strong effect. Diamagnetic materials

cause lines of magnetic flux to curve away from the material, and superconductors can

exclude them completely (except for a very thin layer at the surface).

50

Figure: Diamagnetically Stabilized Sphere

4.4.2 SUPERCONDUCTORS

Superconductors may be considered perfect diamagnets and have the additional property

of completely expelling magnetic fields when the superconductivity initially forms. The

levitation of the magnet is further stabilized due to flux pinning within the

superconductor; this tends to stop the superconductor leaving the magnetic field, even if

the levitated system is inverted.

These principles are exploited by EDS (Electrodynamic Suspension), superconducting

bearings, flywheels, etc.

51

Figure: A superconductor levitating a permanent magnet

4.4.3 SERVOMECHANISM

The attraction from a fixed strength magnet decreases with increased distance, and

increases at closer distances. This is unstable. For a stable system, the opposite is needed,

variations from a stable position should push it back to the target position.

Stable magnetic levitation can be achieved by measuring the position and speed of the

object being levitated, and using a feedback loop which continuously adjusts one or more

electromagnets to correct the object's motion, thus forming a servomechanism.

52

4.4.4 RELATIVE MOTION BETWEEN CONDUCTORS AND MAGNETS

If one moves a base made of a very good electrical conductor such as copper, aluminum

or silver close to a magnet, an (eddy) current will be induced in the conductor that will

oppose the changes in the field and create an opposite field that will repel the magnet

(Lenz's law). At a sufficiently high rate of movement, a suspended magnet will levitate

on the metal, or vice versa with suspended metal.

4.4.5 OSCILLATING ELECTROMAGNETIC FIELDS

A conductor can be levitated above an electromagnet (or vice versa) with an alternating

current flowing through it. This causes any regular conductor to behave like a diamagnet,

due to the eddy currents generated in the conductor. Since the eddy currents create their

own fields which oppose the magnetic field, the conductive object is repelled from the

electromagnet, and most of the field lines of the magnetic field will no longer penetrate

the conductive object.

4.5 DYNAMIC STABILITY

Magnetic fields are conservative forces and therefore in principle have no built-in

damping, and in practice many of the levitation schemes are under-damped and in some

cases negatively damped. This can permit vibration modes to exist that can cause the item

to leave the stable region.

Damping of motion is done in a number of ways:

External mechanical damping (in the support), such as dashpots, air drag etc.

eddy current damping (conductive metal influenced by field)

tuned mass dampers in the levitated object

electromagnets controlled by electronics

53

REFERENCES

http://en.wikipedia.org/wiki/Magnetic_levitation

http://blog.innomats.de/2010/06/single-plate-diamagnetic-levitation.html

Eddy current magnetic levitation, models and experiments by Marc T. Thompson

Superconducting Levitation: Applications to Bearings and Magnetic

Transportation , Francis Moon, Wiley & Sons, New York, 1994

Electromagnetic Levitation and Suspension Techniques, B.V. Jayawant, Edward

Arnold Publishers, London, 1981

54

5- RARE EARTH MAGNETSRare-earth magnets are strong permanent magnets made from alloys of rare earth

elements. Developed in the 1970s and 80s, rare-earth magnets are the strongest type of

permanent magnets made, producing significantly stronger magnetic fields than other

types such as ferrite or alnico magnets. The magnetic field typically produced by rare-

earth magnets can be in excess of 1.4 teslas, whereas ferrite or ceramic magnets typically

exhibit fields of 0.5 to 1 tesla. There are two types: neodymium magnets and samarium-

cobalt magnets. Rare earth magnets are extremely brittle and also vulnerable to corrosion,

so they are usually plated or coated to protect them from breaking and chipping.

The term "rare earth" can be misleading as these metals are not particularly rare or

precious; they are about as abundant as tin or lead.

The rare earth (lanthanide) elements are metals that are ferromagnetic, meaning that like

iron they can be magnetized, but their Curie temperatures are below room temperature, so

in pure form their magnetism only appears at low temperatures. However, they form

compounds with the transition metals such as iron, nickel, and cobalt, and some of these

have Curie temperatures well above room temperature. Rare earth magnets are made

from these compounds.

The advantage of the rare earth compounds over other magnets is that their crystalline

structures have very high magnetic anisotropy. This means that a crystal of the material is

easy to magnetize in one particular direction, but resists being magnetized in any other

direction.

Atoms of rare earth elements can retain high magnetic moments in the solid state. This is

a consequence of incomplete filling of the f-shell, which can contain up to 7 unpaired

electrons with aligned spins. Electrons in such orbitals are strongly localized and

therefore easily retain their magnetic moments and function as paramagnetic centers.

55

5.1 TYPES

5.1.1 SAMARIUM-COBALT

Samarium-cobalt magnets (chemical formula: SmCo5), the first family of rare earth

magnets invented, are less used than neodymium magnets because of their higher cost

and weaker magnetic field strength. However, samarium-cobalt has a higher Curie

temperature, creating a niche for these magnets in applications where high field strength

is needed at high operating temperatures.

Figure: Samarium-Cobalt Magnets

5.1.2 NEODYMIUM

These magnets are made of an alloy of neodymium, iron and boron: (Nd2Fe14B)

Neodymium magnets are used in numerous applications requiring strong, compact

56

permanent magnets, such as electric motors for cordless tools, hard drives, and magnetic

hold-downs and jewelry clasps. They have the highest magnetic field strength and have a

higher coercivity (which makes them magnetically stable), but have lower Curie

temperature.

Figure: Nickel-plated neodymium magnet cubes

5.2 NEODYMIUM MAGNETS

The tetragonal Nd2Fe14B crystal structure has exceptionally high uniaxial magneto

crystalline anisotropy (HA~7 teslas). This gives the compound the potential to have high

coercivity (i.e., resistance to being demagnetized). The compound also has a high

saturation magnetization (Js ~1.6 T or 16 kG) and typically 1.3 tesla. Therefore, as the

maximum energy density is proportional to Js2, this magnetic phase has the potential for

storing large amounts of magnetic energy (BHmax ~ 512 kJ/m3 or 64 MG·Oe),

considerably more than samarium cobalt (SmCo) magnets, which were the first type of

57

rare earth magnet to be commercialized. In practice, the magnetic properties of

neodymium magnets depend on the alloy composition, microstructure, and

manufacturing technique employed.

5.2.1 MAGNETIC PROPERTIES

Some important properties used to compare permanent magnets are: remanence (M r),

which measures the strength of the magnetic field; coercivity (Hci), the material's

resistance to becoming demagnetized; energy product (BHmax), the density of magnetic

energy; and Curie temperature (TC), the temperature at which the material loses its

magnetism. Neodymium magnets have higher remanence, much higher coercivity and

energy product, but often lower Curie temperature than other types. Neodymium is

alloyed with terbium and dysprosium in order to preserve its magnetic properties at high

temperatures. The table below compares the magnetic performance of neodymium

magnets with other types of permanent magnets.

Magnet Mr (T) Hci (kA/m) BHmax (kJ/m3) TC (°C)

Nd2Fe14B (sintered) 1.0–1.4 750–2000 200–440310–

400

Nd2Fe14B (bonded) 0.6–0.7 600–1200 60–100310–

400

SmCo5 (sintered) 0.8–1.1 600–2000 120–200 720

Sm(Co, Fe, Cu,

Zr)7 (sintered)

0.9–

1.15450–1300 150–240 800

58

Alnico (sintered) 0.6–1.4 275 10–88700–

860

Sr-ferrite (sintered) 0.2–0.4 100–300 10–40 450

5.2.2 PHYSICAL AND MAGNETIC PROPERTIES

Comparison of physical properties of sintered neodymium and Sm-Co magnets

Property Neodymium Sm-Co

Remanence (T) 1–1.3 0.82–1.16

Coercivity (MA/m) 0.875–1.99 0.493–1.59

Relative permeability 1.05 1.05

Temperature coefficient of remanence (%/K) −0.12 −0.03

Temperature coefficient of coercivity (%/K) −0.55..–0.65 −0.15..–0.30

Curie temperature (°C) 320 800

Density (g/cm3) 7.3–7.5 8.2–8.4

59

CTE, magnetizing direction (1/K) 5.2×10−6 5.2×10−6

CTE, normal to magnetizing direction (1/K) −0.8×10−6 11×10−6

Flexural strength (N/mm2) 250 150

Compressive strength (N/mm2) 1100 800

Tensile strength (N/mm2) 75 35

Vickers hardness (HV) 550–650 500–550

Electrical resistivity (Ω·cm) (110–170)×10−6 86×10−6

60

REFERENCES

http://en.wikipedia.org/wiki/Rare-earth_magnet

McCaig, Malcolm (1977). Permanent Magnets in Theory and Practice.

http://en.wikipedia.org/wiki/Neodymium_magnet

http://en.wikipedia.org/wiki/Samarium-cobalt_magnet

61

6- WIND ENERGY STATISTICSWind energy has continued the worldwide success story as the most dynamically

growing energy source again in the year 2008. Since 2005, global wind installations

more than doubled. They reached 121188 MW, after 59024 MW in 2005, 74151 MW in

2006 and 93927 MW in 2007. The market for new wind turbines showed a 42 %

increase and reached an overall size of 27261 MW, after 19776 MW in 2007 and

15127 MW in the year 2006. Ten years ago, the market for new wind turbines had a

size of 2187 MW, less than one tenth of the size in 2008. In comparison, no new

Nuclear reactor started operation in 2008, according to the International Atomic Energy

Agency.

Source: WWEA, “World Wind Energy Report 2008”

Pakistan has the indigenous wind energy potential of more than 50,000 MW, which in

itself is colossal. If harnessed adequately wind energy alone would eradicate energy

62

shortages in the country. Pakistan is currently looking to build wind farms in the Gharo -

Keti Bandar Wind Corridor in Sindh, some of which are regions where electricity supply

through the national grid has been a challenge.

6.1 PAKISTAN’S WIND ENERGY RESOURCES

26,400 sq. km, about 3% of Pakistan’s total land area (800,000 sq km) is in good-to-

excellent condition for wind energy.

MAJOR AREAS:

– Southeastern Pakistan especially

• Hyderabad to Gharo region in southern Indus Valley

• Coastal areas south of Karachi

63

• Hills and ridges between Karachi and Hyderabad

–Northern Indus Valley especially

• Hills and ridges in northern Punjab

• Ridges and wind corridors near Mardan and Islamabad

– Southwestern Pakistan especially

• Near Nokkundi and hills and ridges in the Chagai area

• Makran area hills and ridges

– Central Pakistan especially

• Wind corridors and ridges near Quetta

• Hills near Gendari

64

6.2 WHY WIND ENERGY?

Wind turbines of all sizes have become a familiar sight around the world for a wide

variety of reasons, including their economic, environmental, and social benefits. The

potential for wind energy is immense, and experts suggest wind power can supply up to

20% of U.S. and world electricity. The advantages and disadvantages of wind energy are

detailed here to help you decide what the future of wind should be in the Pakistan.

6.2.1 ECONOMIC ADVANTAGES:

REVITALIZES RURAL ECONOMIES:

Wind energy can diversify the economies of rural communities, adding to the tax

base and providing new types of income. Wind turbines can add a new source of property

taxes in rural areas that otherwise have a hard time attracting new industry.

FEWER SUBSIDIES:

All energy systems are subsidized, and wind is no exception. However, wind

receives considerably less than other forms of energy.

FREE FUEL:

Unlike other forms of electrical generation where fuel is shipped to a processing

plant, wind energy generates electricity at the source of fuel. Wind is a native fuel

that does not need to be mined or transported, taking two expensive aspects out of

long-term energy costs.

PRICE STABILITY:

The price of electricity from fossil fuels and nuclear power can fluctuate greatly

due to highly variable mining and transportation costs. Wind can help buffer these

costs because the price of fuel is fixed and free.

65

CREATES JOBS:

Wind energy projects create new short and long term jobs. Related employment

ranges from meteorologists and surveyors to structural engineers, assembly

workers, lawyers, bankers, and technicians. Wind energy creates 30% more jobs

than a coal plant and 66% more than a nuclear power plant per unit of energy

generated.

6.2.2 ENVIRONMENTAL ADVANTAGES:

CLEAN WATER:

Turbines produce no particulate emissions that contribute to mercury

contamination in our lakes and streams. Wind energy also conserves water

resources.

CLEAN AIR:

Other sources of electricity produce harmful particulate emissions which

contribute to global climate change and acid rain. Wind energy is pollution free.

MINING AND TRANSPORTATION:

Harvesting the wind preserves our resources because there is no need for

destructive resource mining or fuel transportation to a processing facility.

LAND PRESERVATION:

Wind farms are spaced over a large geographic area, but they are actual “foot

print” covers only a small portion of land is resulting in a minimum impact on

crop production or livestock grazing. Large buildings cannot be built near the

turbine, thus wind farms preserve open space.

66

7- DESIGNThe theoretical maximum power efficiency of any design of wind turbine is 0.59 (i.e. no

more than 59% of the energy carried by the wind can be extracted by a wind turbine).

Once you also factor in the engineering requirements of a wind turbine - strength and

durability in particular - the real world limit is well below the Betz Limit with values of

0.35-0.45 common even in the best designed wind turbines. By the time you take into

account other ineffiencies in a complete wind turbine system - e.g. the generator,

bearings, and power transmission and so on - only 10-30% of the power of the wind is

ever actually converted into usable electricity.

The efficiency factor CP typically reaches a maximum at a wind speed of 7-9 m/sec and,

normally, it does not exceed 50%.

Usually the Value of efficiency factor ranges between 20% - 40%.

SETTING THE PARAMETERS:

Power to be produced: P = 60 Watts

Wind Speed = v = 7 m/s

Co-efficient of Performance: Cp = 0.4

Air Density: 1.23 kg/m3

The swept area can be calculated as:

60 = 1/2 x 1.23 x 73 x A x 0.4

60 = 84.378 A

A = 0.711 m2

For VAWT,

A = Diameter x Length

67

Let,

Length = 2 x D.

0.711 = 2 x D2

D = 0.596 m

Take,

Diameter of Rotor = D = 50 cm

Length of Blades = L = 75 cm.

CURVATURE OF THE BLADE:

68

The curve of the blade can be chosen from a circle whose center lies at the intersection of

two perpendiculars, one to the direction of relative velocity V r at A, and the other to the

tangent to the inner periphery intersecting at B.

From triangles AOC and BOC

69

CENTRAL ANGLE:

BLADE SPACING:

70

71