Wind is the flow of gases on large scale. On the surface of the earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases and charged particles from the sun though space, while planetary wind is the outgassing of light chemical from a planet’s atmosphere into space. Wind by their spatial scale, their speed, the type of force that cause them, the region in which they occur and their effect. The strongest observed winds on planet in solar system occur on Neptune and Saturn. Winds have various aspects, an important one being its velocity, density of the gas involved and energy content of the wind. Wind is almost entirely caused by the effects of the sun which, each hour, delivers 175 million watts of energy to the earth. This energy heats the planet’s surface, most intensively at the equator, which causes air to rise. This rising air creates an area of low pressure at the surface into which cooler air is sucked, and it is this flow of air that we know as “wind”. In reality atmospheric circulation is much more complicated and, after rising at the equator air travels pole wards. As it travels the air cools and eventually descends to the earth’s surface at about 30° latitude (north and south), from where it returns once again to the equator (a closed loop known as a Hadley Cell). Similar cells exist between 30° and 60° latitude (the Ferrell Cells) and between 60° latitude and each of the poles (the Polar Cells). Within these cells, the flow of air is further impacted by the rotation of the earth or the "Coriolis Effect". This effect creates a sideways force which causes air to circulate anticlockwise around areas of low pressure in the northern hemisphere and clockwise in the southern hemisphere In summary, the origin of winds may be traced basically to uneven heating of the earth’s surface due to sun. This may lead to circulation of widespread winds on a global basis, producing planetary winds or may have a limited influence in a smaller area to cause local winds.

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SOKOINE UNVERSITY OF AGRICULTURE
FACULTY OF AGRICULTURE
DEPARTMENT OF AGRICULTURAL ENGINEERING AND LAND PLANNING
BSc. IRRIGATION AND WATER RESOURCES ENGINEERING.
COURSE NAME: SOURCES OF FARM POWER
COURSE CODE: AE 215
TYPE OF ASSIGNMENT: GROUP WORK (GROUP NO 4.)
STUDENT NAME REGISTRATION
NUMBER
SIGNATURE
BIRUSYA, LILIAN MEDARD IWR/D/2016/0063
MBELWA JUSTA IWR/D/2016/0033
MUSHI, NOEL R. IWR/D/2016/0038
ZEITA, ROBERT JOHN IWR/D/2016/0060
MONYO, ISMAIL BAKARI IWR/E/2016/0084
YASSON, ANDREA BEZAEL IWR/D/2016/0059
LUHENDE,NTUGWA SAILENSA IWR/D/2016/0026
JORAM GEORGE IWR/D/2016/0066
MBAGO, MARTIN HABAKUKI IWR/D/2016/0032
PELLO RICKOYAN IWR/D/2016/0081
NDYAMKAMA, FIDELIS F IWR/D/2016/0044
FILBERT FRANK IWR/D/2016/0028
LWESHA, GABRIEL E. IWR/D/2016/0027
DAUDI SAID JAFARY IWR/D/2016/0010
KAIZA GEOFREY IWR/D/2016/0016
AMANZI ABUBAKARI IWR/D/2016/0003
KWEKA, DANIEL E. IWR/D/2016/0023
HENRY, PAULO B IWR/D/2016/0012
SAID, MOHAMED BAKARI IWR/D/2016/0052
MAYO AHMED IWR/D/2016/0070
DUE DATE: 15 MAY, 2018.
INSTRUCTOR NAME: HIERONIMO (Dr. PROCHES)

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WIND POWER
1. NATURE AND ORIGIN OF THE WIND
Introduction
Wind is the flow of gases on large scale. On the surface of the earth, wind
consists of the bulk movement of air. In outer space, solar wind is the
movement of gases and charged particles from the sun though space, while
planetary wind is the outgassing of light chemical from a planet’s atmosphere
into space. Wind by their spatial scale, their speed, the type of force that cause
them, the region in which they occur and their effect. The strongest observed
winds on planet in solar system occur on Neptune and Saturn. Winds have
various aspects, an important one being its velocity, density of the gas
involved and energy content of the wind.
Wind is almost entirely caused by the effects of the sun which, each hour,
delivers 175 million watts of energy to the earth. This energy heats the
planet’s surface, most intensively at the equator, which causes air to rise. This
rising air creates an area of low pressure at the surface into which cooler air is
sucked, and it is this flow of air that we know as “wind”. In reality atmospheric
circulation is much more complicated and, after rising at the equator air
travels pole wards. As it travels the air cools and eventually descends to the
earth’s surface at about 30° latitude (north and south), from where it returns
once again to the equator (a closed loop known as a Hadley Cell). Similar cells
exist between 30° and 60° latitude (the Ferrell Cells) and between 60° latitude
and each of the poles (the Polar Cells). Within these cells, the flow of air is
further impacted by the rotation of the earth or the "Coriolis Effect". This
effect creates a sideways force which causes air to circulate anticlockwise
around areas of low pressure in the northern hemisphere and clockwise in the
southern hemisphere
In summary, the origin of winds may be traced basically to uneven heating of
the earth’s surface due to sun. This may lead to circulation of widespread
winds on a global basis, producing planetary winds or may have a limited
influence in a smaller area to cause local winds.

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Fig. 1. World Wind Pattern

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2. POWER CONTENT OF WIND.
The terms "wind energy" or "wind power" describe the process which the
wind is used to generate mechanical power or electricity. Wind power, as an
alternative to burning fossil fuels, is plentiful, renewable, widely distributed,
clean, produces no greenhouse gas emissions during operation, consumes no
water, and uses little land. The net effects on the environment are far less
problematic than those of nonrenewable power sources. Wind power has
been used as long as humans have put sails into the wind. For many years
wind-powered machines have ground grain and pumped water.
The kinetic energy in wind is utilized in form of electricity and mechanical
energy. This is done by using a large wind turbine usually consisting of
propellers; the turbine can be connected to a generator to generate electricity,
or the wind energy is transmitted through gears and shafts to mechanical
perform tasks such as pumping water or grinding grain. As the wind passes
the turbines it moves the blades, which spins the shaft. There are currently
two different kinds of wind turbines in use, the Horizontal Axis Wind Turbines
(HAWT) or the Vertical Axis Wind Turbines (VAWT). HAWT are the most
common wind turbines, displaying the propeller or ‘fan-style’ blades and
VAWT are usually in an ‘egg-beater’ style.
2.1. Kinetic Energy of The Undisturbed Wind Stream
Conservation Of Energy
The fundamental concept of wind kinetic energy is firstly to be considered.
The kinetic energy of an air flow of mass through a unit area is
perpendicular to the wind direction assuming a constant flow velocity
v(m/s) is
K.E=
Where v is the wind speed in (m/s)
m is the wind mass in kg

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The kinetic energy per unit volume V or energy density is thus
K.E =
=
Where V is the considered air volume in m3
The specific wind energy or kinetic energy per unit mass is given as
KE'=KE/m= [joules/kg]
The specific wind energy is proportional to the square of wind speed
Large wind farms consist of hundreds of individual wind turbines which are
connected to the electric power transmission network. Offshore wind is
steadier and stronger than on land, and offshore farms have less visual impact,
but construction and maintenance costs are considerably higher. The Haliade-
X 12 MW, is the most powerful offshore wind turbine in the world to date,
featuring a 12 MW capacity (the world’s first), 220-meter rotor, a 107-meter
blade designed by LM Wind Power, and digital capabilities. In addition, the
Haliade-X will also be the most efficient of wind turbines in the ocean. Best of
all, it’s capable of transforming more wind into power than any other offshore
wind turbine today.
Haliade-X Specifications
Rated Power 12 MW
Rotor Diameter 220m
Blade Length 107m
Rotor Swept Area 38,000m²
Total Height 260m
Capacity Factor 63%
Net AEP 67 GWh

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Fig. 2. Haliade Offshore Wind Farm
The main advantages of offshore wind farms are
a) Windmills can be built a lot bigger and taller allowing for more energy
collection from larger windmills.
b) Typically out at sea, there is a much higher wind speed/force allowing
for more energy to be created at a time.
c) There are no physical restrictions such as hills or buildings that could
block the wind flow.

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The disadvantages of offshore wind farms are:
a) The biggest disadvantage of an offshore wind farm is the cost. Offshore
wind farms are 90% more expensive than fossil fuel generators, and
50% more than nuclear. This is down to the fact that to build an
offshore farm, a whole platform has to be built to support the farm, but
also the cables required have to travel a long distance to get to an
onshore battery.
b) The long cables result in voltage drop off meaning that a loss of power
occurs the further the cable runs.
Small onshore (turbines located on land) wind farms provide electricity to
isolated locations. Utility companies increasingly buy surplus electricity
produced by small domestic wind turbine.
The advantages of onshore wind farms are:
a) The cost of onshore wind farms is relatively cheap, allowing for mass
farms of wind turbines.
b) The shorter distance between the windmill and the consumer allows for
less voltage drop off on the cabling.
c) Wind turbines are very quick to install, unlike a nuclear power station,
which can take over twenty years, a windmill can be built in a matter of
months.
Despite of the good of onshore wind farm, the following are their
disadvantages:
a) One of the biggest issues of onshore wind farms is that many deem them
to be an eye sore on the landscape.
b) They don’t produce energy all year round due to often poor wind speed
or physical blockages such as buildings or hills.
c) The noise that wind turbines create can be compared to as the same as a
lawn mower often causing noise pollution for nearby communities.

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Fig.3. German onshore wind farm
A unique feature of a wind turbine is that the energy extraction process uses a
change in the wind speed and not in the temperature like in the case of a heat
engine such as a steam or a gas turbine, a change in the head of a hydraulic
system or the change in potential of an electrical system. Wind speed and
direction are important design parameters in wind power systems. They vary
both in short and long terms.
2.2. Wind Power Density, Energy Flux Conservation Of Mass
For an air stream flowing through a cross sectional area A, the mass flow rate
is given
Mass flow rate=Density x Area x velocity
=ρ A v…… (1)
Since Power is kinetic energy per unit time

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P=
P=
Where by P=Power
ρ=Density
A=Area
V=Velocity

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3. WIND SPEED AND HEIGHT MEASUREMENT
3.1. Wind Speed Measurement
Wind speed is caused by air moving from high pressure to low pressure,
usually due to changes in temperature as seen in an introductory part of this
assignment. Wind speed is commonly measured with an anemometer. In the
absence of an anemometer, it is possible to estimate the wind speed through
the Beaufort wind scale which is based on people's observation of specifically
defined wind effects.
Anemometer
A simple type of anemometer was invented in 1845 by Dr. John Thomas
Romney Robinson, of Armagh Observatory. It consisted of four hemispherical
cups mounted on horizontal arms, which were mounted on a vertical shaft.
The air flow past the cups in any horizontal direction turned the shaft at a rate
that was roughly proportional to the wind speed. Therefore, counting the
turns of the shaft over a set time period produced a value proportional to the
average wind speed for a wide range of speeds.
Fig.4. Anemometer

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Beaufort scale
Beaufort scale is an empirical measure for describing wind intensity based on
on the sea or land. The scale was devised in 1805 by the Irish hydrographer
Francis Beaufort (later Rear Admiral Sir Francis Beaufort), a Royal Navy
officer, while serving on HMS Woolwich (Nine ships of Royal Navy) . The scale
was made in order to get common wind standards scales.
Wind speed on the 1946 Beaufort scale is based on the empirical relationship
V= 0.836 m/s where v is the equivalent wind speed at 10 meters above
the sea surface and B is Beaufort scale numbers correspond to 0.5, 1.5, 2.5, etc.
Beaufort Wind Scale
Developed in 1805 by Sir Francis Beaufort, U.K. Royal Navy
Force
Wind
(Knots)
WMO
Classification
Appearance of Wind Effects
On the Water On Land
0
Less
than 1
Calm
Sea surface smooth and
mirror-like
Calm, smoke rises
vertically
1 1-3 Light Air
Scaly ripples, no foam
crests
Smoke drift indicates
wind direction, still
wind vanes
2 4-6 Light Breeze
Small wavelets, crests
glassy, no breaking
Wind felt on face,
leaves rustle, vanes
begin to move
3 7-10 Gentle Breeze
Large wavelets, crests
begin to break,
scattered whitecaps
Leaves and small
twigs constantly
moving, light flags
extended
4 11-16
Moderate
Breeze
Small waves 1-4 ft.
becoming longer,
numerous whitecaps
Dust, leaves, and
loose paper lifted,
small tree branches
move

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5 17-21 Fresh Breeze
Moderate waves 4-8 ft
taking longer form,
many whitecaps, some
spray
Small trees in leaf
begin to sway
6 22-27 Strong Breeze
Larger waves 8-13 ft,
whitecaps common,
more spray
Larger tree branches
moving, whistling in
wires
7 28-33 Near Gale
Sea heaps up, waves
13-19 ft, white foam
streaks off breakers
Whole trees moving,
resistance felt
walking against
wind
8 34-40 Gale
Moderately high (18-25
ft) waves of greater
length, edges of crests
begin to break into
spindrift, foam blown in
streaks
Twigs breaking off
trees, generally
impedes progress
9 41-47 Strong Gale
High waves (23-32 ft),
sea begins to roll, dense
streaks of foam, spray
may reduce visibility
Slight structural
damage occurs, slate
blows off roofs
10 48-55 Storm
Very high waves (29-41
ft) with overhanging
crests, sea white with
densely blown foam,
heavy rolling, lowered
visibility
Seldom experienced
on land, trees broken
or uprooted,
"considerable
structural damage"
11 56-63 Violent Storm
Exceptionally high (37-
52 ft) waves, foam
patches cover sea,
visibility more reduced
12 64+ Hurricane
Air filled with foam,
waves over 45 ft, sea
completely white with
driving spray, visibility
greatly reduced

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3.2. Wind Height Measurement
Wind gradient, more specifically wind speed gradient or wind velocity
gradient, or alternatively shear wind, is the vertical gradient of the mean
horizontal wind speed in the lower atmosphere. It is the rate of increase of
wind strength with unit increase in height above ground level. In metric units,
it is often measured in units of meters per second of speed, per kilometer of
height (m/s/km), which reduces to the standard unit of shear rate, inverse
seconds (s−1).
In general, the wind speed increases with height from the surface to the upper
troposphere. There are several reasons that explain this tendency. First,
especially in the middle latitudes, the pressure gradient increases with height.
The height of the troposphere is taller in warmer air since warmer air is less
dense and thus occupies a greater volume. Going up in altitude, the pressure
gradient between the warm air and the cold air increases with height.
A second reason for the wind speed increasing with height, especially near the
ground, is due to surface friction. Surface objects such as trees, rocks, houses,
etc. slow the air as it collides into them. The influence of this friction is less
with height above the ground, thus the wind speed increases with height.
A third reason is due to air density. The density of the air is highest at the
surface and decreases with height. A force imparted on air will cause the air to
move more easily when the mass of the air is less. Dense air requires a greater
force to move it the same speed as less dense air. With air density decreasing
with height, it is easier to move the less dense air at a higher wind speed.
In wind energy studies, two mathematical models or 'laws' have generally
been used to model the vertical profile of wind speed over regions of
homogenous, flat terrain. The first approach, the log law, has its origins in
boundary layer flow in fluid mechanics and in atmospheric research. It is
based on a combination of theoretical and empirical research. The second
approach is the power law. Both approaches are subject to uncertainty caused
by the variable, complex nature of turbulent flows. (Manwell, J. F., Wind
Energy Explained, Wiley, 2003)

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Power Law
This calculator extrapolates the wind speed to a certain height by using the
power law.
Where by:
V1 = Velocity at height Z1
V2 = Velocity at height Z2
Z1 = Height 1 (lower height)
Z2 = Height 2 (upper height)
α = wind shear exponent it changes with different roughness, often assumed 0.14
over flat open terrain but can increase to 0.25 for area with forest or taller
building.
Log law
This is an approximation of wind speed at a certain height by using the log
law. The increase of wind speed with height in the lowest 100m can be
described by this logarithmic expression:
where:
V = velocity to be calculated at height z
Z = height above ground level for velocity v
Vref = known velocity at height Zref
Zref = reference height where vref is known
Z0 = roughness length in the current wind direction

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Fig.5 Graph of vertical profile (Height, m) with respect to wind speed (m/s)
A reliable prediction of the annual energy yield of wind farms is only possible
if it is based on accurate on-site wind speed measurements. Wind energy
applications require a higher standard of wind speed measurements than is
necessary for meteorological purposes. Particularly critical aspects are the
selection of the measuring site, the selection and calibration of anemometers,
and the installation of the sensors on met masts. The costs involved in high-
quality wind speed measurements are small in comparison to the reduction of
the financial risk of wind farm projects.
Therefore, responsible wind farm planning should be based on wind speed
measurements carried out by independent and recognized experts.
Apart from wind measurements there are other special wind measurements
such as site calibration, wind measurements for wind farm monitoring and
designing of special measuring set-ups, for example for determining the
turbulence characteristics by means of ultrasonic anemometers or wind
profile evaluations.

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4. COMPONENTS OF WIND POWER SYSTEM
Wind power is the use of air flow through wind turbines to mechanically
power generators for electricity. Wind power, as an alternative to burning
fossil fuels, is plentiful, renewable, widely distributed, clean, produces no
greenhouse gas emissions during operation, consumes no water, and uses
little land. Wind is caused by uneven heating of the earth from the sun making
wind a renewable and free source of energy. Wind turbines are an alternate
source of energy that harnesses this renewable wind power to make
electricity. Since wind turbines run solely on wind, they cause no pollution
making them environmentally friendly. Basically, wind turns blades that are
connected to a generator; the generator then makes electricity (more on this
later).
The wind power system made up by the following components which enable
the system in the process of collecting the energy through wind and
converting it for various appliance uses.
i) Batteries (For Off-Grid And Backup System): Provide energy storage
for periods of calm or during utility grid outages.
ii) A Charge Controller and/or Voltage Clamp: Take raw material energy
from a wind generator and condition it so it can charge batteries
safely and effectively.
iii) Disconnects And Over current Protection: Provide safety from
overloaded circuits and allow you to isolate different parts of the
system.
iv) A Dump Load: This is the place to divert excess energy in of-grid
system or when the utility grid is down, it’s windy and your batteries
are full.
v) An Inverter: This converts direct (DC) electricity to conventional
household alternating current (AC) electricity.

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vi) Metering: This gives you data display and logging so you can tell what
your system is doing and weather it’s performing well.
vii) A Tower: Support a wind generator getting it up into the smooth,
strong wind that is needed to generate meaningful amounts of
electricity. The following components makes up a tower
a) A rotor, consisting of blades with aerodynamic surfaces. When the
wind blows over the blades, the rotor turns, causing the generator
or alternator in the turbine to rotate and produce electricity.
b) A gearbox, which matches the rotor speed to that of the
generator/alternator. The smallest turbines (under 10 kW)
usually do not require a gearbox.
c) An enclosure, or nacelle, which protects the gearbox, generator
and other components of the turbine from the elements.
d) A tailvane or yaw system, which aligns the turbine with the wind.
viii) Transmission Wiring And Conduct: Allow you to transfer energy from
where it is made to where it is stored and used.
ix) Wind Generators: Collect the energy in the wind and use it to make
electricity. The whole system of wind power system is shown below;

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Fig. 6. Components of Wind power system
Fig.7. Components of a wind energy system. (Source: Natural Resources
Canada).

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5. WIND MACHINE (WIND TURBINES/ WINDMILL
CLASSIFICATION)
A. According to Design There are two kinds of wind turbines,
i) The Vertical axis wind turbine design, the vertical axis type is
designed like an egg-beater. Vertical Axis Wind Turbines are
designed to be economical and practical, as well as quiet and
efficient. There are two different styles of vertical wind turbines
out there. One is the Savonius rotor, and the second is the
Darrieus model ( Darrieus , a French man, invented it).
Advantages of Vertical Axis Wind Turbines:
 They can operate even in area with wind obstruction such as hills as
they function better.
 Since VAWT are mounted closer to the ground they make maintenance
easier, reduce the construction costs, are more bird friendly and does
not destroy the wildlife.
 No need any mechanisms in order to operate the wind turbine
 Lower wind startup speed
 The main advantage of VAWT is it does not need to be pointed towards
the wind to be effective. In other words, they can be used on the sites
with high variable wind direction.
 You can use the wind turbine where tall structures are not allowed.
 VAWT’s are quiet, efficient, economical and perfect for residential
energy production, especially in urban environments.
 They are cost effective when compare to the HAWTs. It is still best to
shop around and check prices before making a purchase, however.
Disadvantages of Vertical Axis Wind Turbines: There are also
disadvantages that come with the use of this type of wind turbine. While the
many advantages are certainly great, it is imperative that we must be aware of
its disadvantages.
 Decreased level of efficiency when compared to the HAWT. The reason
for the reduced amount of efficiency is usually due to the drag that
occurs within the blades as they rotate.
 You are unable to take advantage of the wind speeds that occur at
higher levels.

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 VAWT’s are very difficult to erect on towers, which means they are
installed on base, such as ground or building.
Fig.8. Savonious Vertical Axis Wind Turbine

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Fig.9. Darrieus Vertical Axis Wind Turbine
ii) The Horizontal axis wind turbine design. A horizontal-axis wind
turbine (HAWT) is a wind turbine in which the axis of the rotor's
rotation is parallel to the wind stream and the ground. All grid-
connected commercial wind turbines today are built with a
propeller-type rotor on a horizontal axis (i.e. a horizontal main
shaft). The horizontal wind turbine, has two to three blades. This
type functions best when it is directly facing the wind. Farmers
with great land area found out another source of income. When
wind turbines became the newest source of electricity, these
farmers leased their lands to power developers. Wind farms
mushroomed all throughout the Midwest. HAWTs can be
subdivided into upwind wind turbines (The rotor faces the wind)
and downwind wind turbines (rotor is downwind which is the lee
side) of the tower.

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Advantages of Horizontal Axis Wind Turbines
 Variable blade pitch, which gives the turbine blades the optimum angle
of attack. Allowing the angle of attack to be remotely adjusted gives
greater control, so the turbine collects the maximum amount of wind
energy for the time of day and season.
 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%.
 High efficiency, since the blades always move perpendicularly to the
wind, receiving power through the whole rotation. In contrast, all
vertical axis wind turbines, and most proposed airborne wind turbine
designs, involve various types of reciprocating actions, requiring airfoil
surfaces to backtrack against the wind for part of the cycle.
Backtracking against the wind leads to inherently lower efficiency.
Disadvantages of Horizontal Axis Wind Turbines
 Taller masts and blades are more difficult to transport and install.
Transportation and installation can now cost 20% of equipment costs.
 Stronger tower construction is required to support the heavy blades,
gearbox, and generator.
 Reflections from tall HAWTs may affect side lobes of radar installations
creating signal clutter, although filtering can suppress it.
 Mast height can make them obtrusively visible across large areas,
disrupting the appearance of the landscape and sometimes creating
local opposition.
 Downwind variants suffer from fatigue and structural failure caused by
turbulence when a blade passes through the tower’s wind shadow (for
this reason, the majority of HAWTs use an upwind design, with the rotor
facing the wind in front of the tower).
 They require an additional yaw control mechanism to turn the blades
toward the wind.

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Fig.10 Horizontal Axis Wind Turbine
B. According to Size Wind turbines vary not only with their designs but also
with their sizes.
 Smaller turbines
They are usually lower than 100 kilowatts and they are most often
found in homes. They are associated with simple diesel generators and
water pumping needs.
 Utility-scale wind turbines.
They start at 100 kilowatts and reach up to even a few megawatts.
There are also the really large turbines seen in wind farms. These
turbines serve as the primary source of electricity in the electrical grid.

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Parts of a Wind Turbine/Windmill
The nacelle contains the key components of the wind turbine, including the
Gear box, and the electrical generator.
 The rotor blades capture wind energy and transfer its power to the rotor
hub.
 The generator converts the mechanical energy of the rotating shaft to
Electrical energy.
 The gearbox increases the rotational speed of the shaft for the
generator.
 Blades: are the main electricity-generating parts of the turbine. Once
wind passes through it, they will rotate thereby causing a series of
reaction which will eventually lead to electricity production.
 Brake: as with any other break, this is used to stop the turbines in
emergency cases. This could be a mechanical, electrical, or hydraulic
break.
 Controller: this dictates the wind speed at which turbines start and stop.
It usually starts the machine when the wind hits 8 mph and stops it
upon reaching 55 mph. It is an important part of the machine since it
automatically stops any machine activity when wind speed is more than
55 mph because blades may easily be damaged.
 Shaft: signals the generator to conduct electricity.
 Tower: is a place where turbines may be placed to get more wind.

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Fig.11. Inside the wind turbine

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6. GENERATION OF ELECTRICAL ENERGY FROM WIND TURBINES
A wind turbine is in many ways the opposite of a fan. Instead of providing the
electricity to get the fan to rotate, wind rotates the turbine to generate
electricity.
Converting Wind to Mechanical Energy.
Wind is converted by the blades of wind turbines. The blades of the wind
turbines are designed in two different ways, the drag type and lift type.
Drag type: this blade design uses the force of the wind to push the blades
around. These blades have a higher torque than lift designs but with a slower
rotating speed.
The drag type blades were the first designs used to harness wind energy for
activities such as grinding and sawing. As the rotating speed of the blades are
much slower than lift type this design is usually never used for generating
large scale energy.
Lift type: most modern HAWT use this design. Both sides of the blade has air
blown across it resulting in the air taking longer to travel across the edges. In
this way lower air pressure is created on the leading edge of the blade, and
higher air pressure created on the tail edge. Because of this pressure
difference the blade is pushed and pulled around, creating a higher rotational
speed that is needed for generating electricity.
Mechanism of Creating Electricity from Wind
The Kinetic Energy in the wind is converted into rotation motion by the
turbine blades. This low rotation speed is transmitted to a gear box by the
main shafts. The gear box increases the rotation speed to the appropriate
rotation speed required by the generator. This increased speed of rotation is
transmitted to the generator by a fast rotation shaft. The generator uses the
turning motion of the shaft to rotate a rotor which has oppositely charge
magnets and is surrounded by copper wire loops. Electromagnetic induction
is created by the rotor spinning around the inside of the core, generating
electricity. The electric energy generated is transmitted to the grid by the
cable.

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Generation of electricity from the turbine is not as simple as it has been stated.
This can be pronounced as the wind is not blowing with the same speed and
with the same direction all the time. To overcome these problems, wind
turbine is usually equipped with several additional equipments.
Changes in the wind speed are measured by anemometer found at the top of
the turbine blades which sends data to a control computer inside the nacelle.
The control computer sends the signal to the control system which changes
the angle of attack of the blades (Pitch control action). Some small wind
turbines are designed for optimum wind condition and they don’t use pitch
control system. In these cases the price outweighs the efficiency.
Also the changes in wind direction affect the performance of the wind
turbines as they should always face to the wind. A change in wind direction
causes the wind vane, at the top of the turbine, to change direction in a similar
manner for a pitch control. Changes in wind direction are handled by an
internal computer and activates control motors to turn the nacelle in the
direction of the wind.
If the wind goes above the preset condition, things get tougher for the turbine
to handle it, so it needs to stop operating. This is achieved by combination of
two actions. First action is by turning the blades around their axis with pitch
control to minimize the area of blades exposed to the wind. The decreased
area reduces the rotation speed of the blades substantially. Secondly, the
breaking system on the fast rotating shaft is activated to stop the rotation of
the blades completely.
During the generation heat is generated inside the generator and the gearbox
and this should be handled by cooling system installed inside the nacelle.
In summary, the rotor blade on a wind turbine catches the kinetic energy in the
wind and transfers it via a rotor shaft to the generator. The wing blades can be
rotated and adjusted to the wind direction and strength, for maximum
utilization of energy. When the rotor spins, the power is transferred via the drive
shaft and gearbox. Then, the generator converts the kinetic energy from the
turbine into electrical energy. The electricity is sent to the substation, where it is
converted and then transported out on the network.

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Distribution of Electricity
The electricity generated by harnessing the wind’s mechanical energy must go
through a transformer in order increase its voltage and make it successfully
transfer across long distances. Power stations and fuse boxes receive the
current and then transform it to a lower voltage that can be safely used by
business and homes.
7. PUMPING OF WATER USING WIND POWER
Introduction
Wind pump is the type of windmill which is used to pump water. Wind pumps
were used to pump water since the 9th century. Wind Water Pumping by
windmills is possibly one of man’s earliest inventions with wind energy
historically being used for a wide range of applications, ranging from grinding
grain to sawing wood, with many other applications as well. About one million
windmills are pumping water in the world today. The most common
application is to install a windmill directly over a drilled or dug well. Pumping
water from an aboveground source is also an easy task for a windmill. If you
need to pump water on your property and the site has access to reliable
winds, a water-pumping windmill may be a good option.
Sitting wind mill
To avoid turbulence caused by surrounding objects, the blades of water-
pumping windmills should be at least 9m (30 feet) above any obstructions
such as trees or buildings in a 90m (300-feet) radius. Access to “clean wind”
helps the windmill operate smoothly, ensures a more effective operation, and
extends its life. This often means installing a tall tower, so you can get well
above nearby buildings, trees, and land features. Although you can select and
site a windmill without using local wind-speed data, correctly sizing the
windmill and pump cylinder (see How Much Will it Pump?) using real data
will remove much of the guesswork about how much the ‘mill will pump. A
well-selected and well-suited windmill should start pumping water at wind
speeds between 9.5 and 13km/h. Most windmill manufacturers rate a
windmill’s pumping capacity for winds in the 16 to 32km/h range.

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Fig. 12. Wind mill pump at the site
How the Windmill pump works:
Water-pumping windmills are simple devices that use mechanical advantage
in multiple ways. It’s a direct-drive device that transfers energy via gears,
rods, simple valves, and a piston in a cylinder—and uses high torque to move
water.
The blades of the windmill wheel catch the wind which turns the wheel
(rotor). The wheel is attached to a shaft by long arms. The shaft has small
pinion gears at the other end, inside a gearbox. The pinion gears drive larger
bull gears, which move pitman arms. The pitman arms push a sliding yoke up
and down, above the bull gears (much like a crankshaft, connecting rod, and
piston in a standard vehicle engine). The moving yoke lifts and drops the
pump rod to do the work down below.
The pump rod goes down the tower through a watertight seal at the top of the
well’s drop pipe, and to the pump cylinder, the part that moves the water. The
cylinder is attached to the bottom of the drop pipe below the water level, and
has a simple piston and two check valves.
As the piston rises, water moves up the pipe above it. At the same time, water
is sucked through a screen and the lower check valve below the piston, into
the lower section of the pump cylinder. When the pump rod reverses and

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begins to descend, the lower check valve closes and the piston check valve
opens. This allows water in the cylinder to pass through, and the water that is
trapped above the piston to be pushed up out of the cylinder and ultimately to
its final delivery height. One might think of the pump as a cup with a trap door
in the bottom that opens when the cup falls and shuts when the cup rises. This
cycle is constantly repeated as the wind wheel turns to move the pump rod up
and down.
If the wind wheel is moving, the pump piston is moving. As the wind speed
increases, the speed and frequency of the piston stroke increases, so more
water is pumped. But the windmill’s efficiency drops because the airfoil is not
optimized for higher wind speeds—it doesn’t make as much use of the cubic
effect of wind power as a wind generator does. (The power available in the
wind is proportional to the cube of the wind speed.) But then, water needs do
not increase in proportion to the wind speed either, so this is not a major
impediment. In fact, water pumpers do the job they are designed for
efficiently and well.
Block Diagram Of Windmill Pump

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Fig. 12. Internal Parts Of The Wind Mill Pump

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8. REPAIR AND MAINTENANCE OF WIND POWER SYSTEM
Wind power system can be repaired or maintained. The repair and
maintenance can be done on any part of the wind system including the turbine
as whole or simple repair on small parts of the turbine such as Foundation,
Connection to the electric grid, Tower, Access ladder, Wind orientation control
(Yaw control), Nacelle, Generator, Anemometer, Electric or Mechanical Brake,
Gearbox, Rotor blade, Blade pitch control, Rotor hub
Methods of repairing will differ depending on the type of turbine itself
whether it is onshore turbine or offshore turbine.
Two types of maintenance can be done which are either Preventive
maintenance or Corrective maintenance
Preventive maintenance (PM)
 The care and servicing by personnel for the purpose of maintaining
equipment in satisfactory operating condition by providing for
systematic inspection, detection and correction of incipient failures
either before they occur or before they develop into major defects.
 The work carried out on equipment in order to avoid its breakdown or
malfunction. It is a regular and routine action taken on equipment in
order to prevent its breakdown
 Maintenance including tests, measurements, adjustments, parts
replacement, and cleaning, performed specifically to prevent faults from
occurring.
The primary goal of maintenance is to avoid or mitigate the consequences of
failure of equipment. This may be by preventing the failure before it actually
occurs which Planned Maintenance and Condition Based Maintenance help to
achieve. It is designed to preserve and restore equipment reliability by
replacing worn components before they actually fail.
Corrective maintenance is a maintenance task performed to identify, isolate,
and rectify a fault so that the failed equipment, machine, or system can be
restored to an operational condition within the tolerances or limits
established for in-service operations.

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Corrective maintenance can be subdivided into "immediate corrective
maintenance" (in which work starts immediately after a failure) and "deferred
corrective maintenance" (in which work is delayed in conformance to a given
set of maintenance rules
Predictive and preventive maintenance
 Laser alignment
 Vibration and Modal Analysis
 Thermography
 Bore Scoping
Aims For Repair And Maintenance Of Wind Power System
The repair and maintenance of wind power system is done so that to ensure
the following;
 Increase efficiency and energy delivery (kWh/kW)
 Decrease downtime (hours/year)
 Ensure safety and reduce risk
 Extend system lifetime
 Often required in financing and warranty
General Wind Power Services and Capabilities
The following are the general wind power services that should be done where
necessary so that to ensure the proper performance of the wind power
system.
 Wyes ring replacement
 Generator shaft repair
 Rotor lead change outs
 Bearing change outs and upgrades
 Slip ring change outs, upgrades & turning
 Brush holder upgrades
 Wind generator and gearbox repair
 Gearbox oil changes
 Grounding system upgrades
 Housing and component rebuilds
 General labor and maintenance

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 Scheduled and emergency repair and maintenance
Fig. 13. Wind Generator Bearing Changeout
Fig. 14. Wind Turbine Main Shaft Repair

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Pre end-of-warranty wind turbine inspections to detect and address:
 Imbalance
 Misalignment
 Mechanical looseness
 Shaft bends
 Lubrication condition
 Abnormal slip ring wear
 Bearing condition
 Generator faults
 Winding issues
 Natural frequency and resonance
Offshore Turbine Maintenance
Offshore wind power or offshore wind energy is the use of wind farms
constructed in bodies of water, usually in the ocean on the continental shelf, to
harvest wind energy to generate electricity. Higher wind speeds are available
offshore compared to on land, so offshore wind power’s electricity generation
is higher per amount of capacity installed.
Turbines are much less accessible when offshore (requiring the use of a
service vessel or helicopter for routine access, and a jackup rig for heavy
service such as gearbox replacement), and thus reliability is more important
than for an onshore turbine. Some wind farms located far from possible
onshore bases have service teams living on site in offshore accommodation
units.
A maintenance organization performs maintenance and repairs of the
components, spending almost all its resources on the turbines. The
conventional way of inspecting the blades is for workers to rappel down the
blade, taking a day per turbine. Some farms inspect the blades of three
turbines per day by photographing them from the monopile through a 600mm
lens, avoiding to go up. Others use camera drones.
Because of their remote nature, prognosis and health-monitoring systems on
offshore wind turbines will become much more necessary. They would enable
better planning just-in-time maintenance, thereby reducing the operations
and maintenance costs. According to a report from a coalition of researchers
from universities, industry, and government (supported by the Atkinson

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Center for a Sustainable Future), making field data from these turbines
available would be invaluable in validating complex analysis codes used for
turbine design. Reducing this barrier would contribute to the education of
engineers specializing in wind energy.
Fig. 15. Offshore Wind Turbine

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9. SELECTION OF WIND POWER COMPARED TO OTHER ENERGY
SOURCE
a) Wind energy does not produce any toxin, greenhouse gases, waste or by
product.
b) The fire risk at wind farm is very low. The flammable part are located
high above the ground, away from the vegetation and high voltage
connections are underground. They are equipped with comprehensive
lighting production system that transfers voltage and currents safely to
the ground.
c) Wind farm have minimal local environmental impacts. The land can still
be used for other purpose like farming and grazing, this is because
livestock appears an affected by presence of wind farm
d) Wind power is the good method of supplying electricity to remote areas
e) Wind power uses less water in cooling.
f) Wind power blows day and night; hence the wind allows the wind mill
to produce electricity throughout the day.
g) Wind power does not require any fuel.

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REFERENCES
NES Global Talent. https://www.nesgt.com/blog/2016/07/offshore-and-onshore-wind-farms
Katabatic power. https://websites.pmc.ucsc.edu/~jnoble/wind/extrap/
Royal Meteorological. https://www.rmets.org/weather-and-climate/observing/beaufort-scale
The weather Prediction. https://www.theweatherprediction.com/habyhints3/749/
David Darling. http://www.daviddarling.info/encyclopedia/H/AE_horizontal-
axis_wind_turbine.html
Azo CleanTech. https://www.azocleantech.com/article.aspx?ArticleID=191