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Wind Energy
Technology
Chapter-3
Prepared by: SSGP, Surat

INTRODUCTION
 Winds are horizontal movement of AIR from an area of HIGH
pressure(H) to an area of low pressure(L).
 Wind energy is a kinetic energy associated with movement of
large masses of air.
 It is clean, cheap, and eco-friendly renewable source.
 Wind energy is utilized as mechanical energy with the help of a
wind turbine.
 Moderate to high-speed winds, typically from 5m/s to about
25m/s are considered favorable for most wind turbines.
 The electric power generation through wind was first proposed
in Denmark in 1890

What Makes Wind ?
 Wind energy is created when
the atmosphere is heated
unevenly by the Sun, some
patches of air become
warmer than others.
 These warm patches of air
rise, other air rushes in to
replace them – thus, wind
blows.

 The wind is a by-product of solar energy.
Approximately 2% of the sun's energy
reaching the earth is converted into wind
energy.
 The surface of the earth heats and cools
unevenly, creating atmospheric pressure
zones that make air flow from high- to low
pressure areas.
 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.

Wind data
 wind speed or wind flow speed is a fundamental
atmospheric quantity caused by air moving from
high to low pressure, usually due to changes in
temperature.
 Wind speed is measured by an anemometer and
wind direction is measured by a wind vane
attached to the direction indicator.
 A cup anemometer consists of three or four cups
mounted symmetrically about a vertical axis. The
speed of rotation indicates wind speed.
 Wind speed measurement should be made at an
effective height 10m above the ground.
 Wind rose Graph : An elegant method of
describing average wind speed duration and
direction on a single graph. Length of the bars
represent the Wind rose percentage of duration.

 Wind Power Density (WPD) is a
quantitative measure of wind energy
available at any location. It is the mean
annual power available per square meter
of swept area of a turbine, and is
calculated for different heights above
ground.
 Wind shear : Rate of change of wind
speed with height.
 At the earth’s surface, wind speed is
always zero. It increases with height above
the ground. The wind near the earth’s
surface is retarded by surface roughness.

WIND TURBINE SITE SELECTION FEATURE
A suitable site should preferably have some of the following features:
1. No tall obstructions for some distance (about 3 km) in the upwind direction (i.e.
the direction of incoming wind
2. A wide and open view, i.e. open plain, open shoreline or offshore locations
3. Top of smooth well-rounded hill with gentle slopes (about 1:3 or less) on a flat
plain
4. An island in a lake or the sea
5. A narrow, mountain gap through which wind is channeled
6. The site should be reasonably close to power grid
7. The soil conditions must be such that building of foundations of the turbines
and transport of road construction material loaded on heavy trucks must be
feasible
8. If there are already wind turbines in the area, their production results are an
excellent guide to local wind conditions.

Power in Wind
 If uo is the speed of free wind in unperturbed state, the volume of air column
passing through an area A per unit time is given by AUo. If ρ is the density of air,
the air mass flow rate, through area A, is given as, ρAUo. Power (Po) available
in wind, is equal to kinetic energy rate associated with the mass of moving air,
i.e.:
 Power available in wind per unit area:
 where P is air pressure in Pa, T is air temperature in kelvin and R is the gas
constant, (= 287 J/kg K). At the standard value of air pressure, 1.0132 × 105 Pa
(i.e. 1 atmosphere), and at 15 °C, the value of air density,

Installed wind capacity by state
State
Total
Capacity
(MW) in
2015
% share
Total Capacity
(MW) in 2023
% share
Gujarat 3645.4 15.55 10,415.82 24.12
Tamil Nadu 7455.2 31.8 10,124.52 23.44
Karnataka 2636.4 11.25 5,303.05 12.28
Rajasthan 3307.2 14.11 5,193.42 12.03
Maharashtra 4450.8 18.99 5,026.33 11.64
Andhra Pradesh 1031.4 4.4 4,096.65 9.49
Madhya Pradesh 879.7 3.76 2,844.29 6.59
Telangana - - 128.10 0.3
Kerala 35.1 0.15 62.50 0.15
Others 6.3 0.03 4.30 0.01
Total 23447.5 100 43,198.98 100

Wind Turbine or Wind Mill
 A windmill is defined as a machine that converts the kinetic energy
of the wind into mechanical energy.
 A wind turbine turns wind energy into electricity using the
aerodynamic force from the rotor blades.
 Wind turbines are the modern version of a windmill. Put simply, they
use the power of the wind to create electricity.
 The difference in air pressure across the two sides of the blade
creates both lift and drag.
 The force of the lift is stronger than the drag and this causes the
rotor to spin.

Types of Wind Mills
1. According to orientation of rotor:
a) Horizontal Axis (HAWT)
b) Vertical Axis (VAWT)
2. According to useful electrical power output:
a) Small output: up to 2 kW
b) Medium output: 2 to 100 kW
c) Large Output: more than 100 kW
3. According to types of rotor:
a) Propeller Type- it is horizontal axis high speed rotor
b) Multiple Blade Type- it is horizontal axis low speed rotor
c) Savonius type- it is vertical axis rotor

4. According to wind direction on rotor:
a) Up wind rotor wind mill
b) Down wind rotor wind mill
5. According to number of blades:
a) Single blade
b) Double blade
c) Three blade
d) Multi blade

Horizontal Axis Wind Turbine (HAWT)
 HAWTs have emerged as the most successful type of turbines.
 They can be defined as the turbine in which the shaft of the
rotor is in the direction of the wind
 could be single-bladed, double-bladed, or three-bladed
 Main Components:
o Rotor
o Blades
o Hub
o Nacelle
o Low speed shaft
o Brake gear box
o High speed shaft
o Generator
o Controller
o Anemometer and wind vane
o Yaw system
o Tower
o Foundation

Rotor
 The rotor connects to the generator, either directly (if it's a direct drive turbine) or
through a shaft and a series of gears (a gearbox) that speed up the rotation and
allow for a physically smaller generator.
Blade:
 Main part, convert free flowing wind energy to useful work
 Approx. 20% of the wind turbine cost
 Uses Lift and Drag principle.
 Three blade rotor is best compared to two and single blade turbine.
 The blades rotate at 10 to 22 rpm. At 22 rpm the tip speed exceeds 90 m/s.
Higher tip speeds means more noise and blade erosion.

Single blade HAWT:
 Reduces cost and weight of the turbine.
 Rarely used due to tower shadow effects, needs counter weights on
the other side of the blade, less stability.
Two blade HAWT:
 Requires more complex design due to sustain of wind shocks.
 less stable, saves cost & weight of one rotor blade.
Three blade HAWT:
 High strength .
 Less effect due to tower shadow.
 Produces high output.

CH-3 WIND POWER Technology as a Renewable Energy

Hub
 In simple designs, blades are directly bolted to hub.
 In sophisticated designs they are bolted to the pitch mechanism,
which adjust their angle of attack according to their wind speed.
 The hub is fixed to the rotor shaft which derives the generator
through a gear box.

Nacelle
It is a cover housing that houses all of the generating components in a
wind turbine, including the generator, gearbox, drive train, and brake
assembly.
Low speed shaft
 The shaft from the hub to the gear box
 Speed is typically between 40 to 400 rpm
 Generator typically rotated at 1200 rpm to 1800 rpm
Brake Gear box
 Gear box increases the speed of the shaft
 Meet the requirement of the generator
High speed shaft
 Gear box shaft is followed by the high speed shaft
 Connects to generator

Braking mechanism
 A mechanical drum brake is used to stop turbine in emergency
situation.
 This brake is also used to hold at rest for maintenance.
Main shaft

Generator
 Converts mechanical energy to electrical energy. which is
approx. 34% of the wind turbine cost.
 generate electricity through asynchronous machines that are
directly connected with the electricity grid.
 One end attached to the wind turbine, other end connected to
the Electrical grid.
 Require cooling system to prevent overheating.
Controller
 Starts when the machine at wind speed of about 4 m/s and shuts
off the machines at about 25m/s , may damage wind turbine.
 It gets wind speed data from the anemometer and accordingly.

Yaw system
 Responsible for the orientation of the wind turbine
rotor towards the wind.
 It is the mean of rotatable connection between
nacelle and tower.
 The nacelle is mounted on a roller bearing and the
azimuth is achieved via a plurality of powerful
electrical drives.
 Yaw system consist of
 Yaw bearing
 Yaw drives
 Yaw brake
Yaw
System

Yaw bearing
 Can be of the roller or gliding type, servers as a rotatable
connection between the tower and nacelle of the wind
turbine.
Yaw drive
 Used to keep the rotor facing into the wind as the wind
direction changes.
 The yaw drives exist only on the active yaw system and are
the mean of active rotation of the wind turbine nacelle .
 Each yaw drives consists of powerful electric motor (usually
AC) with its electric drive and a large gearbox , which
increases the torque.

Tower
Typically, 2 types of towers exist
o Floating towers
o Land based tower
 Floating towers can be seen in offshore wind
farms where the towers are float on water.
 Land based towers can be seen in the onshore
wind farm where the tower are situated on the
land.
 For HAWTs, tower heights approx. 2 to 3 times
the blade length have been found to balance
material costs of the tower against better
utilization of the expensive active components.
 At the bottom level of the tower there will be
step up transformers for the connection for the
connection to the grid.

Advantages of HAWT
 The output power is high as compared to the vertical axis wind
turbine.
 The efficiency of a HAWT is high.
 It is less expensive than a VAWT (see following section).
 It is more consistent and its rotational speed is high.
 On variation in the wind shear, the tall tower captures more wind.
 Reliability is high.
 The blades of the turbine can be bent using a gearbox to get the
best wind attack angle, which results in better performance under
stormy conditions.
 The rotor can be tilted by the blades during storms.

Disadvantages of HAWT
 HAWTs are available only in large sizes and are challenging to use in
distributed generation.
 As they are of large size and heavyweight, transportation from one
place to another is difficult.
 The mounting of a heavy generator and gearbox at the top of the
tower requires a stronger structure, which increases the complexity
and cost of the structure.
 Installation and maintenance of a HAWT is a difficult process
because of the tall tower and heavy turbines.
 Noise from the HAWT is high compared to other wind turbines.
 To design and manufacture a HAWT, heavy machinery is required.

HAWT Technological Evolution
 Useful wind speeds-There is a range of wind speeds within which the rotor
can move and function properly.
 Lower limit - “Cut-in” = 4 m/s (approx. 14 km/h). With wind speeds below
this value, it is not possible to activate the rotation of the blades and the
rotor remains stationary.
 Upper limit - “Cut-off” ~ 25 m/s (approx. 90 km/h). Above this speed, the
rotor is stopped to avoid serious structural problems.
 Wind limit value - “Survival Speed”, representing the maximum design
wind speed which the structure of turbine & blades can withstand
without incurring damage. This value varies depending on the type of
wind turbine and generally is approx. 60m/s, (approx. 216 km/h).

Conversion efficiency :
 Conversion of kinetic energy into electricity of modern-day wind machines is
around 25%.
 The maximum theoretical efficiency of a wind turbine system is defined by
Betz’s law, which identifies the so-called “Betz limit” corresponding to a
maximum efficiency of 59%.
Capacity factor:
 Equivalent number of hours of operation (at the maximum rated system
power) throughout the year.(8760 hours).
 Capacity Factor values vary from 20% (1750 hours/ year at full power) to 40%
(3500 hours/year at full power);
 In certain exceptional cases it is possible to reach values close to 50% (4400
hours/year at full power).
 In Italy the current Capacity Factor of the entire national wind farm is 25%,
corresponding to approx. 2,200 hours per year of system operation at nominal
power.

Vertical axis wind turbines (VAWT)
 Vertical axis wind turbines (or VAWTs) have the main rotor shaft
arranged vertically.
 Darrieus designs are the most common VAWTs
Main attractions of a VAWT are:
 it can accept wind from any direction, eliminating the need of
yaw control.
 gearbox, generator etc. are located at the ground, thus
eliminating the heavy nacelle at the top of the tower. This
simplifies the design and installation of the whole structure,
including tower.
 the inspection and maintenance also gets easier and
 it also reduces the overall cost.

Main Components of VAWT
Tower (or Rotor Shaft):
 The tower is a hollow vertical rotor shaft, which rotates freely about the
vertical axis between the top and bottom bearings.
 It is installed above a super structure.
 The upper part of the tower is supported by guy ropes.
 The height of the tower of a large turbine is around 100m.
Blades-
 It has two or three thin, curved blades shaped like an egg beater in a
profile, (Troposkien profile) with blades curved in a form that minimizes
the bending stress caused by centrifugal forces.
 The blades have an airfoil cross section with constant chord length.
 The pitch of the blades cannot be changed.
 The diameter of the rotor is slightly less than the tower height.
Support –
 The support struStructurecture is provided at the ground to support the
weight of the rotor.
 Gearbox, generator, brakes, electrical switchgear and controls are
housed within this structure.

TYPES OF ROTORS
1. Cup type rotor
2. Savonius or S-rotor
3. Darrieus rotor
4. Musgrove rotor
5. Evans rotor

CUP TYPE ROTOR
 The simplest being a three-or four-cup structure
attached symmetrically to a vertical shaft.
 The drag force on the concave surface of the cup facing
the wind is more than that on the convex surface. As a
result, structure starts rotating. Some lift force also helps
rotation.
 However, it cannot carry a load and therefore cannot
used as power source.
 The main characteristic of this rotor is that its rotational
frequency is linearly related to wind speed. i.e., it is used
for measuring the wind speed and the apparatus is
known as CUP ANEMOMETER.

SAVONIUS OR S-ROTOR
 It consists of two half cylinders attached to a vertical
axis and facing in opposite directions to form a two-
vane rotor.
 It has high starting torque, low speed and low
efficiency.
 It can extract power even from very slow wind, making
it working most of the time. These are used for low-
power applications.
 A high starting torque particularly makes it suitable for
pumping applications.

DARRIEUS ROTOR (HIGH SPEED, HIGH EFFICIENCY)
 It is used for large-scale power generation. Its
power coefficient is considerably better than that
of an Srotor.
 Drawback : it is usually not self-starting. Movement
may be initiated by using electrical generator as
motor (or S-rotor).
 As the pitch of the blade cannot change, the rotor
frequency and, thus the output power cannot be
controlled. Hence, at high wind speed it becomes
difficult to control the output.
 For better performance and safety of the blades,
gearbox and generator, it is desirable to limit the
output to a level much below its maximum possible
value.

MUSGROVE ROTOR
 He suggested the use of H-shaped rotor where
blades with a fixed pitch are attached vertically to a
horizontal cross arm.
 Power control is achieved by controlled folding of
the blades.
 Inclining the blades to the vertical provides an
effective means of altering the blade angle of
attack and hence controlling the power output.

EVANS ROTOR (GYRO MILL)
 It is an improvement over H-shaped rotor.
 Here, the rotor geometry remains fixed (blades
remains straight) , but the blades are hinged on a
vertical axis and the blade pitch is varied
cyclically (as the blade rotates about the vertical
axis) to regulate the power output.
 But the need to vary the pitch cyclically through
every rotor revolution introduces considerable
mechanical complexity.
 However, this enables it to self-start.

How Does a Wind Turbine work?
1. When wind blows past the blades of the rotor, it makes them
rotate.
2. The low-speed shaft is connected to the rotor. This shaft rotates
when the rotor rotates. There is a brake on the low-speed shaft
if the blades need to be stopped,
3. A large gear is connected to the low-speed shaft. When the
shaft rotates, so does this gear.
4. A smaller gear meshes with the large gear. The smaller gear
turns faster than the large gear. This is because of the gear
ratio.
5. The small gear converts the slow rotation of the turbine blades
to a speed of approximately 1500 revolutions per minute (rpm).
6. The small gear is connected to another shaft. This is the high-
speed shaft. This shaft is connected to the generator.
7. The generator converts mechanical energy into electrical
energy using a powerful magnet in motion near a wire.
8. A control box in the nacelle receives information from an
anemometer and a wind vane. Controllers on the ground use
this information to turn the nacelle or switch the turbine on and
off.

Distribution of Electricity
 The electricity generated by harnessing the wind’s mechanical
energy must go through a transformer in order increase its voltage
(115 kv) make it successfully transfer across long distances.
 Power stations and fuse boxes receive the current and then
transform it to a lower voltage 220/380 volt that can be safely used
by business and homes.

Advantages of VAWT
 The generator and gearbox can be placed on the ground
 The structure is usually simpler.
 You do not need a yaw (pointing) mechanism to turn the rotor
against the wind.
 These are easier for hobbyists to build – little detailed knowledge
of aerodynamics is needed for simple designs.

Disadvantages of VAWT
 These structures are low to the ground, where wind speeds are
lowest.
 The overall efficiency is much lower than horizontal axis
machines.
 Most vertical axis machines are not self starting.
 Many vertical axis machines require guy wires which greatly
increase the structural footprint.
 Maintenance is usually more difficult.
For example, replacement of the generator typically requires
disassembly of the entire machine.

HAWT vs VAWT
Basis of Difference Horizontal Axis Wind Turbine Vertical Axis Wind Turbine
Definition
This is the one whose axis of rotation is
horizontal.
its axis of rotation is vertical.
Abbreviated name
HAWT is the abbreviation used for
horizontal axis wind turbine.
VAWT is the abbreviation used for
vertical axis wind turbine.
Axis of rotation with
respect to wind stream
the axis of rotation of turbine is
parallel to the wind stream.
the axis of rotation of the turbine is
perpendicular to the wind stream.
Location of electric
generator
the electric generator is installed at
the top of the tower.
the generator is installed on the
ground.
Location of gearbox
In HAWT, the gearbox is installed at
the top of the turbine tower.
In VAWT, the gearbox is installed at
the bottom of the turbine.

Need of yaw mechanism
the yaw mechanism is required to
orient the turbine in the direction of
wind.
it does not require yaw mechanism
because it receives wind from all
directions.
Self-starting
Horizontal axis wind turbine is self-
starting.
It is not self-starting, a starting
mechanism is required to start it
Design and installation
The design and installation is
complex.
The design and installation is
comparatively simple.
Operation space of blades
It requires large space for blade’s
operation.
It requires small space for blade’s
operation.
Dependency on wind
direction
The operation is dependent on wind
direction.
The operation is independent of the
wind direction because it receives
wind from all directions.
Height from ground
The height of the horizontal axis wind
turbine from ground is large.
The vertical axis wind turbine is installed
at comparatively smaller distance from
the ground.
Need of nacelle
In case of horizontal axis wind
turbines, a heavy nacelle is installed
at the top of the tower.
There is no need of nacelle in case of
vertical axis wind turbines.

Power coefficient
Horizontal axis wind turbine has a
high power coefficient.
Vertical axis wind turbine has a
low power coefficient.
Tip speed ratio (TSR)
Horizontal axis wind turbine has
high tip speed ratio.
Vertical axis wind turbine has
considerably low tip speed ratio.
Noise produced
The operation of horizontal axis
wind turbine is noisy.
Vertical axis wind turbines
produce comparatively less
noise.
Efficiency
The ideal efficiency of horizontal
axis wind turbine is around 50% to
60 %.
The ideal efficiency of vertical
axis wind turbine is usually more
than 70%.
Hindrance for birds
Horizontal axis wind turbines
cause high obstruction for birds.
Vertical axis wind turbines cause
less hindrance for birds.
Cost
Horizontal axis wind turbines are
more expensive due their
complex design and installation.
Vertical axis wind turbines are less
expensive because their design
and installation is quite simple.

ENVIRONMENTAL ASPECTS
 Indirect Energy Use and Emissions- pollution (emission of CO2, etc.) is
caused due to use of energy during construction.
 Bird Life
 Noise-The disturbance caused by the noise produced by wind
turbine. (a) mechanical noise ( b) aerodynamic noise (swishing sound
from the rotating blades)
 Visual Impact-massive structures quite visible over a wide area
 Telecommunication Interference- obstacle for incident
electromagnetic waves
 Safety
 Effects on Ecosystem

Advantages of wind power
1. The wind is free and with modern technology it can be captured
efficiently.
2. Once the wind turbine is built the energy it produces does not cause
green house gases or other pollutants.
3. Many people find wind farms an interesting feature of the landscape.
4. Wind turbines have a role to play in both the developed and third
world.
5. Remote areas that are not connected to the electricity power grid
can use wind turbines to produce their own supply.

Disadvantages of wind power
1. Many people feel that the countryside should be left untouched,
without these large structures being built. The landscape should left in its
natural form for everyone to enjoy.
2. Many people see large wind turbines as unsightly structures and not
pleasant or interesting to look at. They disfigure the countryside and are
generally ugly.
3. When wind turbines are being manufactured some pollution is
produced. Therefore wind power does produce some pollution.
4. The strength of the wind is not constant and it varies from zero to storm
force. This means that wind turbines do not produce the same amount of
electricity all the time. There will be times when they produce no
electricity at all.
5. Wind power must compete with other low-cost energy sources

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CH-3 WIND POWER Technology as a Renewable Energy

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