Wind energy is a renewable source of energy that
occurs in the nature spontaneously and can be
harnessed to meet the necessity of power. It is
being used from a very early age and the
technology of using this energy efficiently is
being improved with time. It is often termed as
wind power when it is converted to some useful
forms to serve human needs of power.
Wind power is the conversion of wind energy into a
useful form of energy to meet the need of mechanical
and electrical power. To obtain mechanical power we
use wind mills, wind pumps etc. When wind energy is
converted to electrical power, the machinery used is
called wind turbine.
Wind energy has been used for centuries to serve
different purposes such as for sailing ships, for
irrigation as wind pumps, for grinding crops as wind
mills etc. Wind energy became more prominent in 19th
century in United States.
Wind is defined as the atmospheric air in motion
.Differentially absorbed solar radiation by
earth’s surface heats up the atmospheric air
through convection process and that causes
temperature differences in air from place to place.
This phenomenon results in air motion.
The basic theory of wind energy is to use the
updraft and downdraft of wind  to rotate wind
turbine and with necessary mechanism this
rotation of turbine is used to produce mechanical
or electrical power. Main components of a wind
energy plant are- wind turbine, generator, control
system and necessary mechanism for grid
Figure 3: Basic principle of wind energy technology (a-wind
mechanism. b- wind electricity generation)
Wind turbine is the most important part in the
wind power system. It converts rectilinear flow
motion into shaft rotation through rotating air
foils. In general, wind turbines are of two
types- vertical axis type and horizontal axis
Nacelle- contains key components of the
wind turbine such as gear box, generator etc.
Tower- carries the nacelle and the rotor. High
towers provide higher efficiency
Rotor blades-capture the wind energy and
transfer the power to the rotor hub.
Gear box-increases the rotational speed of
the shaft for the generator
Not capable of taking advantage of higher wind
speeds at higher elevations above the ground.
Savonius wind turbine- ‘s’ shaped, drag type, moves slowly
but yields a high torque, prominently used for grinding crops,
pumping water etc, not very suitable to be used in electricity
Flapping panel wind turbine- does not
depend on the direction of wind.
Darrieus wind turbines-C shaped rotor
blades, “egg beater” appearance. high
rotational speed, prominently used in
electricity generation plants.
Very commonly used type of wind turbines
The axis of blade rotation is parallel to the ground
Common types of HAWT are upwind and
Upwind HAWT-designed to operate with the blades
upwind of the tower, Large turbines use a motor
mechanism that turns the machine according to the
wind direction. In small scale turbine, a tail vane is
used to keep the blades facing towards the wind.
Downwind HAWT-operates in a downwind mode,
wind passes the tower before striking the blades,
Without a tail vain the machine rotor automatically
tracks the wind in a downwind mode.
Drive train speed
To control drive train speed-
Fixed type system-wind turbine system is directly
connected to the main grid.
Variable type control system-involves power
electronics, the system indirectly connected to the
To control blade regulation-
Stall type-blade position fixed, angle of
attack increases with the wind speed untill
stall occurs behind the blade.
Pitch type-blade position is varied with wind
speed to actively control low speed shafts to
obtain a better power curve
‘Lift’ and ‘drag’ force on the turbine blade that
causes the rotation
Lift force-rotate upward (clockwise)
Drag force- rotate downward (counter clockwise).
Combined effect-turbine rotation
Figure 7:combined effect of lift and drag force on turbine blade 
amount of air,
velocity of the air,
mass of the air and the area of interest (area
through which air is passing).
Wind power equation-
An alternative to fossil fuels
No green house gas emissions
Uses a little land
Does not affect environment and natural
Significant variation over shorter time scales.
Higher installation cost
Off shore and on shore wind power plants need
Power management techniques such as having
excess capacity storage, geographically distributed
turbines, dispatch able backing sources, storage
such as pumped-storage hydroelectricity etc
causes cost and labor.
As of 2011, Denmark is generating more than a
quarter of its electricity from wind and 83
countries around the world are using wind
power to supply the electricity grid.
In 2010 wind energy production was over
2.5% of total worldwide electricity usage, and
growing rapidly at more than 25% per annum.
Figure 8: current status of top 5 countries using wind energy 
Figure 9: Increase in total installation of wind power plants from
left side respectively in (a) Africa, (b) Asia 
Figure 10: increase in total installation of wind power plants from
left side respectively in Europe and Oceania and Pacific 
using higher heights, larger blades
using super conducting magnets
advanced control systems for better wind
site specific designs etc are being conducted to
improve the performance if wind power plants.
Grid integration and storage of power
Application of flywheels, compressed air,
pumped hydro systems, V2G (vehicle to grid)
Weather forecasting, wind prediction technology
etc are also being considered in the studies.
Wind energy is dependent on the location of
installation. It has certain limitations as
discussed in previous sections. But, it has the
benefit that it does not pollute the
environment. So, that day is not very far when
wind energy will be playing a major role in
meeting our increasing need of electrical
Denis G. shepherd “Historical Development Of Wind
Mill”, NASA contractor report 4337, DOE/NASA/5266-
Robert Castellano , “ Alternative Energy Technologies”,
p. 26. ISBN 978-2813000767.
Alex Kalmikov, Katherine Dykes, “Wind Power
Fundementals”, MIT online lecture notes
Holttinen, Hannele "Design and Operation of Power
Systems with Large Amounts of Wind Power" (PDF). IEA
Wind Summary Paper, Global Wind Power Conference
18–21 September 2006, Adelaide, Australia.
“World energy report 2013”, published in 12th world
Wind Energy Conference and Renewable Energy
Exhibition, 3-5 June, Havana, Cuba.