Notes on Wind Energy Engineering by H Janardan_Prabhu


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Wind Electric Conversion Systems

  * Wind Energy Availability
  • Energy in wind, speed
  • Wind Turbine, Design
  • Variables – wind power density
  • Generator and power output
  • PV-Wind, Diesel-set-Wind Hybrid System
  • Tower design
  • Wind Electric Conversion System
Wind Energy Engineering Syllabus-1
  Wind energy Assessment by
  Measurement and instrumentation –
  Beaufort number -Gust parameters –
  Wind type – power law index -Betz
  constant -Terrain value.
  Energy in wind– study of wind data
  and applicable Indian standards –
  Steel Tables, Structural Engineering
  for tower design- Wind farms––
  fatigue stress – Tower design.

                   CEESAT NITT NOTES     2
Wind Energy Engineering Syllabus-2
 Wind Energy Conversion Systems: Variables
 – wind power density – power in a wind
 stream – Wind turbine efficiency – Forces on
 the blades of a propeller –Solidity and
 selection curves.
 Horizontal Axis –WT and Vertical Axis -WT-
 Power duration curves- wind rose diagrams -
 study of characteristics - actuator theory-
 Controls and instrumentations.
 Grid-Connected WECS and Independent
 WECS- Combination of WECS and diesel
 generator, Battery storage – Wind Turbine
                     CEESAT NITT NOTES          3
ENGINEERING: Text & Reference Books

  1. S. Rao & B. B. Parulekar, “Energy Technology”,
  3rd Edition, Khanna publishers, 1995.
  2. Wind and Solar Power Systems, Mukund. R.
  Patel, 2nd Edition, Taylor & Francis, 2001
  3. Wind Energy Handbook, Edited by T. Burton, D.
  Sharpe N. Jenkins and E . Bossanyi, John Wiley
  & Sons, N.Y. 2001
  4. . L .L. Freris, Wind Energy Conversion Systems,
  Prentice Hall, 1990.
  5. D. A. Spera, Wind Turbine Technology:
  Fundamental concepts of Wind Turbine
  Engineering, ASME Press
                       CEESAT NITT NOTES               4
 From wind to electricity.
    The first wind powered electricity was produced in
1888. It had a rated power of 12 kW (direct current - dc).
In the 1930's the first large scale AC turbine was
constructed in the USA.
     In the 1970's the fuel crises sparked a revival in R & D
work in America (USA and Canada) and Europe (Denmark,
Germany, the Netherlands,Sweden and the UK) and
 modern wind turbine-generators were developed. This was
achieved due to improvements in aerodynamic and
structural design, materials technology and mechanical,
electrical and control engineering and led to capablilty to
produce several megawatts of electricity.
                          CEESAT NITT NOTES                     5
Wind energy basics
Kinetic energy >
Mechanical [Rotational] >
Electrical energy
Wind is created by the unequal
heating of the Earth’s surface by
the sun. Wind turbines convert
the kinetic energy in wind into
mechanical power that runs a
generator to produce electricity.
     CEESAT NITT NOTES              8
horizontal-axis vs vertical-axis

  There are two basic designs of wind electric
  turbines: vertical-axis, or "egg-beater" style,
  and horizontal-axis (propeller-style)
  Horizontal-axis wind turbines are most
  common today, constituting nearly all of the
  "utility-scale" (100 kilowatts, kW, capacity and
  larger) turbines in the global market.

                    CEESAT NITT NOTES            9
Small wind turbines
 Usually machines under about 10 kW in
  In developing countries small wind turbines
 are used for rural energy applications, and
 there are many "off-grid" applications in the
 developed world as well - such as providing
 power for navigation beacons.
 Since most are not connected to a grid, many
 use DC generators and run at variable speed.
 A typical 100 W battery-charging machine
 has a shipping weight of only 15 kg
                  CEESAT NITT NOTES          12
Wind power for developing countries

Large-scale grid connected wind turbines
are common with wind farm; This can be
the main national network, in which case
electricity can be sold to the electricity
Micro-grids distribute electricity to smaller
areas, typically a village or town. When
wind is used for supplying electricity to
such a grid, a diesel generator set is often
used as a backup for the periods when
windspeeds are low.

                    CEESAT NITT NOTES           14
Figure: The Practical Action small
   wind turbine ©Practical Action
                                   Image:Windelectricity 02.jpeg

               CEESAT NITT NOTES                                   15
Performance of WECS
 The availability of wind resources are
 governed by the climatic conditions of the
 region concerned- for which wind survey is
 extremely important to exploit wind energy.
 Performance of W E C S depends upon:
 Subsystems like
 wind turbine (aerodynamic),
  gears (mechanical),
 generator (electrical) and Control (electronic)
                   CEESAT NITT NOTES               16
Wind Electric Potential in India
                              Potential: 45,000 MW
                           Technical Potential:13,000
                           Sites with Annual Average
                           Power Density > 200
                           generally viable, 208 such
                           in 13 states identified
                           States with high potential :
                              Gujarat, Andhra Pradesh,
                              Tamil Nadu, Karnataka,
                              Kerala, Madhya Pradesh,
                              and Maharashtra.

                 CEESAT NITT NOTES                        17
India’s Installed Wind Power
Gen Capacity at end of 2001
State         Installed capacity, MW
Tamil Nadu       828
Maharashtra       236
Gujarat          167
Andhra           92
Karnataka        50
M.P.             23
All Others       111
                CEESAT NITT NOTES      18
            Wind resources

Apart from having a good wind turbine, the
most critical aspects for the success of
investment in the wind energy sector are

having a good site and

an accurate assessment of the wind
resource at the site.

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Wind Resource Monitoring

 Site selection

 Wind Monitoring

 Wind Resource Mapping

                   CEESAT NITT NOTES   20
Choosing an exact location for the
monitoring tower:

 Place the tower as far away as possible

 from local obstructions to the wind

 Select a location that is representative of

  the majority of the site.

                     CEESAT NITT NOTES         22
An instrument for measuring the force or
velocity of wind. There are various types:
A cup anemometer, is used to measure
the wind speed from the speed of rotation
of a windmill which consist of 3 or 4
hemispherical or conical cups, each fixed
to the ends of horizontal arms attached to
a vertical axis.
A Byram anemometer is a variety of cup
                  CEESAT NITT NOTES          24
A counting anemometer has cups or a fan whose
rotation is transmitted to a counter which integrates
directly the air movement speed.

A hand anemometer is small portable anemometer
held at arm's length by an observer making a wind
speed measurement.

A pressure tube anemometer (Dines anemometer)
is an instrument that derives wind speed from
measurements of the dynamic wind pressures. Wind
blowing into a tube develops a pressure greater
than the static pressure, while wind blowing across
a tube develops a pressure less than the static. This
pressure difference is proportional to the square of
the wind speed.         CEESAT NITT NOTES               25
                          WIND    SPEED           SCALE
   Wind Speed at 10 m height   Beaufort scale     Wind

0.0-0.4 m/s (0.0-0.9 knots)       0               Calm
0.4-1.8 m/s (0.9-3.5 knots)       1               Light
1.8-3.6 m/s (3.5-7.0 knots)       2               Light
3.6-5.8 m/s (7-11 knots)          3               Light
5.8-8.5 m/s (11-17 knots)         4               Moderate
8.5-11 m/s (17-22 knots)          5               Fresh
11-14 m/s (22-28 knots)           6               Strong
14-17 m/s (28-34 knots)           7               Strong
17-21 m/s (34-41 knots)           8               Gale
21-25 m/s (41-48 knots)           9               Gale
25-29 m/s (48-56 knots)           10              Strong Gale
29-34 m/s (56-65 knots)           11
>34 m/s (>65 knots)               12              Hurricane
                              CEESAT NITT NOTES                 27
For wind data from selected stations,
essential attributes are:

 Station location
 Local topography
 Anemometer height and exposure
 Type of observation (instantaneous or
 Duration of record.

                    CEESAT NITT NOTES    30
Topographic maps
 provide the analyst with a preliminary look
 at other site attributes, including:
 Available land area
 Positions of existing roads and dwellings
 Land cover (e.g., forests)
 Political boundaries
 Proximity to transmission lines.

                   CEESAT NITT NOTES           31
For verifying site conditions items of
importance include:
 Available land area
 Land use
 Location of obstructions
 Trees deformed by persistent strong winds (flagged
 Accessibility into the site
 Potential impact on local aesthetics
 Cellular phone service reliability for data transfers
 Possible wind monitoring locations.

                      CEESAT NITT NOTES                  32
Cost – economics-1
The cost of producing electricity form the wind is
heavily dependent on the local wind regime.
 The power output from the wind machine is
proportional to cube of the windspeed and so a
slight increase in windspeed will mean a
significant increase in power and a subsequent
reduction in unit costs.
Capital costs for windpower are high, but running
costs are low and so access to initial funds,
subsidies or low interest loans are an obvious
advantage when considering a wind-electric
                      CEESAT NITT NOTES              33
Cost – economics-2

If a hybrid system is used a careful cost-
benefit analysis needs to be carried out.
 A careful matching of the load and
energy supply options should be made to
maximise the use of the power from the
wind - a load which accepts a variable
input is ideally matched to the intermittent
nature of windpower.
                    CEESAT NITT NOTES          34
India- Implemented through :
 (i) State Nodal Agencies
 (ii) Centre for Wind Energy Technology (C-
 Financial Assistance :
  (i) Full establishment costs of Wind Resource
    Assessment Project (WRAP) of C-WET by
    the Central Government.

                    CEESAT NITT NOTES         35
Implemented through…. :

(ii) The cost of setting up the wind monitoring
  stations would be shared between MNRE
  and State Nodal agencies in 80:20 ratio,
  except for North-eastern and hilly States,
  where it would be in 90:10 ratio.

                    CEESAT NITT NOTES             36
Resource Survey in India

 Centre for Wind Energy Technology (C-WET)

 6 Volumes of “Wind Energy –Resource Survey in
 India” , containing wind data have been published

 Master Plans for 87 sites prepared and available
 from C-WET at nominal cost.

 Wind data available from C-WET on CD ROM.
                     CEESAT NITT NOTES               37
                         Government of India
               Ministry of New and Renewable Energy
                        (Wind Power Division)
                    Block No.14, CGO Complex,
                  Lodhi Road, New Delhi – 110003

•C-WET would evaluate the eligibility of manufacturer,
who approaches for Type. Certification, as per the
evaluation criteria in vogue, which is being followed by C-
•Validity of Self-Certification facility for models specified in
the List of Models and Manufacturers thereof issued by C-
WET is extended up to 30th September, 2007.
•Self-Certification facility would be available for a
maximum period of 18 months from the date of signing of
the agreement with C-WET for the models hereinafter
including in the category "Model under Testing and
Certification at C-WET" in the List to be issued by C-WET.

                            CEESAT NITT NOTES                      38
Wind Turbine, tail, support tower
                                    The amount of power a
                                    turbine will produce
                                    depends primarily on the
                                    diameter of its rotor.
                                    The diameter of the rotor
                                    defines its “swept area,” or
                                    the quantity of wind
                                    intercepted by the turbine.
                                    The turbine’s frame is the
                                    structure onto which the
                                    rotor, generator, and tail are
                                    attached. The tail keeps the
                                    turbine facing into the wind.

                CEESAT NITT NOTES                                  42
  Horizontal Axis upwind
      Wind Turbine

Most turbines today are Horizontal Axis

upwind machines with two or three blades,

made of a composite material like

                 CEESAT NITT NOTES        43
Some definitions:
 Solidity: In reference to a wind energy
 conversion device, the ratio of rotor blade
 surface area to the frontal, swept area that
 the rotor passes through.
 wind rose: A diagram that indicates the
 average percentage of time that the wind
 blows from different directions, on a monthly
 or annual basis.
 power curve: A plot of a wind energy
 conversion device's power output versus
 wind speed.
 power coefficient: The ratio of power
 produced by a wind energy conversion
 device to the power in a reference area of
 the free wind stream.
                    CEESAT NITT NOTES            44
The formula for calculating the
power from a wind turbine is:

                CEESAT NITT NOTES   48
Some definitions….
 1 m/s = 3.6 km/h = 2.237 mph = 1.944 knots
 1 knot = 1 nautical mile per hour = 0.5144 m/s =
                             1.852 km/h = 1.125 mph
 average wind speed: The mean wind speed over a
 specified period of time.

 PITCH CONROL: A method of controlling the
 speed of a wind turbine by varying the orientation,
 or pitch, of the blades, and thereby altering its
 aerodynamics and efficiency.
                     CEESAT NITT NOTES                 49
Tip Speed Ratio
 The tip-speed is the ratio of the rotational
 speed of the blade to the wind speed. The
 larger this ratio, the faster the rotation of the
 wind turbine rotor at a given wind speed.
 Electricity generation requires high rotational
 speeds. Lift-type wind turbines have
 maximum tip-speed ratios of around 10

                    CEESAT NITT NOTES                50
Operating Characteristics
All wind machines share certain operating
  characteristics, such as cut-in, rated and cut-
  out wind speeds.
  Cut-in Speed
  Cut-in speed is the minimum wind speed at which the
  wind turbine will generate usable power. This wind speed
  is typically between 7 and 10 mph.
  Rated Speed
  The rated speed is the minimum wind speed at which the
  wind turbine will generate its designated rated power. For
  example, a "10 kilowatt" wind turbine may not generate 10
  kilowatts until wind speeds reach 25 mph. Rated speed
  for most machines is in the range of 25 to 35 mph.
                         CEESAT NITT NOTES                 51
Rated Speed…

 At wind speeds between cut-in and rated, the
 power output from a wind turbine increases
 as the wind increases. The output of most
 machines levels off above the rated speed.
 Most manufacturers provide graphs, called
 "power curves," showing how their wind
 turbine output varies with wind speed.

                  CEESAT NITT NOTES         52
  Cut-out Speed
At very high wind speeds, typically between
45 and 80 mph, most wind turbines cease
power generation and shut down. The wind
speed at which shut down occurs is called
the cut-out speed. Having a cut-out speed is
a safety feature which protects the wind
turbine from damage. Shut down may occur
in one of several ways. In some machines an
automatic brake is activated by a wind speed
                 CEESAT NITT NOTES         54
Cut out speed & yaw

 Some machines twist or "pitch" the blades to
 spill the wind. Still others use "spoilers," drag
 flaps mounted on the blades or the hub which
 are automatically activated by high rotor
 rpm's, or mechanically activated by a spring
 loaded device which turns the machine
 sideways to the wind stream. Normal wind
 turbine operation usually resumes when the
 wind drops back to a safe level.
                    CEESAT NITT NOTES            55
number of blades
The number of rotor blades and the total area they
cover affect wind turbine performance. For a lift-
type rotor to function effectively, the wind must flow
smoothly over the blades.
To avoid turbulence, spacing between blades
should be great enough so that one blade will not
encounter the disturbed, weaker air flow caused by
the blade which passed before it.
 It is because of this requirement that most wind
turbines have only two or three blades on their

                         CEESAT NITT NOTES               56
      Transmission- Gear box

The number of revolutions per minute (rpm)
of a wind turbine rotor can range between
40 rpm and 400 rpm, depending on the
model and the wind speed.
Generators typically require rpm's of 1,200
to 1,800. As a result, most wind turbines
require a gear-box transmission to increase
the rotation of the generator to the speeds
necessary for efficient electricity production.
                    CEESAT NITT NOTES             57
Electrical Generators
 It converts the turning motion of a wind
 turbine's blades into electricity. Inside
 this component, coils of wire are rotated
 in a magnetic field to produce electricity.
 Different generator designs produce
 either alternating current (AC) or direct
 current (DC),

                    CEESAT NITT NOTES          59
 generators for wind turbines

At the present time and for the near future,
  generators for wind turbines will be
 synchronous generators,
 permanent magnet synchronous
 generators, and
 induction generators, including the squirrel-
 cage type and wound rotor type.

                    CEESAT NITT NOTES          60
Squirrel cage induction generator

               CEESAT NITT NOTES    61
Doubly Fed Wounded Rotor
Asynchronous Generator.

                CEESAT NITT NOTES   62
Grid Connected Permanent Magnets
Synchronous Generator in full converter

                  CEESAT NITT NOTES       63
generators for SMALL wind

 For small to medium power wind turbines,
 permanent magnet generators and squirrel-cage
 induction generators are often used because of
 their reliability and cost advantages. Induction
 generators, permanent magnet synchronous
 generators, and wound field synchronous
 generators are currently used in various high
 power wind turbines.
                     CEESAT NITT NOTES              64
Induction generator

 Induction generator offers many advantages over a
 conventional synchronous generator as a source of
 isolated power supply.

 Reduced unit cost, ruggedness, brush less (in
 squirrel cage construction), reduced size, absence
 of separate DC source and ease of maintenance,
 self-protection against severe overloads and short
 circuits, are the main advantages
                     CEESAT NITT NOTES                65
induction generator…

 Further induction generators are loosely
 coupled devices, i.e. they are heavily damped
 and therefore have the ability to absorb slight
 change in rotor speed and drive train

 transient to some extent can therefore be
                   CEESAT NITT NOTES           66
drawback of the induction

  Reactive power consumption and poor
  voltage regulation under varying speed are
  the major drawback of the induction
  generators, but the development of static
  power converters has facilitated the control of
  induction generator, regarding output voltage
  and frequency.

                    CEESAT NITT NOTES           67
Synchronous generator

 Synchronous generators are closely coupled
 devices and when they are used in wind
 turbines which is subjected to turbulence and
 requires additional damping devices such as
 flexible couplings in the drive train or to
 mount gearbox assembly on springs and
                    CEESAT NITT NOTES          68
range of output power ratings.

 Generators are available in a large
 range of output power ratings.

 The generator's rating, or size, is
 dependent on the length of the wind
 turbine's blades because more energy is
 captured by longer blades.

                    CEESAT NITT NOTES      70
Range of power
 <100 kW
 101 kW - 250 kW
 251 kW - 500 kW
 501 kW - 750 kW
 750 kW - 1000 kW
 1001 kW - 2000 kW
 >2000 kW

                CEESAT NITT NOTES   71
Applications adapted to run on

 • Storage systems using batteries store DC

   and usually are configured at voltages of

    between 12 volts and 120 volts in USA.

 • A typical 100 W battery-charging machine

     has a shipping weight of only 15 kg.
                  CEESAT NITT NOTES            72
A .C. Generators…..
• Generators that produce AC are
  generally equipped with features to
  produce the correct voltage (120 or 240
  V) and
• constant frequency (60 / 50 cycles) of
  electricity, even when the wind speed is

                    CEESAT NITT NOTES        73
Advantages of Induction
generator over synchronous
 Induction generator offers many advantages over a
 conventional synchronous generator as a source of
 isolated [A .C] power supply.

 Reduced unit cost, ruggedness, brush less (in
 squirrel cage construction), reduced size, absence
 of separate DC source and ease of maintenance,
 self-protection against severe overloads and short
 circuits, are the main advantages
                     CEESAT NITT NOTES                74
Environmental Aspects of
Power Generation Using WECs
 Wind turbines are most environment friendly method
 of producing electricity.
 They do not pose any adverse effect on the global
 environment, unlike the conventional coal or oil-fired
 power plants. The pollution that can be saved per
 year from a typical 200 kW wind turbine, involving of
 substitution of 120 - 200 tonnes of coal which
 contain pollution contents as, Sulphur dioxide
 (SO2): 2 –3 tonnes, Nitrogen oxide (NOX): 1.2 to
 2.4 tonnes, and other particulates of 150-300 kg. .

                      CEESAT NITT NOTES               75
Audible noise
 The wind turbine is generally quiet. The wind turbine
 manufacturers generally supply the noise level data
 in dB versus the distance from the tower.
 A typical 600 kW wind turbine may produce 55 dB
 noise at 50 meter distance from the turbine and 40
 dB at a 250 meter distance [4, 22] comparable with
 the noise level in motor car which may be
 approximately 75 dB.
 This noise is, however, is a steady state noise. The
 wind turbine makes loud noise while yawing under
 the changing wind direction. Local noise ordinance
 must be compiled with.
                      CEESAT NITT NOTES              76
 Tower on which a wind turbine is mounted is
 not just a support structure. It also raises the
 wind turbine so that its blades safely clear
 the ground and so it can reach the stronger
 winds at higher elevations.
 Maximum tower height is optional in most
 cases, except where zoning restrictions
 apply. The decision of what height tower to
 use will be based on the cost of taller towers
 versus the value of the increase in energy
 production resulting from their use.

                     CEESAT NITT NOTES              77

   Studies have shown that the added
cost of increasing tower height is often
justified by the added power generated
from the stronger winds.
 Larger wind turbines are usually
mounted on towers ranging from 40 to 70
meters tall.
                  CEESAT NITT NOTES        78
The tower must be strong enough to
support the wind turbine and to sustain
vibration, wind loading and the overall
weather elements for the lifetime of the
wind turbine.
Tower costs will vary widely as a function
of design and height.

                 CEESAT NITT NOTES           79
Research and development
 Research and development is going on to make
 wind power competitive with fossil fuel and nuclear
 power in strict sense, without taking into account of
 wind power’s social factors such as environment
 Efforts are being made to reduce the cost of wind
 power by: design improvement, better
 manufacturing technology, finding new sites for wind
 systems, development of better control strategies
 (for output and power quality control), development
 of policy and instruments, human resource
 development, etc

                     CEESAT NITT NOTES               80
About Enercon - E-30-230 kW-
      Gearless type--1
Variable speed drive, Continuous pitch
Starts gen. at low speed of 2.5 m/s,
Gearless construction, no transmission loss,
Synchronous gen., draws < one % reactive
power from grid,
By using AC_DC_AC conversion, pumps the
power at ‘grid frequency’,

                 CEESAT NITT NOTES             81
About Enercon - E-30-230 kW-
      Gearless type--2
Produces power at all loads at near unity
power factor without using capacitors
Supply reactive power to the grid to improve
grid power factor
Slow speed generator of maximum 50 rpm
Three independent air breaks, no
mechanical breaks
Lightning protection
                 CEESAT NITT NOTES             82
Wind Turbine Design
 Design efforts benefit from
 knowledge of the wind speed distribution and
 wind energy content corresponding to the
 different speeds and
  the comparative costs of different systems to
 arrive at the optimal rotor/generator combination.
 Optimizing for the lowest overall cost considers
 design factors such as relative sizes of rotor,
 generator, and tower height.

                      CEESAT NITT NOTES               83
   Thanks to extensive R&D efforts during the
past 30 years, wind energy conversion has
become a reliable and competitive means for
electric power generation.
   The life span of modern wind turbines is
now 20-25 years, which is comparable to many
other conventional power generation

The average availability of commercial wind
power plants is now around 98%.

                Thank You
                     CEESAT NITT NOTES          84

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