Unit 5 Wind Energy
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Questions and Answers

What is the primary source of wind energy?

  • Ocean currents
  • Earth's rotation
  • Atmospheric pressure
  • Solar radiation (correct)

    • What is the direction of the global winds due to the Coriolis force?

  • Easterly
  • Westerly (correct)
  • Northerly
  • Southerly

    • What is the main reason for the generation of local winds?

  • Atmospheric pressure
  • Earth's rotation
  • Ocean currents
  • Differential heating (correct)

    • What is the purpose of windmills or turbines?

    <p>To generate mechanical energy</p> Signup and view all the answers

    What is the relationship between wind speed and the amount of energy available in the wind?

    <p>The amount of energy is proportional to the cube power of the wind speed</p> Signup and view all the answers

    What is the primary function of the gearbox in a wind turbine?

    <p>To regulate the output rotation from the rotor with the speed of the generator</p> Signup and view all the answers

    What is the main advantage of a vertical axis wind turbine?

    <p>It can accept wind from any direction, eliminating the need for yaw control</p> Signup and view all the answers

    What is the purpose of electromagnetic brakes in a wind turbine?

    <p>To slow down the rotor during high winds</p> Signup and view all the answers

    What type of rotor is commonly used in medium- and large-sized wind turbines?

    <p>Three-bladed rotor</p> Signup and view all the answers

    What is the typical height of the tower in a vertical axis wind turbine?

    <p>100 meters</p> Signup and view all the answers

    What is the primary function of topography in wind turbine installation?

    <p>To channelize and speed up winds</p> Signup and view all the answers

    What is the purpose of nearness to load centre in wind turbine installation?

    <p>To reduce the cost of transmission of the generated power</p> Signup and view all the answers

    What is the definition of solidity in rotor design?

    <p>The ratio of the projected area of the rotor blades to the swept area of the rotor</p> Signup and view all the answers

    What is the purpose of pitch angle or blade setting angle in wind turbine design?

    <p>All of the above</p> Signup and view all the answers

    What is the result of large angles of attack in wind turbine design?

    <p>Airflow is separated from the aero foil</p> Signup and view all the answers

    What is the main reason for air currents to move to the hill slope during the day and to the low-lying land during night?

    <p>Temperature difference between hill and low land</p> Signup and view all the answers

    What is the device used to measure wind speed?

    <p>Anemometer</p> Signup and view all the answers

    What is the term used to describe the rate of change of wind speed with height?

    <p>Wind shear</p> Signup and view all the answers

    Above which height does the wind speed become uniform and unaffected by ground conditions?

    <p>2000 m</p> Signup and view all the answers

    What is the main consideration for selecting a site for wind generator?

    <p>High annual mean wind speed</p> Signup and view all the answers

    What is the force that acts in the direction of wind?

    <p>Drag force</p> Signup and view all the answers

    What is the function of the yaw control mechanism in a horizontal axis wind turbine?

    <p>To control the direction of the rotor</p> Signup and view all the answers

    What is the advantage of a two-bladed rotor over a three-bladed rotor?

    <p>It is simpler to construct and erect</p> Signup and view all the answers

    What is the purpose of the nacelle in a wind turbine?

    <p>To mount the rotor at the top of a tower</p> Signup and view all the answers

    What is the type of wind turbine that has an axis of rotation parallel to the airstream?

    <p>Horizontal axis wind turbine</p> Signup and view all the answers

    What is the main advantage of a variable speed drive system?

    <p>Capturing maximum power at various wind speeds</p> Signup and view all the answers

    What is the purpose of larger wind turbines?

    <p>To generate significant power output at an economical rate</p> Signup and view all the answers

    What is the main reason for improved plant operations in wind turbines?

    <p>Ensuring the supply of power from the wind turbine plant as high as 95%</p> Signup and view all the answers

    Which of the following is NOT a factor in the acceleration and development of wind power?

    <p>Nuclear power technology</p> Signup and view all the answers

    What is the energy payback period of a wind turbine?

    <p>1 year</p> Signup and view all the answers

    What is the main advantage of the Darrieus rotor?

    <p>It can harness wind energy from any direction</p> Signup and view all the answers

    Which rotor is used for wind speed measuring instruments?

    <p>Cup type rotor</p> Signup and view all the answers

    What is the main drawback of the Darrieus rotor?

    <p>It is not self-starting</p> Signup and view all the answers

    What is the main advantage of the S-rotor?

    <p>It can produce high starting torque at low wind speed</p> Signup and view all the answers

    Why does wind energy require storage?

    <p>Because wind energy is an intermittent source of power</p> Signup and view all the answers

    What is the purpose of storing energy in compressed air in a suitable storage tank?

    <p>To generate electricity through a directly coupled generator</p> Signup and view all the answers

    What is the environmental impact of wind turbines on bird's life?

    <p>Wind turbines pose a threat to bird's life</p> Signup and view all the answers

    What is the purpose of yaw and tilt control in recently developed windmills?

    <p>To shift the rotor axis out of wind direction during high wind speeds</p> Signup and view all the answers

    What is the benefit of using wind turbines as a source of energy?

    <p>They have no pollution or emission of carbon dioxide during operation</p> Signup and view all the answers

    What is the purpose of pitch control in recently developed windmills?

    <p>To maintain constant turbine speed</p> Signup and view all the answers

    Study Notes

    Wind Energy

    • Wind is air in motion, and its energy is proportional to the cube of its speed.
    • Wind energy is an indirect form of solar energy, generated by the differential heating of the earth's surface.

    Origin of Winds

    • Global winds are caused by the differential heating of the earth's surface at the equator and polar regions.
    • The rotation of the earth creates the Coriolis force, which makes global winds move towards the westerly direction.
    • Local winds are generated by uneven heating of land and water surfaces.

    Nature of Wind

    • Wind varies from place to place, depending on the climate, geography, and terrain.
    • Knowledge of wind behavior and structure is essential for installing wind turbines.

    Wind Speed Variations

    • Wind speed increases with height, but falls to zero at the earth's surface.
    • The rate of change of wind speed with height is called wind shear.
    • The gradient height is the height at which wind speed no longer increases with height.

    Wind Turbine Siting

    • Key considerations for selecting a wind turbine site include:
      • High annual mean wind speed
      • No obstruction within a certain distance
      • Open plain or coastal area
      • Height to take advantage of increased wind speed
      • Proximity to load centers and transportation links
      • Availability of wind data

    Rotor Design

    • A rotor extracts energy from the wind by transforming kinetic energy into rotational motion.
    • Rotor design parameters include:
      • Solidity: the ratio of projected blade area to swept area
      • Chord: the width of the blade
      • Angle of incidence: the angle between the blade and the wind direction
      • Pitch angle: the angle between the blade and the direction of motion
      • Different velocities: wind velocity, incident wind velocity, blade linear velocity, and relative velocity

    Wind Energy Conversion

    • The principle of wind energy conversion is to extract energy from the wind by partially decelerating and expanding the airstream.
    • The rotor collects wind from the whole area swept by the rotor, and the energy is extracted through the deceleration of the airstream.

    Aerodynamic Considerations

    • Lift and drag forces are created when wind moves over an aerofoil.
    • The shape of the aerofoil determines the relative magnitude of lift and drag forces.
    • Lift devices are more efficient due to their lower drag forces.

    Types of Windmills

    • Horizontal Axis Wind Turbine (HAWT): axis of rotation is parallel to the airstream.
    • Vertical Axis Wind Turbine (VAWT): axis of rotation is perpendicular to the airstream.
    • HAWTs are commonly used for electric power generation.
    • VAWTs are suitable for applications where low speeds are required, such as piston pumps.

    Rotors of HAWT and VAWT

    • HAWT rotors can be single-bladed, two-bladed, three-bladed, or multi-bladed.
    • VAWT rotors can be cup-type, Savonious, Darrieus, Musgrove, or Evans-type.
    • Darrieus rotors are commonly used for large power generation due to their good power coefficient.### Advantages of Darrieus Wind Turbine
    • Simple in construction
    • Low cost of construction and installation
    • Higher power coefficient and tip speed ratio compared to S-rotor

    Disadvantages of Darrieus Wind Turbine

    • Not self-starting machine
    • Works on drag force, leading to low efficiency in converting wind energy
    • Limited height, unable to utilize high wind speeds available at higher levels
    • Unable to yaw out of the wind, requires special high torque braking system during high wind speeds

    Starting Arrangements for Darrieus Rotor

    • Attaching S-rotors at the top and bottom of the shaft to help start up
    • Designing the generator to run as a motor to start up the wind turbine initially
    • Partly shielding the rotor from the wind stream to behave as an unsymmetrical rotor and develop starting torque

    Wind Energy Storage

    • Chemical energy storage through batteries
    • Thermal energy storage through heating water
    • Compressed air storage
    • Electrolysis of water to produce hydrogen and oxygen gases
    • Pumping water to a high tank for storage
    • Integration to electric grid

    Environmental Impacts of Wind Turbine

    • Zero emission during operation
    • Threat to bird's life due to rotating rotors
    • Noise disturbance due to aerodynamic noise
    • Interference to transmission of TV and communication signals
    • Visual intrusion due to high towers
    • Safety concerns due to rotating blades
    • Impact on ecosystem due to large-scale interception and use of wind energy

    Recent Developments in Wind Turbines

    • Yaw and tilt control for safety and speed control
    • Pitch control to regulate rotor blades for maximum output
    • Stall control to shift blades to a safe position during high winds
    • Fixed blades with constant pitch for constant turbine speed
    • Eddy current braking system to control speeds
    • Variable speed drive system to capture maximum power

    Factors Accelerating Wind Power Development

    • Improved materials for large-sized rotor blades
    • Power electronics for regulation and control
    • Variable speed drive system for maximum energy capture
    • Larger wind turbines for economical power output
    • Short energy payback period
    • Improved plant operations for high power supply
    • Increased expertise in development and operation
    • Renewable resource competing with conventional power sources

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    Learn about wind energy, its source, and how it's harnessed. Discover the connection between wind energy and solar radiation, and the factors that affect its availability.

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