Unit 5 Wind Energy
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Questions and Answers

What is the primary force behind global winds?

  • Differential heating of the earth surface at the equator and polar regions (correct)
  • Coriolis force
  • Ocean currents
  • Wind speed

    • What is the direction of the global winds?

  • Westerly (correct)
  • Easterly
  • Northerly
  • Southerly

    • How does the wind energy originate?

  • From ocean currents
  • Directly from solar energy
  • Indirectly from solar radiation (correct)
  • From mechanical devices

    • What happens to the direction of local winds at night?

    <p>It changes direction</p> Signup and view all the answers

    What is the purpose of windmills or turbines?

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

    What is the primary reason for air currents moving to the hill slope during the day?

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

    What is the purpose of an anemometer?

    <p>To measure wind speed</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

    What is the typical height above which wind speed becomes uniform?

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

    What is a crucial consideration when selecting a site for a wind turbine?

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

    What is the purpose of studying topography in the context of wind turbines?

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

    What is the definition of solidity in the context of wind turbines?

    <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 turbines?

    <p>To control the output power, speed or torque of the turbine</p> Signup and view all the answers

    What is the relative velocity (vr) in the context of wind turbines?

    <p>The vector sum of incident wind velocity and blade linear velocity</p> Signup and view all the answers

    What is the result of large angles of incidence in wind turbines?

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

    Which method of energy storage involves heating water using the power output of wind turbines?

    <p>Thermal energy</p> Signup and view all the answers

    What is a major environmental impact of wind turbines on bird life?

    <p>Birds are killed when they fly into the rotating blades</p> Signup and view all the answers

    What is the purpose of yaw and tilt control in modern wind turbines?

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

    What is the purpose of pitch control in wind turbines?

    <p>To regulate the pitch of rotor blades</p> Signup and view all the answers

    What is the purpose of an eddy current braking system in wind turbines?

    <p>To control speeds during high wind conditions</p> Signup and view all the answers

    What is the primary benefit of variable speed drive systems in wind turbines?

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

    What has enabled the production of large-sized rotor blades at a low cost?

    <p>High-strength fiber composites</p> Signup and view all the answers

    What is the approximate energy payback period of a wind turbine?

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

    What is the primary advantage of larger wind turbines?

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

    What is the purpose of pitch control in wind turbines?

    <p>To improve the efficiency of energy extraction</p> Signup and view all the answers

    What is the component of total force parallel to the direction of airflow called?

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

    What is the component of the total force on the body in the direction perpendicular to airflow called?

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

    What is the purpose of the axial force in a wind turbine?

    <p>To be balanced by a suitable reaction force</p> Signup and view all the answers

    What is the shape of the aero foil that has a small drag force and a large lift force?

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

    What is the main difference between a horizontal axis wind turbine (HAWT) and a vertical axis wind turbine (VAWT)?

    <p>The axis of rotation</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 using 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 apply brakes automatically if the wind speed exceeds the designed speed</p> Signup and view all the answers

    Which type of rotor is suitable for applications requiring high starting torque, such as piston pumps?

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

    What is the typical shape of the blades in a vertical axis wind turbine?

    <p>Curved and thin, similar to an eggbeater</p> Signup and view all the answers

    What is the main advantage of the Darrieus rotor over the S-rotor?

    <p>Higher power coefficient and tip speed ratio</p> Signup and view all the answers

    What is the major limitation of the cup type rotor?

    <p>It cannot extract enough energy from winds</p> Signup and view all the answers

    What is the main advantage of the S-rotor over other types of rotors?

    <p>It can extract power even from low-speed winds</p> Signup and view all the answers

    Why is the Darrieus rotor not self-starting?

    <p>It has full directional symmetry</p> Signup and view all the answers

    What is the purpose of energy storage in wind turbines?

    <p>To meet the varying loads of customers</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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    Description

    Learn about wind energy, its relation to solar energy, and how it is harnessed. This quiz covers the basics of wind energy, including its generation and availability.

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