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Questions and Answers
What is the primary force behind global winds?
What is the direction of the global winds?
How does the wind energy originate?
What happens to the direction of local winds at night?
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What is the purpose of windmills or turbines?
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What is the primary reason for air currents moving to the hill slope during the day?
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What is the purpose of an anemometer?
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What is the term used to describe the rate of change of wind speed with height?
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What is the typical height above which wind speed becomes uniform?
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What is a crucial consideration when selecting a site for a wind turbine?
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What is the purpose of studying topography in the context of wind turbines?
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What is the definition of solidity in the context of wind turbines?
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What is the purpose of pitch angle or blade setting angle in wind turbines?
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What is the relative velocity (vr) in the context of wind turbines?
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What is the result of large angles of incidence in wind turbines?
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Which method of energy storage involves heating water using the power output of wind turbines?
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What is a major environmental impact of wind turbines on bird life?
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What is the purpose of yaw and tilt control in modern wind turbines?
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What is the purpose of pitch control in wind turbines?
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What is the purpose of an eddy current braking system in wind turbines?
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What is the primary benefit of variable speed drive systems in wind turbines?
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What has enabled the production of large-sized rotor blades at a low cost?
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What is the approximate energy payback period of a wind turbine?
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What is the primary advantage of larger wind turbines?
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What is the purpose of pitch control in wind turbines?
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What is the component of total force parallel to the direction of airflow called?
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What is the component of the total force on the body in the direction perpendicular to airflow called?
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What is the purpose of the axial force in a wind turbine?
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What is the shape of the aero foil that has a small drag force and a large lift force?
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What is the main difference between a horizontal axis wind turbine (HAWT) and a vertical axis wind turbine (VAWT)?
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What is the primary function of the gearbox in a wind turbine?
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What is the main advantage of using a vertical axis wind turbine?
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What is the purpose of electromagnetic brakes in a wind turbine?
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Which type of rotor is suitable for applications requiring high starting torque, such as piston pumps?
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What is the typical shape of the blades in a vertical axis wind turbine?
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What is the main advantage of the Darrieus rotor over the S-rotor?
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What is the major limitation of the cup type rotor?
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What is the main advantage of the S-rotor over other types of rotors?
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Why is the Darrieus rotor not self-starting?
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What is the purpose of energy storage in wind turbines?
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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.
