Wind Energy and Its Origins

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Questions and Answers

What is the primary force that produces global winds?

Movement of sailing ships across the ocean

Cooling of the air in touch with ocean water

Rotation of the earth on its axis

Differential heating of the earth's surface between the equator and polar regions (correct)

Why do cold winds move from polar regions to equatorial regions?

Due to the movement of sailing ships

Due to the uneven heating of the earth's surface

Due to the difference in temperature between the equator and polar regions (correct)

Due to the Coriolis force

What happens to the direction of local winds at night?

The direction of the wind is reversed (correct)

The direction of the wind remains the same

The speed of the wind increases

The wind stops blowing

What is wind energy a form of?

Indirect solar energy Signup and view all the answers

What is the purpose of a windmill or turbine?

To convert wind energy into mechanical energy Signup and view all the answers

What is the primary function of the yaw control system in a wind turbine?

To adjust the nacelle around the vertical axis to face the wind stream Signup and view all the answers

What is the advantage of a Vertical Axis Wind Turbine (VAWT) over a Horizontal Axis Wind Turbine (HAWT)?

It can accept wind from any direction, eliminating the need for a yaw control system Signup and view all the answers

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

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

What is the advantage of a multi-bladed rotor over a single-bladed rotor?

It has high solidity and can operate at low speeds Signup and view all the answers

What is the characteristic of the blades in a Vertical Axis Wind Turbine (VAWT)?

They are thin and curved shaped like an 'eggbeater' Signup and view all the answers

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

Lift force Signup and view all the answers

What is the purpose of the yaw control mechanism in a wind turbine?

To rotate the nacelle to face the wind direction Signup and view all the answers

What is the main advantage of a streamlined aero foil?

It has a lower drag force Signup and view all the answers

What is the primary difference between a horizontal axis wind turbine and a vertical axis wind turbine?

The axis of rotation Signup and view all the answers

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

It is simpler to construct and erect Signup and view all the answers

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

Thermal energy Signup and view all the answers

What is the primary advantage of a variable speed drive system over a fixed speed drive system?

It captures more power at various wind speeds Signup and view all the answers

What is a major environmental impact of wind turbines on ecosystems?

Disruption of natural wind patterns Signup and view all the answers

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

Increased fossil fuel prices Signup and view all the answers

What is the purpose of yaw control in wind turbines?

To shift the rotor axis out of wind direction Signup and view all the answers

What is the energy payback period of a wind turbine?

1 year Signup and view all the answers

What is the primary function of the stall control system in wind turbines?

To shift the blades to a position in which high winds cannot damage the machine Signup and view all the answers

Which of the following is a factor that has led to improved plant operations in wind turbines?

Field trials and experiences Signup and view all the answers

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

To control speeds during high wind conditions Signup and view all the answers

What is the purpose of yaw control in a wind turbine?

To change the direction of the rotor blades Signup and view all the answers

What causes air currents to move to the hill slope during the day and to the low-lying land during night in hilly areas?

The temperature difference between the hill slope and low-lying land Signup and view all the answers

What is the primary purpose of recording wind speed at three heights of 10, 50, and 150 m during strong winds?

To specify the nature of winds in these regions Signup and view all the answers

What is the primary function of topography in the context of wind turbines?

To channelize and speed up winds Signup and view all the answers

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

Wind shear Signup and view all the answers

At what height does the wind speed become uniform and is not affected by ground conditions?

2000 m Signup and view all the answers

What is the main difference between high-solidity rotors and low-solidity rotors?

The force used for rotation, drag or lift Signup and view all the answers

What is the primary consideration for selecting a site for a wind turbine?

High annual mean wind speed Signup and view all the answers

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

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

What is the relative velocity of wind with respect to the moving blade?

The vector sum of incident wind velocity and blade linear velocity Signup and view all the answers

What is the result of a large angle of attack on the airflow around an aero foil?

The airflow is separated from the aero foil Signup and view all the answers

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

Higher power coefficient and tip speed ratio Signup and view all the answers

Why is the Darrieus rotor not self-starting?

It has a low starting torque due to its symmetrical design Signup and view all the answers

What is the purpose of attaching S-rotors to the top and bottom of the Darrieus rotor shaft?

To help the Darrieus rotor start up Signup and view all the answers

Why is energy storage important for wind turbines?

To ensure a constant output of power Signup and view all the answers

What is a major drawback of the Evans rotor?

The blades have a fixed pitch 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 the forces that create global and local winds. Discover how the earth's surface and rotation influence wind patterns.