Wind Energy and Its Origin

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Questions and Answers

What is the primary reason for the formation of air currents in hilly areas?

Temperature difference between the hill slope and low-lying land (correct)

Difference in air pressure between the hill slope and low-lying land

Topography of the hill

Wind patterns in the region

What is the purpose of recording wind speed at three different heights?

To calculate the mean wind speed of a region

To determine the wind shear of a region

To specify the nature of winds in a region (correct)

To measure the wind direction

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

Wind height

Wind speed variation

Wind gradient

Wind shear (correct)

What is the term used to describe the atmosphere with uniform wind speed above the gradient height?

Free atmosphere Signup and view all the answers

What is the minimum distance required around a windmill to ensure no obstruction of wind?

S km Signup and view all the answers

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

Drag force Signup and view all the answers

In the context of wind turbines, what is the purpose of the yaw control mechanism?

To control the direction of the turbine towards the wind Signup and view all the answers

What is the primary advantage of a two-bladed rotor compared to a three-bladed rotor?

Smoother power output Signup and view all the answers

What is the name of the model that describes the area swept by the rotor as an expanding airstream tube?

Betz model Signup and view all the answers

What is the primary reason why axial force should be minimized in a wind turbine?

To reduce waste energy Signup and view all the answers

What is the primary function 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 using a yaw control system in HAWT?

To adjust the rotor blades according to wind direction Signup and view all the answers

What is the characteristic of a single-bladed rotor?

Simple construction with low cost, but producing more noise during operation Signup and view all the answers

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

VAWT eliminates the necessity of a yaw control system Signup and view all the answers

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

Curved and eggbeater-shaped Signup and view all the answers

What is the primary factor responsible for generating global winds?

The differential heating of the earth's surface at the equator and polar regions Signup and view all the answers

What is the Coriolis force responsible for in the context of global winds?

Forcing the winds towards the westerly direction Signup and view all the answers

What is the ultimate source of energy for wind energy?

Solar radiation Signup and view all the answers

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

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

What is the primary reason for the difference in wind direction between day and night in local winds?

The difference in temperature between land and water bodies Signup and view all the answers

What is the primary function of the rotor blades in a wind turbine?

To generate the requisite forces to turn the rotor Signup and view all the answers

What is the effect of a large angle of incidence on the airflow around the aero foil?

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

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

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

What is the result of resolving the total force exerted by the wind on the body in the direction parallel to airflow and perpendicular to the airflow?

Two forces, drag force and lift force 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

What is the purpose of considering the nearness to load centre when selecting a site for a wind turbine?

To reduce the cost of transmission of the generated power Signup and view all the answers

What is the main drawback of the Darrieus rotor?

It is not self-starting Signup and view all the answers

Why is the Savonious rotor used for applications where low power is required?

It can extract power from low-speed winds Signup and view all the answers

What is the main reason why wind turbines require energy storage?

Wind speed varies on hourly, daily, and seasonal basis Signup and view all the answers

What is the advantage of the Evans rotor over the Musgrove (H-shaped) rotor?

The blades have variable pitch Signup and view all the answers

What is the primary advantage of storing energy through electrolysis of water?

It allows for the storage of energy in the form of hydrogen and oxygen gases Signup and view all the answers

Which of the following environmental impacts of wind turbines is related to the disturbance of natural beauty?

Visual intrusion Signup and view all the answers

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

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

What is the primary reason for using eddy current braking system in windmills?

To control speeds so that windmills can perform at high wind conditions Signup and view all the answers

What is the primary advantage of storing energy through pumping water?

It enables the storage of energy in a high tank Signup and view all the answers

What is the primary function of a variable speed drive system in a wind turbine?

To capture maximum energy at various wind speeds Signup and view all the answers

Which of the following factors has contributed the most to the acceleration and development of wind power?

Improved materials for rotor blades Signup and view all the answers

What is the primary advantage of using larger wind turbines?

They generate more power at a lower cost Signup and view all the answers

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

To adjust the angle of the wind turbine blades Signup and view all the answers

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

1 year 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 factors that contribute to its origin, including global and local winds.