Chapter 4-Wind Energy

Wind Energy

Energy and Environment by Toossi

Outline History of Wind Power Global and Local Wind Patterns Wind Turbines

Maximum Theoretical Wind Power Turbine Efficiency Power Density Design Consideration: Size, Performance, Rotor, Tower

Height, Power Train Hybrid Systems Safety and Control

Power Quality On-shore and Off-shore Wind Turbines Summary

Energy and the Environment by Toossi

History of Wind Energy• Ancient Egyptians used

wind to sail ships on the Nile River.

• Persians used wind mills for baking and pumping water from the wells.

• American colonists used windmills used to grind wheat and corn.

• Germany and Denmark are taking the leads.


Persians invented the first practical windmills for grinding wheat and pumping water.

History…


Dutch horizontal wind turbine Brush windmill in Cleveland, Ohio Modern two-bladed wind turbine

Usage

Country % Total usage

Denmark 23Spain 8Germany 6India 3USA 0.4World 1


Wind Patterns Source

(1) Non-uniform heating of the Earth surface by the sun(2) Rotation of the Earth

Wind Patterns (1) Global winds(2) Sea and land breezes(3) Valley winds


Surface Heating


Global Wind


Coriolis Force

Geostrophic Winds

Sea-Land, and Valley-Mountain breezes

Sea - Land Breezes Valley - Mountain Breezes


Wind Rose A single, graphical

representation of speed, direction, and frequency of

occurrence.


Wind Turbines Wind turbines are devices that convert

the kinetic energy of wind into the mechanical energy of rotating blades.

Wind Turbine Classification: Aerodynamic

Drag type Lift type

Orientation of Axis of rotation VAWT (Vertical Axis Wind Turbine) HAWT (Horizontal Axis Wind Turbine)

Upwind Downwind


Wind Turbine Principle of operation


Wind Turbine Types


VAWT (Vertical Axis Wind Turbine) Features:

VAWT are designed to capture wind from any direction and therefore no yawing mechanisms are needed.

VAWTs could be of either a drag type or a lift type. Advantage: The heavy components (the gearbox,

generator, and controllers) can be placed near, or on, the ground where wind is weaker.

Disadvantages: not self-starting. Torque is continuously varied as the blades move into

and out of the wind Efficiencies are relatively smaller.


VAWT


Cup Savonius Darrieus Gyromills Windspire

HAWT (Horizontal Axis Wind Turbine)


Wind Turbine Generator Components Hub Gearbox Electrical

Generator Controller Cooling system


Maximum Theoretical Wind Power Energy delivered by a wind turbine, is

proportional to… Change in K.E. of air (mass) that is sweeping

through the rotor. Mass of increase with density and area of the blade.

The Power delivered by a wind turbine, is proportional to…

Air density Swept Diameter Blade, i.e. square of the blade

diameter Cube of Wind Velocity


Scaling (Example) A wind turbine (d=3m) generates 10

kW of power at wind speed of 4 m/s. How much power will it produce,

If the turbine diameter were increased to 6 m? If wind speed suddenly increased to 12 m/s? With the same wind conditions, would turbine

produce more power in winter or summer?


Turbine Efficiency


Geographical Classes

Wind classes and power density at 50 m heightWind Class

Wind Power Density (W/m2)

Average Wind Speed(m/s)

1 0-200 0-5.62 200-300 5.6-6.43 300-400 6.4-7.04 400-500 7.0-7.55 500-600 7.5-8.06 600-800 8.0-8.87 800-2000 8.8-11.0


Performance Wind Speed –

Power Curve

Wind Speed – Frequency Distribution


WT: Design Consideration Size of the Rotor Shape and Number of Blades Height of the Tower Gearbox Generator Control Mechanism


Rotor Size Criteria:

Application of wind turbine

Distribution of wind energy throughout the year

Manufacturing Transportation


The world’s largest wind turbine is now the Enercon E-126Rotor diameter = 126 meters (413 feet). Power = 7 megawatts (or 60 million kilowatt hours per year), enough to power about 5,000 German homes.

Image courtesy of Enercon Corporation.

Rotor = Blades + Hub HAWT

For a given wind speed and direction, the angle of attack remains positive throughout their complete rotation.

The blades are designed to maximize lift for a particular design point (rated velocity).

VAWT The angle of attack is changing constantly and

remains positive during one half of the rotation and negative during the second half.

Blades use a symmetrical profile, since there is no preferred direction.


How many Blades? Theoretically, only ONE. Greater the no. of blades, the more stable the turbines

are, but also are heavier and more expensive. Single-, and to some extent, double-blade turbines

cheaper but must operate at much higher speeds to capture the same amount of wind and are, therefore, noisier.

They also have low to moderate starting torque, which makes their operation difficult at very low wind speeds.

Multi-bladed rotors used in older designs are less efficient, but provide more torque and have been used,

traditionally, for pumping water, even at low wind speeds.

Most modern wind turbines use three blades.


Hybrid System

(a) (b)


Hybrid systems involving a variety of energy sources can be used to power remote villages and generate income for their owners. (a) Stand-alone, (b) Grid-connected.

Safety and Control Vibration

High wind speed Shut-off control mechanism Noise (Mechanical + Aerodynamic) Temperature

Air or Water cooling system Speed

Pitch and Yaw(tilt) Controller Stall Regulation


Wind Turbine Siting Wide areas with open

views in all direction Valleys and ridges Close to power grid Away from towns and

population centers


Off-shore wind farms


Advantages and DisadvantagesAdvantages• Clean• Renewable

Disadvantages• Intermittent• Wind speed not too slow, not too fast• Noise• Aesthetic• Dangers to birds


Future


Documents

Chapter 4-Wind Energy