Wind TurbinesBY:

RAHEEL AHMADMech Engg.06-mech-28(RCET GJW)

TOPIC:

Outline

• Wind Turbines• Why Wind – causes?• How Wind Works?• How Wind Turbine Works?• Types & Sizes of Wind Turbines• Inside the Wind Turbine• Potential Turbine Power• Terms used in Wind Turbine• Advantages & Disadvantages

Wind Turbines

A wind turbine is a rotating machine which converts the kinetic energy in wind into mechanical energy.

If the mechanical energy is used directly by machinery, such as a pump or grinding stones, the machine is usually called a windmill. If the mechanical energy is then converted to electricity, the machine is called a wind generator, wind turbine, wind power unit (WPU), wind energy converter (WEC), or aero generator.

Why wind Energy – Causes?

Most of our electricity is generated with non-renewable resources:

-Coal-Natural Gas-Uranium for nuclear-power

Energy

Why ?• COAL

– Mine & transport coal burn coal boil water make steam steam pushes turbine turbine coupled to generator

• NATURAL GAS– Drill for & transport gas burn gas

push turbine turbine coupled to generator

• NUCLEAR POWER– Mine & transport uranium uranium

gets hot & boils water make steam steam pushes turbine turbine coupled to generator

• WIND POWER– Wind pushes turbine turbine

coupled to generator

Wind is a form of solar energy. Winds are caused by the uneven heating of the atmosphere by the sun, the irregularities of the earth's surface, and rotation of the earth.

Wind

Wind Energy

The terms wind energy or wind power describes the process by which the wind is used to generate mechanical power or electricity. Wind turbines convert the kinetic energy in the wind into mechanical power

Wind Turbine

How Wind Turbine Works ?So how do wind turbines make electricity?

A wind turbine works the opposite of a fan.

The wind turns the blades, which spin a shaft, which connects to a generator and

makes electricity.

This aerial view of a wind power plant shows how a group of wind turbines can make electricity for the utility grid. The electricity is sent through transmission and distribution lines to homes, businesses, schools, and so on.

Aerodynamics of Wind Turbine Blades•Forces are transmitted from a moving fluid to an object in the flow stream

–Lift = the force component perpendicular to the original flow direction–Drag = the force component in line with the original flow direction

Lift

Drag

http://www.grc.nasa.gov/WWW/K-12/airplane/newton3.html

How Wind Works ?

LIFT AND DRAG• Old-fashioned windmills

use DRAG• DRAG devices are

pushed by the wind• Modern wind turbines

(not windmills) use LIFT• LIFT devices work like

airplane wings• This is why modern

wind turbines have 3 blades

Wind – what causes it ?Wind Flow Over an Air Foil Generates LIFT

Inside Wind Turbine

Inside Wind Turbine

Yaw system

Types of Wind TurbineTurbines can be categorized into two overarching classes based on the orientation of the rotor.

1.Vertical Axis 2.Horizontal Axis

Types of Wind Turbine

1.Vertical Axis Wind Turbine

• Savonius• Darrieus

A type of wind turbine in which the axis of rotation is perpendicular to the wind stream and the ground .

Vertical-axis wind turbines fall into two major categories: 

Vertical axis turbines work whatever direction the wind is blowing, but require a lot more ground space to support their guy wires than horizontal axis wind turbines.

Savonius Wind Turbine

The Savonius is a drag-type VAWT which operates in the same way as a cup anemometer

•15 % efficiency

•Applications

Cup Anemometer

An Anemometer is a wind speed measuring device.

Cup Anemometer

Darrieus Wind Turbines A Darrieus is a type of vertical axis wind turbine (VAWT) generator.

Unlike the Savonius wind turbine, the Darrieus is a lift-type VAWT. Rather than collecting the wind in cups dragging the turbine around, a Darrieus uses lift forces generated by the wind hitting aerofoil to create rotation.

Lift vs. Drag VAWTsLift Device

“Darrieus”– Low solidity,

aerofoil blades– More efficient

than drag device

Drag Device “Savonius”– High solidity, cup

shapes are pushed by the wind

– At best can capture only 15% of wind energy

Horizontal Axis wind Turbine

Horizontal axis turbines (more common) need to be aimed directly at the wind.

A wind turbine in which the axis of the rotor's rotation is parallel to the wind stream and the ground.

The wind passes over both surfaces of the airfoil shaped blade but passes more rapidly over the upper side of the airfoil. The pressure differential between top and bottom surfaces results in aerodynamic lift like aeroplane blades

HAWT

•Foundation•Tower•Nacelle•Rotor•Turbine blades

Main Components

Common HAWT Construction

Rotor

• Blades are connected to a hub, which is connected to a shaft• Rotational speed will depend on blade geometry, number of blades,

and wind speed (40 to 400 revolutions per minute typical speed range)

• Gear box needed to increase speed to 1200-1800 RPM for generator

TowersLattice tower

Guyed Pole Tower

Concrete tower

Tubular steel towers

Nacelle

Types Of HAWTIt has two basic types

• Upwind Wind Turbine

• Downwind Wind Turbine

Upwind Wind Turbine• A type of wind turbine in which the rotor faces the

wind. The wind starts bending away from the tower

before it reaches the tower itself.

• The power from the wind turbine drops slightly.

• The basic drawback of upwind designs is that the rotor needs to be made rather inflexible, and placed at some distance from the tower.

• In addition an upwind machine needs a yaw mechanism to keep the rotor facing the wind.

Downwind Wind Turbine• A horizontal-axis wind turbine in which the rotor is downwind (i.e. on the lee side) of the tower.

• They may be built without a yaw mechanism.

• The rotor may be made more flexible. So the blades will bend at high wind speeds.

Number of Blades

Single Blade

Captures 10% less energy than two blade design

Double Blade

Capture 5% less energy than three blade designs

Number of Blades - Three

Increase in Number of Turbine Blade•Number of blades

–Increasing the number of blades tends to increase the aerodynamic efficiency–Increasing the number of blades increases the cost (material and manufacturing–Turbines with fewer blades tend to run most efficientlyat lower tip speed ratios(ratio of tip speed to wind speed)

http://en.wikipedia.org/wiki/Wind_turbine_design

Blade Composition

Wood

-Strong, light weight, cheap, abundant, flexible-Popular on do-it yourself turbines

Blade Composition

• Steel– Heavy & expensive

• Aluminum– Lighter-weight and

easy to work with– Expensive– Subject to metal

fatigue

Metal

Development of HAWT

SPEED n 20 17 13 5 – 15 3 – 10 rpm

Horisontal-Axis Wind Turbines

HAWT vs. VAWT

Multibrid M5000•Power output: 5 MW•Diameter: 116 m.•Turbine speed: 5,9 -14,8 rpm

•Masses:  •Blade: 16.500 kg •Hub: 60.100 kg •Nacelle: 199.300 kg 

Old Fashioned Turbines

The Persian windmill

The Chinese wind wheel

Wind Turbine Sizes• “SMALL”

– Residential use– 20 kW or less

• “MEDIUM”– Commercial use– 20 kW – 660 kW

• “LARGE”– Utility-scale use– 660 kW – 2+

MW

Wind Energy and Power• Atmospheric pressure differences

accelerate and impart kinetic energy into the air

• Wind energy conversion machines (WEC) convert wind energy into electrical or mechanical forms

• How much power can we extract?

time

)()(

time

K.E. Power

22

1 velocitymass

velocityareadensitytime

mass

2)()( Power

33

21

AVvelocityareadensity

Wind Turbine Size-Power Comparison

Power output

0

1 000

2 000

3 000

4 000

5 000

6 000

7 000

8 000

9 000

10 000

0 5 10 15 20 25

Wind Speed [m/s]

Po

wer

[kW

]

Growth of Wind Energy Capacity Worldwide

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06

MW

Ins

talle

d

Year

Jan 2003 Cumulative MW

Rest of World = 2,803

North America = 5,018

Europe = 21,319

Sources: BTM Consult Aps, March 2001

Windpower Monthly, January 2003

Actual Projected

Rest of World Rest of World

North America North America

Europe Europe

Tip-Speed Ratio

Tip-speed ratio is the ratio of the speed of the rotating blade tip to the speed of the free stream wind.

There is an optimum angle of attack which creates the highest lift to drag ratio.

Because angle of attack is dependant on wind speed, there is an optimum tip-speed ratio

ΩRV

TSR =

ΩR

R

Where,

Ω = rotational speed in radians /sec

R = Rotor Radius

V = Wind “Free Stream” Velocity

Rotor Solidity

Solidity is the ratio of total rotor planform area to total swept area

Low solidity (0.10) = high speed, low torque

High solidity (>0.80) = low speed, high torque

R

A

a

Solidity = 3a/A

Swept AreaThe area through which the rotor blades of a wind turbine spin, as seen when directly facing the center of the rotor blades. The power output of a wind turbine is directly related to the swept area of its blades

Advantages Of Wind Turbine

Environmental Economic Development No air pollution Wind energy is renewable No greenhouse gasses Expanding Wind Power development

brings jobs to rural communities

Disadvantages

May create a lot of noise.

Wind can never be predicted.

Wind energy depends upon the wind in an area and therefore is a variable source of energy.

It covers a large area.