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EE4511 Sustainable Energy

Systems: Part II

Dr. Panida Jirutitijaroen

Department of Electrical and Computer Engineering

9/29/2010 1

Lecture1: Types of Wind turbine, Power

in the Wind

Lecture Notes on Sustainable Energy Systems by Dr. Panida Jirutitijaroen

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Announcement

Start reading chapter 6.

This lecture covers materials from section 6.1

to 6.5.

Tutorial problems are problems 6.2, 6.4, 6.5,

6.8, 6.12

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Outline

Types of wind turbine

Power in the wind

Power extractedfrom the wind


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TYPE OF WIND TURBINE

Horizontal axis wind turbinesVertical axis wind turbines

How does it work?

Inside wind turbine


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Wind Power System Terminology

Wind-driven generator

Wind generator

Wind turbine Wind-turbine generator (WTG)

Wind energy conversion system (WECS)


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Types of Wind Turbine


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Horizontal Axis

Upwind turbine

Complex yaw control

system.

Keep blade facing wind. Operate more smoothly.

Deliver more power.

Downwind turbine

Let the wind control left-

right motion (the yaw).

Orient itself correctly towind direction.

Wind shadowing effect by

the tower, cause the blade

to flex. Increase noise and reduce

power output.


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Number of Blades

Multi-blade windmill need high starting torque

and low wind speed for continuous water

pumping function.

As rpm increases, turbulence caused by oneblade affects efficiency of the blade that follows

Fewer blades allow the turbine to spin faster =>

smaller generator. Two and three blades are the most common in

modern wind turbine.


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http://www.wind-energy-the-facts.org/images/fig/chap1/3-4.jpg http://www.climatechangeconnection.org/Solutions/Windenergy.ht

http://www.sti.nasa.gov/tto/Spinoff2009/images/Aerostar_2.jpg

http://www.windpowerengineering.com/wp-content/uploads/2009/07/windflow-Te-Rere-Hau-windfarm-300x200.jpg

http://www.wind-energy-the-facts.org/images/fig/chap1/3-4.jpghttp://www.climatechangeconnection.org/Solutions/Windenergy.htmhttp://www.sti.nasa.gov/tto/Spinoff2009/images/Aerostar_2.jpghttp://www.windpowerengineering.com/wp-content/uploads/2009/07/windflow-Te-Rere-Hau-windfarm-300x200.jpghttp://www.windpowerengineering.com/wp-content/uploads/2009/07/windflow-Te-Rere-Hau-windfarm-300x200.jpghttp://www.windpowerengineering.com/wp-content/uploads/2009/07/windflow-Te-Rere-Hau-windfarm-300x200.jpghttp://www.windpowerengineering.com/wp-content/uploads/2009/07/windflow-Te-Rere-Hau-windfarm-300x200.jpghttp://www.windpowerengineering.com/wp-content/uploads/2009/07/windflow-Te-Rere-Hau-windfarm-300x200.jpghttp://www.windpowerengineering.com/wp-content/uploads/2009/07/windflow-Te-Rere-Hau-windfarm-300x200.jpghttp://www.windpowerengineering.com/wp-content/uploads/2009/07/windflow-Te-Rere-Hau-windfarm-300x200.jpghttp://www.windpowerengineering.com/wp-content/uploads/2009/07/windflow-Te-Rere-Hau-windfarm-300x200.jpghttp://www.windpowerengineering.com/wp-content/uploads/2009/07/windflow-Te-Rere-Hau-windfarm-300x200.jpghttp://www.windpowerengineering.com/wp-content/uploads/2009/07/windflow-Te-Rere-Hau-windfarm-300x200.jpghttp://www.windpowerengineering.com/wp-content/uploads/2009/07/windflow-Te-Rere-Hau-windfarm-300x200.jpghttp://www.windpowerengineering.com/wp-content/uploads/2009/07/windflow-Te-Rere-Hau-windfarm-300x200.jpghttp://www.windpowerengineering.com/wp-content/uploads/2009/07/windflow-Te-Rere-Hau-windfarm-300x200.jpghttp://www.windpowerengineering.com/wp-content/uploads/2009/07/windflow-Te-Rere-Hau-windfarm-300x200.jpghttp://www.sti.nasa.gov/tto/Spinoff2009/images/Aerostar_2.jpghttp://www.climatechangeconnection.org/Solutions/Windenergy.htmhttp://www.wind-energy-the-facts.org/images/fig/chap1/3-4.jpghttp://www.wind-energy-the-facts.org/images/fig/chap1/3-4.jpghttp://www.wind-energy-the-facts.org/images/fig/chap1/3-4.jpghttp://www.wind-energy-the-facts.org/images/fig/chap1/3-4.jpghttp://www.wind-energy-the-facts.org/images/fig/chap1/3-4.jpghttp://www.wind-energy-the-facts.org/images/fig/chap1/3-4.jpghttp://www.wind-energy-the-facts.org/images/fig/chap1/3-4.jpghttp://www.wind-energy-the-facts.org/images/fig/chap1/3-4.jpghttp://www.wind-energy-the-facts.org/images/fig/chap1/3-4.jpg

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Vertical Axis

http://www.youtube.com/watch?v=4uJCiJmVbjM&feature=player_embedded http://www.youtube.com/watch?v=-rQUdRMTnyM&feature=player_embedded

http://www.youtube.com/watch?v=NxMh18SGhyA&feature=player_embedded http://www.youtube.com/watch?v=fqvMjOKKjpU&feature=player_embedded

http://www.youtube.com/watch?v=4uJCiJmVbjM&feature=player_embeddedhttp://www.youtube.com/watch?v=-rQUdRMTnyM&feature=player_embeddedhttp://www.youtube.com/watch?v=NxMh18SGhyA&feature=player_embeddedhttp://www.youtube.com/watch?v=fqvMjOKKjpU&feature=player_embeddedhttp://www.youtube.com/watch?v=fqvMjOKKjpU&feature=player_embeddedhttp://www.youtube.com/watch?v=NxMh18SGhyA&feature=player_embeddedhttp://www.youtube.com/watch?v=-rQUdRMTnyM&feature=player_embeddedhttp://www.youtube.com/watch?v=-rQUdRMTnyM&feature=player_embeddedhttp://www.youtube.com/watch?v=-rQUdRMTnyM&feature=player_embeddedhttp://www.youtube.com/watch?v=4uJCiJmVbjM&feature=player_embedded

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Inside Wind Turbine

http://www1.eere.energy.gov/multimedia/video_wind_turbines.html

How Does it Work?

http://www1.eere.energy.gov/multimedia/video_wind_turbines.htmlhttp://www1.eere.energy.gov/multimedia/video_wind_turbines.html

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POWER IN THE WIND

Power densityTemperature correction for air density

Altitude correction for air density

Impact of tower height


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Power in the Wind

Kinetic energy

?9/29/2010 13Lecture Notes on Sustainable Energy Systems by Dr. Panida Jirutitijaroen

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Power Density

Mass flow rate:

= Air density (kg/m) = 1.225 kg/m at 15C and 1 atm

is power in the wind (watts)


Power density (specific power) = power per square meter

(Watts/m)

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Wind in the US

http://www1.eere.energy.gov/windandhydro/wind_potential.html

http://www1.eere.energy.gov/windandhydro/wind_potential.htmlhttp://www1.eere.energy.gov/windandhydro/wind_potential.html

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Observations from Power Equation

Power in the wind depends on,

Air density,

Area that wind flow through (i.e. swept area of

the turbine rotor), and

Wind speed.

Power increases as the cube of wind speed.

Will it be correct to calculate power using

average wind speed?


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Example 6.1

Compare the energy at 15C, 1 atm pressure,

contained in 1 m of the following wind

regimes:

a. 100 hours of 6-m/s winds (13.4 mph),

b. 50 hours at 3 m/s plus 50 hours at 9 m/s (i.e.,

an average wind speed of 6 m/s)


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Power VS Wind Speed


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Power VS Swept Area

Power increases as proportional to swept area

of the rotor.

This implies that power is proportional to

square of the diameter; the bigger, the better.

This explains economies of scale of wind

turbines.


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Observations from Power Equation

Power in the wind depends on,

Air density,

Area that wind flow through (i.e. swept area of

the turbine rotor), and

Wind speed.


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Air Density

At 15C and 1 atmosphere, = 1.225 kg/m.


Density = weight/volume,

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Ideal Gas Law

Air density varies according to ideal gas law,

P: absolute pressure (atm)

V: volume (m)

n: mass (mol)

R: ideal gas constant (matmKmol)

T: absolute temperature (K, K = C +273.13 )

9/29/2010 Lecture Notes on Sustainable Energy Systems by Dr. Panida Jirutitijaroen 22

Intuitive idea about ideal gas law: http://www.youtube.com/watch?v=WScwPIPqZa0
http://www.youtube.com/watch?v=WScwPIPqZa0http://www.youtube.com/watch?v=WScwPIPqZa0

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Air Density VS Temperature

RT

P

V

n

Molecular weight of air can be approximated. Air is a mix of molecules,

78.08% Nitrogen (N = 28.02), 20.95% Oxygen (O = 28.02), 0.93% Argon (Ar

= 39.95), 0.035% Carbon dioxide (CO = 44.01), 0.0018% Neon (Ne = 20.18).

Equivalent molecular weight of air is 28.97.


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Air Density VS Altitude

Air density also depends on

atmospheric pressure.

Atmospheric pressure is a

function of altitude.

g = gravitational constant (9.806 m/s)


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Air Pressure VS Altitude

Assume temperature constant throughout the air column,


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Example 6.3

Find the air density

(a), at 15C (288.15 K), at an elevation of 2000 m

(6562 ft).

(b) find it assuming an air temperature of 5C at2000 m.


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Temperature and Altitude Corrections


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Impact of Tower Height

Wind speed near the ground is greatly

affected by the friction that air experiences.

Smooth surface, such as sea --> less friction.

Rough surface, such as city with tall buildings

--> more friction.

Wind speed as a function of,

Height,

Earths surface.


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Characterized by (some) Law

Power law, often used

in US.

H = reference height of

10m.

v = reference wind

speed at H.

= friction coefficient

Alternative law used in

Europe.

z = roughness length

These are just approximation, nothing is better than

actual site measurement!!9/29/2010 29Lecture Notes on Sustainable Energy Systems by Dr. Panida Jirutitijaroen

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Friction Coefficient


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Roughness Class


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Wind Speed and Power Ratio


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Example 6.5

An anemometer mounted at a height of 10 m

above a surface with crops, hedges, and

shrubs shows a wind speed of 5 m/s. Estimate

the wind speed and the specific power in thewind at a height of 50 m. Assume 15C and 1

atm of pressure.


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Example 6.6

A wind turbine with a 30-mrotor diameter is mountedwith its hub at 50 m abovea ground surface that is

characterized by shrubsand hedges. Estimate theratio of specific power inthe wind at the highest

point that a rotor blade tipreaches to the lowest pointthat it falls to.

9/29/2010 34

The resulting flexing of a blade can increase the noise and may contribute to blade fatigue,

which can ultimately cause blade failure.


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POWER EXTRACTED FROM THEWIND

Rotor efficiency

Maximum rotor efficiency

Tip-speed ratio


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Albert Betzs Formulation

9/29/2010 36

Steam Tube

Albert Betz,

German physicist, 1885-1968

That waseasy!


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Power Extracted from the Wind

9/29/2010 37

Assume that the velocity of wind vb is just the average of the

upwind and downwind speed,

Denote the ratio between upwind and downwind speed by

Substitute vd, then we have,


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Rotor Efficiency

9/29/2010 38

Define Rotor efficiency as,

Fundamental relationship for

power delivered by rotor,


How should we design so that

we can have better rotor

efficiency?

We can find maximum possible rotor efficiency!

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Maximum Rotor Efficiency


The blade efficiency will be maximum if it shows the windto one-third of the upwind speed,

We can now find the maximum rotor efficiency,

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Betzs Law

Maximum theoretical efficiency

of a rotor is 59.3%.

Sometimes called Betz efficiency

How close are modern wind

turbine to this Betz limit?

Around 80% of the limit, 45-50%


See how cool

that is?

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Tip-Speed Ratio

For a given wind speed,rotor efficiency is afunction of the rate atwhich a rotor turn. Rotor turns too slow

letting too much windpass -> efficiency drop.

Rotor turns too fastcausing turbulence ->efficiency drop.

TSR is the speed atrotor tip divided by thewind speed.


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Example 6.7

A 40-m, three-bladed wind turbine produces 600kW at a wind speed of 14 m/s. Air density is thestandard 1.225 kg/m3. Under these conditions,

a. At what rpm does the rotor turn when it operateswith a TSR of 4.0?

b. What is the tip speed of the rotor?

c. If the generator needs to turn at 1800 rpm, whatgear ratio is needed to match the rotor speed to thegenerator speed?

d. What is the efficiency of the complete wind turbine(blades, gear box, generator) under these conditions?


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Summary

Types of wind turbine

Vertical axis VS Horizontal axis

Power in the wind

As a function of temperature and altitude Impact of tower height and ground surface on

wind speed and power.

Power extractedfrom the wind Rotor efficiency

Tip-speed ratio


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Next Lecture

Start working on problem 6.2.

Review todays lecture.

Read chapter 6.

Next lecture will cover section 6.6-6.7.

Wind turbine generator

Speed control

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