Betz's law indicates the maximum power that can be extracted from the wind, independent of the design of a wind turbine in open flow. It was published in 1919, by the German physicist Albert Betz.[1] The law is derived from the principles of conservation of mass and momentum of the air stream flowing through an idealized "actuator disk" that extracts energy from the wind stream. According to Betz's law, no turbine can capture more than 16/27 (59.3%) of the kinetic energy in wind. The factor 16/27 (0.593) is known as Betz's coefficient. Practical utility-scale wind turbines achieve at peak 75% to 80% of the Betz limit.[2][3] The Betz limit is based on an open disk actuator. If a diffuser is used to collect additional wind flow and direct it through the turbine, more energy can be extracted, but the limit still applies to the cross-section of the entire structure.A wind turbine is a device that converts kinetic energy from the wind into electrical power. The term appears to have migrated from parallel hydroelectric technology (rotary propeller). The technical description for this type of machine is an aerofoil-powered generator. The result of over a millennium of windmill development and modern engineering, today's wind turbines are manufactured in a wide range of vertical and horizontal axis types. The smallest turbines are used for applications such as battery charging for auxiliary power for boats or caravans or to power traffic warning signs. Slightly larger turbines can be used for making contributions to a domestic power supply while selling unused power back to the utility supplier via the electrical grid. Arrays of large turbines, known as wind farms, are becoming an increasingly important source of renewable energy and are used by many countries as part of a strategy to reduce their reliance on fossil fuels.

1. Wind Turbines
 A Journey into an Understanding of theA Journey into an Understanding of the
Technology used to Harness the power of WindTechnology used to Harness the power of Wind

2. Policy Perspective
 On October 20On October 20thth
, 1956 Israeli forces swept into, 1956 Israeli forces swept into
Egypt and overcame local opposition as they racedEgypt and overcame local opposition as they raced
for the Suez Canalfor the Suez Canal
 British and French forces intervened as part of aBritish and French forces intervened as part of a
“peace initiative” allowed the European powers to“peace initiative” allowed the European powers to
occupy and control the Suez Canal again.occupy and control the Suez Canal again.
 The conflict cost over 1,000 Egyptians their livesThe conflict cost over 1,000 Egyptians their lives

3. Denmark
 In 2001, the Danish Wind industry produced 4.3In 2001, the Danish Wind industry produced 4.3
Terawatt Hours (TWh) of electricityTerawatt Hours (TWh) of electricity
 1 TWh (Terawatt Hour) = 1 trillion Watt Hours1 TWh (Terawatt Hour) = 1 trillion Watt Hours
(1,000,000,000,000)(1,000,000,000,000)
 1 million barrels of oil produce can produce 731 million barrels of oil produce can produce 73
Gigawatt Hours (GWh) of electricityGigawatt Hours (GWh) of electricity
 1 GHw = 1 billion Watt Hours (1,000,000,000)1 GHw = 1 billion Watt Hours (1,000,000,000)
 Denmark used wind energy to create theDenmark used wind energy to create the
equivalent of 59,000,000 barrels of oil in 2001equivalent of 59,000,000 barrels of oil in 2001

4. Introduction to Wind
 Wind is caused by the energy radiated to the EarthWind is caused by the energy radiated to the Earth
by the Sunby the Sun
 Nuclear reactions take place inside the sun’s core,Nuclear reactions take place inside the sun’s core,
where the temperature is 1 x 10where the temperature is 1 x 1077
KK
 This produces 4 x 10This produces 4 x 102626
joules of electromagneticjoules of electromagnetic
radiation every second that is radiated into spaceradiation every second that is radiated into space
 Some of it reaches the earth:Some of it reaches the earth:
 strikes the equator directly (giving it the most radiation)strikes the equator directly (giving it the most radiation)
 diffuses along the Northern and Southern Hemispherediffuses along the Northern and Southern Hemisphere

the poles receive the lowest amount of radiationthe poles receive the lowest amount of radiation

5. Creation of Seasons

6. Wind con’t
 The radiation from the sun heats the Earth'sThe radiation from the sun heats the Earth's
surfacesurface
 Heating process creates temperature differencesHeating process creates temperature differences
between the:between the:
 Land,Water, AirLand,Water, Air
due to their different physical propertiesdue to their different physical properties
• I.e. densityI.e. density
• AAffects their respective abilities to absorbffects their respective abilities to absorb
heatheat

7. Process of Wind Creation
 Wind “current of air (airWind “current of air (air
moving from an A of high P tomoving from an A of high P to
an A of low Pan A of low P
 hot air rises, it expands,hot air rises, it expands,
becomes less dense, and is thenbecomes less dense, and is then
replaced by denser, cooler airreplaced by denser, cooler air
 Heated air rises from equatorHeated air rises from equator
 moves north and south in themoves north and south in the
upper levels of the atmosphereupper levels of the atmosphere
 circulates above cooler aircirculates above cooler air
 At roughly 30° latitude CoriolisAt roughly 30° latitude Coriolis
Effect stops air.Effect stops air.
 high pressure areahigh pressure area
 The Coriolis Effect “ theThe Coriolis Effect “ the
tendency for any movingtendency for any moving
body on or above thebody on or above the
earth's surface to driftearth's surface to drift
sideways from its coursesideways from its course
because of the earth'sbecause of the earth's
rotationrotation
 Northern HemisphereNorthern Hemisphere
deflection rightdeflection right
 Southern Hemisphere it isSouthern Hemisphere it is
to the leftto the left

8. Coriolis Effect: 3 Cell Effect

9. Harnessing the Wind

10. Wind Turbines
 ““rotary engine in which the kinetic energy of arotary engine in which the kinetic energy of a
moving fluid is converted into mechanical energymoving fluid is converted into mechanical energy
by causing a bladed rotor to rotate”by causing a bladed rotor to rotate”
 opposite of a fanopposite of a fan
 turbine blades spin from the wind and maketurbine blades spin from the wind and make
energy, instead of using energy to make windenergy, instead of using energy to make wind
 Wind rotates the turbine bladesWind rotates the turbine blades
spins a shaft connected to a generatorspins a shaft connected to a generator
The spinning of the shaft in the generatorThe spinning of the shaft in the generator
makes electricitymakes electricity

11. Construction: Wind Sheer
 Wind turbines, like windmills, are mounted on aWind turbines, like windmills, are mounted on a
tower to capture the most wind energytower to capture the most wind energy
 wind speed varies by heightwind speed varies by height
 wind current 100m above the ground dropped inwind current 100m above the ground dropped in
speed by 10% when its height declined to 50mspeed by 10% when its height declined to 50m
 property is known asproperty is known as wind sheerwind sheer
 wind speed increases in speed with height,wind speed increases in speed with height,
 due to friction at the Earth’s surfacedue to friction at the Earth’s surface
 The Hub heights of modern wind turbines, which produceThe Hub heights of modern wind turbines, which produce
600 to 1,500 kW of electricity, are usually 40 to 80 meters600 to 1,500 kW of electricity, are usually 40 to 80 meters
above groundabove ground

12. Internal Parts: The “Hub”

13. Turbines: Two Types
 Horizontal Axis Wind TurbinesHorizontal Axis Wind Turbines
 Vertical Axis Wind TurbinesVertical Axis Wind Turbines

14. Two Types
 Vertical Axis AdvantagesVertical Axis Advantages
 Can place generator onCan place generator on
groundground
 You don’t need a yawYou don’t need a yaw
mechanism for windmechanism for wind
angleangle
 DisadvantagesDisadvantages
 Lower wind speeds atLower wind speeds at
ground levelground level
 Less efficiencyLess efficiency
 Requires a “push”Requires a “push”
 Horizontal axis AdvantagesHorizontal axis Advantages
 Higher wind speedsHigher wind speeds
 Great efficiencyGreat efficiency
 DisadvantagesDisadvantages
 Angle of turbine isAngle of turbine is
relevantrelevant
 Difficult access toDifficult access to
generator for repairsgenerator for repairs

15. Energy: Kinetic to Electric
 Wind has kinetic energy: Energy of motionWind has kinetic energy: Energy of motion
 KE = ½ M * UKE = ½ M * U22
 The Mass (M) of Air per second isThe Mass (M) of Air per second is
 volume (V) multiplied by its density (D)volume (V) multiplied by its density (D)
• M = VDM = VD
• density of air = 1.2929 kilograms/mdensity of air = 1.2929 kilograms/m
 The mass of air per second (M)The mass of air per second (M)
 traveling though a hoop is the area of the hoop (A)traveling though a hoop is the area of the hoop (A)
 multiplied by speed of the wind per second (u)multiplied by speed of the wind per second (u)
 multiplied the density of air (D)multiplied the density of air (D)
• M = AuDM = AuD
 area of the hoop (A) is radius (r) squaredarea of the hoop (A) is radius (r) squared
• A =A = ПП rr22

16. Catching the Wind!
 Turbines catch the wind's energy with their propeller-likeTurbines catch the wind's energy with their propeller-like
bladesblades
 Usually, two or three blades are mounted on a shaft to form aUsually, two or three blades are mounted on a shaft to form a
rotorrotor
 The wind turbine blade acts an airplane wingThe wind turbine blade acts an airplane wing
 When the wind blows a pocket of low-pressure air forms onWhen the wind blows a pocket of low-pressure air forms on
the downwind side of the bladethe downwind side of the blade
 Air pressure = force exerted on an object by the weight ofAir pressure = force exerted on an object by the weight of
particles in airparticles in air
 measured in:measured in:
 Inches of MercuryInches of Mercury (“(“Hg),AHg),A
 Amospheres (Atm)Amospheres (Atm)
 Millibars (mb)Millibars (mb)
 1013.25 mb = 29.921013.25 mb = 29.92 ““Hg = 1.0 atm.Hg = 1.0 atm.[2][2] At standard or normalAt standard or normal
atmospheric pressure, and at 15° C, air usually weighs about 1.225atmospheric pressure, and at 15° C, air usually weighs about 1.225
kilograms per cubic meterkilograms per cubic meter
[[

17. Catching the Wind! Continued….
 When air pressure is low in one locality, such as the downwindWhen air pressure is low in one locality, such as the downwind
side of a wind turbine blade, air from another area will rush inside of a wind turbine blade, air from another area will rush in
to equal out the air pressureto equal out the air pressure
 The low-pressure air pocket created by the wind turbine bladeThe low-pressure air pocket created by the wind turbine blade
then pulls the blade toward it, causing the rotor to turnthen pulls the blade toward it, causing the rotor to turn
 This process is referred to as lift.This process is referred to as lift. The force of the lift isThe force of the lift is
actually much stronger than the wind's force against the frontactually much stronger than the wind's force against the front
side of the blade, which is called dragside of the blade, which is called drag
 The combination of lift and drag causes the rotor to spin like aThe combination of lift and drag causes the rotor to spin like a
propellerpropeller
 causes the spinning of the turbine’s shaft.causes the spinning of the turbine’s shaft.
 When shaft spins KE of movement is converted byWhen shaft spins KE of movement is converted by
generator into usable electricitygenerator into usable electricity

18. KE to Usable Energy

19. Bernoulli’s Principle
 Bernoulli’s PrincipleBernoulli’s Principle
 EnergyEnergyKineticKinetic
+ Energy+ EnergyPressurePressure
= Energy= EnergyPressurePressure
++
EnergyEnergyKineticKinetic
 Example:Example:
 If Energy KineticIf Energy Kinetic11
= (5), and Energy= (5), and Energy
PressurePressure11
= (11)= (11)
 and Energy Pressureand Energy Pressure22
drops to (1)drops to (1)
then Kinetic Energythen Kinetic Energy22
Increases to (15)Increases to (15)

20. Setup Types
 stand-alonestand-alone
 not connected to a power gridnot connected to a power grid
 power created is directly channeled into poweredpower created is directly channeled into powered
sitesite
 utility power gridutility power grid
 Stores energyStores energy
 connection must be availableconnection must be available
 Combined w/ a photovoltaic (solar cell) systemCombined w/ a photovoltaic (solar cell) system
 has solar cells mounted on it.has solar cells mounted on it.
 Solar cells - thin wafers of silicon which, whenSolar cells - thin wafers of silicon which, when
exposed to sunlight, produce…electric currentexposed to sunlight, produce…electric current

21. Efficiency
 large number of wind turbines are usually builtlarge number of wind turbines are usually built
close together to form what is referred to as a windclose together to form what is referred to as a wind
plantplant
 The world’s largest wind plant located off theThe world’s largest wind plant located off the
coast of Oregon has 450 wind turbinescoast of Oregon has 450 wind turbines
 generates 300 MWh of energygenerates 300 MWh of energy
 meets the needs of 70,000 homesmeets the needs of 70,000 homes
 This practice utilizes an area suited for windThis practice utilizes an area suited for wind
energy by deploying multiple unitsenergy by deploying multiple units

22. Limitations
 limit to the amount of energy that can be harnessed by anlimit to the amount of energy that can be harnessed by an
individual wind turbineindividual wind turbine
 The more kinetic energy that a wind turbine pulls out of theThe more kinetic energy that a wind turbine pulls out of the
wind, the more the wind will be slowed down as it leaveswind, the more the wind will be slowed down as it leaves
 If a designer tried to extract all the energy from the windIf a designer tried to extract all the energy from the wind
 air would move away with the speed zeroair would move away with the speed zero
 air prevented from entering the rotor of the turbineair prevented from entering the rotor of the turbine
 If the designer did the exact opposite and allowed the wind toIf the designer did the exact opposite and allowed the wind to
pass through the wind turbine without being hindered at all,pass through the wind turbine without being hindered at all,
again,again,
 energy will not be cultivated,energy will not be cultivated,
 since the rotor blades would not be spun, thesince the rotor blades would not be spun, the
 shaft wouldn’t spinshaft wouldn’t spin
 kinetic energy would not be converted into electricitykinetic energy would not be converted into electricity

23. Betz Law
 designer of a wind turbine must find an idealdesigner of a wind turbine must find an ideal
balance between these two extremesbalance between these two extremes
 Fortunately for wind energy advocates andFortunately for wind energy advocates and
enthusiasts there is a simple answer to thisenthusiasts there is a simple answer to this
dilemmadilemma
 Under Betz Law an ideal wind turbine would slowUnder Betz Law an ideal wind turbine would slow
down the wind by 2/3 of its original speed (thedown the wind by 2/3 of its original speed (the
capture of 59.6% of the wind’s speed).capture of 59.6% of the wind’s speed).

24. Site Limitations
 The direction that wind travels inThe direction that wind travels in
 angel of the turbine’s rotors areangel of the turbine’s rotors are
 important limitations and considerationsimportant limitations and considerations
 Wind at a site is being slowed down by eachWind at a site is being slowed down by each
turbineturbine
 limit to the amount of individual units a site canlimit to the amount of individual units a site can
supportsupport
 NIMBYNIMBY
 BirdsBirds

25. byby
M.V.V.AJAYM.V.V.AJAY