chapter 6 renewable energy systems. wind energy
TRANSCRIPT
Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
Introduction Use of wind energy for human purposes entails the
conversion of the kinetic energy that is presentintermittently in the wind into mechanical energy, usuallyin the form of rotation of a shaft.
From there, the energy can be applied to mechanical workor further converted to electricity using a generator.
No location is continuously windy, and the power in thewind is highly variable, requiring provision both foralternative energy supplies during times of little or nowind, and means of protecting the wind energy conversiondevice from damage in times of extremely high wind.
World use of wind power has been growing rapidly as wellin recent years.
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Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
Early Wind Generators An early example:
Brush Electric Generator, Cleveland, OH, 1880s, 12kW Early adaptation of wind-powered mechanical pump to generatingelectricity
First attempt at > 1 MW turbine Smith-Putnam Turbine, Vermont, 1940s, 1.25 MW Failed prematurely, not repeated
Development of modern utility-scale turbine California, Denmark in 1970s and 1980s Experimentation with vertical axis turbines, but eventually settled onhorizontal axis design.
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Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
Total installed capacity, 2005 and 2010
Source: Global Wind Energy Consortium
Total = 59.1 GW Total = 195.0 GW
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Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
Classification of wind resource by wind speed range in m/s and mph at hub height of turbine
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Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering 6
Madison utility-scale wind farm with seven 1.5-MW turbines near Utica, New York.
Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
Not to scale
Main parts of a utility-scale wind turbine
Wind Turbines
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Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
“Windmill”- used to grind grain into flour (or pumpwater in Holland)
Can have be horizontal axis wind turbines (HAWT) orvertical axis wind turbines (VAWT)
Groups of wind turbines are located in what is calledeither a “wind farm” or a “wind park”
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Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
How Lift Based Turbines Extract Energy from Fluid
Bernoulli’s Principle - air pressure on top is lower thanair pressure on bottom because it has further to travel,creates lift
Airfoil – could be the wing of an airplane or the blade of a wind turbine
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Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
Angle of Attack, Lift, and DragIncreasing angle of attack increases lift, but it also increases drag
When angle of attack is too great, “stall” occurs where turbulence destroys the lift
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Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
Wind Turbines extract energy from the force of the wind on anaerofoil, in this case a turbine blade.
The relative motion between the air flow and the turbine blade,is the same as for the aircraft wing, but in this case the wind isin motion towards the turbine blades and the blades are passiveso that the external thrust provided by the moving air flow is inthe opposite direction to the thrust provided by the aircraftwing.
The turbine blades thus experience lift and drag forces, similarto the aircraft wing, which set the blades in motion transferringthe wind energy into the kinetic energy of the blades.
The turbine blades are connected to a single rotor shaft and theforce of the wind along the length of the blades creates a torquewhich turns the rotor.
As with aircraft wings, the magnitudes of the lift and drag onthe turbine blade are dependent on the angle of attack betweenthe apparent wind direction and the chord line of the blade.
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Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering 12
More energy can be extracted from wind using lift rather than drag, but this requires specially shaped airfoil surfaces, like those used on airplane wings.
Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
Lots of ideas, only a few good…
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Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
Vertical Axis Wind TurbinesDarrieus rotor - the only vertical axis machine with any
commercial successWind hitting the vertical blades (airfoils) generates lift
to create rotation
Advantages• No yaw (rotation about vertical axis)
control needed to keep facing into wind• Heavy machinery located on the ground
Disadvantage• Blades are closer to ground where
windspeeds are lower
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Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
Horizontal Axis Wind Turbines“Upwind” HAWT – blades are in front of (upwind of)
the tower
Most modern wind turbines are this type
Because blades are “upwind” of the tower Require active yaw control to keep facing into wind Operate more smoothly and deliver more power
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Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
Power in the WindConsider the kinetic energy of a “packet” of air with
mass m moving at velocity v
Divide by time and get power
The mass flow rate is
21KE2mv
21 passing though APower through area A 2m v
t
passing though A = = A m m vt
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Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
Power in the WindCombining we get
21Power through are A A 2
a v v
31P A2
v
P (Watts) = power in the windρ (kg/m3)= air density (1.225kg/m3 at 15˚C and 1 atm)A (m2)= the cross-sectional area that wind passes throughv (m/s)= windspeed normal to A (1 m/s = 2.237 mph)
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Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
Power increases as (wind speed)3
Doubling the wind speed increases the power by eight 1h x 20mph wind is same energy as 8h x 10 mph wind
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Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
Power in the Wind (cont.)Power in the wind is also proportional to A
For a conventional HAWT, A = (π/4)D2, so wind power isproportional to the blade diameter squared
Cost is roughly proportional to blade diameter
31P A 2
v
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Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
Maximum Rotor EfficiencyConsider wind passing though turbine: as energy extracted, air
slows down
2 212 dP m v v
ṁ = mass flow rate of air within stream tubev = upwind windspeedvd = downwind windspeed
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Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
Mass Flow RateAt the rotor with area A and, mass flow rate is
If velocity through the rotor vb is the average of upwindvelocity v and downwind velocity vd
bm Av
= 2 2
d dbv v v vv m A
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Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
Power Extracted by the BladesThen power relationship at the rotor could be
Define new parameter such that
We can rewrite the power relationship as
2 21 2 2
db d
v vP A v v
dvv
2 2 21 2 2b
v vP A v v
3 21 1 1 1 2 2bP Av
Power in the wind Rotor efficiency (CP) 23
Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
Maximum Rotor Efficiency
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Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
Number of Rotating BladesWindmills have multiple blades
need to provide high starting torque to overcome weight ofthe pumping rod
must be able to operate at low windspeeds to provide nearlycontinuous water pumping
a larger area of the rotor faces the wind
Turbines with many blades must operate at lowerrotational speeds – as speed increases, turbulencecaused by one blade impacts other blades
Most modern wind turbines have two or three blades
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Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
Estimates of Wind Turbine EnergyNot all of the power in the wind is retained - the rotor spills high-
speed winds and low-speed winds are too slow to overcomelosses,
Depends on rotor, gearbox, generator, tower, controls, and thewind
Overall conversion efficiency (Cp·ηg) is around 30%
WPBP EP
Power inthe Wind
Power Extracted by Turbine
Electric Power
PCRotor Gearbox &
Generator
g
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Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
Power Generated by H-Wind Turbine
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Air density is lower at higher elevation. For 1000 feet above sea level, ρ is about 1.16 kg/m3
Power = ½ (ρ)(A)(V)3 (η)
= 0.5(1.16)(502)(12)3(0.4)
= 3.15 x 106 Watt
= 3.15 MW
where we assumed the turbine efficiency is 40%.
How much power a wind turbine with 50 meters long blade can generate with a wind speed of 12 m/s? The site of the installation is about 1000 feet above sea level. Assume 40% efficiency (η).
Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
Wind FarmsIt makes sense to install a large number of wind turbines
in a wind farm or a wind park
Benefits Able to get the most use out of a good wind site Reduced development costs Simplified connections to the transmission system Centralized access for operations and maintenance
How many turbines should be installed at a site?What is a sufficient distance between wind turbines so thatwindspeed has recovered enough before it reaches the nextturbine?
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Dr. Anwar Abu-Zarifa . Islamic University Gaza . Department of Industrial Engineering
Wind Farms Rectangular arrays with only a few long rows are better Recommended spacing is 3-5 rotor diameters between
towers in a row and 5-9 diameters between rows. (to avoidnegative effects of turbulence)
Offsetting or staggering the rows is common
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Using Software to Optimize Wind Farm Layout Data requirements
Topographical data Wind data Technology characteristics of turbines
Given number of devices, wind, optimizes location to maximize output.