lecture 18 wind power systemswiki.ece.rose-hulman.edu/.../7/72/ece371_wind_power_1.pdf · 2020. 6....
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LECTURE 18WIND POWER
SYSTEMS
ECE 371Sustainable Energy Systems
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HISTORICAL DEVELOPMENT
The first wind turbine used to generate electricity was built by La Cour of Denmark in 1891
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HISTORICAL DEVELOPMENT
Diameter = 23 m, P = 18 kW, 4 Blades
The electricity was used to electrolyze water
The produced hydrogen was used for gas lights in the local schoolhouse
He was 100 years ahead of his time3
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HISTORICAL DEVELOPMENT
In the U.S. the first wind-electricity system was build in late 1890s
In 1941, one of the largest wind-powered systems went into operation in Vermont to produce 1.25 MW from a 53-meter diameter, two bladed prop (Smith-Putnam Wind Turbine)
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HISTORICAL DEVELOPMENT
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HISTORICAL DEVELOPMENT
It catastrophically failed in 1945 due to a 25 mph wind, while before it had withstood winds as high as 115 mph
The activity in this area died until 1970s
Thousands of wind turbines were installed in California from mid-1970s through 1985
Due to oil crisis of 1970s and tax incentives6
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HISTORICAL DEVELOPMENT
After that the tax credits were terminated and the industry was wiped out in the US until early 1990s
Meanwhile, wind turbine technology development continued in Europe Germany Spain Denmark (Vestas)
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HISTORICAL DEVELOPMENT
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HISTORICAL DEVELOPMENT
The following figure shows the global installed wind power capacity
By the end of 2016, the global installed capacity was 430 GW
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HISTORICAL DEVELOPMENT
The countries with most installed wind capacity are shown below (as of beginning of 2012)
By the end of 2016, the U.S. installed capacity was 82 GW
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HISTORICAL DEVELOPMENT
The fraction of electricity generated from wind is shown below (Now Denmark is 41.2%)
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TYPES OF WIND TURBINES
One way of classifying wind turbines is in terms of the axis around which the turbine blades rotate
Horizontal axis wind turbines (HAWT) Upwind Downwind
Vertical axis wind turbines (VAWT) Darrieus, developed in 1920s by a French engineer
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TYPES OF WIND TURBINES
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Nacelle
noun 1. the enclosed part of an airplane, dirigible, etc.,
in which the engine is housed or in which cargo or passengers are carried.
2. the car of a balloon.
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TYPES OF WIND TURBINES
Advantages of VAWT Don’t need yaw control Equipment in nacelle are at ground level Tower and blades are light weight and inexpensive
Disadvantages of VAWT Blades are close to ground where wind speeds are low At low wind speeds they have low starting torque At high speeds they can’t spill power to protect
equipment15
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TYPES OF WIND TURBINES
Advantages of downwind turbines Wind controls the yaw, so it naturally orients itself
Disadvantages of downwind turbines Wind shadowing of a blade swings behind the tower
it encounters a brief period of reduced wind, which causes the blade to flex This can cause blade fatigue, increased blade noise, and
reduced power
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TYPES OF WIND TURBINES
Advantages of upwind turbines Operate more smoothly Deliver more power
Disadvantages of upwind turbines Complex yaw control system
Most modern wind turbines are upwind with 3 blades Smoother operation Quieter
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TYPES OF WIND TURBINES
Key components of WTG is shown below
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ROTORS
At the beginning of the 21st century most turbines were rated at Capacity of 1-2 MW Hub height of 50-80 m Blade diameter of 80-100 m
A decade later the largest machines for off-shore applications are rated for 7 MW
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ROTORS
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ROTORS
To understand wind turbine performance, extraction power from the wind by the rotor blades needs to be looked at
To do this, we need to consider a simple airfoil cross section
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ROTORS
An airfoil, whether it is the wing of an airplane or the blade of a windmill, takes advantage of the Bernoulli’s principle to obtain lift
Air moving over the top of the airfoil has a greater distance to travel before it can rejoin the air that took the short cut under the foil Air pressure on top is lower than that under the
airfoil This creates the lifting force that holds an airplane
up or wind turbine blade to rotate22
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ROTORS
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ROTORS
A rotating turbine blade sees air moving toward it not only from the wind itself, but also from the relative motion of the blades as it rotates This results in the two wind vectors add up to a
resultant vector moving across the airfoil at the correct angle to obtain the lift that moves the rotor
Since the blade is moving much faster at the tip than near the hub, the blade must be twisted along its length to keep the angles correct
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ROTORS
The angle of attack is the angle between the airfoil and the wind
Increasing the angle of attack improves lift at the expense of increased drag
But increasing the angle of attack too much can result in a phenomenon known as stall
When a wing stalls, air flow over the top no longer sticks to the surface, and the resulting turbulence destroys lift
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ROTORS
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ROTORS
Power delivered by the wind turbine increases with increasing windspeed
At some point, the generator reaches its maximum capacity
Must shed some of the wind’s power
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ROTORS
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ROTORS
Three approaches are common for large machines
Passive Stall Control
Active Pitch Control
Active Stall Control
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ROTORS
For stall-controlled machines, the blades are designed to reduce power for excessive winds
Stall Controlled Machines- Due to aerodynamics of rotor blades The blades are fixed on the rotor and pitch is fixed. Blade aerodynamics are designed such that lift is reduced as
windspeed increases Sacrifices power at low windspeed - less than 1 MW size
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ROTORS
Active Pitch Control - Due to rotor blades rotationElectronic system monitors generator output power If it exceeds the rated value, pitch of the blades is
adjusted Hydraulic system slowly rotates the blades
Angle of attack is reduced at high wind speeds to reduce lift
Once the rotor is stopped, a brake locks the rotor shaft
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ROTORS
Active Stall Control - Due to rotor blades rotationElectronic system monitors generator output power If it exceeds the rated value, pitch of the blades is
adjusted Hydraulic system slowly rotates the blades
Angle of attack is increased at high wind speedsStall is inducedOnce the rotor is stopped, a brake locks the rotor shaft
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