LECTURE 18 WIND POWER SYSTEMS ECE 371 Sustainable Energy Systems 1
HISTORICAL DEVELOPMENT The first wind turbine used to generate electricity was built by La Cour of Denmark in 1891 2
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 time 3
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) 4
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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 incentives 6
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) 7
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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 9
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 10
HISTORICAL DEVELOPMENT The fraction of electricity generated from wind is shown below (Now Denmark is 41.2%) 11
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 12
TYPES OF WIND TURBINES 13
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. 14
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 equipment 15
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 16
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 17
TYPES OF WIND TURBINES Key components of WTG is shown below 18
ROTORS At the beginning of the 21 st 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 19
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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 21
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 rotate 22
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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 24
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 25
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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 27
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ROTORS Three approaches are common for large machines Passive Stall Control Active Pitch Control Active Stall Control 29
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 30
ROTORS Active Pitch Control - Due to rotor blades rotation Electronic 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 31
ROTORS Active Stall Control - Due to rotor blades rotation Electronic 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 speeds Stall is induced Once the rotor is stopped, a brake locks the rotor shaft 32