Wind Power Systems
Energy Systems Research Laboratory, FIU Historical Development of Wind Power
• In the US - first wind-electric systems built in the late 1890’s • By 1930s and 1940s, hundreds of thousands were in use in rural areas not yet served by the grid • Interest in wind power declined as the utility grid expanded and as reliable, inexpensive electricity could be purchased • Oil crisis in 1970s created a renewed interest in wind until US government stopped giving tax credits • Renewed interest again since the 1990s
Energy Systems Research Laboratory, FIU Global Installed Wind Cappyacity
Source: Global Wind Energy Council
Energy Systems Research Laboratory, FIU Annual Installed Wind Capacity
Source: Global Wind Energy Council
Energy Systems Research Laboratory, FIU Growth in US Wind Power Capacity
Source: AWEA Wind Power Outlook 2 nd Qtr, 2010 For more info: http://www.windpoweringamerica.gov/pdfs/wpa/wpa_update.pdf
Energy Systems Research Laboratory, FIU Top 10 Countries - Installed Wind Capacit y ( as of th e end of 2009)
Total Capacity 2009 Growth
Source: Global Wind Energy Council
Energy Systems Research Laboratory, FIU US Wind Resources
50 meters
Energy Systems Research Laboratory, FIU http://www.windpoweringamerica.gov/pdfs/wind_maps/us_windmap.pdfhttp://www.windpower.org/en/pictures/lacour.htm US Wind Resources
80 meters
http://www.windpoweringamerica.gov/pdfs/wind_maps/us_windmap_80meters.pdf
Energy Systems Research Laboratory, FIU Cape Wind off-shore wind farm
• For about 10 years Cape Wind Associates has been attempting to build an off-shore 170 MW wind farm in Nantucket Sound, Massachusetts. Because the closest turbine would be more than three mil es f rom sh ore (4 .8 mil es) it i s subj ect t o f ed eral , as opposed to state, jurisdiction. – Federal approval was given on May 17, 2010 – Cape Wind would be the first US off-shore wind farm • There has been significant opposition to this project, mostly out of concern that the wind farm would ruin the views from private property, decreasing property values.
Energy Systems Research Laboratory, FIU Massachusetts Wind Resources
Energy Systems Research Laboratory, FIU Cape Wind Simulated View, Nantucket Sound , 6 .5 miles Distant
Source: www.capewind.org Energy Systems Research Laboratory, FIU State Wind Capacities (7/20/2010) State Existing Under Rank Construction (Existing) Texas 9,707 370 1 Iowa 3,670 0 2 California 2, 739 443 3 Oregon 1,920 614 4 Washington 1,914 815 5 Illinois 1,848 437 6 Minnesota 1,797 673 7 New York 1,274 95 8 Colorado 1,248 552 9 North Dakota 1, 222 37 10 http://www.awea.org/projects/ Energy Systems Research Laboratory, FIU Types of Wind Turbines
• “Windmill”- used to gggrind grain into flour • Many different names - “wind-driven generator”, “wind generator”, “wind turbine”, “wind-turbine generator (WTG)”, “wind energy conversion system (WECS)” • Can have be horizontal axis wind turbines (HAWT) or vertical axis wind turbines (VAWT) • Groups of wind turbines are located in what is called either a “wind farm” or a “wind park”
Energy Systems Research Laboratory, FIU Vertical Axis Wind Turbines • Darrieus rotor - the only vertical axis machine with any commercial success • Wind hitting the vertical blades, called aerofoils, generates lift to create rotation
• No yaw (rotation about vertical axis) control needed to keeppg them facing into the wind • Heavy machinery in the nacelle is located on the ground • Blades are closer to ground where windspeeds are lower
http://www.reuk.co.uk/Darrieus-Wind-Turbines.htm Energy Systems Research Laboratory, FIU http://www.absoluteastronomy.com/topics/Darrieus_wind_turbine Horizontal Axis Wind Turbines
• “Downwind” HAWT – a turbine with the blades behind (downwind from) the tower • No yaw control needed - they naturally orient themselves in line with the wind • Sha dow ing e ffec t – whbldihen a blade swings behind the tower, the wind it encounters is br iefly fl red uced and th e bl ad e fl exes
Energy Systems Research Laboratory, FIU Horizontal Axis Wind Turbines
• “Upwind” HAWT – blades are in front of (upwind of) the tower • Most modern wind turbines are this type • Blades are “upwind” of the tower • Require somewhat complex yaw control to keep them facing into the wind • OtOperate more smoothly thlddli and deliver more power
Energy Systems Research Laboratory, FIU Number of Rotating Blades
• Windmills have multiple blades – need to provide high starting torque to overcome weight of the pumping rod – must be able to operate at low wind speeds to provide nearly continuous water pumping – a larger area of the rotor faces the wind • Turbines with many blades operate at much lower rotational speeds - as the speed increases, the turbulence caused by one blade impacts the other blades • Most modern wind turbines have two or three blades
Energy Systems Research Laboratory, FIU Power in the Wind (for reference solar is about 600 w/m 2 in summer) • Power increases like the cube of wind speed • Doubling the wind speed increases the power by eight • Energy in 1 hour of 20 mph winds is the same as energy in 8 hours of 10 mph winds • Nonlinear, so we cannot use average wind speed Figure 6.5 Energy Systems Research Laboratory, FIU Power in the Wind
1 PA(64)PA v3 (6.4) W 2 • Power in t he w ind is a lso p ropo rt io na l to A • For a conventional HAWT, A = (π/4)D2, so wind ppppower is proportional to the blade diameter sq uared • Cost is roughly proportional to blade diameter • This explains why larger wind turbines are more cost effective
Energy Systems Research Laboratory, FIU Nikola Tesla: Inventor of Induction Motor (and many other things) • Nikola Tesla (1856 to 1943) is one of the key inventors associated with the development of today’s three phase ac system. His contributions include the induction motor and polyphase ac systems. – Unit of flux density is named after him
• TlTesla concei ved dfthidti of the induction motor while walking through a park in Budapest in 1882. • He emigrated to the US in 1884
Energy Systems Research Laboratory, FIU World’s Largest Offshore Wind Farm Opens Turbines are located in water depth of 20-25m. Rows are 800m apart; 500m between turbines
• “Thanet” located off British coast in English Channel • 100 Vestas V90 turbines,,py 300 MW capacity http://www.vattenfall.co.uk/en/thanet-offshore-wind-farm.htm http://edition.cnn.com/2010/WORLD/europe/09/23/uk.largest.wind.farm/?hpt=Sbin Energy Systems Research Laboratory, FIU Off-shore Wind • Offshore wind turbines currently need to be in relatively shallow water, so maximum distance from shore depends on the seabed • Capacity factors tend to increase as tbiturbines move further off-shore
Image Source: National Renewable Energy Laboratory Energy Systems Research Laboratory, FIU Maximum Rotor Efficiency
Rotor efficiency CP vs. wind speed ratio λ
Figure 6.10
Energy Systems Research Laboratory, FIU Tip-Speed Ratio (TSR)
• Efficiency is a function of how fast the rotor turns • Tip-Speed Ratio (TSR) is the speed of the outer tip of the blade divided by windspeed Rotor tip speed rpm D Tip-Speed-Ratio (TSR) = (6.27) Wind speed 60v • D = rotor diameter (m) • v = upwind undisturbed windspeed (m/s) • rpm = rotor speed, (revolutions/min) • One meter per second = 2.24 miles per hour
Energy Systems Research Laboratory, FIU Tip-Speed Ratio (TSR)
• TSR for various rotor types • Rotors with fewer blades reach their maximum efficiency at higher tip-speed ratios
Figure 6 .11
Energy Systems Research Laboratory, FIU Synchronous Machines
• Spin at a rotational speed determined by the number of poles and by the frequency • The magnetic field is created on their rotors • Create the magnetic field by running DC through windings around the core • A gear box is needed between the blades and the generator • 2 complications – need to provide DC, need to have slip rings on the rotor shaft and brushes
Energy Systems Research Laboratory, FIU Asynchronous Induction Machines
• Do not turn at a fixed speed • Acts as a motor during start up as well as a generator • Do not require exciter, brushes, and slip rings • The magnetic field is created on the stator instead of the rotor • Less expensive , require less maintenance • Most wind turbines are induction machines
Energy Systems Research Laboratory, FIU The Induction Machine as a Generator
• Slip is negative because the rotor spins faster than synchronous speed • Slip is normally less than 1% for grid- connected generator • TilTypical rot or speed
NsNRS(1 ) [1 ( 0. 01)] 3600 3636 rpm
Energy Systems Research Laboratory, FIU Speed Control
• Necessary to be able to shed wind in high-speed winds • Rotor efficiency changes for different Tip-Speed Ratios (TSR) , and TSR is a function of windspeed • To maintain a constant TSR, blade speed should change as windspeed changes • A challenge is to design machines that can accommodate variable rotor speed and fixed generator speed
Energy Systems Research Laboratory, FIU Blade Efficiency vs. Windspeed
Figure 6.19 At lower windsppyeeds, the best efficiency is achieved at a lower rotational sp eed
Energy Systems Research Laboratory, FIU Power Delivered vs. Windspeed
Figure 6.20 Impppjpgggact of rotational speed adjustment on delivered power, assuming gear and generator efficiency is 70%
Energy Systems Research Laboratory, FIU Variable Slip Example: Vestas V8018MWV80 1.8 MW • The Vestas V80 1.8 MW turbine is an example in which an induction generator is operated with variable rotit(tor resistance (opti-slip) . • Adjusting the rotor resistance changes the torque -speed curve • Operates between 9 and 19 rpm
Source: Vestas V80 brochure Energy Systems Research Laboratory, FIU Vestas V8018MWV80 1.8 MW
Energy Systems Research Laboratory, FIU Doubly-Fed Induction Generators
• Another common approach is to use what is called a doubly-fed induction generator in which there is an electrical connection between the rotor and supply electrical system using an ac-ac converter • This allows operation over a wide-range of speed, for example 30% with the GE 1.5 MW and 3.6 MW machines
Energy Systems Research Laboratory, FIU GE 1.5 MW and 3.6 MW DFIG Examples
GE 1.5 MW turbines are the best selling wind turbines in the US with 43% market share in 2008
Energy Systems Research Laboratory,Source: FIU GE Brochure/manual Indirect Grid Connection Systems
• Wind turbine is allowed to spin at any speed • Variable freq uenc y AC from the generator goes through a rectifier (AC-DC) and an inverter (DC- AC)to60HzforgridAC) to 60 Hz for grid-connection • Good for handling rapidly changing wind speeds
Figure 6.21
Energy Systems Research Laboratory, FIU Example: GE 2.5 MW Turbines
Energy Systems Research Laboratory, FIU Wind Turbine Gearboxes
• A significant portion of the weight in the nacelle is due to the gearbox – Needed to change the slow blade shaft speed into the higher speed needed for the electric machine • Gearboxes require periodic maintenance (e.g., change the oil), and have also be a common source of wind turbine failure • Some wind turbine designs are now getting rid of the gearbox by using electric generators with many pole pairs (direct-drive systems) • Enercon is the leader in this area, with others considering direct drives
Energy Systems Research Laboratory, FIU Enercon E126, World’s Largest Wind Turbine at 6 MW (7.5 MW Claimed)
This turbine uses direct drive technology. The hub height is 135m while the rotor diameter is 126m.
Source: en.wikipedia.org/wiki/File:E_126_Georgsfeld.JPG Energy Systems Research Laboratory, FIU Average Power in the Wind
• How much energy can we expect from a wind turbine? • To figggp,ure out average power in the wind, we need to know the average value of the cube of velocity:
11 PAvAv 33 (6.29) avg avg 22avg
• This is wh y we can’t use a verage windspeed vavg to find the average power in the wind
Energy Systems Research Laboratory, FIU Example Windspeed Site Data
Energy Systems Research Laboratory, FIU Figure 6.22 Wind Probability Density Functions Windspeed probability density function (p.d.f) – between 0 and 1, area under the curve is equal to 1
Energy Systems Research Laboratory, FIU Figure 6.23 Altamont Pass , CA
• Old windfarm with various-sized turbines • 576 MW total capacity • Average output is 125 MW • Wind t urbi nes are on hilltop ridges
http://en.wikipedia.org/wiki/File:Altamont_Wind_Turbines_7-11-09.JPG
http://xahlee.org/Whirlwheel_dir/livermore.html Energy Systems Research Laboratory, FIU Wind Power Classification Scheme
Table 6.5
Energy Systems Research Laboratory, FIU Classes of Wind Power Density at 10 m and 50 m(a) 10 m (33 ft) 50 m (164 ft) Wind Wind Speed(b) Wind Speed(b) Power Power m/s (mph) Power m/s (mph) Class Density Density (W/m2) (W/m2) 1 <100 <4.4 (9.8) <200 <5.6 (12.5) 5. 6 (12. 5)/6.4 2 100 - 150 4.4 (9.8)/5.1 (11.5) 200 - 300 (14.3) 6.4 (14.3)/7.0 3 150 - 200 5.1 (11.5)/5.6 (12.5) 300 - 400 (15.7) 7.0 (15.7)/7.5 4 200 - 250 5.6 (12.5)/6.0 (13.4) 400 - 500 (16.8) 7.5 (16.8)/8.0 5 20250 - 300 60(134)/64(143)6.0 (13.4)/6.4 (14.3) 500 - 600 (17.9) 8.0 (17.9)/8.8 6 300 - 400 6.4 (14.3)/7.0 (15.7) 600 - 800 (()19.7) 7 >400 >7.0 (15.7) >800 >8.8 (19.7)
Energy Systems Research Laboratory, FIU http://www.awea.org/faq/basicwr.html Wind Power Classification Scheme
50 meters• Table 6.5
http://www.windpoweringamerica.gov/pdfs/wind_maps/us_windmap.pdf Energy Systems Research Laboratory, FIU Estimates of Wind Turbine Energy
• Not all of the power in the wind is retained - the rotor spills high -speedidd winds and dl low-speedidd winds are too sl ow to overcome losses • Depends on rotor, gearbox, generator, tower, controls, terrain, and the wind
P P W P E B PtPower to Power in CP Power g Electricity the Wind Rotor Extracted Gearbox & by Blades Generator
• Overall conversion efficiency (Cp·ηg) is around 30%
Energy Systems Research Laboratory, FIU Wind Farms
• Normally, it 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 – Simp lifie d connec tions to the t ransmi ssi on system – Centralized access for operations and maintenance • How many turbines should be installed at a site?
Energy Systems Research Laboratory, FIU Wind Farms
• We know that wind slows down as it ppgasses through the blades. Recall the power extracted by the blades:
1 22 Pmvvbd (6.18) 2 • Extracting power with the blades reduces the available power to downwind machines • What is a sufficient distance between wind turbines so that windspeed has recovered enough before it reachhhes the next tur bi?bine?
Energy Systems Research Laboratory, FIU Wind Farms
Figure 6.28
Energy Systems Research Laboratory, FIU Wind Farms – Optimum Spacing
Ballpark figure f or GE 1.5 MW in Midwest is one per 80 acres
3 D to 5D Optimum spacing is estimated to be Figure3- 6.29 5 rotor diameters between towers and 5-9 between rows 5 D to 9D
Energy Systems Research Laboratory, FIU Time Variation of Wind
• We need to not just consider how often the wind blows but also when it blows with respect to the electric load. • Wind patterns vary quite a bit with geography, with coastal and mountain regions having more steady winds. • In the Midwest the wind tends to blow the strongest when the electric load is the lowest.
Energy Systems Research Laboratory, FIU Upper Midwest Daily Wind Variation
August April
Graphs show the mean, and then the 75% and 90% probability values; note for August the 90% probability is zero.
Source: www.uwig.org/XcelMNDOCwindcharacterization.pdf Energy Systems Research Laboratory, FIU California ISO Daily Wind Energy
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Energy Systems Research Laboratory, FIU How Rotor Blades Extract Energy from the Wind
Airfoil – could be the wing of an airplane or the blade of a wind turbine
Figure 6.30 (a)
Bernoulli’s Principle - air pressure on top is greater than air pressure on bottom because it has further to travel, creates lift Energy Systems Research Laboratory, FIU How Rotor Blades Extract Energy from the Wind • Air is moving towards the wind turbine blade from the wind but also fthltibldfrom the relative blade motion • The blade is much faster at the tip than at the hub, so the blade is twisted to keep the angles correct
Figure 6 .30 (b)
Energy Systems Research Laboratory, FIU Angle of Attack, Lift, and Drag
• Increasinggg angle of attack increases lift, but it also increases drag Figure 6.31 (a)
• If the angle of attack is too gg,reat, “stall” occurs where turbulence destroys the lift
Energy Systems Research Laboratory,Figure 6.31 FIU (b) - Stall Idealized Power Curve
Cut –in windspeed, rated windspeed, cut -out windspeed
Energy Systems Research Laboratory, FIU Figure 6.32 Idealized Power Curve
• Before the cut-in windspeed, no net power is generated • Then, power rises like the cube of windspeed • After the rated windspeed is reached, the wind turbine operatttdtes at rated power ( (hdsheds excess wi id)nd) • Three common approaches to shed excess wind – Pitch control – physically adjust blade pitch to reduce angle of attack – Stall control (passive) – blades are designed to automatically reduce efficiency in high winds – Active stall control – physically adjust blade pitch to create stall
Energy Systems Research Laboratory, FIU Idealized Power Curve
• Above cut-out or ffgurling windspeed, the wind is too strong to operate the turbine safely, machine is shut down, output power is zero • “Furling” –refers to folding up the sails when winds are too strong in sailing • Rotor can be stopped by rotating the blades to purposely create a stall • Once the rotor is stopped, a mechanical brake locks the rotor shaft in place
Energy Systems Research Laboratory, FIU Current Prices for Small Wind
• The Amazon is selling a 900W wind turbine for $1739; inverter (maybe $250) , tower and batteries are extra (65’ tower goes for about $1000 plus installation) (Whisper 100; designed for 100 kWh per month)
Source: www.homedepot.com; www.kansaswindpower.net Energy Systems Research Laboratory, FIU Government Credits
• Federal ggpovernment provides tax credits of 30% of cost for small (household level) solar, wind, geothermal and fuel cells (starting in 2009 the total cap of $4000 was removed) • I don’t think Illinois has a wind credit, but they do have a sol ar credi t (30% of cost) • For large systems the Federal Renewable Electricity Pro duc tion T ax C redit pays 1 .5¢/kWh (1993 d oll ars, inflation adjusted, currently 2.1¢) for the first ten years of production Source for federal/state incentives: www.dsireusa.org Energy Systems Research Laboratory, FIU Small Wind Turbine Cost
• Assume total cost is $3000 – Federal credit reduces cost to $2100 • With an assumed lifetime of 15 years and simple payback, the annual cost is $140. . • Say unit produces 100 kWh per month, or 1200 per year. • This unit makes economic sense if electricity prices are at or above 100/1200 = $0.083/kWh. • With modest annual O&M, say $50, this changes to $0.125/kWh.
Energy Systems Research Laboratory, FIU Energy Systems Research Laboratory, FIU Energy Systems Research Laboratory, FIU Economies of Scale
• Presently large wind farms produce electricity more economillhically than small operati ons • Factors that contribute to lower costs are – Wind power is proportional to the area covered by the blade (square of diameter) while tower costs vary with a value less than the square of the diameter – Larger blades are higher, permitting access to faster winds – Fixed costs associated with construction (permitting, management) are spread over more MWs of capacity – Efficiencies in managing larger wind farms typically result in lower O&M costs (on-site staff reduces travel costs)
Energy Systems Research Laboratory, FIU Environmental Aspects of Wind Energy
• US National Academies issued report on issue in 2007 • Wind system emit no air pollution and no carbon dioxide; they also have essentially no water requirements • Wind energy serves to displace the production of energy from other sources (usually fossil fuels) resulting in a net dillidecrease in pollution • Other impacts of wind energy are on animals, primarily bird s and b at s, and on h umans
Energy Systems Research Laboratory, FIU Environmental Aspects of Wind Energy, Birds and Bats
• Wind turbines certainly kill birds and bats, but so do lots of other things; windows kill between 100 and 900 million birds per year
Esti mated C auses of Bi rd F atali ti es, per 10 ,000
Source: Erickson, et.al, 2002. Summary of Anthropogenic Causes of Bird Mortality Energy Systems Research Laboratory, FIU Environmental Aspects of Wind Energy, Human Aesthetics , Offshore
• Offshore wind turbines currently need to be in relatively shallow water, so maximum distance from shore depends on the seabed • Capacity factors tend to increase as turbines move further off-shore
Energy Systems Research Laboratory, FIU Image Source: National Renewable Energy Laboratory Cape Wind Simulated View, Nantucket Sound, 6. 5 miles Distant
Source: www.capewind.org Energy Systems Research Laboratory, FIU In the News: NREL Report on US Offshore Wi nd Potenti al • NREL just issued a report discussing US off-shore wind potential, with a key conclusion being that we could get about 54 GW of new off-shore wind by 2030. • Offshore wind has a significant advantage that the generation is located relatively closely to the high load urban areas. Offshore wind is also more constant. • Offsetting are the higher costs of locating in water. • Report cl ai ms 43 ,000 permanent j ob s b ut d oesn’t di scuss loss of jobs in other areas. • World off -shore wind UK (1041 MW), Denmark (664) Source (full report) http://www.nrel.gov/docs/fy10osti/40745.pdf Energy Systems Research Laboratory, FIU Wind Turbines and Radar • “Wind Turbines interfere with radar. This has led the FAA, DHS and DOD to contest many proposed wind turbine sites.” – Either through radar shadows , or doppler returns that look like false aircraft or weather patterns • No fundamental constraint with respect to radar interference, but mitigation might require either upgrades to radar or regulation changes to require, for exampllle, telemetry f rom wi idfnd farms to rad ar – For Cape Wind project the developer agreed to pay $1.5 million to upgrade radar at a nearby military base , with an escrow of $15 million. Source: www.fas.org/irp/agency/dod/jason/wind.pdf (2008) Energy Systems Research Laboratory, FIU Power Grid Integration of Wind Power
• Wind power had represented a minority of the generation in power system interconnects, so its impact of grid operations was small, but now the impact of widind need s t o b e consid ered di in power syst em anal ysi s – Largest wind farm in world is Roscoe Wind Farm in Texas with a total capacity of 781 MW, which matches the size of many conventional generators. • Wind power has impacts on power system operations ranging from that of transient stability (seconds) out to steady-state (power flow) – Voltage and frequency impacts are key concerns
Energy Systems Research Laboratory, FIU In the News: Off-shore Transmission System Proposed • Several companies, including Trans-Elect and Google are proposing a 6000 MW, 350 MW long off-shore “superhighway for clean energy.” – It would b e l ocated b etween 1 5 to 20 mil es off sh ore – Would go in shallow trenches – Four connection points to ac grid – First stage would go into service in 2016. – Cost is estimated at $5 billion
Source: Google Blog; NYTimes also thanks to Pallav Pathak
Energy Systems Research Laboratory, FIU Wind Power, Reserves and Regulation
• A key constraint associated with power system operations is pretty much instantaneously the total power system generation must match the total load plus losses – Excessiiihfive generation increases the system frequency, whil e excessive load decreases the system frequency • Generation shortfalls can suddenly occur because of the loss of a generator; utilities plan for this occurrence by maintainingg(g sufficient reserves (generation that is on-line but not fully used) to account for the loss of the largest single generator in a region (e.g., a state)
Energy Systems Research Laboratory, FIU Wind Power, Reserves and Regulation, cont.
• A fundamental issue associated with “free fuel” systems like wind is that operating with a reserve margin requires leaving free energy “on the table.” – A similar issue has existed with nuclear energy, with the fossil fueled units usually providing the reserve margin • Because wind turbine output can vary with the cube of the wind speed, under certain conditions a modest drop in the wind speed over a region could result in a major loss of generation – Lack of other fossil-fuel reserves could exacerbate the sstuatoituation
Energy Systems Research Laboratory, FIU