12 2 Wind Turbine Systems Wind Turbine Theory
12. 2 Wind Turbine Systems Wind Turbine Theory Frank R. Leslie, B. S. E. E. , M. S. Space Technology, LS IEEE 3/2/2010, Rev. 2. 0. 5 fleslie @fit. edu; (321) 674 -7377 www. fit. edu/~fleslie Crude oil ~$47. 46 on 3/10/2009 $78 on 3/1/10
In Other News. . . l 160 m diameter, 10 MW under development u http: //www. cpi. umist. ac. uk/Eminent/public. Files/brno/RISO_Future_10 MW_Wind_Turbine. pdf l Clipper building “Brittanica” 10 MW turbine for offshore use at Newcastle, UK 100223
12. 2 Overview: Wind Turbine Systems l Wind energy turbines stem from early Persian panemones – a vertical axis spinner for grinding grain l Not all power (59. 3% max) can be extracted from the wind, but the turbines are relatively simple technology l This presentation discusses the types and construction of wind turbines l Wind turbine is a generic term, and it generally denotes an electrical power generator; windmills are specifically for grinding corn, wheat, or other grains l NASA used term “WECS” for Wind Energy Convertor System l There also wind pumps for water; wind mills are for grinding grain http: //telosnet. com/wind/early. html 090309
12. 2 About This Presentation l l l l 060217 12. 2. 1 History 12. 2. 2 Turbine Types 12. 2. 3 Small Turbines 12. 2. 4 Large Systems 12. 2. 5 Components and Airfoils 12. 2. 6 Turbine Power Issues 12. 2 Conclusion
12. 2. 1 Early History l 5000 BCE (before common era): Sailing ships on the Nile River were likely the first use of wind power l Hammurabi, ruler of Babylonia, used wind power for irrigation l Hero (Heron) created a wind-pumped organ l Persians created a Vertical Axis WT (VAWT) in the mid 7 th Century l 1191 AD: The English used wind turbines l 1270: Post-mill used in Holland l 1439: Corn-grinding in Holland l 1600: Tower mill with rotating top or cap l 1750: Dutch mill imported to America l 1850: American multiblade wind pump development; 6. 5 million until 1930; was produced in Heller-Allen Co. , Napoleon, Ohio l 1890: Danish 23 -meter diameter turbine produced electricity 060219
12. 2. 1 Later History l 1920: Early Twentieth Century saw wind-driven water-pumps commonly used in rural America, but the spread of electricity lines in 1930 s (Rural Electrification Act) caused their decline l 1925: Windcharger and Jacobs turbines popular for battery charging at 32 V; 32 Vdc appliances common for gas generators l 1940: 1250 k. W Rutland Vermont (Putnam) 53 m system (center) l 1957 -1960: 200 k. W Danish Gedser mill (right) l 1972: NASA/NSF wind turbine research l 1979: 2 MW NASA/DOE 61 m diameter turbine in NC l Now, many windfarms are in use worldwide 050217 http: //telosnet. com/wind/20 th. html
12. 2. 2 Types of Turbines: HAWT & VAWT l HAWT (Horizontal Axis Wind Turbines) have the rotor spinning around a horizontal axis u The rotor vertical axis must turn to track the wind u Gyroscopic precession forces occur as the turbine turns to track the wind l VAWT (Vertical Axis Wind Turbines) have the rotor spinning around a vertical axis u This Savonius rotor will instantly extract energy regardless of the wind direction u The wind forces on the blades reverse each halfturn causing fatigue of the mountings u The two-phase design with the two sections at right angles to each other starts more easily n This is available in parts for experimenter 100223 Photo by F. Leslie, 2001
12. 2. 2. 1 HAWT Examples l Charles Brush (arc light) home turbine of 1888 (center) u 17 m, 1: 50 step-up to drive 500 rpm generator l NASA Mod 0, 1, 2 turbines l The Mod-0 A at Clayton NM produced 200 k. W (below left) http: //telosnet. com/wind/govprog. html 060221 http: //telosnet. com/wind/20 th. html http: //www. windmission. dk/ projects/Nybroe%20 Home/l
12. 2. 2. 1 Horizontal Axis Wind Turbines (HAWT) Sailwing, 1300 A. D. Dutch post mill Experimental American Farm, 1854 Dutch with fantail 1. 8 m Ref. : WTC 060221 Wind farm Modern Turbines 75 m
12. 2 VAWT Examples l Darrieus troposkein blades (jump rope) l Savonius rotor ~1925 l Madaras rotor using the Magnus Effect u. Rotors placed on train cars to push them around a circular track l Vortex Turbine l The SANDIA Darrieus turbine was destroyed when left unbraked overnight 090309 http: //telosnet. com/wind/govprog. html
12. 2. Vertical Axis Wind Turbines (VAWT) l This sample shows the diversity of VAWT over the years Panemone, 1000 B. C. Savonius Darrieus with Savonius Giromill 060221 Experimental Savonius
12. 2. 2 Location of Turbines: USA States l If wind projects are measured by commercial success, the Southeast USA isn’t the best area to use! l The Florida Keys would be a likely area to evaluate coastal breezes 2003 http: //telosnet. com/wind/recent. html http: //www. awea. org/projects/index. html, showing MW in each state 9/30/2007 100223
12. 2. 3 Small Wind Turbines: American l In 1854, patented wind pumpers were popular across the US, later spreading to other nations l By 1870, improvements made with sheet steel blades stamped to an aerodynamic contour l These turbines use 2 turns of the rotor to 1 stroke of the pump lift rod gear ratio to allow starting at a low wind speed l AEI states that there are some 30, 000 farm wind pumps in the Southern Great Plains at 0. 25 k. W each, or some 5 MW total l Typical present-day at www. ohio-windmill. com 100222
12. 2. 3 Small Wind Turbines: Bergey produces small wind turbines up to 50 k. W http: //www. bergey. com/ • Equipment: BWC 7. 5 k. W Wind Turbine, 3 k. W Solar, ~ 90 k. Wh Battery Bank • Performance: ~ 40 k. Wh / Day at 240 VAC, 60 Hz • Customer: Renegade Radio • Installation: May 1996 • Results: Over 98% 030307 /090310 availability. Alternator replaced in May 1998 following wiring fault.
12. 2. 3 Small Wind Turbines: Southwest Windpower l We are have two 400 -watt Air-X turbines and a 1000 -watt, 10 -ft diameter H-80 in our Florida Tech Wind/Solar Sea Breeze study l These turbines are available in several variations 090310 http: //www. windenergy. com/
12. 2. 3 Small Wind Turbines: “Homemade” l Amateur or hobbyist wind turbines are often somewhat crude, but many sources of construction information are available l Books by Paul Gipe and Hugh Piggott are essential references l Blades are usually made of fir, pine, fiberglass, or metal l Turbine at right uses a bicycle front axle for strength, PVC blades, and a permanent magnet servomotor as a generator Malabar Days FL 2002? 040218 Photos by F. Leslie, 2003
12. 2. 4 Large Systems: Size and Numbers l Rotor hub is high above turbulent ground wind layer l Production line assembly l 660 k. W to 7 MW power models l Groups of 10 to 1000 s of turbines l Attractive, modern appearance 070221 www. windenergy. org
12. 2. 4 Large Systems: Examples & Locations l l WA: FPL Stateline and Vansycle Ridge Wind Farms HI: Honolulu, OR: Wasco, TX: Mc. Camey, Amarillo NM: Clayton; near House NM Many others in IL, NY, OH, PA, CO, WV, WY, IA, PA, MN; see AWEA website NACELLE 1 MW The nacelle is the enclosure at the top of the tower 060219 http: //www. windenergy. org/Land 302_files/frame. htm
12. 2. 4 State Line Wind Farm, WA & OR l This telephoto from the anti-Cape Wind Project group, “Save Our Sound”, shows a string of turbines from the end to emphasize ugliest visual effect l. Windfarm companies usually show a side view of the string, which looks less crowded and interesting 100223
12. 2. 4 Large Systems: SE Washington/Oregon l FPL Stateline and Vansycle Ridge Wind Farms in southeast WA and northeast Oregon l Wasco OR shown; plowed fields for wheat underneath 060219 Photos by F. Leslie, 2002
12. 2. 4. 1 Large Systems: Offshore Installation 080218 Manwell, J. A. . Univ. Mass.
12. 2. 4. 1 Large Systems: Synchronous Generation l Initial matching of alternating current frequency/phase to the utility grid used induction alternators (the a. c. form of a generator) l Induction phase-matching to the grid required that the rotor turn synchronously with the utility power frequency, usually 1800 or 3600 rpm (multiples of 60 cycles per second l These fixed speeds meant that the blade operation efficiency varied greatly with the wind speed l The field frequency that provides generator magnetic fields can be dynamically changed with electronic conversion to produce synchronized output from a variable speed rotor 070221
12. 2. 4. 1 Large Systems: Asynchronous Generation l A return to asynchronous (variable speed) operation allowed the rotor speed to change with wind speed, avoiding many blade airflow inefficiencies l Electronic convertors were used to change the variable frequency and voltage, or “wild”, electricity to the standard; i. e. , 60 hertz u. Electronic conversion circuitry has decreased in price over the last decade as high power MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) became available u Single-phase can be converted to three-phase power 060221
12. 2. 4. 1 Offshore Wind Farms l Wind farms are often placed offshore a few miles because the winds are unimpeded (have a good “fetch”, or upwind distance, of the wind) l Depths of less than 60 feet are preferable l Undersea cables carry power to shore terminals l The turbines are clearly visible if close and often are attacked by NIMBYs who want their “viewscape” unblemished u. The proposed Cape Wind farm would appear a fingerwidth high at arm’s length n NIMBYs want only things found in nature like ships, yachts and windsurfers (John Kerry) in view 100223
12. 2. 4. 1 Offshore Wind Farms: UK l There are numerous wind fields established offshore where the wind speed is continuously high and unimpeded l Atlantic Ocean winds are strong here 060221 http: //www. offshorewindfarms. co. uk/sites. html
12. 2. 4. 1. 1 Blythe Windfarm l Northumberland 2 MW turbines on an existing seawall 090309 http: //www. power-technology. com/projects/blyth 1. html
12. 2. 4. 1. 2 Middelgrunden l. R Photo Copyright Jens H. Larsen Twenty 2 MW turbines 76 m diameter 64 m above sea level http: //www. middelgrunden. dk/MG_UK/construction_photos/photosoffshore. htm The Middelgrunden offshore windfarm is located near Copenhagen, Denmark 040223
12. 2. 4. 1. 2 Middelgrunden Photos l Turbines turn slowly at 8 to 20 rpm l There is a staging platform and entry hatch at the base l Some have a raised platform about 30 feet above sea level 080218
12. 2. 4. 1. 3 Cape Wind Politics l The Cape Wind Project http: //www. capewind. org/ of 170 turbines has many detractors who don’t want to see wind turbines on Horseshoe Shoal offshore of Cape Cod MA l Environmentalist organizations are divided as to lower GHGs with clean wind power instead of coal or possible bird/bat strikes or other disturbances l Greenpeace is supporting the project; Audubon and Humane Society protest it; Sierra Club waffles on it l Robert Kennedy, Jr. opposes the windfarm although the Natural Resources Defense League organization that employs him as their lawyer endorses windfarms l A heavily funded, posh website by http: //www. saveoursound. org/site/Page. Server protests the project 090309
12. 2. 4. 1. 3 From the “Save Our Sound” Website 060221 Area is within view of nearby islands with expensive homes
12. 2. 4. 1. 3 From the “Save Our Sound” Website 080218 I presume this family is looking in horror at the simulation? - FRL
12. 2. 4. 1. 3 Cape Wind Construction Plan l Pile-climbing barges are used to support the lift cranes and transport the rotor l The barge is jacked up to get a steady platform l A tall crane lifts the rotor to be pulled into place and bolted on l Not good for a windy day! http: //www. capewind. org/harnessing/pcons 02. htm 060219
sgroup. cms. schunk-group. com 12. 2. 5 Large Turbine Components Note railing Ref. : www. freefoto. com/pictures/general/ windfarm/index. asp? i=2 060217
12. 2. 5 Small Turbine Components http: //homepages. enterprise. net/hugh 0 piggott/download/windrotord. pdf l A small turbine has a free-spinning assembly that the wind turns in azimuth by pushing on the tail 060217
12. 2. 5. 1 Rotor Aerodynamics l The blades of an airplane propeller are curved on the front and flatter on the back towards the plane l The blades not only pull the plane forward by their angle, but the airflow over the curve develops lift or pulling forces that move the plane forward l Turbine rotors are reversed with the curve at the downwind side and with the angle of the blade reversed; wind hits the flatter side l A model airplane propeller can’t be used as a turbine blade since the key dimensions are backwards from a wind rotor l Possibly a propeller manufacturer could be persuaded to make a “standard” profile blade that could be used in 2 s, 3 s, or 4 s l Model helicopter blades can be used since they are just one bolt-on blade instead of a double-sided propeller; hub sets the angle 060219 http: //homepages. enterprise. net/hugh 0 piggott/download/windrotord. pdf
12. 2. 5. 2 Airfoils and their Design l Propellers pull the rotor into the air, which is why the British call them “airscrews” l Rotors for wind turbines are pushed by the wind, and use lift on the downwind side of the blades to pull them around the shaft faster l Blade numbers vary from 2 to perhaps 5 l Blade solidity is the percent of the disk area that is solid with blades l Thrust force is the force of the wind pressing back on the rotor that the tower must resist l Stall occurs when the airstream over the blade separates due to an excessive angle of attack 060219
12. 2. 5. 2. 1 Airfoils and their Design l Rpm = wind speed x tip-speed-ratio x 60 / (diameter x ); TSR often ~6 l Revolutions (rpm) = V x TSR x 60 / (2πR) l Bergey Windpower Co. uses an advanced pultruded blade shape made without a twist (below right) u. The plastic is stretched through a die to form the shape 080218
12. 2. 5. 2. 2 Airfoils Design: Tip Speed Ratio l The rotational tip speed divided by the wind speed yields the tip speed ratio or TSR l Drag rotors that have no lift always have a TSR of ~1 or less; they are just dragged around by the wind; Savonius or cup anemometer l Airfoil rotors gain “lift” from the wind flowing over the blade and can turn up to ~14 times the wind speed; a TSR of 6 is more likely l Matching the generator speed is helpful l The TSR should be low enough to keep the blade tip below ~135 mph to avoid loud noise 060219
12. 2. 5. 3 Lift and Drag Forces on Blade l Lift = Cl ρ/2 AV 2 l Drag = Cd ρ/2 AV 2; note similarity between lift and drag l Nominal lift and drag curves for the profile are used to select the values required l These curves are measured in a wind tunnel and can’t be computed 050224 www. windmission. dk
Resultant Force 12. 2. 5. 3. 1 Blade Angle and Wind Forces l The blade is moving rapidly and the direction of the relative wind changes with rotor speed Lift Force Chord Line Maximize F = L sin Θ – D cos Θ L Drag Force Thrust u Blade Pitch β Rotational Velocity D cos Θ L sin Θ Angle of Attack α Relat ive W ind, W V 1 = ~2/3 x wind velocity, V 0, due to slowed wind Wind 080228 Rotation Force, F φ
12. 2. 5. 3. 2 Prop vs. Rotor Lift Airplane Propeller Wind CW WT Rotor Wind Driven Motion Lift pulls Airplane Propeller Flipped Over Weak Motion; Backwards! Poor Lift Rotor “lift” helps pull rotor around CCW WT Rotor No good for rotor Motion Lift pulls An airplane propeller won’t work as a wind turbine rotor; it’s backwards 060219
12. 2. 5. 4 Blade Design l Since the relative wind near the hub is closer to the true wind speed, the pitch of the blade must be higher there l Near the tip, the pitch is just 0 -2 degrees and the blade is nearly parallel to the direction of rotation l Still, since so much of the torque comes from the end of the blade, suboptimal shapes that are designed without twist are often used for economic reasons l The angle is then optimized at about 80 -100% of the blade radius l The hub attachment must be very strong to resist flexing that would break the blade at the root l The leading edge is rounded so the wind “attaches” to the surface of the blade as the direction changes 080228
12. 2. 5. 4. 1 Blade Construction: Shape l The blade profile changes angle and shape from the root to the tip l. A knot-free plank is rough cut to get the outside shape l. Edges are marked and excess cut away l. A pattern is used to form each station along the blade l. The area between blades is cut away and sanding finishes the surface smoothly 090309 http: //homepages. enterprise. net/hugh 0 piggott/download/windrotord. pdf
12. 2. 5. 4. 2 Blade Construction: Shape l The blade profile changes angle and shape from the root to the tip l The width from nose to tail is called the chord l The thickness is from one side to the other in percent of chord; in NACA shape designation 4412 has a 12% thickness (NACA now NASA) l The round nose reduces the tendency to stall chord 080228 http: //homepages. enterprise. net/hugh 0 piggott/download/windrotord. pdf
12. 2. 5. 4. 3 Blade Construction: Shape l PE 9 is not as wide as the previous root profile, but is much larger than PE 15 at the tip l Note the slope is flatter 030306 http: //homepages. enterprise. net/hugh 0 piggott/download/windrotord. pdf
12. 2. 5. 4. 4 Blade Construction: Shape l These profiles must now be made in the material, perhaps by carving wood or grinding/molding plastic l Profile templates are made to test the remaining material l When slicing or planing off the wood, when it needs just one more stroke to be done, don’t do it! l Sand the profiles to smooth the shape and fair in the curves; the blades must weigh the same on each side l The blade root must remain as thick and strong as possible to avoid breaking in gusts l Coat the blades with thin polyurethane sanding sealer and then sand with fine 250 grit sandpaper l When finished, coat with two coats of polyurethane varnish to keep water out of the wood 060219 http: //homepages. enterprise. net/hugh 0 piggott/download/windrotord. pdf
12. 2. 5. 4. 5 Rotor Construction: Balance l The rotor support might be made from steel 4 -5/16 inch electrical box covers; these are strong and galvanized ($0. 85 each) l Some use a drilled pulley to bolt to the blades for strength l The center must attach to the generator shaft, and the blades attach to both plates, preventing blade canting from centrifugal force l With the blades somewhat loosely assembled, balance the hub plates horizontally on a point to detect a heavy blade l Next, measure the distance between the blade tips and move them slightly to equalize the distances between tips l Tighten the blade root bolts more, and fasten the rotor on a horizontal shaft in oiled bearings – perhaps a bicycle hub l If the rotor turns because one blade is heavier than the others, balancing is needed; trim the surface a little or swap blades l A temporary weight is placed on lighter blades to assess how much material is to be removed or in moving the blades in the bolt holes 080228
12. 2. 5. 5 Rotor Speed, Torque, and Power l Direct-drive generators or alternators avoid the losses of gearing or a belt transmission l The rotor is designed to turn at some optimum speed, and will perform less efficiently at lower or higher speeds l The generator must reach the required voltage at a reasonable rotor speed, thus must perform well at 200 to 600 rpm at perhaps the top 30% of wind speeds l If the generator is available first, design of the rotor blades must match the generator speed l If the rotor is available first, selection of the generator must match rotor speed l Rotor torque sets the starting speed, yet if the wind speed is too low to start spin, there is little wind power; don’t worry! 080228
12. 2. 6 RPM and Torque; Starting Speed l Power = Torque, Q, x Speed, Ω (omega) or N, so Torque = P/Ω l The rotor must overcome bearing resistance, residual unbalances, magnetic cogging attraction, etc. , and accelerate to a useful speed to generate charging power l During a gust of perhaps two to four seconds, the rotor must accelerate to a new speed to extract energy from the gust; light, small rotors can do this; 100 m ones can’t l Otherwise, the wind may cause airflow stall over the blades as the rotor angular momentum changes too slowly due to inertia l Momentary stall protects the turbine from throwing blades 090309
12. 2. 6. 1 Power Is Proportional to Wind Speed Cubed l Recall that the average wind power is based upon the average of the speed cubed for each occurrence l The wind energy varies from trivial to useful to disastrous! l Precautions are needed to protect the turbine l Energy is power times the time of energy persistence Ref. : Bergey 090309
12. 2. 6. 1. 1 Turbine Power Curves l Since power is negligible at low speeds of 6 mph or less, it doesn’t matter that the turbine won’t start then l The distribution of wind speeds indicates the relative probability that wind will exceed a given value l Much of the power occurs in the top 30% of the wind speeds, so these speeds set the design parameters l For this reason, it is desirable to keep the turbine extracting power in strong winds while still protecting it from damage l Large turbines are turned out of the wind at approximately 30 to 35 mph or their blades are turned (rotated) into the wind to produce less torque 050224
12. 2. 6. 1. 2 Turbine Power Curves l Fortis Montana 5800 080228 http: //www. gale force. nireland. co. uk/turbine_power_curve. htm
12. 2. 6. 1. 2 Turbine Power Curves l Fortis Passat 1400 080228 http: //www. galeforce. nireland. co. uk/turbine_power_curve. htm
12. 2 Conclusion: Wind Turbine Theory l The rotor must be matched to the generator or alternator to obtain the maximum extracted energy over a year l Although most turbines won’t rotate until the wind speed reaches 6 mph; there is no significant energy lost below this speed; power is proportional to the cube of speed l If turbine placement can increase the wind speed by 10%, the power increases by 33% l All parts must be designed to survive high winds, say 130 mph; this is important to survive a hurricane u. We lowered our 10 -ft diameter turbine on Roberts Hall and removed the blades for Hurricane Jeanne u. The anemometer remains on the WFIT tower during hurricanes so speed can be read or logged 080228
Olin Engineering Complex 4. 7 k. W Solar PV Roof Array Questions? 080116
References: Books l Gipe, Paul. Wind Power: Renewable Energy for Home, Farm, and Business. VT: White River Junction, Chelsea Green Publishing Company, 2004. ISBN 1 -931498 -14 -8. l Piggott, Hugh. Windpower Workshop. Centre for Alternative Technology publications, 2000. ISBN 1 898049 27 0. l Boyle, Godfrey, ed. . Renewable Energy: Power for a Sustainable Future. Oxford Univ. Press, Oxford, England, 477 pp. , 1996. l Gipe, Paul. Wind Energy for Home & Business. White River Junction, VT: Chelsea Green Pub. Co. , 1993. 0 -930031 -64 -4, TJ 820. G 57, 621. 4’ 5 l Patel, Mukund R. Wind and Solar Power Systems. Boca Raton: CRC Press, 1999, 351 pp. ISBN 0 -8493 -1605 -7, TK 1541. P 38 1999, 621. 31’ 2136 l Sørensen, Bent. Renewable Energy, Second Edition. San Diego: Academic Press, 2000, 911 pp. ISBN 0 -12 -656152 -4. 050224
References: Websites, etc. http: //www. windpower. org/index. htm http: //groups. yahoo. com/group/awea-wind-home/ Join this group for access to experts http: //www. ndsu. nodak. edu/ndsu/klemen/Perfect_Turbine. htm basics of small turbines http: //www. windturbine-analysis. com/index. htm Darrieus turbine analysis as a student project – Excellent! http: //www. sandia. gov/wind/ http: //www. power-technology. com/ http: //telosnet. com/wind/index. html Excellent history and progress review http: //www. eere. energy. gov/windpoweringamerica/ http: //www. middelgrunden. dk/MG_UK/project_info/turbine. htm Offshore windfarm http: //www. capewind. org/harnessing/pcons 02. htm http: //www. bergey. com/ http: //homepages. enterprise. net/hugh 0 piggott/download/windrotord. pdf Learn how to build a turbine! http: //homepages. enterprise. net/hugh 0 piggott/pmgbooklet/index. htm Build a PM generator http: //users. aber. ac. uk/iri/WIND/TECH/WPcourse/page 2. html How blades work http: //www. espace-eolien. fr/ouest/Images_Gou. HTM French turbine photos http: //www. windpowerindia. com/index. asp _________________________________________awea-windnet@yahoogroups. com. Wind Energy elist awea-wind-home@yahoogroups. com. Wind energy home powersite elist rredc. nrel. gov/wind/pubs/atlas/maps/chap 2/2 -01 m. html PNNL wind energy map of CONUS windenergyexperimenter@yahoogroups. com. Elist for wind energy experimenters telosnet. com/wind/20 th. html solstice. crest. org/ dataweb. usbr. gov/html/powerplant_selection. html 060219
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