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

12.2 Wind Turbine Systems

Wind Turbine Theory

Crude oil ~$47.46 on 3/10/2009

$78 on 3/1/10

In Other News . . .

160 m diameter, 10 MW under development http://www.cpi.umist.ac.uk/Eminent/publicFiles/brno/RISO_Future_10MW_Wind_Turbine.pdf

Clipper building “Brittanica” 10 MW turbine for offshore use at Newcastle, UK

100223

Wind energy turbines stem from early Persian panemones – a vertical axis spinner for grinding grain

Not all power (59.3% max) can be extracted from the wind, but the turbines are relatively simple technology

This presentation discusses the types and construction of wind turbines

Wind turbine is a generic term, and it generally denotes an electrical power generator; windmills are specifically for grinding corn, wheat, or other grains

NASA used term “WECS” for WindEnergy Convertor System

There are also wind pumps for water;wind mills are for grinding grain

12.2 Overview: Wind Turbine Systems

090309

http://telosnet.com/wind/early.html

12.2 About This Presentation

12.2.1 History12.2.2 Turbine Types12.2.3 Small Turbines12.2.4 Large Systems12.2.5 Components and Airfoils12.2.6 Turbine Power Issues12.2 Conclusion

060217

12.2.1 Early History

5000 BCE (before common era): Sailing ships on the Nile River were likely the first use of wind power

Hammurabi, ruler of Babylonia, used wind power for irrigation Hero (Heron) created a wind-pumped organ Persians created a Vertical Axis WT (VAWT) in the mid 7th

Century 1191 AD: The English used wind turbines 1270: Post-mill used in Holland 1439: Corn-grinding in Holland 1600: Tower mill with rotating top or cap 1750: Dutch mill imported to America 1850: American multiblade wind pump development; 6.5

million until 1930; was produced in Heller-Allen Co., Napoleon, Ohio

1890: Danish 23-meter diameter turbine produced electricity

060219

12.2.1 Later History

1920: Early Twentieth Century saw wind-driven water-pumps commonly used in rural America, but the spread of electricity lines in 1930s (Rural Electrification Act) caused their decline

1925: Windcharger and Jacobs turbines popular for battery charging at 32V; 32Vdc appliances common for gas generators

050217

http://telosnet.com/wind/20th.html

http://telosnet.com/wind/20th.html

1940: 1250kW Rutland Vermont (Putnam) 53m system (center)

1957-1960: 200kW Danish Gedser mill (right)

1972: NASA/NSF wind turbine research

1979: 2MW NASA/DOE 61m diameter turbine in NC

Now, many windfarms are in use worldwide

12.2.2 Types of Turbines: HAWT & VAWT

HAWT (Horizontal Axis Wind Turbines) have the rotor spinning around a horizontal axisThe rotor vertical axis must turn to track the

windGyroscopic precession forces occur as the

turbine turns to track the wind

VAWT (Vertical Axis Wind Turbines) have the rotor spinning around a vertical axisThis Savonius rotor will instantly extract energy

regardless of the wind directionThe wind forces on the blades reverse each

half-turn causing fatigue of the mountingsThe two-phase design with the two sections at

right angles to each other starts more easilyThis is available in parts for experimenter

100223 Photo by F. Leslie, 2001

12.2.2.1 HAWT Examples

Charles Brush (arc light) home turbine of 1888 (center) 17 m, 1:50 step-up to drive 500 rpm generator

NASA Mod 0, 1, 2 turbines The Mod-0A at Clayton NM produced 200kW (below left)

060221

http://telosnet.com/wind/govprog.htmlhttp://telosnet.com/wind/20th.html

http://www.windmission.dk/projects/Nybroe%20Home/l

060221

12.2.2.1 Horizontal Axis Wind Turbines (HAWT)

Ref.: WTC

1.8 m

75 m

American Farm, 1854

Sailwing,1300 A.D.

Dutch with fantail

Modern Turbines

Experimental Wind farm

Dutch post mill

12.2.2.2 VAWT Examples

Darrieus troposkein blades (jump rope)Savonius rotor ~1925Madaras rotor using the Magnus Effect

Rotors placed on train cars to push them around a circular track

Vortex TurbineThe SANDIA Darrieus turbine

was destroyed when left unbraked overnight

090309 http://telosnet.com/wind/govprog.html

12.2. Vertical Axis Wind Turbines (VAWT)

060221

Savonius

Darrieuswith Savonius

Panemone, 1000 B.C.

Giromill

This sample shows the diversity of VAWT over the years

ExperimentalSavonius

If wind projects are measured by commercial success, the Southeast USA isn’t the best area to use!

The Florida Keys would be a likely area to evaluate coastal breezes

12.2.2 Location of Turbines: USA States

100223

http://telosnet.com/wind/recent.html

http://www.awea.org/projects/index.html, showing MW in each state

2003

9/30/2007

12.2.3 Small Wind Turbines: American

100222

In 1854, patented wind pumpers were popular across the US, later spreading to other nations

By 1870, improvements made with sheet steel blades stamped to an aerodynamic contour

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

AEI states that there are some 30,000 farm wind pumps in the Southern Great Plains at 0.25 kW each, or some 5 MW total

Typical present-day at www.ohio-windmill.com

12.2.3 Small Wind Turbines: Bergey

030307 /090310

Equipment: BWC 7.5 kW Wind Turbine, 3 kW Solar, ~ 90 kWh Battery Bank

Performance: ~ 40 kWh / Day at 240 VAC, 60 Hz

Customer: Renegade Radio Installation: May 1996

Results: Over 98% availability. Alternator replaced in May 1998 following wiring fault.

http://www.bergey.com/

Bergey produces small wind turbines up to 50 kW

12.2.3 Small Wind Turbines: Southwest Windpower

090310 http://www.windenergy.com/

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

These turbines are available in several variations

Amateur or hobbyist wind turbines are often somewhat crude, but many sources of construction information are available

Books by Paul Gipe and Hugh Piggott are essential references

Blades are usually made of fir, pine, fiberglass, or metal Turbine at right uses a bicycle front axle for strength,

PVC blades, and a permanent magnet servomotor as a generator

12.2.3 Small Wind Turbines: “Homemade”

040218 Photos by F. Leslie, 2003

Malabar Days FL 2002?

12.2.4 Large Systems: Size and Numbers

Rotor hub is high above turbulent ground wind layer

Production line assembly

660kW to 7 MW power models

Groups of 10 to 1000s of turbines

Attractive, modern appearance

070221 www.windenergy.org

WA: FPL Stateline and Vansycle Ridge Wind FarmsHI: Honolulu, OR: Wasco, TX: McCamey, AmarilloNM: Clayton; near House NMMany others in IL, NY, OH, PA, CO, WV, WY, IA, PA,

MN; see AWEA website

12.2.4 Large Systems: Examples & Locations

060219

NACELLE 1 MW

http://www.windenergy.org/Land302_files/frame.htm

The nacelle is the enclosureat the top of the tower

12.2.4 State Line Wind Farm, WA & OR

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

100223

Windfarm companies usually show a side view of the string, which looks less crowded and interesting

Photos by F. Leslie, 2002

12.2.4 Large Systems: SE Washington/Oregon

FPL Stateline and Vansycle Ridge Wind Farms in southeast WA and northeast Oregon

Wasco OR shown; plowed fields for wheat underneath

060219

12.2.4.1 Large Systems: Offshore Installation

080218

Renewable Energy Research Laboratory

University of Massachusetts

Installation

Photos: Courtesy GE Wind

Manwell, J.A.. Univ. Mass.

Initial matching of alternating current frequency/phase to the utility grid used induction alternators (the a.c. form of a generator)

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

These fixed speeds meant that the blade operation efficiency varied greatly with the wind speed

The field frequency that provides generator magnetic fields can be dynamically changed with electronic conversion to produce synchronized output from a variable speed rotor

12.2.4.1 Large Systems: Synchronous Generation

070221

12.2.4.1 Large Systems: Asynchronous Generation

A return to asynchronous (variable speed) operation allowed the rotor speed to change with wind speed, avoiding many blade airflow inefficiencies

Electronic convertors were used to change the variable frequency and voltage, or “wild”, electricity to the standard; i.e., 60 hertzElectronic conversion circuitry has decreased

in price over the last decade as high power MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) became available

Single-phase can be converted to three-phase power

060221

12.2.4.1 Offshore Wind Farms

Wind farms are often placed offshore a few miles because the winds are unimpeded (have a good “fetch”, or upwind distance, of the wind)

Depths of less than 60 feet are preferableUndersea cables carry power to shore terminalsThe turbines are clearly visible if close and often

are attacked by NIMBYs who want their “viewscape” unblemishedThe proposed Cape Wind farm would appear a

finger-width high at arm’s lengthNIMBYs want only things found in nature like ships,

yachts and windsurfers (John Kerry) in view

100223

12.2.4.1 Offshore Wind Farms: UK

060221 http://www.offshorewindfarms.co.uk/sites.html

There are numerous wind fields established offshore where the wind speed is continuously high and unimpeded

Atlantic Ocean winds are strong here

12.2.4.1.1 Blythe Windfarm

Northumberland 2 MW turbines on an existing seawall

090309http://www.power-technology.com/projects/blyth/blyth1.html

12.2.4.1.2 Middelgrunden

The Middelgrunden offshore windfarm is located near Copenhagen, Denmark040223

Photo Copyright Jens H. Larsen

http://www.middelgrunden.dk/MG_UK/construction_photos/photosoffshore.htm

Twenty 2 MW turbines

76m diameter

64m above sea level

R

12.2.4.1.2 Middelgrunden Photos

080218

Turbines turn slowly at 8 to 20 rpm

There is a staging platform and entry hatch at the base

Some have a raised platform about 30 feet above sea level

12.2.4.1.3 Cape Wind Politics

090309

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

Environmentalist organizations are divided as to lower GHGs with clean wind power instead of coal or possible bird/bat strikes or other disturbances

Greenpeace is supporting the project; Audubon and Humane Society protest it; Sierra Club waffles on it

Robert Kennedy, Jr. opposes the windfarm although the Natural Resources Defense League organization that employs him as their lawyer endorses windfarms

A heavily funded, posh website by http://www.saveoursound.org/site/PageServer protests the project

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

080218I presume this family is looking in horror at the simulation? - FRL

12.2.4.1.3 Cape Wind Construction Plan

060219

http://www.capewind.org/harnessing/pcons02.htm

Pile-climbing barges are used to support the lift cranes and transport the rotorThe barge is

jacked up to get a steady platform

A tall crane lifts the rotor to be pulled into place and bolted on

Not good for a windy day!

12.2.5 Large Turbine Components

060217Ref.: www.freefoto.com/pictures/general/ windfarm/index.asp?i=2

sgroup.cms.schunk-group.com

Note railing

12.2.5 Small Turbine Components

A small turbine has a free-spinning assembly that the wind turns in azimuth by pushing on the tail

060217

http://homepages.enterprise.net/hugh0piggott/download/windrotord.pdf

The blades of an airplane propeller are curved on the front and flatter on the back towards the plane

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

Turbine rotors are reversed with the curve at the downwind side and with the angle of the blade reversed; wind hits the flatter side

A model airplane propeller can’t be used as a turbine blade since the key dimensions are backwards from a wind rotorPossibly a propeller manufacturer could be persuaded to make

a “standard” profile blade that could be used in 2s, 3s, or 4s Model helicopter blades can be used since they are just one bolt-on

blade instead of a double-sided propeller; hub sets the angle

12.2.5.1 Rotor Aerodynamics

060219 http://homepages.enterprise.net/hugh0piggott/download/windrotord.pdf

12.2.5.2 Airfoils and their Design

Propellers pull the rotor into the air, which is why the British call them “airscrews”

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

Blade numbers vary from 2 to perhaps 5Blade solidity is the percent of the disk area

that is solid with bladesThrust force is the force of the wind pressing

back on the rotor that the tower must resistStall 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

080218

Rpm = wind speed x tip-speed-ratio x 60 / (diameter x ); TSR often ~6

Revolutions (rpm) = V x TSR x 60 / (2πR)Bergey Windpower Co. uses an advanced

pultruded blade shape made without a twist (below right)The plastic is stretched through a die to form

the shape

12.2.5.2.2 Airfoils Design: Tip Speed Ratio

The rotational tip speed divided by the wind speed yields the tip speed ratio or TSR

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

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

Matching the generator speed is helpfulThe TSR should be low enough to keep the

blade tip below ~135 mph to avoid loud noise060219

Lift = Cl ρ/2 AV2

Drag = Cd ρ/2 AV2; note similarity between lift and drag

Nominal lift and drag curves for the profile are used to select the values required

These curves are measured in a wind tunnel and can’t be computed

12.2.5.3 Lift and Drag Forces on Blade

050224 www.windmission.dk

u

L

Blade Pitchβ

α

The blade is moving rapidly and the direction of the relative wind changes with rotor speed

Angle of Attackφ

Drag Force

12.2.5.3.1 Blade Angle and Wind Forces

080228

Relative Wind, W

Chord Line

V1 = ~2/3 x wind velocity, V0,due to slowed wind

Lift Force

Resultant Force

RotationForce, F

RotationalVelocity

Thrust

Wind

L sin ΘD cos Θ

Maximize F = L sin Θ – D cos Θ

An airplane propeller won’t work as a wind turbine rotor; it’s backwards

Poor Lift

Lift pulls

12.2.5.3.2 Prop vs. Rotor

060219

AirplanePropeller CW WT Rotor

CCW WT Rotor

AirplanePropeller

Flipped Over

Wind

Wind

Motion

Weak Motion;

Backwards!

Driven Motion

Motion

No good for rotor

Lift pulls

Lift

Rotor “lift” helps pull rotor around

12.2.5.4 Blade Design

080228

Since the relative wind near the hub is closer to the true wind speed, the pitch of the blade must be higher there

Near the tip, the pitch is just 0-2 degrees and the blade is nearly parallel to the direction of rotation

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 reasonsThe angle is then optimized at about 80-100%

of the blade radiusThe hub attachment must be very strong to resist

flexing that would break the blade at the rootThe leading edge is rounded so the wind

“attaches” to the surface of the blade as the direction changes

12.2.5.4.1 Blade Construction: Shape

090309

The blade profile changes angle and shape from the root to the tip

http://homepages.enterprise.net/hugh0piggott/download/windrotord.pdf

A knot-free plank is rough cut to get the outside shape

Edges are marked and excess cut away

A pattern is used to form each station along the blade

The area between blades is cut away and sanding finishes the surface smoothly

The blade profile changes angle and shape from the root to the tip

The width from nose to tail is called the chord 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)

The round nose reduces the tendency to stall

12.2.5.4.2 Blade Construction: Shape

080228 http://homepages.enterprise.net/hugh0piggott/download/windrotord.pdf

chord

12.2.5.4.3 Blade Construction: Shape

030306

PE9 is not as wide as the previous root profile, but is much larger than PE15 at the tip

Note the slope is flatter

http://homepages.enterprise.net/hugh0piggott/download/windrotord.pdf

12.2.5.4.4 Blade Construction: Shape

060219

These profiles must now be made in the material, perhaps by carving wood or grinding/molding plastic

Profile templates are made to test the remaining material

When slicing or planing off the wood, when it needs just one more stroke to be done, don’t do it!

Sand the profiles to smooth the shape and fair in the curves; the blades must weigh the same on each side

The blade root must remain as thick and strong as possible to avoid breaking in gusts

Coat the blades with thin polyurethane sanding sealer and then sand with fine 250 grit sandpaper

When finished, coat with two coats of polyurethane varnish to keep water out of the wood

http://homepages.enterprise.net/hugh0piggott/download/windrotord.pdf

12.2.5.4.5 Rotor Construction: Balance

080228

The rotor support might be made from steel 4-5/16 inch electrical box covers; these are strong and galvanized ($0.85 each)

Some use a drilled pulley to bolt to the blades for strength The center must attach to the generator shaft, and the

blades attach to both plates, preventing blade canting from centrifugal force

With the blades somewhat loosely assembled, balance the hub plates horizontally on a point to detect a heavy blade

Next, measure the distance between the blade tips and move them slightly to equalize the distances between tips

Tighten the blade root bolts more, and fasten the rotor on a horizontal shaft in oiled bearings – perhaps a bicycle hub

If the rotor turns because one blade is heavier than the others, balancing is needed; trim the surface a little or swap blades

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

12.2.5.5 Rotor Speed, Torque, and Power

Direct-drive generators or alternators avoid the losses of gearing or a belt transmission

The rotor is designed to turn at some optimum speed, and will perform less efficiently at lower or higher speeds

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

If the generator is available first, design of the rotor blades must match the generator speed

If the rotor is available first, selection of the generator must match rotor speed

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

090309

Power = Torque, Q, x Speed, Ω (omega) or N,so Torque = P/Ω

The rotor must overcome bearing resistance, residual unbalances, magnetic cogging attraction, etc., and accelerate to a useful speed to generate charging power

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; 100m ones can’tOtherwise, the wind may cause airflow stall

over the blades as the rotor angular momentum changes too slowly due to inertia

Momentary stall protects the turbine from throwing blades

12.2.6.1 Power Is Proportional to Wind Speed Cubed

Recall that the average wind power is based upon the average of the speed cubed for each occurrence

The wind energy varies from trivial to useful to disastrous!

Precautions are needed to protect the turbineEnergy is power times the time of energy persistence

Ref.: Bergey

090309

12.2.6.1.1 Turbine Power Curves

050224

Since power is negligible at low speeds of 6 mph or less, it doesn’t matter that the turbine won’t start then

The distribution of wind speeds indicates the relative probability that wind will exceed a given value

Much of the power occurs in the top 30% of the wind speeds, so these speeds set the design parameters

For this reason, it is desirable to keep the turbine extracting power in strong winds while still protecting it from damageLarge 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

12.2.6.1.2 Turbine Power Curves

080228

Fortis Montana 5800

http://www.gale force.nireland.co.uk/turbine_power_curve.htm

12.2.6.1.2 Turbine Power Curves

080228

Fortis Passat 1400

http://www.galeforce.nireland.co.uk/turbine_power_curve.htm

12.2 Conclusion: Wind Turbine Theory

The rotor must be matched to the generator or alternator to obtain the maximum extracted energy over a year

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

If turbine placement can increase the wind speed by 10%, the power increases by 33%

All parts must be designed to survive high winds, say 130 mph; this is important to survive a hurricaneWe lowered our 10-ft diameter turbine on Roberts Hall

and removed the blades for Hurricane JeanneThe anemometer remains on the WFIT tower during

hurricanes so speed can be read or logged

080228

Olin Engineering Complex 4.7 kW Solar PV Roof Array

080116

Questions?

References: Books

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.

Piggott, Hugh. Windpower Workshop. Centre for Alternative Technology publications, 2000. ISBN 1 898049 27 0.

Boyle, Godfrey, ed.. Renewable Energy: Power for a Sustainable Future. Oxford Univ. Press, Oxford, England, 477 pp., 1996.

Gipe, Paul. Wind Energy for Home & Business. White River Junction, VT: Chelsea Green Pub. Co., 1993. 0-930031-64-4, TJ820.G57, 621.4’5

Patel, Mukund R. Wind and Solar Power Systems. Boca Raton: CRC Press, 1999, 351 pp. ISBN 0-8493-1605-7, TK1541.P38 1999, 621.31’2136

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.htmhttp://groups.yahoo.com/group/awea-wind-home/ Join this group for access to expertshttp://www.ndsu.nodak.edu/ndsu/klemen/Perfect_Turbine.htm basics of small turbineshttp://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 reviewhttp://www.eere.energy.gov/windpoweringamerica/ http://www.middelgrunden.dk/MG_UK/project_info/turbine.htm Offshore windfarmhttp://www.capewind.org/harnessing/pcons02.htmhttp://www.bergey.com/http://homepages.enterprise.net/hugh0piggott/download/windrotord.pdf Learn how to build a turbine!http://homepages.enterprise.net/hugh0piggott/pmgbooklet/index.htm Build a PM generatorhttp://users.aber.ac.uk/iri/WIND/TECH/WPcourse/page2.html How blades workhttp://www.espace-eolien.fr/ouest/Images_Gou.HTM French turbine photoshttp://www.windpowerindia.com/index.asp__________________________________________________________________________________-awea-windnet@yahoogroups.com. Wind Energy elistawea-wind-home@yahoogroups.com. Wind energy home powersite elistrredc.nrel.gov/wind/pubs/atlas/maps/chap2/2-01m.html PNNL wind energy map of CONUS windenergyexperimenter@yahoogroups.com. Elist for wind energy experimenterstelosnet.com/wind/20th.htmlsolstice.crest.org/dataweb.usbr.gov/html/powerplant_selection.html

060219