Wind is caused from the Uneven heating of the earth.

Wind is caused from the Uneven heating of the earth.

The extraction of energy from Wind, especially in the form of

Electricity, has enjoyedRenewed interest among

Both utilities and governments.

Wind energy is the fastest growingForm of energy today, up to

400% increase in the past 20 years.

Today, there are over 30,000 Wind turbines worldwide, with

An installed capacity of Over 40,000 MW.

Wind power’s environmental Impact is almost insignificant,Its main problem being visual “pollution,” although concernsAbout noise, communications

Interference have been expressed.

With current wind construction,Bird mortality has fallen

Substantially.

Infact, bird collisions with Automobiles and windows in high

Buildings cause more bird Deaths, by a factor of a million!

Favorable California tax incentives resulted in major U.S. wind farms Altamonte Pass Tehachapi San Gorgonio Pass

Other turbines are located in Dakotas, Iowa, OR, Texas, Minnesota, NY, WA, Wyoming, Iowa, PA, VA, Vermont, etc.

US wind power estimate map

Wind Statistics and Assessment

Wind speed and direction are measured by an anemometerSpeed is derived from rotating cups or a spinning

propeller driving an interrupter device or a small electric generator

Data are logged electronically for later processingThe mean (average) and peak (gust) speeds are of the

greatest importanceTurbulence may affect turbine efficiency, but yawing points

the turbine into the average windTen-minute averages are used for power assessment,

while gust studies may require two to ten points per second

Wind resources vary greatly with latitude, season, and surrounding terrain

Extensive data and wind maps exist for wind prospectingAt the mesoscale level, topographic information is being used

to create predictions of wind speed from scattered real dataAnemometers can be erected to obtain wind speeds in a likely

locale for comparison to NWS long-term recordsAn alternative is to erect a small wind turbine to sample the

energy and help determine where a large turbine should be placed

Wind resources may be excellent, but there is much more to installing a turbine

Anemometers

Anemometers measure the speed and direction of the wind as a function of timeSpinning cups or propellerUltrasonic reflection (Doppler)Sodar (Sound detection and ranging with a large horn)RadarDrift balloonsEtc.

Wind data are usually collected at ten-minute rate and averaged for recording

Gust studies are occasionally used, and require fast sampling at a higher rate to avoid significant information loss (4 pts/gust)

Spectral analysis indicates the frequency components of the wind structure and permits sampling frequency selection to minimize loss

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

Don’t average the speed and cube it! Cube the various speeds and average those cubes to estimate the power The Bergey wind turbine curve below indicates the energy output in

nonturbulent flow

Ref.: Bergey

Power Is Proportional to Wind Speed Cubed

How to find the Wind Power

A turbine power curve is cubic to start, but becomes intentionally less efficient at very high wind speeds to avoid damage

At very high winds, the power output may fall to zero, usually by design to prevent damage

Wind Energy Derivation Equations (also applies to water turbines)

Assume a “tube” of air the diameter, D, of the rotorA = π D2/4 (could be rectangular for a VAWT)

A length, L, of air moves through the turbine in t secondsL = u·t, where u is the wind speed

The tube volume is V = A·L = A·u·tAir density, ρ, is 1.225 kg/m3 (water density ~1000 kg/m3, or

832 times more than air)Mass, m = ρ·V = ρ·A·u·t, where V is volumeKinetic energy = KE = ½ mu2

Wind Energy Equations (continued)

Substituting ρ·A·u·t for mass, and A = π D2/4 , KE = ½·π/4·ρ·D2·u3·t

Theoretical power, Pt = ½·π/4·ρ·D2·u3·t/t = 0.3927·ρa·D2·u3, ρ (rho) is the density, D is the diameter swept by the rotor blades, and u is the speed parallel to the rotor axis

Betz Law shows 59.3% of power can be extractedPe = Pt·59.3%·ήr·ήt·ήg, where Pe is the extracted power, ήr is

rotor efficiency, ήt is mechanical transmission efficiency, and ήg is generator efficiency

For example, 59.3%·90%·98%·80% = 42% extraction of theoretical power

Advantages and Disadvantages of Wind Systems

Wind systems, more than solar, provide variable energy as the weather changes rapidly

Storage is required to have energy available when the wind isn’t blowing and smooth it somewhat; batteries now exist for this

This highly variable wind sends variable power to lines; each turbine has different outputs, reducing electrical line variability by the square root of the number of turbines

Large utility size turbines now produce energy at a cost competitive with fossil fuels, but it takes a lot of them to get comparable energyA typical utility plant may have nearly 1000 MW or 1 GW peak power,

while a “large” turbine might be rated at 4 MW at 25 mph wind --- that’s 250 turbines for rated wind speed!

Largest now is the Enercon E-126: 126 m diameter and 7+ MW nameplate rating at Emden, Germany

10 MW to come: http://www.cpi.umist.ac.uk/Eminent/publicFiles/brno/RISO_Future_10MW_Wind_Turbine.pdf

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

Overview: Wind Turbine Systems

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

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

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

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

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

Photo by F. Leslie, 2001

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)

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

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

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

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

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

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

Location of Turbines: USA States

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

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

2003

9/30/2007

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

Turbine Power Curves

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

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

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

NACELLE 1 MW

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

The nacelle is the enclosureat the top of the tower

Large Systems: Examples & Locations

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

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

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

Cape Wind Politics

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

From the “Save Our Sound” Website

Area is within view of nearby islands with expensive homes

From the “Save Our Sound” Website

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

Cape Wind Construction Plan

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 platformA tall crane lifts the rotor

to be pulled into place and bolted on

Not good for a windy day!

Large Turbine Components

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

sgroup.cms.schunk-group.com

Note railing

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 4sModel helicopter blades can be used since they are just one bolt-on

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

Rotor Aerodynamics

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

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

Turbine Installation

Turbine installations consist of many stepsLand acquisitionLocal permittingPossibly provide living

quarters for crewsBuild a control and

operations centerProvide maintenance shops Install the turbine(s)Build a switchyardConnect the turbines through

underground wiring to the distribution switchyard

http://www.afm.dtu.dk/wind/turbines/wts4.jpg

Large Turbines

Large turbine installations usually require new road access for trucks to bring the parts

Monopod towers may be in long sectionsTurbine blades are in one piece and may require special long

trucks and long-radius-turn roadsDeep (~20 ft) concrete foundations are poured, the tower

assembled, and the complete nacelle mounted on topThe blades are hoisted by crane and bolted to the rotor hub

on the nacelleSometimes, the blades and hub are hoisted together

Small Turbines

Small turbines weigh from 10 to 1000 pounds

Manual or crane lifting may be usedA “gin pole” may be clamped to a tower

to hold a hoisting pulley overhead to lift tower sections or the generator

Some turbines are light enough that the turbine and tower may be erected as a unit

Towers may also be designed to tilt over for turbine maintenance

http://www.w9iix.com/ii00008.htm

Turbine Power Control

Turbine StatesStop

Slow rotor, feather blades (turn into wind), apply brakesStart

Release brakes, set blade attack angle, continually yaw nacelle to wind direction, at speed engage power contactors

Storm ProtectionYaw to 90° from wind, feather blades, apply rotor brakes,

continue to yaw to avoid wind on turbine rotor diskMaintenance

Lock out to “Stop” state to protect workers from backfeed from wiring, engage interlocks, set warning indicators

Wind Turbine Siting and Installation

Turbine siting is somewhat of an art, but science is providing tools that speed the selectionWind modeling provides energy density mapping

Accurate siting strongly determines the economic and energy success of the system

Energy storage is likely to be in batteries for the foreseeable future; more exotic methods are slow in reaching a cost-effective market entry

Since wind energy is the fastest developing energy source, the economic fall of prices will speed its adoption in areas where the wind is powerfulWind energy is about $2.50/W and comparable with a

new coal power plant

Grants and Assistance

In some cases, grants and/or anemometer loans from a state or the US Federal government may be approved to stimulate interest in wind energy systems

Some states provide a rebate of up to 50% of the costAnemometers for energy testing might consist only of a wind

distance indicator with a digital readout of miles of wind (difference the readings & divide by time elapsed)

The tower used should approximate the height of the turbine rotor, but the tower may be a temporary mast like a television antenna would be mounted on

Some experts advise that it is better to simply put up a substantial tower and mount a small wind turbine on it

Wind energy can be used from the small turbine before buying a larger size

070212

Conclusion: Wind Theory

The theory of wind energy is based upon fluid flow, so it also applies to water turbines (water has 832 times the density)

While anemometers provide wind speed and usually direction, data processing converts the raw data into usable information

Because of the surface drag layer of the atmosphere, placing the anemometer at a “standard” height of 10 meters above the ground is important; airport anemometer heights often historically differ from 10 meters

For turbine placement, the anemometer should be at turbine hub height

The average of the speeds is not the same as the correct average of the speed cubes!

The energy extracted by a turbine is the summation of each speed cubed times the time that it persisted

070212

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

Questions?