Transcript Slide 1
Wind is caused from the
Uneven heating of the earth.
The extraction of energy from
Wind, especially in the form of
Electricity, has enjoyed
Renewed interest among
Both utilities and governments.
Wind energy is the fastest growing
Form 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 concerns
About 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!
US wind power estimate map
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.
Wind Statistics and Assessment
Wind speed and direction are measured by an anemometer
Speed is derived from rotating cups or a spinning
propeller driving an interrupter device or a small electric
generator
Data are logged electronically for later processing
The mean (average) and peak (gust) speeds are of the
greatest importance
Turbulence may affect turbine efficiency, but yawing points
the turbine into the average wind
Ten-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 prospecting
At the mesoscale level, topographic information is being used
to create predictions of wind speed from scattered real data
Anemometers can be erected to obtain wind speeds in a likely
locale for comparison to NWS long-term records
An 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 time
Spinning cups or propeller
Ultrasonic reflection (Doppler)
Sodar (Sound detection and ranging with a large horn)
Radar
Drift balloons
Etc.
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
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
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
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 rotor
A = π D2/4
(could be rectangular for a VAWT)
A length, L, of air moves through the turbine in t seconds
L = u·t, where u is the wind speed
The tube volume is V = A·L = A·u·t
Air 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 volume
Kinetic 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 extracted
Pe = 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 energy
A 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
Overview: Wind Turbine Systems
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 Wind
Energy Convertor System
There are also wind pumps for water;
wind mills are for grinding grain
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
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
http://telosnet.com/wind/20th.html
http://telosnet.com/wind/20th.html
Types of Turbines: HAWT & VAWT
HAWT (Horizontal Axis Wind Turbines) have the rotor
spinning around a horizontal axis
The rotor vertical axis must turn to track the wind
Gyroscopic precession forces occur as the turbine
turns to track the wind
VAWT (Vertical Axis Wind Turbines) have the rotor
spinning around a vertical axis
This Savonius rotor will instantly extract energy
regardless of the wind direction
The wind forces on the blades reverse each half-turn
causing fatigue of the mountings
The two-phase design with the two sections at right
angles to each other starts more easily
This 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.html
http://telosnet.com/wind/20th.html
http://www.windmission.dk/
projects/Nybroe%20Home/l
Horizontal Axis Wind Turbines (HAWT)
Sailwing,
1300 A.D.
Dutch post
mill
Experimental
Wind farm
American
Farm, 1854
Dutch with
fantail
1.8 m
Ref.: WTC
Modern
Turbines
75 m
VAWT Examples
Darrieus troposkein blades (jump rope)
Savonius rotor ~1925
Madaras rotor using the Magnus Effect
Rotors placed on train cars to push them
around a circular track
Vortex Turbine
The SANDIA Darrieus turbine
was destroyed when left
unbraked overnight
http://telosnet.com/wind/govprog.html
Location of Turbines: USA States
If wind projects are measured by commercial success, the
Southeast USA isn’t the best area to use!
2003
http://telosnet.com/wind/recent.html
http://www.awea.org/projects/index.html, showing MW in each state
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 turbine
Energy 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 damage
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
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
Large Systems: Examples & Locations
WA: FPL Stateline and Vansycle Ridge Wind Farms
HI: Honolulu, OR: Wasco, TX: McCamey, 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
http://www.windenergy.org/Land302_files/frame.htm
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 preferable
Undersea cables carry power to shore terminals
The turbines are clearly visible if close and often are attacked
by NIMBYs who want their “viewscape” unblemished
The proposed Cape Wind farm would appear a fingerwidth high at arm’s length
NIMBYs 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
Pile-climbing barges are
used to support the lift
cranes and transport the
rotor
The 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!
http://www.capewind.org/harnessing/pcons02.htm
sgroup.cms.schunk-group.com
Large Turbine Components
Note railing
Ref.: www.freefoto.com/pictures/general/ windfarm/index.asp?i=2
Rotor Aerodynamics
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 rotor
Possibly 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
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 5
Blade solidity is the percent of the disk area that is
solid with blades
Thrust force is the force of the wind pressing back on
the rotor that the tower must resist
Stall occurs when the airstream over the blade
separates due to an excessive angle of attack
Turbine Installation
Turbine installations consist of
many steps
Land acquisition
Local permitting
Possibly provide living
quarters for crews
Build a control and
operations center
Provide maintenance shops
Install the turbine(s)
Build a switchyard
Connect 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 sections
Turbine blades are in one piece and may require special long
trucks and long-radius-turn roads
Deep (~20 ft) concrete foundations are poured, the tower
assembled, and the complete nacelle mounted on top
The blades are hoisted by crane and bolted to the rotor hub
on the nacelle
Sometimes, the blades and hub are hoisted together
Small Turbines
Small turbines weigh from 10 to 1000
pounds
Manual or crane lifting may be used
A “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 States
Stop
Slow rotor, feather blades (turn into wind), apply brakes
Start
Release brakes, set blade attack angle, continually yaw
nacelle to wind direction, at speed engage power contactors
Storm Protection
Yaw to 90° from wind, feather blades, apply rotor brakes,
continue to yaw to avoid wind on turbine rotor disk
Maintenance
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 selection
Wind 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 costeffective 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 powerful
Wind 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 cost
Anemometers 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
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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 hurricane
We lowered our 10-ft diameter turbine on Roberts Hall
and removed the blades for Hurricane Jeanne
The anemometer remains on the WFIT tower during
hurricanes so speed can be read or logged
Questions?