fundemantals of wind energy and micrositing of a wind turbine using

YILDIZ TECHNICAL UNIVERSITY
FACULTY OF MECHANICAL ENGINEERING
FUNDEMANTALS OF WIND ENERGY AND
MICROSITING OF A WIND TURBINE USING
WASP IMPLEMENTATIONS
06065137 Emre BARLAS
06065078 Dogukan KUCUKSAHIN
DEPARTMENT OF HYDROMECHANICS and HYDRAULIC MACHINES
BSc THESIS
Thesis Advisor: Prof. Dr. Yunus CENGEL
ISTANBUL, 2011
FUNDEMANTALS OF WIND ENERGY
AND MICROSITING OF A WIND
TURBINE USING WASP
IMPLEMENTATIONS
ii
CONTENTS
Page
LIST OF SYMBOLS ................................................................................................................. 5
LIST OF ABBREVIATIONS .................................................................................................... 6
LIST OF FIGURES .................................................................................................................... 7
LIST OF TABLES ................................................................................................................... 10
SUMMARY ............................................................................................................................. 11
1
INTRODUCTION ................................................................................................. 13
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.7.1
1.7.2
1.7.3
1.7.4
1.8
Historical Uses of Wind ........................................................................................ 13
History of Wind Electric Generation ..................................................................... 15
Horizontal Axis Wind Turbine Research .............................................................. 17
Darrieus Wind Turbines ........................................................................................ 26
Innovative Wind Turbines ..................................................................................... 29
Description of the System ..................................................................................... 36
Applications........................................................................................................... 39
Electrical Energy ................................................................................................... 39
Mechanical Energy ................................................................................................ 40
Thermal Energy ..................................................................................................... 41
Wind Hybrid Systems ........................................................................................... 41
Storage ................................................................................................................... 42
2
WIND CHARACTERISTICS ............................................................................... 42
2.1
2.2
2.3
2.3.1
2.3.2
2.3.3
2.3.4
Global Circulation ................................................................................................. 42
Wind Shear ............................................................................................................ 45
Wind Measurements .............................................................................................. 47
Eoalian Features .................................................................................................... 48
Biological Indicators ............................................................................................. 49
Rotational Anemometers ....................................................................................... 53
Wind Direction ...................................................................................................... 55
3
SITING .................................................................................................................. 57
3.1
3.1.1
3.1.2
3.2
3.2.1
3.2.2
3.3
Small Wind Turbines............................................................................................. 57
Noise ...................................................................................................................... 62
Visual Impact ........................................................................................................ 64
Wind Farms ........................................................................................................... 65
Long-Term Reference Stations ............................................................................. 65
Siting for Wind Farms ........................................................................................... 66
Digital Maps .......................................................................................................... 67
iii
3.4
3.5
3.6
3.6.1
3.6.2
3.6.3
3.7
Numerical Models ................................................................................................. 68
Micrositing ............................................................................................................ 69
Energy Production ................................................................................................. 75
Generator Size ....................................................................................................... 76
Rotor Area and Wind Map .................................................................................... 77
Manufacturer's Curve ............................................................................................ 79
Calculated Annual Energy..................................................................................... 79
4
AN ANALYSIS OF A MID-SCALE WIND TURBINE THAT WILL BE ERECTED
ON DAVUTPASA CAMPUS IN THE NEAR FUTURE .................................... 81
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
4.10
4.11
4.12
4.12.1
4.12.2
4.12.3
The Study Area and the Characteristics of the Region ......................................... 81
The Software Tools Used During the Analysis ..................................................... 83
The Measurement Technique and the Anemometer Used During the Analysis ... 83
Digital Map ............................................................................................................ 85
Wind Data.............................................................................................................. 86
Specifying the Nearby Obstacles .......................................................................... 87
Wind Rose ............................................................................................................. 88
Histogram and Weibull Distribution ..................................................................... 91
Wind Resource Mapping ....................................................................................... 92
Sample Wind Turbines Used in the Project .......................................................... 93
Annual Energy Production Analysis with WAsP Software ................................ 100
The Installation Cases of the Chosen Wind Turbine ........................................... 103
The Case of Installation of Redriven Turbine Behind the Sports Hall Building 103
The Case of Installation of Redriven Turbine Behind the Dormitory Building .. 104
The Case of Installation of Redriven Turbine Close to Faculty of Electronics... 106
5
CONCLUSION ................................................................................................... 108
REFERENCES
RESUMES
iv
LIST OF SYMBOLS
AKWH
Annual energy production, kilowatt hour per year
C
Scale parameter
CF
Capacity factor
E
East
H
Height
H0
Height of known wind speed
Hb
Height of the building
Href
Wind speed at the reference site
K
Shape parameter
km
Kilometer
kW
Kilowatt
M
Meter
MWh
Megawatt hour
N
North
NE
Northeast
NNE
North- Northeast
PW
Power density
R
Radius
S
Second
v0
Measured wind speed
W
West
W/m²
Watt per squaremeter
5
LIST OF ABBREVIATIONS
AC
Alternative Current
AEP
Annual Energy Production
BWEA
British Wind Energy Association
DC
Direct Current
DOE
Department of Energy
ERDA
Energy Research and Development Administration
EU
European Union
GIS
Geographic Information Systems
HAWT
Horizontal Axis Wind Turbine
LED
Light Emitting Diode
LIDAR
Light Detection and Ranging
NASA
National Aeronautics and Space Administration
NREL
National Renewable Energy Laboratory
NSF
National Science Foundation
SODAR
Sonic Detection and Ranging
UWT
Urban Wind Turbine
WAsP
Wind Atlas Analysis and Application Program
WECS
Wind Energy Collection Systems
6
LIST OF THE FIGURES
Figure 1.1
NSF–NASA MOD-0 Wind Power System General View
Figure 1.2
MOD-0A Located at Kahuku Point, Oahu, Hawaii
Figure 1.3
MOD-1 Located at Boone, North Carolina
Figure 1.4
MOD-2 Located at the Goodnoe Hills Site Near Goldendale, Washington
Figure 1.5
Sandia Laboratories 17-m Darrieus, Rated at 60 kW in a 12.5-m/s Wind
Figure 1.6
Extruded Aluminum Blade of 17-m Darrieus During Fabrication
Figure 1.7
Kansas State University Savonius, Rated at 5 kW in a 12-m/s Wind
Figure 1.8
Typical Performances of Wind Turbines
Figure 1.9
Magnus Force on a Spinning Cylinder
Figure 1.10
Madaras Concept for Generating Electricity
Figure 1.11
Augmented Vortex Turbine
Figure 1.12
Schematic of Major Components for Large Wind Turbines
Figure 1.13
Photos of Components, Suzlon 64 m Diameter, 1,000 kW. Bottom right: Cutaway
of Gearbox, Winergy
Figure 2.1
General Atmospheric Circulation, Northern Hemisphere
Figure 2.2
Sea Breeze, Day ; Land Breeze, Night
Figure 2.3
Wind Shear, Change in Wind Speed with Height
Figure 2.4
Left: Wind Shear Caused by a Difference in Wind Speed with Height. Right:
Wind Shear Caused by a Difference in Wind Direction
Figure 2.5
Example of Vertical Wind Shear
Figure 2.6
Representation of the Rating Scale Based on the Shape of the Crown and Degree
of Bending of Twigs, Branches and the Trunk
Figure 2.7
Propeller-type Wind Speed Sensor
Figure 2.8
Cup-type Wind Speed Sensor
7
Figure 2.9
Annual Average Wind Direction at 25 and 50 m Height, 10° Sectors
Figure 2.10
Wind Direction Vane and Transmitter
Figure 3.1
Wind Power Map for Rural Applications, Mexico
Figure 3.2
Height of Small Wind Turbine Close to Obstacles of Height H
Figure 3.3
Estimates of Speed and Power Decrease and Turbulence Increase for Flow over a
Building
Figure 3.4
Three Stacked Wind Turbines (Darrieus), 4 kW Each, Next to Building
Figure 3.5
Eight Helical Wind Turbines, 1 kW, Horizontal Axis, on Top of Building, 8 kW
Total
Figure 3.6
Wind Turbines, 1 kW Each, Mounted on Parapet of Building
Figure 3.7
West Side of Wind Farm in the Plains, near White Deer, Texas
Figure 3.8
Wind Farm in Rolling Terrain, Lake Benton, Minnesota
Figure 3.9
Wind Farm on Southwest Mesa, near McCamey, Texas
Figure 3.10
Wind Farm in Complex Terrain, Northwest Spain
Figure 3.11
Nysted Wind Farm in the Baltic Sea, Denmark
Figure 3.12
Satellite Image of West Side of Trent Mesa Wind Farm, Texas
Figure 3.13
Estimated Annual Energy Production Based on Annual Average Wind Speed
Figure 3.14
Calculated Annual Energy Production for 1 MW Wind Turbine in the Panhandle
of Texas
Figure 4.1
A Satellite Image of Istanbul
Figure 4.2
The Digitized Contour Map of 4 km² Area
Figure 4.3
A Photo of the Anemometer
Figure 4.4
The Location of the Anemometer on the Campus Plan
Figure 4.5
Digitized Contour Map with Imported Roughness Values
8
Figure 4.6
A Satellite Image Associated with the Digitized Contour Map by WAsP Map
Editor
Figure 4.7
Location of the Obstacles near the Anemometer
Figure 4.8
October 2009 Wind Rose Graph
Figure 4.9
November 2009 Wind Rose Graph
Figure 4.10
December 2009 Wind Rose Graph
Figure 4.11
January 2010 Wind Rose Graph
Figure 4.12
February 2010 Wind Rose Graph
Figure 4.13
March 2010 Wind Rose Graph
Figure 4.14
April 2010 Wind Rose Graph
Figure 4.15
May 2010 Wind Rose Graph
Figure 4.16
June 2010 Wind Rose Graph
Figure 4.17
July 2010 Wind Rose Graph
Figure 4.18
August 2010 Wind Rose Graph
Figure 4.19
September 2010 Wind Rose Graph
Figure 4.20
Weibull Probability Distribution Graphic
Figure 4.21
Wind Resource Map
Figure 4.22
„Aircon‟ Turbine
Figure 4.23
Power Curve of „Aircon 10 S‟
Figure 4.24
„Redriven‟ Wind Turbine
Figure 4.25
Power Curve of „ReDriven‟ Wind Turbine
Figure 4.26
„Huayin‟ Wind Turbine
Figure 4.27
Power Curve of „Huaying‟
Figure 4.28
Comparison of Annual Energy Productions of All Three Turbines
9
Figure 4.29
Comparison of Power Densities of All Three Turbines
Figure 4.30
WAsP Application of the First Case
Figure 4.31
WAsP Application of the Second Case
Figure 4.32
WAsP Application of the Third Case
LIST OF THE TABLES
Table 1.1
Specifications of ERDA and DOE. Two-Bladed Horizontal-Axis Wind Turbines
Table 2.1
Time and Space Scale for Atmospheric Motion
Table 2.2
Summary of Global Values for Renewable Sources
Table 2.3
Putnam‟s Calibration of Balsam Deformation Versus Average Wind Speed in New
England
Table 3.1
Criteria for Points for Visual Impact of Small Wind Turbines
Table 3.2
Rating of Visual Impact of Small Wind Turbines
Table 3.3
Texas, Intercepted and Capturable Wind Power and Annual Energy Potential from
Land That Satisfies the Screening Parameters
Table 4.1
The Properties of the Obstacles nearby
Table 4.2
12 Sectioned Histogram
Table 4.3
Total Annual Energy Production of „Aircon 10‟
Table 4.4
Total Annual Energy Production of „ReDriven‟
Table 4.5
Total Annual Energy Production of „Huaying‟
Table 4.6
Total Annual Energy Production of the First Case
Table 4.7
Total Annual Energy Production of the Second Case
Table 4.8
Total Annual Energy Production of the Third Case
Table 4.9
Comparison of Annual Energy Productions of All Three Turbines
10
SUMMARY
The importance of energy first came up with an oil embargo in 1973 and thus the oil prices
peaked unexpectedly. With the U.S. actions which seems initiating, the first and the basic long
term solution was energy efficiency. Then the world realized how significant was to supply the
energy demand.
Nowadays, it is commonly known that the world-wide demand of energy increases day by day, as
the global population grows and the developing countries expand their economies. The only way
to meet this demand is, beyond the energy efficiency, to utilize the resources of energy.
The world‟s current consumption has largely relied on oil, natural gas, coal, nuclear and
hydropower. In order to address the energy issues in a comprehensive manner, it is vital to
consider all the resources of energy. But instead of fosil fuels, it is very critical to supply the
demand from renewables as much as possible.
Renewable energy is an energy produced from easily-replenished sources like the sun, wind,
water, biological and geothermal processes. Compared to fosil fuels and coals, these natural
resources are usually referred to as clean forms of energy since they do not produce harmful
emissions and polluting agents into the atmosphere and thus have a very minimal environmental
impact during the process of production which is a very good factor in the preservation of our
environment.
The Earth is unevenly heated by the sun, such that the poles receive less energy from the sun than
the equator; along with this, dry land heats up and cools down more quickly than the seas do. The
differential heating drives a global atmospheric convection system reaching from the Earth's
surface to the stratosphere which acts as a virtual ceiling. Most of the energy stored in these wind
movements can be found at high altitudes where continuous wind speeds occur. Eventually, the
wind energy is converted through friction into diffuse heat throughout the Earth's surface and the
atmosphere…
In this study, we mentioned the fundamentals of wind energy in the first three chapters. The
analysis part of the thesis took us almost six months to finish. During this period, one of the
difficulties and time taking part we faced was learning the software for wind assessment called
11
WAsP. The most important and the distinguishing issue about our thesis is that every study we
made are all to go through with. We mean that all the calculations and wind assessments are for
installing a concrete wind turbine on Yildiz Technical University Davutpasa Campus. We started
getting in touch with the companies and hope to get a result during summer period.
We assume this thesis to be a milestone for the studies especially in the Student Association of
Wind Energy which was prerequisite for our study to come this level.
Dogukan Kucuksahin
&
Emre Barlas
12
1.
1.1
INTRODUCTION
Historical Uses of Wind
The wind has been used to power sailing ships for many centuries. Many countries owed their
prosperity to their skill in sailing. The New World was explored by wind powered ships. Indeed,
wind was almost the only source of power for ships until Watt invented the steam engine in the
18th Century.
On land, wind turbines date back many centuries. It has been reported that the Babylonian
emperor Hammurabi planned to use wind turbines for irrigation in the seventeenth century B.C.
Hero of Alexandria, who lived in the third century B.C., described a simple horizontal axis wind
turbine with four sails which was used to blow an organ.
The Persians were using wind turbines extensively by the middle of the seventh century A.D.
Theirs was a vertical axis machine with a number of radially-mounted sails.
These early machines were undoubtedly crude and mechanically inefficient, but they served their
purpose well for many centuries. They were made from local materials by cheap labor.
Maintenance was probably a problem which served to keep many people at work. Their size was
probably determined by the materials available. A need for more power was met by building
more wind turbines rather than larger ones. There are many of the lesser developed countries of
the world today which could profitably use such low technology machines because of the large
amounts of cheap, unskilled labor available. Such countries often have difficulty acquiring the
foreign exchange necessary to purchase high technology machines, and then have difficulty
maintaining them.
The earliest recorded English wind turbine is dated at 1191. The first corn-grinding wind turbine
was built in Holland in 1439. There were a number of technological developments through the
centuries, and by 1600 the most common wind turbine was the tower mill. The word mill refers
to the operation of grinding or milling grain. This application was so common that all wind
turbines were often called windmills even when they actually pumped water or performed some
other function. We will usually use the more general terms wind turbine or wind machine rather
than windmill, unless the application is actually that of grinding grain.
13
The tower mill had a fixed supporting tower with a rotatable cap which carried the wind rotor.
The tower was usually built of brick in a cylindrical shape, but was sometimes built of wood, and
polygonal in cross section. In one style, the cap had a support or tail extending out and down to
ground level. A circle of posts surrounded the tower where the support touched the ground. The
miller would check the direction of the prevailing wind and rotate the cap and rotor into the wind
with a winch attached between the tail and one of the posts. The tail would then be tied to a post
to hold the rotor in the proper direction. This process would be repeated when the wind direction
changed. Protection from high winds was accomplished by turning the rotor out of the wind or by
removing the canvas covering the rotor latticework.
The optimization of the rotor shape probably took a long time to accomplish. It is interesting to
note that the rotors on many of the Dutch mills are twisted and tapered in the same way as
modern rotors and appear to have nearly optimized the aerodynamic parameters necessary for
maximum efficiency. The rotors presently on the tower mills probably do not date back to the
original construction of the tower, but still indicate high quality aerodynamic engineering of a
period much earlier than the present. Dutch settlers brought this type of wind turbine to America
in the mid-1700‟s. A number were built but not in the quantity seen in Europe.
Then in the mid 1800‟s a need developed for a smaller wind turbine for pumping water. The
American West was being settled and there were wide areas of good grazing lands with no
surface water but with ample ground water only a few meters under the surface. With this in
mind, a distinctive wind turbine was developed, called the American Multibladed wind turbine. It
had high starting torque and adequate efficiency, and suited the desired water pumping objective
very well. If the wind did not blow for several days, the pump would be operated by hand. Since
this is a reasonably good wind regime, hand pumping was a relatively rare occurrence.
An estimated 6.5 million units were built in the United States between 1880 and 1930 by a
variety of companies. Many of these are still operating satisfactorily. By providing water for
livestock, these machines played an important role in settling the American West.
14
1.2
History of Wind Electric Generation
Denmark was the first country to use the wind for generation of electricity. The Danes were using
a 23 m diameter wind turbine in 1890 to generate electricity. By 1910, several hundred units with
capacities of 5 to 25 kW were in operation in Denmark.
About 1925, commercial wind-electric plants using two- and three-bladed propellers appeared on
the American market. The most common brands were Wincharger (200 to 1200 W) and Jacobs
(1.5 to 3 kW). These were used on farms to charge storage batteries which were then used to
operate radios, lights, and small appliances with voltage ratings of 12, 32 or 110 volts. A good
selection of 32 Vdc appliances was developed by industry to meet this demand. Then the Rural
Electric Administration (REA) was established by Congress in 1936. Low interest loans were
provided so the necessary transmission and distribution lines could be constructed to supply
farmers with electricity. In the early days of the REA, around 1940, electricity could be supplied
to the rural customer at a cost of 3 to 6 cents per kWh. The corresponding cost of wind generated
electricity was 12 to 30 cents per kWh when interest, depreciation, and maintenance were
included. The lower cost of electricity produced by a central utility plus the greater reliability led
to the rapid demise of the home wind electric generator.
After 1940, the cost of utility generated electricity continued a slow decline, dipping under 3
cents per kWh in the early 1970‟s. This was accomplished by their using larger and more
efficient generating plants. A trend of decreasing cost for electricity while other costs are
increasing could not be continued forever, and utility generated electricity started increasing in
cost in the early 1970‟s reaching the 1940 cost level around 1976. This was accompanied by
many consumer complaints, of course, which were largely unjustified when the long term
performance of the utilities in providing low cost, reliable electricity is considered.
In addition to home wind electric generation, a number of utilities around the world have built
larger wind turbines to supply power to their customers. The largest wind turbine built before the
late 1970‟s was a 1250 kW machine built on Grandpa‟s Knob, near Rutland, Vermont, in 1941.
The concept for this started in 1934 when an engineer, Palmer C. Putnam, began to look at wind
electric generators to reduce the cost of electricity to his Cape Cod home. In 1939, Putnam
presented his ideas and the results of his preliminary work to the S. Morgan Smith Company of
15
York, Pennsylvania. They agreed to fund a wind-energy project and the Smith-Putnam wind
turbine experiment was born. The wind machine was to be connected into the Central Vermont
Public Service Corporation‟s network. This utility had some hydro-electric capacity, which
makes a good combination with wind generation in that water can be saved when the wind is
blowing and used later when the wind is not blowing.
The Smith-Putnam machine had a tower which was 34 m high and a rotor 53 m in diameter. The
rotor had a chord (the distance from the leading to the trailing edge) of 3.45 m. Each of the two
blades was made with stainless steel ribs covered by a stainless steel skin and weighed 7300 kg.
The blade pitch (the angle at which the blade passes through the air) was adjustable to maintain a
constant rotor speed of 28.7 r/min. This rotational speed was maintained in wind speeds as high
as 32 m/s. At higher wind speeds, the blades were feathered and the machine stopped. The rotor
turned an ac synchronous generator that produced 1250 kW of electrical power at wind speeds
above 13 m/s.
Between 1941 and 1945 the Smith-Putnam machine accumulated about 1100 hours of operation.
More would have been accumulated except for the problem of getting critical repair parts during
the war. In 1945 one of the blades failed, due more to inadequate design than to technological
limitations. The project was reviewed and was determined to be a technical success. The
economics did not justify building more machines at that time, however. It appeared that
additional Smith-Putnam machines could be built for about $190/installed kW. Oil and coal fired
generation could be bought in 1945 for $125/installed kW. This was too large a difference to
justify to the stock-holders, so the project was stopped and the wind machine was dismantled.
The technical results of the Smith-Putnam wind turbine caused Percy H. Thomas, an engineer
with the Federal Power Commission, to spend approximately 10 years in a detailed analysis of
Wind Power Electric Generation. Thomas used economic data from the Smith-Putnam machine
and concluded that even larger machines were necessary for economic viability. He designed two
large machines in the size range he felt to be best. One was 6500 kW and the other was 7500 kW
in size. The tower height of the 6500 kW machine was to be 145 m with two rotors each 61 m in
diameter. Each rotor was to drive a dc generator. The dc power was used to drive a dc to ac
synchronous converter which was connected to the power grid.
16
Thomas estimated the capital costs for his machine at $75 per installed kW. This was low enough
to be of interest so the Federal Power Commission approached Congress for funding a prototype
of this machine. It was in 1951 when the Korean War was starting, and Congress chose not to
fund the prototype. The project was later canceled. This basically marked the end of American
wind power research for over twenty years until fuel supplies became a problem.
Other countries continued wind research for a longer period of time. Denmark built their Gedser
wind turbine in 1957. This machine produced 200 kW in a 15 m/s wind. It was connected to the
Danish public power system and produced approximately 400,000 kWh per year. The tower was
26 m high and the rotor was 24 m in diameter. The generator was located in the housing on the
top of the tower. The installation cost of this system was approximately $250/kW. This wind
turbine ran until 1968 when it was stopped.
Dr. Ulrich Hutter of Germany built a 100 kW machine in 1957. It reached its rated power output
at a wind speed of 8 m/s, which is substantially lower than the machines mentioned earlier. This
machine used lightweight, 35 m diameter fiberglass blades with a simple hollow pipe tower
supported by guy wires. The blade pitch would change at higher wind speeds to keep the
propeller angular velocity constant. Dr. Hutter obtained over 4000 hours of full rated power
operation over the next 11 years, a substantial amount for an experimental machine. This allowed
important contributions to the design of larger wind turbines to be made.
1.3
Horizontal Axis Wind Turbine Research
The Federal Wind Energy Program had its beginning in 1972 when a joint Solar Energy Panel of
the National Science Foundation (NSF) and the National Aeronautics and Space Administration
(NASA) recommended that wind energy be developed to broaden the Nation‟s energy options for
new energy sources. In 1973, NSF was given the responsibility for the Federal Solar Energy
Program, of which wind energy was a part. The Lewis Research Center, a Federal Laboratory
controlled by NASA, was selected to manage the technology development and initial deployment
of large wind turbines. Early in 1974, NASA was funded by NSF to (1) design, build, and operate
a wind turbine for research purposes, designated the MOD-0, (2) initiate studies of wind turbines
17
for utility application, and (3) undertake a program of supporting research and technology
development for wind turbines.
In 1975, the responsibility within the Federal government for wind turbine development was
assigned to the newly created Energy Research and Development Administration (ERDA).
ERDA was then absorbed by the Department of Energy (DOE) in 1977. The NASA Lewis
Research Center continued to direct the technology development of large turbines during this
period.
During the period following 1973, other Federal Laboratories became involved with other aspects
of Wind Energy Collection Systems (WECS). Sandia Laboratories, a DOE Laboratory located at
Albuquerque, New Mexico, became responsible for federally sponsored research on Darrieus
wind turbines. Battelle Pacific Northwest Laboratories, Richland, Washington, became
responsible for wind resource assessments. Solar Energy Research Institute, (now the National
Renewable Energy Laboratory) Golden, Colorado, became responsible for innovative wind
turbines. Small wind turbine research was handled by Rockwell, International at their Rocky
Flats plant near Golden, Colorado. Agricultural applications were handled by the U. S.
Department of Agriculture from facilities at Beltsville, Maryland, and Bushland, Texas. This
division of effort allowed existing personnel and facilities to be shifted over to wind power
research so that results could be obtained in a relatively short time.
It was decided very early in the program that the MOD-0 would be rated at 100 kW and have a
38-m-diameter rotor with two blades. This machine would incorporate the many advances in
aerodynamics, materials, controls, and data handling made since the days of the Smith-Putnam
machine. The choice of the two bladed propeller over some more unusual wind turbines was
made on the basis of technology development. The two bladed machines had been built in larger
sizes and had been operated more hours than any other type, hence had the highest probability of
working reasonably well from the start. For political reasons it was important to get something
working as soon as possible. This machine became operational in September, 1975, at the NASA
Plumbrook facility near Sandusky, Ohio.
A diagram of the turbine is shown in Figure 1.1. The rotor and nacelle sit on top of a 4-legged
steel truss tower about 30 m high. The rotor is downwind of the tower, so the wind strikes the
18
tower before striking the rotor. Each rotor blade thus sees a change in wind speed once per
revolution when it passes through the tower shadow. This introduces vibration to the blades,
which has to be carefully considered in blade design. An upwind design tends to introduce
vibration in the tower because of blade shadowing so neither design has strong advantages over
the other. In fact, the MOD-0 was operated for brief periods as an upwind machine to assess
some of the effects of upwind operation on structural loads and machine control requirements.
The MOD-0 was designed so the rotor would turn at a constant 40 r/min except when starting up
or shutting down. A gear box increases the rotational speed to 1800 r/min to drive a synchronous
generator which is connected to the utility network. Startup is accomplished by activating a
control which aligns the wind turbine with the wind. The blades are then pitched by a hydraulic
control at a programmed rate and the rotor speed is brought to about 40 r/min. At this time an
automatic synchronizer is activated and the wind turbine is synchronized with the utility network.
If the wind speed drops below the value necessary to get power from the rotor at 40 r/min, the
generator is disconnected from the utility grid, the blades are feathered (pitched so no power
output is possible) and the rotor is allowed to coast to a stop. All the steps of startup,
synchronization, power control, and shutdown are automatically controlled by a microprocessor.
The stresses in the aluminum blades were too high when the unit was first placed into operation,
and it was determined that the tower shadow was excessive. The tower was blocking the airflow
much more than had been expected. A stairway inside the tower which had been added late in the
design was removed and this solved the problem.
Except for this tower blockage problem, the MOD-0 performed reasonably well, and provided a
good base of experience for designing larger and better turbines. The decision was made in 1975
to build several of these turbines, designated as the MOD-0A. The size of tower and rotor
remained the same, but the generator size was doubled from 100 to 200 kW. The extra power
would be produced in somewhat higher wind speeds than the rated wind speed of the MOD-0.
19
Figure 1.1: NSF–NASA MOD-0 Wind Power System General View
The Westinghouse Electric Corporation of Pittsburgh, Pennsylvania was the prime contractor
responsible for assembly and installation. The blades were built by the Lockheed California
Company of Burbank, California. The first MOD-0A was installed at Clayton, New Mexico in
late 1977, the second at Culebra, Puerto Rico in mid 1978, the third at Block Island, Rhode Island
in early 1979, and the fourth at Kahuku Point, Oahu, Hawaii in early 1980. The first three
machines used aluminum blades while the Kahuku MOD-0A used wood composite blades. The
wooden blades weighed 1360 kg each, 320 kg more than the aluminum blades, but the expected
life was longer than their aluminum counterparts. A MOD-0A is shown in Figure 1.2.
20
The Kahuku machine is located in a trade wind environment where relatively steady, high speed
winds are experienced for long periods of time. The machine produced an average power output
of 178 kW for the first 573 hours of operation. This was an outstanding record compared with the
output of the other MOD-0A machines of 117 kW at Culebra, 89 kW at Clayton, and only 52 kW
at Block Island during the first few months of operation for these machines. This shows the
importance of good site selection in the economical application of large wind turbines.
Figure 1.2: MOD-0A Located at Kahuku Point, Oahu, Hawaii
Following the MOD-0 and MOD-0A was a series of other machines, the MOD-1, MOD-2, etc.
Design parameters for several of these machines are shown in Table 1.1. The MOD-1 was built
as a 2000 kW machine with a rotor diameter of 61 m. It is pictured in Figure 1.3. Full span pitch
control was used to control the rotor speed at a constant 35 r/min. It was built at Howard‟s Knob,
near Boone, North Carolina in late 1978. It may be noticed from Table 1.1 that the rated
windspeed for the MOD-1 was 14.6 m/s at hub height, significantly higher than the others. This
21
allowed the MOD-1 to have a rated power of 10 times that of the MOD-0A with a swept area
only 2.65 times as large.
The gearbox and generator were similar in design to those of the MOD-0A, except larger. The
tower was a steel, tubular truss design. The General Electric Company, Space Division, of
Philadelphia, Pennsylvania was the prime contractor for designing, fabricating, and installing the
MOD-1. The Boeing Engineering and Construction Company of Seattle, Washington,
manufactured the two steel blades.
As the MOD-1 design effort progressed, it became clear that the MOD-1 would be relatively
heavy and costly and could not lead to a cost competitive production unit. Weight and cost were
being determined by a number of factors, the most significant of which were the stiff tower
design criteria, the full span pitch control which required complicated, heavy mechanisms and
excessive space in the hub area, and a heavy bedplate supporting the weight on top of the tower.
A number of possible improvements in the design became evident too late to be included in the
actual construction. Only one machine was built because of the predicted production costs. Like
the MOD-0, it was operated as a test unit to help the designs of later generation turbines.
Figure 1.3: MOD-1 Located at Boone, North Carolina
22
Table 1.1: Specifications of ERDA and DOE
Two-Bladed Horizontal-Axis Wind Turbines
One early problem with the MOD-1 was the production of subaudible vibrations which would
rattle the windows of nearby houses. The rotor would interact with the tower to produce two
pulses per revolution, which resulted in a vibration frequency of about 1.2 Hz. Techniques used
to reduce the annoyance included reducing the speed of rotation and replacing the steel blades
with fiberglass blades. Other operational problems, including a broken low speed shaft, plus a
reduction in federal funding, caused the MOD-1 to be disassembled in 1982.
The next machine in the series, the MOD-2, represented an effort to build a truly cost competitive
machine, incorporating all the information gained from the earlier machines. It was a second
generation machine with the Boeing Engineering and Construction Company serving as the
prime contractor. The rotor had two blades, was 91.5 m in diameter, and was upwind of the
tower. Rotor speed was controlled at a constant 17.5 r/min. Rated power was 2500 kW (2.5 MW)
at a wind speed of 12.4 m/s measured at the hub height of 61 m. In order to simplify the
configuration and achieve a lower weight and cost, partial span pitch control was used rather than
full span pitch control. That is, only the outer 30 percent of the span was rotated or pitched to
control rotor speed and power. This construction feature can be seen in Figure 1.4. To reduce the
23
loads on the system caused by wind gusts and wind shear, the rotor was designed to allow teeter
of up to 5 degrees in and out of the plane of rotation. These load reductions saved weight and
therefore cost in the rotor, nacelle, and tower. The word teeter is also used for the motion of a
plank balanced in the middle and ridden by children so one end of the plank goes up while the
other end goes down. This described the same type of motion in the rotor except that motion was
around a horizontal pivot point rather than the vertical one used on the playground.
Figure 1.4: MOD-2 Located at the Goodnoe Hills Site Near Goldendale, Washington
The MOD-2 tower was designed to be soft or flexible rather than stiff or rigid. The softness of the
tower refers to the first mode natural frequency of the tower in bending relative to the operating
frequency of the system. For a two-bladed rotor, the tower is excited (receives a pulse) twice per
revolution of the rotor. If the resonant frequency of the tower is greater than the exciting
frequency, the tower is considered stiff. A tower is considered soft if the resonant frequency is
less than the exciting frequency, and very soft if the resonant frequency is less than half the
exciting frequency. The tower of the MOD-2 was excited at its resonant frequency for short time
24
periods during startup and shutdown, so extreme care had to be taken during these times so the
oscillations did not build up enough to damage the tower.
The MOD-2 tower was a welded steel cylindrical shell design. This design was more cost
effective than the stiff, open-truss tower of the first generation machines. The MOD-2 was
significantly larger than the MOD-1, yet the above ground mass was less, 273,000 kg as
compared with 290,000 kg.
The first installation of the MOD-2 was a three machine cluster at the Goodnoe Hills site near
Goldendale, Washington, built in early 1981. Two additional units were built, one in Wyoming
and one in California.
The numbering system hit some difficulties at this point, since the next machine after the MOD-2
was the MOD-5. Actually, this third generation machine was designed by two different
companies, with the General Electric version being named the MOD-5A while the Boeing
version was named the MOD-5B. Objectives of the MOD-2 and MOD-5 programs were
essentially identical except that the target price of electricity was reduced by 25 percent, to 3.75
cents per kWh in 1980 dollars.
The General Electric MOD-5A design called for a rotor diameter of 122 m (400 ft) and a rated
power of 6.2 MW. Rated power would be reached in wind speeds of 13 m/s (29 mi/h) at the hub
height of 76 m (250 ft). The wood rotor would turn at two rotational speeds, 13 or 17 r/min,
depending on wind conditions.
The Boeing MOD-5B was designed to be an even larger machine, 7.2 MW with a rotor diameter
of 128 m (420 ft). The rotor was designed to be built of steel with wood tips. A variable speed
generator was selected as opposed to the fixed speed generator used on the MOD-2.
Federal research on the MOD series of turbines was terminated in the mid 1980s, and all the
turbines have been scraped. One reason was that smaller turbines (in the 100-kW range) could be
built at lower costs and with better performance than the large turbines. Many of us
underestimated the difficulty of building large reliable wind turbines. The technology step was
just too large.
25
A second reason was that the American aerospace industry did not have a desire to produce a cost
effective commercial product. Wind turbine research was viewed as just another government
contract. A given company would build a turbine on a cost plus basis. When it broke, it would be
repaired on a cost plus basis. When the federal money ran out, the company‟s interest in wind
power vanished. Hindsight indicates it would have been far better to have spent the federal
money on the small, mostly undercapitalized, companies that were dedicated to producing a
quality wind turbine.
A third reason for the lack of interest in wind was the abundance and depressed costs of
petroleum products throughout the 1980s and into the 1990s. In the mid 1970s, it was Standard
wisdom that we were running out of natural gas. Many utilities converted from burning natural
gas as a boiler fuel, instead using coal or nuclear energy. The price of natural gas increased
substantially from its artificially low values. But by the mid 1980s, it was discovered that we had
substantial reserves of natural gas (at this higher price), and utilities started converting back to
natural gas as a fuel, especially for peaking gas turbines. The development of wind power has
certainly been delayed by these various actions of the government, aerospace, and oil industries.
1.4
Darrieus Wind Turbines
Most wind turbines designed for the production of electricity have consisted of a two or three
bladed propeller rotating around a horizontal axis. These blades tend to be expensive, high
technology items, and the turbine has to be oriented into the wind, another expensive task for the
larger machines. These problems have led many researchers in search of simpler and less
expensive machines. The variety of such machines seems endless. One that has seen considerable
development is the Darrieus wind turbine. The Darrieus was patented in the United States by G.
J. M. Darrieus in 1931. It was reinvented by engineers with the National Research Council of
Canada in the early 1970‟s. Sandia Laboratories built a 5 m diameter Darrieus in 1974, and has
been strongly involved with further research on the Darrieus turbine since that time.
Figure 1.5 shows a 17 meter Darrieus built at Sandia. The diameter of the blades is the same as
the height, 17 m. The extruded aluminum blades were made by Alcoa (Aluminum Company of
America, Alcoa Center, Pennsylvania). This machine is rated at 60 kW in a 12.5 m/s wind. Figure
26
1.6 shows one of the blades during fabrication. Several models of this basic machine were built
during 1980.
The Darrieus has several attractive features. One is that the machine rotates about a vertical axis,
hence does not need to be turned into the wind. Another is that the blades take the shape of a
jumping rope experiencing high centrifugal forces. This shape is called troposkein, from the
Greek for turning rope. Since the blade operates in almost pure tension, a relatively light,
inexpensive blade is sufficient. Another advantage is that the power train, generator, and controls
are all located near ground level, hence are easier to construct and maintain. The efficiency is
nearly as good as that of the horizontal axis propeller turbine, so the Darrieus holds considerable
promise as a cost effective turbine.
One disadvantage of the Darrieus is that it is not normally self starting. That is, if the turbine has
stopped during a period of low wind speeds, it will not usually start when the wind speed
increases. Starting is usually accomplished by an induction motor connected to the local utility
network. This is not necessarily a major disadvantage because the same induction motor can be
used as an induction generator to supply power to the utility network when the turbine is at
operating speed. Induction machines are simple, rugged, and inexpensive, requiring essentially no
controls other than a contactor to connect the machine to the utility network. For these reasons,
they are seeing wide use as wind turbine generators.
Figure 1.5: Sandia Laboratories 17-m Darrieus, Rated at 60 kW in a 12.5-m/s Wind
27
The first large Darrieus constructed was a 230-kW machine on Magdalen Island, Quebec, Canada
in May, 1977 by Dominion Aluminium Fabricators, Limited of Ontario, Canada. The average
power output of this machine was 100 kW over the first year of operation, which is quite good.
Then a noise was observed in the gearbox so the machine was stopped for inspection and repairs.
During the inspection process, the brakes were removed, which should have been safe because
the turbine was not supposed to be able to self start. Unfortunately, on July 6, 1978, the turbine
started, and without a load or any way of stopping it, went well over the design speed of 38 r/min.
The spoilers did not activate properly,and when the turbine reached 68 r/min a guy wire broke,
letting the turbine crash to the ground. Perhaps the main lesson learned from this accident was
that the Darrieus will sometimes start under unusual gust conditions and that braking systems
need to be designed with this fact in mind.
A major design effort on Darrieus turbines has been made by Alcoa. They first designed a 5.5 m
diameter machine which would produce about 8 kW of power, but dropped that size in favor of
more economical larger machines. Other sizes developed by Alcoa include a 12.8 m diameter (30
to 60 kW), 17 m diameter (60 to 100 kW), and a 25 m diameter (300 or 500 kW depending on the
gear ratio).
The Alcoa effort has been plagued by a number of accidents. A 12.8 m diameter machine
collapsed at their Pennsylvania facility on March 21, 1980, when its central torque tube started
vibrating and eventually buckled when the machine was running above rated speed. Then in
April, 1981, a 25 m machine crashed in the San Gorgonio Pass east of Los Angeles.
The machine itself worked properly to a speed well above rated speed, but a software error in the
microcomputer controller prevented proper brake application in high winds. When the machine
rotational speed reached 60 r/min, well above the rated speed of 41 r/min, a bolt broke and
allowed a blade to flare outward and cut one of the guy wires. The machine then crashed to the
ground.
28
Figure 1.6: Extruded Aluminum Blade of 17-m Darrieus During Fabrication
Accidents like these are not uncommon in new technology areas, but they are certainly frustrating
to the people involved. It appears that the various problems are all solvable, but the string of
accidents certainly slowed the deployment of Darrieus turbines as compared with the horizontal
axis turbines.
Sandia continued work on the theory of the Darrieus turbine during the 1980s, with the result that
the turbine is well understood today. It appears that there is no reason the Darrieus could not be
an important contributor to the production of power from the wind. It just needs a large aluminum
company that is willing and able to do the aluminum extrusions and possibly wait for several
years before seeing a significant return on investment.
1.5
Innovative Wind Turbines
Another type of turbine developed at about the same time as the Darrieus was the Savonius
turbine, developed in Finland by S. J. Savonius. This is another vertical axis machine which
needs no orientation into the wind. Alternative energy enthusiasts often build this turbine from
used oil barrels by cutting the barrels in half lengthwise and welding the two halves back together
29
offset from one another to catch the wind. A picture of a somewhat more advanced unit
developed at Kansas State University, Manhattan, Kansas, is shown in Figure 1.7.
Figure 1.7: Kansas State University Savonius, Rated at 5 kW in a 12-m/s Wind
The tower of the KSU Savonius was 11 m high and 6 m wide. Each rotor was 3 m high by 1.75 m
in diameter. The rotors were connected together and drove a single 5 kW, three-phase, permanent
magnet generator. At the rated wind speed of 12 m/s, the rotor speed was 103 r/min, the generator
speed was 1800 r/min, and the frequency was 60 Hz. Output voltage and frequency varied with
wind speed and load, which meant that this particular turbine could not be directly paralleled with
the utility grid. Applications for this asynchronous (not synchronized with the utility grid)
30
electricity are limited to electric heating and driving three-phase induction motors in situations
which can tolerate variable speed operation. These include heat pumps, some water pumps, and
fans. Such applications consume large quantities of electrical energy, so variable frequency
operation is not as restrictive as it might appear. Asynchronous systems do not require complex
blade pitch, voltage, and frequency controls, hence should be less expensive.
The main advantages of the Savonius are a very high starting torque and simple construction. The
disadvantages are weight of materials and the difficulty of designing the rotor to withstand high
wind speeds. These disadvantages could perhaps be overcome by good engineering if the turbine
efficiency were high enough to justify the engineering effort required.
Agreement on the efficiency of the Savonius turbine apparently has finally been reached a half
century after its development. Savonius claimed an efficiency of 31 per cent in the wind tunnel
and 37 per cent in free air. However, he commented: “The calculations of Professor Betz gave 20
% as the highest theoretical maximum for vertical airwheels, which under the best of
circumstances could not produce more than 10 % in practical output.” The theoretical and
experimental results failed to agree. Unfortunately, Savonius did not specify the shape and size of
his turbine well enough for others to try to duplicate his results.
A small unit of approximately 2 m high by 1 m diameter was built and tested at Kansas State
University during the period 1932-1938. This unit was destroyed by a high wind, but efficiencies
of 35 to 40 % were claimed by the researchers. Wind tunnel tests were performed by Sandia on
1.5 m high by 1 m diameter Savonius turbines, with a maximum efficiency measured of 25 % for
semicircular blades. Different blade shapes which were tested at the University of Illinois showed
a maximum efficiency of about 35 %. More Savonius turbines were tested at Kansas State
University, with efficiencies reported of about 25 %. It thus appears that the Savonius, if properly
designed, has an efficiency nearly as good as the horizontal axis propeller turbine or the Darrieus
turbine. The Savonius turbine therefore holds promise in applications where low to medium
technology is required or where the high starting torque is important.
A chart of efficiency of five different turbine types is shown in Figure 1.8. The efficiency or
power coefficient varies with the ratio of blade tip speed to wind speed, with the peak value being
the number quoted for a comparison of turbines. This will be discussed in more detail in Chapter
31
4. It may be noticed that the peak efficiencies of the two bladed propeller, the Darrieus, and the
Savonius are all above 30 %, while the American Multiblade and the Dutch windmills peak at
about 15 %. These efficiencies indicate that the American Multiblade is not competitive for
generating electricity, even though it is almost ideally suited and very competitive for pumping
water.
The efficiency curves for the Savonius and the American Multiblade have been known for a long
time. Unfortunately, the labels on the two curves were accidentally interchanged in some key
publication in recent years, with the result that many authors have used an erroneous set of curves
in their writing. This historical accident will probably take years to correct.
Another vertical axis machine which has interested people for many years is the Madaras rotor.
This system was invented by Julius D. Madaras, who conducted considerable tests on his idea
between 1929 and 1934. This concept uses the Magnus effect, which refers to the force produced
on a spinning cylinder or sphere in a stream of air. The most familiar example of this effect is the
curve ball thrown by a baseball pitcher. The Madaras rotor is a large cylinder which is spun in the
wind by an electric motor. When the wind is from the left and the cylinder is spinning
counterclockwise as shown in Figure 1.9, the cylinder will experience a lift force in the direction
shown. There will also be a drag force in the direction of the wind flow.
If the cylinder is mounted on a special type of railroad car and if the wind speed component
perpendicular to the railroad tracks is sufficiently strong, the lift force will be adequate to move
the car along the tracks. The basic idea is shown in Figure 1.10. The railroad car or tracked
carriage must be heavy enough that it will not overturn due to the drag forces. Power can be
extracted from the system by electrical generators connected to the wheels of the tracked
carriage. The cars roll around a circular or racetrack shaped track. Twice during each orbit of a
rotor car around the track (when the wind is parallel to the track), each spinning rotor in turn must
be de-spun to a stop, and then spun-up in the opposite direction. This cycle is necessary in order
to assure that the propulsive force changes direction so that all rotors are propelling the train in
the same angular direction.
32
Figure 1.8: Typical Performances of Wind Turbines
Figure 1.9: Magnus Force on a Spinning Cylinder
33
Figure 1.10: Madaras Concept for Generating Electricity
The original system proposed by Madaras consisted of 27 m high by 6.8 m diameter cylinders
which were vertically mounted on flat cars and rotated by electric motors to convert wind energy
to Magnus-effect forces. The forces would propel an endless train of 18 cars around a 460 m
diameter closed track. Generators geared to the car axles were calculated to produce up to 18
MW of electric power at a track speed of 8.9 m/s in a wind speed of 13 m/s.
More recent studies have shown that energy production is greater with a racetrack shaped plant
perhaps 3 km wide by 18 km long which is oriented perpendicular to the prevailing winds. This
modern design includes cylinders 4.9 m in diameter by 38.1 m tall, cars with a length of 19.2 m
and a width of 17.4 m, and a track with 11 m between rails. Individual cars would have a mass of
328,000 kg. Each rotor would be spun with a 450 kW, 500 volt dc motor. Each of the four wheels
would drive a 250 kW induction generator. There would be about 200 cars on the track with a
total rating of about 200 MW. Power would be extracted from the system by a 4160 V, threephase, 500 A overhead trolley bus.
Cost estimates for the electricity costs from this large system were comparable to those from the
MOD-1. Wind tunnel tests and field tests on a rotating cylinder on a fixed platform indicate that
the concept will work. The questions remain whether the aerodynamic, mechanical, and electrical
34
losses will be acceptable and whether the reliability will be adequate. Only a major development
effort can answer these questions and there will probably not be sufficient interest in such a
development if the horizontal axis wind turbines meet the basic requirements for cost and
reliability.
All the wind turbines discussed thus far have a problem with capital costs. Although these
machines work satisfactorily, capital costs are large. The Darrieus may become more cost
effective than the two-bladed propeller turbine, but neither is likely to produce really inexpensive
electricity. There is a desire for a breakthrough, whereby some new and different concept would
result in substantial cost reductions. One candidate for such a wind machine is the augmented
vortex turbine studied by James Yen at Grumman Aerospace Corporation. An artist‟s concept of
the machine is shown in Figure 1.11.
The turbine tower has vertical vanes which direct the wind into a circular path around the inside
of the tower. Wind blowing across the top of the tower tends to pull the air inside in an upward
direction, causing the entering air to flow in a spiral path. This spiral is a vortex, which is
characterized by a high speed, low pressure core. The vortex is basically that of a confined
tornado. The pressure difference between the vortex core and outside ambient air is then used to
drive a relatively small, high speed turbine at the base of the tower. The vortex machine is
extracting power from pressure differences or the potential energy in the air, rather than directly
from the kinetic energy of the moving air. The potential energy in the air due to pressure is vastly
more than the kinetic energy of the air in moderate wind speeds, so there is a possibility of large
energy outputs for a given tower size which could result in very inexpensive electricity.
One problem with the vortex machine is the potential for spawning tornadoes. If the vortex
extending out of the top of the tower should become separated from the tower, grow a tail, and
become an actual tornado, a permanent shutdown would be highly probable. In fact, based on the
experience of the nuclear industry, fear of such an occurrence may prevent the implementation of
such a wind machine.
Many other wind machines have been invented over the last few hundred years. The propeller
type and the Darrieus have emerged as reasonably reliable, cost competitive machines which can
provide a significant amount of electrical energy. Barring a major breakthrough with another type
35
of wind machine, we can expect to see a wide deployment of these machines over the next few
decades.
Figure 1.11: Augmented Vortex Turbine
1.6
Description of the System
The total system consists of the wind turbine and load. A typical wind turbine consists of the
rotor (blades and hub), speed increaser (gearbox), conversion system, controls, and tower (Figure
1.12). The nacelle is the covering or enclosure. The output of the rotor, rotational kinetic energy,
can be converted to electrical, mechanical, or thermal energy. Generally, it is electrical energy, so
the conversion system is a generator.
36
Figure 1.12: Schematic of Major Components for Large Wind Turbines
Blade configuration may include a nonuniform platform (blade width and length), twist along the
blade, and variable (blades can be rotated) or fixed pitch. The pitch is the angle of the chord at the
tip of the blade to the plane of rotation. The chord is the line from the nose to the tail of the
airfoil.
Components for a large unit mounted on a bedplate are shown in Figure 1.13. Most large wind
turbines, which are pitch regulated, have full-span (blade) control, and in this case, electric
motors are used to rotate, change the pitch of the blades. All blades must have the same pitch for
all operational conditions.
37
Figure 1.13: Photos of Components, Suzlon 64 m Diameter, 1,000 kW. Bottom right: Cutaway
of Gearbox, Winergy
For units connected to the utility grid, 50 or 60 Hz, the generators can be synchronous or
induction connected directly to the grid, or a variable-frequency alternator or direct current
generator connected indirectly to the grid through an inverter. Most direct current (DC)
generators and permanent magnet alternators on small wind turbines do not have a speed
increaser. One type of large wind turbine has no gearbox, which means it has very large
generators. Some HAWTs use slip rings to transfer power and control signals from the top of the
tower to ground level, while others have wire cords that have extra length for absorbing twist.
38
After so much twist, it must be removed by yawing the turbine or by a manual disconnect. For
large wind turbines, the transformer or a winch may be located in the nacelle. A total system is
called a wind energy conversion system.
1.7
Applications
The kinetic energy of the wind can be transformed into mechanical, electrical, and thermal
energy. Historically, the transformation was mechanical where the end use was grinding grain,
powering ships, and pumping water.
The applications can be divided into wind-assist and stand-alone systems. In the wind-assist
system the wind turbine works in parallel with another source of energy to provide power. The
advantages of such systems are power is available on demand, generally there is no storage, and
there is better matching between the power sources and the load. Stand-alone systems will
provide power only when the wind is blowing and the power output is variable, unless a storage
system is connected to the wind turbine. Wind-diesel is an application where the wind turbine is
primarily a fuel saver, which is a wind-assist system. Another application, which is now
emerging, is a hybrid system for villages and telecommunications.
1.7.1 Electrical Energy
Most wind turbines are designed to provide electrical energy. In a wind-assist system, wind
turbines are connected to the utility line either directly through induction generators and
synchronous generators or indirectly where variable-frequency alternators and DC generators are
connected through inverters. The utility line and generating capacity of the power station act as
the storage system. For stand-alone systems, battery storage is the most common option.
The U.S. Department of Agriculture (USDA), Bushland, Texas, and the Alternative Energy
Institute (AEI), West Texas A&M University, are evaluating stand-alone, electric-to-electric
systems for pumping water. The wind turbine generator is connected directly to an induction
motor or a submersible pump, which is run at variable rpm. The advantages of such a system are
39
higher efficiency and higher volumes of water, enough for village water supply and low-volume
irrigation. Such systems are now commercially available.
1.7.2 Mechanical Energy
The major use for windmills has been the pumping of water. The farm windmill is well designed
to pump small volumes of water at low wind speeds. Since the farm windmill has a large number
of blades (vanes), it will start under a load because it has a large torque. However, the large
number of blades means it takes a lot of material, and the unit is inefficient at high wind speeds.
Power ratings are around 0.5 kW for a 5 m diameter rotor.
The Brace Research Institute combined a modern three-bladed wind turbine, a transmission from
a truck, and a conventional centrifugal pump on a prototype project to pump irrigation water on
the Island of Barbados. The rotor was not self-starting, and the blades of fiberglass were
expensive. A person had to manually shift the transmission to match the load of the pump to the
output of the wind turbine at different wind speeds.
In 1976, AEI and USDA studied the feasibility of using wind turbines for pumping irrigation
water with positive displacement pumps and airlift pumps. There are problems in matching the
power output of the wind turbine with the power needed by the irrigation pump. Calculated
maximum efficiencies were very low, on the order of 10%, for both types of pumps.
The airlift pump has the advantages of no moving parts in the well, and the wind turbine does not
have to be located at the well. Airlift pumps were in use at the turn of the century for pumping
water from mines, but were replaced by other types. Two companies in the United States have
manufactured a wind-powered airlift pump to compete with the farm windmill; however, only
Airlift Technologies has units for sale today. For maximum efficiency, the submergence, depth of
pump below the water level, should be equal to the lift. Wells with little water at large depths
present a problem for airlift pumps. Also, there is the problem of load matching between the wind
turbine and the air compressor, a constant torque device, and the inherent inefficiencies.
40
A wind turbine can be connected mechanically to another power source, a wind-assist system for
pumping water. The other power source could be an electrical motor or an internal combustion
engine. Both systems have been tested.
1.7.3 Thermal Energy
Thermal energy can be obtained directly by churning water or some fluid with viscosity. The load
matching between the wind turbine and the churn is very good. A prototype system for providing
heat to a dairy was tested by a research group at Cornell University. Conversion of electrical
energy to thermal energy by resistance heating has been tested a few times. At one time, a
company marketed such a wind system.
1.7.4 Wind Hybrid Systems
A large market exists for wind-assist to diesel-generated electricity for isolated communities,
businesses, farms, and ranches. There are around 2 billion people without electricity, and hybrid
systems consisting of wind, photovoltaic, hydro or diesel, battery storage, and an inverter are now
part of the planning process to provide alternating current (AC) electricity for villages with an
energy use of 20 to 200 kWh/day. Hybrid systems have also been installed in very remote
locations,
such
as
remote
military locations
and
telecommunication
systems.
For
telecommunications the emphasis is on continuous power, so redundancy is important to achieve
the high reliability.
NREL has a site for hybrid systems for village power, Renewables for Sustainable Village Power
(RSVP). The RSVP Village Power Project Database contained around 150 projects (wind is part
of 50 projects) from over 30 countries. Project information included basic, technological,
economic, financial, host country, lessons learned, pictures and graphics, and contact
information. The database is now archived and is not available online, and there have been a
large number of projects installed since 2004. For example, China now has over 700 village
installations (capacity, 16 MW) powered by mini hydro, PV, or wind/PV hybrid systems. China
has also installed a few wind/PV/diesel systems.
41
1.8
Storage
Of course if a way could be found to cheaply store energy, then there would not be a need to
construct new electrical power plants for some time. In addition, the economics of renewable
energy, including wind systems, would improve and wind farms could provide firm power.
Batteries are used with stand-alone systems and hybrid systems, and even provide load leveling
for short-term fluctuations. XCEL Energy will begin a demonstration project consisting of 1 MW
of battery storage to store energy from wind farms. There will be 20 battery modules (50 kW
each) that will store around 72 MWh. Other storage ideas have been to change the electrical
energy to chemical energy, such as the production of hydrogen or fertilizer. Village power
systems that include wind turbines and the production of hydrogen are now on the market.
Another idea would be to store the energy in flywheels, which would be a good load match
between the wind turbine and the load. Compressed air, pumped water storage, and
superconducting magnets have all been considered, and some prototype systems with wind
turbine input have even been constructed. In general, the efficiency of storage systems is around
60 to 70%.
2.
2.1
WIND CHARACTERISTICS
Global Circulation
The motion of the atmosphere can vary in distance and time from the very small to the very large
(Table 2.1). There is an interaction between each of these scales and the flow of air is complex.
The global circulation encloses eddies, which enclose smaller eddies, which enclose smaller
eddies, until finally the microscale is reached.
The two main factors in global circulation are the solar radiation and the rotation of the earth and
the atmosphere. The seasonal variation is due to the tilt of the earth‟s axis to the plane of the
earth‟s movement around the sun. Since the solar radiation is greater per unit area when the sun is
directly overhead, there is a transport of heat from the regions near the equator toward the poles.
Because the earth is rotating on its axis and there is conservation of angular momentum, the wind
will be shifted as it moves along a longitudinal direction. The three-cell model explains the
42
predominant surface winds (Figure 2.1). Those regions in the trade winds are generally good
locations for the utilization of wind power; however, there are exceptions, as Jamaica is not
nearly as windy as Hawaii.
Superimposed on this circulation is the migration of cyclones and anticyclones across the
midlatitudes, which disrupt the general flow. Also, the jet streams, the fast core of the central
westerlies at the upper levels, influence the surface winds.
Local winds are due to local pressure differences and are influenced by the topography, friction
of the surface due to mountains, valleys, etc. The diurnal (24 h) variation is due to temperature
differences between day and night. The temperature differences between the land and sea also
cause breezes; however, they do not penetrate very far inland (Figure 2.2).
Table 2.1: Time and Space Scale for Atmospheric Motion
43
Figure 2.1: General Atmospheric Circulation, Northern Hemisphere
Figure 2.2: Sea Breeze, Day ; Land Breeze, Night
44
Table 2.2: Summary of Global Values for Renewable Sources
2.2
Wind Shear
Wind shear is the change in wind speed or direction over some distance (Figure 2.4). There can
even be a vertical wind shear (Figure 2.5). The change in wind speed with height, a horizontal
wind shear, is an important factor in estimating wind turbine energy production. The change in
wind speed with height has been measured for different atmospheric conditions.
The general methods of estimating wind speeds at higher heights from known wind speed at
lower heights are power law, logarithm with surface roughness, and logarithm with surface
roughness that has zero wind velocity at ground level. The power law for wind shear is
where v0 = measured wind speed, H0 = height of known wind speed v0, and H = height.
The wind shear exponent α is around 1/7 (0.14) for a stable atmosphere (decrease in temperature
with height); however, it will vary, depending on terrain and atmospheric conditions. From
Equation 3.6 the change in wind speed with height can be estimated (Figure 2.3). Notice that for
α = 0.14, the wind power at 50 m is double the value at 10 m, a convenient way to estimate
power, so many wind maps give wind speed and power classes for 10 and 50 m heights.
45
However, for wind farms, wind power potential is determined for heights from 50 m to hub
heights.
Figure 2.3: Wind Shear, Change in Wind Speed with Height. Calculations are for given wind
speed of 10 m/s at 10 m, α = 1/7
The wind shear exponent values in continental areas will be closer to 0.20 for heights of 10–40 m
and above, with large differences from low values during the day to high values at night.
Figure 2.4: Left: Wind Shear Caused by a Difference in Wind Speed with Height. Right: Wind
Shear Caused by a Difference in Wind Direction
46
Figure 2.5: Example of Vertical Wind Shear
2.3
Wind Measurements
Measurement of wind speed is very important to people such as pilots, sailors, and farmers.
Accurate information about wind speed is important in determining the best sites for wind
turbines. Wind speeds must also be measured by those concerned about dispersion of airborne
pollutants.
Wind speeds are measured in a wide variety of ways, ranging from simple go-no go tests to the
most sophisticated electronic systems. The variability of the wind makes accurate measurements
difficult, so rather expensive equipment is often required.
Wind direction is also an important item of information, as well as the correlation between speed
and direction. In the good wind regime of the western Great Plains, prevailing winds are from the
north and south. Winds from east and west are less frequent and also have lower average speeds
than the winds from north and south. In mountain passes, the prevailing wind direction will be
oriented with the pass. It is conceivable that the most economical wind turbine for some locations
will be one that is fixed in direction so that it does not need to turn into the wind. If energy output
47
is not substantially reduced by eliminating changes in turbine orientation, then the economic
viability of that wind turbine has been improved. But we must have good data on wind direction
before such a choice can be made.
2.3.1 Eolian Features
The most obvious way of measuring the wind is to install appropriate instruments and collect data
for a period of time. This requires both money and time, which makes it desirable to use any
information which may already be available in the surface of the earth, at least for preliminary
investigations. The surface of the earth itself will be shaped by persistent strong winds, with the
results called eolian features or eolian landforms. These eolian landforms are present over much
of the world. They form on any land surface where the climate is windy. The effects are most
pronounced where the climate is most severe and the winds are the strongest. An important use of
eolian features will be to pinpoint the very best wind energy sites, as based on very long term
data.
Sand dunes are the best known eolian feature. Dunes tend to be elongated parallel to the
dominant wind flow. The wind tends to pick up the finer materials where the wind speed is
higher and deposit them where the wind speed is lower. The size distribution of sand at a given
site thus gives an indication of average wind speed, with the coarser sands indicating higher wind
speeds.
The movement of a sand dune over a period of several years is proportional to the average wind
speed. This movement is easily recorded by satellite or aerial photographs.
Another eolian feature is the playa lake. The wind scours out a depression in the ground which
fills with water after a rain. When the water evaporates, the wind will scour out any sediment in
the bottom. These lakes go through a maturing process and their stage of maturity gives a relative
measure of the strength of the wind. Other eolian features include sediment plumes from dry
lakes and streams, and wind scour, where airborne materials gouge out streaks in exposed rock
surfaces.
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Eolian features do not give precise estimates for the average wind speed at a given site, but can
identify the best site in a given region for further study. They show that moving a few hundred
meters can make a substantial difference in a wind turbine output where one would normally
think one spot was as good as another. We can expect to see substantial development of this
measurement method over the next few decades.
2.3.2 Biological Indicators
Living plants will indicate the effects of strong winds as well as eolian features on the earth itself.
Eolian features are most obvious where there is little plant cover, so the plants which hide eolian
features may be used for wind information instead. Strong winds deform trees and shrubs so that
they indicate an integrated record of the local wind speeds during their lives. The effect shows up
best on coniferous evergreens because their appearance to the wind remains relatively constant
during the year. Deciduous trees shed their leaves in the winter and thus change the exposed area
tremendously. If the average wind speed is high but stil below some critical value, above which
deciduous trees cannot survive, they will not indicate relative differences in wind speeds very
well, although they do show distinctive wind damage.
Putnam lists five types of deformation in trees: brushing, flagging, throwing, wind clipping, and
tree carpets. A tree is said to be brushed when the branches are bent to leeward (downwind) like
the hair in an animal pelt which has been brushed one way. Brushing is usually observable only
on deciduous trees and then only when the leaves are off. It will ocur with light prevailing winds,
and is therefore of little use as a wind prospecting tool.
A tree is said to be flagged when the wind has caused its branches to stretch out to leeward,
perhaps leaving the windward side bare, so the tree appears like a flagpole carrying a banner in
the breeze. This is an easily observed and measured effect which occurs over a range of wind
speeds important to wind power applications.
A tree is said to be windthrown when the main trunk, as well as the branches, is deformed so as to
lean away from the prevailing wind. This effect is produced by the same mechanism which
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causes flagging, except that the wind is now strong enough to modify the growth of the upright
leaders of the tree as well as the branches.
Trees are said to be wind clipped when the wind has been sufficiently severe to suppress the
leaders and hold the tree tops to a common, abnormally low level. Every twig which rises above
that level is promptly killed, so that the upper surface is as smooth as a well-kept hedge.
Tree carpets are the extreme case of clipping in that a tree may grow only a few centimeters tall
before being clipped. The branches will grow out along the surface of the ground, appearing like
carpet because of the clipping action. The result may be a tree 10 cm tall but extending 30 m to
leeward of the sheltering rock where the tree sprouted.
Hewson and Wade have proposed a rating scale for tree deformation which is shown in Figure
2.6. In this scale 0 corresponds to no wind damage, I, II, III, and IV to various degrees of
flagging, V to flagging plus clipping, and VI to throwing. Class VII is a flagged tree with the
flagging caused by other factors besides a strong prevailing wind, such as salt spray from the
ocean or mechanical damage from a short, intense storm.
The average wind speed at which these effects occur will vary from one species to another so
calibration is necessary. This is a long, laborious process so refinements can be expected for a
number of years as new data are reported. Putnam has reported calibration data for balsam trees
in New England, which are given in Table 2.3. The wind velocity at the top of the specimen is
given. This must be translated to wind speed at wind turbine hub height by the shear equations
found in the previous chapter, when wind turbine power estimates are required.
50
Figure 2.6: Representation of the Rating Scale Based on the Shape of the Crown and Degree of
Bending of Twigs, Branches and the Trunk
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Table 2.3: Putnam‟s Calibration of Balsam Deformation Versus Average Wind Speed in New
England
It can be seen in Table 2.3 that the full range of observed deformations occur over the speed
range of 7 to 12 m/s, which is an important range of interest to wind turbines. The balsam trees
can be used to effectively rank various sites and to eliminate many marginal locations.
Deformations also show the location of high wind speed zones produced by standing waves or
gravity waves in the air flow over rough surfaces. A high wind striking a mountain top may be
deflected downward and hit in the valley or on the side of a hill with much greater force than the
expected prevailing wind at that altitude. Putnam mentions the Wamsutta Ridge of Mt.
Washington as a good example of this effect. Along most of the crest of the ridge the trees grow
between 5 and 10 m high. But in one patch, a hundred meters wide, the high speed upper level
winds have been deflected downward and sear the ridge. Here balsam grows only in the lee of
rocks and only to a height of 0.3 m. The transition from the high wind zone to the normal wind
zone occurs in a matter of meters. Finding such a zone is to the wind prospector what finding
gold is to the miner.
Once such zones have been identified, it is still important to place wind instrumentation at those
sites. The eolian and biological indicators help identify the very best sites and eliminate the poor
sites without giving the precise wind data needed for wind turbine deployment.
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2.3.3 Rotational Anemometers
Anemometers, instruments that measure wind speed, have been designed in great variety. Each
type has advantages and disadvantages, as we shall see. Anemometer types include the propeller,
cup, pressure plate, pressure tube, hot wire, Doppler acoustic radar, and laser. The propeller and
cup anemometers depend on rotation of a small turbine for their output, while the others basically
have no moving parts.
Figure 2.7 shows a propeller type anemometer made by Weathertronics. This particular model
includes both speed and direction in the same sensor. The propeller is made of aluminum and the
tail is made of fiberglass. The sensor is able to withstand wind speeds of 90 m/s.
Figure 2.7: Propeller-type Wind Speed Sensor
53
Anemometers may have an output voltage, either dc or ac, or a string of pulses whose frequency
is proportional to anemometer speed. The dc generator is perhaps the oldest type and is still
widely used. It requires no external power source and is conveniently coupled to a simple dc
voltmeter for visual readout or to an analog-to-digital converter for digital use. The major
disadvantages are the brushes required on the generator, which must be periodically maintained,
and the susceptibility to noise in a recording system dependent on voltage level. The long runs of
cable from an anemometer to a recording station make electromagnetic interference a real
possibility also. Anemometers with permanent magnet ac generators in them do not require
brushes. However, the ac voltage normally needs to be rectified and filtered before being used.
This is difficult to accomplish accurately at the low voltages and frequencies associated with low
wind speeds. This type of anemometer would not be used, therefore, where wind speeds of below
5 m/s are of primary interest.
The digital anemometer uses a slotted disk, a light emitting diode (LED), and a phototransistor to
obtain a pulse train of constant amplitude pulses with frequency proportional to anemometer
angular velocity. Wind speed can be determined either by counting pulses in a fixed time period
to get frequency, or by measuring the duration of a single pulse. In either case, the noise
immunity of the digital system is much better than the analog system. The major disadvantages of
the digital anemometer would be the complexity, and the power consumption of the LED in
battery powered applications. One LED may easily draw more current than the remainder of a
data acquisition system. This would not be a consideration where commercial power is available,
of course.
Figure 2.8 shows a cup type anemometer made by Electric Speed Indicator Company. This is the
type used by most NationalWeather Service stations and airports. The cups are somewhat cone
shaped rather than hemispherical and are about 11 cm in diameter. The turning radius of the tip of
the cup assembly is about 22 cm. The cups turn a small dc generator which has a voltage output
proportional to wind speed. The proportionality constant is such that for every 11.2 m/s increase
in wind speed, the voltage increases by 1 volt. Wind speeds below 1 m/s do not turn the cups so
there is an offset in the curve of voltage versus wind speed, as shown in Fig. 4. Since the straight
line intercepts the abscissa at 1 m/s, an output voltage of 1 V is actually reached at 12.2 m/s.
54
Figure 2.8: Cup-type Wind Speed Sensor
2.3.4 Wind Directıon
Changes in wind direction are due to the general circulation of atmosphere, again on an annual
basis (seasonal) to the mesoscale (4–5 days). The seasonal changes of prevailing wind direction
could be as little as 30° in trade wind regions to as high as 180° in temperate regions. In the
plains of the United States, the predominant directions of the winds are from the south to
southwest in the spring and summer, and from the north in the winter. Traditionally, wind
direction changes are illustrated by a graph, which indicates percent of winds from that direction,
or a rose diagram (Figure 2.9).
55
Figure 2.9: Annual Average Wind Direction at 25 and 50 m Height, 10° Sectors
There can also be change in wind direction on a diurnal basis. However, a wind shear of change
in wind direction with height is generally nonexistent or small, except for very short time periods
as weather fronts move through. Wind direction data (hour average wind speeds) from sixteen
stations in Texas and one in New Mexico did not find any significant wind shear of change in
direction. Even on Padre Island, Texas, the land–sea breeze was not significant. Pivot tables were
used to check on the relation between wind speed, wind direction, and time of day for the above
seventeen met stations, plus two tall-tower met stations.
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Figure 2.10: Wind Direction Vane and Transmitter
3.
3.1
SITING
Small Wind Turbines
For small wind turbines, a measuring program may cost more than the wind turbine; therefore,
other types of information are needed. As wind maps are developed for potential wind farms by
countries, these maps can be used as guides to determine regions with enough wind for small
wind turbines. Also, wind maps for countries and large regions obtained from numerical models
have sufficient resolution for siting of small wind turbines. Since small wind turbines will be
located close to the load, local topography will influence the decision on estimating wind speeds
and siting. If the location is on exposed terrain, hills, or ridges, then the wind speeds would be
higher than those in the valley. In complex terrain, some sites will be adequate for small wind
turbines and other sites will be sheltered.
One of the factors in the settlement of the Great Plains of the United States was the farm
windmill, which provided water for people and livestock. Therefore, if farm windmills are used
or were used in the past in a region, then there is enough wind for small wind turbines in that
57
region. Another possibility is to install met towers for reference data for a region. Generally, this
would be done by regional or state institutions or governments, not by individuals interested in
siting of small wind turbines.
Small wind turbines can be cost-effective for stand-alone systems using the general rule that the
average wind speed for the lowest wind month should be 3 to 4 m/s. Also, general maps of wind
power or wind energy potential for small wind turbines have been developed for large regions
(Figure 3.1). These gross wind maps will be supplanted by national wind maps developed for
determining wind energy potential for wind farms. Finally, if there are wind farms in the area,
there is definitely enough wind for small wind turbines.
It is obvious that a small wind turbine should be located above (10 m if possible) obstructions and
away from buildings and trees. Towers for small wind turbines should be a minimum of 10 m and
preferably 20 m, as higher towers generally capture more energy (Figure 3.2). Again, the tradeoff is the extra energy versus the cost of a taller tower. Even towers of 35 m are sometimes used.
As a general rule for avoiding most of the adverse effects of building wakes, the turbine should
be located (1) upwind a distance of more than two times the height of the building, (2) downwind
a minimum distance of ten times the building height, or (3) at least twice the building height
aboveground if the turbine is immediately downwind of the building. The above rule is not
foolproof because the size of the wake also depends upon the building‟s shape and orientation to
the wind (Figure 3.3). Downwind from the building, power losses become small at a distance
equal to fifteen times the building height. However, a small wind turbine cannot be located too
far away from the load, as the cost of wiring will become prohibitive. Also, there will be more
losses in the wires if you have DC rather than AC from the wind turbine to the load. In general,
small wind turbines should not be mounted on occupied buildings because of possible problems
of noise, vibration, and even turbulence. For the very small wind turbines, tower heights vary
from stub poles on sailboats to short, 3 to 5 m towers, and some are even mounted on buildings.
Paul Gipe has written numerous articles on all aspects of wind energy, and two of his books are
for small wind systems.
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Figure 3.1: Wind Power Map for Rural Applications, Mexico. Notice difference in definition of
wind power class and height is at 30 m.
Figure 3.2: Height of Small Wind Turbine Close to Obstacles of Height H
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Figure 3.3: Estimates of Speed and Power Decrease and Turbulence Increase for Flow over a
Building. Estimates shown are for building height H.
A unique concept is a wind cooperative of small wind turbines for farms, ranches, and public and
private facilities in the Northwest United States. Ten 10 kW wind turbines have been installed,
and the map gives the location for each site. There are photos, comments from the owners, and
details on wind turbines, wind resource, anticipated, actual performance and interconnection.
Is there such a concept as wind rights if a neighbor erects a tall structure that obstructs the flow of
wind to your turbine. From a visual standpoint, a wind turbine in every backyard in a residential
neighborhood is much different than a PV panel on the roof of every home.
The American Wind Energy Association and the Canadian Wind Energy Association have
sections for small wind turbines, which include information on siting. A guide for small wind
turbines is available from the National Renewable Energy Laboratory (NREL) with information
on siting similar to the information presented above. The British Wind Energy Association
section on small wind includes information on a wind speed database and map (annual mean
wind speed at 25 m height), small wind technologies, planning, and case studies. National wind
energy associations in other countries probably have sections on small wind turbines.
There have been a number of designs by architects and inventors and even people selling wind
systems (most not built or tested) to integrate wind turbines into the building structure in urban
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areas. The designs usually tout the increase of wind speed due to the building; however, in the
real world, incorporating wind turbines into buildings is a difficult choice, due to noise, vibration,
and safety concerns. In some concepts of installations on buildings, the wind turbines have to be
mounted perpendicular to the predominant wind direction, as the wind turbines are fixed in yaw.
The estimated energy production is in the range of 1.7–5.0 TWh in the built environment
(turbines in urban areas, turbines mounted on buildings, turbines integrated into buildings) in the
United Kingdom. The technical feasibility and various configurations are also discussed. There is
an Internet site for urban wind with downloads available: European Urban Wind Turbine
Catalogue; Urban Wind Turbines, Technology Review, a companion text to EU UWT Catalogue;
and urban wind turbine guideline for small wind turbines in the built environment and windy
cities, and wind energy for the urban environment. The wind turbine guidelines include images of
flow over buildings and example projects.
A newspaper in Clearwater, Florida, had a stacked Darrieus next to the building. It consisted of
three Darrieus turbines, 4.5 m diameter, 6 m tall, 4 kW each (Figure 3.4). Fortis mounted three
wind turbines (5 m diameter, at 2 kW rather than the nominal 5 kW) on a factory/office building.
There was a small problem with vibration at high wind speeds due to the flexibility of the roof.
The Aeroturbine has a helical rotor mounted in a 1.8 by 3 m frame, rated power of 1 kW. A
building in Chicago has eight units mounted horizontally on top of a building (Figure 3.5), while
other buildings have units mounted vertically. Two 6 kW wind turbines were mounted on the
roof of a civic center in the United Kingdom, which is described in a case study. A different
concept mounts a number of small wind turbines on the parapets of urban and suburban
buildings. The horizontal-axis wind turbine has a rated power of 1 kW mounted in modular
housing (approximately 1.2 by 1.2 m). Fourteen wind turbines are on the corner of the Energy
Adventure Aquarium building (Figure 3.6) in California, resulting in a kinetic sculpture.
The most spectacular structure with integrated large wind turbines is the Bahrain World Trade
Center, where the two 240 m towers with sail silhouettes have three cross bridges that have wind
turbines. The wind turbines are 29 m diameter, 225 kW, and predicted to generate around 1100 1300 MWh/year, 11 - 15% of the energy needed by the buildings. The aerodynamic design of the
towers funnels the prevailing onshore Gulf breeze into the path of the wind turbines.
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3.1.1 Noise
Although zoning is an institutional issue, the regulations will affect the possibility of erecting a
small wind turbine and, if possible, then the size of the wind turbine, tower height, how much
space is needed around the tower, and the possibility of the effect of noise and even visual
concerns of the neighbors. The noise from a small wind turbine is around the level of noise in an
office or in a home. Noise from a small wind turbine is rarely a problem since the level drops by
a factor of 4 at a distance of 15 m, and it is generally masked by background noise. A sound
study with a 10 kW wind (wind speeds were 9–11 m/s) showed levels of 49–46 dBA for the
turbine running and off at a distance of 15 m, and essentially no difference at a distance of 30 m
and greater. However, if the wind turbine rotor is downwind, then there is a periodic sound every
time the blade passes the tower, and even though the sound is the same level as the background
sound, it can be annoying. In California, noise from a wind turbine must not exceed 60 dBA at
the closest inhabited building.
Figure 3.4: Three Stacked Wind Turbines (Darrieus), 4 kW Each, Next to Building. Notice man
on top.
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Figure 3.5: Eight Helical Wind Turbines, 1 kW, Horizontal Axis, on Top of Building, 8 kW
Total
Figure 3.6: Wind Turbines, 1 kW Each, Mounted on Parapet of Building
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3.1.2 Visual Impact
The State of Vermont has a scoring system for possible adverse visual impact of small wind
turbines from two different vantage points: private property (the neighbors‟ view) and public
views (roads, recreation, and natural areas). For the neighbors‟ view the considerations are: (1)
What is the position of the turbine in the view? (2) How far away is the turbine seen? (3) How
prominent is the turbine? (4) Can the turbine be screened from view? For public views there are
two additional considerations: (5) Is the turbine seen from an important scenic or natural area? (6)
What is the duration of the view? Each is rated by a point system (Table 3.1), with a total of 12
points for the residential viewpoint and 18 for the public viewpoint. If the score (Table 3.2) is
below the significant range, the wind turbine is unlikely to have a visual impact unless it is close
to and at the center of a scenic view. The score is only a general indicator for visual impact of
small wind turbines. Wind turbines will be visible, at least from some viewpoints, as they will be
above surrounding trees. In the Plains areas with few trees, small wind turbines will be noticeable
from 1 to 3 km, the same as the trees around a farmhouse. Notice that there are comparableheight towers, such as cell phone towers, towers for lights at highway interchanges, radio towers,
and the long rows of towers for utility transmission lines. The difference is that those towers do
not have moving rotors.
Table 3.1: Criteria for Points for Visual Impact of Small Wind Turbines
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Table 3.2: Rating of Visual Impact of Small Wind Turbines
3.2
Wind Farms
For wind farms, long-term data are a necessity, and data should be collected on site for 2 to 3
years. Then the questions are: What is the long term annual variability? and How well can you
predict the energy production for a wind farm? The siting of turbines over an area the size of a
wind farm, about 5–20 km2, is termed micrositing. Thus, the wind turbines should be located
within the wind farm to maximize annual energy production, which gives the largest financial
return. Array losses have to be considered in the siting process.
3.2.1 Long-Term Reference Stations
To determine if data from a historical site are adequate to describe the long-term wind resource at
another site, the analysis should be done rigorously. Simon and Gates recommend that the annual
hourly linear correlation coefficient be at least 0.90 between the reference site and off-site data.
Remember to take into account wind shear if the heights are different at the two locations. If the
two sites are not similar in wind speed and direction trends and do not have similar topographic
exposure, then they will probably not have that correlation value. Longterm reference stations
should be considered in all locations in the world where there is wind power potential. These
stations should continue to collect data even after a wind farm has been installed. Not only will
this improve siting of wind farms, but it will provide reference sites for delineating the wind
resource for single or distributed wind turbines in that region. As wind turbines have increased in
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size, the hub heights are higher, and because in most locations wind speed increases with height,
there is a need for reference stations to collect data at least at 50 m, and if possible to 100 m.
3.2.2 Siting for Wind Farms
The number of met stations and the time period for data collection to predict the energy
production for a wind farm vary depending on the terrain and the availability of long-term base
data in the vicinity. In general, numerical models of wind flow will predict wind speeds to within
5% for relatively flat terrain and 10% for complex terrain, which means an error in energy of 15 30%. Therefore, a wind measurement program is imperative before a wind farm is installed.
However, if a number of wind farms are already in the region, then 1 year of data collection
might suffice.
For complex terrain, you may need one met station per three to five wind turbines. For wind
turbines of 500 kW to megawatts, you may need a met station per one or two wind turbines in
complex terrain. With more homogeneous terrain, as in the Plains, a primary tall met station and
one to four smaller met stations may suffice. The tallest met station should be a representative
location on the wind farm area, not the best point.
Contour maps are used for location of wind turbine pads and for roads. In general, the wind
turbines will be located on the higher elevations within the wind farm area. Topozone has
interactive topography maps (all different scales) online for the entire United States. These maps
are very useful in selection of met tower locations, micrositing, roads, and other physical aspects
of the wind farm.
The key factors for array siting for the Zond wind farms in Tehachapi Pass were an extensive
anemometer data network, the addition of new stations during the planning period, a time frame
of 1 year to refine the array plans, a project team approach to evaluate the merits of different
siting strategies, and the use of initial operating results to refine the rest of the array. A large
number of met stations were needed because the spatial variation of the wind resource over short
distances in complex terrain was greater than expected. The energy output from 2 projects, 98
wind turbines and 342 wind turbines, was within 3% of the predicted value. This experience
66
shows it is possible to estimate long-term production from a wind plant with acceptable accuracy
for the financial community. One of the key factors is an extensive network of met towers.
In some older wind plants, the lowest producing wind turbines were relocated (these were small
wind turbines). The money spent on micrositing is a small fraction of the project cost, but the
value of the information gained is critical to accurately estimating the energy production. Many
of the problems with low energy production are because of poor siting.
Wind turbines have become larger, with rotor diameters from 60 to 100 m and hub heights of 60
to 100 m. There are very little data at or above these heights; however, NREL had a program for
tall tower data. The problem is that any tall tower data collected by wind farm developers are
proprietary.
Because of wind shear, wind turbines are located on the higher elevations for rolling terrain, on
mesas, and on ridges in complex terrain. In the past, turbulence was considered a big problem for
siting at the edges of mesas and ridges. However, with the taller towers, wind turbines are placed
on the edges, which are perpendicular to the predominant wind direction. As an example, for
wind turbines on mesas in Texas, the north edge of the mesa would have increased winds from
northern storms in the winter due to the rise in elevation, and then in the summer with southern
winds, there is room for expansion of the wake. Data on turbulence for these sites are proprietary,
primarily because it affects operation and maintenance.
3.3
Digital Maps
Digital maps are useful as they give a general overview of the wind resource, confidence of the
data, and other data (land use, transmission lines, etc.), which can easily be displayed on the same
maps. NREL has created a higher-resolution digital wind map for the United States and is in the
process of updating the maps by state using terrain enhancement and Geographic Information
Systems (GIS).
A very useful interactive tool, windNavigator, based on Google Maps, is a wind resource map
and data for the continental United States. The map (2.5 km resolution) provides wind speeds at
60, 80, and 100 m and a pointer to give minimum and maximum mean annual wind speeds on a
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200 m scale. Selectable areas at 200 m resolution (PDF or GIS data set) can be purchased.
Satellite, hybrid, and terrain views are available for the world.
A similar interactive wind resource map (map, satellite, hybrid, and terrain views) and data for
the world, FirstLook, has wind speeds at 20, 50, and 80 m, and presently wind data for the United
States, Alaska, Canada, and Mexico are online. With FullView Assessment, resolution is at 90 m.
In addition, a solar resource map is available. Remember, wind speed maps are useful for an
indication of wind energy, but wind power maps are the next step.
3.4
Numerical Models
Numerical models for predicting winds are becoming more accurate and useful, especially for
those areas of the world where surface wind data are scarce or unreliable. Models were primarily
derived from numerical models for weather prediction. Remember that a small difference in wind
speed can make a large difference in energy. Therefore, in the final analysis, surface wind data
are stil needed for wind farms.
Table 3.3: Texas, Intercepted and Capturable Wind Power and Annual Energy Potential from
Land That Satisfies the Screening Parameters
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MesoMap: The MesoMap system was developed specifically for near-surface wind forecasting.
It is a modified version of the Mesocale Atmospheric Simulation System (MASS) weather
model. MesoMap uses historical atmospheric data spanning 20 years and a fine grid (typically 15 km). MesoMap simulates sea breezes, mountain winds, low-level jets, changing wind shear due
to solar heating of the earth‟s surface, the effects of temperature inversions, and other
meteorological phenomena. MesoMap does not depend on surface wind measurements although
surface measurements are desirable for calibration.
The model provides descriptive statistics at any height above ground, such as wind speed
histograms, Weibull frequency parameters, turbulence and maximum gusts, maps of wind energy
potential within specific geographical regions, and even the annual energy production of wind
turbines at selected sites in the region.
WAsP: Wind Atlas Analysis and Application Program is software developed by Riso National
Laboratory for predicting wind climate and power production from wind turbines. The
predictions are based on wind data measured at stations in the region. The program includes a
complex terrain flow model. WAsP was used for developing the European wind map and is used
by many others across the world. Other models are available, so check the links listed below and
the Internet.
3.5
Micrositing
Wind maps, meteorological data from met towers, models, and other criteria are used for
selection of the wind farm locations. Other considerations for the wind farm developer are the
type of terrain (complex to plains); wind shear; wind direction; spacing of the wind turbines,
which then depends on predominant wind direction and availability and cost of the land; and
other items, such as roads, turbine, and substation. Terrain can be classified as complex, mesas,
rolling, and plains. Passes may be primarily one type or a mixture. In general, spacing is given in
terms of the diameter, D, of the wind turbine, so larger turbines will be farther apart.
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As turbines have become larger, are wind shear data from 25 to 50 m sufficient to predict wind
speeds at 70 to 100 m heights? The first answer is yes, for that site, although there is not a
definitive answer at this point if the prediction is for another location in the same region.
In complex terrain, such as mountains and ridges, micrositing is very important, whereas in the
flat plains, the primary consideration is spacing between turbines in a row and spacing between
rows. On mesas, the highest wind speed is on the edge of the mesa facing the predominant wind
direction, so there may be only one row of turbines. In rolling terrain such as hills, the wind
turbines will be placed on the higher elevations.
In California, the high wind classes are due to the hot desert air rising and cooler air from the sea
coming through the passes. There they have the complex terrain at Tehachapi Pass, rolling terrain
of Altamont Pass (east of San Francisco), and both ridges and flat terrain at San Gorgonia Pass
near Palm Springs. The winds in the passes are predominantly from the west, so the rows are
primarily north–south. At San Gorgonia Pass some wind turbines were only 2D apart in the rows,
and then 4D to 5D between rows because of the high cost for leasing the land for wind farms.
With tight spacing, turbines could also be placed at different heights. As expected, the array
losses are fairly large. Starting in 1998, the smaller-size turbines were being replaced with larger
turbines.
The wind farm near White Deer, Texas, has eighty 1 MW wind turbines, which are 56 m
diameter. The wind turbines have a spacing of 4D within the row and 8D between rows (Figure
3.7). North is at the top of the figure, and the lines indicate roads at 1 mile (1.6 km). Notice the
buffer zone on the west, as that land was not under lease to the wind farm. Predominant winds are
southsouthwest during the spring and summer, and from the north in winter. As lower winds are
in July and August, rows are situated perpendicular to those predominant winds. There are low
spots due to playa lakes (only contain water after rain), so there are no wind turbines in those
locations. Only the west side of the wind farm is visible in the photo, as there are more turbines to
the east. Examples of wind farms in other terrain are shown in Figures 3.8 to 3.10. A photo of an
offshore wind farm is shown for comparison (Figure 3.11).
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Figure 3.7: West Side of Wind Farm in the Plains, near White Deer, Texas. White lines are for
roads, 2.5 km2, 1 square mile.
The amount of land taken out of production depends primarily on length and width of roads
constructed on the wind farm. Values vary from 0.5 to 2 ha per wind turbine. If there are county
roads, the wind farm developer will use less land; however, the developer will probably have to
improve the county roads for the heavier traffic. If it is on a mountain ridge, the roads may be
very expensive. The road from the bottom to the top for access to the Texas Wind Project at the
Delaware Mountains cost $1 million in 1993.
There are the civil engineering aspects for wind farm site, such as location of assembly area,
electrical substation, and roads (width and grade in complex terrain). Note that roads have to have
wide turns for trucks hauling the long blades. In many cases a batch cement plant is on site,
especially for complex terrain of ridges and mesas.
A general rule of thumb is that around 5–9 MW/km2 can be installed on land that is suitable for
wind farms. However, on ridgelines, at 2D to 3D spacing, the value would be around 8-12 MW/
linear km. This assumes that the ridge is more or less perpendicular to the predominant wind
flow. As wind turbines become larger, the megawatts per square or linear kilometer will increase
due to energy output increasing as the square of the radius. Notice that the landowner will lease
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blocks or areas of land, not just the places where turbines are located. It is interesting in the Texas
Wind Power Project that land leased for the wind farm included all land at the 1,453 m contour
and above (elevation of ridges is 1,830 m). The landowner is now trying to determine if any of
the land below the contour has any wind potential.
Figure 3.8: Wind Farm in Rolling Terrain, Lake Benton, Minnesota
Figure 3.9: Wind Farm on Southwest Mesa, near McCamey, Texas. Example of mesa with one
row.
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Satellite and aerial images are used in micrositing and are available from different sources; some
are free. Flash Earth (www.flashearth.com) has the option of switching between different
sources, such as Google Maps, Microsoft VE, and others. The wind farms are fairly distinctive in
the images, primarily because of the roads within the site and the area around each wind turbine.
Be sure to zoom in enough to see the wind turbines, as oil fields show the same pattern, but the
roads are not as wide. In some farming areas, round circles for irrigation sprinklers are very
prominent; large circles are section sprinklers (1 square mile, 260 ha), and small circles are ¼section sprinklers. Notice that the shadow of the wind turbines is more obvious than the wind
turbines, and the angle of the shadow may be different from one part of the wind farm to an
adjacent part, as the image was taken at a different date and time. Images from different sources
will also be taken at different dates and times. New wind farms will not appear in the satellite
images until they are updated, which could be more than a year.
Figure 3.10: Wind Farm in Complex Terrain, Northwest Spain
Micrositing techniques of wind farm developers are proprietary. However, satellite images show
the actual layout of wind farms, and from the images and topographic maps, a good idea can be
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obtained about the siting. If the type and model of wind turbine are known, then the spacing can
be estimated from the image. The image of Trent Mesa, Texas (Figure 3.12), shows about half of
the layout of the wind farm, which has 100 wind turbines, 66 m diameter, rated 1,500 kW.
Economic and institutional issues also affect micrositing. A good example of all phases of a
project is the Waubra wind farm (192 MW) in Australia, as the website has a description and
photos from community relations, environmental to construction. A detailed site layout map is
also shown.
Figure 3.11: Nysted Wind Farm in the Baltic Sea, Denmark
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Figure 3.12: Satellite Image of West Side of Trent Mesa Wind Farm, Texas
3.6
Energy Production
Annual energy production is the most important factor for wind turbines. Of course, that is
combined with economics to determine feasibility for installation of wind turbines and wind
farms.
Approximate annual energy can be estimated by the following methods:
1. Generator size (rated power)
2. Rotor area and wind map
3. Manufacturer‟s curve of energy versus annual wind speed
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3.6.1 Generator Size
This method gives a rough approximation because wind turbines with the same size rotors can
have different size generators:
AKWH = CF*GS*8760
AKWH: annual energy production, kwh/year
CF: capacity factor
8769 = number of hours in a year
The effect of the wind regime and the rated power for the rated wind speed can be estimated by
changing the capacity factor. The capacity factor is the average power divided by the rated power
(generator size). The capacity factor is estimated from energy production over a selected time
period, and in general, capacity factors are quoted on an annual basis, although some are
calculated for a quarter of a year. Capacity factors can also be calculated for wind farms, and they
should be close to the same values as capacity factors calculated for individual wind turbines.
However, if the wind farm is composed of different wind turbines, it should be noted. For
example, the Green Mountain Wind Farm at the Brazos near Fluvana, Texas, has 160 1 MW
wind turbines; however, 100 have rotor diameters of 61.4 m and 60 have rotor diameters of 56 m.
Therefore, the capacity factor will be larger for the units with the larger rotor. Notice that
capacity factor is like an average efficiency. In general, the generator size method gives
reasonable estimates if the rated power of the wind turbine is around 10–13 m/s. If the rated
power is above that range, or for wind regimes below class 3, then the capacity factor should be
reduced accordingly.
Example 5.1
Wind turbine has the following specifications:
Rated power = 25 kW at 10 m/s
Rotor diameter = 10 m
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Estimated capacity factor = 0.25
AKWH = 0.25 *25 kW*8,760 h/year = 55,000 kWh/year
For a poor wind regime, AKWH would be closer to 30,000 kWh/year.
A capacity factor of 0.25 would suffice for a generator rated at a wind speed of 10 m/s and the
wind turbine is in a medium wind regime. Wind farms are located in good to excellent wind
regimes, and capacity factors should be 32–40%. There have been reported capacity factors up to
50% for a wind farm located in the Isthmus of Mexico.
3.6.2 Rotor Area And Wind Map
The amount of energy produced by a wind turbine primarily depends on the rotor area, also
referred to as cross-sectional area, swept area, or intercept area. The swept area for different types
of wind turbines can be calculated from the dimensions of the rotor.
HAWT area = πr2, where r = radius.
VAWT, where H = height and D = diameter of rotor:
Giromill area = H*D
Savonius area = H*D
Darrieus area = 0.65 H*D
The annual average power/area can be obtained from a wind map, and then the energy produced
by the rotor can be calculated from;
AKWH = CF*Ar*WM*8.76
Ar: are of the rotor, m2
WM: power/area from a wind map, W/m2
8.76 = gives the answer in kWh/year, the conversion W to kW
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Again, the capacity factor reflects the annual average efficiency of the wind turbine, around 0.20
to 0.35.
Example 5.2
Use the wind turbine in Example 5.1, and from wind map:
WM = 200 W/m2
Area = πr2 = 3.14*25 m2 = 78.5 m2
AKWH = 0.25 *78.5 m2*200 W/m2*8.76 kWh/year = 34,000 kWh/year
Figure 3.13: Estimated Annual Energy Production Based on Annual Average Wind Speed
Notice the large difference in the answers for the two examples, which could be related to two
factors: generator size is too large for rotor size, or the wind regime is low, that is, the wind map
value is low. With this estimate of energy production, the wind map value should be selected or
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estimated for the hub height of the wind turbine, especially when estimating energy production
for large wind turbines.
3.6.3 Manufacturer’s Curve
Manufacturers assume a Rayleigh distribution for the wind speed at 1 m/s intervals and then
calculate the annual energy production at standard density using the power curve for their wind
turbine at a selected hub height. An example graph of the annual energy production versus
average wind speed is given for a 1 MW wind turbine (Figure 3.13). Notice the average wind
speed at your location should be somewhat close to the hub height. At 10 m height, the average
wind speed was around 6 m/s for the High Plains of Texas (1,100 m elevation), and at 50 m
height, the wind speed was 8.2 m/s. So, from the graph, a wind speed of 8.2 m/s means the
turbine should produce around 2,800,000 kWh/year.
3.7
Calculated Annual Energy
If the wind speed histogram or wind speed distribution is known from experimental data, then a
good estimation of energy production can be calculated from the histogram and the power curve
for the wind turbine. Manufacturers will supply power curves for their wind turbines, and most of
the power curves are available online. For each interval (a bin width of 1 m/s is adequate), the
number of hours at that wind speed is multiplied by the corresponding power to find the energy.
These values are added together to find the energy production for the total number of hours. This
is the method that wind farm developers use to estimate the energy production. Wind speed
histograms should reflect annual values, not the value for part of a year or even 1 year, which
could be above or below the annual values. A 1-year histogram could be adjusted to annual
values if long-term regional data are available. Two to 3 years of wind speed data, averaged to an
annual histogram, will suffice.
Wind speed histograms and power curves have to be corrected to the same height and adjusted
for air density due to location of the data compiled for the power curve. So when the density
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correction is made from 1.2 to 1.1 kg/m3 for the Texas Panhandle and an availability of 98% is
assumed, that reduces 3,061,000 kWh/year to 2,750,000 kWh/year.
Availability is the time that the wind turbine is in operational mode, and it does not depend on
whether the wind is blowing. Availability is related to reliability of the wind turbine, which is
affected by both the quality of the turbine and operation and maintenance. Experimental values of
availability of wind turbines in the field were poor for first production models; however,
availabilities of 98% are now reported for later units, which have a good program of ongoing
maintenance. Remember, a wind turbine does not have problems when the wind is not blowing.
Therefore, preventive maintenance is imperative to maintain energy production.
Figure 3.14: Calculated Annual Energy Production for 1 MW Wind Turbine in the Panhandle of
Texas
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Calculation of estimated energy production is simple using spreadsheets or by writing a program
to do the calculation from a histogram and a power curve. The data would be in tabular form and
can be graphed using spreadsheets or generic plot programs. Spreadsheets for calculation of
energy production are available at the accompanying website for Renewable Energy and the
Environment.
4.
AN ANALYSIS OF A MID-SCALE WIND TURBINE THAT WILL BE ERECTED
ON DAVUTPASA CAMPUS IN THE NEAR FUTURE
4.1
The Study Area and the Characteristics of the Region
The campus, where this research project was conducted, is located in the central southern part of
Istanbul and six kilometers far away from the city center. Below the campus is depicted through a
screenshot. Year by year the energy demand of this campus is gradually increasing due to the
faculty buildings and recreation areas which have been constructed recently.
Figure 4.1: A Satellite Image of Istanbul
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The structure of the terrain is complex and rugged. Both in the campus and in the surrounded area
of 5 square kilometers, altitude difference is very high. The coordinates of this 5 km² rectangular
area are;
655477,1 E - 4540011,5 N ve 661667.4E - 4546121,5 N
and in this area the altitude range differs from 5 m (lowest) to 110 m (highest). Besides, in the
campus borders the highest and the lowest altitudes are 90 m and 48 m. The campus is located
amid the urban area; therefore the roughness value of the terrain is relatively high. The campus
extends an area of up to 1885.2 m². The contour line map of a 4km² area is shown below;
Figure 4.2: The Digitized Contour Map of 4 km² Area
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4.2
The Software Tools Used During the Analysis
WAsP package program, which has been released by Risoe National Laboratory for Sustainable
Energy, constitutes the basis of this analysis. In addition, the analysis was enriched with other
well-known programs such as WindPRO, Windographer, Microsoft Excel and Matlab. WAsP is
a PC program for predicting wind climates, wind resources and energy productions from wind
turbines and wind farms. The predictions are based on wind data measured at stations in the same
region. The program includes a complex terrain flow model, a roughness change model and a
model for sheltering obstacles. WAsP defines the wind data, that is measured by anemometer,
under two main titles;
1) Wind Direction
2) Wind Speed
hereby the wind atlas of a region can be calculated and characterized. The wind atlas portrays the
frequency of the wind and through Weibull distribution graphic we can easily assess the wind
characteristic. WAsP has a few sub modules that help to import the data you have been collecting
throughout the project. Among these sub modules we can count OWC Wizard (observed wind
climate) which is used for importing the wind data into the main WAsP package program.
Another sub module is Turbine Editor which is also a very useful tool to modify an existing
turbine power curve file or create a new one from scratch.
With the main WAsP tool, you are able to define the nearby obstacles, which allow you to give
more details about the terrain where it is planned to build a wind farm. The more details about the
terrain you provide to WAsP, the more accurate results you receive in the end. The porosity,
height, width and other sorts of properties of the nearby obstacles have significant effect on the
roughness value that determines the wind characteristic of the area.
4.3
The Measurement Technique and the Anemometer Used During the Analysis
Throughout this research project, a 10 m high anemometer that is located at the elevation of 62 m
has collected wind data 16 months. The coordinates of this anemometer are 658608 N 4543167 E
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and the model is Campbell CR 1000. The data has been collected with the frequency of “per
minute” and in total 16 months were observed; the dates from September 2009 until March 2011.
On the next page, a photo of this anemometer and the location on the campus plan is shown.
Figure 4.3: A Photo of the Anemometer
Figure 4.4: The Location of the Anemometer on the Campus Plan
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4.4
Digital Map
For more accurate calculations it is preferable to use maps with the scales of either 1:25000 or
1:50000. In this project the digitized map is obtained from the academician Prof. Dr. Fatmagül
Batuk at Faculty of Civil Engineering. WAsP is able to recognize the digitized maps by using one
of its sub modules, “WAsP Map Editor”. Through “WAsP Map Editor” the topography of the
study terrain can be imported into WAsP Main Module. The main objective is to import as many
as details, characteristics of the terrain so that WAsP would get more acquainted with the terrain
and with the area as well. Providing a digital map is an essential step however, merely doing so is
not adequate. Therefore for a better description of the terrain the roughness values are manually
introduced in „WAsP Map Editor‟.
Figure 4.5: Digitized Contour Map with Imported Roughness Values
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Another capability of “WAsP Map Editor” is loading a background image that is associated with
the digitized map. It is a very useful tool to link a satellite image with the digitized map which
makes the whole process easy to manage. By determining the pixels on the image and assigning
the exact coordinates to those pixels it is possible to load a background image. The satellite image
taken from Google Earth is loaded by using the same technique through WAsP map editor in this
project as shown in Figure 4.6
Figure 4.6: A Satellite Image Associated with the Digitized Contour Map by WAsP Map Editor
4.5
Wind Data
The measurement site lies at an elevation of 62 meters and the wind data is recorded by an
anemometer at 10 meters height. As it will be distinctly seen by the histogram the maximum
wind speed measured was 21.4 m/s. If we observe the whole data, we come across with many
“Gust” values which cause a higher standard deviation value. Therefore it may also be a
turbulence wind flow which would also affect the continuity of the electricity generation
negatively.
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The wind data has been collected from the date 21.10.2009 14.59 until 31.02.2011 00.00. The
amount of missing data is 3 weeks in March 2010 and a few other days throughout the year.
There may be many reasons for which the anemometer stopped collecting data but as long as it
does not hinder the analysis, the missing data is either ignored or taken out.
4.6
Specifying the Nearby Obstacles
Each obstacle present near the measuring site, affect the wind data collected and it depends upon
the porosity and roughness of the terrain. Obstacles are considered by WAsP as “boxes” with a
rectangular cross-section and footprint. Each obstacle must be specified by its position relative to
the site and its dimensions must be assigned to a porosity value. The position of an obstacle is
specified in a local polar coordinate system. One of the most important steps of this stage was the
field/scene survey that was conducted by first hand twice with GPS. This provided us a better
understanding of the terrain.
As a general rule, the porosity can be set equal to zero for buildings and ~ 0.5 for trees. A row of
similar buildings with a separation between them of one third the length of a building will have a
porosity of about 0.33. For windbreaks the characteristics defined in WAsP may be applied. The
porosity of trees changes with the level of foliation, i.e. the time of year and similar to the
roughness length, the porosity should be considered as a climatologically influenced parameter.
Table 4.1: The Properties of the Obstacles nearby
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Figure 4.7: Location of the Obstacles near the Anemometer
4.7
Wind Rose
According to the monthly wind data the prevailing wind direction was calculated and shown in
the figures that are depicted by the program Matlab and WindRose. These figures, so called wind
roses, are diagrams that show the temporal distribution of wind direction and azimuthal
distribution of wind speed at a given location. A wind rose is a convenient tool for displaying
anemometer data (wind speed and direction) for siting analysis. The most preferable way to draw
a wind rose is dividing the directions into either 12 or 16 equally spaced sections. The origin
centered circles represent the frequency of the wind data. Basically, the longest lines identify the
prevailing wind directions. Below monthly wind rose graphics are shown;
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Figure 4.8: October 2009 Wind Rose Graph
Figure 4.9: November 2009 Wind Rose Graph
Figure 4.10: December 2009 Wind Rose Graph
Figure 4.11: January 2010 Wind Rose Graph
Figure 4.12: February 2010 Wind Rose Graph
Figure 4.13: March 2010 Wind Rose Graph
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Figure 4.14: April 2010 Wind Rose Graph
Figure 4.15: May 2010 Wind Rose Graph
Figure 4.16: June 2010 Wind Rose Graph
Figure 4.17: July 2010 Wind Rose Graph
Figure 4.18: August 2010 Wind Rose Graph
Figure 4.19: September 2010 Wind Rose Graph
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4.8
Histogram and Weibull Distribution
One of the most important phases of the wind assessment process is; drawing the “Weibull
Probability Distribution Graphic”. Weibull distribution is a two parameter distribution where c
and k are, the scale parameter and shape parameter. In this research project these parameters are
calculated; k=1.76 and c= 3.7m/s. As it is seen from Weibull Distribution Graph, although there
is a considerable percentage of wind speed above 10 m/s, it is less likely that wind speed reaches
to these high values at Davutpasa Campus.
Figure 4.20: Weibull Probability Distribution Graphic
Secondary approach for the wind speed probability distribution factor is a Histogram. A
histogram basically stands for the probability density distribution of the wind data. Wind speed
tends to be closer to the mean value than far from it, and that it is nearly as likely to be below the
mean as above it. Hence, the frequency of higher wind speeds is close to zero. In this research
project the highest wind speed value in Histogram is 24 m/s, as shown in the figure above.
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However, we read these “Gust” values from the anemometer, only a few times throughout the
whole year, therefore we assume these probabilities as zero. Another issue that needs to be paid
attention in this “12 sectioned Histogram” is the fact that the total amounts of the probability
values reach to the peak at 3 m/s, which is the closest integer to the mean wind speed value at the
elevation of 10 meters.
Table 4.2: 12 Sectioned Histogram
4.9
Wind Resource Mapping
Resource grids allow you to manage a rectangular set of points for which summary predicted
wind climate data are calculated. The points are regularly spaced and are arranged into rows and
columns. This lets you see a pattern of wind climate or wind resources for an area. You don't
need to create each point in the grid individually. Instead you just specify the location of the grid,
the number of rows and columns and the distance between the points. These resource maps are
particularly used for the optimization of the wind farms and calculating the wind power density in
the whole area as well. As it is seen in the figure on the next page;
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Figure 4.21: Wind Resource Map
4.10 Sample Wind Turbines Used in the Project
First part of the analysis was based on the terrain characteristics and wind gradient. The latter part
consists of the calculation of the annual energy productions of each wind turbine and micro-siting
the optimum one.
In this project 3 mid-scale wind turbines are used and all the required information was requested
from the manufacturer companies. Firstly, these 3 different wind turbines are located at the same
place one by one; thereby the annual energy production of each wind turbine was calculated
under the same circumstances. Among these 3 samples, the most efficient one was chosen and
considering the prospective constructions they are located at various sites in the borders of the
campus. This analysis was executed to figure out the optimum site where the turbine may be
erected by supplying the most amount of energy annually.
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1- The company “Aircon Windcraft” is located in a small village called Leer in the state of
Niedersachsen in Germany. Having acknowledged that the product range of this company
is not that wide, Aircon has installed more than 80 small scale wind turbines in 17
different countries. Excluding the inverters (they are exported from the UK) rest of the
components are manufactured in the factory in Leer since 2003. The required information
such as the technical data and the official price offer was provided through the contact
with the company. The most important and essential information regarding the AEP
calculation is the power curves of the wind turbines. The experimental values were also
requested from the company.
Figure 4.22: „Aircon‟ Turbine
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Power: 10 kW
Rotor Diameter: 7.13 m
Cut-in Speed: 3.5 m/s
Breaking Systems: Hydraulic Azimuth
Nominal Speed: 13 m/s
System: Direct-Drive
Yaw System: Active Yaw
Generator: Permanent magnet synchronous
Tower Type and Height: Lattice Tower / 18 meters (can be increased on demand)
Price Offer: Excluding certain costs such as transportation, crane etc. the price offered is
€43000
Figure 4.23: Power Curve of „Aircon 10 S‟
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2- The company Redriven was founded in the year of 2007 in Ontario, Canada. Redriven
possesses a product range from 5kW – 50 kW wind turbines. Redriven has many
representatives throughout the Europe and ample implementations of Redriven turbines
are in various sites all around the world. Some part of the manufacture process is executed
in China. We got in contact with the office in Italy and received the required information.
One of the noticeable characteristics of Redriven wind turbines is the hydraulic tower.
Thereby it is no longer required to use a crane, during installation and the maintenance
phases. Besides, another predominant benefit of Redriven turbines is the low cut-in wind
speed.
Figure 4.24: „Redriven‟ Wind Turbine
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Power: 20 kW
Rotor Diameter: 12 m
Cut-in Speed: 2 m/s
Breaking Systems: Dynamic
Nominal Speed: 11 m/s
System: Direct Drive
Yaw System: Electric Yaw
Generator: Permanent magnet synchronous
Tower Type and Height: Hydraulic / 24 meters (can be increased on demand)
Price Offer: Excluding certain costs such as transportation, crane etc. the price offered is
$60000
Figure 4.25: Power Curve of „ReDriven‟ Wind Turbine
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3- The company Huaying is located 120 km far from the city center of Shangai, China.
Huaying is a subsidiary company of Tongkun Group, one of the leading industry
companies in China. Huaying is focused on manufacturing small and middle scale wind
turbine. The product range extends from 1kW up to 50 kW, however the company ,so far,
has only applications in the borders of China.
Figure 4.26: „Huayin‟ Wind Turbine
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Rotor Diameter: 11 m
Cut-in Speed : 3 m/s
Breaking Systems : Dynamic
Nominal Speed : 12 m/s
System : Gearbox
Yaw System : Electric Yaw
Tower Type and Height : Monopole / 18 meters (can be increased on demand)
Price Offer : Excluding certain costs such as transportation, crane etc. the price offered is
$73000
Figure 4.27: Power Curve of „Huaying‟
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4.11 Annual Energy Production Analysis with WAsP Software
The technical data of each turbine was elaborated in the preceding section. The analysis is
conducted in the first step, supposing all of the turbines will be erected on the current site of the
anemometer. In consequence of this analysis, the most efficient turbine under the same wind
gradient circumstances will be determined.
The AEP of each turbine is respectively;
Table 4.3: Total Annual Energy Production of „Aircon 10‟
The annual energy production of „Aircon 10‟ is 24 MWh. The most amount of the energy was
generated from the second sector, with 5.6 MWh/year. The column on the left side of AEP
shows the power density values distributed into sectors. The mean value for „Aircon 10‟ is 197
W/ m. This value is the decisive factor in comparison of the wind turbines.
Table 4.4: Total Annual Energy Production of „ReDriven‟
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The total AEP of ReDriven turbine is 54 MWh at the same site. Likewise, from the second sector
the most amount of energy can be generated.
Table 4.5: Total Annual Energy Production of „Huaying‟
Huaying wind turbines‟ AEP is 41.9 MWh. Although the nominal power of this turbine is 30 kW,
the most predominant factor that causes the low energy production is the high cut-in wind speed.
According to the analysis results in the first part, Redriven 20 turbine appears to have the highest
power density value. The low cut-in speed and the height of the tower plays an important role.
Therefore in the latter part of this analysis section Redriven turbine will be sited in 3 different
locations and through the results the site where the most amount of energy is generated, will be
released.
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Figure 4.28: Comparison of Annual Energy Productions of All Three Turbines
Figure 4.29: Comparison of Power Densities of All Three Turbines
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4.12 The Installation Cases of the Chosen Wind Turbine
4.12.1 The Case of Installation of Redriven Turbine Behind the Sports Hall Building
In this case, as it is shown below on the WAsP screenshot, the wind turbine is located at the
coordinates „658468.1E 4543515.0W‟. This site is located northwestern part of the anemometer
and the elevation is 72 meters. This area is advantageous because of several reasons. First of all
there are fewer obstacles nearby and besides, the altitude is relatively high. According to the
results, if the turbine was erected at this site the AEP would increase dramatically and the power
density would double itself in comparison to the site where anemometer is currently located.
Figure 4.30: WAsP Application of the First Case
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Table 4.6: Total Annual Energy Production of the First Case
4.12.2 The Case of Installation of Redriven Turbine Behind the Dormitory Buildings
For a better understanding and to give more emphasis to the effect of the close obstacles in this
case the turbine is sited behind high buildings. The coordinates of this site is „658529.4 N
4543854.0 E‟and the elevation is 85 meters. Although, due to the higher elevation, a higher AEP
is expected, the buildings nearby impede the wind substantially. Also, the fact that the prevailing
wind direction is north-northeast and the buildings are located northeastern of this site, they
basically hinder the wind. AEP decreases 15% in comparison to the preceding site.
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Figure 4.31: WAsP Application of the Second Case
Table 4.7: Total Annual Energy Production of the Second Case
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4.12.3 The Case of Installation of Redriven Turbine Close to Faculty of Electronics
Another micro-siting option was the area that is closer to the Electronics Faculty Building which
has been recently built. In this case, there aren‟t any close obstacles in the direction of the
prevailing wind; however the urban area outside the campus affects the power density negatively.
Hence, both the power density and the AEP reach bottom values in this case.
Figure 4.32: WAsP Application of the Third Case
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Table 4.8: Total Annual Energy Production of the Third Case
Including the current site of the anemometer, 4 different micro-siting options are analyzed.
Among these 4 sites, considering the comparison criteria such as AEP or power density values,
the first location has given the best results. These results are elaborated in the conclusion section
and they are depicted through a graphic below.
Table 4.9: Comparison of Annual Energy Productions of All Three Turbines
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5. CONCLUSION
The objective of this project was to find out the optimized turbine and the site for a middle scale
wind turbine that is planned to be erected on Yildiz Technical University Davutpasa Campus in
the near future. The main goal of the installation of a mid-scale wind turbine is both supplying
the electricity demand of the closest workshop building and creating an open-air laboratory,
where pioneer research can be conducted. The outcome is summarized below;
During this analysis, in order to ensure that it is based on scientific criteria, the well known
package program WAsP is used. Firstly, the wind data that is collected since October 2009 by a
10 meters high anemometer is analyzed by various software. Second step was to locate this
anemometer on a digitized topographical map. Through several site surveys that are carried out
with GPS, the coordinates of the map and the actual coordinates are synchronized. Site surveys
generally underlie any sort of wind assessment project.
The calculations and the measurements that are made on scratch papers are imported into WAsP
by the help of WAsP‟s sub-modules. Consequently, the required information about the
characteristics of wind turbines was demanded from the manufacturers. Technical data and the
official price offers of 3 different-sized wind turbines were requested from 3 different companies.
The objective of the first part of the analysis was to find out the most efficient turbine among
these three under the same circumstances, which means that they were located at the same site,
where the anemometer is currently located. This comparison allowed us to distinguish the right
turbine for the wind gradient at Davutpasa Campus. During this analysis the cut-in wind speeds
and the tower heights of the turbines played vital roles and affected AEP and power density
values critically.
Second step of the analysis was based on the micro-siting of the chosen wind turbine, which was
in this case „Redriven 20‟. The aim was to find out the site where the most amount of energy is
generated. Hence, this turbine is sited in 4 different locations. According to the results that are
derived from WAsP, Site 1 where is located behind the sports hall, had the most amount of
energy generated.
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REFERENCES
[1]
Nelson, V., “Wind Energy Renewable Energy and the Environment”, CRC Press, 2009.
[2]
Chiras, D., “Wind Power Basics”, New Society Publishers, 2010.
[3]
Jonhson, G.L., “Wind Energy Systems”, Electronic Edition, 2006.
[4]
Mortensen, N.G., Duncan, N.H., Myllerup, L., Landberg, L., Rathman, O., “Getting
Started with WAsP 9”, Riso National Laboratory, 2007.
[5]
Bailey, B.H., McDonald, S.L., “Wind Resource Assessment Handbook”, AWS Scientific,
Inc., 1997.
[6]
Ayotte, K.W., Davy, R.J., Coppin, P.A., “A Simple Temporal and Spatial Analysis of
Flow in Complex Terrain in the Context of Wind Energy Modeling”, Bound.-Lay
Meteorol, 2001.
[7]
“Technology Road Map – Wind Energy”, International Energy Agency, 2009.
[8]
“World Meteorological Organization, Meteorological Aspects of the Utilization of Wind
as an Energy Source”, WMO, Geneva, 1981.
[9]
http://www.nrel.gov/wind/pdfs/22223.pdf/
[10]
http://www.ewea.org/
[11]
http://www.redriven.ca/
[12]
http://www.aircon-international.com/
[13]
http://www.huaying.com/
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