This windmill will aerate a pond or pump water out of your pond or river
to water your animals or garden. This windmill will pump out of a shallow
(up to 15m) well.
They have been manufactured since 1888 and are the old standard of
windmills. They will pump out of a well but will not efficiently aerate a
pond or pump water out of the pond or river.
The Wind Turbine
The wind turbine, also called a windmill, is a means of harnessing the
kinetic energy of the wind and converting it into electrical energy.
Modern low speed wind turbines seem to become more efficient as they scale
up. A 3m diameter home turbine (unless in a rare ideal location) will be
rather fickle and not very reliable. A 30m blade such as those in
Ravehshoe Queensland are too expensive for single household use, more
efficient in producing electricity but still affected by terrain effects.
The 150m turbines at Mount Emerald are relatively free of ground effects
and the most efficient. Kinetic wind energy turns blades called
aerofoils, which drive a shaft, which drive a motor (turbine) and ar e
connected to a generator.
"It is estimated that the total power capacity of winds surrounding the
earth is 1 x 1011 Gigawatts" (Cheremisinoff 6). The total energy of
the winds fluctuates from year to year. Windmill expert Richard
Hills said that the wind really is a fickle source of power, with wind
speeds to low or inconsistent for the windmill to be of practical
use. However, that hasn't stopped windmill engineers from
trying. Today, there are many kinds of windmills, some of which
serve different functions. They are a complex alternative energy
There are a number of types of windmills. They are divided into
Horizontal-Axis and Vertical-Axis types. Low speed horizontal-axis
windmills are used for water pumping and air compressing. Southern
Cros windmills are an example. Earlier windmills such as
the ones in England and Holland build a couple hundred years ago are
example. The horizontal-axis
was invented in Egypt and Greece in 300 BCE. "It had 8 to 10 wooden
beams rigged with sails, and a rotor which turned perpendicular to the
wind direction" (Naar 5). This specific type of windmill became
popular in Portugal and Greece. In the 1200's, the crusaders built
and developed the post-mill, which where used to mill grain. It was first
used to produce electricity in Denmark i n the late 1800's and spread soon
after to the U.S. In America, windmills made the great plains.
They were used to pump water and irrigate crops. During World War I,
farmers rigged windmills to generate 1 kW of DC current. They
mounted their devices on the tops of buildings and towers. On
western farms and railroad stations, the pumping windmill was 6-16m high
with a 2-3m wheel diameter"
(45)]. With 15kmh wind speed, a 2m-diameter wheel, a 60cm diameter
pump cylinder, a windmill-pump could lift 200L per hour to a height of
12m. A 4m in diameter wheel could lift 250L per hour to a
height of 38m.
The growth of wind-electricity in Australia was greatly peaked in the
1930's and 40's . However, in the 1970's, due to oil shortages,
earlier prototypes of high-speed horizontal-axis windmills were developed.
High-speed horizontal-axis types are used for many purposes, come in many
sizes. These include the typical windmills on windmill farm
and any other wind turbines in which the shaft turned by the aerofoils is
horizontal. High-speed horizontal types may have 1, 2, 3, 4, or many
Low-speed types such as European ones have much larger aerofoils in
relation to their height above the ground. Low speed types such as western
Queensland ones are usually a pinwheel, with many small blades encircled
with an outer frame like a wheel. Vertical-axis windmills
were first developed in the Persians in 1500 BCE to mill corn and
were still in use in the 1970's in the Zahedan region. Sails
were mounted on a boom, which was attached to a shaft that turned
vertically. By 500 BCE, the technology had spread to Northern Africa
and Spain. Low-speed ve rtical-axis windmills are popular in
Finland. They are about 150 years old. They consist of a 200L
oil drum split in half. They are used to pump water and aerate
land. They are inefficient.
High-speed vertical-axis windmills
include the Darrieus models. These have long, thin, curved
outer blades, which rotate at 3 to 4 times the wind speed. They have
a low starting torque and a high tip-speed ratio. They are
inexpensive and are used for electricity generation and irrigation.
There are three types, the delta, chi, and gamma models. All models
are built on a tripod. The advantages to a Darrieus-windmill are
that it can deliver mechanical power at ground level. The generator,
gearbox, and turbine components are on the ground, instead of at the top
of a tower as in horizontal-axis windmills. They cost much less to
construct, because there is less material, and the pitch
of the blades does not have to be adjusted.
Another type of HSVAW's are the Madaras and Flettner types, revolving
cylinder s which sit on a tracked carriage. "The motion of a
spinning cylinder causes the carriage to move over a circular track and
the carriage wheels to drive an electric generator" (Justus). The
Savonius model, which originated in Finland in the 1920's, is a n S-shaped
blade, which rotates and turns a vertical shaft. Today, these types
of windmills are very popular with scientists
and their technology is being developed.
Factors to Consider When Building A Windmill
What to consider when building a windmill In choosing where to build a
windmill, there are many important factors to consider.
First is the location:
1) Available wind energy is usually higher near the seacoast or coasts of
very large lakes and offshore islands. 2) Available wind energy is
generally high in the central Austrsalia because of the wide expanses of
level (low surface roughness) terrain.
3) Available wind energy is generally low throughout eastern Australia
with the exception of mountain passes but higher on the southern and
Also important to consider the wind characteristics where you are going to
build: 1) the mean wind speed (calculated my cubing the averages and
taking the mean of the cubes) and its seasonal variations. 2) The
probability distribution of wind speed and of extreme winds. The mean wind
speed must be high enough, and the distribution must be so that all the
data points are very similar.
3) The height variation of wind speed and wind direction. Wind
cannot be too high or too low in relation to the ground or it is too
difficult to harness.
4) The gustiness of the wind field in both speed and direction.
Gusty winds greatly affect the power output of the windmills and are
5) The wind direction distribution and probability of sudden large shifts
in di rection. The wind must be
unlikely to suddenly shift direction. It must blow in the same
6) the seasonal density of the air, and variations of density of the air
with height. The denser the air, the worse it will be for windmills.
7) Hazard conditions such as sandstorms, humidity, and salt-spray, which
are bad for windmills.
8) Trade winds in the subtropics, and the channeled wind through
mountain passes are especially beneficial to windmills.
Once a suitable location is found, the wind is analysed extensively, and
the criteria is met, there are still more requisites.
1) The terrain upon which the windmills are built must be
relatively flat. The elevation difference between the turbine
site and the terrain is no larger than 60 meters over a 12-km
radius. You may have seen windmills such as those in Ravenshoe,
Far North Queensland on little hills, but this is because the
requirement is met. The hill may be the only one in a mountain pass
2) All hills must have small height to width ratios: h:l
must be < 0.016.
3) The elevation difference between the highest and lowest point
must be 1/3 or less of the height difference between the bottom of the
rotor disk and the lowest
point in the terrain strip.
The surface roughness of the terrain upon which the windmill is to be
built must be low. If it varies by more than 10%, this is no
good. The terrain must be smooth, and consistently so. A rough
surface has more of a negative effect on the wind than a smooth
surface. There is a value n, called, which is assigned to the
terrain in terms of its roughness. This value is used to calculate
the height of the windmill. For instance, over the sea, the index
location, n is 0.14. Over rough inland country, n is 0.34.
Wind Mill Efficiency
Windmills are turbines. The two names can be used synonymously.
Turbines are a means of harnessing the a fluid's power (the wind) by
converting the kinetic energy of the fluid (the wind) into mechanical
power (the rotating shaft) When the shaft of a w indmill is hooked up to a
generator, electrical energy can be formed. The generator can be used to
produce either DC or AC current. Generators that produce DC can be
connected to batteries, an inverter to produce AC, or to power DC loads.
Some generators are connected to heating coils. Generators that
produce AC can be hooked up to AC motors such as water pumps.
Windmills are NOT efficient. At the very most, a windmill can
extract only 16/27ths of the kinetic energy from the wind. This is
called the Betz Limit and it can be mathematically proven through
calculus. Most of today's windmills extract about 30 perc ent of the
The Southern Cross farm windmill can only extract 10%. An important
equation used to find the wind power density, how much power is available
per square meter is the equation P = .5 pu³
where P is the wind power density in W/m2, p is the density of the air,
and u³ is the cube of the wind velocity.
An equation for the power available is :
where p is the kinetic energy density J/m³, V is the velocity of the
wind, A is the cross sectional area of the wind on the turbine.
The equation for determining the power of the shaft, (which is
less than the final power output, since gear trains and generators cause
power to be lost) is as follows: Cp = P(0.5 p V ³ (D2)/4
Where Cp is the power coefficient (Power of shaft), p is the air
D is the rotor diameter, V is the velocity of the wind and P is the net
power output. Also Cp = P available/P turbine The power available is a function of elevation. At ground
level, 100% of
the power is available. At 30m, 97% is available. At 1500m , 86% is
The Purpose of
Some turbines are shrouded like jet engines. The shroud is a way
to channel the wind.
An equation for the power harnessed by a shrouded wind turbine is: P(Pe) = ( QT ((p + (k) where P is the power, Pe is the power extracted, ( is the turbine efficiency, QT is the
volumetric flow rate of air on the turbine, (V/A), ((p + (k) is the
in pressure energy between the inlet and the exit of the wind turbine,
k is the cane in kinetic energy of a unit volume of air that passes
through the machine.
Shrouds concentrate and diffuse the wind as it passes through a
horizontal access wind-turbine. They reduce the turbulence of the
wind and "direct it".
The advantages of shrouds, as told by Cheremisinoff (pg. 61 of
Fundamentals of Wind Energy), are:
a ) the axial velocity of the turbine increases, meaning that
smaller rotors can operate at higher revolutions,
b) the shroud can greatly reduce tip-losses, and
c) the aerofoils would not have to be rotated in a direction parallel to
the wind if the wind-direction changed.
The cut in speed is the lowest wind speed below which no usable power
can be produced by a wind turbine. This means that the wind must
be fast enough to move the aerofoils to drive the shaft to create enough
power, after much is lost, so that the end amount of power isgreater
Rated power is the maximum power output of a turbine, which is
dependent on a number of factors, especially the generator. In
calculating the height of the windmill, it is important to keep in mind
that the windmill must be high enough to be above obstructions.
The wind velocity decreases as one approaches the surface. That means
that the higher you build, the better chance there will be that
the wind speed is higher, however, you must find the perfect
medium--there are often more variables as you increase in
In calculating how high a windmill should be the following
equation is used: V1/V2 = (H1/H2)n,
Where V1 is the wind speed at the highest point of the highest blade, V2
is the wind speed at the lowest
point of the lowest blade, H1 is the height of the highest point, and H2
is the height of the lowest point. n is the index location of the
site, a value that measures the roughness of the terrain.
The support of the windmill is generally made out of steel. The
windshaft is the shaft which carries the windwheel or aerofoils.
It is turned as the aerofoils turn. It is made of steel or wood.
Aerofoils are the blades on a windmill. They can be made
out of any material. They were first made of wood or wood
composites. Steel was used after that. Aluminum is used in
the Darrieus windmills because it is much stronger. Unfortunately,
Aluminum fatigues quicker. Some windmills use fiberglass
blades. New materials such as strong alloys are being used in
today's windmills experimentally.
It is important that the blades have a large lift force and a small drag
The lift force is the force needed to bend the flow of the
(fluid) air. It is the force perpendicular to the stream of the
The drag force is the force parallel to the stream.
The aerofoil must be able to develop a lift force at least 50 times
greater than the drag. Torque acts on the aerofoil with a vector from
the center of rotation away.
Other forces that act on the blades of windmills are wind shears, wind
gusts, which push on the aerofoils, gravity, a pull towards the earth,
and shifts in the direction of the wind. Shifts in the direction
of the wind are often accounted for by having a small blade,
called a tailvane, on the backside of a windmill. The wind blows
on a flat side of the tail, which is oriented differently from the
aerofoils. Then, the aerofoils can be rotated to face into the
wind. If the wind is blowing in the direction of this tail instead
of the direction of the aerofoils, the tail rotates a shaft, which
rotates the whole windmill in the proper direction so as to orient it
towards the wind.
Wind gusts can greatly affect a windmill. A turbulent gust is a
gust greater than two minutes with a certain mean wind speed.
Gusts are analyzed extensively, with magnitudes, one fo r the lull
speed, which is the wind speed of a negative gust amplitude, and the
peak speed, which is the wind speed for a positive gust amplitude.
The gust amplitude is the difference between the largest speed
in the gust and the mean speed.
The gust duration is the time from the beginning to the end of a
The gust frequency is the number of positive gusts, which occur
per unit time.
The gust formation time is the time it takes from the beginning
of a gust to the time it attains the peak gust spe ed.
The gust decay time is the time it takes for the gust the end
after it reaches its highest amplitude.
There is quite a bit of terminology with aerofoils.
The angle of the surface to the fluid flow is the angle of attack,
alpha. The angle of attack must be just right. If it
is too great, the lift will dramatically decrease and the drag will
increase, st alling the windmill. At rest, (when the windmill is
not in operation), the angle of attack is 85°. When in motion, the
angle of attack is anywhere from 2-10 degrees. Newer and more
advanced windmills have an angle of attack in the upper end of this
The pitch angle, ß is the angle between the chord of the
aerofoil and its plane of rotation. The pitch angle can be
adjusted. Solidity is the ratio of the blade width (at widest point) to the
distance between the centers of the blades. A typical "pinwheel
Southern Cross windmill" might have a ratio of about 1:1, because the
blades are very narrow and very close together, whereas a new
two-bladedaerofoil would have a ratio of about 0.03. There is a
transfer of work between the wind stream and the moving blade. In
order for this transfer to be efficient, a typical blade is usually 1/4
the width of its length. (If the blade is 3m long, it will be
750mm wide at its widest point).
Aerofoils come in many shapes. Some blades are made a little wider
than this ratio, because it is easier to start such a windmill.
However, blades like this aren't as efficient. No matter what the
shape, "most have a blunt nose and a finely tapering tab le"
(Calvert). A flow must be able to follow the curved surfaces of
the aerofoil without being separated. The mass flow rate is given
by the equation: m = p Vb A
, where p is the air density, Vb is the air speed at the blades and A is
The number of blades on a windmill varies. There are many
different types of windmills. The following equation helps figure
out how fast the a certain-bladed windmill
will rotate in relation to windmills with different numbers of blades:
Speed of windmill = 1 / sq. root of number of blades
The aerofoils of a four bladed machine rotate 71% as fast as that of a 2
bladed machine. A six bladed machine rotates at 58% and an 8
bladed machine rotates at 56% as fast as a 2 bladed machine.
Electricity and Storage of
As mentioned previously, the generators in a wind turbine can convert
the mechanical energy produced by the rotation of the shaft into
electrical energy, DC. From there, some windmills have synchronous
inverters, complex electronic devices which convert the DC
generated by the turbines into AC. This is an expensive option.
There is a loss of power as well through its processes. Others
have induction generators, which produce AC current without a
synchronous inverter and less power loss. The energy extracted
from the wind and converted into mechanical energy then electrical
energy by the generator must be stored, since it is not used generally
used all at once. It is important to keep a surplus of energy for
usage when the wind is not blowing fast enough, despite the corrections
that can be made in the pitch of the aerofoil blades and when the
windmill is out of service or the demand is especially high.
Storing the wind's energy effectively is the key to its long-term
use. Windmills used as water pumpers or air-compressors can pump
excess water, hydrogen or air into reserve tanks. Today, there are a
number of ways to store the wind's energy. Windmills are used to
charge Electrolyte batteries. Lead-acid or Lead-cobalt car
batteries are commonly used as well. However, batteries may be
expensive and inefficient--they may lose 10-25% of the energy stored in
Nickel-Iron, Nickel-cadmium, and zinc-air cells are often used as well.
These tend to be more efficient. Some windmills are now using
organic electrolyte batteries such as CuCl2, Ni Cl2, and NiF2 batteries
as well as sodium-sulfur batteries, which operate at high temperature,
are used. Although uncommon and still in experimental phases, some
energy is stored not by being converted directly into electrical energy,
but rather by being stored as thermal or electromagnetic energy,
Sound Fluids are elastic. Pressure waves are constantly being
created and propagated by the aerofoils and the turbine as a whole
(entire components excepting the support). We can hear them in the
sound given off. The sound intensity is directly proportional with
the speed of the windmill.
The frequency of the waves is directly proportional to the angular speed
of the blades on the rotor. The flutter you hear has aerodynamic
and elastic properties. The higher speed the aerofoils are, the
louder the sound a nd the louder the flutter they will make, as more
pressure waves are being created and propagated. The generators
are noisy. They often confuse birds and cause them to fly towards
Windmills can be very noisy. A 300 kW turbine at 1 mile away has a
dB level equal to a traffic light 100 feet away (Gipe). Windmill
sound levels are regulated.
The sound level must be kept under 46 dB in a residential area.
Wind turbines can cause interference, disturbances with TV and radio
reception (ghost images on TVs), affect microwaves and disrupt satellite
communication. These problems are currently being resolved.
Many have already been fixed. There is also a .009 probability of
a bird or insect being struck by the blades. Windmill makers must
use artificial sound or florescent paint or scents to scare away flying
Mechanical brakes are used to hold windmills at rest when they
are not needed, are not functioning, or are under repair. Greek
windmills used sticks or logs jammed into the ground to keep the
windmill stopped, but modern brakes are more sophisticated. Many
windmills today use airbrakes like those used in planes. Other
windmills have rope brakes.
Ropes connected to the aerofoils are simply pulled and tethered to a
post to keep the aerofoils from turning. The torque on a rope
brake can be calculated by the equation :
(M-m)(R2 + r)g
Many windmills are used today. They are used to heat water,
refrigerate storage buildings or rooms, refrigerate produce, dry crops,
irrigate crops, heat buildings, and charge batteries for tr actors on
farms . Ever since the energy shortages of the 70's, the growing
concern of pollution due to the burning of fossil fuels and the
depletion of natural resources, windmills have been greatly studied and
developed. Today, Sandia National Laboratories, Alcoa, GE, Boe ing,
Grumman, UTC, Westinghouse, and other scientists are researching and
developing Darrieuses and new types of windmills. Today, windmills
are used to operate sawmills and oil mills in Europe. They are
used in mining to extract minerals, to pump water , to generate
electricity, and to charge
batteries. "Windmills have been used on buoys moored far out in
the ocean, the power being used for the collection and transmission of
oceanographic and weather data. They also work in deserted places
as an aid to radio and telephone communications and they are used to
work navigation lights on isolated hazards" (Calvert 77).
The Future will likely bring bigger and better things for the wind
turbine. Many new wind turbine models are being built. The
wind turbine holds much promise for energy production in the years to
Calvert, N. G. Windpower Principles: Their
application on the small scale. London: Charles Griffin and
Co., Ltd., 1979. Cheremisinoff, Nicholas P. Fundamentals of Wind
Energy. Ann Arbor: Ann Arbor Science Publishers, Inc. 1978.
Gipe, Paul. Wind Energy Comes of Age. New York: John
Wiley and Sons, Inc. 1995.
Hau, E., J. Langenbrinck, and W. Palz. Large Wind Turbines.
Berlin: Springer-Verlag, 1993.
Hills, Richard L. Power From the Wind: A History of Windmill
Technology. London: Cambridge University Press, 1994.
Justus, C. G. Winds and Wind System Performance.
Philadelphia: The Franklin Institute Press, 1978.
Naar, Jon. The New Wind Power. New York: Penguin
Taylor, R. H. Alternative Energy Sources for the Centralized
Generation of Electricity. Bristol, England: Adam Hilger,