A windmill is a machine that converts the energy of wind into rotational energy by means
of vanes called sails or blades. The reason for the name "windmill" is that the devices
originally were developed for milling grain for food production; the name stuck when in
the course of history, windmill machinery was adapted to supply power for many industrial
and agricultural needs other than milling. The majority of modern windmills take the
form of wind turbines used to generate electricity, or windpumps used to pump water, either for
land drainage or to extract groundwater.
Windmills in antiquity
The windwheel of the Greek engineer Heron of Alexandria in the first century AD is the
earliest known instance of using a wind-driven wheel to power a machine. Another early example
of a wind-driven wheel was the prayer wheel, which was used in ancient Tibet and China
since the fourth century. It has been claimed that the Babylonian emperor Hammurabi planned
to use wind power for his ambitious irrigation project in the seventeenth century BC.
Horizontal windmills
The first practical windmills had sails that rotated in a horizontal plane, around a vertical
axis. According to Ahmad Y. al-Hassan, these panemone windmills were invented in eastern
Persia as recorded by the Persian geographer Estakhri in the ninth century. The authenticity
of an earlier anecdote of a windmill involving the second caliph Umar is questioned on the
grounds that it appears in a tenth-century document. Made of six to 12 sails covered
in reed matting or cloth material, these windmills were used to grind grain or draw up water,
and were quite different from the later European vertical windmills. Windmills were in widespread
use across the Middle East and Central Asia, and later spread to China and India from there.
A similar type of horizontal windmill with rectangular blades, used for irrigation, can
also be found in thirteenth-century China, introduced by the travels of Yelü Chucai
to Turkestan in 1219. Horizontal windmills were built, in small
numbers, in Europe during the 18th and nineteenth centuries, for example Fowler's Mill at Battersea
in London, and Hooper's Mill at Margate in Kent. These early modern examples seem not
to have been directly influenced by the horizontal windmills of the Middle and Far East, but
to have been independent inventions by engineers influenced by the Industrial Revolution.
Vertical windmills Due to a lack of evidence, debate occurs among
historians as to whether or not Middle Eastern horizontal windmills triggered the original
development of European windmills. In northwestern Europe, the horizontal-axis or vertical windmill
is believed to date from the last quarter of the twelfth century in the triangle of
northern France, eastern England and Flanders. The earliest certain reference to a windmill
in Europe dates from 1185, in the former village of Weedley in Yorkshire which was located
at the southern tip of the Wold overlooking the Humber estuary. A number of earlier, but
less certainly dated, twelfth-century European sources referring to windmills have also been
found. These earliest mills were used to grind cereals.
Post mill
The evidence at present is that the earliest type of European windmill was the post mill,
so named because of the large upright post on which the mill's main structure is balanced.
By mounting the body this way, the mill is able to rotate to face the wind direction;
an essential requirement for windmills to operate economically in north-western Europe,
where wind directions are variable. The body contains all the milling machinery. The first
post mills were of the sunken type, where the post was buried in an earth mound to support
it. Later, a wooden support was developed called the trestle. This was often covered
over or surrounded by a roundhouse to protect the trestle from the weather and to provide
storage space. This type of windmill was the most common in Europe until the nineteenth
century, when more powerful tower and smock mills replaced them.
Hollow-post mill In a hollow-post mill, the post on which the
body is mounted is hollowed out, to accommodate the drive shaft. This makes it possible to
drive machinery below or outside the body while still being able to rotate the body
into the wind. Hollow-post mills driving scoop wheels were used in the Netherlands to drain
wetlands from the fourteenth century onwards. Tower mill
By the end of the thirteenth century, the masonry tower mill, on which only the cap
is rotated rather than the whole body of the mill, had been introduced. The spread of tower
mills came with a growing economy that called for larger and more stable sources of power,
though they were more expensive to build. In contrast to the post mill, only the cap
of the tower mill needs to be turned into the wind, so the main structure can be made
much taller, allowing the sails to be made longer, which enables them to provide useful
work even in low winds. The cap can be turned into the wind either by winches or gearing
inside the cap or from a winch on the tail pole outside the mill. A method of keeping
the cap and sails into the wind automatically is by using a fantail, a small windmill mounted
at right angles to the sails, at the rear of the windmill. These are also fitted to
tail poles of post mills and are common in Great Britain and English-speaking countries
of the former British Empire, Denmark, and Germany but rare in other places. Around some
parts of the Mediterranean Sea, tower mills with fixed caps were built because the wind's
direction varied little most of the time. Smock mill
The smock mill is a later development of the tower mill, where the tower is replaced by
a wooden framework, called the "smock." The smock is commonly of octagonal plan, though
examples with more, or fewer, sides exist. The smock is thatched, boarded or covered
by other materials, such as slate, sheet metal, or tar paper. The lighter construction in
comparison to tower mills make smock mills practical as drainage mills as these often
had to be built in areas with unstable subsoil. Having originated as a drainage mill, smock
mills are also used for a variety of purposes. When used in a built-up area it is often placed
on a masonry base to raise it above the surrounding buildings.
Mechanics Sails
[[ File:Kuremaa mõisa tuuleveski.jpg|thumb|Windmill
in Kuremaa, Estonia]] Common sails consist of a lattice framework
on which a sailcloth is spread. The miller can adjust the amount of cloth spread according
to the amount of wind available and power needed. In medieval mills, the sailcloth was
wound in and out of a ladder type arrangement of sails. Postmedieval mill sails had a lattice
framework over which the sailcloth was spread, while in colder climates, the cloth was replaced
by wooden slats, which were easier to handle in freezing conditions. The jib sail is commonly
found in Mediterranean countries, and consists of a simple triangle of cloth wound round
a spar. In all cases, the mill needs to be stopped
to adjust the sails. Inventions in Great Britain in the late eighteenth and nineteenth centuries
led to sails that automatically adjust to the wind speed without the need for the miller
to intervene, culminating in patent sails invented by William Cubitt in 1813. In these
sails, the cloth is replaced by a mechanism of connected shutters.
In France, Pierre-Théophile Berton invented a system consisting of longitudinal wooden
slats connected by a mechanism that lets the miller open them while the mill is turning.
In the twentieth century, increased knowledge of aerodynamics from the development of the
airplane led to further improvements in efficiency by German engineer Bilau and several Dutch
millwrights. The majority of windmills have four sails.
Multiple-sailed mills, with five, six or eight sails, were built in Great Britain, Germany,
and less commonly elsewhere. Earlier multiple-sailed mills are found in Spain, Portugal, Greece,
parts of Romania, Bulgaria, and Russia. A mill with an even number of sails has the
advantage of being able to run with a damaged sail and the one opposite removed without
resulting in an unbalanced mill. In the Netherlands the stationary position
of the sails, i.e. when the mill is not working, has long been used to give signals. Most notably
the positions with the sails just before or just after the main building signal joy or
mourning. Across the Netherlands windmills with the sails tilted to the right were used
to mourn the victims of the 2014 flight MH17. Machinery
Gears inside a windmill convey power from the rotary motion of the sails to a mechanical
device. The sails are carried on the horizontal windshaft. Windshafts can be wholly made of
wood, or wood with a cast iron poll end or entirely of cast iron. The brake wheel is
fitted onto the windshaft between the front and rear bearing. It has the brake around
the outside of the rim and teeth in the side of the rim which drive the horizontal gearwheel
called wallower on the top end of the vertical upright shaft. In grist mills, the great spur
wheel, lower down the upright shaft, drives one or more stone nuts on the shafts driving
each millstone. Post mills sometimes have a head and/or tail wheel driving the stone
nuts directly, instead of the spur gear arrangement. Additional gear wheels drive a sack hoist
or other machinery. The machinery differs if the windmill is used for other applications
than milling grain. A drainage mill uses another set of gear wheels on the bottom end of the
upright shaft to drive a scoop wheel or Archimedes' screw. Sawmills use a crankshaft to provide
a reciprocating motion to the saws. Windmills have been used to power many other industrial
processes, including papermills, threshing mills, and to process oil seeds, wool, paints
and stone products.
Spread and decline
The total number of wind-powered mills in Europe is estimated to have been around 200,000
at its peak, which is modest compared to some 500,000 waterwheels. Windmills were applied
in regions where there was too little water, where rivers freeze in winter and in flat
lands where the flow of the river was too slow to provide the required power. With the
coming of the industrial revolution, the importance of wind and water as primary industrial energy
sources declined and were eventually replaced by steam and internal combustion engines,
although windmills continued to be built in large numbers until late in the nineteenth
century. More recently, windmills have been preserved for their historic value, in some
cases as static exhibits when the antique machinery is too fragile to put in motion,
and in other cases as fully working mills. Of the 10,000 windmills in use in the Netherlands
around 1850, about 1000 are still standing. Most of these are being run by volunteers,
though some grist mills are still operating commercially. Many of the drainage mills have
been appointed as backup to the modern pumping stations. The Zaan district has been said
to have been the first industrialized region of the world with around 600 operating wind-powered
industries by the end of the eighteenth century. Economic fluctuations and the industrial revolution
had a much greater impact on these industries than on grain and drainage mills so only very
few are left. Construction of mills spread to the Cape Colony
in the seventeenth century. The early tower mills did not survive the gales of the Cape
Peninsula, so in 1717, the Heeren XVII sent carpenters, masons, and materials to construct
a durable mill. The mill, completed in 1718, became known as the Oude Molen and was located
between Pinelands Station and the Black River. Long since demolished, its name lives on as
that of a Technical school in Pinelands. By 1863, Cape Town could boast 11 mills stretching
from Paarden Eiland to Mowbray. Wind turbines
and
A wind turbine is a windmill-like structure specifically developed to generate electricity.
They can be seen as the next step in the development of the windmill. The first wind turbines were
built by the end of the nineteenth century by Prof James Blyth in Scotland, Charles F.
Brush in Cleveland, Ohio and Poul la Cour in Denmark. La Cour's mill from 1896 later
became the local powerplant of the village Askov. By 1908 there were 72 wind-driven electric
generators in Denmark, ranging from 5 to 25 kW. By the 1930s, windmills were widely used to
generate electricity on farms in the United States where distribution systems had not
yet been installed, built by companies such as Jacobs Wind, Wincharger, Miller Airlite,
Universal Aeroelectric, Paris-Dunn, Airline, and Winpower. The Dunlite Corporation produced
turbines for similar locations in Australia. Forerunners of modern horizontal-axis utility-scale
wind generators were the WIME-3D in service in Balaklava USSR from 1931 until 1942, a
100-kW generator on a 30-m tower, the Smith-Putnam wind turbine built in 1941 on the mountain
known as Grandpa's Knob in Castleton, Vermont, USA of 1.25 MW and the NASA wind turbines
developed from 1974 through the mid-1980s. The development of these 13 experimental wind
turbines pioneered many of the wind turbine design technologies in use today, including:
steel tube towers, variable-speed generators, composite blade materials, and partial-span
pitch control, as well as aerodynamic, structural, and acoustic engineering design capabilities.
The modern wind power industry began in 1979 with the serial production of wind turbines
by Danish manufacturers Kuriant, Vestas, Nordtank, and Bonus. These early turbines were small
by today's standards, with capacities of 20–30 kW each. Since then, commercial turbines have
increased greatly in size, with the Enercon E-126 capable of delivering up to 7 MW, while
wind turbine production has expanded to many countries.
As the 21st century began, rising concerns over energy security, global warming, and
eventual fossil fuel depletion led to an expansion of interest in all available forms of renewable
energy. Worldwide, many thousands of wind turbines are now operating, with a total nameplate
capacity of 194,400 MW. Europe accounted for 48% of the total in 2009.
Windpumps
Windpump are used extensively on farms and ranches in the United States, Canada, Southern
Africa, and Australia. These mills feature a large number of blades, so they turn slowly
with considerable torque in low winds and are self-regulating in high winds. A tower-top
gearbox and crankshaft convert the rotary motion into reciprocating strokes carried
downward through a rod to the pump cylinder below. Such mills pumped water and powered
feed mills, saw mills, and agricultural machinery. The farm windpump was invented by Daniel Halladay
in 1854. In early California and some other states, the windmill was part of a self-contained
domestic water system including a hand-dug well and a redwood water tower supporting
a redwood tank and enclosed by redwood siding. During the late 19th century steel blades
and steel towers replaced wooden construction. At their peak in 1930, an estimated 600,000
units were in use. Firms such as U.S. Wind Engine and Pump Company, Challenge Wind Mill
and Feed Mill Company, Appleton Manufacturing Company, Star, Eclipse, Fairbanks-Morse, and
Aermotor became the main suppliers in North and South America.
In Australia, the Griffiths Brothers at Toowoomba manufactured windmills from 1876, with the
trade name Southern Cross Windmills in use from 1903. These became an icon of the Australian
rural sector by utilizing the water of the Great Artesian Basin.
See also
List of windmills Horse mill
Tide mill Watermill
Éolienne Bollée Molinology
References
Further reading Chartrand. French Fortresses in North America
1535–1763: Quebec, Montreal, Louisbourg and New Orleans.
Drachmann, A.G. "Heron's Windmill", Centaurus, 7.
Gregory, Roy and Laurence Turner Windmills of Yorkshire ISBN 978-1-84033-475-3.
Hassan, Ahmad Y., Donald Routledge Hill. Islamic Technology: An illustrated history. Cambridge
University Press. ISBN 0-521-42239-6. Lohrmann, Dietrich "Von der östlichen zur
westlichen Windmühle", Archiv für Kulturgeschichte, Vol. 77, Issue 1
Needham, Joseph. Science and Civilization in China: Volume 4, Physics and Physical Technology,
Part 2, Mechanical Engineering. Taipei: Caves Books Ltd.
Shepherd, Dennis G. Historical Development of the Windmill, Ithaca, New York: Cornell
University, NASA Contractor Report 4337 DOE/NASA.5266-1, prepared for National Aeronautics and Space
Administration, Lewis Research Center & Office of Management, Scientific and Technical Information
Division, DOI:10.1115/1.802601. Tunis, Edwin, Colonial living, The Johns Hopkins
University Press, ISBN 0-8018-6227-2, pp. 72 and 73.
Vowles, Hugh Pembroke: "An Enquiry into Origins of the Windmill", Journal of the Newcomen
Society, Vol. 11 External links
Architecture: Windmills at DMOZ Earth Science Australia, Wind Power and Windmills
The International Molinological Society Windmills at Windmill World
Mill Database, Belgium and Netherlands A Geograph article and photo-record of Windmills
in Great Britain