A windmill is a machine with rotating blades that is designed to
convert the energy of the wind into more useful forms. The term also
refers to the entire structure that carries (and includes) the machine.
In much of Europe, windmills have served to grind grain and pump water.
Most modern windmills, more appropriately called wind turbines, are used to generate electric power.
History
A windwheel operating an organ is described as early as the first
century C.E. by Hero of Alexandria, marking probably the first instance
of a wind powering machine in history. Vertical axle windmills were
first used in eastern Persia (Sistan) by the ninth century C.E., as
described by Muslim geographers. Horizontal axle windmills of the type
generally used today were invented in Northwestern Europe in the 1180s.
Horizontal axle windmills
Fixed windmills, oriented to the prevailing wind were, for example,
extensively used in the Cyclades islands of Greece. The economies of
power and transport allowed the use of these 'offshore' mills for
grinding grain transported from the mainland and flour returned. A
one-tenth share of the flour was paid to the miller in return for his
service. This type would mount triangular sails when in operation.
In North Western Europe, the horizontal-shaft or vertical windmill (so
called due to the dimension of the movement of its blades) dates from
the last quarter of the twelfth century in the triangle of northern
France, eastern England, and Flanders. These earliest mills were used to
grind cereals. The evidence at present is that the earliest type was
the post mill, so named because of the large upright post on which the
mill's main structure (the "body" or "buck") is balanced. By mounting
the body this way, the mill is able to rotate to face the (variable)
wind direction; an essential requirement for windmills to operate
economically in North-Western Europe, where wind directions are various.
By the end of the thirteenth century, the masonry tower mill, on which
only the timber cap rotated rather than the whole body of the mill, had
been introduced. Given that only the cap of the tower mill needed to be
turned, the main structure could be made much taller, allowing the
blades to be made longer, which enabled them to provide useful work even
in low winds. Windmills were often built atop castle towers or city
walls, and were a unique part of a number of fortifications in New
France, such as at Fort Senneville.
The familiar lattice style of windmill blades allowed the miller to
attach cloth sails to the blades (while applying a brake). Trimming the
sails allowed the windmill to turn at near the optimal speed in a large
range of wind velocities.
The fantail, a small windmill mounted at right angles to the main sails
which automatically turns the heavy cap and main sails into the wind,
was invented in England in 1745. The smock mill is a later variation of
the tower mill, constructed of timber and originally developed in the
sixteenth century for land drainage. With some subsequent development
mills became versatile in windy regions for all kind of industry, most
notably grain grinding mills, sawmills (late sixteenth century),
threshing, and, by applying scoop wheels, Archimedes' screws, and piston
pumps, pumping water either for land drainage or for water supply. In
1807, William Cubitt invented a new type of sail, known there on as
patent sails, that could be regulated whilst moving and became the basis
of self-regulating sails, which avoided the constant supervision that
had been required up till then.
With the Industrial Revolution, the importance of windmills as primary
industrial energy source was replaced by steam and internal combustion
engines. Polder mills were replaced by steam, or diesel engines. These
changes, however, had a lesser effect on the Mills of the Norfolk Broads
in the United Kingdom, as the mills are so isolated (on extensive
uninhabitable marshland). Therefore, some of these mills continued to be
used as drainage pumps till as late as 1959.
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.
In Canada and the United States
Windmills feature uniquely in the history of New France, particularly in
Canada, where they were used as strong points in fortifications. Prior
to the 1690 Battle of Québec, the strong point of the city's landward
defenses was a windmill called Mont-Carmel, where a three-gun battery
was in place. At Fort Senneville, a large stone windmill was built on a
hill by late 1686, doubling as a watch tower. This windmill was like no
other in New France, with thick walls, square loopholes for muskets,
with machicolation at the top for pouring lethally hot liquids and rocks
onto attackers. This helped make it the "most substantial castle-like
fort" near Montréal.
In the United States, the development of the water-pumping windmill
was the major factor in allowing the farming and ranching of vast areas
of North America, which were otherwise devoid of readily accessible
water. They contributed to the expansion of rail transport systems by
pumping water from wells to supply the needs of the steam locomotives of
those early times. Two builders were the Eclipse Model of Windmill
(later bought by Fairbanks-Morse) and Aeromotor. They are still used
today for the same purpose in some areas of the world where a connection
to electric power lines is not a realistic option.
The multi-bladed wind turbine atop a lattice tower made of wood or steel
was, for many years, a fixture of the landscape throughout rural
America. These mills, made by a variety of manufacturers, featured a
large number of blades so that they would turn slowly with considerable
torque in low winds and be self regulating in high winds. A tower-top
gearbox and crankshaft converted the rotary motion into reciprocating
strokes carried downward through a rod to the pump cylinder below.
Windmills and related equipment are still manufactured and installed
today on farms and ranches, usually in remote parts of the western
United States where electric power is not readily available. The
arrival of electricity in rural areas, brought by the Rural
Electrification Administration (REA) in the 1930s through 1950s,
contributed to the decline in the use of windmills in the United States.
Today, the increases in energy prices and the expense of replacing
electric pumps has led to an increase in the repair, restoration, and
installation of new windmills.
Modern windmills
Most modern generations of windmills are more properly called wind
turbines, or wind generators, and are primarily used to generate
electric power. Modern windmills are designed to convert the energy of
the wind into electricity. The largest wind turbines can generate up to
6MW of power. (For comparison, a modern fossil fuel power plant
generates between 500 and 1,300MW).
With increasing concerns about the environment and limits to fossil fuel
availability, wind power has regained interest as a renewable energy
source.
Windpumps
A windpump is a type of windmill used for pumping water from a well or draining land.
Windpumps of the type pictured are used extensively in Southern Africa
and Australia and on farms and ranches in the central plains of the
United States. In South Africa and Namibia thousands of windpumps are
still operating. These are mostly used to provide water for human use as
well as drinking water for large sheep stocks.
Kenya has also benefited from the Africa development of windpump
technologies. At the end of the 1970s, the UK NGO Intermediate
Technology Development Group provided engineering support to the Kenyan
company Bobs Harries Engineering Ltd for the development of the Kijito
windpumps. Nowadays Bobs Harries Engineering Ltd is still manufacturing
the Kijito windpumps and more than 300 Kijito windpumps are operating in
the whole of East Africa.
The Netherlands is well known for its windmills. Most of these iconic
structures situated along the edge of polders are actually windpumps,
designed to drain the land. These are particularly important as much of
the country lies below sea level.
Many windpumps were built in The Broads of East Anglia in the United
Kingdom for the draining of land. They have since been mostly replaced
by electric power. Many of these windpumps still remain, mainly in a
derelict state, but some have been restored.
On U.S. farms, particularly in the Midwest, windpumps of the type
pictured were used to pump water from farm wells for cattle. Today this
is done primarily by electric pumps, and only a few windpumps survive as
unused relics of an environmentally sustainable technology.
Windmills in culture and literature
Miguel de Cervantes' book Don Quixote de La Mancha, which helped
cement the modern Spanish language and is regarded as one of the
greatest works of fiction ever published, features an iconic scene in
which Don Quixote attacks windmills that he believes to be ferocious
giants. This gave international fame to La Mancha and its windmills, and
is the origin of the phrase "tilting at windmills," to describe an act
of futility.
The windmill also plays an important role in Animal Farm, a book by
George Orwell. In the book, an allegory of the Russian Revolution and
the subsequent early Soviet Union, the effort invested construction of a
windmill is provided by the animals in the hope of reduced manual labor
and higher living standards.