Windmill

This article is about machines that convert wind energy into mechanical energy. For machines that convert wind energy into electricity see wind turbines. Other uses, see Windmill (disambiguation).

Dutch windmill (Wageningen)

A windmill is a machine that is powered by the energy of the wind. It is designed to convert the energy of the wind into more useful forms using rotating blades or sails. The term also refers to the structure it is commonly built on. In much of Europe, windmills served originally to grind grain (hence the "mill" derivation), though later applications included pumping water and, more recently, generation of electricity. Contemporary electricity-generating versions are referred to as wind turbines.

History

windmills are for homos

The first practical windmills were the vertical axle windmills invented in eastern Persia, as recorded by the Persian geographer Estakhri in the 9th century. The authenticity of an earlier anecdote of a windmill involving the second caliph Umar (AD 634–644) is questioned on the grounds that it appears in a 10th-century document. Made of six to twelve sails covered in reed matting or cloth material, these windmills were used to grind corn or draw up water, and were quite different from the later European horizontal-axis versions. While it has been claimed in some popular treatments that the Afghanistan-style vertical-axle mills were used throughout the Caliphate by the ninth century and spread to Europe through Islamic Spain, this has been denied by the specialist of European medieval technology, Lynn White Jr., who asserts that there is no evidence that the Afghanistan-style vertical-axle windmill spread as far west as al-Andalus, and who claims that "all Iberian windmills rotated on horizontal axles until towards the middle of the fifteenth century," which is an indication of their European origin (see below). A similar type of vertical shaft windmill with rectangle blades, used for irrigation, can also be found in 13th-century China (during the Jurchen Jin Dynasty in the north), introduced by the travels of Yelü Chucai to Turkestan in 1219.

Fixed horizontal-axle windmills

Medieval depiction of a windmill

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 1/10th share of the flour was paid to the miller in return for his service. This type would mount triangular sails when in operation.

Horizontal-axle windmills that turn to face the wind

In northwestern Europe, the horizontal-axle or vertical windmill (so called due to the dimension of the movement of its sails) dates from the last quarter of the 12th century in the triangle of northern France, eastern England and Flanders. Lynn White Jr. claims that the first certain reference to the European horizontal-axle windmill is dated to 1185 in Weedley, Yorkshire. (This predates Joseph Needham's claim that the earliest known reference is from the 1191 chronicle of Jocelin of Brakelond, in which a Dean Herbert of East Anglia supposedly competed with the mills of the abbey of Bury St Edmunds). These earliest mills were used to grind cereals. The evidence at present is that the earliest type was the sunk 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. In the Netherlands these stone towerlike mills are called "round or eight-sided stone stage mills, ground-sailers (windmills with sails reaching almost down to the ground), mound mills, etc." (Dutch: ronde/achtkante stenen stelling molens, grond-zeilers, beltmolens, etc.). Dutch tower mills ("torenmolens") are always cylindrical (such as atop castle or city wall towers). Because only the cap of the tower mill needed to be turned the main structure could be made much taller, allowing the sails to be made longer, which enabled them to provide useful work even in low winds. Such mills often have a small auxiliary set of sails called a fantail at the rear of the cap and at right angles to the sails; this rotates the cap through gearing so the sails face into the wind.

• Post mills in Germany are Bockwindmühlen, Paltrockmühlen or Wippmühlen.
• Smock mills in Germany can be Sockelgeschoßholländer or Galerieholländer.
• Tower mills in Germany can be Turmholländer, Galerieholländer, Erdholländer or Bergholländer

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.

Diagram of the smock mill at Meopham, Kent which uses a fantail and Cubitt's patent sails

The familiar lattice style of windmill sails (also called "common" sails) allowed the miller to attach sailcloths to the sails (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 by Edmund Lee in 1745, in England. 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 16th century), threshing, and, by applying scoop wheels, Archimedes screws, and piston pumps, pumping water either for land drainage or for water supply. In 1772, Scottish millwright, Andrew Meikle developed the spring sail made from a series of connected parallel shutters that could be opened or closed according to windspeed. To do this the sails had to be stopped, but the sails also incorporated a spring which allowed the shutters to open a little more to prevent damage if the wind suddenly strengthens. In 1789, Stephen Hooper invented the roller reefing sail, which allowed automatic adjustment of the sail whilst in motion. In 1807, William Cubitt a Norfolk engineer, invented a new type of sail, known there on as patent sails, using a chain and a rod that passed through the centre of the windshaft. These sails had the shutters of Meikle's spring sails and the automatic adjustment of Hooper's roller reefing sails. This became the basis of self-regulating sails. These 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. The industrial revolution and increased use of Steam and later Diesel power however had a lesser effect on the Mills of the Norfolk Broads in the United Kingdom, these being so isolated (on extensive uninhabitable marshland), therefore some of these mills continued use as drainage pumps till as late as 1959. More recently historic 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.

See Flood control in the Netherlands for use of windmills in land reclamation in the Netherlands.

In Canada and the United States

An isometric drawing of the machinery of the Beebe Windmill. It was built in Bridgehampton, NY in 1820.

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 Montreal.

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 throughout the world, by pumping water from wells to supply the needs of the steam locomotives of those early times. Two prominent brands were the Eclipse Windmill developed in 1867 (which was later bought by Fairbanks-Morse) and the Aermotor, which first appeared in 1888 and is still in production. The effectiveness of the Aermotor's automatic governor, which prevents it from flying apart in a windstorm, led to its popularity over other models. Currently, the Aermotor windmill company is the only remaining water windmill manufacturer in the United States. They continue to be used in 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 US. 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.

1980's Wind Energy Experiment

In the early 1980's, several small companies started "windfarms" for commercial energy production in the San Joaquin valley region of California. The first such windfarm was created in 1981 when John Eckland, of Fayette Manufacturing Corporation placed the first windmills on land leased from Joe Jess, Sr. on the Altamont Pass. Later, as a gift to Mr. Jess for the continued use of his land, Fayette created a ‘stars and stripes’ themed windmill for Mr. Jess.

At one point in the mid-80’s there were over twenty-six windfarm companies operating in this area of the United States. This eventually expanded to areas outside of Palm Springs, as seen as backdrops in several films of the era, such as "Less than Zero." However, later legislative efforts by California lawmakers eliminated the financial incentives and tax breaks that made these early alternative energy projects feasible (Fisher, 1985). Similar tax credits and incentives have brought a resurgence in interest in renewable energy sources in other areas of the country (Maloney, 2006).

Multi-sailed windmills

An eight sailed Windmill at Heckington, Lincolnshire, UK

The majority of windmills had four sails. An increase in the number of sails meant that an increase in power could be obtained, at the expense of an increase in the weight of the sail assembly. The earliest record of a multi-sailed mill in the United Kingdom was the five sail Flint Mill, Leeds, mentioned in a report by John Smeaton in 1774. Multi-sailed windmills were said to run smoother than four sail windmills. In Lincolnshire, more multi-sailed windmills were found than anywhere else in the United Kingdom. There were five, six and eight sail windmills.

If a four sail windmill suffers a damaged sail, the one opposite can be removed and the mill will work with two sails, generating about 60% of the power that it would with all four sails. A six sail mill can run with two, three, four or six sails. An eight sail mill can run with two, four, six or eight sails, thus allowing a number of options if an accident occurs. A five sail mill can only run with all five sails. If one is damaged then the mill is stopped until it is replaced. Apart from the UK, multi-sail mills were built in Malta and the USA.

Modern windmills

A modern Vestas windmill in Sweden

Main article: Wind turbine

The most modern generations of windmills are more properly called wind turbines, or wind generators, and are primarily used to generate electricity. 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 environmental concern, and approaching limits to fossil fuel consumption, wind power has regained interest as a renewable energy source. It is increasingly becoming more useful and sufficient in providing energy for many areas of the world.

One area where turbines have become feasible is in the Midwestern United States, due to great amounts of wind.

Windpumps

Brograve Mill, UK. An example of the derelict state of many Broadland Windpumps

A windpump is a type of windmill used for pumping water from a well or draining land.

Windpumps 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 African 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. 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.

Primitive eight to ten-bladed windmills were used in the Region of Murcia, Spain to raise water for irrigation purposes. The drive from the windmill's rotor was led down through the tower and back out through the wall to turn a large wheel known as a noria. The noria supported a bucket chain which dangled down into the well. The buckets were traditionally made of wood or clay. These windmills were still in use until the 1950s, and many of the towers are still standing.

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 (pictured), however some have been restored.

Windpump on farm in Iowa

On US farms, particularly in the Midwest, windpumps were used to pump water from farm wells for cattle. The self-regulating farm wind pump was invented by Daniel Halladay in 1854. Eventually steel blades and steel towers replaced wooden construction, and at their peak in 1930, an estimated 600,000 units were in use, with capacity equivalent to 150 megawatts. Early wind pumps directly operated the pump shaft from a crank attached to the rotor of the windmill; the installation of back gearing between wind rotor and pump crank allowed the pump to function at lower wind speeds.

Such windpumps can be found worldwide and are still manufactured in the United States, Argentina, New Zealand, and South Africa. A six-foot diameter windpump rotor can lift up to 180 gallons per hour of water with a 15 to 20 mile per hour wind, according to a modern manufacturer (about 700 litres/hour by a 1.8 metre rotor in 24–32 km/hour wind). Wind pumps require little maintenance, only requiring gear oil changes about once per year. Although electric pumps are now the dominant means of lifting water, an estimated 60,000 wind pumps are still in use in the United States. They are particularly economical in remote sites distant from electric power distribution.

Tjasker

A tjasker

A tjasker is a type of drainage windmill found in the Netherlands. It is a simple design used for raising water where only a low head is required.

A tjasker comprises four common sails mounted on a windshaft. The windshaft sits on a tripod which allows it to pivot, and carries an Archimedes screw at its lower end. The screw raises water into a collecting ring, where it is drawn off into a ditch at a higher level, thus draining the land. The tjasker can only raise water to a relatively low height.

• See also: nl:Tjasker

Windmills in culture and literature

Spanish windmills in La Mancha

Books

Miguel de Cervantes's 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 to construct a windmill is provided by the animals in the hope of reduced manual labour and increased living standards.

People

George Green, a famous UK self-taught mathematician and physicist, owned and operated a windmill. Green's Windmill has been restored as cultural heritage. Sir Bernard Montgomery lived in a converted windmill after he retired. Fictional character Jonathan Creek lived in the King's Mill, Shipley.

Films

1937 - Oh, Mr Porter! was partly filmed at Terling windmill in Essex.

1968 - Chitty Chitty Bang Bang features Cobstone Windmill in Buckinghamshire.

1974 - The Black Windmill was partly filmed at Clayton Windmills in Sussex.

1987 - Less Than Zero as the main character, Clay attempts to rescue his addicted friend, Julian, he drives through the California desert. Julian overdoses in the car; during these scenes, windmills are a focal part of the landscape.

2001 - Moulin Rouge! is set in the famous Paris caberet nightclub of the same name famous for its iconic red windmill mounted on the roof.

See also

Windmill at the National Ranching Heritage Center in Lubbock, Texas

• American Wind Power Center - Lubbock, TX
• Don Quixote
• Éolienne Bollée
• Jacobs Wind
• Klopotec
• Land reclamation
• List of windmills
• Mill machinery
• Molinology
• Renewable energy
• Savonius wind turbine
• The International Molinological Society
• Tension leg platform
• Watermill
• Wind generator
• Wind turbine
• Thomas O. Perry
• John Eckland

References

• A.G. Drachmann: "Heron's Windmill," Centaurus, 7 (1961), pp. 145–151

Further reading

• Ahmad Y Hassan, Donald Routledge Hill (1986). Islamic Technology: An illustrated history. Cambridge University Press. ISBN 0-521-42239-6.
• Chartrand, French Fortresses in North America 1535–1763: Québec, Montréal, Louisbourg and New Orleans.
• Dietrich Lohrmann, "Von der östlichen zur westlichen Windmühle", Archiv für Kulturgeschichte, Vol. 77, Issue 1 (1995)
• A.G. Drachmann, "Heron's Windmill", Centaurus, 7 (1961).
• Needham, Joseph (1986). Science and Civilization in China: Volume 4, Physics and Physical Technology, Part 2, Mechanical Engineering. Taipei: Caves Books Ltd.
• Hugh Pembroke Vowles: "An Enquiry into Origins of the Windmill", Journal of the Newcomen Society, Vol. 11 (1930-31)

External links

• Architecture: Windmills at Curlie
• Earth Science Australia, Wind Power and Windmills
• The International Molinological Society
• Windmills at Windmill World
• The Mill Database, Europe
• A short video demonstrating how to generate electricity from a windmill by the Vega Science Trust