The wind wheel 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 17th century BC.
Horizontal windmills
The first practical windmills had sails
that rotated in a horizontal plane, around a vertical axis 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 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 13th-century
in China.
Horizontal windmills were built, in
small numbers, in Europe during the 18th and 19th centuries, for example Fowler's Mill at Batter
Sea 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
Vertical-axis wind turbines(VAWT's)are a type of wind turbine where the main rotor shaft is set
vertically and the main components are located at the base of the turbine.
Among the advantages of this arrangement are that generators and gearboxes can
be placed close to the ground, which makes these components easier to service
and repair, and that VAWTs do not need to be pointed into the wind. Major drawbacks for the early designs
included the pulsatory torque that can be produced during each
revolution and the huge bending moments on the blades. Later designs solved the
torque issue by using the helical twist of the blades almost similar to Gorlov's water turbines.
A VAWT tipped sideways, with the axis
perpendicular to the wind streamlines, functions similarly. A more general term
that includes this option is "transverse axis wind turbine". For example,
the original Darrieus patent includes both options.
Drag-type VAWTs,
such as the Savonius rotor, typically operate at lower tip speed ratios than lift-based VAWTs such as Darrieus
rotors and cycloturbines.
A unique, mixed Darrieus - Savonius
VAWT type has recently been developed and patented. The main benefits obtained
are improved performance at lower wind speeds and a lower r.p.m. regime at
higher wind speeds resulting in a silent turbine suitable for residential
environments.
Post Windmill
The post mill is the
earliest type of European windmill. The defining feature is that the whole body of
the mill that houses the machinery is mounted on a single vertical post, around
which it can be turned to bring the sails into the wind. The earliest post
mills in England are thought to have been built in the 12th century. The earliest working post mill
in England still used today is to
be found at Out wood in Surrey. It was built in 1665. The earliest
remaining example of a non-operational mill can be found in Great Gransden in Cambridgeshire, built in 1612. Their design and usage peaked in the
18th and 19th centuries and then declined after the introduction of high-speed
steam-driven milling machinery. Many
still exist today, primarily to be found in Northern Europe and Great Britain. The term peg mill or peg and post mill(in which the
"post" was the tailpole used to turn the mill into the wind) was used
in north west England, and stob mill in north east England, to describe
mills of this type.
HOLLOW POST MILL
Some post mills are
hollow post mills. In these mills the main post is bored to take a drive shaft,
similar to an Upright Shaft in a smock or tower
mill. This enables the mill to drive machinery in the base or roundhouse.
Hollow post mills were not common in the United Kingdom. In the Netherlands,
they are called Wipmolen and were used for drainage. In France,
the Moulin Cavier was a type of hollow post mill used for
corn milling.
Tower Mill
The tower mill originated in written
history in the late 13th century in western Europe;
the earliest record of its existence is from 1295, from Stephen de Pen castor
of Dover, but the earliest illustrations date from 1390 Other early examples
come from Yorkshire and Buckingham shire. Other
sources pin its earliest inception back in 1180 in the form of an illustration
on a Norman deed, showing this new western-style windmill. The Netherlands has six mills recorded
before the year 1407. One of the earliest tower mills in Britain was Chesterton
Mill, Warwickshire, which has a hollowed conical base with arches. The large part
of its development continued through the late Middle Ages, towards the end of
the 15th century tower mills began appearing across Europe in greater numbers.
The origins of the tower mill can be
found in a growing economy of Europe, which needed a more reliable and
efficient form of power, especially one that could be used away from a river
bank. The spread of tower mills came with a growing economy that called for
larger and more stable sources of power. Post
mills dominated the scene in
Europe until the 19th century when tower mills began to replace them in such
places as Billing ford Mill in Norfolk, Upper Hellesden Mill in Norwich, and
Stretham Mill in Cambridgeshire.
The tower mill
also was seen as a cultural object, being painted and designed with aesthetic
appeal in mind. Styles of the mills reflected on local tradition and weather
conditions, for example mills built on the western coast of Britain were mainly
built of stone to withstand the stronger winds, and those built in the east
were mainly of brick.
In England around 12 eight-sailors,
more than 50 six- and 50 five-sailers were built in the late 18th century and
19th century, half of them in Lincolnshire. Of the eight sailed mills only Pocklingtons Mill in Heckington survived in fully functional state. A
few of the other ones exist as four-sailed mills (Old Buckenham), as residences
(Diss Button's Mill), as ruins
(Leach's Windmill, Wisbech)or
have been dismantled (Holbeach Mill; Skirbeck Mill, Boston). In Lincolnshire some of the six-sailed (Sibsey Trader
Mill, Waltham Windmill) and five-sailed (Dobson's Mil
Mill in Lincoln, Holgate
Windmill in Holgate, York (currently
being restored), Black, Cliff, or Whiting's Mill (a seven-storeyed chalk mill) in Hessle and (with originally six sails) Barton-upon-Humber Tower mill, Brunswick
Mill in Long Sutton, Lincolnshire, Metheringham
Windmill, Penny Hill Windmill in Holbeach, Wragby Mill (built by E. Ingledew in 1831,
millwright of Heckington Mill in 1830), and Wellingore Tower Mill. Another fine
six-sailer can be found in Derbyshire – England's only sandstone towered
windmill at Heage of 1791.
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