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WindmillsA Brief History of Windmills | Further Information | ReferencesA Brief History of WindmillsThe first wind machines were probably vertical axis windmills used for grinding grain in Persia (now Iran) in about 200BCE (Figure 1). They had a number of struts on which sails were mounted, with the sails initially made from bundles of reeds. 
Figure 1 A Sketch of an early Persian Vertical Axis Windmill.
Horizontal axis windmills first appeared in the Mediterranean region in about the 10th Century and were fixed permanently to face the prevailing coastal winds. The earliest European windmills appeared in the 13th Century, with a manually operated mechanism that rotated the whole windmill to face the wind. These were used for grinding grains and pumping water. The Dutch windmill of the 15th Century had a fixed body and a rotatable cap with a ‘fantail’ that pointed the blades into the wind (see Figure 2). 
Figure 2 A painting of a Dutch Windmill
(courtesy of Rijksmuseum Amsterdam Schiphol). These machines had sail diameters up to 25 m with power outputs of up to 30 kW in favourable winds. In general, they were about one quarter the efficiency of modern wind turbine generators. These machines became very widespread until the end of the nineteenth century, when for example, Holland had about 9000 mills. This would have been a total capacity of about 250MW of mechanical power, or about 10% of the Western Australian grid. Less than 1000 of these machines now survive. Windmills have been in use in Australia since the arrival of the first fleet in 1788. The early systems were used to grind grain. The manufacture of windmills for pumping water first commenced in Australia in 1876. Currently the name Windmills is used to refer to the now familiar water pumping machines with multiple steel blades and steel lattice towers that have been manufactured in Australia since 1903 and in WA since the 1920s. 
Figure 3 Multiblade windmills for pumping water
(courtesy of American Windmills.) Generally, windmills pump water using a positive displacement pump. This type of pump forces the fluid from one chamber to another by reducing the volume of the first chamber while increasing the volume of the second. Such a pump produces a constant flow regardless of intake or outlet pressure unless the intake pressure drops below a certain limit, causing cavitation, or the outlet pressure exceeds the capacity of the pump, causing pump failure. These pumps often have a relief valve to prevent this problem (Wikipedia, 2008).
Further InformationRISE Information Portal - Information regarding renewable energy resources, technologies, applications, systems designs and case studies.National Renewable Energy Laboratory (USA)
ReferencesWikipedia, 2008. “Pump” (Online) http://wikipedia.cas.ilstu.edu/index.php/Pump (Accessed 25 November 2008). |
 
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