vrijdag 1 juli 2011

Historical review on Wind Energy

Using the wind as an energy source is not development during the latest decades. Even in ancient times methods were developed to take advantage of the force of the wind. At sea, sails were used to utilize wind’s power in order to propel boats. The invention of windmills was a significant development for any society. The power of the wind alleviated the sweat of the grinding process, as it replaced mulls and bare hands as the drivers. The windmills not only made the core process less costly, it also dramatically improved working conditions and created an industry for windmill production.

Persian vertical axis windmill
When wind was first used to drive machinery is debatable. Ancient scriptures show that there was - at least - early communication about the potentials of wind energy. There is consensus that windmills were widespread used in the Middle East and Central Asia during ancient times, which is said to spread towards China and India. Despite a void of evidence, some suggest that windmill technology may have been present in China and Europe before it came to know about the Persian technology. Also some academics coin that ancient written accounts suggest that wind mills may already have been invented and build in the 7th century in Babylonia, or even earlier. (Ragheb, 2011).

The ancient panemones
The first genuine record of a built wind driven onshore mill was noted in the 9th century in Persia (what is now called Afghanistan). This ancient windmill is called a panemone. A panemone is a device with wind-catching vanes that move in the same direction as the thrusting force of the wind (this is called ‘drag’). This is in contrast to the motion of a propeller, whose blades move at 90 degrees to the thrust of the wind (this is called ‘lift’). Panemones have a vertical axe and its design typically includes stop pegs to control panels as they catch wind. A stop peg - placed at one side of each panel - prevents the panel from rotating as the wind blows against the side of the panel. The Persian model had sails covered in reed matting or cloth material that rotated a vertical shaft. The first historical documentation of a panemone in China dates from 1219 AD.

European wind mills
Doesburgermolen, built around 1620
Photo by Rens Kokke 
In Europe the first windmills can be traced back to the second half of the 11th century. It is disputable if and to what extend the ancient technologies influenced the development of windmills in Europe. The technology employed was quite different as these were equipped with an horizontal axe and a shaft so that the (entire) mill could spin around its axe. By manually wheeling the shaft, the mill was able to catch wind at all corners. While development continued, the ‘standard mill’ became the popular model. The first documentation of the famous ‘standard mill’ stems from around 1180. In comparison, the oldest still working Dutch ‘standard mill’ is the Doesburgermolen, built around 1620. (Wikipedia, 2011a) During those ages important technological breakthroughs were (a) the security of operation at different speeds; (b) the transmission from the twisting to a pumping motion and; (c) the separation of a fixed compartment from its rotatory top floor.

Wind Turbines
While windmills were increasingly popular, their reliability on the presence of wind, was always a huge disadvantage when compared to watermills. During the 18th and 19th century of the industrial revolution, the popularity of mind mills declined as wind driven labor was superseded by the introduction of the more superior steam engines. It was only in the end of the 19th century that wind mills had an answer on its future. New scientific knowledge in the field of electricity, led to the first experimental wind turbines that generated electricity. The first serious wind turbine was build in 1888 in Cleveland (Ohio, United States) and generated 12 KW. In 1890 An experiment by the scientist Poul La Court to illuminate a high school by a mixture of oxygen and hydrogen caused an impetus for wind turbines, as the production of electricity was necessary for hydrogen to split from water. Around 1900 there were like 2500 wind turbines in Denmark. 40 years later, In 1931 a vertical axis wind turbine (VAWT) was developed, called Darrius. The advantage of the vertical axis is the low maintenance costs, but In practice horizontal models tend to be more efficient. It were the horizontal axis wind turbines (HAWT’s) that became increasingly popular at rural areas across the United States. This expansion lasted until the end of the thirties, when most farms got wired to the grid. In the mean time the accumulation of technological knowledge on aerodynamics led to greater capabilities. In 1941 a 1.25-megawatt Smith-Putnam turbine was placed on the mountain Grandpa’s Knob, Vermont, United States.

The NASA/GE Mod-1 Wind Turbine
could generate 2MW of electricity 
The 1973-oil crisis induced interests in independent energy sources. Just like nuclear energy, wind turbines were catching renewed attention. In response the US government instructed NASA to aim its technological knowledge at harnessing wind energy. During its program to develop utility-scale wind turbines, two-bladed models were improved. One of the majors achievements was a 2MW turbine build by General Electric in 1979. Three years later a 4MW wind turbine was build by United Technologies. (wikipedia, 2011b). Next to more efficient, NASA’s technological inventions attributed to models that were stronger, more durable, less noisy, and equipped with generators on variable speeds. This influenced how contemporary windmills look like today. Other inventions during the 90’s were predominantly esthetically, such as the implementation of an internal stairway for maintenance. (Jan Giesen, 2011)

As yet, the wind is an untamed, and unharnessed force;  and quite possibly one of the greatest discoveries hereafter to be made, will be the taming, and harnessing of it.
— Abraham Lincoln, 1860

Recent developments
World's record holding wind turbine
from Energon generates 7,58MW 
Yet, all the technological break-troughs did not make wind energy competitive with fossil fuels. Even in the face of rising fuel prices, the cost of renewable energy from wind turbines appears to be on unequal foot with fossils. But there are positive developments. Currently, the wind turbine E-126 - produced in 2007 by the German producer Energon - reaches world’s largest-capacity of 7.58 MW. Its size is 198m overall-height and 126 diametrically. The question is whether capacity improvements are feasible. The EU project UpWind researched for 60 months whether a 20MW wind turbine is possible. After taking more than 120 wind scientists’ opinions into the equation, they recently published that this is indeed the case. Still, they mention that several innovations are necessary before wind turbines can be scaled-up to an axis-height of 250m (Upwind, 2011). Also the price development of wind energy looks promising. Bloomberg’s latest issue of its Wind Turbine Price Index shows that in some regions of Brazil, Mexico, Sweden, and the United States, the cost of wind powered electricity is on par with coal-fired power. This is due to dropping prices of wind turbines, as a result of increasing scale, improved efficiency and over-capacity (Bloomberg, 2011).


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