11-07-2012, 04:54 PM
WIND POWER
WIND POWER.doc (Size: 562.5 KB / Downloads: 54)
Introduction
For every activity to be accomplished we require energy. Electricity, which is one of the forms of energy, is utilized in various activities from residential and commercial to industrial establishments worldwide.
Energy production happens from various sources - renewable and non-renewable. Wind energy is one of the renewable energy sources. Others include solar, tidal, bio mass and geothermal. It is widely accepted fact that electrical power produced from non-renewable energy source is much costlier than renewable sources.
There is growing demand to produce power from wind-based establishments as there are many associated advantages. Conventional form of energy production from fossil fuels is being replaced by wind; primary reason being depleting resources and the adverse effects on environment.
History
Wind machines were used in Persia as early as 200 B.C. This type of machine was introduced into the Roman Empire by 250 A.D. However, the first practical
windmills were built in Sistan, Iran, from the 7th century. These were vertical axle windmills, which had long vertical driveshafts with rectangle shaped blades. Made of six to twelve sails covered in reed matting or cloth material, these windmills were used to grind corn and draw up water, and were used in the gristmilling and sugarcane industries.
By the 14th century, Dutch windmills were in use to drain areas of the Rhine River delta. In Denmark by 1900 there were about 2500 windmills for mechanical loads such as pumps and mills, producing an estimated combined peak power of about 30 MW. The first known electricity generating windmill operated was a battery charging machine installed in 1887 by James Blyth in Scotland, UK[citation needed]. The first windmill for electricity production in the United States was built in Cleveland, Ohio by Charles F Brush in 1888, and in 1908 there were 72 wind-driven electric generators from 5 kW to 25 kW. The largest machines were on 24 m (79 ft) towers with four-bladed 23 m (75 ft) diameter rotors. Around the time of World War I, American windmill makers were producing 100,000 farm windmills each year, most for water-pumping. By the 1930s windmills for electricity were common on farms, mostly in the United States where distribution systems had not yet been installed. In this period, high-tensile steel was cheap, and windmills were placed atop prefabricated open steel lattice towers.
A forerunner of modern horizontal-axis wind generators was in service at Yalta, USSR in 1931. This was a 100 kW generator on a 30 m (100 ft) tower, connected to the local 6.3 kV distribution system. It was reported to have an annual capacity factor of 32 per cent, not much different from current wind machines.
The first utility grid-connected wind turbine operated in the UK was built by the John Brown Company in 1954 in the Orkney Islands. It had an 18 meter diameter, three-bladed rotor and a rated output of 100 kW.
Types of Wind Turbines
Vertical axis
Vertical-axis wind turbines (or VAWTs) have the main rotor shaft arranged vertically. Key advantages of this arrangement are that the turbine does not need to be pointed into the wind to be effective. This is an advantage on sites where the wind direction is highly variable. VAWTs can utilize winds from varying directions.
With a vertical axis, the generator and gearbox can be placed near the ground, so the tower doesn't need to support it, and it is more accessible for maintenance. Drawbacks are that some designs produce pulsating torque. Drag may be created when the blade rotates into the wind.
VAWT advantages
• A massive tower structure is less frequently uses, as HAWTs are more frequently mounted with the lower bearing mounted near the ground.
• Designs without yaw mechanisms are possible with fixed pitch rotor designs.
• A VAWT can be located nearer the ground, making it easier to maintain the moving parts.
• VAWTs have a higher airfoil pitch angle, giving improved aerodynamics while decreasing drag at low and high pressures.[citation needed]
• Straight bladed VAWT designs with a square or rectangular cross-section have a larger swept area for a given diameter than the circular swept area of HAWTs.
VAWT disadvantages
• Most VAWTs produce energy at only 50% of the efficiency of HAWTs in large part because of the additional drag that they have as their blades rotate into the wind. Versions that reduce drag produce more energy, especially those that funnel wind into the collector area.
• VAWTs will rotate faster in stronger winds at higher elevations as they rotate at least as fast as the wind velocity.
• A VAWT that uses guy-wires to hold it in place puts stress on the bottom bearing as all the weight of the rotor is on the bearing. Guy wires attached to the top bearing increase downward thrust in wind gusts. Solving this problem requires a superstructure to hold a top bearing in place to eliminate the downward thrusts of gust events in guy wired models.
Picking the Best Location for a Wind Turbine
Where you choose to build your wind turbine is important. Remember that if nearby houses, tree lines and silos obstruct the full force of the wind from your wind turbine, you will not be able to generate as much power.