Wind Power - Term Paper Example

Windmill started a long time ago with the first machine with vanes attached to an axis being built as early as 2000 B.C. In the ancient Babylon about 10 A.D, there were windmills with wind catching surfaces. The wind mills were used to grind grain and were 16 feet in length and 30 feet in height. This is especially in the areas of eastern Iran and Afghanistan. The earliest written references on wind machines date back to 12th century. These were also used for milling grains and it was not until years later that they were used to pump water and reclaim Holland from sea (Burton et al., 2001). Fig.

1, traditional wind mill (Burton et al., 2001) In the latter half of the 19th century, US the multi-vane farm windmill was invented. By 1989, USA had over 77 wind factories and windmills were becoming a major export. The wind mills played a very vital role in the rail industry of US. They were used to pump water used by the steam locomotives long before the diesel engines were invented. At the moment, farm windmills are still being used today. They are especially useful for pumping small amount of water for the livestock (Anaya-Lara, Jenkins, Ekanayake, Cartwright & Hughes, 2011).

The electricity producing wind turbine came into production by 1930s and 1940s. There was a hundred of electricity producing wind turbines around US. The wind turbines had two or three blades which rotated at high speeds to drive the electrical generators. Over the years, the wind turbines provided power to the firms that were far away from the national grid. They could be used for lighting, charge storage batteries and operate radios. By the 1950s, rural electrification administration eliminated the use of wind turbines.

This made the wind turbines industry in US to lay dormant for over 20 years. Despite this, some other parts of the world had already adopted the technology (Burton et al., 2001).

2.2 Modern windmill The modern windmill has about three blades which are mounted in a horizontal axis tower. There is a turbine which is connected to a generator both fixed at the horizontal axis. There are two types of wind turbines; horizontal and vertical axis. A horizontal wind turbine has its blades rotating on an axis which is parallel to the ground. A vertical axis machine has its blades rotating on an axis which is perpendicular to the ground. The most type of wind turbines are based on horizontal axis.

Very few vertical axis turbines are available in the commercial market (Blanco, 2009). Fig.2, Modern wind power plant (Blanco, 2009) The modern wind turbines used globally have three bladed rotors. The rotors have a diameter of 70 to 80 metres and can produce about 1.5MW of electrical power. The power output of the turbine is controlled by rotating the blades along the axis to alter the angle of attack relative to wind. The turbine can also be pointed into the wind through rotating the nacelle about the power.

This is known as the yaw control. Modern turbines operate with their rotor in the windward position of the tower. This is referred as upwind rotor (Blanco, 2009). The wind sensors are placed on the nacelle and tell the yaw controller on the direction to point the turbine. When the wind sensors are combined with the sensors on the generator and the drive train, they are able to assist the blade pitch controller. The blade pitch controller is able to regulate the rotor speed to prevent overloading of the structural components.

A modern turbine is capable of producing power with a wind of speed of 5.4m/s. the turbine reaches maximum power at about 12.5m/s to 13.4m/s. the turbine tops power production and rotation when the wind reaches 26.8m/s. this is known as feathering the blades (Holdsworth, Ekanayake & Jenkins, 2004). The energy available from the wind increases with the cube of wind speed. This implies that 105 increase in the wind speed leads to 33% increase in the available energy. Despite this, a wind turbine will only capture a portion of this.

This is due to the power level in which the system is designed. At the moment, the height and size of the wind turbines have been increased. This is aimed at capturing more energetic winds on higher elevations. The land based turbines have a maximum diameter of 100 metres and power output ranges from 3 to 5 MW. It is possible to produce larger sizes but the logistic constraints and large cranes to lift the blades are a hindrance (Anaya-Lara et al., 2011). Over the last 20 years, turbine size has grown linearly.

The commercial rated turbines are capable of producing 1.5MW. Over the year, the size has increased through a liner curve. The drive to have larger turbines is based on the need to take advantage of higher energetic winds found in high elevation. The speed of wind increases with the height above the ground. Despite this, the cost constraints have been hampering the building of larger turbines. The size of the wind turbine is based on the square cube law (Anaya-Lara et al., 2011). The law states that as the wind turbine rotor increase in size, the energy output generated increases based on the root swept area, while the material used, mass and cost rises based on the cube of the diameter.

This implies that at a certain size, the cost of a larger turbine will be higher than the resultant energy. This implies that at a certain size, the turbine starts losing its value economically. This has made the engineers to come up with ways of reducing costs and weight by being more efficient (Holdsworth, Ekanayake & Jenkins, 2004). The land transportation of the turbines has been a major constraint in the industry. The most cost effective transportation of the wind turbines is through over the road trailers with dimensions a 4.1 M by 2.6M.

Rail transport is limited in dimensions which eliminates the option of their use. Crane requirement are also very stringent. This is due to the large mass of nacelle and the height of the lift.