Wind energy has been in use as far back as 3000 B.C., when sailors in Egypt utilized this energy to move their boats. Today, wind energy is hailed as an important source of energy and is tapped in various regions around the world. Its importance stems from two factors: (1) it is renewable and (2) it is a clean source of energy that does not generate environmentally harmful emissions. To harness wind energy, a wind turbine is used. A turbine converts the kinetic energy of the wind into rotary mechanical energy, which can then be converted to electrical energy (“Wind turbine,” n.d.). The ultimate aim is to explore the various parts of the wind turbine and discuss the choice of materials used for each part. However, it should be noted that a wind turbine contains many components, each of which has subcomponents. For instance, one part of a turbine (the nacelle) contains the generator among other components. The generator can be considered to be a separate electrical system with other components. In particular, large turbines have generators that are pretty complicated with several subcomponents and electrical circuit boards. The circuit boards contain electrical components such as diodes and transistors, each of which is made from carefully selected materials. A discussion of engineering materials to the minutest detail is therefore impossible in a report of this size. However, great effort will be made to explain the major parts (and choice of materials for those parts).
Parts of a Wind Turbine and their Functions
Before diving into the various parts of a wind turbine, it would be prudent to mention that there are two main types of wind turbines: Vertical Axis Wind Turbines (VAWTs) and Horizontal Axis Wind Turbines (HAWTs) (Layton, 2006).
Figure 1. Vertical Axis Wind Turbine (VAWT). This figure shows a common type of VAWT known as the Darrieus VAWT.
Figure 2. Horizontal Axis Wind Turbine (HAWT). This figure shows a common type of HAWT.
VAWTs are less common and most wind turbines around the world are HAWTs. A wind turbine consists of several parts as can be seen in figure 3 below.
Figure 3. Parts of a wind turbine. This figure shows the major parts of a general-purpose wind turbine.
The rotor basically consists of blades, which simply operate as obstructions to the wind. As the wind compels the blades into motion, some of its kinetic energy is conveyed to the turbine’s rotor as mechanical energy.
This is the wind vane whose main aim is to quantify the speed of the wind and convey this information to the turbines’ controller.
The rotor is connected to this crucial part of the turbine. Therefore, one of its functions is to support the rotor. However, its main role is to convert the rotary’s mechanical energy into electrical energy (McManus, 2008). To this end, the nacelle contains various mechanical and electrical components such as the hub, generator, gear box, low-speed shaft, high-speed shaft, gear box, controller and brakes (Hau, 2006). These parts are shown in figure 4 below.
Figure 4. Parts of the nacelle. This figure is an illustration of the internal components that make up the nacelle of a turbine.
All these parts have their own functions and the turbine would not function without each of these components. The hub acts as the intermediary between the rotor and the low-speed shaft and connects the two together (Renewable energy, 2001). The purpose of the low-speed shaft is simply to join the hub to the turbines gearbox. The gearbox is an extremely important component that contains gears that connect the low-speed and the high-speed shafts together and, due to differences in gear teeth ratios between the two, helps to maintain a certain ratio of speed between the two shafts. The ultimate aim of the gear box is to amplify shaft speed many times (about fifty for a typical 600 kilo watts turbine). As can be seen in figure 4 above, the high-speed shaft is attached to the generator. Its purpose is to drive the generator (“Wind and water,” 2010). Inside the generator, electromagnetic principles are utilized to convert the mechanical energy of the rotating high-speed shaft to electrical energy (McManus, 2008). The high speed shaft has a mechanical break, which “is used as backup to the aerodynamic brake, or when the turbine is being serviced” (Renewable energy, 2001, p. 78). The controller is an electronic device that is responsible for observing wind conditions as well as the state of the turbine itself and acting accordingly. For instance, if some parts of the turbine (such as the generator) were to overheat, it will be the responsibility of the controller to detect this and stop the turbine.
The tower simply acts as a mechanical support of the rotor and nacelle. It is a well known fact that the speed of the wind increases with height (“Kenya electricity,” n.d.). Therefore, the tower’s other function is to ensure that the parts of the turbine that interact with the wind to generate energy are high enough to maximize on wind-speed.
Choice of Materials for Each Part
The choice of materials for each component of the turbine is dependent on several factors. The most important factor is the function of the part. Other factors that may determine the kind of material used is the size of the turbine and the availability of funds to effectively assemble the turbine. Some materials are more expensive than others and hence, when deciding on the materials to use to make a wind turbine, it is important to consider the funds available for the function. The choice to make is usually a trade-off of several factors. For instance, a certain material may provide more efficiency but is too expensive to be afforded.
Deciding on which material to utilize in making the rotor can be a tedious and sophisticated task. Several types of materials can be used. The different types of materials that can be utilized for this purpose “include steel, aluminum, copper, glass reinforced plastic, wood epoxy, permanent magnetic materials and pre-stressed concrete” (“Which material,” n.d.).The choice of the particular material to use is dependent on what purpose the turbine is intended for, as well as the eventual power that the turbine is to generate.
Another key factor that should guide an engineer when making the rotor is the weight of the material in question. The rotor blades are the ones which are forced into motion by the wind thus converting the wind’s kinetic energy to mechanical energy (Renewable energy, 2001). Therefore, since the blades are the ones that move, it is imperative that they be as light as possible. If the engineer has been tasked to make a small turbine, he will most likely go for die-cast aluminum. This is because for a small turbine, the total weight of the rotor parts has to be minimized to reduce expenses and still achieve considerable efficiency. However, when designing and building larger wind turbines, die-cast aluminum would probably be a bad choice since it would not be able to withstand the required strength. In this case, it would make more sense to use steel forgings.
The choice of material to use for the rotor would also depend on a factor known as material fatigue. A typical wind turbine rotor will undergo a fatigue of approximately four by a billion cycles during its approximate thirty years lifetime (“Which material”, n.d.). Thus, it is important to use a material that will withstand the fatigue for the duration of time that the turbine is expected to be in operation. Permanent magnetic materials such as steel as well as pre-stressed concrete are known to last for long and should be given first priority if the most important consideration is longevity (“Which material, n.d.”).
The anemometer used in wind turbines is usually the hemispherical one (McManus, 2008). Whether the turbine is small or big, the size of the anemometer will most likely remain constant and the only major factor to consider here is weight. Aluminum would suffice as the right material to use.
This is one complicated part of the turbine and consists of several parts, each of which may be made using different materials. The hub is usually made from the same material that is used for the rotor. Therefore, the considerations mentioned under rotor also apply in this case. The best material to use for the low-speed and high-speed shafts is steel (McManus, 2008). Since the turbine is build outside where there is moisture, iron would not be a good choice as it is likely to more quickly than steel. The shafts need to be made of a strong material that can last long and steel is good choice for this purpose.
The gear box contains gears with teeth that grind against one another leading to wear and tear. It is therefore important to select a material that can withstand this wear and tear. Diamond is one of the most excellent materials to use for wear parts (GRUNDFOS, 2009). However, it is too expensive and might not be a good choice to use in a wind turbine. A wide range of materials are available for use in gears and these include steel, aluminum, wood, copper, brass and cast iron (“Gear material,” n.d.). If the turbine is expected to have high loads (large turbine), then steel, which is a strong and robust material should naturally be used. However, for small turbines with a short lifetime, brass and even aluminum can be used (“Gear material”, n.d.).
The generator is an electrical device that consists of other components. The selection of material for each component depends on its functions. When the high-speed shaft rotates in a magnetic field, electricity is generated (McManus, 2008). To create a magnetic field, materials that have magnetic properties should be chosen. These include iron and steel (McManus, 2008). Iron has strong magnetic properties and is the best choice to use to make the generator’s iron core (McManus, 2008). A material that has good electrical conductivity such as copper should be used to conduct the generated electricity (McManus, 2008). Materials such as wood and glass cannot be used for this purpose as they are insulators and do not conduct electricity. The controller is an electrical device with several components such as diodes, transistors and capacitors and the choice of materials depends on the desired electrical properties (McManus, 2008).
The main consideration when building the tower is that it should be strong enough to withstand strong winds and the weight of the rotor, anemometer and nacelle (McManus, 2008). Steel is a great choice of material for this function. Towers are usually firmly fixed on the ground using concrete foundations (“Kenya electricity,” n.d.).
Summary and Conclusion
In conclusion, a wind turbine converts the wind’s kinetic energy to electrical energy, which can then be consumed (McManus, 2008). A turbine consists of four main parts: rotor, anemometer, nacelle and tower (McManus, 2008). The choice of materials to use for each of the parts of the turbine depends on factors such as the size of turbine, availability of funds, expected longevity and the functions of the parts.
Gear material. (n.d.). Retrieved from http://www.gear-gears.com/gear-material.html
Management. (2009). Mechanical shaft seals for pumps. Retrieved from http://cbs.grundfos.com/export/sites/dk.grundfos.cbs/GIT_Italy/downloads/Download_Files/manualetenutemeccaniche.pdf
Hau, E. (2006). Fundamentals, technologies, application, economics. Krailling, Germany: Springer.
Kenya electricity generating company: Wind. (n.d.). Retrieved from http://www.kengen.co.ke/index.php?page=aboutus&subpage=wind
Wind and water power program: How wind turbines work. (2010). Retrieved from http://www1.eere.energy.gov/windandhydro/wind_how.html#f
Layton, J. (2006). How wind power works. Retrieved from http://science.howstuffworks.com/environmental/green-science/wind-power2.htm
McManus, J. D. (2008). Wind turbines: Design and specifications. Sebastopol, CA: Lawrence Erlbaum Publishers.
Renewable energy 2000: Issues and trends. (2001). Washington, DC: US Department of Energy.
Which material is best for wind turbine? (n.d.). Retrieved from http://www.doityourself.com/stry/which-material-is-best-for-a-wind-turbine-rotor
Wind turbine. (n.d.). Retrieved from http://www.madehow.com/Volume-1/Wind-Turbine.html