Electrification Through Alternative Energy Sources - Wind

Wind power

In the simplest sense, the process of generating power from the energy of moving air is known as wind power. Moving air or the wind contains kinetic energy which is the function of the square of its velocity. A wind turbine is used in the process which is coupled to a generator that produces electricity. Wind energy can also be harnessed to perform other tasks such as grinding grain or pumping water.

The wind turns the blades or rotors which are coupled to a generator by some suitable form of the coupling mechanism. The faster the wind blows, the greater is the output of the generator.

Calculation of theoretical wind power

The kinetic energy carried by the wind is expressed as,

KE = 0.5 × mass × velocity², where mass of the wind is measured in kg and the velocity is measured in meters per second

We have the relation,

mass = density × volume = ρ × V = ρ × area swept by the blades × velocity of the wind, where ρ is the air density

Thus, KE = 0.5 × ρ × area swept by the blades × v³

or, KE = 0.5 × ρ × × r ²× v³, where r is the length of a blade

Thus P_wind = KE/t = 0.5 × ρ × × r ²× v³ Watts

or, P_{wind/sq. m} = 0.5 × ρ × v³ Watts = 0.6 × v³ Watts

The density of wind is assumed to be 1.2 kg/m³ and it varies according to temperature.

Thus, it is seen that the wind power per square meter varies as the cube of wind velocity. Therefore, wind power systems are best suited for windy areas like Mustang of Nepal.

Components of a wind power system

The schematic diagram of a wind-based power system is shown in the diagram below with all the necessary components.

Rotor

The rotor consists of rotating blades that rotate when struck by the wind. The blades are generally constructed of either wood or metal or fiberglass and rotate about a horizontal or vertical axis. The blades are attached to a hub which in turn is connected to the main shaft. The main shaft drives a generator by means of a suitable transmission system which transmits mechanical power generated by the rotating blades to the generator.

Generator

The AC generators used in the system should have a feature of producing the required voltage at required frequency even if the wind speed is fluctuating. For this purpose, induction generators are widely used in the process. DC generators can also be used which can charge a battery bank to store electrical energy for later use.

Towers

The towers house all the necessary mechanical and electrical equipment and also provide the necessary ground clearance to the blades. The towers can be made of wood, steel or even concrete. Small towers need guy wires which anchor the tower to ground to increase the stability of the tower. Large wind turbines can be mounted on lattice towers.

Gearbox

The blades typically rotate at variable speeds depending upon the model and the wind velocity. Generators typically require rotational speeds ranging from 1000 to 1,500 RPM. Thus to obtain this required speed, a gearbox should be used that contains a set of gears and trains which change the speed of the shaft connected to the box.

In addition to these components, a wind system may also contain a battery bank for backup and protection devices.

Advantages of wind power system

• The Wind in a perpetual source of energy so a wind power plant can act as an intermittent source of energy.
• Wind turbines can be installed at windy locations where land is not utilized for settlement.
• Wind power systems are non-polluting as they do not emit harmful gases into the environment.
• Although the towers used in wind energy systems can be very tall, each tower takes up only a small plot of land. Therefore, the land below the towers can be used for other activities such as farming, grazing, etc.
• Wind farms can provide interesting features to the landscape.

Disadvantages of wind power system

• Wind-based power systems are noisy. Each wind system can generate noise comparable to that of the noise generated by a car travelling at a speed of 112 kmph.
• As the wind velocity is variable in nature, the amount of electricity generated can vary considerably. Sometimes the electricity generated can be negligible if the wind speed is very small.
• Wind-based systems require high investment. About 80% of the investment is made on machinery and 20% investment is made on site preparation and installation.
• Wind-based systems can be dangerous to birds.
• Windy areas are often located at distant locations from the areas where energy demand is high.
• Very large wind-based systems are required if the number of consumers is large.

References

1. John Wiley & Sons, Inc. (2016). The Basic Components of a Solar Home System. Retrieved fromhttp://www.dummies.com/

In addition to the link mentioned above, the article was prepared on the basis of class notes and the handouts provided by my subject teacher Mr. Gopal Joshi subedi as well.

The images were taken from:

1. http://www.renewableenergymagazine.com/article/renewables-generate-10-000-jobs-in-netherlands
2. http://science.howstuffworks.com/environmental/green-science/wind-power2.htm