Wind Power Overview
Wind Energy
Wind energy has been used over centuries for sailing boats, for pumping water, for power generation etc. Wind is a clean and replenish able source of energy.
Large differences in the solar flux incident on various parts on earth’s upper surface lead to different air temperatures all over the globe. At places where radiation is less, air gets cooler giving rise to a low pressure region. These air pressure differences cause acceleration of air particles as a result of which air movement begins. This accelerated air current or movement is called wind.
The theoretical potential of wind is about 2% of the radiant energy from the sun on earth. Due to technological limitations we are not able to utilize wind energy very effectively.
Advantages of Wind Energy:
• It is a renewable source of energy
• Wind is available in plenty and free of cost
• No pollution problem
• Less costly on a small scale power generation
Disadvantages:
• High wind velocity will not be available year round
• It needs storage capacity because of irregular and fluctuating power production
• Installation of equipment is very costly
• larger swept areas are required; wind mill of 1 to 3 m in diameter deliver power in 30 to 300 watts range only
TYPES OF WIND MILLS
Wind mills are wind-driven machines. There are two basic types of wind mills.
1. Horizontal - axis wind mills (wind-axis machines) Axis of rotation of this wind mill is parallel to the direction of the wind.
Ex : Horizontal - axis wind mill with two aerodynamic blades, multi bladed type, single bladed propeller type, Dutch type and Soil Type.
2. Vertical - axis wind mills (cross wind - axis machines) Axis of rotation of this wind mill is perpendicular to the direction of the wind.
Ex : Savonius wind machine and Darrieus wind machine.
HORIZONTAL - AXIS WIND MILL :
Figure shows a simple horizontal - axis wind mill. It is also called a wind - axis machine. Its axis of rotation is parallel to the direction of wind. Various components of the wind mill are shown in figure. Tail vane acts as a sensor of wind direction. It protects the main vanes or blades from unsafe wind speeds. It helps rotor always to be parallel to wind direction.
Figure - Horizontal Axis Wind Mill
Horizontal - axis wind mills are further classified as single bladed, two bladed, multi bladed propeller type wind mills, and Sail type and Dutch type wind mills depending on the type of rotor used.
(a) Single Bladed Rotor
(b) Double Bladed Rotor
(c) Triple Bladed Rotor
(d) Multi Bladed Rotor
For propeller type wind mills, blades are usually made of sheet metal or aluminium. Blades of Dutch type mill are made of wooden slats. This is the oldest form of wind mill. Sail type mill is of recent origin. Its blades are made of cloth, nylon or plastics.
This type of wind mills has better performance. They have been used for various applications. Two major applications are electric power generation and pumping water.
Wind Mill for Power Generation:
Wind mill is a wind energy converter known to mankind ever since 4000 years B.C. Its applications ranged from drawing water from deep wells and grinding cereals to generation of power.
Essential components of this wind mill are
• A tall tower with a central pipe which supports the head and rotor assembly.
• A tail vane attached to the head which acts as a (wind) direction sensor. It also protects the main vanes from unsafe wind speeds. It helps rotor always to be parallel to wind direction.
• Rotor assembly with sheet metal blades fixed symmetrically as shown. Rotor shaft rotates freely in the antifriction bearings mounted on the head of the wind mill.
• Drive gear connected to the rotor shaft.
• An electric generator (alternator) coupled to the drive gear.
Rotor along with its blades or sails rotates when wind blows. Rotor shaft is coupled to electrical generator through a gear drive (A) so as to run at constant rated speed. Electric power thus generated is used for rural electrification, farms, small industrial units and for irrigation.
The axis of rotor may be horizontal as shown in figure or vertical.
Wind energy conversion devices are commonly known as wind turbines. Rotor of wind mill is synonymous to turbine. The combination of wind turbine and electrical generator is called 'aerogenerator'. A step up transmission gear is required to match the slow speed of rotor to the higher speed of an electrical generator.
It is not economical to build industrial wind power generators of higher capacities than 2 MW. A wind mill developed by BHEL, Hyderabad with a 6 m diameter rotor and three parabolic shaped blades and which is about 7.5 m high develops 1.5 kW D.C. at 600 rpm. Attempts are made all over the world to develop wind turbines to generate as large as 600 MW electric power.
Proper location of site, constant wind velocities, size of supporting structure etc., arc a few factors which pose a problem for the construction and operation of large wind power generators.
If T is rotor torque at angular speed ω rad/sec then, Pr = T.ω gives power developed by rotor.
Performance of a wind mill is evaluated by a term called coefficient of performance CP.
Wind mill for Pumping Water:
Rotor facing the wind starts rotating automatically when wind flows on it. The connecting rod is actuated by the rotor shaft. This connecting rod is attached to the plunger of the pump. The plunger reciprocates inside the cylinder. The upward motion of the plunger creates suction opening the foot valve fitted at the bottom of cylinder. When plunger moves down due to reverse gearing fixed at rotor centre, water gets pressurized. Piston valve fixed at the top of cylinder opens and water rushes out of it and delivered out through delivery pipe.
VERTICAL AXIS WIND MILL
This is also called Cross - wind axis machine. Axis of rotation of this wind mill is perpendicular to the direction of wind. There are two popular types of vertical axis wind machines, namely Darrieus type and Savonius type. Figure shows a Darrieus type vertical axis machine.
In this wind mill blades are curved and attached to hubs on the vertical shaft at both ends. It looks like a magnified 'egg beater' or churner'.
It has three symmetrical aerofoil blades. When wind blows normal to axis of the machine, the blades rotate producing a torque on the vertical shaft. This shaft torque is transmitted to an electrical generator installed at the base of the machine for power generation.
Advantages :
• rotor blades can accept the wind from anypoint of compass
• blades do not require variable pitch mechanism
• huge tower structure is eliminated by installing generator and reducing gear at ground level.
• relatively cheap
Disadvantages :
• these machines will not start themselves like horizontal axis machines
• just like an aeroplane wings, Darrieus blades will not create lift until brought upto speed. A starter is required to set the machine in motion
• high torque braking system is required
• power output and efficiency is low compared to that of horizontal axis machines
• rorot has to withstand greater vibratory stresses
Wind Mills for Power Generation in India are as Follows
- APSRTC wind power project Hyderabad
- Puthlur power plant
- Lamda Danida wind farm
- Jogimatti BSES wind farm
- Kappatagudda wind power plant
- Ramakkalmedu windmill farm
- Jamgodrani wind farm
- Supa wind power plant
- Vankusawade Wind Farm
- Cape Comorin I Wind Farm
- Chennai Mohan Wind farm
- Gudimangalam wind farm
- Kayathar wind power station
- Kethanur wind farm
- Muppandal Wind Farm
- Perungudi Newam Wind Farm
- Poolavadi Chettinad Wind Farm