A windmill is a machine used to convert wind energy into a usable form of energy by the rotation of a wheel which is made up of blades. At the beginning, energy given out by a windmill was used to grind the grain into flour. Windmill can be designed only by skilled craftsmen using hand tools. During the 18th century, windmill achieved most prominence in Europe. But today, they were largely replaced as a power generating structure. And now majority of the modern windmill take the form of wind turbines used to produce electricity and windpumps used to pump water mainly for agricultural purposes.
Pinwheels are a simple craft idea which can be used by the children to know how the wind energy can turn the sails of the windmill. A pinwheel is generally made up of a wheel of paper attached to its axle to a stick by using a pin. It is designed to spin when a person or wind blows. These windmill are proved to be an endless enjoyment to the many children. In the 19th century. Redding, Ca., Brittany Penland invented this.
Wind Turbines is a device where kinetic energy produced due to the movement of wind is converted into mechanical energy which is then converted to electric power by a generator to generate electricity. The resultant power from wind turbines are used for small applications like phone charging to large scale applications like electricity supply for a wide area. Being a natural renewable form of solar energy and non-polluted to its core, wind, formed due to the uneven heating of the surrounding atmosphere, can be used in the production of electric energy without polluting any other natural resources. Wind turbines works opposite to the concept of fan, that is, fan converts electricity to wind whereas turbine uses wind to generate electricity.
Wind turbines are classified into two groups: vertical-axis wind turbines (VAWT) and horizontal-axis wind turbines (HAWT). Wind turbines is placed on-shore as well as off-shore in water bodies like lakes and oceans. HAWT can be two blades or three blades pointed towards the direction of wind whereas VAWT have eggbeater-style or savonius style which need are not pointed towards the wind direction to work effectively.
The wind energy is converted to rotational motion by the rotor blades. When the rotor blade turns, shaft is turned by the rotor which does the transferring of rotational mechanical motion to the nacelle. This low-speed shaft enters the gearbox which increases rotational speed of shaft. This high-speed shaft is connected to generator where rotational motion is converted to electricity at a medium voltage. This electricity is transferred to the transformer kept below the tower via heavy cables and then increases electric voltage to a level meant for distribution voltage. Distribution voltage from different turbines is collected at one point by passing it through underground lines. The electricity thus formed is supplied to nearby residences and towns.
The basic parts of a HAWT are foundation, tower, rotor blades, nacelle, yaw mechanism.
Foundation: As the wind turbines weighs in tons, the foundation need to be a good one providing enough support for the turbine.
Tower: Tower in wind turbines supports nacelle and rotor blades on top of it. Tubular steel, steel lattice or concrete are used in the construction of tower. Speed of the wind increases with height, that is, turbines with taller towers captures more energy thereby generating more electricity. Thus, height is an important factor in tower design. Turbulence in wind is also reduced with height. There are different types of towers like tubular towers, lattice tower, guyed wind tower, tilt up wind towers, free standing tower.
Blades: Rotor blades or wind turbine blades are made of fiber glass-reinforced wood-epoxy or polyester. Usually wind turbines consist of one to three blades depending on the construction and its purpose is to extract the kinetic energy from wind. These blades are connected to the rotor hub which converts the extracted wind energy to mechanical energy. Three blades are seen in most of the HAWTs. In the wind turbines design, length of the blade is important as more the length, greater the energy output. Usually, blades are of the diameter between 30 to 80 meters with rotation happening at constant speed at 10-30 revolutions per minute. Pitch angle can be changed with the blade rotation so as to modify power output.
Nacelle: Nacelle is a housing fitted to the top of the tower which includes components that are essential for the efficient operation of the turbine. Nacelle consists of gear box, generator, low-and high-speed shafts, brakes, controllers, anemometer and wind vane.
Hub: Rotor blades and shaft is coupled using rotor hub. Hub, bolts, pitch system, blade bearings and internals are part of hub assembly. Welded sheet steel, forged steel and cast iron is used in the making of rotor hub. Hine-less hub and teetering hub are different types of rotor hubs.
Shaft: Shafts are hollow or solid steel which is hardened under considerable torque and very high stresses. These shafts also called drive shafts transfers rotational mechanical form of energy from the rotor blade hub to generator to produce electricity. Two shafts are normally found in wind turbines.
Low-speed shaft: Also known as main shaft, blade hub is connected to the input of the gear box. This shaft rotates at low speeds and thus the name ‘low speed shaft’.
High-speed shaft: Also known as generator shaft, gear box output is connected to the generator input. This shaft rotates at very high speed which equals to the generator rating.
Gear box: Wind energy systems consists of gear box which is used to convert low speed high torque power that comes from rotor blade to high speed low torque power which is used in case of generator. Gear box sits between low-speed shaft and high-speed shaft to increase speed of rotation from 30 to 60 rpm to about 1000 to 1800 rpm. Aluminum alloys, cast iron, stainless steels etc. are used for the construction of gear boxes. Planetary gear box, helical gear box, worm gear box are the various gear boxes used in wind turbine.
Generator: Gear box output of rotational mechanical energy is given to the generator through high-speed shaft. This mechanical energy is converted to electrical energy. Generator works with the principle of electromagnetic induction. Generator consists of a conductor and magnets. Generator includes a shaft that connects a permanent magnets assembly that is surrounding the conductor which typically a coiled wire. Voltage is induced in conductor due to electromagnetic induction which proves that magnets surrounding the conductor with rotation happening to one of the parts relative to other induce voltage in the coiled wire conductor. Voltage is generated in the coil due to chain of actions beginning from spinning of shafts by the rotor which in turn spins the assembly of magnets. The voltage produced drives current out for distribution through power lines.
Anemometers: Nacelle consists of anemometer on top of it, which is a device used for measuring wind speed. Power content in the wind is determined using wind speed. Power content is directly proportional to wind velocity’s cube. There are different types of anemometers including rotational anemometer, pressure type anemometer, thermoelectric anemometer, phase shift anemometer.
Wind vane: Wind directions are measured using wind vane and this information is communicated to the yaw system so as to orient the turbines properly with respect to the wind directions. This orientation change extracts power at a maximum rate from wind. Either the wind turbines are oriented to the downstream wind or upstream wind.
Yaw mechanism: This is a mean of controlling mechanism in case of high speed winds. As the direction of wind changes, yaw mechanism is supposed to change the rotor to the upwind direction. Gear boxes and electric motors are used to move turbine with respect to the wind.
In general, simple wind vane is used to point small wind turbines, whereas, a servo motor coupled with wind sensor is generally used in large turbines. Wind Turbines are equipped with enough protective features so as to avoid any damage caused due to high speed winds. HAWTs usually operate in two modes, that is, upwind and downwind turbines. In Upwind turbine, wind strikes the rotor blades first then the tower. Turbulence due to tower is produced behind the tower which makes turbines positioned to upwind when compared to the supporting tower. Any sort of destruction of rotor blades is avoided by making it stiff so as to prevent the pushing of the blades into the tower due to high speed winds. Rotor blades are positioned in the tower frontage with a considerable distance and tilted forward sometimes towards the wind by small amount. In Downwind turbines, wind first strikes the tower before falling onto the rotor blades. Despite the issues of turbulence, downwind machines are built because they don’t require an extra mechanism for placing them in pace with wind. Also in case of high winds, blades can bend so that the swept area is reduced and also the wind resistance. But cyclical or repetitive turbulences can cause fatigue failures which makes upwind design common in most of the HAWTs.
The low-speed (main rotor) shaft in VAWT is arranged vertically. In this type of turbine, pointing of turbines in the direction of wind is not necessary which helps in areas where wind directions are highly variable. The gearbox and generator can be kept on ground, using direct drive to connect ground-oriented gearbox from the rotor assembly which improves the accessibility in case of maintenance. Due to this is also an issue of large space being used by VAWT. VAWTs are usually used for small-scale turbines and in rural areas for pumping purposes. VAWT consists of different types of wind turbines.
The Darrieus-typed wind turbines with C-shaped rotor blades which resemble eggbeater appearance. This type of turbine is usually built with two or three blades and is not self-starting. This type needs external power source to start turning the turbine before the wind starts rotating it. Efficiency is good enough for this turbine but has poor reliability due to the production of large cyclical stress and torque ripple over the tower. Darrieus type turbines are held up using guy-wires. To reduce torque ripple more than three or even three blades are used resulting in greater rotor solidity. Newer turbines do not use guy-wires and have superstructure connected to top bearing externally.
The Giromill Wind turbines is a type of Darrieus wind turbine having straight blades. This turbine is self-starting and features variable pitch so as to reduce torque pulsation. High starting torque, coefficient of performance that is higher, efficient operation during turbulent conditions, blade bending stress is lowered with a lower speed of rotor blade ratio, relatively flat and wide torque curve are the advantages of variable pitch. This turbines use curved, V or straight blades.
The Savonius Wind Turbines is S-shaped from top view. Aerodynamic resistance of the wind is used in this turbine. This consists of two semi-cylindrical blades with axes staggered. High starting torque turns out to be the virtue for this type of turbine whereas lateral thrust is formed due to gas flow that is asymmetrical around the rotor. This drag-type turbine yields a higher torque while turning relatively slowly. These turbines are self-starting and used in case of low-efficiency high-reliability turbine applications like pumping water, grinding grains etc. but it is unsuitable for large scale electricity generation due to slow rotational speeds. The twisted savonius turbine, a modified version of savonius turbine, provides smooth torque with the help of long scoops in helical shape. These care used in rooftops and is also used in ships.
Onshore wind turbines are a common and special type of wind turbines usually installed and maintained at cheap land foundations.
Advantages:
Disadvantages:
Offshore wind turbines are a special type of wind turbines that are commonly installed on water surfaces, i.e. offshore.
Advantages:
Disadvantages
Wind Turbines are good to use for standalone applications. As an integrated system with a solar cell or a power grid, wind turbines find great applications to the society. For utility applications, large number of wind turbines is built close together to form a wind farm. Today, electricity providers use this wind farm to supply power to the users. Through residential, water pumping, agriculture, industrial and other sectors wind turbines are gaining high popularity.
Starting from irrigation purpose to lighting and heating applications, agricultural farms consume big amount of electricity for their daily operations. Some of the key benefits of using wind turbines in agricultural sector are:
Apart from these benefits, wind turbines have many applications and uses at the agriculture farm leading to the improvement in the productivity.
Today, there is a great need for off grid signaling and signage in places where grid connection is not easy and cheap. Road signage and Rail signaling finds great application by using wind turbines. It is said that the LED based road signs consumes more power consumption and here the wind turbines can be used efficiently to reduce the power consumption. Today foreign countries are trying to efficiently implement this scheme.
Cost and use of electricity is increasing today in great amount. Harnessing the wind power for electricity generation is a renewable and pure way to make a change.
As a step, battery charging today is done by utilizing the wind power. Urban environments, outdoor advertising, developing countries, security and other applications make use of the wind turbines effectively thereby reducing the electricity usage. Vertical and Horizontal axis wind turbines can be used widely for residential installations.
Environmental
The major advantage of windmills is their ability to produce large amount of renewable energy. This is because their major power source, wind, will never disappear. Windmills also release no waste or gases, so they there is no chance on environmental pollution. These devices also take up small space, so the remaining land can still be used for farming or other agricultural activities.
Financial and Economic
With the increase in popularity of wind energy, more number of jobs is now available today. Production, Maintenance, Research and Installation of Windmills are the sectors were windmills can provide financial growth to the society. Windmills help to eliminate cost of electricity once installed and excess electricity can be sold back to the companies. They function freely and allow owners to grind grain or move water without constant supervision.
Aesthetic
Windmills offer a creative, artistic or modern addition to a landscape or architectural design. These types of windmills add an element of whimsy to a home or piece of land.
Cost
The most obvious problem with wind mills is the initial cost involved. Since many wind plants are built in offshore areas, the cost of transporting the energy to population centers can also be substantial.
Unreliability
Even Though the technology behind the wind mills is simple, in many cases or situations they seem to be unreliable. In unreliable climate patterns the lack of constant availability of wind power is a problem. Due to this, lower production levels are obtained for the applications. Also, damages due to lightening are another problem.
Environmental Impact
Noise pollution is one of the major problems to the society due to windmills. It is said that windmills are hazardous to the migrating birds.
Political Issues
The political issues are another drawback to the use of wind mills. Zoning regulations and safety requirements play a major role to build a wind mill. Tax credits are also an important issue and may affect the price of construction in a positive or negative way.
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