notes India ranks fifth amongst the wind-energy-producing countries of the world after USA, China, Germany and Spain. India's position was 3rd in the World till September 96, thereafter it became 4th upto December 98, 5th upto December 04, it was 4th upto December 08 and now it is 5th again. Estimated potential is around 45000 MW at 50 m above ground level. Exhaustive wind resource assessment has been carried out in 650 stations spread over 27 States in the country. As on date 225 Wind Monitoring stations have indicated wind power density more than 200 W/m2 at 50 m above ground level. Micro Survey of Wind Resource for 97 Wind Monitoring Stations have been completed to know the zone of influence and Wind Power Potential around the stations to meet the requirement of wind energy developers in the country. Windfarms have been installed in 11 States. More than 95% of installed capacity belongs to Private Sector in seven states A good number of wind turbine manufacturers are active in India and producing Wind Electric Generators (WEGs) of rating 225 kW to 2100 kW. A large number of agencies have come up to supply components/spares/ accessories and to provide services like Erection, O&M, Civil & Electrical Construction, Consultancy etc. A large number of water pumping windmills and small aero-generators have been installed in the country. Wind-Solar and Wind-Diesel Hybrid systems have also been installed at a few places. The Central Ministry and several State Nodal Agencies encourage growth of Wind Energy Sector through financial incentives and policy support. The Ministry of New & Renewable Energy (MNRE), Govt. of India has established a Centre for Wind Energy Technology at Chennai with field test station at Kayathar to act as technical focal point for wind power development in the country. Financial assistance for Renewable sources of energy is available through Indian Renewable Energy Development Agency (IREDA), a supporting arm of MNRE, GOI. Figures aand facts Largest Rating of WEG installed 2100 kW, Suzlon Highest Hub Height of WEG installed 85 m, Regen PowerTech 1500 kW Maximum Rotor diameter of WEG installed 88 m, Suzlon 2100 kW Maximum Installation in a State 4875 MW, Tamil Nadu (as on 31 March 2010) Maximum Installed Capacity by a WEG Manufacturer 5255 MW, Suzlon Maximum estimated gross wind power potential in a State 9675 MW, Gujarat Maximum estimated technical wind power potential in a State 3750 MW, Tamil Nadu Maximum extrapolated Mean Annual Wind Power Density of a Site at 50 m height amongst the MNRE notified sites 721 W/m2, Perampukettimedu, Kerala Maximum No. of Wind Monitoring Stations Installed in a State 119 Nos., Maharashtra Highest elevation at which windfarm Established 1100 m.a.s.l. at Vankusawade, Maharashtra Highest elevation at which Wind Monitoring Station Established 3360 m.a.s.l. at Basgo, J&K Highest elevation amongst the MNRE notified sites 1768 m.a.s.l. at B.B. Hills, Karnataka Highest capacity addition in a financial year 1778 MW during the year 2006-07 Highest capacity addition in a financial year by a WEG Manufacturer 929 MW during the year 2007-08, Suzlon Highest capacity addition in a financial year in a State 861 MW during the year 2005-06, Tamil Nadu Largest Private Windfarm Developer MSPL Group of Companies, 191.60 MW Overall average rating of WEGs installed in India as on 31-03-2010 644 kW Overall average rating of WEGs installed in India during 2009-10 932 kW First Concrete Tower for WEG Enercon, 230 kW WEG at Gudimangalam, Dist : Coimbatore First WEG Installed under Demonstration projects 55 kW & 110 kW, Micon make at Mandvi, Gujarat, commissioned on 15.01.1986 First Private Windfarm Developer M/s.Pandian Chemicals, Madurai (T.N) 250 kW WEGs, NEPC-Micon make at Kattadimalai (T.N) commissioned on 28.03.1990. First Wind Monitoring Station Sultanpet (T.N.) established on 28.07.1986 First Wind-Diesel Project Sagar Island (WB), supplied by Auroville Wind Systems for WBREDA First Joint Sector Company M.P. Windfarms Ltd., Bhopal, M.P. (Promoted by Consolidated Energy Consultants Ltd., IREDA & M.P. Urjavikas Nigam Ltd.) formed in the year 1994. First exclusive web-site on wind power programme in India www.windpowerindia.com developed by Consolidated Energy Consultants Ltd., Bhopal in the year 2000. First Directory on wind power programme in India Directory on Indian Wind Power published by Consolidated Energy Consultants Ltd., Bhopal, in the year 2001 What is Wind Power and How Does It Work? Wind Power Generates Clean, Renewable Energy Is Wind Power the Answer? When Bob Dylan first sang Blowin’ in the Wind in the early 1960s, he probably wasn’t talking about wind power as the answer to the world’s ever-increasing need for electricity and sources of clean, renewable energy. But that is what wind has come to represent for millions of people, who see wind power as a better way to generate electricity than plants fueled by coal, hydro (water) or nuclear power. Wind Power Starts with the Sun Wind power is actually a form of solar power, because wind is caused by heat from the sun. Solar radiation heats every part of the Earth’s surface, but not evenly or at the same speed. Different surfaces—sand, water, stone and various types of soil— absorb, retain, reflect and release heat at different rates, and the Earth generally gets warmer during daylight hours and cooler at night. As a result, the air above the Earth’s surface also warms and cools at different rates. Hot air rises, reducing the atmospheric pressure near the Earth’s surface, which draws in cooler air to replace it. That movement of air is what we call wind. Wind Power is Versatile When air moves, causing wind, it has kinetic energy—the energy created whenever mass is in motion. With the right technology, the wind’s kinetic energy can be captured and converted to other forms of energy such as electricity or mechanical power. That’s wind power. Just as the earliest windmills in Persia, China and Europe used wind power to pump water or grind grain, today’s utility-connected wind turbines and multi-turbine wind farms use wind power to generate clean, renewable energy to power homes and businesses. Wind Power is Clean and Renewable Wind power should be considered an important component of any long-term energy strategy, because wind power generation uses a natural and virtually inexhaustible source of power—the wind—to produce electricity. That is a stark contrast to traditional power plants that rely on fossil fuels. And wind power generation is clean; it doesn’t cause air, soil or water pollution. That’s an important difference between wind power and some other renewable energy sources, such as nuclear power, which produces a vast amount of hard-to- manage waste. Wind Power Sometimes Conflicts with Other Priorities One obstacle to increasing worldwide use of wind power is that wind farms must be located on large tracts of land or along coastlines to capture the greatest wind movement. Devoting those areas to wind power generation sometimes conflicts with other priorities, such as agriculture, urban development, or waterfront views from expensive homes in prime locations. The Future Growth of Wind Power As the need for clean, renewable energy increases, and the world more urgently seeks alternatives to finite supplies of oil, coal and natural gas, priorities will change. And as the cost of wind power continues to decline, due to technology improvements and better generation techniques, wind power will become increasingly feasible as a major source of electricity and mechanical power. HOW DOES SOLAR NAVIGATOR BENEFIT FROM WIND TURBINES ? A wind turbine is a machine that converts the kinetic energy in wind into mechanical energy. If the mechanical energy is used directly by machinery, such as a pump or grinding stones, the machine is usually called a windmill. If the mechanical energy is converted to electricity, the machine is called a wind generator, or more commonly a wind turbine (wind energy converter WEC). A wind turbine is old technology applied to meet new challenges. We need to adapt and use every means at our disposal to combat global warming and carbon dioxide build up, yet still provide energy for our modern (lavish) lifestyles. Whatever your views as to the use of alternative energy, as an engineering student you will probably want to know how these beautiful machines work. I know I have always been fascinated by them. NK Find Out How the Turbine Works This aerial view of a wind power plant shows how a group of wind turbines can make electricity for the utility grid. The electricity is sent through transmission and distribution lines to homes, businesses, schools, and so on. These three-bladed wind turbines are operated "upwind," with the blades facing into the wind. The other common wind turbine type is the two-bladed, downwind turbine. So how do wind turbines make electricity? Simply stated, a wind turbine works the opposite of a fan. Instead of using electricity to make wind, like a fan, wind turbines use wind to make electricity. The wind turns the blades, which spin a shaft, which connects to a generator and makes electricity. Utility-scale turbines range in size from 50 to 750 kilowatts. Single small turbines, below 50 kilowatts, are used for homes, telecommunications dishes, or water pumping. Look at the Wind Turbine Close Up Wind turbines can be separated into two types based on the axis about which the turbine rotates. Turbines that rotate around a horizontal axis are more common. Vertical-axis turbines are less frequently used. Wind turbines can also be classified by the location in which they are to be used. Onshore, offshore, or even aerial wind turbines have unique design characteristics. Wind turbines may also be used in conjunction with a solar collector to extract the energy due to air heated by the Sun and rising through a large vertical solar updraft tower. Horizontal axis Horizontal-axis wind turbines (HAWT) have the main rotor shaft and electrical generator at the top of a tower, and must be pointed into the wind. Small turbines are pointed by a simple wind vane, while large turbines generally use a wind sensor coupled with a servo motor. Most have a gearbox, which turns the slow rotation of the blades into a quicker rotation that is more suitable for generating electricity. Since a tower produces turbulence behind it, the turbine is usually pointed upwind of the tower. Turbine blades are made stiff to prevent the blades from being pushed into the tower by high winds. Additionally, the blades are placed a considerable distance in front of the tower and are sometimes tilted up a small amount. Downwind machines have been built, despite the problem of turbulence, because they don't need an additional mechanism for keeping them in line with the wind, and because in high winds, the blades can be allowed to bend which reduces their swept area and thus their wind resistance. Because turbulence leads to fatigue failures and reliability is so important, most HAWTs are upwind machines. Doesburger windmill, Ede, The Netherlands There are several types of HAWT: These four- (or more) bladed squat structures, usually with wooden shutters or fabric sails, were developed in Europe. These windmills were pointed into the wind manually or via a tail-fan and were typically used to grind grain. In the Netherlands they were also used to pump water from low-lying land, and were instrumental in keeping its polders dry. Windmills were also located throughout the USA, especially in the Northeastern region. Modern Rural Windmills These windmills, invented in 1876 by Griffiths Bros and Co (Australia), were used by Australian and later American farmers to pump water and to generate electricity. They typically had many blades, operated at tip speed ratios (defined below) not better than one, and had good starting torque. Some had small direct-current generators used to charge storage batteries, to provide a few lights, or to operate a radio receiver. The American rural electrification connected many farms to centrally-generated power and replaced individual windmills as a primary source of farm power in the 1950's. Such devices are still used in locations where it is too costly to bring in commercial power. Wind turbines near Aalborg, Denmark A standard doorway can be seen at the base of the pylon for scale Common modern wind turbines Usually three-bladed, sometimes two-bladed or even one-bladed (and counterbalanced), and pointed into the wind by computer-controlled motors. The rugged three-bladed turbine type has been championed by Danish turbine manufacturers. These have high tip speeds of up to 6x wind speed, high efficiency, and low torque ripple which contributes to good reliability. This is the type of turbine that is used commercially to produce electricity. The blades are usually colored light gray to blend in with the clouds and range in length from 20 to 40 metres (60 to 120 feet) or more. Cyclic stresses and vibration Cyclic stresses fatigue the blade, axle and bearing material, and were a major cause of turbine failure for many years. Because wind velocity often increases at higher altitudes, the backward force and torque on a horizontal-axis wind turbine (HAWT) blade peaks as it turns through the highest point in its circle. The tower hinders the airflow at the lowest point in the circle, which produces a local dip in force and torque. These effects produce a cyclic twist on the main bearings of a HAWT. The combined twist is worst in machines with an even number of blades, where one is straight up when another is straight down. To improve reliability, teetering hubs have been used which allow the main shaft to rock through a few degrees, so that the main bearings do not have to resist the torque peaks. When the turbine turns to face the wind, the rotating blades act like a gyroscope. As it pivots, gyroscopic precession tries to twist the turbine into a forward or backward somersault. For each blade on a wind generator's turbine, precessive force is at a minimum when the blade is horizontal and at a maximum when the blade is vertical. This cyclic twisting can quickly fatigue and crack the blade roots, hub and axle of the turbine. Vertical axis 12 m Windmill with rotational sails in the Osijek CroatiaVertical-axis wind turbines (or VAWTs) have the main rotor shaft running vertically. Key advantages of this arrangement are that the generator and/or gearbox can be placed at the bottom, near the ground, so the tower doesn't need to support it, and that the turbine doesn't need to be pointed into the wind. Drawbacks are usually pulsating torque that can be produced during each revolution and drag created when the blade rotates into the wind. It is also difficult to mount vertical-axis turbines on towers, meaning they must operate in the often slower, more turbulent air flow near the ground, resulting in lower energy extraction efficiency. Windmill with rotational sails This is a new invention. This windmillstarts making electricity above a windspeed of 2m/s. Its sails contract and expand as the wind speed changes. This windmill has three sails of variable surface area. The speed is controlled through a magnetic rev counter that expands or contracts the sails according to windspeed. A (microprocessor type) control unit controls the sails either manually or automatically. In case of a control unit failure, strong winds would tear the sails, but the frame would remain intact. Neo-AeroDynamic This has an airfoil base designed to harness the kinetic energy of the fluid flow via an artificial current around its center. It is differentiated from others by its capability to unitize most of the air mass passing through redirecting it to flow over the upper chamber of the airfoils, and causing a lift force all around. It is applicable not only to wind, but also to a variety of hydroelectric applications, including free-flow (rivers, creeks), tidal, oceanic currents and wave motion, via ocean wave surface currents. Views of Hydro model, :Portable aero model 30 m Darrieus wind turbine in the Magdalen Islands Darrieus wind turbine "Eggbeater" turbines. They have good efficiency, but produce large torque ripple and cyclic stress on the tower, which contributes to poor reliability. Also, they generally require some external power source, or an additional Savonius rotor, to start turning, because the starting torque is very low. The torque ripple is reduced by using 3 or more blades which results in a higher solidity for the rotor. Solidity is measured by blade area over the rotor area. Newer Darrieus type turbines are not held up by guy wires but have an external superstructure connected to the top bearing. Giromill A type of Darrieus turbine, these lift-type devices have vertical blades. The cycloturbine variety have variable pitch to reduce the torque pulsation and are self-starting . The advantages of variable pitch are: high starting torque; a wide, relatively flat torque curve; a lower blade speed ratio; a higher coefficient of performance; more efficient operation in turbulent winds; and a lower blade speed ratio which lowers blade bending stresses. Straight, V, or curved blades may be used. Savonius wind turbine These are drag-type devices with two- (or more) scoops that are used in anemometers, the Flettner vents (commonly seen on bus and van roofs), and in some high-reliability low-efficiency power turbines. They always self-starting if there are at least three scoops. They sometimes have long helical scoops to give a smooth torque. The Banesh rotor and especially the Rahai rotor improve efficiency with blades shaped to produce significant lift as well as drag. Windstar turbines These lift-type devices made by Wind Harvest have straight, extruded aluminum blades attached at each end to a central rotating shaft and are operated as Linear Array Vortex Turbine Systems (LAVTS). Vertical-axis rotors each with their own 50-75kW generator are placed in three to any number of rotors in linear arrays with each rotor’s blades passing within two feet of its neighbor. In this configuration, the center rotors gain an increase in output and efficiency (reaching the high efficiencies of HAWTs). This increased efficiency is protected under patent (number 6784566) as the "vortex effect". Each rotor unit has a dual braking system of pneumatic disc brakes and blade pitch. The newest Windstar LAVTS stand 50 feet tall, have 1500 and 3000 square feet of swept area per rotor and are designed to be placed in the turbulent winds within the understory of wind farms. Offshore Offshore wind turbines near CopenhagenOffshore wind development zones are generally considered to be ten kilometers or more from land. Offshore wind turbines are less obtrusive than turbines on land, as their apparent size and noise can be mitigated by distance. Because water has less surface roughness than land (especially deeper water), the average wind speed is usually considerably higher over open water. Capacity factors (utilisation rates) are considerably higher than for onshore and near-shore locations which allows offshore turbines to use shorter towers, making them less visible. In stormy areas with extended shallow continental shelves (such as Denmark), turbines are practical to install — Denmark's wind generation provides about 25-30% of total electricity demand in the country, with many offshore windfarms. Denmark plans to increase wind energy's contribution to as much as half of its electrical supply. Locations have begun to be developed in the North American Great Lakes - with one project by Trillium Power approximately 20 km from shore and over 700 MW in size. Ontario, Canada is aggressively pursuing wind power development and has many onshore wind farms and several proposed near- shore locations but presently only one offshore development. In most cases offshore environment is more expensive than onshore. Offshore towers are generally taller than onshore towers once the submerged height is included, and offshore foundations are more difficult to build and more expensive. Power transmission from offshore turbines is generally through undersea cable, which is more expensive to install than cables on land, and may use high voltage direct current operation if significant distance is to be covered — which then requires yet more equipment. The offshore environment can also be corrosive and abrasive in salt water locations but locations such as the Great Lakes are in fresh water and do not have many of the issues found in the ocean or sea. Repairs and maintenance are usually much more difficult, and generally more costly, than on onshore turbines. Offshore wind turbines are outfitted with extensive corrosion protection measures like coatings and cathodic protection however some of these measures may not be required in fresh water locations. While there is a significant market for small land-based windmills, offshore wind turbines have recently been and will probably continue to be the largest wind turbines in operation, because larger turbines allow for the spread of the high fixed costs involved in offshore operation over a greater quantity of generation, reducing the average cost. For similar reasons, offshore wind farms tend to be quite large—often involving over 100 turbines—as opposed to onshore wind farms which can operate competitively even with much smaller installations. There are some conceptual designs that might make use of the unique offshore environment. For example, a floating turbine might orient itself downwind of its anchor, and thus avoid the need for a yawing mechanism. One concept for offshore turbines has them generate rain, instead of electricity. The turbines would create a fine aerosol, which is envisioned to increase evaporation and induce rainfall, hopefully on land. Near-shore Near-shore turbines are generally considered to be within a zone that is on land three kilometers of a shoreline and on water within ten kilometers of land. Wind speeds in these zones share wind speed characteristics of both onshore wind and offshore wind. Issues that are shared within near-shore wind development zones are ornithological (including bird migration and nesting), aquatic habitat, transportation (including shipping and boating) and visual aesthetics. Sea shores also tend to be windy areas and good sites for turbine installation, because a primary source of wind is convection from the differential heating and cooling of land and sea over the course of day and night. Winds at sea level carry somewhat more energy than winds of the same speed in mountainous areas because the air at sea level is denser. Near-shore wind farm siting can sometimes be highly controversial as coastal sites are often picturesque and environmentally sensitive (for instance, having substantial bird life). Onshore Wind turbines near Walla Walla in WashingtonOnshore turbine installations in hilly or mountainous regions tend to be on ridgelines generally three kilometers or more inland from the nearest shoreline. This is done to exploit the topographic acceleration where the hill or ridge causes the wind to accelerate as it is forced over it. The additional wind speeds gained in this way make large differences to the amount of energy that is produced. Great attention must be paid to the exact positions of the turbines (a process known as micro-siting) because a difference of 30 m can sometimes mean a doubling in output. Local winds are often monitored for a year or more with anemometers and detailed wind maps constructed before wind generators are installed. For smaller installations where such data collection is too expensive or time consuming, the normal way of prospecting for wind-power sites is to directly look for trees or vegetation that are permanently "cast" or deformed by the prevailing winds. Another way is to use a wind-speed survey map, or historical data from a nearby meteorological station, although these methods are less reliable. Wind farm siting can sometimes be controversial, particularly as the hilltop, often coastal sites preferred are often picturesque and environmentally sensitive (for instance, having substantial bird life). Local residents in a number of potential sites have strongly opposed the installation of wind farms, and political support has resulted in the blocking of construction of some installations. Turbine blade at Southampton docks - Nelson Kruschandl in foreground Turbine design and construction Advantages of vertical wind turbines Easier to maintain because most of their moving parts are located near the ground. This is due to the vertical wind turbine’s shape. The airfoils or rotor blades are connected by arms to a shaft that sits on a bearing and drives a generator below, usually by first connecting to a gearbox. As the rotor blades are vertical, a yaw device is not needed, reducing the need for this bearing and its cost. Vertical wind turbines have a higher airfoil pitch angle, giving improved aerodynamics while decreasing drag at low and high pressures. Mesas, hilltops, ridgelines and passes can have higher and more powerful winds near the ground than up high because of the speed up effect of winds moving up a slope or funneling into a pass combining with the winds moving directly into the site. In these places, VAWTs placed close to the ground can produce more power than HAWTs placed higher up. Low height useful where laws do not permit structures to be placed high. Smaller VAWTs can be much easier to transport and install. Does not need a free standing tower so is much less expensive and stronger in high winds that are close to the ground. Usually have a lower Tip-Speed ratio so less likely to break in high winds. Disadvantages of vertical wind turbines Most VAWTs produce energy at only 50% of the efficiency of HAWTs in large part because of the additional drag that they have as their blades rotate into the wind. This can be overcome by using structures to funnel more and align the wind into the rotor (e.g. "stators" on early Windstar turbines) or the "vortex" effect of placing straight bladed VAWTs closely together (e.g. Patent # 6784566). There may be a height limitation to how tall a vertical wind turbine can be built and how much sweep area it can have. Most VAWTS need to be installed on a relatively flat piece of land and some sites could be too steep for them but are still usable by HAWTs. Most VAWTs have low starting torque. A VAWT that uses guyed wires to hold it in place puts stress on the bottom bearing as all the weight of the rotor is on the bearing. Guyed wires attached to the top bearing increase downward thrust in wind gusts. Solving this problem requires a superstructure to hold a top bearing in place to eliminate the downward thrusts of gust events in guyed wired models. Advantages of horizontal wind turbines Blades are to the side of the turbine's center of gravity, helping stability. Ability to wing warp, which gives the turbine blades the best angle of attack. Allowing the angle of attack to be remotely adjusted gives greater control, so the turbine collects the maximum amount of wind energy for the time of day and season. Ability to pitch the rotor blades in a storm, to minimize damage. Tall tower allows access to stronger wind in sites with wind shear. In some wind shear sites, every ten meters up, the wind speed can increase by 20% and the power output by 34%. Tall tower allows placement on uneven land or in offshore locations. Can be sited in forests above the treeline. Most are self-starting. Can be cheaper because of higher production volume, larger sizes and, in general higher capacity factors and efficiencies. Disadvantages of horizontal wind turbines HAWTs have difficulty operating in near ground, turbulent winds because their yaw and blade bearing need smoother, more laminar wind flows. The tall towers and long blades (up to 180 feet long) are difficult to transport on the sea and on land. Transportation can now cost 20% of equipment costs. Tall HAWTs are difficult to install, needing very tall and expensive cranes and skilled operators. Supply of HAWTs is less than demand and between 2004 and 2006, turbine prices increased up to 60%. At the end of 2006, all major manufacturers were booked up with orders through 2008. The FAA has raised concerns about tall HAWTs effects on radar in proximity to air force bases. Their height can create local opposition based on impacts to viewsheds. Offshore towers can be a navigation problem and must be installed in shallow seas. HAWTs can't be floated on barges. Downwind variants suffer from fatigue and structural failure caused by turbulence. Horizontal-axis wind turbine aerodynamics The aerodynamics of a horizontal-axis wind turbine are complex. The air flow at the blades is not the same as the airflow far away from the turbine. The very nature of the way in which energy is extracted from the air also causes air to be deflected by the turbine. In addition, the aerodynamics of a wind turbine at the rotor surface include effects that are rarely seen in other aerodynamic fields. Special wind turbines One E-66 wind turbine at Windpark Holtriem, Germany carries an observation deck, open for visitors to see. Another turbine of the same type, with an observation deck, can be located in Swaffham, England. A series of floating wind turbines utilizing the Magnus Effect are in development in Canada by Magenn Power. They deliver power to the ground by a tether system. History The world's first megawatt wind turbine on Grandpa's Knob, Castleton, VermontWind machines were used for grinding grain in Persia as early as 200 B.C. This type of machine was introduced into the Roman Empire by 250 A.D. By the 14th century Dutch windmills were in use to drain areas of the Rhine River delta. In Denmark by 1900 there were about 2500 windmills for mechanical loads such as pumps and mills, producing an estimated combined peak power of about 30 MW. The first windmill for electricity production was built in Cleveland, Ohio by Charles F Brush in 1888, and in 1908 there were 72 wind-driven electric generators from 5 kW to 25 kW. The largest machines were on 24 m (79 ft) towers with four-bladed 23 m (75 ft) diameter rotors. By the 1930s windmills were mainly used to generate electricity on farms, mostly in the United States where distribution systems had not yet been installed. In this period, high-tensile steel was cheap, and windmills were placed atop prefabricated open steel lattice towers. A forerunner of modern horizontal- axis wind generators was in service at Yalta, USSR in 1931. This was a 100 kW generator on a 30 m (100 ft) tower, connected to the local 6.3 kV distribution system. It was reported to have an annual load factor of 32 per cent, not much different from current wind machines. Records The world's largest turbines are manufactured by the Northern German companies Enercon and REpower. The Enercon E112 delivers up to 6 MW , has an overall height of 186 m (610 ft) and a diameter of 114 m (374 ft). The REpower 5M delivers up to 5 MW , has an overall height of 183 m (600 ft) and a diameter of 126 m (413 ft). The turbine closest to the North Pole is a Nordex N-80 in Havoygalven near Hammerfest, Norway. The ones closest to the South Pole are two Enercon E-30 in Antarctica, used to power the Australian Research Division's Mawson Station. Offshore wind farm off Danish coast Wind Turbine Glossary Anemometer: Measures the wind speed and transmits wind speed data to the controller. Blades: Most turbines have either two or three blades. Wind blowing over the blades causes the blades to "lift" and rotate. Brake: A disc brake which can be applied mechanically, electrically, or hydraulically to stop the rotor in emergencies. Controller: The controller starts up the machine at wind speeds of about 8 to 16 miles per hour (mph) and shuts off the machine at about 65 mph. Turbines cannot operate at wind speeds above about 65 mph because their generators could overheat. Gear box: Gears connect the low-speed shaft to the high-speed shaft and increase the rotational speeds from about 30 to 60 rotations per minute (rpm) to about 1200 to 1500 rpm, the rotational speed required by most generators to produce electricity. The gear box is a costly (and heavy) part of the wind turbine and engineers are exploring "direct-drive" generators that operate at lower rotational speeds and don't need gear boxes. Generator: Usually an off-the-shelf induction generator that produces 60-cycle AC electricity. High-speed shaft: Drives the generator. Low-speed shaft: The rotor turns the low-speed shaft at about 30 to 60 rotations per minute. Nacelle: The rotor attaches to the nacelle, which sits atop the tower and includes the gear box, low- and high-speed shafts, generator, controller, and brake. A cover protects the components inside the nacelle. Some nacelles are large enough for a technician to stand inside while working. Pitch: Blades are turned, or pitched, out of the wind to keep the rotor from turning in winds that are too high or too low to produce electricity. Rotor: The blades and the hub together are called the rotor. Tower: Towers are made from tubular steel (shown here) or steel lattice. Because wind speed increases with height, taller towers enable turbines to capture more energy and generate more electricity. Wind direction: This is an "upwind" turbine, so-called because it operates facing into the wind. Other turbines are designed to run "downwind", facing away from the wind. Wind vane: Measures wind direction and communicates with the yaw drive to orient the turbine properly with respect to the wind. Yaw drive: Upwind turbines face into the wind; the yaw drive is used to keep the rotor facing into the wind as the wind direction changes. Downwind turbines don't require a yaw drive, the wind blows the rotor downwind. Yaw motor: Powers the yaw drive. ADVANTAGES OF WIND POWER: 1. The wind is free and with modern technology it can be captured efficiently. 2. Once the wind turbine is built the energy it produces does not cause green house gases or other pollutants. 3. Although wind turbines can be very tall each takes up only a small plot of land. This means that the land below can still be used. This is especially the case in agricultural areas as farming can still continue. 4. Many people find wind farms an interesting feature of the landscape. 5. Remote areas that are not connected to the electricity power grid can use wind turbines to produce their own supply. 6. Wind turbines have a role to play in both the developed and third world. 7. Wind turbines are available in a range of sizes which means a vast range of people and businesses can use them. Single households to small towns and villages can make good use of range of wind turbines available today. DISADVANTAGES OF WIND POWER: 1. The strength of the wind is not constant and it varies from zero to storm force. This means that wind turbines do not produce the same amount of electricity all the time. There will be times when they produce no electricity at all. 2. Many people feel that the countryside should be left untouched, without these large structures being built. The landscape should left in its natural form for everyone to enjoy. 3. Wind turbines are noisy. Each one can generate the same level of noise as a family car travelling at 70 mph. 4. Many people see large wind turbines as unsightly structures and not pleasant or interesting to look at. They disfigure the countryside and are generally ugly. 5. When wind turbines are being manufactured some pollution is produced. Therefore wind power does produce some pollution. 6. Large wind farms are needed to provide entire communities with enough electricity. For example, the largest single turbine available today can only provide enough electricity for 475 homes, when running at full capacity. How many would be needed for a town of 100 000 people? erate the same level of noise as a family car travelling at 70 mph. 4. Many people see large wind turbines as unsightly structures and not pleasant or interesting to look at. They disfigure the countryside and are generally ugly. 5. When wind turbines are being manufactured some pollution is produced. The refore wind powe r does produce some pollution. 6. Large wind farms are needed to provide entire communities with enough electricity. For example, the largest single turbine available today can only provide enough electricity for 475 homes, when running at full capacity. How many would be needed for a town of 100 000 people?