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Large, modern wind turbines have become very quiet; the swishing sound of rotor blades is usually masked completely by wind noise in the leaves of trees or shrubs. There are two potential sources of noise from a wind turbine: Mechanical noise from the gearbox or generator, and Aerodynamic noise from the rotor blades.

Mechanical noise has virtually disappeared from modern wind turbines. This is due to better engineering with more concern about avoiding vibrations. Other technical improvements include elastically dampened fastenings and couplings of the major components, and to a certain extent sound insulation. Finally, the basic components themselves, including gearboxes where used, have developed considerably over the years. Modern wind turbine gearboxes use "soft" gearwheels, i.e. toothed wheels with hardened surfaces and relatively elastic interiors.

Aerodynamic noise, i.e. the "swish" sound of the rotor blades passing the tower of a wind turbine, primarily arises at the tip and the back edge of the rotor blade. The higher the rotational speed, the louder the sound. Aerodynamic noise has been cut dramatically during the past ten years due to better design of rotor blades (particularly blade tips and back edges. Pure tones can be very annoying to a listener, while "white noise" is hardly noticed at all. Quality rotor blade manufacturers take extreme care to ensure a smooth surface, which is important to avoid pure tones. Likewise, manufacturers who install wind turbines take great care to ensure that the rotor blades are not damaged when a wind turbine is being installed.

Can a wind turbine ever recover the energy spent in producing maintaining, and servicing it? Yes. Wind turbines use only the energy from the moving air to generate electricity. A modern wind turbine in an average location will annually displace 1 tonne of carbon dioxide from other electricity sources per kWh of energy produced, i.e. usually coal fired power stations. The energy produced by a wind turbine throughout its 20-year lifetime (in an average location) is up to eighty times larger than the amount of energy used to build, maintain, operate, dismantle, and scrapping it again. In other words, on average it takes only several months for a wind turbine to recover all the energy required to build and operate it.

Wind resources are plentiful. Wind will not run out. Australia is one of the countries that are planning for substantial amounts of electricity consumption to be provided by wind energy. The wind resources along the coastal waters around southern Australia alone could theoretically provide all of Australia’s electricity requirements.

Wind Turbines have grown dramatically in size and power output. A typical commercial Danish wind turbine of 1980 vintage had a 26 kW generator and a rotor diameter of 10.5 metres. A modern commercial wind turbine has a rotor diameter of up to 80 metres and a 4,000 kW generator.

Wind energy has become the least expensive renewable energy technology in existence. Since the energy contents of the wind varies with the cube of the wind speed, the economics of wind energy depends heavily on how windy the site is.

Wind energy leaves no harmful emissions or residue in the environment. Wind turbines only produce energy when the wind is blowing, and energy production varies with each gust of wind. The variable forces acting on a wind turbine throughout its expected lifetime could be expected to exert significant wear and tear on the machine. Turbines therefore have to be built to very exacting industrial standards.

Wind turbines obviously have to be highly visible, since they must be located in windy, open terrain to be economic. Some people prefer lattice towers instead of tubular steel towers, because they make the tower itself less visible. There are no objective guidelines, however. Much depends on the landscape and the match with architectural traditions in the area. Since wind turbines are visible in any case, it is usually a good idea to use them to emphasise natural or man-made features in the landscape. Like other man-made structures, well-designed wind turbines can give an interesting perspective and furnish the landscape with new architectural values. Wind turbines have been a feature of the cultural landscape of Europe for more than 800 years. Deer and cattle habitually graze under wind turbines, and sheep seek shelter around them. While birds tend to collide with man-made structures such as electrical power lines, masts, or buildings, they are very rarely affected directly by wind turbines. (A recent Danish study suggests that the impact of overhead power lines leading electricity away from wind farms have far greater impact on bird mortality than the wind farms themselves, in fact falcons are nesting and breeding in cages attached to two Danish wind turbines).
Studies from the Netherlands, Denmark, and the US show that the total impact on birds from wind turbines is negligible compared to the impact from road traffic.

The energy content of the wind varies with the cube, (i.e. the third power) of the wind speed. Twice as much wind yields eight times as much energy. The terrain surface, its contours, and even the presence of buildings, trees, plants, and bushes affect the local wind speed. Very rough terrain or nearby large obstacles may create turbulence, which may decrease energy production and increase wear and tear on the turbine. Calculating the annual energy production from a wind turbine is quite a complex task: It requires detailed maps of the area (up to three kilometres in the prevailing wind directions), and accurate meteorological wind measurements for at least a one-year period. Qualified advice from experienced manufacturers or consulting firms is therefore essential for the economic success of a wind project.

Although wind conditions near seashores tend to be ideal for wind projects, it is indeed possible to find highly economic inland areas for wind turbines. As the wind passes over a hill, or through a mountain pass, it becomes compressed and speeds up significantly. Rounded hilltops with a wide view in the prevailing wind directions are therefore ideal as wind turbine sites. Tall wind turbine towers are a way of increasing the energy yield of a wind turbine, since wind speed usually increases significantly with height above ground level. In low wind areas, manufacturers may be able to supply special wind turbine versions with large rotors compared to the size of the electrical generator. Such machines will reach peak production at relatively low wind speeds, although they will waste some of the energy potential of high winds. Manufacturers are increasingly optimising their machines to local wind conditions worldwide.

Wind energy can be used in all sorts of applications - from small battery chargers in lighthouses or remote dwellings to industrial scale turbines of 1.8 megawatts capable of supplying the equivalent of the electricity consumption of over one thousand households. Other interesting and highly economic applications include wind energy used in combination with diesel powered backup generators in several small, isolated electrical grids throughout the world. Desalination plants in island communities in the Atlantic and the Mediterranean Sea is another recent application.

Opinion polls in several European countries, Denmark, Germany, Holland, and the UK, show that more than 70 per cent of the population is in favour of using more wind energy in the electricity supply. People who live near wind turbines are on average even more favourable towards wind energy, with a score of more than 80 per cent in favour of wind energy. In Denmark, more than 100,000 families own shares in one of the 5,200 modern wind turbines scattered throughout the country. Private individuals or wind co-operatives own more than 80 per cent of the wind power capacity in Denmark.

The tower of the wind turbine carries the generator and the rotor/blades. Generally, it is an advantage to have a high tower, since wind speeds increase farther away from the ground. A typical modern turbine will have a tower of 20 to 30 metres Towers may be either tubular towers or lattice towers. Guyed tubular towers are usually the preferred tower type for domestic and small systems, they do not attract birds as there is no-where for them to perch, they only require a 4 wheel drive vehicle to erect, and they are usually the most cost-effective option.

 

An excellent site for more information on wind power is the Danish Wind turbine Manufacturers Association website. This site has no interest in any particular brands, and is seen as one of the best sources of information on wind power anywhere in the world, for beginners and professionals alike.