What is a wind turbine?
A wind turbine transforms the kinetic energy of the wind into mechanical or electrical energy. Wind turbines consist of a foundation, a tower, a nacelle and a rotor. The foundation prevents the turbine from falling over; it is usually 13m across and 1-2m deep. The tower holds up the rotor and a nacelle (or box). The nacelle contains large primary components such as the main axle, gearbox, generator, transformer and control system. The rotor includes the blades and the hub, which holds them in position as they turn. Most commercial wind turbines have three rotor blades. The length of the blades can be more than 44 metres.
What are wind turbines made of?
The towers are mostly tubular and made of steel or concrete, generally painted white. The blades are made of glass-fibre reinforced polyester. They are white because it is inconspicuous under most lighting conditions. The finish is matt, to reduce reflected light.
How does a wind turbine generate electricity?
The wind passes over the blades creating lift, which causes the rotor to turn. The blades turn a low-speed shaft inside the nacelle: gears connect the low speed shaft of the rotor with a high speed shaft that drives a generator. Here, the slow rotation speed of the blades is increased to the high speed of generator revolution. The rapidly spinning shaft drives the generator to produce electric energy. Electricity from the generator passes through to a transformer which converts it to the correct voltage for the distribution system. The electricity is then transmitted via the electricity network.
How much electricity does a wind turbine generate?
The output of a wind turbine depends on the turbine's size and the wind's speed through the rotor. Wind turbines manufactured today have power ratings ranging from 250 watts to 7 MW.
What is the wind?
The Earth is surrounded by the atmosphere, which is made up of air. Air is a mixture of gas, and solid and liquid particles. Energy from the sun heats up the atmosphere and the Earth unevenly. Cold air contains more air particles than warm air. Cold air is therefore heavier and sinks down through the atmosphere, creating high pressure areas. Warm air rises through the atmosphere, creating low pressure areas. The air tries to balance out the low and high pressure areas – air particles move from areas of high pressure (cold air) to areas of low pressure (warm air). This movement of air is known as the wind.
The wind is also influenced by the movement of the Earth. As it turns on its axis the air does not travel directly from areas of higher pressure to areas of lower pressure. Instead, the air is pushed to the west in the northern hemisphere and to the east in the southern hemisphere. This is known as the Coriolis force.
The Earth’s surface is marked with trees, buildings, lakes, sea, hills and valleys, all of which also influence the wind’s direction and speed. For example, where warm land and cool sea meet, the difference in temperature creates thermal effects, which causes local sea breezes.
How can wind be measured?
Wind is usually measured by its speed and direction. Wind atlases show the distribution of wind speeds on a broad scale, giving a graphical representation of mean wind speed (for a specified height) across an area. They are compiled by local meteorological station measurements or other wind-related recorded data. Traditionally, wind speed is measured by anemometers – usually three cups that capture the wind rotating around a vertical axis. The wind direction is measured with weather vanes.
After measuring wind data for at least one year, the mean annual wind speed can be correlated to a long-term reference point to calculate mean wind speed. Wind speed and wind direction statistics are visualised in a wind rose, showing the statistical repartition of wind speed per direction.
Wind source maps show the best sites to locate wind farms according to the best wind resources. They also provide further information on how the turbines should be positioned in relation to each other and what the distance between the turbines should be.
How fast do the blades turn?
The blades rotate at anything between 15-20 revolutions per minute at constant speed. For more information, visit: http://ewea.org/index.php?id=1884.
How long does a wind turbine work for?
Wind turbines can carry on generating electricity for 20-25 years. Over their lifetime they will be running continuously for as much as 120,000 hours. After this time they may be refurbished.
How efficient are wind turbines?
Maximum energy which a wind turbine can extract from the wind blowing across is just under 60%. For more information, visit: http://ewea.org/index.php?id=1884.
What are a wind turbine's lifetime emissions?
Wind turbines produce no greenhouse gas emissions during their operation. It takes a turbine just three to six months to produce the amount of energy that goes into its manufacture, installation, operation, maintenance and decommissioning after its 20-25 year lifetime. During its lifetime a wind turbine delivers up to 80-100 times more energy than is used in its production, maintenance and scrapping. Wind energy has the lowest lifecycle emissions of all energy production technologies. For more information, visit: http://ewea.org/index.php?id=1884.
How are wind farms designed?
There are many factors at play when designing a wind farm. Ideally, the area should be as wide and open as possible in the prevailing wind direction, with few obstacles. The turbines need to be easily accessible for maintenance and repair work when needed.
Noise levels can be calculated so the wind farm is compatible with the levels of sound stipulated in relevant legislation. The turbine supplier defines the minimum turbine spacing, taking into account the effect one turbine can have on others nearby – the ‘wake effect’. Then, the right type of turbine must be chosen. This depends on the wind conditions and landscape features of the location, local/national rules such as on turbine height, noise levels and nature conservation, the risk of extreme events such as earthquakes, how easy it is to transport the turbines to the site and the local availability of cranes.
For acoustic studies conducted in wind farms in Australia, please review the study1 conducted by Sonus Pty Ltd, an acoustic consulting firm, which found that "the infrasound generated by wind turbines is well below established guideline perception thresholds".
1 - "Infrasound Measurement from Wind Farms and Other Sources" Prepared for Pacific Hydro LTD, Sonus Pty LTD, November 2010.
How long does it take to construct a wind farm?
Construction time is relatively short – a 10 MW wind farm can easily be built in two months. A larger 50 MW wind farm can be ready in 18 months to three years. It takes 2-3 years to develop, and 1-2 years to build.
How much does it cost to build a wind farm?
The capital cost of the WTG typically accounts for 75% of the costs and is paid upfront. According to the European Wind Energy Association and the Global Wind Energy Association, the cost of installing wind turbines is between $1.5 to 2.5 million per MW. For more information, visit: http://ewea.org/index.php?id=1884 and http://www.gwec.net/index.php?id=180.
Why do turbines sometimes stand still?
There are a number of reasons why turbines are not always spinning:
- Turbines have to be stopped for scheduled maintenance, for repairing components or if there is a failure that needs to be checked.
- Another reason can be too little or too much wind: if the wind is too strong, the turbine needs to be shut down because it could be damaged.
- When electricity demand is low, then electricity from wind turbines is not needed and they switch off.
What are the environmental benefits of wind energy?
Wind energy emits no toxic substances such as mercury and air pollutants like smog-creating nitrogen oxides, acid rain-forming sulphur dioxide and particulate deposits. These pollutants can trigger cancer, heart disease, asthma and other respiratory diseases, can acidify terrestrial and aquatic ecosystems, and corrode buildings. Wind energy creates no radioactive waste or water pollution.
What is the outlook for global wind energy industry?
The Global Wind Energy Council forecasts that the wind energy sector will grow at an average rate of 19.4% pa between 2010 and 2015. It forecasts that a total of 459 000 MW of wind energy capacity will be installed by the end of 2015, an increase of 133% from the 197,000 MW of installed capacity at the end of 2010.
Asia is expected to be the fastest growing region in the world, driven mainly by China, which is expected to continue the rapid up-scaling of its wind energy capacity. Wind energy development in North America, particularly the US, is also expected to grow strongly, supported by a package of measures agreed by the US Congress and the prospect of a national emissions trading scheme.
Europe will continue to have the largest installed capacity, as a region, up until 2013, driven by large scale offshore developments and growth from the less mature European nations.
For more information, please visit: Outlook for Global Wind Energy Industry.
How is electricity transported?
It is important to distinguish between the financial aspects and the physical National Electricity Market. The flow of electricity around the network does not care about contracts. Electricity transportation is governed by physical laws.
When an appliance is switched on, power is instantly transmitted from a power station to the appliance. Although this occurs instantaneously, a specific sequence of events takes place to ensure the delivery of the required electricity.
Electricity often travels long distances to reach the point where it is required because the sites where electricity is generated are often in remote areas where cheap fuel resources are abundant. During the transportation process, a percentage of electricity is always lost through electrical resistance, which heats up electrical equipment (such as conductors and transformers) along the way. To reduce the amount of electricity lost, a transformer at the generating plant converts the electricity from low to high voltage (which is more efficient way to transport large amounts of electricity). Transmission lines then transport bulk supplies of power from generating sites to locations closer to consumers.
At these locations, a substation transformer converts the high voltage electricity to lower voltage for distribution. Distribution lines carry low voltage electricity to consumers who access it through the power outlets in homes, offices and factories. The distribution network has more power line than the transmission network. This is because transmission lines can carry a large anount of power that will then require many distribution lines to take to consumers.
What is the grid and how does it work?
Electricity is distributed to the consumers via the grid – the physical infrastructure of the electricity network. The grid is made up of transmission and distribution networks. The transmission network – made up of the cables and pylons you see dotting the countryside – moves electrical power with a high voltage over long distances, and sometimes across international boundaries. The consumers are connected to the distribution system, which has a medium voltage level.
What is a substation?
The substation is the link between the transmission and distribution network, where the power is stepped down in voltage from the transmission to the distribution level. Once it reaches its final destination, the power is stepped down again to the required local level.
Are wind turbines noisy?
The noise of wind turbines has been reduced significantly with newer technologies. Improved design has drastically reduced the noise of mechanical components so that the most audible sound is that of the wind interacting with the rotor blades. This is similar to a light swishing sound, and much quieter than other types of modern-day equipment. Even in generally quiet rural areas, the sound of the blowing wind is often louder than the turbines.
What is infrasound?
Infrasound is a term used to refer to "acoustic oscillations whose frequency is below the low frequency limit of audible sound"1. Audible noise is a term used to refer to the frequency range between 20 to 200 Herz, however, audibility extends to frequencies below 20 Herz2.
1 - "International Electrotechnical Vocabulary - Chapter 801: Acoustics and Electroacoustics", International Standard IEC 60050-801:1994, International Electrotechnical Commission, (1994).
2 - O'Neal, R., Hellweg, R. D. Jr & Lampeter, R. M., "Low Frequency Noise and Infrasound from Wind Turbines", Noise Control Engineering Journal J. 59 (2), March-April 2011.
Do wind turbines harm human health?
Wind energy is one of the cleanest, most environmentally-friendly energy sources. It emits no greenhouse gases or air pollutants1. It emits no particles, unlike fossil fuels, which are carcinogenic and severely affect human health. According to the public statement made by the National Health and Medical Research Council in Australia, "there is currently no published scientific evidence to positively link wind turbines with adverse health effects"2.
1- For more information, visit: http://ewea.org/index.php?id=1884
2 - Wind Turbines and Health, NHRMC Public Statement, July 2010.
Do wind turbines harm animals and birds?
Big environmental and nature conservation groups like WWF, Greenpeace, Friends of the Earth, and Birdlife support wind energy. Wind farms are always subject to an Environmental Impact Assessment1 to ensure that their potential effect on the immediate surroundings, including fauna and flora, are carefully considered before construction is allowed to start. Deaths from birds flying into wind turbines represent only a small fraction of those caused by other human-related sources such as airplanes and buildings.
According to the European Wind Energy Association2, in Europe, a 2003 study in Navarra (Spain) of 692 turbines in 18 wind farms found that the annual mortality rate of medium and large birds was 0.13 per turbine. In the UK, the Royal Society for the Protection of Birds (RSPB) stated that "in the UK, we have not so far witnessed any major adverse effects on birds associated with wind farms". It has been estimated that wind turbines in the US cause the direct deaths of only 0.01-0.02% of all of the birds killed annually by collisions with man-made structures and activities.
1 - NSW has adopted, with a slightly different criteria, the South Australian EPA Environmental Noise Guideline that is amongst the most stringent in the world. For more information, please visit: www.environment.nsw.gov.au/noise/ and www.epa.sa.gov.au/environmental_info/noise.
2 - For more information, visit: http://ewea.org/index.php?id=1884