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Small Wind Turbine SystemsSmall Wind Turbines | Benefits | Constraints | Costs | Conclusion | Further Information | ReferencesSmall Wind TurbinesWind turbines that have a rated capacity of less than 10kW are usually classified as small-scale turbines. These turbines can also be connected to the grid, but more commonly are used to generate electricity as part of a Remote Area Power Supply (RAPS) - also commonly known as stand-alone power supply (SPS) systems. A wind turbine installed in an area with a good wind resource can produce energy cost-effectively. However, the available wind resource typically varies from season to season, which creates a significant variation in the wind turbine output. Backup generation devices may be required to meet any shortfall of energy during these times of low wind speeds. Small turbines come in many shapes and sizes Figure 1a, 1b and 1c are some examples, but are by no means the only designs available.   
Figures 1a, 1b & 1c
Figure 1a This is the US Department of Energy’s (DOE) National Renewable Energy Laboratory (NREL) 10-meter diameter research wind turbine that was tested in the world’s largest wind tunnel. Figure 1b This is a wind turbine that Hagbourne Primary School in the UK installed for lighting their bike shed and to educate pupils. Figure 1c This is another style of wind turbine (vertical axis). Photo's copyright owned by Cideon Engineering. The many designs available have their own unique advantages and disadvantages. However by far the most common type of wind turbine, small and large, is what is known as the danish style three bladed horizontal axis wind turbine. See Figure 2. 
Figure 2 A three bladed horizontal axis small wind turbine. (courtesy of the Eco Center)
For further information on wind turbine technology, see RISE Wind Technology page.
BenefitsWind power is a renewable resource, which means using it will not deplete the earth's supply of fossil fuels. It also is a clean energy source, and does not directly produce carbon dioxide, sulfur dioxide, mercury, particulates, or any other type of air pollution, as do conventional fossil fuel power sources. If a comparison is made on production costs, wind energy is extremely competitive in many cases relative to conventional technologies. Furthermore, wind energy costs are continuously decreasing due to technological development. (Wikipedia, 2008). Small wind turbines are also commonly incorporated as a generating technology in a hybrid stand-alone power supply system in conjunction with other technologies, such as solar arrays, micro-hydro turbines and diesel gen sets. Alternatively if electricity grid infrastructure is available, these turbines can be connected to the grid via an inverter and be used to produce small amounts of power that can be incorporated in what is known as net metering. Net metering is a simple idea. As no electricity is stored with the vast majority of electricity utilities, net metering is literally recording how much electricity is consumed and how much is produced. This can be viewed as "turning back" the power meter when the domestic supply system, such as a wind turbine or a solar array produces power and exports it to the grid. When net metering is supported by electricity utilities this can result in reduced electricity bills, or even a credit, depending on how much people use and produce.
ConstraintsSmall wind systems, without sufficient storage technologies are not useful for supply mains quality electricity without some form of power conditioning and storage, such as inverters, batteries, backup diesel generators or a grid system. Due to the nature of the variable wind resource the output of wind turbines cannot be predicted to a precise output at a certain time. Noise and vibration produced by the blades, gears, and motors can cause problems and introduce complexities when choosing a type and size of wind turbine. Many small wind turbines are noisy at medium to high wind speeds, which is a significant issue for residential systems. Different designs have vastly different power and noise characteristics and choosing a particular turbine that conforms to your particular requirements can be difficult.
CostsCosts for these systems vary as there are many different types of turbines available for small scale applications. In addition there are many other components that will be needed depending on the application that the wind turbine will be used for. For example no storage will be needed if the wind turbine is used to pump water with an electric pump, or for a grid connected system. The majority of small wind turbines are used for domestic power supplies and therefore the wind systems may need to provide an amount and quality of electricity similar to the local grids voltage and frequencies. This will add extra complexity and more components and will result in increased cost. Along with buying a turbine, the wind system will generally require the following components:
The vast majority of manufacturers and suppliers provide a system package that include all the components and expertise for a desired application. The costs of small wind systems are falling and the quality and efficiency of turbines and other support structures are improving with a larger variety and longevity. The economics of installing a wind system is very sensitive to the average wind speed in your area, as the power received from a turbine increases much more than the relative change in wind speed, due to the cubic relationship of wind speed and power output. For example if the wind speed doubles, the power available increases by a factor of eight. If the wind speed triples then twenty seven times more power is available.
ConclusionIt is most important to obtain accurate and comprehensive wind resource assessment over a few years at the actual proposed turbine site in order to successfully utilise wind turbines to produce electricity. This is generally done using an anemometer (which measures wind speed) and a wind vane (which measures wind direction), coupled with a data taker to record the results. However there are other methods to assess the wind resource, such as information from local airports on wind speed, wind resource maps, effects of wind on the surrounding vegetation, etc. This is of utmost importance as the higher the average wind speed of the site, the power that can be generated increases cubically, which can mean the difference between an economical system and an uneconomical one.
Further InformationRISE Information Portal - Information regarding renewable energy resources, technologies, applications, systems designs and case studies.Alternative Energy Store's Small Wind Turbines Primer AUSWEA's Siting a Small Wind Turbine AUSWEA's Wind Energy in Agriculture American Wind Association's Wind Web Tutorial British Wind Energy Association's FAQ's on Wind Energy Canadian Wind Energy Association's FAQ's on Wind Energy EERE's Consumers Guide to Small Wind Electric Systems Green Pages - Wind Power Systems Westwind's Small Wind Electric Systems - An Irish User's Guide Wikipedia - Wind Turbine Windustry's Small Wind Turbine Resources (USA) (manufactures, Maps Publications, Distributors, Standards & Incentives)
ReferencesWikipedia, 2008. "Wind Turbine" (Online) http://en.wikipedia.org/wiki/Wind_turbine (Accessed 2 December 2008). |
 
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