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Concept
Small wind turbine
Summary
Small wind turbines, also known as micro wind turbines, generate electricity for small-scale use. These turbines are typically smaller than those found in wind farms. Small wind turbines often have passive yaw systems as opposed to active ones. They use a direct drive generator and use a tail fin to point into the wind, whereas larger turbines have geared powertrains that are actively pointed into the wind.
They usually produce between 500 W and 10 kW, with some as small as 50 W. The Canadian Wind Energy Association considers small wind turbines to be up to 300 kW, while the IEC 61400 standard defines them as having a rotor area smaller than 200 m2 and generating voltage below 1000 Va.c. or 1500 Vd.c.
Turbine blades for small-scale wind turbines are typically in diameter and produce 0.5-10 kW at their optimal wind speed. Most small wind turbines are horizontal-axis wind turbines, but vertical axis wind turbines (VAWTs) may have benefits in maintenance and placement, although they are less efficient at converting wind to electricity. To optimize efficiency, the tip speed ratio (the ratio of blade tip speed to wind speed) and lift-to-drag ratio should be kept at optimal levels.
A range of synthetic materials including carbon fiber reinforced polymers, nanocomposites, and E-glass-polyester are available. Although natural fibers are susceptible to quality variations, high moisture uptake and low thermal stability that make them undesirable for larger blades, small turbines can still take advantage of them. Wood can be used, and the type of wood should be chosen based on availability, cost and growth time, average density, high stiffness, and breaking strain. Coatings are generally used to reduce moisture, and white enamel with primer has been found to be particularly effective. Sitka spruce (used in propellers), and Douglas Fir have been used in turbine blades. Nepal has used small blade turbines made of coated timber including Sal, Saur, Sisau, Uttish, Tuni, Okhar, pine, and lakuri wood.
Official source
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