Analytical – theoretical study on SWTs in terms of pre-selection of the aero layouts best suited for further optimization

terms of pre-selection of the aero layouts best suited for further optimization Abstract The first task within the STOW project was 'analytical – theoretical study in terms of pre-selection of the aero layouts best suited for further optimization' for universal Polish wind conditions. It was carried out by an extensive literature study on classic wind turbine configurations (two, tree –bladed horizontal axis machines), shrouded wind turbines, and other. Literature investigation included both manufactures data and independent expertise. It allowed for objective evaluation of different design approaches (advantages and disadvantages), which in turn enabled systematic identification of actual limitations as well as opportunities for specific design solutions. High rate of growth and specific structure of the industry, which is characterized by highly fragmented production, resulting in tens of various models of these devices on offer at this time. At the end of 2013 there was over800000 Small Wind Turbines (SWTs) operating worldwide, with almost half a million in China. There is more than 330 firms in 26 countries manufacturing these machines. Wind turbines in general can be divided into subgroups according to their construction technology where the major groups are: Horizontal Axis Wind Turbines – HAWTs and Vertical Axis Wind Turbines – VAWTs. Currently Horizontal Axis Turbines have the highest market share due to their performance at high wind speed (high tip speeds, high efficiency and low torque ripple), good reliability, easy maintenance and low cost. At the moment HAWTs constitutes about 75% of SWT's designs available. About 99% of the installed horizontal axis wind turbines is three-bladed, which provides a better balance of aerodynamic forces and better mechanical stability. In an up-wind configuration of a HAWT the rotor is in the front of the unit. This solution is characterized by high efficiency due to reduced tower shading, but such turbines do not self-align onto the wind direction and therefore they need a tail vane or a yaw system. Downwind turbines have the rotor in a trailing configuration, therefore they are self-aligning and the rotor blades can be flexible since there is no danger of them striking the tower. Shrouded wind turbines (called also ducted rotors) consists of a turbine inside a duct that flares out at the back (diffusor). It is said that they can operate in a wide range of wind speeds and generate higher power per a unit of rotor area than regular designs. On the other hand, …