"(Castillo, SMALL-SCALE VERTICAL AXIS WIND TURBINE DESIGN, december 2011)3 Where, V is the velocity of the wind [m/s] and ? is the air density [kg/m ] theo 3 * reference density used its standard sea level value [1.225 kg/m at 15 C], for othervalues the source (Aerospaceweb.org, 2005) can be consulted.The power the wind turbine takes from wind is calculated using power coefficient,(Castillo, SMALL-SCALE VERTICAL AXIS WIND TURBINE DESIGN, december 2011)Cp value represents the part of the total available power that is actually taken fromwind, which can be understood as its efficiency.Tip speed ratio The power coefficient is strongly dependent on tip speed ratio, defined as the ratiobetween the tangential speed at blade tip and the actual wind speed.(Castillo, SMALL-SCALE VERTICAL AXIS WIND TURBINE DESIGN, december 2011)Where ? is the angular speed [rad/s], R is the rotor radius [m] and V is theo ambient wind speed [m/s].Blade ChordThe chord is the length between leading edge and trailing edge of the blade profile.The blade thickness and shape is determined by the airfoil used.Number of BladesThe number of blades has a direct effect in the smoothness of rotor operation asthey can compensate cycled aerodynamic loads. A single blade turbine has theleast efficiency as it requires greater lift to complete rotation. A design with highernumber of blades, increases the efficiency but in a diminishing manner.SolidityThe solidity s is defined as the ratio between the total blade area and the projectedturbine area (S. Tullis, 2012). It is an important non-dimensional parameter whichaffects self-starting capabilities and for straight bladed VAWT, solidity is calculatedas (Claessens, 2006): Where N is the number of blades, c is the blade chord, L is the blade length and Sis the swept area. It is believed that each blade sweeps twice. This formula is notapplicable for HAWT as they have different swept areas.Initial angle of attack The angle, at which wind is incident to the chord axis, is the angle of attack. This isan important parameter for measuring the output of wind turbine. When the angleof attack changes due to volatility of wind nature, the blade direction also needs tobe changed. The angle, by which the blade is rotated, is called the pitch angle.Unless this is done, the efficiency of the turbine stays low.Structural Analysis:This analysis allows us to define the operational limitations of the rotor bladedesigns. The analysis depends upon the following factors:1) Rotor ConfigurationThe first configuration attaches each blade at 2 points which minimize themaximum bending moment. The second and third configurations have the samebending strength thus the third is discarded as the second configurationreduces the resulting drag because it has lower exposed area per same strength.(Castillo, SMALL-SCALE VERTICAL AXIS WIND TURBINE DESIGN, 2011)2) Selected Material3) Load AnalysisFor a modern wind turbine, multiple loads are accountable for operationalperformance of the wind turbine. The most important load cases are dependent on individual designs. Under different operational scenarios, 5 main sources ofblade loading have been identified:- Aerodynamic- Gravitational- Centrifugal- Gyroscopic- OperationalIf an optimum rotor design is considered then the aerodynamic loads areunavoidable. As the turbines increase in size, the mass of blades also increase inthe proportion at a cubic rate, thus gravitational and centrifugal loads act verystrongly. Gyroscopic loads result from yawing during the operation. They are lessintensive than the gravitational forces and are system dependent. OperationalLoads are also system dependent and are affected due to yawing, pitching andbreaking. Since Gyroscopic and Operational loads are system dependent thus,these are not studied under this research. (Peter J. Schubel, 2012)1. Aerodynamic LoadsSuch loads are generally generated due to lift and drag forces of the bladeswhich are dependent on wind velocity, blade velocity, surface finish, angle ofattack and the yaw. The resultant forces (called Thrust), in the direction ofrotation is absorbed by generator and reaction forces. These reaction forces areto be tolerated by the blade with limited deformation. (Peter J. Schubel, 2012)2. Gravitational & Centrifugal LoadsThese loads are primarily mass dependent which generally increase at cubicrate with increasing turbine diameter. With this increasing turbine size, theblades also need to increase. This increases the gravitational load which causesalternating cyclic load case. (Peter J. Schubel, 2012)The centrifugal load always acts radial outwards hence demands higher tipspeeds.3. Flap wise and Edgewise BendingThese are resultants of aerodynamic loads only.Flap wise bending occurs along the chord axis creating compressive and tensilestresses in blade cross section.On the other hand, Edgewise bending is the resultant of blade mass andgravity. The maximum bending occurs when the blade is in horizontal position."