WIND ENERGYThe wind is a clean and plentiful source of energy. A wind turbine is a machine that converts the kinetic energy in wind into mechanical energy.The mechanical energy is used directly by machinery, such as a pump or grinding stones, the machine is usually called a windmill.The mechanical energy is then converted to electricity, the machine is called a wind generator, wind turbine, or wind energy converter (WEC).
VARIETY OF WINDMILL SIZESLarge wind turbines- installed in clusters called wind farms-generate large amounts of electricity(MW).Small wind turbines-generates 100 kW of electricity-installed at homes, farms and small businesses . Used as a source of backup electricity, or tooffset use of utility power and reduce electricitybills. Very small wind turbines -20-500w- charge batteries for sailboats and other recreational uses.Applications water pumping, telecommunications powersupply and irrigation.
SIMPLE WIND TURBINE MODEL WITH CONTROL ELEMENTS
OPERATIONA wind turbine converts kinetic energy in a moving air stream to electric energy.Mechanical torque created by aerodynamic lift from the turbine blades is applied to a rotating shaft. An electrical generator on the same rotating shaft produces an opposing electromagnetic torque.
In steady operation, the magnitude of themechanical torque is equal to that of theelectromagnetic torque, so the rotational speedremains constant, real power (the product ofrotational speed and torque) is delivered to thegrid.Since the wind speed is not constant, a variety ofcontrol mechanisms are employed to manage theconversion process and protect the mechanicaland electrical equipment from conditions thatwould result in failure or destruction.
WIND POWERThe formula used for calculating the power in the wind is shown below:Power = ½ .density of air. swept area.velocity^3P = ½.ñ.A.V³In practical PM = ½.Cp.ñ.A.V³ Cp is the coefficient of performance of the wind machine
PRINCIPLES OF WIND ENERGY CONVERSIONThere are two primary physical principles of extraction: Either lift or drag force or through a combination of thetwo. The difference between drag and lift is illustrated by thedifference between using a spinnaker sail, which fills like aparachute and pulls a sailing boat with the wind, and aBermuda rig, the familiar triangular sail which deflects withwind and allows a sailing boat to travel across the wind.Drag forces provide the most obvious means of propulsion,these being the forces felt by a person (or object) exposedto the wind. Lift forces are the most efficient means ofpropulsion but being more subtle than drag forces are notso well understood.
BASIC FEATURES THAT CHARACTERIZE LIFT & DRAG Drag is in the direction of air flow . Lift is perpendicular to the direction of air flow . Generation of lift always causes a certain amount of drag to be developed . With a good aerofoil, the lift produced can be more than thirty times greater than the drag. Lift devices are generally more efficient than drag devices Types and characteristics of rotors .
IMPORTANT WIND SPEEDS TO CONSIDERStart-up wind speed - the wind speed that will turn an unloaded rotor.Cut-in wind speed - the wind speed at which the rotor can be loaded.Rated wind speed - the windspeed at which the machine is designed to run (this is at optimum tip-speed ratio).Furling wind speed - the windspeed at which the machine will be turned out of the wind to prevent damage.Maximum design wind speed - the windspeed above which damage could occur to the machine.
Two main families of windmachines: vertical axis machines Horizontal axis machines. These can in turn use either lift or drag forces to harness the wind.The horizontal axis lift device is the type most commonly used. The tipspeed ratio : It is defined as the ratio of the speed of theextremities of a windmill rotor to the speed of thefree wind.
Drag devices-tipspeed ratios less than one -turn slowlyLift devices -high tip-speed ratios(up to 13:1)- turn quickly relative to the wind.The proportion of the power in the wind that the rotor can extract is termed the coefficient of performance (Cp) and its variation as a function of tipspeed ratio is commonly used to characterise different types of rotor. As mentioned earlier there is an upper limit of Cp = 59.3% Although in practice real wind rotors have maximum Cp values in the range of 25%-45%.
COMPONENTS OF WIND ENERGY SYSTEMSThese basic components include:A rotorA gearboxThe smallest turbines (under 10 kW) usually do not require a gearbox.An enclosure which protects the gearbox, generator and other components of the turbine from the elements.A tail vane or yaw system, which aligns the turbine with the wind.
MAINTENANCE OF WIND TURBINE It requires periodic maintenance - oiling and greasing,and regular safety inspections. Check bolts and electricalconnections annually; tighten if necessary. Once a year check wind turbines for corrosion and theguy wires supporting the tower for proper tension.If the turbine blades are wood, paint to protect from theelements. Apply a durable leading edge tape to protect theblades from abrasion due to dust and insects in the air. If the paint cracks or the leading edge tape tears away,the exposed wood will quickly erode. Moisture penetratinginto the wood causes the rotor become unbalanced,stressing the wind generator. Inspect wooden bladesannually, and do any repairs immediately. After 10 years, blades and bearings may need to becompletely replaced. With proper installation andmaintenance, wind turbine can last 20-30 years or longer.Proper maintenance will also minimize the amount ofmechanical noise produced by your wind turbine
SAFETY CONCERNSInternal brake and lock To prevent maximum wind speed- survivalspeed [they will not operate above].Insulation cold winter conditions, be prepared to de-iceas required, and store batteries in an insulatedplace.Mounting turbines on rooftops is generally not recommended