Blade for a 10kW Horizontal Axis Wind Turbine - Term Paper Example

Blade for a 10kW horizontal axis wind turbine Wind has some energy, which can be tapped to give us the electric power. Wind turbine is a rotating device, which converts this wind energy called kinetic energy into mechanical energy. When this mechanical energy is applied to drive a pump etc., the product is called a windmill. However, the ultimate aim is to convert the mechanical energy into the electric power and the equipment needed for doing so is called the wind generator or a wind turbine. Types of wind turbines There are mainly two types of wind turbines, based on the rotational axis of the turbine rotor. Turbines rotating around a horizontal axis are called Horizontal axis wind turbines (HAWT) and those rotating around a vertical axis are named as vertical axis wind turbines (VAWT) Most of the commonly used turbines are HAWT only. Horizontal axis wind turbines These are placed on the top of a tower and they have a rotor shaft with an electric generator placed there. It is a necessary to point the turbine into the wind , so that it can face the wind power. Small turbine use wind wanes to find the wind direction and big turbines go for a wind sensor, which is coupled with a servo motor. Since the generator will need a igher speed for giving the proper output, many turbines also have gearboxes attached to the rotor, which converts slower blade rotation to higher speed. There is always wind turbulence behind the tower. Therefore, t is necessary to point the turbine upwind of the tower. The blades have to be stiff to resist the force of the high winds, which may push the blades into the tower itself. Further, the blades can be placed at a distance in front of the tower, may be with a little tilt in blades. Down-wind machines have also been built in the past, as they are simple without needing any additional mechanism for keeping them in line with the wind. Further, the blades are allowed to bend, in such machines, which reduce their wind resistance. However, the turbulence may lead to fatigue failure. This can affect the reliability of the turbine machine. Therefore, it is advisable to use HAWT that are upwind machines only Common types of wind turbines used for the production of electric energy are usually three bladed wind turbines. Computer controlled motors can be utilized to point the blades into the wind. While HAWT machines are commonly used, they have certain advantages and disadvantages Advantages of Horizontal axis turbines Positioning of blades helps in the rotor shaft and turbine stability, as they are on the side of the turbine’s center of gravity Blade angle of wind attack can be remotely adjusted, enabling the turbine to collect maximum wind energy at a particular time and day. During a storm, HAWT machines have the ability to pitch the rotor blades, which can reduce the damage. In case of sites, where the wind share is higher, the wind speed goes up by almost 20% with every 10m rise in the tower height,. This means an increase in power output by more than 30%. Sine HAWT machines are placed on tall towers, this becomes an advantage. Disadvantages of HAWT machines It is difficult to operate them in near ground turbulent wend conditions. Transportation for tall towers and long blades is a burden on the cost. Installation may be difficult, needing skilled manpower and cranes for installing the towers. The tower heights may raise concerns with local authorities and nearby air force bases. All wind turbines from 0 to 10 Kw power output are small machines used for residential uses. These can have direct driven generators giving the output in direcct current for utilization in the household. These machines have aero-elastic blades, lifetime bearings and vane to point into the wind. Turbine machines with larger capacity can have the generator and gear chains to give alternating current output. Smaller turbines can be installed on the rooftops itself. Lightweight material can be designed for the blades, so that they rapidly respond to the wind gusts, in urban areas. Power output ranges from 1Kw to 10Kw for most these machines. Blade for a 10Kw wind turbine In a wind turbine machine, blades are the only component designed and manufactured keeping in view the wind applications. There are a few types of blades depending on the material used to manufacture them. However, while designing a turbine blade, the following parameters are vital: To analyze the aerodynamic performance of the blade Capability for reduction in fatigue loading Development with advanced controls. As design is the important part of the wind turbine blade manufacture, the concepts need to be clarified for making a blade, which works for domestic purpose small turbines, generating electricity up to 10 Kw. The basic concept is that the wind turbine blade takes power from the wind, as it slows down in the process. The following simple sketch shows how the wind and blade apply forces to push each other. Drag and lift are the two forces involved. While drag is the wind force pushing downward, lift is the force, which works at 90 degrees to the wind direction. Horizontal axis wind turbine blades use only the lift force, as they do not work downwards. This sketch shows the blade using lift force in a HAWT.( courtesy WWW.windmission .dk ) Material for blade manufacture Usually, the small wind turbine blades are made from wood. However, it is a time consuming process and is labor intensive. Therefore, modern blades are made from PVC or glass fiber or other laminated material. However for a residential wend turbine the wood becomes a cheaper proposition. Wooden blades The first step is to choose the right wood for these blades. Red cedar wood is perfect for making the small wind turbine blades. It has nice grains, and is relatively cheaper. It is tough, strong, durable, and easy to carve. Many layers of laminates can be glued together by using polyurethane glue to join standard lengths of 2 by 4 cedar, which can give a strong and durable ten feet long thick blade. Next step is to carve the turbine blade from the wood chosen for this purpose. The basic tools required for this purpose could be: This is a draw knife Next, we will require a saw, hammer and chisel along with a plane. A power plane and power saw can do the job faster. With these basic tools, the blade will ready from the wood planks or laminates. We will also need drills, clamps etc for doing the perfect job. The weather, rain and other elements do affect the working of wooden blades as blade tips and edges are worn out soon due to high speed of wind. A coat of waterproof marine paint can protect the blade from such hazards, However the use of linseed oil on these blades gives a protective layer as it absorbs into the wood, so that water does not penetrate into it. The final shape of these blades can be like this PVC blades for wind turbines For wind turbines producing electricity up to 10Kw, the PVC blades are ideal as they are flexible to the wind force. This makes the blades take out some energy out of the wind so that the wind turbine generator does not spin too fast, thus getting damaged in case of strong winds. The material and tools required to make such blades include a PVC pipe, jigsaw or hacksaw blades. Jeremy parsons suggest the following PVC blade design. He also suggests that the trailing edge of the blade should be away from the centerline to improve the lift force and thus the rotation generated. While the diameter of the pipe will determine the width of the blade, for a blade with average width of 4 inches and hub angle of 20 degree, a pipe having 10 to 12 inches diameter will be required. This may give a blade of 4 to 5 feet length. Marking the centerline inside of both ends of the plane will give the trailing edge of the blade. The center point mark between the ends of the pipe will be the position for the bolt hole A jig saw or reciprocating saw will do the cutting job. The cuts have to be done as per the design given above to get the correct hub angle of 25 degrees.. Fiberglass blades While reinforced fiberglass blades are the better choice for improved results and shear resistance. This material is known for its tough and strong qualities, which makes it ideal to face the strong winds even in the event of the storms. The bend and tear damages are reduced by using such blades. However, the manufacture of these blades is expensive and it may not be the correct choice for the blades of a small wind turbine producing electricity of 10 kw, which is mainly required for residential and home use. Fiberglass blades are for high capacity, turnover, wind turbines, that are installed for commercial purposes. The manufacture of this type of blade will require the mold making process, which is based on the patterns or plugs made from wood or other similar material. The plugs are usually in pairs of male and female, as male plug gives a female mold and vice versa. The molten material is casted in these moulds as per the blade design. to get the proper shape of the blade. These types of blades require machining and finishing meeting the design requirements. However, for a 10 Kw horizontal axis wind turbine machine the best option is to use PVC blades as they are flesible and strong as well. ( the sketch and picture is courtesy “otherpower.com”) Quality inspection and assurance for the blades The manufacture of any type of blade for a 10Kw horizontal axis wind turbine should meet the following parameters for quality check. The blade manufacture should be perfectly as per the design specifications The blade hub angle and the curvature as well as the bend should be checked to meet the required parameters. In case of wooden blades, the quality of wood needs to be checked. The perfect bonding of the laminates should be checked to measure the durability and strength of the blade. In case of using a PVC molding, the patterns for casting the material, the edges of the plugs as well as the mold edges should be sharp, so that there is no undue accumulation of the material to cause fatigue stress on the blades during the actual run. The best quality check is done during the field tests itself. The application of the drag or lift forces can be judged during the filed test only. As horizontal axis wind turbine blades do not use drag force, their ability to make use of the lift force should be checked The best check is to find the strength of the blade material during the actual conditions of windstorm etc. This will also reveal the wear resistance of the blades as well as the resistance to shear at the edges. Sources http://www.scoraigwind.com/wpNotes/bladeDesign.pdf Hugh Piggotte-----Wind turbine blade profiles PVC wind turbine blades.....reuk.co.uk Blade construction for horizontal axis wind turbine rotors Free patentsonline.com http://www.scoraigwind.com/wpNotes/bladeDesign.pdf Read More