Vertical Axis Wind Turbine - Case Study Example

Summary In this paper the introduction gives an overview on wind energy then narrowing down to VAWT. The technical details have been given under description. VAWT has been seen to be sustainable because operation cost is low. Under analysis the advantages and disadvantages of VAWT have been discussed and also the cost and performance has been addressed. Introduction There has been a substantial increase in uptake of wind energy in resent years with an increase of 20% being recorded. In 2010 the global increase in wind energy use was at 39GWe this being an investment of US$65billion, an increase of 41GWe was recorded in 2012 and 35GWe for 2013. This increases so the world winds capacity increase to 318GWe with tens of thousands more turbines being brought into operation (Schatzle, P. R. et al.,1981). Currently there are wind turbines of power capacity of up to 6MWe in operation in some countries but the wind turbines that are mostly being brought into market currently are 1-3MWe. Te power output of wind turbines proportional to the cube of the wind speed, meaning that when the speed of wind is doubled the energy potential of the turbine is increased by 8 times (Cal, R. et al,2010). Vertical axis wind turbines With the objective of introducing practical and innovative wing energy in the market there has been introduction of the vertical axis wind turbine which are known for being economical and energy efficient. Some of the features that make VAWT superior are It has significant aerodynamic performance improvement that make use large vertical blade configurations which are mounted on the vertical axis so as to derive more energy from the wind VAWT are described as being omni-directional and thus they are able to make full use of wind power with direction not being a hindrance Through the incorporation of aerodynamic load controls there is braking in high winds with computerization there can be simple operation that involve integration with Smart Grid Manager control system to enable operation, management and monitoring to be done remotely. With energy storage and power transfer system involving proprietary backup battery being provided it makes it possible for electrical power to be available at when required including when the there is no wind or when the speed of wind is very low. Description The forces and velocities involved in a wind turbine are as shown in figure 1 where the resultant vector is and represents a vector sum upstream air velocity and velocity vector of the turbine blade Five-kilowatt vertical axis wind turbine This shows that there is a variation of oncoming fluid velocity one cycle with maximum velocity being reached at while the minimum being at, with being the azimuthal or the orbital blade position. The formed by the oncoming air speed, W and the cord of blade is referred to as angle of attack There is creation of varying resultant airflow, where there is a positive blade angle of attack for upstream zone of machine, with the signs changing downstream. Applying geometry, the angle of attack and the resultant airspeed are given by Where the tip speed ratio is given by There can be resolution of aerodynamic force into lift ( FL)and drag (D) components or normal (N) and tangential (T) components. The forces are taken as acting at the quarter-chord point with the pitching moment being found through resolving of aerodynamic forces. Here the terms lift and drag are used in reference to force across and force along the approaching net relative airflow respectively. The tangential force is applied along the velocity of the blade such that the blade is pulled around while the normal force act in a radial manner with a push against shaft bearings. The lift force and the drag force become of use when the aerodynamic forces around the blades such as boundary layer and dynamic stall are being dealt with, while the normal-tangential frame becomes useful when dealing with global performance and fatigue loads. There is normalization of the lift and drag coefficients through the dynamic pressure of relative airflow, and for normal and tangential coefficients normalization is achieved through dynamic pressure in the undisturbed upstream fluid velocity A = Surface Area The power, P, that can be absorbed by a wind turbine is given by With being the power coefficient, is air density, the swept area of the turbine, and with being the wind speed. Sustainability The VAWT does not use fossil energy but renewable energy and this makes it environment friendly. Use of VAWT is economical because there is no use of fuel Socially: Use of VAWT will ensure that there is accessibility to affordable electricity even in remote places not covered by the grid. With development of windmill farms reliance on fossil energy for generation of electricity is reduced considerably. Ethical consideration The appearance of wind turbines is considered to be unappealing The establishment of wind turbine farms results into birds being killed by the rotating blades and this raises an ethical issue on whether loss of birds is not important in comparison to generation of clean energy from the turbines Generation of power by wind turbines require use of a larger area of land in comparison with other forms of power generation such as fossil fuel electricity generators (Ivanell, 2007). In most engineering solution there is encouragement of introducing vegetation to improve the environment. When it comes to wind turbines introduction of vegetation like trees is not possible since this would result into reduced wind speed. The wind turbines make noise which might be disturbing to people in the neighborhood. Impact of VAWTs on community Technologies like VAWTs are viable are supplying energy local communities, government agencies, industrial complexes, military bases and institutions. When power is supplied to local communities it makes it possible for them to access modern technologies such as use of computers. This also means that institutions can be set close to marginalized communities in addition to military bases which will provide security. Communities can easily utilize such technologies because of low cost of running and require little maintenance. Relevance to engineers VAWTs just like any other wind turbine require less maintenance and this for an engineer is a reliable solution to human problem. Setting up of turbines requires small concrete base which means little distance of the soil. Thus setting on VAWTs is engineering solution that deviates from many engineering solutions that comes with substantial interferences of the landscapes. The VAWTs also require bare lands with no trees meaning that there is no ecosystem interference instead what could be regarded as land of little use is put to economical use through generation of electricity. (Manwell. J. F., et al. 2002) With VAWTs the engineers will have made achievements of overcoming some short comings that are associated with horizontal axis wind turbines (HAWT). With VAWTs there is much more economical use of land as there can be closer spacing of the turbines. VAWTs has lower centre of gravity and this means lower materials use as compared to what could be used in HAWTs to achieve the same level of stability. This is important for an engineer as it means less transportation costs and also it means that less demand for construction materials. VAWT is an improvement on wind power and for engineers it means that technologies of storage of power gains more relevance. This is because wind power is produced intermittently. Generation of hydrogen through hydrolysis of power generated by VAWTs need to be ventured into. Analysis and evaluation Advantages of VAWTs VAWTs have several advantages in comparison to traditional HAWTs. There is more economical use of space as they can be set much closer. VAWTs operate with less noise in comparison to HAWTs, they are omni-directional and the force subjected to the supporting structure is much less. VAWTs do not as much wind as that required by HAWTs for production of power and the fact that they can be set closer to the ground makes it easy to be maintained in addition to making it possible to set them on structures like chimneys. Research has also shown that with careful design of wind farms with VAWTs would achieve power generation ten times more than that from HAWTs farm of equal size. Disadvantages of VAWTs The tendency of stalling in gusty winds is a shortcoming associated with VAWTs. The starting toques they produce is also low and have dynamic stability problems. VAWTs have low height of installation and this restricts them to operating in low wind speed environments in addition to their sensitivity to off-design conditions. The blades of VAWTs are subjected to fatigue as a result there being a wide variation in the forces they are to withstand in each rotation. In early models there was twisting and bending in the vertically oriented blades and this resulted in their cracking. In the long run this led to breaking apart and this sometimes led to catastrophic failure. These problems have made VAWTs to be less reliable in comparison to HAWTs. A research programme was undertaken in 2011with aim of looking of coming up with a solution in oevercoming the deficiencies of VAWTs through optimization of turbine placement in wind farms. The findings indicates that even with a lower wind-speed environment asa result of low elevation, the prediction from scaling up of physical forces indicates that VAWTs wind farms can be set up by use of less expensive materials, less processes of manufacture and less maintenance requirement than can be use in HAWTs. Cost and performance The initial cost of installing wind power may be high but in the long run it is economical because there is no fuel cost. There is also no cost of storage of power using batteries or any other form storage like hydrolysis of hydrogen. But all this cost cancelled by the low operation cost more so considering that VAWTs can be used in remote areas where there is no access to grid power and poverty level may be high thus making it regular payment power unmanageable. Conclusion From this paper it has been seen that VAWTs is one of the promising ways of addressing the ever increasing energy demand globally. Through innovation the challenges of storage are likely to be overcome and thus increasing the popularity of VAWTs References Schatzle, P. R. et al (1981), “Aerodynamic interference between two Darrieus wind turbines,” Sandia National Laboratories Report No. SAND8l-0896. Kiranoudis C. T. and Maroulis, Z. B. (1997) Renewable Energy 11, 439. Ivanell, S. et al. (2007).Wind Energy (Springer, Berlin,). Cal, R. et al (2010). Renewable Sustainable Energy 2, 013106. Manwell. J. F., et al. (2002). “Wind Energy Explained”. John Wiley & Sons, West Sussex , England. John F. Walker and Nicholas Jenkins, (1997). “Wind Energy Technology”. John Wiley & Sons. West Sussex , England. V.H.Morcos and O.M.E. Abdel-Hafez, (1996). “Testing of an arrow-head vertical axis wind turbine model”. Renewable energy, Vol. 7, No 3, pp. 223-231 Read More