14 In the early twenty-first century, attentions turned again toward renewable energy. The fact that oil and gas are limited and will be finished in the near future, along with population growth, which results in increasing demand for energy, were not the only reasons for turning the attention toward renewable energy this time. While those reasons were part of the transition another problem was discovered. “In 2001 an international panel of distinguished climate scientists announced that the world was warming at a rate without precedent during at least the last ten millennia, and that warming was possibly caused by the build-up of greenhouse gases from human activity” Spencer Weart (R. Weart, 2008). Since the climate change issue had been raised and indicated that a major reason was usage of fossil fuels, the focus on advancing and developing the renewable energy sector, in this instance wind power, became more intense. At this stage the focus was mainly on increasing the efficiency of wind turbines by applying aerodynamic principals to design new blades and on making bigger wind turbines to harness more wind power (Sahin, 2004, p. 517). This led to the construction of larger wind farms all over the world; in Asia by India, Japan and China; in Europe by Germany, followed by Denmark and Spain; and in the West by the US and Canada (Hatziargyriou et al., 2010, p. 1765).
The most prevalent wind direction in the month of August 2017, September 2017, and October 2017 is SSE with that of November 2017, December 2017 and January 2018 being eastwards. These findings are supported by the NEMA report that south easterly (SE) winds dominate the East Africa region from April to October while the northern easterlies drive the prevailing winds from November to March . The directional behavior of wind is well understood by plotting a wind direction rose which is a tool to demonstrate the percentage of total time that wind flows with a given speed from a particular direction and also the percentage energy content from a particular direction thus giving the percentage of time the system is able to generate useful power. Wind roses were plotted for every month under study as shown in Figure 5.
crop insurance industry, the challenge in this study is whether this programme can be adapted to small-scale farmers in SouthAfrica. A major problem with crop insurance in the USA has been the high cost of administration which would be larger per hectare of land for smallscale farmers. Special attention will thus be given in this study to the economic feasibility of an area insurance programme as a way to reduce costs associated with administration, asymmetric information and systemic risk. The writer has benefited from discussions with Dr I van Rooyen, Sentraoes, Ficksburg who has experience in the provision of hail insurance to smallscale wheat farmers and Mr C Oliver of Grocane, Durban which provides fire insurance to smallscale cane farmers.
Once the parties consult the agency, the rules and regulations should be properly and thoroughly explained to the parties. They must understand that once the baby is born the commissioning parents become the legal parents – no backing out. The surrogate must understand that the baby is completely unrelated to her and that she will have no right over that baby. The aforementioned regular counselling will make the process easier on the surrogate mother as well as properly prepare her. If all the parties know and understand their rights, duties and obligations from the start, it should help avoid any unpleasantries in the future. Furthermore, the surrogate mother should not be required to pay for membership or any of their services. Their expenses must be for the commissioning parents‘ account. The surrogate mother should be free to choose which medical or other professional she chooses to consult with and should not be forced to abide by the recommendation of the agency. As pointed out by Nicholson, 198 the agency‘s recommended professional might not be so recommended as a result of his or her skill; the recommendation could be financially driven. Complete transparency is required, especially with regard to payments. The agency‘s account should be audited annually to avoid any illegality or behind-the-scenes dealings. To avoid hundreds of these agencies springing up at once and causing chaos with all attempts to regulate them, only a few clinics should be allowed to operate in SouthAfrica. These should have regular unscheduled inspections by an agency governing body. Severe penalties, such as imprisonment, should be imposed for any breach of any regulation by the agency or any other party. The threat of severe repercussions in the event of a contravention will supply a necessary deterrent factor.
Abstract: A preliminary study of a windturbine design is carried out using a wind tunnel to obtain its aerodynamic characteristics. Utilization of data from the study to develop large-scalewind turbines requires further study. This paper aims to discuss the use of windturbine data obtained from the wind tunnel measurements to estimate the characteristics of wind turbines that have field size. The torque of two small-scale turbines was measured inside the wind tunnel. The first small-scaleturbine has a radius of 0.14 m and the second smallturbine has a radius of 0.19 m. Torque measurement results from both turbines were analyzed using Buckingham π theorem to obtain a correlation between torsion and diameter variations. The obtained correlation equation is used to estimate the field measurement of turbine power with a radius of 1.2 m. The resulting correlation equation can be used to estimate the power generated by the turbine by the size of the field well in the operating area of the tip speed ratio of the turbine design.
Many previous researchers have studied the role of smallscale businesses in national economies; however, the extent studies have focused on specific smallscale sector is li- mited or has been postponed. This article seeks to provide a concise overview of the role of SSECs in national economies with specific reference to SouthAfrica and high- light the significant role of SSECs in the economy as well as the challenges experienced by SSECs in the industry. There is little clarity on the extent to which SSECs in con- struction industry have been evaluated. This demonstrates that fewer researchers have done some work on the role of SSECs in SouthAfrica and none in particular on this topic. Through the focus of this paper, it is perceived that the outcome would set a precedent for similar studies in other smallscale businesses and this would give uniqueness to the future studies on small businesses. Data for the review were pre- dominantly sourced from, University of SouthAfrica databases, South African journals, overseas journals, online journals, South African media and CIDB databases.
Results: Both malaria-related morbidity and mortality have decreased significantly across all three malaria-endemic provinces since 2000. The greatest decline was seen in KwaZulu-Natal where cases decreased from 42,276 in 2000 to 380 in 2010 and deaths dropped from 122 in 2000 to six in 2010. Although there has been a 49.2 % (8,553 vs 4,214) decrease in the malaria cases reported in Limpopo Province, currently it is the largest contributor to the malaria incidence in SouthAfrica. Despite all three provinces reporting average insecticide spray coverage of over 80%, malaria incidence in both Mpumalanga and Limpopo remains above the elimination threshold. Locally transmitted case numbers have declined in all three malaria provinces but imported case numbers have been increasing. Knowledge gaps in vector distribution, insecticide resistance status and drug usage were also identified. Conclusions: Malaria elimination in SouthAfrica is a realistic possibility if certain criteria are met. Firstly, there must be continued support for the existing malaria control programmes to ensure the gains made are sustained. Secondly, cross border malaria control initiatives with neighbouring countries must be strongly encouraged and supported to reduce malaria in the region and the importation of malaria into SouthAfrica. Thirdly, operational research, particularly on vector distribution and insecticide resistance status must be conducted as a matter of urgency, and finally, the surveillance systems must be refined to ensure the information required to inform an elimination agenda are routinely collected.
CHAPTER 1. BACKGROUND ON WIND ENERGY 5 calibrated for various ows, and therefore their use arguably introduces addi- tional uncertainty to the computed results. One such turbulence model is the Spalart-Allmaras (SA) turbulence model which is a one-equation mixing model that models turbulent eddy viscosity. The SA turbulence model is calibrated for external ows and is considered an adhoc turbulence model due to its sim- plicity, robustness and ability to yield results in a prompt manner. Another more superior turbulence model that is used for general engineering ows is the Menter k-omega shear stress transport (k − ω SST) turbulence model which is a two-equation eddy viscosity turbulence model . It has the capability of switching between the standard k-epsilon (k − )  model and the original Wilcox  k − ω model with the shear stress transport model that gives good results in prediction of adverse pressure gradient ows. This model is often used in turbo-machinery models and gives good results, however requires a thin mesh to resolve the boundary layer and is quite prone to instability issues especially in terms of solution convergence. Grid convergence studies make it possible to obtain a optimum solution mesh that requires fewer mesh cells but still giving accurate results, saving on computation overheads and time. With such computer based models it is possible to perform permutations on windturbine designs which would cost a lot of time and money if done in the eld. Given the availability of High Performance Computing (HPC) resources, one can pursue the use of these computation methods.
Modern WTs are using more intelligent control. For example, initial WTs were passive stall-regulated load control, fixed-speed machines working in a narrow wind speed range. Subsequently, they evolved to active pitch-regulated, variable-speed machines. The application of collective blade pitch control has allowed modern WTs to be larger in size and work over wider wind speed ranges. The newly developed individual blade pitch control is enabling modern WTs to deliver higher power with lower blade and tower loads [9, 10] . Today, more advanced blade control technology, the Intelligent Blade  , is being researched to allow the blade to measure wind speed and adapt automatically to wind conditions. It is believed that with the aid of the Intelligent Blade, the efficiency and reliability of new generation of WTs will be further enhanced. However, it is already recognized that the increase use of intelligent control loops in the rotor and generator systems also creates reliability and power quality challenges for the WT.
Wind has been recognized as one of major realistic clean energy sources for power generation to meet the continuously increased energy demand and to achieve the carbon emission reduction targets. However, the utilisation of wind energy encounters an inevitable challenge resulting from the nature of wind intermittency. To address this, the paper presents the recent research work at Warwick on the feasibilitystudy of a new hybrid system by integrating a windturbine with compressed air energy storage. A mechanical transmission mechanism is designed and implemented for power integration within the hybrid system. A scroll expander is adopted to serve as an ‘‘air-machinery energy converter’’, which can transmit additional driving power generalized from the stored compressed air to the turbine shaft for smoothing the wind power ﬂuctuation. A mathematical model for the complete hybrid process is developed and the control strategy is investigated for corresponding cooperative operations. A prototype test rig for implementing the proposed mechanism is built for proof of the concept. From the simulated and experimental studies, the energy conversion efﬁciency analysis is conducted while the system experiences different operation conditions and modes. It is proved that the proposed hybrid windturbine system is feasible technically.
The hub is the fixture for attaching the blades to the rotor shaft. It usually consists of nodular cast iron components for distribution of the blade loads to the wind support structure, i.e. ultimately to the tower. A major reason for using cast iron is the complex shape of the hub, which makes it hard to produce in any other way. In addition hereto, it must be highly resistant to metal fatigue. Thus, any welded hub structure is regarded as less feasible . For designing the hub for loading the following consideration are used,
farm. Determination of the thresholds of visual impact of a windturbine has been discussed by Bishop . Computational analysis and public surveys were used to draw conclusions regarding the distance and not just the line of sight from which a viewer observes a windturbine. It was stated that light scattering due to moisture or particles in the air contributes significantly to the distance at which a windturbine can be seen. In extremely clear weather situations there can be a visual impact up to 20 km from the site but 5-7 km is more typical. Multiple wind turbines will increase this effect and so the number of turbines simultaneously visible from these distances must be taken into consideration. Torres Sibille et al.  have provided a good summary of all of the factors influencing onshore wind farm aesthetic impact and attempts to develop a method for assessing this impact. This has been a difficult parameter to measure due to the subjectivity of a wind farm‘s visual appearance for an individual observer. It could even be speculated that a population would become accustomed to seeing them in the same way that sky scrapers or power lines have been accepted. Offshore wind farm aesthetic impact is lessened due to the reduced visibility from the general public. However, as indicated in Gee  the visibility of a wind farm in the ‗seascape‘ can create a large resistance in the public opinion. In general, wind farm aesthetics is a complicated area of study that is substantially influenced by public opinion. As wind farms grow in size and number, visual impacts and the cumulative effect of multiple turbines cannot be
Recently, in the WTs, the PMSGs have been more attractive the IGs because of direct drive and high efficiency. Moreover, the PMSGs have the high torque density and the power factor characteristics. The direct-drive train wind power on system generation can be seen in Figure 1.Four main components are contained in this system and the PMSG connects to the grid through a back to back converter, converting the mechanical energy produced by the windturbine to the electrical energy.
The rotor computational domain consists of a rotating zone surrounding the blades and a stationary far-field zone. A mesh interface was created between the two zones. The interface was necessary because the nodes on the boundaries of the far-field and rotational zones were intentionally non-conformal. The interface paired these so that interpolation can occur and fluid may pass into the rotating region. For each case, a static simulation with moving reference frame (MRF) and a dynamic sliding mesh model (SMM) were performed. The rotation was first de- fined using the steady-state solver with MRF, and the simulation was then solved in a transient manner using a sliding mesh motion. The converged static result from the MRF simulation was used to initialize the transient SMM solver. The moment Coefficient (Cm) was monitored over time with accurate reference val- ues for one full rotation. At 477 RPM, one rotation is completed in 0.1258 sec. A time step of 0.001747 sec was chosen so that the Cm was calculated for every 5 degrees of rotation. This resulted in 72 time steps per simulation and 60 iterations per time step. From the Cm data, the power coefficient (Cp) of the windturbine can be easily calculated. Boundary conditions for the simulations included air ve- locity inlet, rotational speed of the blades, and pressure outlet. The rotating zone was set to 477 RPM for each simulation. The blade walls inside the rotating do- main were given a no slip condition. Constant wind speeds along the z direction were set at the velocity inlet. Five different wind speeds of 4, 6, 8, 10, and 12 m/s were tested for each model. The pressure outlet was kept at constant atmospheric pressure.
This paper describes a computer method to allow the design of smallwindturbine blades for the multiple objectives of rapid starting, efficient power extraction, low noise, and minimal mass. For the sake of brevity, only the first two and the last objectives are considered in this paper. The optimization aimed to study a range of blade materials, from traditional fibreglass through sustainable alternatives to rapid prototyping plastic. Because starting performance depends on blade inertia, there is a complex interaction between the material properties and the aerodynamics. Example blades of 1.1 m length were designed to match a permanent magnet generator with a rated power of 750 W at 550 rpm. The materials considered were (a) traditional E-glass and polyester resin; (b) flax and polyester resin; (c) a typical rapid prototyping plastic, ABS-M30; and (d) timber. Except for (d), hollow blades were used to reduce the rotor inertia to help minimize starting time. Two airfoils are considered: the 10% thick SG6043 which has excellent lift:drag performance at low Reynolds number and the SD7062 whose extra thickness (14%) has some structural advantages, particularly for the weaker material (c). All blade materials gave feasible designs with material (d) the only one that required a blade shell thickness greater than the specified minimum value of 1% of the blade chord. Generally, the blade chord and twist increased as starting was given greater importance. In all cases, the associated increase in blade inertia was outweighed by the larger aerodynamic torque. Materials (a), (b), and (d) were better suited to the SG6043 airfoil whereas ABS-M30 benefitted from the thicker SD7062 section.