- Title
- An optimum wind power output model for concentrator augmented wind turbines (CAWTs)
- Creator
- Shonhiwa, Chipo
- Subject
- Wind power Wind turbines
- Date Issued
- 2017
- Date
- 2017
- Type
- Thesis
- Type
- Doctoral
- Type
- PhD
- Identifier
- http://hdl.handle.net/10353/8692
- Identifier
- vital:33427
- Description
- The aim of this study was to develop an optimum wind power output model for concentrator augmented wind turbines (CAWTs), which can operate in low wind speed areas. This study was done using computational fluid dynamics modelling (CFD), theoretical and experimental work. Currently the wind resource is contributing 2.5percent of the global electricity supply and is anticipated to increase to by 2050. Despite this, the contribution to wind energy consumption share by South Africa is still low having just exceeded in 2015. Like many other countries, South Africa agrees that climate change is one of the biggest challenges currently being faced by mankind and acknowledges that tackling it requires collaborative effort from all. The Integrated Resource Plan (IRP 2010-2030) passed in 2010 targets 26.3percent renewable energy contribution to national energy consumption by the year 2030 with 10.3percent coming from wind energy hence contributing to abatement of climate change. 1518percent 1 000 MW Small wind turbines are known for their vital contribution to providing electricity in remote areas. Their power output is mainly influenced by the turbine rotor diameter and wind speed which depend on tower height. A cost benefit analysis conducted basing on increasing wind speed by increasing the turbine tower height revealed that for small wind turbines, the optimal height is . Concentrator Augmented Wind Turbines (CAWTs) are one of several concepts that have been suggested to increase the power output per unit rotor cross-sectional area by increasing the wind speed upstream of the turbine. Although some research effort has been put in this area, the major drawback is that the effect of concentrator geometry and environmental conditions on the aerodynamics and hence ultimate performance of CAWTs is still not clear. Also, the CAWTs systems that have been made so far, do not track the wind resulting in CAWT systems receiving wind from one direction thus limiting their performance. 25 m Wind has a very low energy density in nature implying that a bigger rotor area is required to harness kinetic energy for generation of meaningful electrical energy. This has resulted in higher costs of producing energy from wind than conventional sources of energy such as fossil fuels and hydro. To lower the cost of wind energy, researchers have come up with several initiatives to boost wind turbine power output. A brief review of various concepts that have been used in this study included: history of wind turbines, South Africa’s political will to abatement of climate change, wind resource assessment, power output augmentation, estimation of air density, historical development of CAWTs, fundamental parameters influencing the performance of CAWTs, mathematical modelling of wind turbines and dynamic similarity. Some facts were borrowed from these concepts to come up with the current study and explain the observations. With a view to assess any concept, it is necessary to study the fundamental basis from which it originates. Thus, it was vital to develop a fundamental basis of CAWT performance from which solutions to currently prevailing questions on the relationships among the governing parameters were obtained. The momentum theory of bare wind turbines, which is also found in literature was described. A similar approach was then used for developing the theory of CAWT systems. The theories of concentrator losses, density variation with weather conditions and turbulence modelling were also described. It was of utmost significance to evaluate the wind power potential of the Western part of the Eastern Cape Province to assess whether there would be a need for the concentrator augmented wind turbines (CAWTs) in the province and all other regions with similar or lower wind speeds in the country. In this study, five-year-long, hourly average wind speed series between January 2009 and December 2013 for six weather stations in the western part of the Eastern Cape (Bisho, Fort Beaufort, Graaff–Reinet, Grahamstown, Port Elizabeth and Queenstown) were statistically analysed using the Weibull distribution function. The dimensionless Weibull shape parameter varied from 1.7 to 2.2. All the values were low indicating that there is widely dispersed data. This means that the data tend to be distributed uniformly over a relatively wide range wind speed. Therefore, this has a positive implication on wind power generation in all the studied areas because if a suitable turbine is installed, it would get enough wind speed to run for the greater part of the year. The scale parameter varied between 3.5 and 6.3. The values for all the sites except Port Elizabeth were relatively low implying that the days of high wind speeds are few. Therefore, wind turbines that require high wind speeds for operation are not suitable here.
- Format
- 152 leaves
- Format
- Publisher
- University of Fort Hare
- Publisher
- Faculty of Science and Agriculture
- Language
- English
- Rights
- University of Fort Hare
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