3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item An interface for a photovoltaic module to an ad-hoc, low voltage, DC distributed grid(2019) Dangor, Mohammed Raees EbrahimThis research has contributed to the advancement of the Personal Consumer (PeCo) grid concept and has furthered the technology from a conceptual prototype to becoming a viable rural electrification solution. The PeCo grid is a conceptual ad-hoc, 12V, DC distributed grid aimed at providing an electrification solution for singe rural households. The grid is composed of an interconnection of renewable energy sources, battery storage and loads. A shortcoming of the PeCo grid, exposed on the first experimental prototype grid, was that undesirable over-voltages occurred during load removal events due to an over-supply of power to the grid after the load was disconnected. This research entails the development of an interface for a photovoltaic (PV) module to the PeCo grid that aims to overcome this shortcoming and to extend the capabilities of and further the technology. At the interface, the voltage of the PV module is matched to the grid voltage. Power flow from the PV module to the grid is controlled according to a control strategy modelled as a state diagram and executed by a micro controller unit (MCU). The power converter at the interface is a Flyback converter operating in discontinuous conduction mode (DCM). A model was derived to estimate the primary-side inductor current of a DCM Flyback converter and applied to perform model-based maximum power point tracking (MPPT). This obviated the need for any current sensors at the interface. The response of the MCU to a load removal event was tested and validated to overcome the shortcoming of the experimental grid. The model-based MPPT solution was tested using the PeCo grid as a test platform and validated to successfully perform MPPT. The real world application of the interface was validated and the technology deemed suitable for rural electrification.Item Knowledge management determinants of breakthrough research productivity(2018) Rubin, AsafRecent technological advancements have brought about a wave of drastic change in the global supply and demand of knowledge and subsequently, in the generation of innovation. However, it has been argued that some industries and academic fields do not sufficiently take advantage of new opportunities afforded by the widespread, free and open availability of knowledge. Terms such as the Death of Innovation, Innovation Failure and Academic Failure have been used to describe the market failure of industrial Research and Development (R&D) and certain forms of academic research to sufficiently leverage these new opportunities, particularly with regard to societal problem-solving. An extensive and rapidly growing body of literature pertaining to new modes of knowledge productivity, such as open innovation, crowdsourcing and crowdfunding, through the use of the Internet, has demonstrated evidence that certain new technologies and methodologies may indeed offer significant economies of scope and scale in innovative problem solving. However, misaligned incentives may in some cases prevent the efficient leveraging of these new modes of productivity. These effects may be particularly pronounced in the academic context, which has long been criticised for its strict adherence to tradition and paradigmatic convergence. Despite this body of literature, there is a lack of knowledge as to the extent that academic researchers do indeed take advantage of these new modes of productivity, and furthermore, the extent to which their adoption influences research productivity. Thus, this research seeks to investigate the relationship between a behavioral orientation called ‘technological propensity’, or the extent to which individuals seize opportunities that offer significant economies of scale (such as crowdsourcing) and productivity. This research is undertaken at the individual level of analysis, which necessitates corresponding measurements of proximal, human-resources management determinants which may impact this relationship. These include personality, motivational values, work climate perceptions and human capital investments. Three studies are conducted to ascertain the extent of the relationships between these variables, and to provide a holistic perspective of the relationships between variables. First, a qualitative study, which samples award-winning scientists, academics researchers and innovators from across the world was conducted to develop theory. Amongst these are 3 Nobel Prize winners, 3 Lasker Award winners and 1 Fields Medal winner, among others. Second, a quantitative study, which sampled South African academic researchers, was conducted to test theory. Third and finally, a second quantitative study, which sampled ‘crowd-workers’, or users of an Internet-based crowdsourcing platform known as Amazon’s Mechanical Turk, was conducted to provide ii further insights into the relationships under study, in the open knowledge space (i.e. over the Internet). Qualitative data is analysed inductively, using thematic content analysis. Quantitative data is analysed through a series of statistical analyses, including multiple regression, mediation and moderation analyses. The findings of these studies suggest that the relationship between technological propensity and productivity is context-dependent and may only be suitable as a complementary methodology to certain forms of academic research, which is especially constrained by outside influences. Certain new modes of productivity may indeed enhance the rate at which ‘breakthrough’, or radically innovative research outputs are generated. The findings also suggest that differences in certain values-configurations and human capital investments may significantly impact this relationship. Based on the research findings, recommendations are made to improve research productivity in these contexts and recommendations for practice and for further research are made.Item Solar cell device simulations from ab initio data and the implementation of efficiency enhancing techniques(2018) Mokgosi, Itumeleng SiphiweWith the global energy consumption at an all-time high and the demand for energy estimated to triple by 2050, renewable energy sources such as solar are pivotal in an addressing this global energy demand. Solar power generation by photovoltaic cells enjoys several advantages compared to other forms of electricity generation such as a reduced fossil fuel dependence, modularity, easy and flexible installation, and scalability. The development of novel solar cells that offer increased efficiencies is an integral component of the process of addressing the global energy needs. Solar cell device simulations offer a cost-effective means to explore the impact of different material properties on the overall efficiency of the solar cell. The use of ab initio calculated material properties that serve as an import for the device simulations offers a means to easily study and estimate the typical solar cell efficiencies of different types of solar cells. The implementation of new light harnessing features, like frequency conversion layers or plasmonic nanoparticles, and the integration of these futures into existing device simulation codes serves as a useful tool that aids solar cell development. This work explores the theoretical and numerical background for the simulation of solar cell devices. A brief explanation of how ab initio calculated parameters can be used, together with the implementation of frequency conversion techniques in existing simulation codes is given. It is shown that the solar cell performance parameters can be well approximated using ab intio parameters. Also, the positive effect of frequency conversion techniques is demonstrated with examples of how this tool can be implemented in existing solar cell device simulation codes. The approaches discussed in this work can serve as a good framework for the modeling of novel solar cell devicesItem Synthesis of N-doped broken hollow carbon spheres and inorganic-organic hybrid perovskite materials for application in photovoltaic devices(2018) Baloyi, HajeccarimThe mandate for renewable energy sources to replace the current reliance on fossil fuels as a primary energy source has recently attracted a lot of research interest. The research has also focussed on bringing the technologies that take into consideration the goal of reducing environmental pollution. Consequently, approaches using photovoltaic (PV) technologies have been a promising arena to tackle the problem facing energy sources. Recently, more focus has been placed on improving the power conversion efficiency (PCE) of PV devices, such as organic and/or organic-inorganic hybrid perovskite solar cells. Therefore, in this work two different materials were applied in two independent PV devices, namely organic and/or organic-inorganic hybrid perovskite solar cells. One study employed nitrogen doped broken hollow carbon spheres (N-bHCSs), with an aim of enhancing the electronic properties of the P3HT:PCBM active layer of an organic photovoltaic (OPV) solar cell. N-bHCSs were successfully synthesized using a horizontal chemical vapour deposition method (H-CVD) employing a template-based method and the carbon was doped using in-situ and ex-situ doping techniques. Pyridine, acetonitrile and toluene were used as both carbon and nitrogen precursors. The dispersity of the SiO2 spheres (i.e. templates) was found to play a role on the breakage of the N-bHCSs. Incorporation of the N-bHCSs into the P3HT:PCBM active layer was found to enhance the charge transfer and this led to less recombination of photogenerated charges in the interface between the donor and acceptor. The current-voltage (I-V) characteristics of the ITO/PEPOT:PSS/P3HT:PCBM:N-bHCSs/Al solar cell devices revealed an increased chargetransport distance due to increased electron density by n-type doping from the N-bHCSs. The second study employed the organic-inorganic hybrid perovskite (CH3NH3PbI3) material as a light harvesting layer in an ITO/PEDOT:PSS/CH3NH3PbI3/PC6BM/Al solar cell device. Initially, the device parameters were optimised to obtain the best performing device. These include parameters such as the degradation of the hybrid film as a function of time and air exposure. A rapid degradation was seen on the device after 24 h of air exposure which was accompanied by the decrease in the PV performance of the device. The degradation was visually seen by the formation of crystal grains (i.e. “islands”) on the perovskite film.Item Solar PV for decentralised generation for commercial buildings in Nigeria: a case study of the architecture building at Kodi state poltechnic(2017) Adejoro, Ipinmoroti SamuelThe centralised energy generation system has been constantly criticised for not meeting the demand of Nigerian consumers. Recent studies on Nigeria’s energy crises suggest that there should be an urgent adoption of decentralized generation (DG) as a means of alleviating energy poverty in the country, and as a way of reducing greenhouse gas emission (GHG) from the popular fossil-fuel based standalone generators. However, businesses today are anxiously trying to find ways to lower their energy related expenditures. In line with these assertions, and using a case study of the Department of Architectural Office Building (DAOB) to incorporate rooftop solar PV system, the study uses a Design Builder and Energy plus simulation software to model and analyse the DAOB. This study is based on primary and secondary data sources. The study assessed policy regulatory and market structures which could stimulate the increased deployment of such systems in Nigeria. The electricity bills for one year reported an annual consumption of 12,407 kWh, at the cost of N297, 762 ($945) and likewise the cost of operating a building on diesel generator for a period of one year was calculated at N2, 688,000 ($8,513) while the status-quo baseline energy consumption of the building from simulation and the cost implication per annum was 69,733 kWh and ₦1,673,592 ($5,579) respectively. Optimisation of the baseline consumption through a combination of three feasible energy efficiency initiatives reduced the baseline annual consumption by 47% from 69,733kWh to 37,298 kWh. The roof had the capacity to generate 155,347kWh which could cover for both the baseline and the optimised annual electricity consumption. The analysis revealed further that the roof could generate a surplus of 118,045 kWh/annum based on the optimised energy consumption. Using financial analysis tools of payback period, return on investment and net present value, the study undertook a number of business case scenarios to establish a viable business model. Based on the financial analysis performed, a Solar Power Purchase Agreement (SPPA) business model was identified as the most suitable to overcome the barrier of upfront cost.Item Synthesis and characterisation of hybrid nanocomposites using polyvinylcarbazole and metal selenides to demonstrate photovoltaic properties(2017) Govindraju, Stefan JoelDue to a high global demand for energy, research groups have been focusing a lot of energy into finding alternative and cleaner energy sources. Solar power has all the attributes to be the energy of the future. Solar power is abundantly available and is a cleaner form of energy as compared to the market-leading fossil fuels. In this thesis, we consider new materials that can be used in hybrid solar cells. These new materials combine the properties of inorganic nanomaterials and polymers. The nanomaterials possess unique properties that can be exploited and the polymers allow for the thin films to potentially be light weight and flexible. Copper selenide was synthesized and characterized to produce particles with different sizes as a function of time. These size variations are shown to emit a spectrum of different colours. In addition the particles synthesized at various temperatures are reported. Temperature had an effect on the size of the particles with bigger sizes obtained as the temperature was increased. Also shown in the results is that Cu2Se nanocrystals were quite resistant to changes with the sizes marginally increasing with increasing time and temperature. A hybrid material using a conductive polymer polyvinylcarbazole (PVK) and copper selenide was synthesized and used as the active layer via a spin coating technique to fabricate a solar cell. Varying amounts (10% - 50%) of Cu2Se nanocrystals were used in the polymer nanocomposites. The 10% weight loading resulted in the highest efficiency of 0.74% whilst successive addition of the nanocrystals affected the polymeric structure of PVK thus resulting in solar cells with even lower efficiencies. Niobium selenide was synthesized via the colloidal method using TOP/HDA combination for the first time. The effect of time on the particles synthesized using a 1:1 mole ratio of Nb:Se was negligible with particles showing similar properties. The XRD of the samples revealed that they were amorphous thus making it difficult to conclusively say that niobium selenide was synthesized successfully. The samples were then annealed however only small improvements were observed. The concentration of the selenium was then increased in order to form the more common NbSe2 and NbSe3. The XRD showed the formation of NbSe2 and NbSe3 for 1:2 and 1:3 Nb:Se ratios respectively. In addition, the particles resembled 2D nanostructures readily observed in layered materials such as NbSe2 and NbSe3. However, some impurities in the form of oxides were still observed. Hybrid solar cells prepared from the amorphous 1:1, 1:2 and 1:3 Nb:Se samples were fabricated. The NbSe3 composite had the best performing solar cell with the power conversion efficiency of 3.234% with the amorphous particles generating no current.Item Approaches to enhance optical absorption and efficiency of photovoltaic device(2017) Mayimele, NhluvukoOrganic Photovoltaic (OPV) is an environmental friendly technology that promises e cient and e ective harvesting of solar energy. The organic polymers used in the fabrication of OPVs are characterized by low weight, tunable electrical and optical properties. However, the low photo-conversion e ciency (PCE) and instability in air remains a major drawback that limits their commercialization. The project seeks to increase the PCE of a cheap photovoltaic device using plasmonic e ects and rare earth doped waveguides to modify the optical response in the active layer. Incorporating regularly shaped silver (Ag) nanoparticles (NPs) in OPVs through the surface plasmon resonance will enhance tunable absorption and scattering of light. These NPs are prepared by reducing AgNO3 with N,N-dimethylformamide (DMF) and using 2,2- Poly(vinylpyrrolidone) (PVP) as a stabiliser at di erent reaction times. The Ag NPs have shown di erent shapes such as spherical and prism shapes of 14, 15 and 16 nm visualised by TEM.Item Investigating the feasibility & impact of a solar array for Wits West Campus by using historical solar and power data(2016) Singh, AjeshniThis dissertation uses historical electrical consumption/load and actual solar radiation data to design a solar array for the University of the Witwatersrand’s West Campus. The array must meet the campus’s minimum demand as selling excess generated power back to the utility is not possible at this stage. The financial and spatial impact of adjusting the size of the array, design losses and cloud cover are also investigated. In addition to this, the influence on the payback period of financial variables such as taxes, electricity and start-up costs are also explored. The solar array system design process starts by determining the amount of power that the array must produce or supplement. Thereafter, load estimates and electrical consumption figures that are provided by utility bills or measured with load monitoring equipment are analysed. Furthermore, system losses are factored in which ultimately increases the size of the array. Once all the input variables are analysed, the amount of available solar radiation in the area where the array will be installed is required to determine the amount of energy that the array can produce. Several free databases with this information are available but it is found that this data over predicts the availability of solar radiation. The University has been monitoring the electrical consumption of West Campus since 2012 and solar radiation data is also available for this site. Comparing the satellite derived and measured datasets found that the ground monitored data is 25 % more accurate and therefore better suited for designing a solar array. Individually adjusting the design and financial variables changes the payback period between 3 – 17 %. Combining all the variables can reduce the payback of option 1 from 9.6 years to 6.1 years. Clear legislation needs to be developed for the uptake of renewable energy resources and supported by better rebates for renewable users and harsher taxes for non-renewable users. Should legislation change and if additional capital is available, a larger array will benefit the University more and should be installed as the difference between payback periods is not significant. This is mainly due to decreased costs associated with a higher yield. The financial benefits of a larger array will also be more lucrative if better rebates are enforced.Item Synthesis and characterization of solid, hollow, core-shell and worm-like carbon nanostructures for applications in organic photovoltaic devices and chemical sensors(2016) Mutuma, Bridget KaniniThe synthesis of carbon spheres (solid and hollow) for application in organic photovoltaics and chemical sensors is a means of using inexpensive and readily processable carbons to eliminate global warming and to monitor harmful gases. The synthesis conditions used to make solid carbon spheres can also be used to tailor their structural, paramagnetic and thermal properties. More so, the ability to tailor the morphology, surface, structural and electronic properties of the hollow carbon spheres by a templating method is an added advantage to their applicability in electronic devices. Solid carbon spheres were synthesized by a vertically oriented chemical vapor deposition (CVD) reactor using acetylene as a carbon source and argon or hydrogen as the carrier gas. The flow rates of the acetylene or carrier gases determined the particle sizes of the carbon spheres. Annealing of carbon spheres in hydrogen resulted in an increase in thermal stability, fewer defects and narrower paramagnetic signals relative to the carbon spheres annealed in argon gas. In contrast, carbon spheres annealed in argon exhibited an increase in the number of defects, a decrease in thermal stability and broader paramagnetic signals. Doped carbon spheres portrayed an increase in ID/IG ratios, a decrease in thermal stability and stronger paramagnetic signals due to the presence of defects induced by nitrogen. The N doped carbon spheres synthesized in H2 comprised of 48% pyridinic-N, 22% pyrrolic-N and 24% quaternary -N while the N doped spheres obtained in the presence of Ar had 17% pyridinic- N, 20% pyrrolic-N and 49% quaternary-N. The presence of a higher percentage of pyridinic- N confirms the presence of more edge defects in carbon spheres synthesized under H2 gas corroborating with the stronger paramagnetic signal observed from the ESR spectra. Consequently, a higher N/C ratio was exhibited in the N doped CSs obtained in the presence of H2 (4.96) than in the presence of Ar (3.68). This could be attributed to the presence of edge defects in carbon spheres synthesized in the presence of H2 gas. The induction of edge defects in carbon spheres in the presence of H2 gas without the aid of a metal catalyst opens a platform for regulating surface and catalytic reactions using H2 gas. Pristine and mesoporous SiO2 spheres were synthesized using a modified Stober method. Carbonization of the pristine SiO2, pristine SiO2@PVP, mesoporous SiO2 and mesoporous SiO2@PVP spheres was carried out using a bubbling method with toluene as the carbon source and argon as the carrier gas in a CVD reactor for 1 h. Upon SiO2 removal, hollow carbon nanostructures of varying morphologies were obtained. The polyvinylpyrrolidone (PVP) adsorption time, PVP concentration, SiO2 mesoporosity, SiO2 particle size dispersion, and carbonization time played a role in the formation of unique hollow carbon nanostructures; complete HCSs, broken HCSs, deformed HCSs, edge connected, open ended, wormlike and bubble-like HCSs. The mesoporous broken HCSs and open ended HCSs portrayed a hierarchical structure with a bimodal pore size distribution. The surface area properties of these materials and the ease of control of the carbon morphology gives an insight into the application of these materials as dye adsorbents. The effect of the size dispersion of Au@SiO2 sphere templates for the synthesis of hollow carbon structures was evaluated using a CVD nanocasting method. The diameter of the template, the presence of the gold nanoparticles and the amount of PVP determined the size, thickness and shape of the synthesized carbon nanostructures. Carbonization (and SiO2 removal) of Au@polydispersed silica spheres for 1 h gave a graphene-like HCS layer while longer times (2-4 h) gave nanotube like (or worm like) HCSs. These results highlight the potential use of Au@carbon core shell structures for the generation of few layered graphene-like unusual nanostructures. As a proof of concept, the wormlike carbon structures were incorporated in organic solar cells and found to give a measurable photovoltaic response. The incorporation of Au nanospheres and nanorods in a hole transport layer (PEDOT:PSS) of a solar cell device increased the current density and the photo-conversion efficiency of the device due to the local surface plasmon resonance and enhanced light scattering effects of gold. However, high series resistance and leakage currents were obtained due to barrier centres created by uneven dispersion of Au nanaorods within the polymer matrix. The performance of bulk heterojunction organic photovoltaic cells based on poly(3-hexylthiophene- 2,5-diyl) (P3HT) and 6,6-phenyl-C61-butyric acid methyl ester (PCBM) processed from chlorobenzene solution can be enhanced by solution heat treatment of the blend. The morphology of films spin coated from the heat treated blend solution reveals a more favourable diffusion of PCBM into the P3HT matrix than heating of the individual solutions separately. The films obtained from heat treated P3HT and PCBM solutions had a more homogeneous dispersion and enhanced light absorption than those obtained from solutions heat treated separately. There was a significant improvement in the performance for devices made from a solution heat treated blends relative to the non-treated blend; a maximum power conversion efficiency of 3.5% and a fill factor up to 43% was achieved under Air Mass 1.5 at 100 mW/cm2 illumination. This study also reports on the sensing characteristics of ammonia in humid environment by hollow carbon spheres, hollow carbon spheres-polyvinylpyrrolidone composite and annealed hollow carbon spheres, at 20°C and 40°C. For device fabrication, a surfactant assisted method was used to homogeneously disperse the hollow carbon spheres, allowing their deposition onto an interdigitated electrode by casting. An enhanced response and recovery time of the devices was observed at the higher working temperature. Annealing of the hollow carbon spheres resulted in a tremendous decrease in the humidity dependent ammonia sensing due to a decrease in the number of the oxygenated groups and defects in their structure. The presence of hydroxyl groups on the pristine hollow carbon sphere surface resulted in an enhanced proton conductivity. However, the ammonia sensitivity at high relative humidity in the pristine hollow carbon spheres is negligible due to the inhibition of ammonia adsorption sites by the high concentration of water molecules. The sensor response was investigated by varying both ammonia concentration and relative humidity, determining the topology of the response as a function of these two variables, and applying a tristimulus analysis in an attempt to determine the ammonia concentration independently of the relative humidity. This study demonstrates the critical role played by humidity and surface chemistry in the ammonia sensing properties of hollow carbon spheres. The studies reveal the day to day application of ammonia sensors, with temperature and humidity playing a critical role in the carbon based sensor response and recovery of the materials. These carbon based sensors that simultaneously measure ammonia and relative humidity could be applied in agricultural industries to monitor ammonia concentration in soils, fishponds and in food industries to monitor meat spoilage.