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 Assessing potential for net-zero energy building retrofits in commercial buildings using on-site photovoltaic (PV) generation: a case study of Durban-South Africa(2019) Davies, GarethRetrofitting existing buildings towards NZEB (net-zero energy building) offers significant benefits in terms of reducing operational electricity consumption and operating costs as well as reducing GHG emissions. The increased efficiency and economic cost competitiveness of renewable energy technologies, as well as the advances in building science and energy modelling, continue to evolve along with the increased demand for energy security, thus allowing for advancement of NZEB. But to what extent is NZEB viable for all existing commercial buildings, and what are the technical and contextual parameters that would influence the potential of NZEB retrofits? The study substantiates on these questions via a simulated performance-based analysis of four existing commercial buildings in Durban, with energy modelling and simulation as the primary data sources. The simulation data were then applied towards the assessment of the potential of retrofitting for NZEB based on passive interventions in conjunction with energy-use optimisation of active/mechanical systems and integrated RE technology in the form of site PV. The study demonstrated a reduction of 27% - 56% in overall grid-electricity consumption and carbon emissions across the case study samples. Lower FAR buildings achieved greater percentage reductions in grid-electricity consumption due to less site shading combined with larger site-area (for PV) to net floor area ratio. Longer operating schedules were also found to increase annual energy consumption while also being better suited for on-site PV generation due to consistent levels of self-consumption. User-density was found to have less significant impacts on overall electricity consumption. Payback periods for NZEB-targeting interventions were enhanced by the recent introduction of the RE tax allowance, which reduced overall payback periods by 2-3 years with two of the case study buildings achieving 4-6 year yields which is considered to be within an acceptable range based on prevailing efficiency and cost levels of the assessed interventions. The study found that the efficacy and practicality of on-site generation PV is limited by grid constraints for building use-types with a high export balance, and for certain high-density sites due to high shading levels. The study recommends smart-grid integration which would connect buildings that can benefit from either consuming or exporting RE and thus ensure annual energy consumption and GHGemissions in the sub-sector could be brought into line with the 38% reduction compared to the 2050 Nationally Determined Contribution GHG emission reduction targetItem Innovative green finance for renewable energy interventions in gap housing for South Africa: a case study of rooftop PV for Windmill park residential complex Johannesburg(2018) Kaluba, BesaIn light of the current rapid growth of the gap housing market segment, the electricity crisis facing South Africa and adverse impacts of coal-based electricity generation on climate change, this study helps to qualify the viability of integrating rooftop solar pv in gap housing towards improving gap housing affordability and mitigating power challenges currently facing the country. Using a case study approach, the study addressed four key research questions which are: affordability of housing in the gap housing market in South Africa, estimating the generation potential from the available rooftop space in the case study area, establishing a business model for integrating rooftop solar pv in the gap housing market, and the extent to which rooftop solar pv can augment housing affordability in the gap market segment. Various software and web-based applications were utilized to establish the solar pv generation potential of the study area. From the available rooftop space of 36 593.65m2 in Windmill Park Estate, a production potential of 7 848 124.71 kW/h per annum was estimated. This is sufficient to make the estate a net-zero grid electricity consumer. Based on these findings, two scenarios were analysed using the net present value (NPV) to determine the profitability and the business model for integrating rooftop solar pv in the case study. Exporting only 50% of the generated electricity proved the most viable scenario with thirteen to fourteen year payback period. Affordability to purchase housing in the estate increased by R 399,633.30 in the twentieth year and rent affordability increased by R 706.25 per month in the first year. This understanding of the extent to which rooftop solar pv can augment housing affordability is important to encourage, guide and inform policy makers and other stakeholders in the formulation and deployment of various gap housing finance schemes that support such interventions.Item Local contect requirements and the manufacture of solar photovoltaic components in South Africa(2018) Kuzwayo, MandlesizweThe outputs in this report are based on the experiences, beliefs and perceptions of a crosssection of Solar Photovoltaic industry stakeholders on whether Local Content Requirements is an appropriate policy instrument for building a local industry and the extent to which the Local Content Requirements of the Renewable Energy Independent Power Producer Procurement Programme have led to an increase in the South African solar component manufacturing capacity since the programme’s inception in November 2011. Protectionist policies, including Local Content Requirements, were used by now industrialised countries to develop their respective countries, and continue to be used to this day despite World Trade Organisation prohibitions. Four models on building local industries are discussed and their relationship to the two research questions explored. Interview participants agreed that the Renewable Energy Independent Power Producer Procurement Programme was instrumental in building a large-scale local renewable energy industry in the country, created jobs and excitement around manufacturing capacity potential. However, many believe that programme design and implementation interventions are required to improve the programme’s localisation impacts. The latest draft Integrated Resource Plan’s sizeable allocation for Solar Photovoltaic until 2030 presents an opportunity to drastically improve localisation benefits for the country.Item Decentralised electricity generation through rooftop solar photovoltaics (PVs) in Zambia : a case study of the engineering institute of Zambia (EIZ) office building project, Lusaka(2018) Samunete, JosephWhereas there has been significant study and development of national strategic plans on electricity generation from renewable energy in general in Zambia, specific studies and research on decentralised electricity generation via rooftop solar PVs from buildings and their potential to enhance Zambia’s electricity generation goals have not systematically been done. The study applies a case study of the Engineering Institute of Zambia office building that is at construction stage but is determined to incorporate a rooftop solar PV system. Using DesignBuilder and Energyplus simulation software, the building was modelled and analysed for this potential. In addition, based on interview data from various experts and secondary data from national plans, the study evaluated policy, regulatory and market frameworks which could catalyse the increased deployment of such systems in Zambia. Using financial analysis tools of payback period, return on investment and net present value the study undertook a number of business case scenarios in order to conceptualize a responsive business model. The study finds that from the initial estimate, the available roof space had the capacity to net out the baseline annual electricity consumption of 287,707kWh and generate a surplus of 63,519kWh/year before optimisation. Optimisation of the baseline consumption through a combination of two viable energy efficiency interventions reduced the baseline annual consumption by 35% to 186,904kWh with related payback period of nine years, ROI of 518% over a 25 year analysis period and a NPV of 623,344.00 ZMK. Based on these findings, three business case scenarios for the solar PV system were analysed and two out of the three were adopted. One scenario assumed a net-zero building and another one assumed that the surplus electricity generated on non-business days is exported to the grid were adopted. Following this finding, a business model centred on an integrated energy service company (IESCo) was identified as the most appropriate model to respond to the uptake barriers of this technology and thus leverage on the emerging progressive support mechanisms. The overall findings of the study thus support the working hypothesis of the study which deemed that through the framework of a responsive business model, decentralised electricity generation through rooftop solar PV can greatly enhance energy security and mitigate GHG-emission for Zambia.Item Opportunities and challenges for distributed generation with rooftop photovoltaic (PV) for Uganda: a case study crusader house, Kampala(2018) Migisha, CeaserDistributed generation with rooftop PV technology is increasingly attracting attention as a strategy to enhance energy security for cities and as a critical climate-change mitigation intervention globally. In order to interrogate the strategy for a developing country context, the study applies a case study approach to explore responsive business models as well as related opportunities and challenges of DGRTPV deployment in Uganda, given the country’s advantage of abundant solar radiation as a result of favourable location across the equator. The study substantiates on the research question which focuses on rooftop PV business models, policy and legislation environment, energy efficiency interventions and financial mechanisms for expedited adoption of the technological innovation for commercial buildings in Uganda. In order to substantiate on the working hypothesis, interviews were conducted with key informants from the case study building-occupants and property manager, MEMD, ERA, KCCA, and UMEME. Data were collected using semi-structured interviews as well as energy audits and energy performance simulations of the case study building based on Excel and Design-Builder Energy-Plus software in order to ascertain performance under alternative intervention scenarios. The case study building consists of two blocks (the main block which is 5 storeys and the annex which is 4 storeys) and is grid-connected, but has standby generator with diesel consumption of up to 4,800 litres/year. The building was built in 1988 for the main block and 1993 for the annex and no energy efficiency interventions have been implemented so far. Overall, the baseline energy consumption is at 191,127.5kWh/year excluding diesel generation at 100,000kWh/year (2010 blackouts were 8 hours per day but at present, the generator is used for only 2 hours per day). Simulations, manual calculations, and economic feasibility appraisals were applied to guide on the viable energy efficiency and photovoltaic (PV) interventions. This resulted into viable energy reduction of 90,404.5kWh/year with a payback period of 0.6 months for lighting systems and additional energy efficiency interventions. Rooftop PV generation evaluation indicated an output of approximately 124,328.75kWh per year with the payback period of 7.6 years. Overall the study finds that the roof space area (610m2 ) of the building offers potential for generating surplus electricity which can be fed to the grid when responsive policy/regulatory environment is effected. The solar service business model is prioritised as the most viable given the current policy/regulatory landscape for Uganda as well as envisaged policy changes in the short term. Given Uganda’s low-carbon electricity generation mix, the study finds that opportunity for carbon emission reduction for the building would mainly arise from the displacement of the standby diesel generator whose current emission is estimated at 4,000kg/year. The study therefore concludes that DGRTPV deployment is now mature for scale-up in commercial buildings for Uganda.Item OPTO-electrical characterisation of carbon-based thin film solar cells of excitonic descent in bulk heterojuction architecture(2017) Jhamba, LordwellOrganic photovoltaic cells (OPVCs) continue to be intensively investigated due to their low cost and high utility potential. However, their low power conversion efficiency (PCE) has limited their full commercialization. The efficiency of the OPVCs is dependent on charge injection mechanisms, morphology and their underlying kinetics and energetics. Understanding the mechanisms that influence the efficiency of conjugated polymer solar cells is therefore pivotal to the enhancement of the devices‟ performance and the implementation of low priced fabrication technologies. In this regard, we investigated the dependence of the efficiency of organic solar cells on light intensity (I) using thin films of P3HT:PCBM blends, sandwiched between ITO/PEDOT:PSS and Al electrodes, the assembly of which was subjected to differing illumination intensities. Since charge transport through interfaces of such devices depends on charge carrier injection mechanisms, charge injection mechanisms at metal-organic active layer (here-in referred to as „metal-active layer‟) interfaces in the devices were studied under changing external voltage bias. Use was made of the Richardson-Schottky (R-S) thermionic emission currents and those due to Fowler-Nordheim (FN) tunneling in generating complete J(V) curves which were compared with those obtained through combined graphical representations of the variation of open circuit voltage (Voc) and efficiency (η) with light intensity. This led to the findings that under forward bias, the metal- active layer junction of an organic solar cell becomes ohmic after a certain threshold electrical field (Ethresh tunn) associated with quantum mechanical tunneling of charge carriers through the device‟s respective interfaces. Furthermore, we found that the open circuit voltage at which efficiency starts to decrease (Voc thresh eff. decay) approximates in magnitude the internal threshold open circuit voltage (Voc thresh tunn) at which FN quantum mechanical tunneling starts within the device at the electrode (a metal)- active layer interface. Explanatory findings were that for photoactive P3HT:PCBM composite devices, increasing white light intensity incident on them increases the photogenerated open circuit voltages that increasingly bias them with voltages, which with effect from the thresholds due to opto-electrical mechanisms at the devices‟ metal-active layer interfaces, are sufficient to greatly increase the dark currents. The increased dark current reduces the short circuit current density significantly, which in turn inflicts a likewise decrease in the power conversion efficiency of the devices. The theme of the next set of investigations was on the characteristic changes in the opto-electrical properties of the 1:1 blend of P3HT:PCBM with thickness of the active layer in ITO/PEDOT:PSS/P3HT:PCBM/Al solar cells, with intentions of finding out their effect on the threshold voltage at which efficiency starts to decrease (Vthreshold eff decay) and also for purposes of optimizing the thickness of the active layer. To obtain different active layer thicknesses (ALTs), each sample was cast at different spin-coat speeds. The thicknesses determined by surface profilometer through variation of spin-coating speeds were 61.5, 69.4, 77.1 and 84.5 nm. Whilst this study‟s empirical results demonstrated optimal performance at approximately 77.1 nm active layer thickness, the overall findings have been that the existence of a static universal optimum active layer thickness is not practical. Such an optimum rather exhibits contextual dependence. Annealing investigations revolved around attempts to empirically broaden and deepen the presently scarce understanding of the fundamental mechanisms defining thermal annealing process in conjugated polymers. To achieve this, we studied the opto-electrical effects of post-fabrication thermal annealing of bulk heterojunction ITO/PEDOT:PSS/P3HT:PCBM/AL solar cells at different heat treatment temperatures in the range 65 – 180 °C. The photoactive P3HT:PCBM layer was cast in air. The effect of air exposure has been found to chemically dope the polymer. Dedoping brought in by thermal annealing has been demonstrated to be responsible for the aggravated drop of efficiency. Summary findings lead to the generalisation that annealing of polymers is a two-step process, the first of which causes a decrease in conductivity, followed by its increase. Although impurity dedoping decreases „under dark‟ current density in certain regions of the active P3HT:PCBM composite layer during annealing, it has beneficial aftermaths, some of which surface upon illumination of the P3HT:PCBM-based solar cell. When illuminated, photogenerated current density in the illuminated device immediately increases. This happens so, because of less electron capture and immobilization during illumination of the annealed device. Morphologically, thermal annealing has been found to enhance the formation of the deeply quenched bicontinuous network at the nanoscale between P3HT and PCBM, leading to high efficiency devices. We propose that the beneficial structure formation in P3HT:PCBM blends, is initiated by the crystallization of P3HT as it segregates PCBM, possibly to the amorphous P3HT. Thermal annealing renders significant enhancement in Jsc, Voc and FF of the annealed device. The optical absorbance was found to increase with increase in annealing temperature.Item Synthesis and characterization of Cu-based telluride semiconductor materials for application in photovoltaic cells(2017) Ntholeng, NthabisengThe colloidal method has extensively been used to synthesize ternary and quaternary copper sulfides and selenides. Although tellurides form part of the chalcogenides, little has been reported on them particularly the synthesis of these nanostructures. Achieving high-quality nanocrystals through colloidal synthesis requires thorough monitoring of parameters such as time, solvent, precursor as they affect nucleation and growth of the nanocrystals. Herein, we report on the colloidal synthesis of ternary CuInTe2 and quaternary CuIn1-xGaxTe2 nanostructured semiconductor materials. A typical synthesis of CuInTe2 entailed varying reaction temperature. At temperatures below 250 °C, no formation of CuInTe2 was seen. At 250 °C formation of CuInTe2 could be observed with the formation of binary impurities. A change in the sequence in which precursors were added at 250 °C yielded pure CuInTe2. Applying different surfactants aided in achieving differently structured morphologies of CuInTe2 nanocrystals. Morphology varied from rods, cubes, nanosheets etc. Different morphologies resulted in different optical properties with the high optical band gap of 1.22 eV measured for 1D rods. Different precursors were employed in the synthesis of quaternary CuIn1-xGaxTe2. Precursor 2 (entailed the use of Cu (acac)2, In (acac)3 and Ga(acac)3) yielded pure CuIn1-xGaxTe2 phase with no formation of impurities. Variation in reaction time influenced the optical properties of the quaternary CuIn1-xGaxTe2 with high band gap obtained at low reaction time (30 min). A change in Ga and In concentration resulted in reduced lattice parameters a and c with lowest values obtained with the highest Ga concentration. However, achieving the intended concentration proved challenging due to the loss of the material during synthesis. Increasing the Ga concentration resulted in a high optical band gap. Conducting the reaction with Hexadecylamine (HDA) resulted in a relatively high optical band though the formation of impurities was evident. The obtained band gap can be attributed to small sized particles as evident from TEM results. Heterojunction ZnO/CIT and ZnO/CIGT solar cell devices were fabricated through a simple solution approach. The performance of ZnO/CIGT device was superior to that of ZnO/CIT in which efficiency increased from 0.26-0.78%. In the ZnO/CIT device, high Voc of 880 mV was recorded while 573.66 mV was measured for ZnO/CIGT device. Chemical and thermal treatments were performed on the ZnO/CIGT devices. The efficiency increased from 0.78 1.25% when the device was chemically treated with a short-chain EDT ligand. A high conversion efficiency of 2.14% was recorded for devices annealed at 300 °C. High annealing temperatures resulted in poor device performance with the lowest efficiency of 0.089% obtained at annealing temperatures of 500 °C attributed to the leaching out of In and Ga into the ZnO layer.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.