Thesis (M. S.)--Economics, Georgia Institute of Technology, 2010. / Committee Chair: Vivek Ghosal; Committee Member: Byung-Cheol Kim; Committee Member: Chun-Yu Ho; Committee Member: Tibor Besedes. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (M.A.) in History--University of Maine, 2003. / Includes vita. Includes bibliographical references (leaves 69-71).

Thesis (M.S.)--Rochester Institute of Technology, 2005. / Typescript. Includes bibliographical references (leaves 95-100).

Thesis (M.Arch.)--University of Hong Kong, 2001. / Includes special report study entitled : An education and research centre on renewable energy. Includes bibliographical references. Also available in print.

Thesis (M.S.)--Rochester Institute of Technology, 2006. / Typescript. Includes bibliographical references (leaves 182-186).

Energy plays a vital role in socio-economic development and raising living standards of human beings. The overreliance on fossil fuels results in the depletion of fossil fuels as well as environmental pollution from the green-house gases that result from the use of fossil fuels. Biomass feedstock are able to ameliorate this situation by utilizing the CO2 that has been used by plants during photosynthesis. This study investigated the suitability of the three garden grass species (Chloris gayana, Cynodon dactylon and Pennisetum clandestum) as biomass feedstock for gasification purposes. The three garden grass species were collected at the Alice Campus of the University of Fort Hare. These grass species were characterized using elemental analyser (CHNS), FT-IR, EDX and TGA. The Activation energy (Ea) of the three grass species were 48.22 kJ/mol for P. clandestum, 36.8 kJ/mol for C. gayana and 258 kJ/mol for C. dactylon. Of the three grass species, C. gayana had the lowest Activation energy of 36.8 kJ/mol and also had the highest maximum efficiency of 69 percent compared to 65.3 percent for P. clandestum and 63.5 percent for C. dactylon. Actual gasification was not carried out but the results on maximum efficiency were obtained from computer simulation of gasification.

Organo-metallic halide perovskite solar cells (PSCs) are considered as a promising alternative photovoltaic technology due to the advantages of low-cost solution fabrication capability and high power conversion efficiency (PCE). PSCs can be made using a conventional (n-i-p) structure and an inverted (p-i-n) configuration. PCE of the conventional p-i-n type PSCs is slightly higher than that of the inverted n-i-p type PSCs. However, the TiO2 electron transporting layer adopted in the conventional PSCs is formed at a high sintering temperature of >450 °C. The TiO2 electron transporting layer limits the application of conventional PSCs using flexible substrates that are not compatible with the high processing temperature. The hole extraction layer (HEL) in the inverted p-i-n type PSCs can be prepared by low-temperature solution fabrication processes, which can be adopted for achieving high performance large area flexible solar cells at a low cost. Inverted PSCs with a PCE range from 10 to 20% have been reported over the past few years. In comparison with the progresses of other photovoltaic technologies, the rapid enhancement in PCE of the PSCs offers an attractive option for commercial viability. The aim of this PhD project is to study the origin of the improvement in the performance of solution-processable inverted PSCs. The surface morphological and electronic properties of the HEL are crucial for the growth of the perovskite active layer and hence the performance of the inverted PSCs. Enhancement in short circuit current density (Jsc), reduced loss in open circuit voltage (Voc), improvement in cha Organo-metallic halide perovskite solar cells (PSCs) are considered as a promising alternative photovoltaic technology due to the advantages of low-cost solution fabrication capability and high power conversion efficiency (PCE). PSCs can be made using a conventional (n-i-p) structure and an inverted (p-i-n) configuration. PCE of the conventional p-i-n type PSCs is slightly higher than that of the inverted n-i-p type PSCs. However, the TiO2 electron transporting layer adopted in the conventional PSCs is formed at a high sintering temperature of >450 °C. The TiO2 electron transporting layer limits the application of conventional PSCs using flexible substrates that are not compatible with the high processing temperature. The hole extraction layer (HEL) in the inverted p-i-n type PSCs can be prepared by low-temperature solution fabrication processes, which can be adopted for achieving high performance large area flexible solar cells at a low cost. Inverted PSCs with a PCE range from 10 to 20% have been reported over the past few years. In comparison with the progresses of other photovoltaic technologies, the rapid enhancement in PCE of the PSCs offers an attractive option for commercial viability. The aim of this PhD project is to study the origin of the improvement in the performance of solution-processable inverted PSCs. The surface morphological and electronic properties of the HEL are crucial for the growth of the perovskite active layer and hence the performance of the inverted PSCs. Enhancement in short circuit current density (Jsc), reduced loss in open circuit voltage (Voc), improvement in charge collection efficiency (ηcc) through suppression of charge recombination were investigated systematically via controlled growth of the perovskite active layer in solution-processed inverted PSCs. Poly (3,4-ethylenedioxythiophene): poly (4-styrenesulfonate) (PEDOT:PSS) is one of the widely used solution processable conductive materials for hole transporting in different optoelectronic devices. PEDOT:PSS HEL also is a perfect electron blocking layer due to its high LUMO level. However, it has been reported that PEDOT:PSS HEL is related to the deterioration in the stability of PSCs due to its acidic and hygroscopic nature. Modification of PEDOT:PSS using solvent additives or incorporating metallic oxide nanoparticles for improving the processability and the performance of the inverted PSCs were reported. This work has been focused primary on realizing the controlled growth of perovskite active layer via HEL/perovskite interfacial modification using sodium citrate-treated PEDOT:PSS HEL and WO3-PEDOT:PSS composite HEL. Apart from investigating the properties of the modified PEDOT:PSS HELs, the purpose of the work is to improve the understanding of the effect of modified HEL on the growth of the perovskite layer, revealing the charge recombination processes under different operation conditions, analyzing change extraction probability, and thereby improving the overall performance of the PSCs. PCE of >11.30% was achieved for PSCs with a sodium citrate-modified PEDOT:PSS HEL, which is >20% higher than that of a structurally identical control device having a pristine PEDOT:PSS HEL (9.16%). The incident photon to current efficiency (IPCE) and light intensity-dependent J-V measurements reveal that the use of the sodium citrate-modified PEDOT:PSS HEL helps to boost the performance of the inverted PSCs in two ways: (1) it improves the processability of perovskite active layer on HEL, and (2) it enables to enhance the charge extraction efficiency at the HEL/perovskite interface. The suppression of charge recombination in the PSCs with a modified HEL also was examined using photocurrent-effective voltage (Jph-Veff) and transient photocurrent (TPC) measurements. Morphological and structural properties of the perovskite layers were investigated using the scanning electron microscope (SEM) and X-ray diffraction (XRD) measurements. The results reveal that high quality perovskite active layer on the modified HEL was attained forming complete perovskite phase. The surface electronic properties of the modified PEDOT:PSS and pristine PEDOT:PSS layers were studied using X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) measurements. XPS results reveal that treatment of sodium citrate partially removes the PSS unit in the PEDOT:PSS, resulting in an increase in the ratio of PEDOT to PSS from 0.197 for a treated PEDOT:PSS HEL to that of 0.108 for the pristine PEDOT:PSS HEL. UPS measurements also show that there is an observable reduction in the work function of the modified HEL, implying that sodium citrate-modified PEDOT:PSS HEL possesses an improved electron blocking capability, which is beneficial for efficient operation of the inverted PSCs.;The performance enhancement in MAPbI3-based PSCs with a tungsten oxide (WO3)-PEDOT:PSS composite HEL also was analyzed. The uniform composite WO3-PEDOT:PSS HEL was formed on indium tin oxide (ITO) surface by solution fabrication process. The morphological and surface electronic properties of WO3-PEDOT:PSS composite film were examined using AFM, XPS, UPS and Raman Spectroscopy. SEM images reveal that the perovskite films grown on the composite HEL had a full coverage without observable pin holes. XRD results show clearly that no residual of lead iodide phase was observed, suggesting a complete perovskite phase was obtained for the perovskite active layer grown on the composite HEL. The volume ratio of WO3 to PEDOT:PSS of 1:0.25 was optimized for achieving enhanced current density and Voc in the PSCs. It is demonstrated clearly that the use of the WO3-PEDOT:PSS composite HEL helps to improve the charge collection probability through suppression of the charge recombination at the MAPbI3/composite HEL interface. The charge extraction efficiency at the perovskite/PEDOT:PSS and perovskite/composite HEL interfaces were investigated by analyzing the PL quenching efficiency of the MAPbI3 active layer. It is shown that the PL efficiency quenching at the MAPbI3/composite HEL samples is one order of magnitude higher than that measured for the perovskite/pristine PEDOT:PSS sample, suggesting an enhanced hole extraction probability at the MAPbI3/composite HEL interface. The combined effects of improved perovskite crystal growth and enhanced charge extraction capabilities result in the inverted PSCs with a PCE of 12.65%, which is 22% higher than that of a structurally identical control device (10.39%). The use of the WO3-PEDOT:PSS composite HEL also benefits the efficient operation of the PSCs, demonstrated in the stability test, as compared to that of the control cell under the same aging conditions. With the progresses made in improving the performance of MAPbI3-based PSCs, the research was extended to study the performance of efficient PSCs with mixed halide of MA0.7FA0.3Pb (I0.9Br0.1)3. The effect of the annealing temperature on the growth of the mixed MA0.7FA0.3Pb (I0.9Br0.1)3 perovskite active layer was analyzed. It was found that the optimal growth of the mixed perovskite active layer occurred at an annealing temperature of 100°C. UPS results reveal that the ionization potential of 5.76 eV measured for the mixed cation perovskite is lower than that of MAPbI3-based single cation perovskite layer (5.85 eV), while the corresponding electron affinity of the mixed perovskite was 4.28 eV and that for the MAPbI3 layer was 4.18 eV, respectively. The changes in the bandgap and the energy levels of the MA0.7FA0.3Pb (I0.9Br0.1)3 and MAPbI3 active layers were examined using UV-vis absorption spectroscopy and UPS measurements. Compared to the MAPbI3-based control cell, a 23% increase in Jsc, a 15% increase in Voc and an overall 25% increase in PCE for the MA0.7FA0.3Pb (I0.9Br0.1)3 were achieved as compared to that of the MAPbI3-based PSCs. An obvious improvement in charge collection efficiency in MA0.7FA0.3Pb (I0.9Br0.1)3-based PSCs operated at different Veff was clearly manifested by the light intensity dependent J-V characteristic measurements. PL quenching efficiency also shows the charge transfer between MA0.7FA0.3Pb (I0.9Br0.1)3 and PEDOT:PSS HEL is one order of magnitude higher as compare to that in the MAPbI3-based PSCs, suggesting the formation of improved interfacial properties at the MA0.7FA0.3Pb (I0.9Br0.1)3/HEL interface. The impact of incorporating mixed MA0.7FA0.3Pb (I0.9Br0.1)3 perovskite active layer on PCE and the stability of the PSCs was further studied using a combination of TPC measurement and aging test. The stability of MA0.7FA0.3Pb (I0.9Br0.1)3- and MAPbI3-based PSCs with respect to the aging time was monitored for a period of >2 months. The MA0.7FA0.3Pb (I0.9Br0.1)3-based PSCs are more stable compared to the MAPbI3-based PSCs aged under the same conditions. The aging test supports the findings made with the TPC and light intensity dependent J-V measurements. It shows that the improved interfacial quality at the perovskite/HEL and the enhanced charge extraction capability are favorable for efficient and stable operation of MA0.7FA0.3Pb (I0.9Br0.1)3-based PSCs.

Magister Philosophiae - MPhil / Due to an increasing demand for energy, alternative renewable energy sources are investigated globally. However fossil fuels are still one of the main energy sources. The combustion of these fuels produces by-products such as SOx, NOx and CO2, which have detrimental effects on the environment and human health. Therefore, effective methods are needed to minimize the pollution and affects that these by-products cause. Catalysts are commonly employed to convert these by-products to less harmful and/or resalable products. Ceria and ceria based materials are good candidates for the removal and conversion of SOx and NOx. Ceria and ceria related materials are most effective as catalysts when they are in the nano-form with good crystallinity and nanoparticles that are uniform. The growth of nanoparticles is preceded by a nucleation process which can occur by solid-state restructuring of a gel or precipitation from a saturated solution. The precipitation method was selected to synthesize Ceria nanoparticles. Synthesis conditions such as temperature, solution type and ageing time and their effect on the physical and chemical forms of the Ceria particles were investigated. The morphology and structural properties were investigated using Scanning Electron Microscopy, X-ray diffraction and Transmission Electron Microscopy. X-ray Photoelectron Spectroscopy was used to investigate the chemical properties. It was found that low temperatures, low base volume and a solvent with a small dielectric constant favor the formation of small crystallites with a relatively large concentration of defects. These defects are desirable since they enhance the catalytic activity of ceria.

Energy is integral to the quality of life of any society. However, meeting the demand for energy sustainably is the main challenge facing humanity. In general, non-renewable energy resources are used to supply the ever increasing energy demand. However, the extraction and processing of these resources is accompanied by the production of wastes which are a health hazard and impact negatively on climate change. Considering the finite nature of non-renewable sources, the environmental concerns which are associated with their usage and ensuring energy security, renewable energy sources have been brought in the energy supply chain. Wind energy is one of the renewable energy sources which has been supplying electrical energy to the ever increasing energy demand of humanity. Wind energy technology is a mature technology which over and above the bare (conventional) wind turbine technology has seen the development of duct augmented wind turbines. Ducts are used to encase wind turbine rotors to augment the power output of wind turbines especially in low wind speed areas. Though the technology has been under study for decades now, research indicates that there is no known model to estimate the power output of a diffuser augmented wind turbine. This thesis presents the development of the conical Diffuser Augmented Wind Turbine (DAWT) power output estimation model and its validation.

PV systems in practice experience excessive thermal energy dissipation that is inseparable from the photo-electric conversion process. The temperature of PV cells under continuous illumination can approach 40°C above ambient, causing a drop in the electrical performance of about 30%. The significance of elevated temperature on PV cells inspired various thermal management techniques to improve the operating temperature of the cells and hence their conversion efficiency. Hybrid PV/Thermal (PV/T) collectors that can supply both electrical and thermal energy are attractive twofold solution, being able to cool the PV cells and thus improving the electrical power output as well as collecting the thermal energy by-product for practical utilization. The challenges present on the performance of PV systems due to elevated operating temperature is considered the research problem within this work. In this research, an integrated hybrid heat pipe-based PV/Thermoelectric (PV/TEG) collector is proposed and investigated theoretically and experimentally. The hybrid collector considers modular integration of a PV absorber rated at 170W with surface area of 1.3 m2 serving as power generator as well as thermal absorber. Five heat pipes serving as the heat transport mediums were attached to the rear of the module to extract excessive heat accumulating on the PV cells. The extracted heat is transferred via boiling-condensation cycle within the heat pipe to a bank of TEG modules consisting of five 40 mm x 40 mm modules, each attached to the condenser section of each heat pipe. In principle, the incorporation of heat pipe-TEG thermal waste recovery assembly allow further power generation adopting the Seebeck phenomena of Thermoelectric modules. A theoretical numerical analysis of the collector proposed is conducted through derivation of differential equations for the energy exchange within the system components based on energy balance concepts while applying explicit finite difference numerical approach for solutions. The models developed are integrated into MATLAB/SIMULINK environment to assess the cooling capability of the integrated collector as well as the addition power generation through thermal waste heat recovery. The practical performance of the collector proposed is determined experimentally allowing for validation of the simulation model, hence, a testing rig is constructed based on the system requirements and operating principles. Reduction in the PV cell temperature of about 8°C, which account for about 16% reduction in the PV cell temperature response compared to a conventional PV module under identical conditions is attained. In terms of the power output available from the PV cells, enhanced power performance of additional 5.8W is observed, contributing to an increase of 4% when compared with a PV module. The overall energy conversion efficiency of the integrated collector was observed to be steady at about 11% compared to that of the conventional PV module (9.5%) even at high ambient temperature and low wind speeds. Parametric analysis to assess the performance enhancements associated to the number of heat pipes attached to the PV module is conducted. Increasing the number of heat pipes attached to 15 pipes permits improved thermal management of the PV cells realised by further 7.5% reduction in the PV module temperature in addition to electrical output power improvement of 5%.