Research in fluorescent solar concentrators (FSCs) commenced in mid-1970’s to lower the cost of solar cells through the reduction of the required solar cell active area, and by incorporating them in-to buildings, thereby offsetting installation costs. In FSCs, light penetrates the top surface of a waveguide, is absorbed by the fluorescent material (FM) and is emitted at a longer wavelength that is then internally reflected towards edge solar cells. In this project, the use of cerium doped yttrium aluminum garnet (Ce:YAG) was explored as an FM, from which the optical transport of fluorescence must be enhanced towards solar cell edges. Optical spectroscopic techniques were conducted to characterize a sample of Ce:YAG with a doping level of 0.180 mol%. An excitation and emission profile indicated a strong absorption at 476 nm and a strong radiation at 530 nm, where the fluorescence process lasted for only 62.3 ns, with a conversion efficiency of 80.0%. Meanwhile, x-ray analysis concluded that this material had a density of 4.56 g/cm3. An acrylic concentrator with local islands of Ce:YAG was successfully fabricated. A lens sheet was used to provide strong sunlight coupling to Ce:YAG. The concentrator was analysed using Optics Lab, Monte Carlo simulations (MCS) and through experimental flux measurements, the percentage of light that waveguided to the edges was determined. Optics Lab yielded 56.10%, MCS yielded 59.20% and flux measurements resulted in 58.22% (without lenses) and 57.14% with lenses. Also, an overall experimental optical efficiency was determined to be 32.45% without lenses and 53.53% with lenses. These results can be improved by modifying the fabrication techniques and using substrates with higher refractive indices. / Thesis / Master of Applied Science (MASc)

Research on novel solar tracking methods using two polymer-based approaches was conducted. The first design for a solar tracking system with luminescent particles moving along polymer coatings is reported to provide the localized absorption of sunlight by phosphors which can follow the sun and hence provides a higher light intensity to be guided to a solar cell with higher efficiency. The second approach for realizing a polymer-based deformable lens on the surface of patterned ITO glass for light concentrating is reported. Both approaches rely on the application of spatially defined heating to a diluted polymer. These experiments were motivated by a) the well-known Rayleigh-Bénard convection flow within a fluid and b) Bénard-Marangoni flow effects concerning the movement of liquid along the surface of the fluid based on a surface tension gradient as a function of temperature. In the first project, luminescent particles (YAG:Ce) are placed on the surface of a polymer film cast from a hot melt glue stick with a low melting point. When a heating wire 0.5 mm away from the top surface of the polymer film sample is transferred across the polymer, the floating YAG:Ce particles on the polymer surface can be pushed forward. In order to understand the mechanism of the particle movement, a laser-based measuring method was developed to view the surface profile of the melting polymer in situ. The melted glue stick polymer is observed to form a valley-like surface cross section that is able to transport YAG:Ce powder particles much like a surfer is carried forward on a wave. In the second project, a 0.25 mm thick polystyrene polymer containing a toluene solvent is cast on an ITO coated glass substrate with ITO stripe widths of 2, 6, and 10 mm. The heating source comprised of the ITO stripe can produce spatially selective heat when electric current is applied to thermally deform the cast polymer/solvent layer (polystyrene) on the substrate surface. After the deformation is complete an LED light source is used to determine the light concentration properties of the thermally formed lenses. The ITO stripe surface temperature profile was measured with a thermocouple and modelled with COMSOL Multiphysics software. The vaporization weight loss of solvent was also determined. The optics of the LED light concentration was modelled by Optics Lab software. When the light emitted from the source passes through the thermally deformed polymer, focusing into two beams occurs in agreement with modelling results. / Thesis / Master of Science (MSc)

The quality of healthcare in low-resource countries is often limited by the environment, lack of funds, staff availability, electricity availability, and more. In the words of a Malawian physician, medicine can feel like improvisation, wherein one must make due with available resources rather than desired resources. One prevalent problem among low-resource hospitals is the functionality and longevity of medical equipment. A large percentage of all medical equipment in Malawian hospitals is donated, resulting in a wide spectrum of models, necessary spare parts, and functionality. These machines can break quickly due to heavy use prior to donation, missing user and maintenance manuals, and a lack of replacement parts. Thus, finding necessary life-saving equipment in Malawian hospital wards can be a challenge. One such piece of equipment is the oxygen concentrator, necessary for treatment of respiratory disease, use with CPAP machines, and in the administration of surgical anesthesia. This device fills many roles in low-resource hospitals, but in many Malawian hospitals it is the most frequently malfunctioning piece of equipment. A survey administered to medical personnel and maintenance personnel in hospitals in Malawi’s Central and Southern Regions isolated some common causes of oxygen concentrator malfunction. Prominent among these were poor oxygen concentrator ventilation and the lack of consumable replacement parts such as the intake bacterial filter. A stand made from locally-sourced materials was developed to encourage better oxygen concentrator exhaust and raise the device out of dust and cleaning fluids on ward floors. Intake bacterial filter alternatives were researched, designed, constructed, and tested, manufactured from housing materials and filter media available in Malawi or continental Africa. A primary source of difficulty for low-resource hospitals is lack of autonomy, requiring aid from affluent nations to supply equipment and consumable materials. This work suggests that sustainable innovations, such as allowing consumables to be produced in-country, can replace aid with development and create more accessible materials to hospital maintenance personnel. Collaboration with material suppliers and engineers in Malawi can provide sustainable designs and systems to help hospitals access the supplies they need to service oxygen concentrators and other equipment. / Master of Science / The quality of healthcare in low-resource countries is often limited by the environment, lack of funds, staff availability, electricity availability, and more. In the words of a Malawian physician, medicine can feel like improvisation, wherein one must make due with available resources rather than desired resources. One prevalent problem among low-resource hospitals is the functionality and longevity of medical equipment. A large percentage of all medical equipment in Malawian hospitals is donated, resulting in a wide spectrum of models, necessary spare parts, and functionality. These machines can break quickly due to heavy use prior to donation, missing user and maintenance manuals, and a lack of replacement parts. Thus, finding necessary life-saving equipment in Malawian hospital wards can be a challenge. One such piece of equipment is the oxygen concentrator. This device fills many roles in low-resource hospitals, but in many Malawian hospitals it is the most frequently malfunctioning piece of equipment. A survey was used in hospitals in Malawi’s Central and Southern Regions to collect information on why oxygen concentrators malfunction. Common reported causes of malfunction were oxygen concentrators overheating due to clogged exhaust vents, and the unavailability of necessary disposable filters. A stand made from locally-available materials was developed to improve oxygen concentrator ventilation. Replaceable filter alternatives were researched, designed, constructed, and tested, made from housing materials and filter materials available in Malawi or continental Africa. A primary source of difficulty for low-resource hospitals is dependence on more developed nations for supplies and aid. This work suggests that designing materials from locally-available materials can lessen this dependency and make necessary medical materials more accessible. Collaboration with material suppliers and engineers in Malawi can provide sustainable designs and systems to help hospitals access the supplies they need to service oxygen concentrators and other equipment.

With the development of the power grid into an automated system, phasor measurement units and phasor data concentrators are essential for real time control of the system. PMUs are time synchronized throughout the power system and take sample measurements in very small windows of time. Phasor Data Concentrators accept PMU data and time align the data so that a snapshot of the power system can be viewed in real time. It is unfeasible to possess enough real PMUs to thoroughly test PDCs, thus a Real Time PMU Simulator is desired. It is possible to implement a UNIX based PMU simulator that can emulate the behavior of real PMUs, while also allowing the user to alter the Synchrophasor data to test the response of a PDC. GPS is used to synchronize a UNIX machine to UTC time to match that of a real PMU. In this way, the PMU simulator will accurately behave as a PMU. This PMU data can be sent to PDCs to test the response of the device. To test extremes of the PDC, alterations were made to the PMU software to send irregular data to a PDC. The results conclude that the open source iPDC software is capable of being used for latency testing, sending late data frames, as well as sending corrupted data. The PMU simulator proved to be successful in the area of PDC testing. The purpose of this thesis is to demonstrate how the iPDC software can be implemented to test PDC's. / Master of Science

Concentrating photovoltaic (CPV) systems are a key step in expanding the use of solar energy. Solar cells can operate at increased efficiencies under higher solar concentration and replacing solar cells with optical devices to capture light is an effective method of decreasing the cost of a system without compromising the amount of solar energy absorbed. CPV systems are however still in a stage of development where new designs, methods and materials are still being created in order to reach a low levelled cost of energy comparable to standard silicon based photovoltaic (PV) systems. This work outlines the different types of concentration photovoltaic systems, their various design advantages and limitations, and noticeable trends. Comparisons on materials, optical efficiency and optical tolerance (acceptance angle) are made in the literature review as well as during theoretical and experimental investigations. The subject of surface structure and its implications on concentrator optics has been discussed in detail while highlighting the need for enhanced considerations towards material and hence the surface quality of optics. All of the findings presented contribute to the development of higher performance CPV technologies. Specifically high and ultrahigh concentrator designs and the accompanied need for high accuracy high quality optics has been supported. A simulation method has been presented which gives attention to surface scattering which can decrease the optical efficiency by 10-40% (absolute value) depending on the material and manufacturing method. New plastic optics and support structures have been proposed and experimentally tested including the use of a conjugate refractive-reflective homogeniser (CRRH). The CRRH uses a reflective outer casing to capture any light rays which have failed total internal reflection (TIR) due to non-ideal surface topography. The CRRH was theoretically simulated and found to improve the optical efficiency of a cassegrain concentrator by a maximum of 7.75%. A prototype was built and tested where the power output increase when utilising the CRRH was a promising 4.5%. The 3D printed support structure incorporated for the CRRH however melted under focused light, which reached temperatures of 226.3°C, when tested at the Indian Institute of Technology Madras in Chennai India. The need for further research into prototyping methods and materials for novel optics was also demonstrated as well as the advantages of broadening CPV technology into the fields of biomimicry. The cabbage white butterfly was proven to concentrate light onto its thorax using its highly reflective and lightweight wings in a basking V-shape not unlike V-trough concentrators. These wings were measured to have a unique structure consisting of ellipsoidal pterin beads aligned in ladder like structures on each wing scale which itself is then tiled in a roof like pattern on the wing. Such structures of a reflective material may be the answer to lightweight materials capable of increasing the power to weight ratio of CPV technology greatly. Experimental testing of the large cabbage white wings with a silicon solar cell confirmed a 17x greater power to weight ratio in comparison to the same set up with reflective film instead of the wings. An ultrahigh design was proposed taking into account manufacturing considerations and material options. The geometrical design was of 5800x of which an optical efficiency of either ~75% with state of the art optics should produce and effective concentration of ~4300x. Relatively standard quality optics on the other hand should give an optical efficiency of ~55% and concentration ratio ~3000x. A prototype of the system is hypothesised to fall between these two predictions. Ultrahigh designs can be realised if the design process is as comprehensive as possible, considering materials, surface structure, component combinations, anti-reflective coatings, manufacturing processes and alignment methods. Most of which have been addressed in this work and the accompanied articles. Higher concentration designs have been shown to have greater advantages in terms of the environmental impact, efficiency and cost effectiveness. But these benefits can only be realised if designs take into account the aforementioned factors. Most importantly surface structure plays a big role in the performance of ultrahigh concentrator photovoltaics. One of the breakthroughs for solar concentrator technology was the discovery of PMMA and its application for Fresnel lenses. It is hence not an unusual notion that further breakthroughs in the optics for concentrator photovoltaic applications will be largely due to the development of new materials for its purpose. In order to make the necessary leaps in solar concentrator optics to efficient cost effective PV technologies, future novel designs should consider not only novel geometries but also the effect of different materials and surface structures. There is still a vast potential for what materials and hence surface structures could be utilised for solar concentrator designs especially if inspiration is taken from biological structures already proven to manipulate light.

Various solar energy technologies are being developed to harness the available environmentally friendly and sustainable solar radiation. New ways of utilizing this "free" power for different energy consuming processes continue to be created. In this thesis, a multi-stage solar energy concentrating system has been developed and its feasibility as a radiation source for polymer processing has been explored. The solar energy concentrator (SEC) facility comprises a modified Cassegrainian configuration combined with auxiliary imaging and non-imaging optics, serving as an alternative energy source for polymer joining, ageing and adhesive curing. Modeling and improvement of various aspects of the operation and performance of the SEC facility have been implemented. Optical ray tracing models of the Cassegrainian concentrator with various conventional imaging components and nonimaging concentrators have been created to optimize the optical layout and system efficiency. On their basis, combined 3D ray tracing computer models integrated with the mechanical components have been developed to simulate the entire SEC facility and predict the image size, location and orientation. Additionally, the energy transfer, radiation absorption and heat generation and transfer in the irradiated polymer have been modeled in order to study the radiation-polymer interaction. One novel contribution of this research is the enhancement of the image forming concentrator with non-imaging cone-like concentrators (conical and compound parabolic concentrator (CPC)), utilizing their inherent disadvantage of excessive length. Compared to the refractive type means of transmitting concentrated solar radiation, the truncated cone and CPC concentrators have been found more efficient enhancing further the concentration and widening the utilized spectral range. The experimental studies have demonstrated that transparent and colored, similar and dissimilar polymers can be successfully joined using the SEC facility. The especially developed through-transmission technique removes the need to use a special absorbing medium of the radiant energy required by current advanced welding techniques. The tensile strengths of the joints achieved are comparable to those achieved for similar polymers with other advanced plastic joining methods. The results from the polymer ageing experiments have shown that ultraaccelerated exposure to concentrated sunlight can be performed with the SEC facility without introducing spurious failure mechanisms. Based on the preliminary investigation on adhesive curing utilizing concentrated solar radiation, it has been concluded that with carefully chosen light-curing adhesives solar radiation can be a useful radiation source for adhesive curing.

Coal spirals are widely used in coal preparation plants around the world to clean fine coal, typically in the 1 x 0.15 mm size range. Despite their popularity and the trend toward increased automation in modern coal preparation plants, adjustments to the critical process variable for coal spirals, i.e., product splitter position, continue to be done manually. Since spiral feed in a plant tends to fluctuate on a regular basis, timely manual adjustment of splitter position in tens or hundreds of spirals operating in a plant is nearly impossible. As a result, the clean coal yield from a spiral and also the overall plant suffers on a regular basis. The main goal of this study was to develop a suitable sensor and control system to adjust the product splitter position of a full-scale spiral. Some of the basic properties of coal slurry were thoroughly investigated for their on-line measurability and for their correlations with the density of the constituent solid particles. After experimenting with electrical capacitance- and conductivity- (i.e., reciprocal of resistivity) based sensing techniques, a conductivity-based tube sensor was developed for measuring density of solid particles in the spiral trough. Two sensors were used to establish a density gradient in the critical region across the spiral trough at the discharge end. Based on this continuously monitored density gradient, a PIC24 microcontroller was programmed to send a signal to a DC gear motor that would move the splitter arm in the appropriate direction when sufficient variation in conductivity was detected. Currently, a cycle time of 5 minutes is used for the spiral control system; however, in a commercial application, the cycle time could be lengthened to 30 or 60 minutes. The automation system has been validated by examining the performance of a full-scale spiral while deliberately changing factors like feed solid content, feed washability characteristics, and feed slurry ionic concentration. With a full-scale compound spiral programmed to achieve a specific gravity of separation at 1.65 by an automatic adjustment of the splitter position, the actual D50 values achieved for two separate tests were 1.64 and 1.73. The close proximity of target and actual D50 values is indicative of the effectiveness of the developed system. The next step in near-term commercialization of this proprietary spiral control system will be a longer term (several months) in-plant demonstration. The main goal of this study was to develop a suitable sensor and control system to adjust the product splitter position of a full-scale spiral. One of the basic properties of coal slurry was thoroughly investigated for its on-line measurability and for its correlation with the constituent solid density of the slurry. After experimenting with electrical capacitance- and conductivity- (i.e., reciprocal of resistivity) based sensing techniques, a conductive-based tube sensor was selected for measuring solids density of particles in the spiral trough. Two sensors were used to establish a density gradient in the critical region across the spiral trough at the discharge end. Based on this continuously monitored density gradient, a PIC24 microcontroller was programmed to send a signal to a DC gear motor that would move the splitter arm when sufficient variation in conductivity was detected. Currently, a cycle time of 5 minutes is used for the spiral control system; however, in a commercial application, the cycle time could be lengthened to 30 or 60 minutes. The automation system has been validated by examining the performance of a full-scale spiral while deliberately changing factors like feed solid content, feed washability characteristics, and feed slurry ionic concentration. With compound spirals programmed to achieve a specific gravity of separation at 1.65, actual D50 values achieved for two separate tests were 1.64 and 1.73. The close proximity of target and actual D50 values is indicative of the effectiveness of the developed system. The next step in near-term commercialization of this proprietary spiral control system will be a longer term (several months) in-plant demonstration.

Submitted by Morgana Silva (morgana_linhares@yahoo.com.br) on 2016-09-23T16:07:12Z No. of bitstreams: 1 Dissertação.pdf: 2848624 bytes, checksum: f5075c15190584601d6a5374e1d06fd7 (MD5) / Made available in DSpace on 2016-09-23T16:07:12Z (GMT). No. of bitstreams: 1 Dissertação.pdf: 2848624 bytes, checksum: f5075c15190584601d6a5374e1d06fd7 (MD5) Previous issue date: 2016-06-22 / Brazil has as a main source for production of electricity the dams using water to drive the turbines and as a secondary source are used the thermoelectric power plants that use fuel oil for electric power production. Both generate a large environmental impact, due to the fact of the dams need huge areas for its construction, which often leads to destruction of important ecosystems in the region where it will be installed the hydroelectric plant, besides the fact that they need the rainfall cycle so that the dams have the operating capacity, while the thermoelectric power plants burn fossil fuels thus increasing emissions of CO2 to the atmosphere. An alternative to the solution of the problems mentioned above is the use of renewable sources of energy, with emphasis on this work. Solar energy can be divided into two parts: thermal and photovoltaic. This work it is focused on thermal use of solar energy, with a Fresnel-type solar concentrator to heat water, which will trigger a cooling system environment with the use of desiccant rotors. The choice of type Fresnel collector gave the field of development of this hub is still in constant growth and by the fact that even occupy a relatively small area when compared to other solar thermal concentrators, in addition to its construction be simple and low cost when again compared to other solar concentrators. / O Brasil tem como fonte principal para produção de energia elétrica as hidrelétricas que utilizam água para movimentar as turbinas e como fonte complementar são utilizadas as termoelétricas que usam óleo combustível para produção de energia elétrica. Ambas geram um grande impacto ambiental, devido ao fato das hidrelétricas necessitarem de enormes áreas para a construção das represas, o que muitas vezes acarreta na destruição de ecossistemas importantes para a região onde irá ser instalada a hidrelétrica, além do fato que elas necessitam do ciclo das chuvas para que as represas possuam capacidade de operação, enquanto que as termoelétricas queimam combustíveis fosseis, aumentando assim as emissões de CO2 para a atmosfera. Uma alternativa para a solução dos problemas citados anteriormente é a utilização de fontes renováveis de energia, dando ênfase neste trabalho a energia solar. A energia solar pode ser dividida em duas vertentes: térmica e fotovoltaica. Este trabalho está voltado para a utilização térmica da energia solar, através da utilização de um concentrador solar do tipo Fresnel para o aquecimento de água, a qual irá acionar um sistema de refrigeração de ambientes com a utilização de rotores dessecantes. A escolha do coletor do tipo Fresnel se deu pelo campo de desenvolvimento deste concentrador estar ainda em constante crescimento e pelo fato do mesmo ocupar uma área relativamente pequena quando comparado com outros concentradores solares térmicos, além de sua construção ser simples e de baixo custo quando novamente comparada a outros concentradores solares.

A prototype solar desalination system (SODESAL) with a parabolic-trough solar concentrator (PTSC) and evacuated tube was designed and analyzed to determine the solar thermal capabilities for small-scale distillation and energy generation. A proof-of-concept study verified that distillation is possible with the system as designed, however a rupture occurred in the copper heat-pipe heat exchanger due to overheating. The internal temperatures of an aluminum heat transfer fin were measured inside an evacuated tube typically used in solar water heater systems to understand the lateral heat distribution and identify possible causes of the rupture. Solar radiation was measured for both the summer and winter solstices to understand the relationship between incident solar radiation and the potential freshwater yield of the system. The lateral heat distribution of the AHTF is dependent upon the PTSC’s solar incident angle. A consistent lateral heat distribution occurred across the AHTF approximately 40 mins after solar noon. The temperature difference between each end of the AHTF can exceed over 225 °C leading up to and following solar noon when the PTSC was set at a static slope. The SODESAL system’s future applications, system improvements and additional research are also discussed along with the capability of small-scale CSP systems.

This study explores in detail design options and simulations of multi-junction solar cells that utilize silicon-germanium-tin (SixGe1-x-ySny or SiGeSn) to achieve high-efficiency solar power conversion devices. SixGe1-x-ySny is an emerging system of alloys that can lattice match with germanium and gallium arsenide and can provide a bandgap higher than that of germanium; useful in the development of multi-junction solar cells. The results herein include designs of four devices: a triple-junction, a quadruple-junction, a seven-junction, and a six-junction, with estimated efficiencies of 41.6%, 42.6%, 41.2%, and 39.2% respectively under 1000x concentrated AM1.5D illumination, where the seven- and six-junction devices relax the thickness requirement of the germanium layer, and have room for improvement via the development of an advanced tunnel-junction component. Visualizations of the potentially available SiGeSn bandgaps are developed. The documentation supports further work in modelling additional compositions of SiGeSn. Loss mechanisms of the devices are calculated and plotted, enabling the design of the device layer components. Tools and techniques are developed to determine and control the resultant output error, and a generalized simulation mesh definition is given that efficiently controls the primary source of error of the calculation, which is related to the optical interaction. Lateral currents and surface recombination effects are included. The software is modularized to enable the development of higher-order segmented devices.