Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2015. / From the electric power generation perspective, the last three decades have been characterized by sustained growth in the amount of Distributed Power Generation (DPG) systems integrated into the electric grid. This trend is anticipated to continue, especially in light of the widespread acceptance of the many benefits envisaged in the increase of renewable-based power generation. The potential for grid-integrated DPG systems to significantly contribute to electric power supply reliability has consistently attracted extensive research in recent times, although concerns continue to be raised over their adverse impact on the normal grid operation at high penetration levels. These concerns largely stem from the limited controllability of most DPG systems, which tend to exhibit large output impedance variation, and non-deterministic power output characteristics. There has therefore also been a growing need to develop effective control strategies that can enhance the overall impact of the DPG systems on the grid operation, thus improving their synergistic properties, and probably also enabling an even higher penetration level into the utility grid. In line with this identified need, this thesis discusses the modeling and controller design for an inverter-based DPG system with the capability to effectively operate both in grid-connected and autonomous (i.e. independent of the utility grid) operational modes. The dual-mode operation of the DPG is made possible by incorporating into the inverter interface control scheme the means to ensure seamless transition of the DPG between the grid-connected and autonomous modes of operation. The intention is to have a grid-integrated inverter-based DPG system whose operation approximates that of an online Uninterruptible Power Supply (UPS) system, in that it is able to sustain power supply to the local load in the absence of the grid supply, which would be desirable for critical loads, for which the level of power supply reliability guaranteed by the grid often falls short of the requirements. The work developed in this thesis considers three of the aspects associated with grid-integrated DPG systems that are equipped with autonomous-mode operation capability.

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2016. / South Africa has raised concerns regarding the development of renewable energy sources such as wind, hydro and solar energy. Integration of a combined photovoltaic and thermal system was considered to transform simultaneous energy into electricity and heat. This was done to challenge the low energy efficiency observed when the two solar energy conversion technologies are employed separately, in order to gain higher overall energy efficiency and ensure better utilization of the solar energy. Therefore, the notion of using a combined photovoltaic and thermal system was to optimize and to improve the overall PV panel efficiency by adding conversion to thermal energy for residential and commercial needs of hot water or space heating or space cooling using appropriate technology. The PV/T model constructed using water as fluid like the one used for the experimental work, presented a marginal increase in electrical efficiency but a considerable yield on the overall PV/T efficiency, because of the simultaneous operation by coupling a PV module with a thermal collectors.

Thesis (DTech (Engineering))--Cape Peninsula University of Technology, 2017. / The world has been experiencing energy-related problems following pressuring energy demands which go along with the global economy growth. These problems can be phrased in three paradoxical statements: Firstly, in spite of a massive and costless solar energy, global unprecedented energy crisis has prevailed, resulting in skyrocketing costs. Secondly, though the sun releases a clean energy, yet conventional plants are mainly being run on unclean energy sources despite their part in the climate changes and global warming. Thirdly, while a negligible percentage of the solar energy is used for power generation purposes, it is not optimally exploited since more than its half is wasted in the form of heat which contributes to lowering efficiency of solar cells and causes their premature degradation and anticipated ageing. The research is geared at addressing the issue related to unsatisfactory efficiencies and anticipated ageing of solar modules. The methodology adopted to achieve the research aim consisted of a literature survey which in turn inspired the devising of a high-efficiency novel thermal electric solar power panel. Through an in-depth overview, the literature survey outlined the rationale of the research interest, factors affecting the performance of PVs as well as existing strategies towards addressing spotted shortcomings. While photovoltaic (PV) panels could be identified as the most reliable platform for sunlight-to-electricity conversion, they exhibit a shortcoming in terms of following the sun so as to maximize exposure to sunlight which negatively affects PVs’ efficiencies in one hand. On the other hand, the inability of solar cells to reflect the unusable heat energy present in the sunlight poses as a lifespan threat. Strategies and techniques in place to track the sun and keep PVs in nominal operational temperatures were therefore reviewed.

Orientador: Carlos Alberto Canesin / Banca: Guilherme de Azevedo e Melo / Banca: Sérgio Augusto Oliveira da Silva / Resumo: Considerando-se as políticas mundiais e nacionais com relação às mudanças climáticas decorrentes da ação humana, no contexto da produção e consumo de energia elétrica, novas fontes renováveis e alternativas para a produção de energia elétrica, com menores impactos ambientais e elevadas eficiências têm sido exploradas na literatura científica. Dentro deste contexto é desenvolvido neste trabalho um sistema de geração de energia elétrica de pequeno porte baseado na associação em série de poucos painéis solares fotovoltaicos. São apresentadas análises e simulações de diversas estruturas monofásicas não isoladas que contemplam o estado da arte e integram parte das estruturas mais utilizadas pela indústria. O sistema proposto para operar como Geração Distribuída (GD) é um sistema a duplo estágio, composto pelo conversor elevador Boost entrelaçado e em cascata com o inversor monofásico em ponte completa. O sistema de GD proposto possui um algoritmo tipo P&O (Perturband Observe) para a extração da máxima potência (MPPT - Maximum Power Point Tracking), mesclando o algoritmo P&O para o rastreamento do MPP, com o potencial do algoritmo Vcte (Tensão constante) para o processo de inicialização do sistema, melhorando o aproveitamento da energia advinda dos painéis fotovoltaicos. Além disso, em virtude da necessidade de conexão segura deste sistema à rede pública de distribuição de energia elétrica em corrente alternada, é implementado um método de sincronismo com a rede CA em baixa tensão; além da análise e síntese de um algoritmo híbrido para detecção e proteção de ilhamento, a fim de garantir a segurança do sistema e dos usuários. O controle do conversor, a técnica de MPPT, a detecção e proteção de ilhamento, bem como o sincronismo com a rede em CA, são implementadas... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Considering the global and national policies related to climate change due to human action, in the context of production and consumption of electricity, new renewable and alternative sources for electricity production with less environmental impacts and high efficiencies have been proposed and analyzed in the scientific literature. In this context, this work it is developed a photovoltaic small electrical generation system in order to operate with a few series connected photovoltaic panels. Moreover, it is presented analyses and simulations of several structures that include the state of the art single-phase non-isolated inverters, where the most of them are commonly used by industry. The proposed structure developed to operate as a distributed generation system is a dual-stage converter, composed by an Interleaved Boost Converter cascaded with a single-phase Full-Bridge Inverter. A maximum power point tracking technique is implemented and tested in order to increase energy utilization, mixing the potential of P&O algorithm together with Vcte algorithm. Furthermore, because of safe-operation grid connection necessities this work presents analysis and implementation of a hybrid anti-island detection technique with a synchronization method with the AC public low voltage grid. The converter control system and MPPT techniques, anti-island detection and management system together with the synchronization are implemented digitally... (Complete abstract click electronic access below) / Mestre

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / This work proposes study and implementation of a DC/DC Z-source converter operating in continuous conduction mode (CCM); It is applied to a photovoltaic system connected to a DC microgrid; aiming to inject the electricity supplied from PV array; To this end; the PV array is connected to the input of Z-source converter; which rises from 167V to 400V and injects the output current at the DC bus; using maximum power point tracking techniques (MPPT); The prototype implemented in the laboratory was developed for 1;38 kW output power; with the possibility to be fed either by a DC current source or DC voltage source; which does not happen with traditional converters (Buck; Boost; etc); The average efficiency achieved yield of 94%; As for the electric power processing from renewable sources; two heuristic methods were tested: Perturbe and Observe (P&O) and Conductance Incremental (IC); The average efficiency of the prototype; using the P&O technique in tracking maximum power was 79;9%; while using the second technique (IC) the average efficiency was a 82;5% ; / O presente trabalho propÃe o estudo e a implementaÃÃo de um conversor CC/CC Z-source; operando em modo de conduÃÃo contÃnuo (MCC); O mesmo à aplicado em um sistema fotovoltaico interligado a uma microrede CC; objetivando injetar a energia elÃtrica fornecida a partir de arranjo fotovoltaico;Para tal; o arranjo fotovoltaico à conectado na entrada do conversor Z-source; que a eleva de 167V para 400V e injeta a corrente de saÃda no barramento CC de 400V; utilizando tÃcnicas de rastreamento do ponto de mÃxima potÃncia (MPPT); O protÃtipo implementado em laboratÃrio foi desenvolvido para uma potÃncia nominal de saÃda de 1;38 kW com possibilidade de ser alimentado tanto por uma fonte CC de corrente ou uma fonte CC de tensÃo; diferenciando-se dos conversores tradicionais (Buck; Boost; etc); O mesmo alcanÃou um rendimento mÃdio de 94%; Quanto ao processamento de energia elÃtrica a partir de fontes renovÃveis; foram testados dois mÃtodos heurÃsticos: Pertube e Observe (P&O) e CondutÃncia Incremental (IC); A eficiÃncia mÃdia do protÃtipo usando a tÃcnica P&O no rastreamento da mÃxima potÃncia foi de 79;9%; enquanto usando a segunda tÃcnica alcanÃou-se uma eficiÃncia de 82;5% ;

Orientador: Luiz Felipe Mendes de Moura / Dissertação (mestrado profissional) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-03T22:37:08Z (GMT). No. of bitstreams: 1 Martins_PaulinoCutrim_M.pdf: 1004109 bytes, checksum: 4a5643b8de366648397d80e7bfc388da (MD5) Previous issue date: 2004 / Mestrado / Refrigeração e Condicionamento Ambiental / Mestre Profissional em Engenharia Mecanica

D.Ing. / Low system efficiency is a critical problem in photovoltaic (PV) applications due to low efficiency of solar cells. Despite this shortcoming, stand-alone PV systems, have proven to be economical and reliable choices in some applications such as telecommunications, vaccine refrigeration and water pumping in remote locations. In this study, CAD algorithms for the design of PV water pumping systems have been developed with the objective of maximizing the conversion efficiency from the solar irradiation to the potential energy of water by taking into account the variations in the pumping head. The study starts by developing loss models of various sub-systems in the photovoltaic dc and ac motor drive water pumping systems. Using MathCad, these models are then used in the simulation of the system. The simulation results are verified experimentally using their equivalent circuit configurations. The efficiency of the array, the pump and the motor are found to be the most critical parameters for the performance of the systems. The efficiencies of other components, such as the inverter, have also been shown to have a significant effect. The study has shown that for operation at the maximum power point, the inclusion of a maximum power tracker is necessary in a dc motor drive system but may be eliminated in PWM inverter-fed induction motor drive systems through proper matching of the system components. The study has further shown that matching of the drive system and the load with the insolation is essential, since maximum system efficiency occurs at a specific head, which varies as the insolation changes. Prior investigation of site insolation variations is therefore a critical requirement.

L’objectif de ce travail de thèse a été d’étudier une alternative à la cellule photovoltaïque à hétérojonction classique de silicium amorphe/cristallin avec un matériau (GaP) qui permettrait une amélioration de rendement grâce à ses propriétés optiques et électriques. L’étude du potentiel des hétérojonctions GaP/Si pour des applications PV nous a amené à étudier chacun des aspects critiques inhérents à leur réalisation. La préparation chimique de la surface des substrats et les mécanismes qui contrôlent la structuration de la surface de Si(100) ont été étudiés afin d’obtenir une surface de silicium mono-domaine (à marches diatomiques) et faiblement rugueuse par homoépitaxie (dépôts par UHV-CVD). Cette étude a été complétée par l’étude de l’influence de la préparation de surface (préparation chimique et homoépitaxie) du substrat sur la qualité cristalline du GaP déposé en deux étapes par MEE et MBE. La croissance de GaP par MEE a par la suite été effectuée sur des substrats de Si(100) ayant uniquement subi une préparation chimique de surface. Les paramètres de la séquence de croissances MEE ont été étudiés et ajustés afin d’optimiser la phase de nucléation du GaP. La qualité structurale des dépôts a été évaluée par des caractérisations par AFM et DRX. Les couches minces de faibles épaisseurs (20nm) présentent une faible rugosité de surface équivalente à une homoépitaxie et une fraction volumique de MTs inférieure à la limite de détection. La croissance MEE permet d’assurer une nucléation 2D. Cependant les caractérisations par TEM et STM révèlent la présence de parois d’antiphase. En parallèle, la simulation de structures HET GaP/Si (effectuée grâce au programme AFORS-HET) et la réalisation de diodes et de démonstrateurs cellules GaP/Si ont permis de démontrer les optimisations apportées par l’utilisation d’un émetteur de GaP. Ces composants ont été étudiés par caractérisations optiques et électriques. Nous avons constaté une limitation des performances due à la présence de pièges à l’interface et dans le volume. Ces différentes études ont donc permis d’identifier les verrous technologiques à lever pour exploiter pleinement les cellules à hétérojonctions GaP sur silicium afin d’obtenir des hauts rendements photovoltaïques. / The main objective of this thesis is to study an alternative to conventional amorphous/crystalline silicon heterojunction solar cell using gallium phosphide (GaP) as an emitter layer. This would allow a performance improvement because of its optical and electrical properties. The potential of GaP/Si heterojunction solar cells have been evaluated by studying each of the critical issues inherent to their fabrication process. The chemical preparation of the substrates surface and the mechanisms controling the structure of the Si (100) surface have been studied in order to obtain a single domain silicon surface (with diatomic steps) and slightly roughened by homoepitaxy (UHV-CVD). This work was completed by the study of the impact of surface preparation (chemical preparation and homoepitaxy) of the substrate on the crystalline quality of GaP deposited in two steps by MBE and MEE. The growth of GaP by MEE was subsequently carried out on Si(100) substrates having only undergone a chemical surface preparation. MEE growth sequence parameters were studied and adjusted to optimize GaP nucleation. The structural quality of the thin films was evaluated by AFM and XRD characterizations. Thin films of 20 nm have lower surface roughness equivalent to an homoepitaxy and a volume fraction of MTs below the detection limit. The MEE growth ensures a 2D nucleation. However, TEM and STM characterizations reveal the presence of antiphase boundaries. In parallel, simulations of the structure HET GaP/Si (with AFORS-HET) have been performed to evaluate the potential of the structure. First, diodes and demonstrator cells with GaP/Si junction have been fabricated and optically/electrically characterized. Limitations in performance due to the presence of traps at the interface and silicon volume degradation have been observed. All this work has allowed us to identify the technological issues to overcome in order to fully exploit the GaP/Si heterojunction cells to improve solar cell performance.

The performance of photovoltaic (PV) modules in terms of their ability to convert incident photon to electrical energy (efficiency) depends mostly on the spectral distribution of incident radiation from the sun. The incident spectrum finally perceived by the module depends strongly on the composition of the medium in which it has traveled. The composition of the earth’s atmosphere, which includes, amongst others, water vapour, gases such as carbon dioxide and oxygen, absorbs or scatters some of the sunlight. The incident solar spectrum is also modified by the diffuse aspect of radiation from the sky which strongly depends on aerosol concentration, cloudiness and local reflection of the earth’s surface. Although it is well known that the changes in outdoor spectrum affect device performance, little work has been conducted to support this theory. This is probably due to lack of spectral data or in certain instances where data is available, little knowledge of interpreting that data. The outdoor spectral data that one obtains in the field does not come clearly for just simple interpretation. Different analytical interpretation procedures have been proposed, all trying to explain and quantify the spectral influence on PV devices. In this study an assessment methodology for evaluating the effects of outdoor spectra on device performance parameters during the course of the day, seasons and or cloudy cover has been developed. The methodology consists of developing a device dependant concept, Weighted Useful Fraction (WUF) using the outdoor measured spectral data. For measuring PV module’s performance parameters, a current-voltage (I-V) tester was developed in order to monitor the performance of six different module technologies. The Gaussian distribution was used to interpret the data. For hot-spot analysis, different techniques were used, which include Infrared thermographic technique for identifying the hot-spots in the solar cells, SEM and EDX techniques. The AES technique was also used in order to identify other elements at hot-spots sites that could not be detected by the EDX technique. iii Results obtained indicate that multicrystalline modules performance is affected by the changes in the outdoor spectrum during summer or winter seasons. The modules prefer a spectrum characterized by WUF = 0.809 during summer season. This spectrum corresponds to AM 2.19 which is different from AM 1.5 used for device ratings. In winter, the mc-Si module’s WUF (0.7125) peaks at 13h00 at a value corresponding to AM 1.83. Although these devices have a wider wavelength range, they respond differently in real outdoor environment. Results for mono – Si module showed that the device performs best at WUF = 0.6457 which corresponds to AM 1.83 during summer season, while it operates optimally under a winter spectrum indicated by WUF of 0.5691 (AM2.58). The seasonal changes resulted in the shift in WUF during day time corresponding to the “preferred” spectrum. This shift indicates that these devices should be rated using AM values that correspond to the WUF values under which the device operates optimally. For poly-Si, it was also observed the WUF values are lower than the other two crystalline-Si counterparts. The pc-Si was observed to prefer a lower AM value indicated by WUF = 0.5813 during winter season while for summer it prefers a spectrum characterized by WUF = 0.5541 at AM 3.36. The performance of the single junction a-Si module degraded by 67 percent after an initial outdoor exposure of 16 kWh/m² while the HIT module did not exhibit the initial degradation regardless of their similarities in material composition. It was established that the WUF before degradation peaks at 15h00 at a value of 0.7130 corresponding to AM 4.50 while the WUF after degradation “prefers” the spectrum (WUF = 0.6578) experienced at 15h30 corresponding to AM value of 5.57. Comparing the before and after degradation scenarios of a-Si:H, it was observed that the device spends less time under the red spectrum which implies that the device “prefers” a full spectrum to operate optimally. The degradation of a-Si:H device revealed that the device spectral response was also shifted by a 7.7 percent after degradation. A higher percentage difference (61.8 percent) for spectral range for the HIT module is observed, but with no effects on device parameters. Seasonal changes (summer/winter) resulted in the outdoor spectrum of CuInSe2 to vary by WUF = 1.5 percent, which resulted in the decrease in Isc. This was ascertained by iv analyzing the percentage change in WUF and evaluating the corresponding change in Isc. The analysis showed that there was a large percentage difference of the module’s Isc as the outdoor spectrum changed during the course of the day. This confirmed that the 17 percent decrease in Isc was due to a WUF of 1.5 percent. In mc-Si solar cells used in this study, it was found that elemental composition across the entire solar cell was not homogenously distributed resulting in high concentration of transition metals which were detected at hot spot areas. The presence of transition metals causes hot-spot formation in crystalline solar cells. Although several transition elements exist at hot-spot regions, the presence of oxygen, carbon, iron and platinum was detected in high concentrations. From this study, it is highly recommended that transition elements and oxygen must be minimized so as to increase the life expectancy of these devices and improve overall systems reliability

No description available.