Made available in DSpace on 2015-03-03T11:52:48Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-07-18Bitstream added on 2015-03-03T12:07:02Z : No. of bitstreams: 1 000801347.pdf: 1246592 bytes, checksum: 2b850076b8670784bd0061c5d3757f39 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O uso da energia térmica provinda da energia solar a partir do uso de aquecedores solares de água residuais associados aos sistemas convencionais vêm crescendo, principalmente com o intuito da redução do uso dos chuveiros elétricos. Porém é necessário que tais equipamentos sejam dimensionados de maneira correta de acordo com cada aplicação e necessidade, já que se isso não ocorrer o sistema não apresentará vantagens. Um sistema de aquecimento de água é basicamente composto por um coletor de placa plana, um reservatório térmico e um sistema de aquecimento auxiliar. Coletores solares são capazes de transformar a energia da radiação solar em energia térmica, que na forma de calor, é transferida para um fluido. O sistema de um coletor solar depende da radiação solar sobre as placas, da temperatura do ar ambiente e da temperatura desejada da água quente. A radiação solar é dependente da localização em que o coletor foi instalado e para que a direção o mesmo está voltado, definindo assim a quantidade de calor útil absorvido pelo coletor e seu rendimento. A eficiência do coletor solar é definida como a razão entre o calor útil recebido pelo fluido e a radiação solar incidente sobre a superfície do coletor, na forma de radiação direta, difusa e a refletida de outras superfícies, em um dado intervalo de tempo. A eficiência do coletor depende de vários fatores de projetos, sendo os principais: o número de coberturas da placa, o tipo de vidro e suas características refletivas, o espaçamento entre o coletor e o vidro, o tipo e espessura do isolamento, o fator de absorção da placa absorvedora, entre outros fatores. Para o dimensionamento correto de sistemas de aquecimento solar de água para o uso doméstico, a partir das curvas de eficiência dos coletores, foram desenvolvidas algumas metodologias, baseadas na equação da energia útil, ou no cálculo da utilizabilidade diária da radição solar, ou na... / The thermal solar energy use for domestic water heaters associated with conventional system, have been growing, especially the aim of reducing the electric showers use. However it is necessary that the equipment is design correctly according to each application, since if that system does not fulfill this will not present advantages. A solar hot water system is composed by a flat-plate collector, a thermal storage and auxiliary heating system. Solar collectors are able to transform solar radiation into thermal energy and in the heat form that is transferred to al fluid. The solar collector depends on the solar radiation over the plates, the ambient temperature and the demand hot water temperature. Solar radiation is depended on the localion which the collector was collector was installed and the direction it is facing, thus the useful heat absorved by the collector and its performance can be define. The solar collector efficiency is defined as the ratio of useful heat received by the fluid and the solar radiation incident on the collector surface, which it is composed by the radiation direct, diffuse and reflected from other surfaces, in a given time interval. The collector efficiency depends on several projects factors, and the main factors are: the number of collectors covers, the kind of the glass and its reflective characteristics, the spacing between the absorber surface and the glass and the thickness of insulation, the absorption factor of the plate, the other factors. The correct design of the domestic solar hot water using, from the collectors efficiency curves, some methodologies based on the useful energy equation, or the calculation of daily utilizability of solar radiation, or the determination of solar fraction of the system that supplied the hot water demand. This paper proposes an analysis of different methods to desing solar hot water system, the economic study of solar heating systems and optimized analysis in order to...

Orientador: Alcides Padilha / Banca: Enio Pedone Bandarra Filho / Banca: Ismael de Marchi Neto / Banca: Vicente Luiz Scalon / Banca: Delson Luiz Modolo / Resumo: As alterações climáticas tem fomentado a busca por fontes renováveis de energia. Assim, novos coletores solares têm sido o foco de pesquisadores em todo o mundo para novos concentradores, novas configurações de instalação e o estudo da estratificação térmica para melhorar o desempenho do sistema de armazenamento térmico. O sistema proposto, ou seja, utilizando concentrador solar com tubo evacuado, proporciona linearidade e constância na sua eficiência em relação aos coletores de placas planas. A alteração proposta, ou seja, tubo com duas aberturas, uma para entrada do líquido frio e outra para saída do líquido aquecido, elimina a interface física entre a água quente na região voltada para o fluxo de calor solar e a água fria na região inferior do tubo. Essa alteração provoca redução na eficiência térmica, porém aumenta o volume de água aquecida por dia. O concentrador CPC mostrou-se um importante equipamento do sistema, uma vez que a os raios solares incidem em uma região longitudinal definida no tubo coletor solar, direcionado pela geometria do CPC. Com a utilização desse equipamento elimina-se a necessidade de espelhos com seguidores solares, tornando o sistema vulnerável a oscilações elétricas, encarecendo o projeto e consumindo energia elétrica. O desempenho do coletor é avaliado a partir de testes experimentais utilizando a Primeira Lei da Termodinâmica como análise da eficiência. Esses resultados são comparados aos conceitos teóricos descritos na literatura científica. ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Climate change has encouraged the search for renewable energy sources. Thus, new solar collectors have been the focus of researchers around the world with new hubs, new installation settings and the study of thermal stratification to improve the performance of the thermal storage system. The proposed system, ie using evacuated tube solar concentrator provides linearity and stability of efficiency compared to flat plate collectors. The proposed change, i.e. a tube with two openings, one for cold liquid inlet and the other for hot liquid outlet, eliminates the physical interface between the hot water in the region facing the solar heat flow and the cold water in the lower region of the tube. This change causes a reduction in thermal efficiency, however increases the volume of water heated per day. Two radiometers were also developed, one thermal and the other optical, and the thermal radiometer was chosen because it had a similar behavior to the solar collectors, thus reducing the cost of the experimental bench. The CPC concentrator proved to be important equipment, once the concentration of sunlight focus on a longitudinal region defined in the solar collector tube, directed by the CPC geometry. Using this equipment eliminates the need for mirrors with solar trackers, making the system vulnerable to electrical oscillations, making the project more expensive and consuming electricity. The collector performance is evaluated from experimental tests using the First Law of Thermody... (Complete abstract click electronic access below) / Doutor

It is essential to make performance measurements of photovoltaics modules in order to quantify the power they will produce under operational conditions. Performance measurements are fundamental throughout the photovoltaic industry, from product development to quality control in manufacturing and installation in the field. Rapid and economic evaluation of photovoltaic performance requires measurements using pulsed illumination solar simulators. However some devices have characteristics which can cause difficulties making these measurements. The aim of this thesis is to overcome these measurement problems focusing particularly on two of the most prevalent and pressing of these problematic characteristics: high capacitance and metastability. A new method for measuring high capacitance modules in a pulsed simulator, based on tailor made voltage ramps, was developed. The voltage ramp is tailor made such that the measurement time is minimised while maintaining high accuracy (0.5 %), allowing the measurement of high capacitance modules in a single 10ms illumination pulse. The necessary inputs for this method are the capacitance and dark current as a function of voltage for each module. In order to make these measurements, at the high forward bias voltages required, a new system was developed. The tailored voltage ramp can be created individually for each module, since the process is rapid an automatic. This makes the method applicable to a production line or to test house measurements. In addition to their use as inputs for the voltage ramp design, the capacitance and dark current also contain other valuable information, including effective minority carrier lifetime. In several thin film technologies, such as CIGS, the efficiency is not a fixed value, rather the module is metastable and the efficiency changes depending on the previous exposure /preconditioning of the device. Preconditioning is normally applied to these devices before measurement in order to put them in a specific state that is repeatable and representative of outdoor operation. Improved preconditioning practices are vital for performance measurements in CIGS modules. Therefore the preconditioning behaviour of a variety of CIGS modules from different manufacturers was investigated. The effect of preconditioning varied for different modules, commonly the fill factor improved substantially, but often changes in open circuit voltage were also seen and in some cases also substantial changes in short circuit current. The rates of preconditioning and relaxation were found to follow stretched exponential behaviour, such that the changes occur linearly on a logarithmic timescale over several orders of magnitude in time. The total time for performance stabilisation was found to vary significantly between different types of module. Because of this stretched exponential behaviour, even though the module took days to fully relax to the dark state, there was significant relaxation within the tens of minutes that it would normally take a module to cool down after light soaking before it could be measured. The major implication of observed kinetics is that in order to achieve repeatable measurement the timing in each element of a preconditioning routine should be controlled such that the fractional error in the duration of each step is small. During the investigation an unexpectedly short timescale preconditioning effect was observed, which occurs on a millisecond timescale and relaxes in seconds. It was shown that the measurement artefacts introduced using this method can be eliminated by using electrical forward bias until immediately before the measurement. Another measurement system was developed to track the dark current and C-V characteristic of the modules during electrical bias preconditioning and subsequent relaxation. These measurements demonstrate that more than one process involved during preconditioning in CIGS. Changes occur both in the doping in the bulk of the absorber and also in charge accumulation occurring near to the absorber / buffer interface. The theoretical models for preconditioning in CIGS were reviewed and compared to the experimental results. A rate model was developed based on the theory of the metastable VSe-VCu defect. This model was shown to correspond well to the rates of preconditioning and relaxation in CIGS. The non-exponential behaviour was shown to be compatible with a distribution of activation energies for the transition between different defect states. The difference in the time taken for modules to stabilise is explained by differences in doping density and the density of VSe-VCu defects. The work presented facilitates more accurate, economical performance measurements for high capacitance devices and CIGS devices, thereby contributing to the large scale implementation of photovoltaics as power source.

abstract: The sun provides Earth with a virtually limitless source of energy capable of sustaining all of humanity's needs. Photosynthetic organisms have exploited this energy for eons. However, efficiently converting solar radiation into a readily available and easily transportable form is complex. New materials with optimized physical, electrochemical, and photophysical properties are at the forefront of organic solar energy conversion research. In the work presented herein, porphyrin and organometallic dyes with widely-varied properties were studied for solar energy applications. In one project, porphyrins and porphyrin-fullerene dyads with aniline-like features were polymerized via electrochemical methods into semiconductive thin films. These were shown to have high visible light absorption and stable physical and electrochemical properties. However, experimentation using porphyrin polymer films as both the light absorber and semiconductor in a photoelectrochemical cell showed relatively low efficiency of converting absorbed solar energy into electricity. In separate work, tetra-aryl porphyrin derivatives were examined in conjunction with wide-bandgap semiconductive oxides TiO2 and SnO2. Carboxylic acid-, phosphonic acid-, and silatrane-functionalized porphyrins were obtained or synthesized for attachment to the metal oxide species. Electrochemical, photophysical, photoelectrochemical, and surface stability studies of the porphyrins were performed for comparative purposes. The order of surface linkage stability on TiO2 in alkaline conditions, from most stable to least, was determined to be siloxane > phosphonate > carboxylate. Finally, porphyrin dimers fused via their meso and beta positions were synthesized using a chemical oxidative synthesis with a copper(II) oxidant. The molecules exhibit strong absorption in the visible and near-infrared spectral regions as well as interesting electrochemical properties suggesting possible applications in light harvesting and redox catalysis. / Dissertation/Thesis / Ph.D. Chemistry 2012

Made available in DSpace on 2014-06-11T19:25:27Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-07-29Bitstream added on 2014-06-13T19:53:13Z : No. of bitstreams: 1 avallone_e_me_bauru.pdf: 1832025 bytes, checksum: 3c9dc17b98ecbc3d0da1306a71d373df (MD5) / A necessidade de fontes renováveis de energia, devido às alterações climáticas e, assim, a busca de fontes limpas de energia, justificam o crescente investimento em novos tipos de coletores solares. As pesquisas têm contribuído com essa expansão no âmbito dos coletores solares concentradores, tendo como objetivo principal seu Desempenho. Muitos trabalhos tem sido desenvolvidos utilizando a estratificação térmica do fluido no interior dos tubos e em reservatórios térmicos, assim como, a modelagem analítica para o problema de fluxo de calor. Baseando-se nas características de operação e em parâmetros de eficiência dos coletores por tubos evacuados convencionais, este trabalho propõe um estudo experimental de aquecimento de água por sistema de captação solar por tubos evacuados modificados em relação a um sistema convencional. Uma abordagem importante refere-se a separação física dos fluxos de água fria e quente no interior do tubo evacuado. O desempenho do sistema foi analisado a partir de testes experimentais ao ar livre com incidência solar. O vácuo no sistema estudado proporciona linearidade e constância na sua eficiência, em relação aos coletores solares por placas planas. Referindo-se a captação de energia do sistema, há um acréscimo de 8,7ºC na temperatura de saída da água aquecida em relação à sua entrada. O sistema ensaiado com um tubo evacuado produziu 105,78 litros de água aquecida, durante o dia solar disponível. Por se tratar de um trabalho experimental inédito, há uma grande dificuldade em localizar pesquisas referentes ao mesmo assunto, dificultando, assim, comparações entre os resultados obtidos e de outros trabalhos científicos / The need for renewable energy, due to climate change and thus search for clean energy sources justify the increased investment in new types of solar collectors. Research has contributed to this expansion within the concentrator solar collectors, with the main objective performance. Many studies have been developed using the thermal stratification of the fluid inside the tubes and in heat reservoirs, as well as the analytic modeling of the problem of heat flow. Based on the the operatining characteristics and performance parameters of evacuated tube collectors for conventional, this work proposes and experimental study of heating water by solar collection system for tubes modified compared to a conventional system. An important approach refers to physically separate the flows of hot and cold water inside the evacuated tube. The system performance was analyzed from experimental tests outdoors in sunlight. In this study the vacuum provides linearity and constancy in efficiency compared to a flat plate solar collectors. Refering to energy harvesting system, there is a increase of 8.7ºC in the outlet temperature of the heated water compared the entrance. With only one evacuated tube were production of 105.78 liters of heated water during the solar day available. Because it is unpublished experiment work, there is great difficulty in locating researches concerning the same subject, thus hampering comparisons between results and other scientific works

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.

Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2015-01-21T10:10:35Z No. of bitstreams: 0 / Made available in DSpace on 2015-01-21T10:10:35Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Thesis (Master Diploma (Electrical Engineering))--Cape Technikon, Cape Town,1996 / In order to design a coolerbox, utilising Thermo-electric technology as a heat pump, it was necessary to determine if this type of technology would be suitable for a coolerbox heat pump application. A detailed TEC (Thermo Electric Cooler) sizing estimation was done, using formulas supplied by the manufacturer, and using thermo-electric themy formulas to calculate the absolute theoretical performance parameters for a suitable TEe The correct heat pumping capability is important since.it is possible to obtain TEes with different input currents, voltages and heat pumping capabilities. Using the TEC as a heat pump, it was decided to use water cooling due to the extremely high cost of a suitable air cooled heatsink. It should be noted that to cool the hot side of theTEe a vel}' efficient heat exchanger should be used. A simulator was constructed to simulate, under variable operating temperatures and input powers, the cooling capacity of the TEC heat exchanger. The cooling characteristics were then used to determine if the theol}' and manufacturers claims correspond with the cooling characteristics of the coolerbox. It might be possible that the performance of the TEC would be drastically influenced, since installation con~itions may not be ideal when installed; and, that the manufacturers performance claims are done when the TEC is operated under ideal conditions. This would ensure optimum results because, should an under sized TEC be used, the result would be poor cooling characteristics; or, if the TEC is over sized, the coolerbox would consume too much power, resulting in an inefficient system.

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2016. / Solar energy is still not being used effectively in countries in the developing world, though it's a partial solution to the problem of shortage and expensive energy. Normally harvested through flat plate collectors, converting solar radiation into heat is the most direct application that can be effected in water heating systems. Many researchers have attempted to develop means of improving the efficiency of the flat plate solar energy collector; however there appears to be no evidence of any work regarding the effect of geometric configuration on the performance of flat plate solar collector. This study presents results obtained when comparing the performance of a solar water heating system equipped with three manufactured flat plate solar collector panels of numerically identical surface area but of different geometric configuration as they were individually attached to a typical geyser. Data was obtained inside a laboratory. The amount of heat acquired from flat plate collectors of solar energy depends primarily on their surface area that is exposed to the solar irradiance, however, the geometry of the collectors was thought that it might affect to some extent the amount of heat harvested. The circulation of the water from the panel to the geyser was due to the self-induced thermo-syphon effect. The results obtained during the test period (7 hours per day for two consecutive days) indicated that the system’s thermal efficiency was best when the square geometrical configuration collector was used. A dimensional analysis using the Π Buckingham method that was performed on the parameters affecting a flat plate solar collector yielded three dimensionless numbers that lead to a power law relationship which might be useful in enhancing solar water heating systems’ design.

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2018. / Until recently, the focus of most solar technology development for space was towards more efficient, more radiation-resistant and increasingly powerful arrays. During a space mission, solar cells are not only exposed to irradiation by electrons, but also to a range of other particles, like protons. Thus, solar cells on robust nanosatellites are extremely exposed to an environment, which includes the high-energy electrons and protons of the earth’s radiation belts, which leads towards the degradation process of the individual solar cell. Solar cell radiation shielding design ensures the protection of the solar cells from the particular radiation environment found in space. While the design principles of a solar photovoltaic automatic switching fault tolerant system which can detect and bypass faulty photovoltaic cells will be presented through this research work. The ability of such a system to be reconfigured using implemented switching matrix system makes it efficient under various environments and faulty conditions. / National Research Foundation (NRF)