Hybrid solar systems as well as concentrating solar collectors are promising solar technologies. To run them efficiently in northern countries is a task Solarus AB is working on.The objective of this MSc project is to investigate and experimentally evaluate the option of implementing a light diffusing sheet in acompound parabolic concentrator (CPC) solar collector, called the “Scania Model”. This component should improve the non-uniform illumination of the photovoltaic cells in concentrating solar collectors.Therefore, scientific publications on this kind of solar collectors were read up on, e.g.Adsten, M. Brogren, M., Roos, A., Karlsson, B. Nilsson, J. and Leutz, R.After researching and procuring possible diffuser materials, experimental tests were carried out and the different materials were reviewed. Implemented in a solar simulator the IV curves of the collector with the different diffusers were generated. Furthermore, the influence of the materials on light was reviewed using daylight, laser light and an artificial light source. In the following, the light intensity distribution on the absorber of the Scania Model was defined and evaluated.The results of this project show that the main problem regarding diffuser material is to provide sufficient diffusion without much transmission losses.

Orientador: Vicente Luiz Scalon / Delson Luiz Modolo / João Batista Campos Silva / Resumo: Nas últimas décadas, o crescente aumento do preço dos combustíveis fósseis associado às crescentes preocupações ambientais têm incentivado as pesquisas sobre o uso de fontes de energia renováveis e os aprimoramentos de seus sistemas e equipamentos. Dentre as fontes alternativas existentes, a energia solar merece ser destacada pelo seu grande potencial de exploração. Os dispositivos solares permitem um amplo espectro de uso, podendo ser utilizados desde operações de grande porte, como hotéis e indústrias, até em sistemas menores típicos de residências. Dentre as aplicações possíveis de energia solar, o sistema de aquecimento de água residencial utilizando coletores solares planos ainda é o mais comum. Este tipo de dispositivo capta a radiação solar por meio de seus coletores e aquece a água que escoa no seu interior e a armazena dentro de um reservatório. Este trabalho propõe estudar uma geometria de coletor alternativa para a captação de energia baseada no coletor de absorção direta. Neste tipo de dispositivo, o fluido de trabalho escoa entre uma placa absorvedora negra e uma placa de vidro e é aquecido indiretamente pela placa absorvedora. Para a avaliação da geometria um modelo numérico bidimensional utilizando o OpenFOAM® foi elaborado. As análises realizadas visaram determinar as condições de contorno ideais para as simulações envolvendo escoamentos de vazão constante e devido ao efeito de termossifão. Com o modelo estabelecido, determinou-se a curva de rendimento da geom... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: On last decades, the increasing price of fossil fuels associated with the growing concern with the environmental have encouraged researches about renewable energy sources and improvements to its systems and equipment. Among the available alternative sources, solar energy deserves to be highlighted for its great exploitation potential. Solar devices allow a wide range of use, since large operations, such as hotels and industries, to typical smaller residences systems. Among possible applications for solar power, residential water heating systems using flat solar collectors are the most common ones. This type of devices capture solar radiation through their collectors, heat the inside flowing water and stores it in a reservoir. The present work intends to study an alternative collector geometry for energy harvesting based on the direct absorption collector. In this device, the working fluid flows between a black absorber plate and a glass cover and is heated indirectly by the absorber plate. For the geometry evaluation a two-dimensional numeric model was created using OpenFOAM. The analysis aimed to determine the optimal boundary conditions for simulations involving a constant flow and a thermosiphon effect flow. With the model stablished, it was determined the efficiency curve for the geometry in order to find the optimal fluid thickness that flows inside the collector. After the analysis, it can be concluded that the thickness effect on the thermal efficiency is small and, am... (Complete abstract click electronic access below) / Mestre

The optical properties of the absorber pipe in a parabolic trough collector isessential for the performance of the solar collector. The desirable propertiesare high absorptance (α) of solar radiation and low emittance (ε) of thermalradiation. A surface with these properties is known as a solar selective surface. There are several techniques used to produce selective surfaces, but one of the most common ones is electroplating. Research done by Vargas, indicates that optical properties of α = 0.98 and ε = 0.03 [1], which is superior to the best commercial alternatives (α = 0.95 and ε = 0.04 [2]), can be achieved by electroplating a Co-Cr coating on a stainless steel substrate. Additionally, Vargas used an electrolyte of trivalent chromium dissolved in a deep eutectic solvent, as opposed to the traditionally used aqueous electrolytes containing hexavalent chromium, which is toxic and carcinogenic. In this project, a coating of Co-Cr was electroplated on a stainless steel substratewith a method similar to that of Vargas in order to obtain a solar selective surface. The electrolyte was composed of ethylene glycol, choline chloride, CrCl3•6H2O and CoCl2•6H2O in a molar ratio of 16:1:0.4:0.2. The plating process was conducted using chronoamperometric electrodeposition with an applied potential of -1.2 V (against an Ag/AgCl reference electrode) for 15 min. The system was investigated using Cyclic Voltammetry (CV). The total absorptance was measured using UV-Vis spectroscopy, while the emittance was measured using an IR-thermometer. The microstructure and chemical composition was investigated using Scanning ElectronMicroscopy (SEM), Focused Ion Beam (FIB), Energy-Dispersive X-ray Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS) and Raman spectroscopy. The thermal stability of the coating was investigated by exposingit to 400°C in air for 24 h. The electroplated coating is approximately 2.8 μm thick and exhibits a porousstructure with a surface of fine fiber-like flakes. The coating consists largely of Co hydroxides with low concentrations of Cr compounds, Co oxides and metallic Co. Hence, a satisfactory co-deposition was not accomplished, as the Cr concentration is low. The coating is not thermally stable up to 400°C, exhibiting signs of at least partially melting in the annealing process. The compounds in the coating were largely oxidized in the process. The electroplated surface does however exhibits strong selectivity, with a total solar absorptance of α = 0.952 and total emittance of ε = 0.32 at 160°C.

A iluminação dos espaços é observada há milênios, desde a utilização do fogo até as mais novas tecnologias em iluminação. Iluminar ambientes procurando, cada vez mais, a eficiência e a economia de energia vem sendo motivo de investigação constante dos pesquisadores. Atualmente, o grande problema enfrentado pela iluminação artificial é o custo da energia elétrica e por isso vários pesquisadores têm procurado soluções alternativas. O presente trabalho realizou um estudo sobre a viabilidade técnica e o desempenho de um equipamento (patenteado como Girassol®) que emprega a fibra óptica para iluminação natural em ambientes que não recebem luz direta, ainda no formato de um protótipo. O aspecto da sustentabilidade visando a economia de energia através da captação solar e condução da luz através dos cabos de fibra óptica até a célula-teste foi analisado. A questão principal a ser observada foi quão eficiente pode ser o sistema de iluminação com fibra óptica utilizando a captação de luz solar. Para isso foram feitos testes do equipamento em um ambiente previamente construído, denominado célula teste, com área aproximada de 4 m². Foi medida a quantidade de luminância e iluminâncias que chegam ao ambiente da célula-teste. Esta pesquisa visou conhecer a tecnologia atual existente no mercado comercial nacional e internacional e a tecnologia do equipamento desenvolvido no Brasil. A pesquisa considerou como a hipótese de que a correta captação de luz solar aliada à correta condução através dos cabos de fibra óptica, que permite com que a iluminação em ambientes iluminados somente com luz artificial passem a ser iluminados com a luz natural conduzida pelos cabos de fibra óptica, pode colaborar para a qualidade da luz para seus usuários e para a eficiência energética da edificação. A metodologia desenvolvida foi através de medições uma vez por semana, durante um ano, três vezes ao dia (às 9, 12 e 15 horas) comprovando a eficiência do equipamento na diversidade de situações impostas por intempéries. Os resultados obtidos comprovaram a viabilidade técnica e o bom desempenho do equipamento confirmando sua potencialidade de contribuição para a eficiência energética quando implantado. Este estudo contribuiu para a comunidade acadêmica por sua interdisciplinaridade e por apresentar avanço em conhecimentos técnicos e teóricos sobre o melhor aproveitamento da luz natural para obtenção de eficiência energética, tema de grande interesse frente a questões estéticas, ambientais e de saúde.\" / The lighting of spaces has been observed for millennia, since the use of fire up the latest lighting technologies. Lighting environments increasingly looking for efficiency and energy being a reason for constant research of the researchers. Currently, the major problem faced by artificial lighting is the cost of electrical energy and that is why several researchers have sought solutions alternatives. The present work carried out a study on the viability technique and the performance of an equipment (patented as Girassol®) that fiber optics for natural lighting in receive direct light, still in the shape of a prototype. The sustainability to save energy through solar and conduction of light through fiber optic cables to the test cell It was analyzed. The main issue to note was how efficient can be the lighting system with fiber optics using the capture of sunlight. For this, equipment tests were performed in a previously constructed environment, called the test cell, with an approximate area of 4sqm. The amount of luminance and illuminances that reached the environment of the test cell. This research aimed to know the technology existing in the national and international commercial market and the equipment technology developed in Brazil. The research considered as the hypothesis that the correct capture of sunlight allied to the correct through fiber optic cables, which allows illuminated areas with only artificial light be illuminated with natural light led by fiber optic cables, can collaborate on the quality of light for its users and for the energy efficiency of the building. The methodology developed was through measurements once a week, for one year, three times (9 am, 12 pm, and 3 pm), demonstrating the efficiency of the equipment in the diversity of situations imposed by inclement weather. The obtained results proved the technical feasibility and good performance of the equipment confirming its potential contribution to efficiency when implanted. This study contributed to the its interdisciplinarity and to present advances in technicians and theorists about the best use of natural light to obtain energy efficiency, a subject of great interest in aesthetic, environmental and health matters.

Tyrimų tikslas – ištirti galimybę panaudoti tiesioginę spinduliuotę džiovinamos medžiagos ir džioviklio įkaitimui džiovinant grūdus Lietuvos sąlygomis . Lietuvoje nuimtų grūdų drėgnumas dažniausiai viršija kondicinį, todėl siekiant išvengti kokybės nuostolių juos būtina nedelsiant konservuoti. Darbe apžvelgti grūdų fizinių savybių pokyčiai džiovinimo metu, plačiau analizuojama tiesioginės saulės spinduliuotės panaudojimas Lietuvos sąlygomis džiovinant grūdus su saulės kolektoriais. Ištirtas tiesioginės saulės spinduliuotės poveikis grūdams ir džioviklio paruošimui. Nustatyta, kad tiesioginė saulės spinduliuotė sutrumpina grūdų džiovinimo laiką ir sutaupo energiją naudojamą grūdų džiovinimui. Nustatyta saulės kolektoriaus pasvirimo kampo priklausomybė nuo spindulių kritimo kampo, džiovinimo greičio priklausomybė nuo oro filtracijos greičio ir grūdų drėgnio. / Purpose of the study - research the possibility of using direct solar radiation to heat desiccant material and siccative when drying grain in Lithuanian weather conditions. In Lithuania, humidity of harvested grain is generally higher than conditioned. To avoid loss of quality grain should be cured immediately. This paper reviews changes in physical properties of grain during drying. A wider analysis of use of solar collectors for drying grain in Lithuania using direct solar radiation is also given. Direct solar radiation impact on grain and preparation of dryer has been investigated. It has been found that direct solar radiation reduces the drying time and lowers energy costs when drying grain. Dependence of solar collector tilt angle and solar radiation incidence angle was established. Drying speed relation to air filtration rate and grain moisture has also been found.

A study of thermal, structural, electrical and optical characteristics of molybdenum black surface coatings on various substrates has been made. The suitability of these coatings for use as selective absorbers for solar collector applications has been assessed. Molybdenum black (Mo black) coatings were prepared by electrodeposition (on aluminium) and a chemcial conversion method (on zinc and electroplated cobalt on nickel plated copper substrates). The solar absorptancer (αs) and thermal emittances (εth) of the coatings were determined from room temperature spectral reflectance measurements in the solar (0.3 to 2.5μm) and infrared regions (2.5 to 50 μm) respectively. The effect of different preparation parameters and substrate pretreatments on the spectral selectivity has been investigated in order to optimize the thermal performance. The spectral selectivity is related to the Mo-black coating thickness and surface roughness together with the microstructure, of the substrate and the intermediate layer. Dip coatings on polished zinc have significant selectivity (αs/ εth = 8.4 when αs = 0.76). The absorptance of the dip coatings is increased to 0.87 with εth = 0.13 by chemical etching of zinc prior to coating deposition. For coatings on electroplated cobalt on nickel plated copper (cobalt (NC) substrate), an absorptance as high as 0.94 has been obtained with an emittance value 0.3. By using an addition agent in the plating solution of cobalt the high emittance can be reduced to 0.1 with αs = 0.91 giving a coating with a relatively high efficiency (82.5%) for photo-thermal energy conversion. A study of the surface composition and microstructure of the coatings has been made using scanning and transmission electron microscopy together with electron diffraction, X-ray diffraction and X-ray photoelectron spectroscopy. The structural investigations indicate that Mo-black coatings contain polycrystals of orthorhombic Mo4O11 with a small proportion of Ni(OH)2. Presence of water and also Mo4O11 in the coatings are evident from IR spectroscopy study. The bandgap of the coating has been determined from optical transmission spectra (1.66 eV) and also from reflectance spectra (0.85 eV). The discrepancy between these two values has been discussed. The refractive indices of the coatings have also been estimated. The band gaps and refractive indices are found to be related to the spectral selectivity of the coatings. The durability test of the coatings shows that the coatings on etched zinc are more resistant to heat treatment than the coatings on unetched zinc. The coatings on cobalt (NC) substrates also show good stability for relatively short periods at temperatures ~400ºC. A study of the electrical properties of Mo-black coatings suggests that at electrical field strengths (greater than 106v/m the dominant conduction process is of the Poole-Frenkel type. The activation energy of the conduction process has been estimated to be -0.56 eV at higher temperatures. The effect of heat treatment on the electrical properties of the coatings has been examined. The dielectric constant of Mo-black has been estimated from A. C. measurements. At high frequency (20 kHz) the value of the dielectric constant is about 4.0.

The purpose of this study is to investigate the performance of a spherical solar collector by using numerical and experimental methods. For this analysis, equations were obtained by choosing appropriate control volumes in the system and applying The First Law of Thermodynamics. The experiments were realized at four different mass flow rates and non-flow situation. For the numerical simulation of the system, a computer program in Mathcad was written. Another computer program in Mathcad was written for the variation of the absorbed solar radiation through out the day. Finally, the performance of the spherical solar collector is compared theoretically to that of flat plate solar collectors.

<p>Tremendous research efforts have been conducted studying the capturing and conversion of solar energy. Solar thermal power systems offer a compelling opportunity for renewable energy utilization with high efficiencies and excellent cost-effectiveness. The goal of this work was to design a non-concentrating collector capable of reaching temperatures above 250 °C, use this collector to power methanol steam reforming, and operate a proton exchange membrane (PEM) fuel cell using the generated hydrogen. The study presents the construction and characterization of a non-concentrating, intermediate-temperature, fin-in-tube evacuated solar collector, made of copper and capable of reaching stagnation temperatures of 268.5 °C at 1000 W/m2 irradiance. The collector was used to power methanol steam reforming, including the initial heating and vaporization of liquid reactants and the final heating of the gaseous reactants. A preferential oxidation (PROX) catalyst was used to remove CO from simulated reformate gas, and this product gas was used to operate a PEM fuel cell. The results show 1) that the outlet temperature is not limited by heat transfer from the absorber coating to the heat transfer fluid, but by the amount of solar energy absorbed. This implicates a constant heat flux description of the heat transfer process and allows for the usage of materials with lower thermal conductivity than copper. 2) It is possible to operate a PEM fuel cell from reformate gas if a PROX catalyst is used to remove CO from the gas. 3) The performance of the fuel cell is only slightly decreased (~4%) by CO2 dilution present in the reformate and PROX gas. These results provide a foundation for the first renewable electricity generation via solar-powered methanol reforming through a hybrid PEM fuel cell system based on novel non-concentrating, intermediate-temperature solar collectors.</p> / Dissertation

abstract: Evacuated tube solar thermal collector arrays have a wide range of applications. While most of these applications are limited in performance due to relatively low maximum operating temperatures, these collectors can still be useful in low grade thermal systems. An array of fifteen Apricus AP-30 evacuated tube collectors was designed, assembled, and tested on the Arizona State University campus in Tempe, AZ. An existing system model was reprogrammed and updated for increased flexibility and ease of use. The model predicts the outlet temperature of the collector array based on the specified environmental conditions. The model was verified through a comparative analysis to the data collected during a three-month test period. The accuracy of this model was then compared against data calculated from the Solar Rating and Certification Corporation (SRCC) efficiency curve to determine the relative performance. It was found that both the original and updated models were able to generate reasonable predictions of the performance of the collector array with overall average percentage errors of 1.0% and 1.8%, respectively. / Dissertation/Thesis / M.S. Mechanical Engineering 2011

Os sistemas solares de aquecimento de água são uma forma de produção de energia não poluente, que já faz parte da matriz energética brasileira. O uso deste tipo de sistemas traz benefícios econômicos ao país e principalmente a quem os utiliza, devido à poupança no uso de outras fontes de energia para o aquecimento da água. No Brasil o aquecimento solar de água é realizado, principalmente, por coletores solares planos, tecnologia bem conhecida e fabricada no país a preços baixos. Mas atualmente há uma outra tecnologia que está sendo difundida no âmbito nacional, os coletores solares de tubos a vácuo, os quais estão sendo produzidos internacionalmente em uma escala maior, importados e comercializados a preços mais competitivos no mercado nacional. Por isto é necessário entender estes sistemas e o seu funcionamento para evitar erros na sua instalação e otimizar sua operação. Nesta dissertação é realizada uma análise comparativa de um sistema de aquecimento de água composto por um coletor solar de tubos de vidro a vácuo de extração de calor por transferência direta operando em circulação forçada com o mesmo sistema operando em circulação por termossifão. Esta comparação foi realizada determinando a energia anual que o sistema pode produzir para cada tipo de circulação, a qual foi calculada usando como referência a norma ISO 9459-2 e os dados climáticos da cidade de Porto Alegre do Estado do Rio Grande do Sul. Também foram realizadas medições da vazão em termossifão, entre o reservatório e o coletor solar, e foi determinado o coeficiente de perdas térmicas do tanque reservatório segundo os procedimentos da mesma norma. Para isto foi realizada a montagem de uma bancada experimental, com sensores e instrumentos de medida que foram calibrados. Para o sistema de aquecimento testado, os resultados mostram que o sistema trabalhando em circulação por termossifão produz maior quantidade de energia no ano do que o sistema em circulação forçada, onde se observou que a estratificação no tanque reservatório era menor. Também foi observado que a máxima vazão em termossifão para este sistema de aquecimento de água foi de 0,5 L/min. / Solar water heating systems are a method of clean energy production, which is already part of the Brazilian energy matrix. The use of these systems brings economic benefits to the country and especially who use them due to savings in the use of other sources of energy for heating water. In Brazil, the solar water heating is carried out mainly by flat solar collectors, which is a widely known technology because it is produced in the country at low prices. But recently, there is another technology that is being used named: evacuated solar collectors. These collectors are being worldwide produced on a large scale and they are imported and inserted at competitive prices in the domestic market. Therefore it is necessary to understand these systems and their operation to avoid errors in its installation and optimize their operation. In this work, it is accomplishing a comparative analysis of a solar water heating system composed by a water-in-glass evacuated tube solar collector working in forced circulation with the same system working in thermosyphon circulation. This comparison was performed by determining the annual energy that the system can produce for each type of circulation, which was calculated based on the ISO 9459-2 standard and the climatic data of the Porto Alegre city, state of the Rio Grande Do Sul. Also, it was performed thermosyphon measurements between the thermal reservoir and the solar collector, and it was calculated the heat loss coefficient from the reservoir tank according to the procedures of ISO 9459-2 standard. To do so, a testing bench was made, with sensors and measuring instruments which were calibrated before use. For the heating system tested, the results show that the system with thermosyphon circulation produces more annual energy than the forced circulation system where the water temperature stratification in the thermal reservoir was lower. Also, it was observed that the maximum thermosyphon flow for this solar water heating system was 0,5 L/min.