955 resultados para Solar Tower Technology


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This work is about a development of a vacuum solar water heater. To accomplish this, some measurements were made, such as flow, water temperature and room temperature, relative humidity, solar power density and wind speed. It first presents a brief explanation about the global situation in relation to the accelerated use of exhaustible energy sources which can result in a breakdown of these for future generations. From this, is proposed to analyze this solar water heater with vacuum tubes during the winter season in Brazil southeastern region, under different environmental conditions. From such ideas became possible to prove through the experimental part, calculations and graphical results that technology and the performance of this device are technical and economically viable, according to the life cycle of this. It was also found that the average monthly production in a maximum heat stroke situation was 193,33kWh and minimum isolation was 57,76kWh. This reveals that this instrument should start to be examined more closely by all, as a way to reduce the use of electricity, which will protect the environment without reducing the comfort of people

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Solar heaters are an appropriate technology in tropical and sub-tropical climates to heat bath water by solar energy. Low-cost solar heaters meet the demand of low-income rural communities which currently do not have access to this technology. Current research analyzes the economic viability of solar heaters, built with recyclable materials, to reduce electric energy bill. A solar heating system was built consisting of recyclable materials in accordance with the manuals provided by the Secretariat of Environment of the state of Paraná (SEMA). Duration of use of electric showers by families of rural properties was determined to calculate expenses and billing of electricity. Simulation and material costs showed that the system was feasible. Commercial solar heaters could be replaced at a cost of R$ 22.61 per month during 13 months.

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Evaluation has been made on the monthly and annual average diurnal evolution of the hourly diffuse radiation as well as its radiometric fractions on surfaces inclined at 12.85, 22.85 and 32.85° to face North, in climate conditions of Botucatu, São Paulo, Brazil (22.85° S and 48.43° W). Measurements were made between 04/1998 to 08/2001 for 22.85°; 09/2001 to 02/2003 for 12.85° and 01/2004 to 12/2007 for 32.85°, with concomitant measures in the horizontal. For all surfaces the diffuse radiation was obtained from different method. Assessment has been performed as well on the radiometric fractions obtained from the ratio of diffuse radiation and global radiation (KDH and KDβ) and between radiation and diffuse radiation at the top of the atmosphere (KʹDH and KʹDβ) for the horizontal and tilted surfaces in hourly partition. The diffuse radiation levels were dependent on variations in precipitation and cloudiness. There was an increase in the differences between the diffuse radiation and the radiometric fractions with the increment of the angle, and in horizontally, which affected higher levels of diffuse radiation in spring and summer. The values of KDH and KDβ present in an inverse behavior were compared to diffuse radiation and theydecreased in the southern passage due to the increase of the direct component in the total of incident radiation.

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Solar reactors can be attractive in photodegradation processes due to lower electrical energy demand. The performance of a solar reactor for two flow configurations, i.e., plug flow and mixed flow, is compared based on experimental results with a pilot-scale solar reactor. Aqueous solutions of phenol were used as a model for industrial wastewater containing organic contaminants. Batch experiments were carried out under clear sky, resulting in removal rates in the range of 96100?%. The dissolved organic carbon removal rate was simulated by an empirical model based on neural networks, which was adjusted to the experimental data, resulting in a correlation coefficient of 0.9856. This approach enabled to estimate effects of process variables which could not be evaluated from the experiments. Simulations with different reactor configurations indicated relevant aspects for the design of solar reactors.

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Photovoltaic (PV) conversion is the direct production of electrical energy from sun without involving the emission of polluting substances. In order to be competitive with other energy sources, cost of the PV technology must be reduced ensuring adequate conversion efficiencies. These goals have motivated the interest of researchers in investigating advanced designs of crystalline silicon solar (c-Si) cells. Since lowering the cost of PV devices involves the reduction of the volume of semiconductor, an effective light trapping strategy aimed at increasing the photon absorption is required. Modeling of solar cells by electro-optical numerical simulation is helpful to predict the performance of future generations devices exhibiting advanced light-trapping schemes and to provide new and more specific guidelines to industry. The approaches to optical simulation commonly adopted for c-Si solar cells may lead to inaccurate results in case of thin film and nano-stuctured solar cells. On the other hand, rigorous solvers of Maxwell equations are really cpu- and memory-intensive. Recently, in optical simulation of solar cells, the RCWA method has gained relevance, providing a good trade-off between accuracy and computational resources requirement. This thesis is a contribution to the numerical simulation of advanced silicon solar cells by means of a state-of-the-art numerical 2-D/3-D device simulator, that has been successfully applied to the simulation of selective emitter and the rear point contact solar cells, for which the multi-dimensionality of the transport model is required in order to properly account for all physical competing mechanisms. In the second part of the thesis, the optical problems is discussed. Two novel and computationally efficient RCWA implementations for 2-D simulation domains as well as a third RCWA for 3-D structures based on an eigenvalues calculation approach have been presented. The proposed simulators have been validated in terms of accuracy, numerical convergence, computation time and correctness of results.

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CIGS-Dünnschichtsolarzellen verbinden hohe Effizienz mit niedrigen Kosten und sind damit eine aussichtsreiche Photovoltaik-Technologie. Das Verständnis des Absorbermaterials CIGS ist allerdings noch lückenhaft und benötigt weitere Forschung. In dieser Dissertation werden Computersimulationen vorgestellt, die erheblich zum besseren Verständnis von CIGS beitragen. Es wurden die beiden Systeme Cu(In,Ga)Se2 und (Cu,In,Vac)Se betrachtet. Die Gesamtenergie der Systeme wurde in Clusterentwicklungen ausgedrückt, die auf der Basis von ab initio Dichtefunktionalrechnungen erstellt wurden. Damit war es möglich Monte Carlo (MC)-Simulationen durchzuführen. Kanonische MC-Simulationen von Cu(In,Ga)Se2 zeigen das temperaturabhängige Verhalten der In-Ga-Verteilung. In der Nähe der Raumtemperatur findet ein Übergang von einer geordneten zu einer ungeordneten Phase statt. Unterhalb separiert das System in CuInSe2 und CuGaSe2. Oberhalb existiert eine gemischte Phase mit inhomogen verteilten In- und Ga-Clustern. Mit steigender Temperatur verkleinern sich die Cluster und die Homogenität nimmt zu. Bei allen Temperaturen, bis hin zur Produktionstemperatur der Solarzellen (¼ 870 K), ist In-reiches CIGS homogener als Ga-reiches CIGS. Das (Cu,In,Vac)Se-System wurde mit kanonischen und großkanonischen MC-Simulationen untersucht. Hier findet sich für das CuIn5Se8-Teilsystem ein Übergang von einer geordneten zu einer ungeordneten Phase bei T0 = 279 K. Großkanonische Simulationen mit vorgegebenen Werten für die chemischen Potentiale von Cu und In wurden verwendet, um die Konzentrations- Landschaft und damit die sich ergebenden Stöchiometrien zu bestimmen. Stabilitätsbereiche wurden für stöchiometrisches CuInSe2 und für die Defektphasen CuIn5Se8 und CuIn3Se5 bei einer Temperatur von 174 K identifiziert. Die Bereiche für die Defektphasen sind bei T = 696 K verschwunden. Die Konzentrations-Landschaft reproduziert auch die leicht Cu-armen Stöchiometrien, die bei Solarzellen mit guten Effizienzen experimentell beobachtet werden. Die Simulationsergebnisse können verwendet werden, um den industriellen CIGS-Produktionspr

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In dieser Dissertation wird die Ladungsträgergeneration und -rekombination in neuen polymeren Absorbermaterialien für organische Solarzellen untersucht. Das Verständnis dieser Prozesse ist wesentlich für die Entwicklung neuer photoaktiver Materialsysteme, die hohe Effizienzen erzielen und organische Solarzellen konkurrenzfähig im Bereich der erneuerbaren Energien machen. Experimentell verwendet diese Arbeit hauptsächlich die Methode der transienten Absorptionsspektroskopie, die sich für die Untersuchung photophysikalischer Prozesse auf einer Zeitskala von 100 fs bis 1 ms als sehr leistungsfähig erweist. Des Weiteren wird eine soft-modeling Methode vorgestellt, die es ermöglicht, photophysikalische Prozesse aus einer gemessenen transienten Absorptions-Datenmatrix zu bestimmen, wenn wenig a priori Kenntnisse der Reaktionskinetiken vorhanden sind. Drei unterschiedliche Donor:Akzeptor-Systeme werden untersucht; jedes dieser Systeme stellt eine andere Herangehensweise zur Optimierung der Materialien dar in Bezug auf Lichtabsorption über einen breiten Wellenlängenbereich, effiziente Ladungstrennung und schnellen Ladungstransport. Zuerst wird ein Terpolymer untersucht, das aus unterschiedlichen Einheiten für die Lichtabsorption und den Ladungstransport besteht. Es wird gezeigt, dass es möglich ist, den Fluss angeregter Zustände vom Chromophor auf die Transporteinheit zu leiten. Im zweiten Teil wird der Einfluss von Kristallinität auf die freie Ladungsträgergeneration mit einer Folge von ternären Mischungen, die unterschiedliche Anteile an amorphem und semi-kristallinem Polymer enthalten, untersucht. Dabei zeigt es sich, dass mit steigendem amorphen Polymeranteil sowohl der Anteil der geminalen Ladungsträgerrekombination erhöht als auch die nicht-geminale Rekombination schneller ist. Schlussendlich wird ein System untersucht, in dem sowohl Donor als auch Akzeptor Polymere sind, was zu verbesserten Absorptionseigenschaften führt. Die Rekombination von Ladungstransferzuständen auf der unter 100 ps Zeitskala stellt hier den hauptsächliche Verlustkanal dar, da freie Ladungsträger nur an Grenzflächen erzeugt werden können, an denen Donor und Akzeptor face-to-face zueinander orientiert sind. Darüber hinaus wird festgestellt, dass weitere 40-50% der Ladungsträger durch die Rekombination von Grenzflächenzuständen verloren gehen, die aus mobilen Ladungsträgern geminal gebildet werden.

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The primary goal of this work is related to the extension of an analytic electro-optical model. It will be used to describe single-junction crystalline silicon solar cells and a silicon/perovskite tandem solar cell in the presence of light-trapping in order to calculate efficiency limits for such a device. In particular, our tandem system is composed by crystalline silicon and a perovskite structure material: metilammoniumleadtriiodide (MALI). Perovskite are among the most convenient materials for photovoltaics thanks to their reduced cost and increasing efficiencies. Solar cell efficiencies of devices using these materials increased from 3.8% in 2009 to a certified 20.1% in 2014 making this the fastest-advancing solar technology to date. Moreover, texturization increases the amount of light which can be absorbed through an active layer. Using Green’s formalism it is possible to calculate the photogeneration rate of a single-layer structure with Lambertian light trapping analytically. In this work we go further: we study the optical coupling between the two cells in our tandem system in order to calculate the photogeneration rate of the whole structure. We also model the electronic part of such a device by considering the perovskite top cell as an ideal diode and solving the drift-diffusion equation with appropriate boundary conditions for the silicon bottom cell. We have a four terminal structure, so our tandem system is totally unconstrained. Then we calculate the efficiency limits of our tandem including several recombination mechanisms such as Auger, SRH and surface recombination. We focus also on the dependence of the results on the band gap of the perovskite and we calculare an optimal band gap to optimize the tandem efficiency. The whole work has been continuously supported by a numerical validation of out analytic model against Silvaco ATLAS which solves drift-diffusion equations using a finite elements method. Our goal is to develop a simpler and cheaper, but accurate model to study such devices.

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Direct imaging of extra-solar planets in the visible and infrared region has generated great interest among scientists and the general public as well. However, this is a challenging problem. Diffculties of detecting a planet (faint source) are caused, mostly, by two factors: sidelobes caused by starlight diffraction from the edge of the pupil and the randomly scattered starlight caused by the phase errors from the imperfections in the optical system. While the latter diffculty can be corrected by high density active deformable mirrors with advanced phase sensing and control technology, the optimized strategy for suppressing the diffraction sidelobes is still an open question. In this thesis, I present a new approach to the sidelobe reduction problem: pupil phase apodization. It is based on a discovery that an anti-symmetric spatial phase modulation pattern imposed over a pupil or a relay plane causes diffracted starlight suppression sufficient for imaging of extra-solar planets. Numerical simulations with specific square pupil (side D) phase functions, such as ... demonstrate annulling in at least one quadrant of the diffraction plane to the contrast level of better than 10^12 with an inner working angle down to 3.5L/D (with a = 3 and e = 10^3). Furthermore, our computer experiments show that phase apodization remains effective throughout a broad spectrum (60% of the central wavelength) covering the entire visible light range. In addition to the specific phase functions that can yield deep sidelobe reduction on one quadrant, we also found that a modified Gerchberg-Saxton algorithm can help to find small sized (101 x 101 element) discrete phase functions if regional sidelobe reduction is desired. Our simulation shows that a 101x101 segmented but gapless active mirror can also generate a dark region with Inner Working Distance about 2.8L/D in one quadrant. Phase-only modulation has the additional appeal of potential implementation via active segmented or deformable mirrors, thereby combining compensation of random phase aberrations and diffraction halo removal in a single optical element.

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A major challenge for a developing country such as Bangladesh is to supply basic services to its most marginalized populations, which includes both rural and urban dwellers. The government struggles to provide basic necessities such as water and electricity. In marginalized urban communities in Bangladesh, in particular informal settlements, meeting basic needs is even direr. Most informal settlements are built to respond to a rapid immigration to urban centers, and are thought of as ‘temporary structures’, though many structures have been there for decades. In addition, as the settlements are often squatting on private land, access to formalized services such as electricity or water is largely absent. In some cases, electricity and water connections are brought in - but through informal and non-government sanctioned ways -- these hookups are deemed ‘illegal’ by the state. My research will focus on recent efforts to help ameliorate issues associated with lack of basic services in informal settlements in Bangladesh – in this case lack of light. When the government fails to meet the needs of the general population, different non-government organizations tend to step in to intervene. A new emphasis on solar bottle systems in informal urban settlement areas to help address some energy needs (specifically day-time lighting). One such example is the solar bottle light in Bangladesh, a project introduced by the organization ‘Change’. There has been mixed reactions on this technology among the users. This is where my research intervenes. I have used quantitative method to investigate user satisfactions for the solar bottle lights among the residents of the informal settlements to address the overarching question, is there a disconnect between the perceived benefits of the ENGO and the user satisfaction of the residents of the informal settlements of Dhaka City? This paper uses survey responses to investigate level of user satisfaction and the contributing factors.