The solar industry has grown considerably in the last few years. This larger scale has introduced more problems as well as possibilities. One of those possibilities is analyzing the data coming from the sites that are now being monitored, and using the information to answer a variety of questions. We have four questions which are of prime importance identified in this thesis: 1. Can data from customers be trusted? 2. Can we use data from existing sites to determine which sites need the most improvement? 3. Can we implement a location-based algorithm to reduce the amount of false positives for performance, or other alarms? 4. Can we improve upon the current predicted power algorithm? We find that not only can we answer these questions definitively, but the improvements found are of significant value. Each of these items represents an important question that either directly or indirectly translates into increased revenue and engineering improvements for the solar industry as a whole.

Photovoltaic solar cells can generate electricity directly from sunlight without emitting harmful greenhouse gases. This makes them ideal candidates as large scale future energy producers for the global energy economy. Ideally, solar cells should be efficient and inexpensive to compete in the global energy market. Unfortunately, a number of fundamental limitations exist for the efficiency due to fundamental loss mechanisms of the semiconductor materials used to make solar cells. One of the dominant loss mechanisms from a conventional silicon solar cell is the transparency of sub-bandgap near-infrared photons. Up-conversion is an optical process involving the sequential absorption of lower energy photons followed by luminescence of a higher energy photon. This mechanism could be exploited to minimise photovoltaic sub-bandgap losses. Rare-earth doped materials have ideal up-conversion luminescent properties and have been utilised for many near-infrared to visible applications. This thesis investigates the near-infrared to near-infrared up-conversion processes required for the sub-bandgap photon utilisation within a silicon photovoltaic device. Various sodium yttrium fluoride phosphors doped with rare-earths were characterised theoretically and experimentally. Erbium doped phosphors were found to be ideal for single wavelength power dependent investigations for the non-linear up-conversion processes. The radiative and non-radiative rates of various erbium doped sodium yttrium fluoride phosphors have been approximated and compared with experimental photoluminescence results. These phosphors have been applied to the rear of a bi-facial silicon solar cell and an enhancement in the near-infrared region has been demonstrated. An external quantum efficiency close to 3.4% was measured at 1523nm under 6mW laser excitation. The non-linear dependence on incident pump power has been investigated along with the dominant up-conversion mechanisms involved. It can be concluded that up-conversion phosphors can enhance the near-infrared spectral response of a silicon device. These phosphors have high luminescent efficiencies once up-conversion occurs, but suffer from poor infrared absorption and low up-conversion efficiencies. The results from this study show that relatively high doping levels of selected rare-earths into low phonon energy crystals can improve the absorption and luminescent properties of the phosphor.

The overall goal of this research is to improve fundamental understanding of the hydrogen passivation of defects in low-cost silicon and the fabrication of high-efficiency solar cells on thin crystalline silicon through low-cost technology development. A novel method was developed to estimate the flux of hydrogen, released from amorphous silicon nitride film, into the silicon. Rapid-firing-induced higher flux of hydrogen was found to be important for higher defect passivation. This was followed by the fabrication of solar cell efficiencies of ~ 17% on low-cost, planar cast multicrystalline silicon. Solar cell efficiencies and lifetime enhancement in the top, middle, and bottom regions of cast multicrystalline silicon ingots were explained on the basis of impurities and defects generally found in those regions. In an attempt to further reduce the cost, high-efficiency solar cells were fabricated on thin crystalline silicon wafers with full area aluminum-back surface field. In spite of loss in efficiency, wafer thinning reduced the module cost. Device modeling was performed to establish a roadmap towards high-efficiency thin cells and back surface recombination velocity and back surface reflectance were identified as critical parameters for high-efficiency thin cells. Screen-printed solar cells on float zone material, with efficiencies > 19% on 300 μm and > 18% on 140 μm were fabricated using a novel low-cost fabrication sequence that involved dielectric rear passivation along with local contacts and back surface field.

For organic electronic device applications materials are needed which display good charge carrier mobility, good processability, and stability towards oxygen and moisture. Alkynylated N-Heteroacenes fulfill many of these requirements. Substitution with alkyne groups as well as the introduction of the pyrazine subunit both inhibits oxidative degradation at sensitive position in the molecules. Additionally the trialkylsilylethynyl group aides in directing the packing motif as well as vastly increases the solubility over unsubstituted analogues. A requisite precursor in the synthesis of alkynylated N-heteroacenes is alkynylated acenothiadiazoles. These thiadiazoles display interesting photophysical properties and can be functionalized to produce a wide range of properties in closely related materials. The acenothiadiazoles themselves have potential applications as an N-type semiconductor. Optical gaps and calculated HOMO-LUMO gaps show that these molecules, when compared to known N-type materials, should be easily injected with electrons. Additionally the crystal packing of these compounds shows favorable π-orbital overlap which should provide excellent charge carrier mobilities.

Organic solar cells have the potential to be portable power sources that are light-weight, flexible, and inexpensive. However, the highest power conversion efficiency for organic solar cells to date is ~8%, and most high-efficiency solar cells have an area of less than 1 cm². This thesis advances the field of organic solar cells by studying the physics and engineering of the devices to understand the reverse saturation current, which is related to efficiency, and the effects of area scaling. The most commonly accepted models to describe the physics of organic photovoltaic devices are reviewed and applied to planar heterojunction solar cells based on pentacene / C60 as a model system. The equivalent circuit model developed for inorganic solar cells is shown to work well to describe the behavior of organic devices and parameterize their current-voltage characteristics with five parameters. Changes in the parameters with different material combinations or device structures are analyzed to better understand the operation of the presented organic solar cells. A one-dimensional diffusion model for the behavior of excitons and treatment of the organic layers as planes is demonstrated to adequately model the external quantum efficiency and photocurrent in pentacene / C60 solar cells. The origin of the open-circuit voltage is studied using cells with different electrodes and different donor materials. While changing the electrodes does not affect open-circuit voltage, it is greatly modified by changes in the donor. Tests with additional semiconductors show the change in open-circuit voltage is not consistent from donor to donor as the acceptor is varied, suggesting a more complex relation than just the difference in energy levels. Study of the temperature dependence of the equivalent circuit parameters shows that the reverse saturation current, which has a significant role in determining the open-circuit voltage, has a thermally activated behavior. From this behavior, the reverse saturation current is related back to charge transfer at the donor / acceptor heterojunction to suggest that both the effective energy barrier presented by the energy levels and the electronic coupling are important in determining the reverse saturation current and open-circuit voltage. This marks a shift from just considering a built-in voltage or the energy levels to also considering the electronic coupling of the donor and acceptor materials. Temperature-dependent performance characteristics are also used to show key differences between organic and inorganic devices. Finally, the effect of area scaling is explored with pentacene / C60 solar cells having areas of 0.11, 7, and 36.4 cm². Analysis with the equivalent circuit model shows that performance decreases as area increases because of an increasing series resistance presented by the transparent electrode. A metal grid, to provide low resistance pathways for current, fabricated on top of the transparent electrode is proposed to reduce the effective resistance. The grid is unique in that it is placed between the electrode and the semiconductor layer and must be passivated to prevent shorts through the thin semiconductor to the back metal electrode. Analysis of the grid predicts greatly reduced series resistance, and experimental results show reduced resistance and improved performance for the 7 cm² and 36.4 cm² devices when including the grid.

The objective of the proposed research is to develop low-cost, screen-printed 20% efficient silicon solar cells. In the first part of this thesis, a ~19% efficient, screen-printed cell was fabricated using the commercially-dominant aluminum back surface field (Al-BSF) cell structure. Device modeling was then used to determine that increasing the efficiency to 20% required improvements in both back surface passivation and rear reflectance. In the second part of this thesis, a passivated, transparent boron BSF (B-BSF) structure was proposed as a high-throughput method for realizing these improvements. The first step in fabricating the proposed B-BSF cell involved the successful development of a water-based, spin-on solution of boric acid as a low-cost, non-toxic and non-pyrophoric alternative to common boron diffusion sources such as boron tribromide. A review of the literature shows that a common problem with boron diffusion is severe bulk lifetime degradation, with Fe contamination being commonly speculated as the cause. An experimental study was therefore devised in which the impact of boron diffusion and subsequent cell process steps on the bulk lifetime and bulk iron contamination was tracked. From this study, a model for boron diffusion-induced Fe contamination was developed along with methods for gettering Fe from the substrate. A key achievement of this thesis was the discovery of a novel, negatively charged, aluminum-doped spin-on glass (SOG) which can, in a short thermal step, simultaneously getter Fe and provide stable, high-quality passivation of planar, boron-diffused Si surfaces. Since past attempts at achieving low-cost, high-efficiency, boron-diffused cells have suffered from bulk lifetime degradation and difficulties with passivating a boron-diffused Si surface, the Al-doped SOG provides a solution to both challenges. Since a high rear reflectance is important for achieving high-efficiencies, an experimental study of various reflectors was undertaken and a silver colloid material was found which exhibits both high electrical conductivity and Lambertian reflectance >95%. The work on boric acid diffusion, iron gettering, surface passivation and rear reflectors was successfully integrated into a 20.2% efficient, screen-printed, B-BSF cell fabricated on 300 µm thick, p-type float-zone (FZ) Si wafers. Both device theory and modeling was used to show that, due to its well-passivated surfaces, this cell would suffer a large loss in efficiency due to light-induced degradation (LID) if it were fabricated on commercial p-type Czochralski (Cz) Si substrates. Since n-type Si substrates do not suffer from LID, the p-type process was slightly tweaked and applied to n-type FZ wafers, resulting in 20.3% efficient cells on 190 µm thick wafers. Computer modeling shows that both the p-type and n-type cells can maintain efficiencies of 20% for wafers as thin as 100 µm.

D. Tech. Electrical Engineering. / Discusses the objectives of thesis in terms of : 1. To formulate and integrate models for the wind-turbine, induction generator, PV array, battery, supercapacitor, and power electronic converters in a form suitable for studying the dynamic behaviour of the microgrid; 2. To develop an online optimisation algorithm and use it to optimise local control algorithms for PV array, energy storage system, and the doubly fed induction generator. 3. To formulate an efficient power sharing strategy between battery and supercapacitor. 4. To implement an overall control system which sets the power reference for the energy storage system and ensures that the requested power demand is supplied to the grid.

The objective of the proposed research is to establish the technology for material growth by molecular beam epitaxy (MBE) and fabrication of indium gallium nitride/gallium nitride (InxGa1-xN/GaN) heterojunction solar cells. InxGa1-xN solar cell have the potential to span 90% of the solar spectrum, however there has been no success with high indium (In) incorporation and only limited success with low In incorporation InxGa1-xN. Therefore, this present work focuses on 15 - 30% In incorporation leading to a bandgap value of 2.3 - 2.8 eV. This work will exploit the revision of the indium nitride (InN) bandgap value of 0.68 eV, which expands the range of the optical emission of nitride-based devices from ultraviolet to near infrared regions, by developing transparent InxGa1-xN solar cells outside the visible spectrum. Photovoltaic devices with a bandgap greater than 2.0 eV are attractive because over half the available power in the solar spectrum is above the photon energy of 2.0 eV. The ability of InxGa1-xN materials to optimally span the solar spectrum offers a tantalizing solution for high-efficiency photovoltaics. Using the metal modulated epitaxy (MME) technique in a new, ultra-clean refurbished MBE system, an innovative growth regime is established where In and Ga phase separation is diminished by increasing the growth rate for InxGa1-xN. The MME technique modulates the metal shutters with a fixed duty cycle while maintaining a constant nitrogen flux and proves effective for improving crystal quality and p-type doping. We demonstrate the ability to repeatedly grow high hole concentration Mg-doped GaN films using the MME technique. The highest hole concentration obtained is equal to 4.26 e19 cm-3, resistivity of 0.5 Ω-cm, and mobility of 0.28 cm2/V-s. We have achieved hole concentrations significantly higher than recorded in the literature, proving that our growth parameters and the MME technique is feasible, repeatable, and beneficial. The high hole concentration p-GaN is used as the emitter in our InxGa1-xN solar cell devices.

Submitted by Wallace Gabriel de Souza (wgs.gabriel@hotmail.com) on 2018-07-16T16:35:11Z No. of bitstreams: 1 dissertacao_wgs.pdf: 3537876 bytes, checksum: 56fef2d280007dba43983b71988d997b (MD5) / Approved for entry into archive by Maria Marlene Zaniboni null (zaniboni@bauru.unesp.br) on 2018-07-17T13:07:06Z (GMT) No. of bitstreams: 1 souza_wg_me_bauru.pdf: 3537876 bytes, checksum: 56fef2d280007dba43983b71988d997b (MD5) / Made available in DSpace on 2018-07-17T13:07:06Z (GMT). No. of bitstreams: 1 souza_wg_me_bauru.pdf: 3537876 bytes, checksum: 56fef2d280007dba43983b71988d997b (MD5) Previous issue date: 2018-05-18 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Esta dissertação apresenta o desenvolvimento e as simulações computacionais de um inversor fotovoltaico de 2,0 kVA para o controle da potência reativa na rede de distribuição, de modo que haja compensação ativa do fator de potência e aumento da qualidade da energia no local da instalação da planta. Para atingir este objetivo, por meio do ambiente de desenvolvimento do MATLAB/Simulink®, o controle da potência ativa foi realizado pelo ajuste do ângulo entre a tensão da rede e a tensão gerada pelo inversor, por meio do equilíbrio do potencial do barramento CC (proveniente do gerador fotovoltaico). A potência reativa, por sua vez, foi ajustada pela amplitude da tensão do ponto de acoplamento de uma carga local. Além disto, utilizaram-se controladores proporcionais-ressonantes nas malhas de tensão e corrente do conversor trifásico, com finalidade de mitigar as correntes harmônicas de cargas não-lineares que podem depreciar o fator de potência. Foi implementado, também, um conversor CC-CC isolado full-bridge do tipo boost com potência nominal de 1,8 kW, responsável por rastrear o ponto de máxima potência dos módulos fotovoltaicos. Os resultados obtidos permitiram a avaliação do desempenho dos controladores e a observação da conservação, pelo inversor, do fator de potência da rede próximo da unidade para situações com variações acentuadas da carga e da irradiação solar, bem como para os casos com a presença de cargas não-lineares no sistema. Com isso, o perfil de tensão entregue à carga é aproximadamente senoidal, com baixa distorção harmônica. / This dissertation presents the development and computational simulations of a 2.0 kVA photovoltaic inverter for the control of the reactive power in the distribution network, so that there is active power factor compensation and an increase in the quality of the energy at the installation site plant. In order to reach this objective, the MATLAB/Simulink® development environment was used to control the active power by adjusting the angle between the grid voltage and the voltage generated by the inverter, by means of the potential balance of the DC (from the photovoltaic generator). The reactive power, in turn, was adjusted by the amplitude of the voltage of the coupling point of a local load. In addition, resonant-proportional controllers were used in the voltage and current loops of the three-phase converter, in order to mitigate the harmonic currents of non-linear loads that may depreciate the power factor. A full-bridge, full-bridge boost converter with nominal power of 1.8 kW was also implemented, responsible for tracking the maximum power point of the photovoltaic modules. The results obtained allowed the evaluation of the performance of the controllers and the observation of the conservation by the inverter of the power factor of the network close to the unit for situations with marked variations of the load and the solar irradiation, as well as for the cases with the presence of loads in the system. Thus, the voltage profile delivered to the load is approximately sinusoidal, with low harmonic distortion. / 2016/03734-3

Orientador: Gilberto de Martino Jannuzzi / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-21T07:52:31Z (GMT). No. of bitstreams: 1 Lima_BrunoWilmerFontes_M.pdf: 4773788 bytes, checksum: 512d3e82e0e392f642f77b5b058267c2 (MD5) Previous issue date: 2012 / Resumo: O consumo de eletricidade no Brasil cresceu 47% na última década e estima-se que aumente outros 55,6% até 2020. A geração da maior parte da eletricidade no país é baseada no modelo de grandes usinas hidrelétricas, distantes dos centros de consumo, assim como a expansão da capacidade de geração para atender o aumento da demanda, mantendo as grandes perdas na transmissão e distribuição da eletricidade. Uma forma de reduzi-las é através do maior uso da geração distribuída, em que a eletricidade é gerada próxima ou no próprio local de consumo, como por exemplo, integrada a edificações. A partir da viabilização deste modelo de geração e dos edifícios eficientes, criou-se o conceito dos chamados Edifícios de Energia Zero (EEZ). EEZs são edifícios com baixas necessidades energéticas e que, ao longo do ano, geram toda a energia que consomem a partir de fontes renováveis de energia. Em 2010, as edificações foram responsáveis por 46,9% do consumo de eletricidade no Brasil e esta participação deve aumentar até o final da década. Dessa forma, um maior emprego da geração distribuída através de fontes renováveis em edificações e também de novos EEZs pode atender parte desta crescente demanda, e consequentemente, adiar ou evitar a construção de novas grandes hidrelétricas e termelétricas movidas a combustíveis fósseis, e reduzindo os impactos socioambientais causados pela sua construção e operação. Esta dissertação propõe uma metodologia para o projeto de sistemas de geração de energia elétrica em EEZs, visando auxiliar engenheiros e arquitetos no dimensionamento destes sistemas, permitindo uma maior adoção deste tipo de edificação. A metodologia consiste de alguns passos simples, que incluem a análise do consumo de energia do edifício e do potencial energético local, o dimensionamento e simulação do sistema de geração, concluindo com a avaliação dos resultados para averiguar se a energia gerada seria suficiente para classificar o edifício como EEZ. Adicionalmente, a metodologia propõe ferramentas para auxiliar na escolha de um sistema de geração, dentre diversas opções de arranjos e tecnologias, como o custo do sistema, da eletricidade produzida por ele e do tempo de retorno de energia. Esta metodologia foi aplicada em um laboratório de ensino, que será construído na Unicamp e tem como meta ter o menor impacto ambiental durante sua construção e operação além de ser um Edifício de Energia Zero. Foi avaliada a viabilidade e contribuição potencial da geração de eletricidade por fontes renováveis de energia no projeto deste laboratório, no caso energia solar fotovoltaica e pequenas turbinas eólicas, como forma de atender a meta EEZ. Também foram avaliados três sistemas fotovoltaicos, cotados com empresas especializadas durante o projeto do laboratório. Adicionalmente, buscando entender melhor a influência da tecnologia e do posicionamento dos sistemas fotovoltaicos na geração de eletricidade, foram realizadas simulações de sistemas com 1kWp, utilizando diferentes tecnologias e orientações. As simulações foram realizadas utilizando o software Homer Energy, de distribuição gratuita / Abstract: Electricity consumption in Brazil increased 47% in the last decade, and it is estimated that it will increase 55.6% until 2020. Most of the electricity generated in the country is based on large hydroelectric dams, located away from the major cities. The planned expansion of the generation park to meet this increase in the demand is also based on this model, leading to great transmission and distribution losses. One way to reduce these losses is through a greater use of distributed generation, where the electricity is generated near or at the point of consumption, e.g., integrated to buildings. With the viabilization of this model of electricity generation and of energy efficient buildings, the concept of Net Zero Energy Buildings (ZEB) was created. A ZEB is a building with low energy needs which, through the course of a year, generated all the energy which it consumes from renewable energy sources. In 2010, the building sector was responsible for 46.9% of all electricity consumption in Brazil, and this share will increase until the end of the decade. That way, a larger use of the distributed generation from renewable sources integrated to buildings and of new ZEB can meet part of this growing demand, and thus postpone or avoid the construction of new large hydroelectric dams and thermoelectric power plants running on fossil fuels, reducing the social and environmental impacts caused by its construction and operation. This dissertation proposes a methodology for the project of electricity generation systems in ZEBs, aiming to help engineers and architects in the dimensioning of these systems, allowing a greater adoption of this kind of building. The methodology consists of a few simple steps, which includes an analysis of the building energy consumption and of the local energy potential, sizing and simulation of the generation system and comparing the results in order to conclude if it is possible for the building to become a ZEB. Additionally, the methodology proposes tools to help choosing the better option among different systems sizes and technologies, including the cost of the system, of the electricity produced by it and the energy payback time. The methodology will be applied to a university's laboratory, which will be built at Unicamp, which aims to have the lowest environmental impact possible during its construction and operation and to be a Net Zero Energy Building. It was addressed the viability and potential contribution of electricity generation from renewable energy sources, solar photovoltaic and small wind turbines, in the laboratory's project as an strategy to reach the ZEB target. Three photovoltaic systems quoted from specialized companies during the project were also analyzed. Also, in order to address the influence of the technology and positioning of the photovoltaic systems on its performance, several simulations of systems with 1kWp were carried out, in different tilts and orientations, and using different technologies of photovoltaic modules. These simulations were performed using the Homer Energy software, which is free of charge / Mestrado / Planejamento de Sistemas Energeticos / Mestre em Planejamento de Sistemas Energéticos