https://repositorio.ufpb.br/jspui/handle/tede/4458 PPGEM Mon, 20 Jul 2026 13:33:21 GMT 2026-07-20T13:33:21Z https://repositorio.ufpb.br/jspui/handle/123456789/38394 Título: Variabilidade climática e estimativa da geração fotovoltaica: análises observacionais e modelagem em diferentes escalas no Brasil Autor(es): Silva, Louise Pereira da Orientador: Abrahão, Raphael Abstract: Climate change may impact the performance of renewable energy systems, as the efficiency of photovoltaic power generation is highly sensitive to variations in meteorological variables. In this context, understanding local climatic conditions becomes essential for the proper sizing, planning, and operation of these systems. Thus, this thesis aims to analyze the influence of climatic variables on photovoltaic power generation in locations across Brazil, through the analysis of historical meteorological data and the evaluation of different generation estimation methods. As a contribution, it incorporates an approach based on cluster analysis to investigate climatic patterns, enabling a more detailed assessment of temporal variability. The thesis is structured into chapters in the format of scientific articles. In Chapter 2, trend analysis was performed using the Mann–Kendall test, associated with Sen’s slope estimator, in conjunction with a method based on cluster analysis. The results indicated a significant increase in mean air temperature at 36 meteorological stations in the Brazilian semi-arid region. The cluster analysis made it possible to identify that more recent years are associated with higher temperature values, as well as to highlight the periods of the year in which these increases were more pronounced. This approach also enabled the detection of variations not identified by traditional trend analysis. In Chapter 3, a comparison was carried out between observed and estimated photovoltaic generation using five empirical models. The results indicated that all models exhibited a tendency to overestimate generation, with relative errors ranging from approximately 19% to 21%, although they showed similar performance in representing data variability. Among the evaluated models, Model 3 presented the best performance, with lower bias and dispersion. In Chapter 4, multiple linear regression, Random Forest, and an empirical model were applied to estimate monofacial photovoltaic generation, using temporal validation with TimeSeriesSplit. The Random Forest model showed superior performance, with an average coefficient of determination of approximately 0.66 and a mean squared error of 7.64 (kWh/day)², while multiple linear regression presented an R² of around 0.61. Hyperparameter optimization led to further improvements, achieving an R² of 0.67 and an MSE of 6.42 (kWh/day)². In Chapter 5, bifacial photovoltaic generation was estimated using empirical equations and the Random Forest method. The results indicated a gain of approximately 12.6% in effective irradiance, resulting in an increase of about 83.42 MWh in energy generation. The Random Forest model showed better performance (RMSE ≈ 175 kWh and R² = 0.76), while the empirical model exhibited a tendency to underestimate generation. Overall, the results highlight the importance of a detailed analysis of local climatic conditions and demonstrate that the combination of statistical methods, machine learning techniques, and cluster analysis enables a more robust evaluation of photovoltaic power generation. Editor: Universidade Federal da Paraíba Tipo: Tese Mon, 30 Mar 2026 00:00:00 GMT https://repositorio.ufpb.br/jspui/handle/123456789/38394 2026-03-30T00:00:00Z https://repositorio.ufpb.br/jspui/handle/123456789/38342 Título: Avaliação integrada do envelhecimento térmico e natural de superfícies solares seletivas multicamadas a base de cromo e sílica via análises óptica, morfológica e eletroquímica Autor(es): Gonçalves, Francielle Cristine Pereira Orientador: Silva, Kelly Cristiane Gomes da Abstract: This research aimed to develop and conduct an integrated evaluation of the optical, microstructural, and electrochemical performance of Cr/Cr₂O₃-based solar selective surfaces produced by magnetron sputtering, targeting applications in solar collectors operating under severe thermal conditions. Three coating configurations were investigated: S3 (Cr/Cr₂O₃ + Cr₂O₃), S4 (Cr/Cr₂O₃ + SiO₂), and S8 (Cr/Cr₂O₃). The coatings were characterized immediately after deposition (2021) and after two years of natural aging (2023), as well as after accelerated thermal treatments at 200 °C and 350 °C. Solar absorptance, determined by UV–Vis–NIR spectroscopy, remained high for all systems, ranging from 94.93% to 97.61% in 2021 and from 91.86% to 96.45% in 2023, demonstrating excellent optical stability. FTIR analysis indicated low emissivity in the mid-infrared region, associated with high spectral reflectance in this range, thereby confirming the selective behavior of the coatings. Band gap estimation revealed values between 0.85 and 4.38 eV in 2021 and between 1.53 and 4.56 eV in 2023, indicating chemical evolution of the films and the predominance of Cr₂O₃- related phases after aging. Morphological analyses by SEM and profilometry revealed homogeneous films with thicknesses ranging from 64.3 to 270 nm and average surface roughness (Ra) below 35 nm, demonstrating that morphology exerted a limited influence on solar absorptance. Electrochemical tests by EIS showed that the film response is strongly governed by microstructure and interfacial properties, with the S4 system standing out due to its higher charge transfer resistance and superior interfacial stability at elevated temperatures. Overall, the results demonstrate that multilayer engineering—particularly through the incorporation of SiO₂ is a key factor in achieving durable and high-performance solar selective surfaces. Editor: Universidade Federal da Paraíba Tipo: Tese Mon, 23 Mar 2026 00:00:00 GMT https://repositorio.ufpb.br/jspui/handle/123456789/38342 2026-03-23T00:00:00Z https://repositorio.ufpb.br/jspui/handle/123456789/38216 Título: Avaliação microestrutural e cristalográfica da ocorrência de Fe em polímeros inorgânicos do sistema Al-Si-O-Na-H Autor(es): Souza, Wesley Maciel de Orientador: Torres, Sandro Marden Abstract: The scientific community has been searching for other binding materials, which are resistant, with high technological efficiency and with little environmental impact. There is a material that can perfectly be an alternative to Portland cement for some applications and that has material characteristics equal or superior to CP. This type of binder comprises alkali activation in materials rich in alumina and silica. This binder is called geopolymer, which in turn has efficient thermomechanical properties, high initial strength, and ecological advantages, since it can be produced at low temperatures without apparent release of CO2 into the atmosphere. The objective of this work is to evaluate the crystallographic and microstructural characteristics of the occurrence of iron cations in crystalline phases in alkaline activated materials. Residual clay samples with different Fe/Al contents were alkaline activated with sodium hydroxyl at 55ºC. The chemical composition of the phases of the activated samples was evaluated by point dispersive energy through phase separation by backscattered electron contrast and electron microscopy. The crystalline phases were studied from the data provided in the IUCr databases. The results show a clear interaction between Fe and the Al and Si cations of the polymer chain. This relationship occurs consistently in the activated systems and in the crystalline phases. The occurrence of Fe occurs with a predominance of tetrahedral sites, but also in octahedrons with oxidation state III. The data show lower chances of formation of Fe-containing phases in oxidation state II and in octahedral and bi pyramidal sites. For the first time, a systematic study categorizes the occurrence and limits of Fe in structures of the Na-Fe-Al-Si-O-H system, indicating that there is a potential for phases with engineering applications, mainly for environmental remediation given the predominance of zeolite-like phases. Editor: Universidade Federal da Paraíba Tipo: Dissertação Wed, 15 Sep 2021 00:00:00 GMT https://repositorio.ufpb.br/jspui/handle/123456789/38216 2021-09-15T00:00:00Z https://repositorio.ufpb.br/jspui/handle/123456789/38096 Título: Desempenho termodinâmico, ambiental e social de colheita de energia a partir de atividades físicas Autor(es): Schultz, Herwin Saito Orientador: Carvalho, Monica Abstract: An Energy Harvesting System (EHS) based on physical exercise can address issues of energy sustainability and public health. Greener&Healthier Power (GHP) is an EHS that features a conceptual innovation: a training app with automatic intensity selection, simulating situations closer to the reality of outdoor exercise, and also controlling environmental parameters. The idea behind GHP is to encourage physical activity, reducing the risk of developing Non-Communicable Chronic Diseases (NCDs) and potentially contributing to lower public health costs. Based on an Energy Harvesting Farm (EHF) composed of 32 stationary bicycles responsible for collecting energy and supplying it to the grid, this study aims to develop a technical analysis and evaluate the thermodynamic, environmental, and social performance of EHF. Life Cycle Assessment (LCA) is used to quantify the Greenhouse Gases (GHG) emissions associated with the EHF composition. The results reveal that a cyclist in one hour can generate an average of 75.5 Wh, that an EHF has a capacity of 8,167.9 kWh/year, and that its emission factor is 0.090 kg CO2-eq/kWh, significantly lower than that of the Brazilian national electricity grid (0.152 kg CO2- eq/kWh). For an investment of R$ 208 million, the estimated reduction in public health costs ranged from R$ 532 million to R$ 2.91 billion. Therefore, it can be concluded that the GHP is an interactive and connected system capable of harvesting energy from indoor cycling, reducing the carbon footprint, improving the population's quality of life, and with the potential to reduce public health costs. Editor: Universidade Federal da Paraíba Tipo: Tese Fri, 27 Feb 2026 00:00:00 GMT https://repositorio.ufpb.br/jspui/handle/123456789/38096 2026-02-27T00:00:00Z