Spatio-temporal solar forecasting

Current and future photovoltaic (PV) deployment levels require accurate forecasting to ensure grid stability. Spatio-temporal solar forecasting is a recent solar forecasting approach that explores spatially distributed solar data sets, either irradiance or photovoltaic power output, modeling cloud advection patterns to improve forecasting accuracy. This thesis contributes to further understanding of the potential and limitations of this approach, for different spatial and temporal scales, using different data sources; and its sensitivity to prevailing local weather patterns. Three irradiance data sets with different spatial coverages (from meters to hundreds of kilometers) and time resolutions (from seconds to days) were investigated using linear autoregressive models with external inputs (ARX). Adding neighboring data led to accuracy gains up to 20-40 % for all datasets. Spatial patterns matching the local prevailing winds could be identified in the model coefficients and the achieved forecast skill whenever the forecast horizon was of the order of scale of the distance between sensors divided by cloud speed. For one of the sets, it was shown that the ARX model underperformed for non-prevailing winds. Thus, a regime-based approach driven by wind information is proposed, where specialized models are trained for different ranges of wind speed and wind direction. Although forecast skill improves by up to 55.2 % for individual regimes, the overall improvement is only of 4.3 %, as those winds have a low representation in the data. By converting the highest resolution irradiance data set to PV power, it was also shown that forecast accuracy is sensitive to module tilt and orientation. Results are shown to be correlated with the difference in tilt and orientation between systems, indicating that clear-sky normalization is not totally effective in removing the geometry dependence of solar irradiance. Thus, non-linear approaches, such as machine learning algorithms, should be tested for modelling the non-linearity introduced by the mounting diversity from neighboring systems in spatio-temporal forecasting

Modeling Energy Communities with Collective Photovoltaic Self-Consumption: Synergies between a Small City and a Winery in Portugal

The recently approved regulation on Energy Communities in Europe is paving the way for new collective forms of energy consumption and production, mainly based on photovoltaics. However, energy modeling approaches that can adequately evaluate the impact of these new regulations on energy community configurations are still lacking, particularly with regards to the grid tariffs imposed on collective systems. Thus, the present work models three different energy community configurations sustained on collective photovoltaics self-consumption for a small city in southern Portugal. This energy community, which integrates the city consumers and a local winery, was modeled using the Python-based Calliope framework. Using real electricity demand data from power transformers and an actual winery, the techno-economic feasibility of each configuration was assessed. Results show that all collective arrangements can promote a higher penetration of photovoltaic capacity (up to 23%) and a modest reduction in the overall cost of electricity (up to 8%). However, there are clear trade-offs between the different pathways: more centralized configurations have 53% lower installation costs but are more sensitive to grid use costs (which can represent up to 74% of the total system costs). Moreover, key actor’s individual self-consumption rate may decrease by 10% in order to benefit the energy community as a whole.info:eu-repo/semantics/publishedVersio

Empirical optimization and implementation of boron emitter on n-type silicon solar cells using BBR3 liquid source

Tese de mestrado integrado em Engenharia da Energia e do Ambiente , apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2014O presente trabalho aborda o estudo e optimização de um processo de difusão com fonte líquida de BBr3 para a formação de uma camada p+ em substrato de silício de tipo-n, sendo este passo uma das maiores limitações actuais para a implementação de células solares de alta eficiência de custo acessível baseadas neste material e com emissor de boro. Uma revisão do estado da arte e apresentada, com os seguintes tópicos: propriedades do silício de tipo-n e seu contexto histórico; metalização e passivação de camadas p+; propriedades de um emissor de boro e difusão de boro baseada numa fonte líquida de BBr3. De seguida, um estudo experimental de diversos parâmetros do processo de difusão e o seu impacto no emissor obtido, sendo os parâmetros: temperatura do borbulhador de BBr3 (e desejável estabilidade); fluxo de N2; fluxo de N2-BBr3; espaçamento entre bolachas na estrutura de suporte e a duração da etapa de pré-depósito. Para cada experiência procurou-se verificar a presença de uma capa rica em boro (BRL) e avaliar a homogeneidade da difusão através de uma avaliação visual do óxido formado e medidas de resistividade de capa. Posteriormente, um processo de difusão em que apenas era dopada uma bolacha foi testado para dopar diversas bolachas num só processo, tendo depois exigido uma optimização dos parâmetros de difusão. A remoção da BRL foi testada através de uma oxidação química e de uma oxidação térmica. Concluindo, verificou-se que um bom controlo da temperatura do borbulhador e um requisito e que esta deveria estar a pelo menos 20ºC de forma a se obter uma dopagem eficaz. Todos os outros parâmetros mostraram ter impacto no emissor obtido e no óxido formado apesar de não se ter obtido nenhuma dopagem nem oxido que fossem homogéneos. Obter um óxido homogéneo e um requisito crucial já que pode indicar tanto uma dopagem como a formação de uma BRL também homogéneas, permitindo uma remoção eficaz da camada que induz recombinação tendo sido verificado que para os óxidos heterogéneos obtidos, tanto a oxidação química como térmica apenas resultaram numa remoção parcial da BRL. Verificou-se ainda que um processo de difusão estudado para uma única bolacha não e imediatamente conversível para dopar várias bolachas num só processo já que uma dopagem ineficaz foi obtida e portanto requerendo uma optimização de parâmetros adicional. Finalmente, são ainda sugeridas linhas de trabalho futuro de forma a dar sequencia ao presente trabalho.The present work focus on the study and optimization of a BBr3 diffusion process for a p+ layer formation on n-type Si wafers, as it is currently one of the main limitations for the implementation of cheap high-efficiency solar cells based on this material with a boron emitter. A state of the art review is presented, covering the following topics: n-type silicon properties and its historical context; p+ layer metallization and passivation; boron emitter properties and boron diffusion based on a BBr3 liquid source. Next, an experimental study of several diffusion process parameters and their impact on the resulting emitter is presented, being the parameters: BBr3 bubbler temperature (and desirable stability); N2 flow; N2-BBr3 flow; wafer spacing in the boat structure and predeposition step duration. For each experiment it was verified the presence of a BRL while evaluating the diffusion homogeneity through a visual evaluation of the formed oxide and sheet resistance measurements. Afterwards, a selected single-wafer process was tested for batch process conversion, which then required a parameters optimization. The removal of the BRL through both chemical and thermal oxidation was also tested. In conclusion, it was verified that a good control of the bubbler temperature is required and that it should be at least at 20 ºC in order to obtain an effective doping. All other parameters showed to have an impact in the formed emitter and resulting oxide, although no homogeneous doping nor oxide thickness were achieved. The formation of a homogeneous oxide is a crucial requirement as it can indicate a good homogeneity in both the doping and BRL formation, impeding an effective removal of this recombination-inducing layer. This was verified as both oxidation techniques tested resulted in only a partial removal of the BRL. It was also verified that a single-wafer process is not immediately convertible into a batch process as an ineffective doping was obtained, therefore requiring further parameter optimization. Finally, future work lines are suggested in order to go on with the present work

Illustrating changes in landscapes of passing opportunities along a set of competitive football matches

This study aims to illustrate the landscape of passing opportunities of a football team across a set of competitive matches. To do so positional data of 5 competitive matches was used to create polygons of pass availability. Passes were divided into three types depending on the hypothetical threat they may pose to the opposing defense (penetrative, support, and backwards passes). These categories were used to create three heatmaps per match. Moreover, the mean time of passing opportunities was calculated and compared across matches and for the three categories of passes. Due to the specificity of player’s interactive behavior, results showed heatmaps with a variety of patterns. Specifically the fifth match was very dissimilar to the other four. However, characterizing a football match in terms of passing opportunities with a single heatmap dismisses the variety of dynamics that occur throughout a match. Therefore, three temporal heatmaps over windows of 10 min were presented highlighting on-going dynamical changes in pass availability. Results also display that penetrative passes were available over shorter periods of time than backward passes that were available shorter than support passes. The results highlight the sensibility of the model to different task constrains that emerge within football matches.info:eu-repo/semantics/publishedVersio

Comparison of metformin, gliclazide MR and rosiglitazone in monotherapy and in combination for type 2 diabetes Comparação de metformina, gliclazida MR e rosiglitazona em monoterapia e em combinação para o diabetes tipo 2

ABSTRACT Objective: To compare the efficacy and tolerability of metformin, rosiglitazone and gliclazide MR as monotherapy and in combination in the treatment of type 2 diabetes. Subjects and methods: 250 patients treated with oral antidiabetic agents for at least 24 weeks in monotherapy or in combination therapy were included in this retrospective study. Results: As monotherapy the reduction of fasting plasma glucose (FPG), postprandial glycemia (PPG) and HbA1c was similar with the three drugs after 24 weeks. Among patients on combination therapy, the reduction in HbA1c, FPG and PPG was significantly lower with rosiglitazone plus metformin, as compared to metformin plus gliclazide MR or gliclazide MR plus rosiglitazone. Patients treated with rosiglitazone achieved less favorable changes in lipid profile. Conclusion: In monotherapy all drugs were equally effective in improving glycemic control, whereas the combination of metformin plus gliclazide MR provided the best results concerning the improvement of both, glycemic control and lipid profile. Arq Bras Endocrinol Metab. 2010;54(3):311-8 Keywords Metformin; glicazide MR; rosiglitazone RESUMO Objetivo: Comparar a eficácia e a tolerabilidade da metformina, rosiglitazona e gliclazida MR em monoterapia ou em combinação no tratamento do diabetes tipo 2. Sujeitos e métodos: 250 pacientes tratados com antidiabéticos orais por pelo menos 24 semanas, em monoterapia ou em terapia combinada, foram incluídos neste estudo retrospectivo. Resultados: Como monoterapia, a redução da glicemia de jejum (GJ), glicemia pós-prandial (GPP) e HbA1c foi similar com as três drogas, após 24 semanas. Entre os pacientes em terapia combinada, a redução da HbA1c, GJ e GPP foi significativamente menor com rosiglitazona e metformina, em comparação com metformina e gliclazida MR ou gliclazida MR mais rosiglitazona. Os pacientes tratados com rosiglitazona obtiveram mudanças menos favoráveis no perfil lipídico. Conclusão: Em monoterapia todos os medicamentos foram igualmente eficazes na melhora do controle glicêmico, enquanto a combinação de metformina e gliclazida MR proporcionou os melhores resultados relativos à melhoria de ambos, controle glicêmico e perfil lipídico. Arq Bras Endocrinol Metab. 2010;54(3):311-