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Processamento de imagem para avaliação da degradação de refletores solares para energia solar de concentração
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Globalmente, verifica-se um aumento das necessidades energéticas decorrente do desenvolvimento económico, social e tecnológico experienciado ao longo das últimas décadas. As energias renováveis têm sido amplamente adotadas como solução para enfrentar o crescimento destas necessidades, sendo a energia solar uma delas. Uma das formas de aproveitar esta energia é através da utilização de espelhos refletores para concentrar a luz solar num recetor, produzindo eletricidade em sistemas de energia solar de concentração, ou como é conhecida em inglês, Concentrated Solar Power (CSP).
O custo associado à implementação de uma central de CSP é considerável, sendo um dos principais constituintes das mesmas os refletores solares. Estes, dependendo da qualidade do material e das condições atmosféricas do local de instalação da central, podem sofrer degradação sob forma de corrosão, o que impacta a rentabilidade do sistema. A fim de eleger o melhor refletor para o local destinado, as amostras de refletores solares são submetidas a uma série de ensaios de corrosão por forma a avaliar a fiabilidade dos materiais durante o tempo de vida de uma central. Um dos ensaios a que as amostras são sujeitas é o ensaio de envelhecimento acelerado que, de certa forma, reproduz, em ciclos de horas, o impacto que as condições atmosféricas do exterior teriam nos refletores ao longo de anos.
Durante o tempo de vida de uma central, assim como nos ensaios de laboratório, é necessário monitorizar a degradação dos refletores solares tendo em conta as implicações que a corrosão tem na perda da refletância solar e consequentemente na eficiência de uma central de CSP. Contudo, esta monitorização deve ser feita de forma rápida e fidedigna. Assim, surge a necessidade da criação de um método eficiente e automatizado de quantificação da corrosão presente em amostras de refletores solares. A necessidade foi colmatada com a construção do apparatus experimental (câmara escura), no qual foi possível capturar fotografias aos refletores solares com condições de luminosidade controladas, aliada também com o desenvolvimento de um algoritmo de raiz capaz de detetar e quantificar a corrosão, utilizando as fotografias capturadas. O trabalho desenvolvido é uma contribuição para a elaboração de uma norma.
O algoritmo desenvolvido através de técnicas de processamento de imagem foi otimizado o que permitiu de forma expedita determinar a penetração máxima e média da corrosão a partir das arestas, número e densidade de pontos de corrosão (spots) e respetiva área ocupada pela corrosão a partir de uma imagem. Contudo, ainda apresenta algumas limitações - no modo automático, no caso de haver sombras na imagem ou delaminação na amostra, a deteção dos limites da mesma falha, não conseguindo detetar 100% a amostra. Por outro lado, os dois modos não são capazes de identificar como spots, corrosão que esteja presente próximo das arestas.
Globally, there has been an increase in energy needs as a result of the economic, social and technological development experienced over the last few decades. Renewable energies have been widely adopted as a solution to meet these growing needs, and solar energy is one of them. One of the ways of harnessing this energy is by using reflective mirrors to concentrate sunlight on a receiver, producing electricity in a Concentrated Solar Power (CSP) plant. The cost associated with implementing a CSP plant is considerable, and one of the main components is the solar reflectors. Depending on the quality of the material and the atmospheric conditions at the plant's location, they can suffer degradation in the form of corrosion, which has an impact on the system's profitability. To choose the best reflector for the location, solar reflector samples are subjected to a series of corrosion tests to assess the reliability of the materials over the lifetime of a power station. One of the tests to which the samples are subjected is the accelerated ageing test which, in a way, reproduces, in cycles of hours, the impact that outdoor atmospheric conditions would have on the reflectors over a period of years. During the lifetime of a power station, as well as in laboratory tests, it is necessary to monitor the degradation of solar reflectors, given the implications that corrosion has on the loss of solar reflectance and consequently on the efficiency of a CSP plant. However, this monitoring must be done quickly and reliably. Thus, the need arose to create an efficient and automated method for quantifying the corrosion present in solar reflector samples. This need was met with the construction of the experimental apparatus (darkroom), in which it was possible to capture photographs of solar reflectors under controlled lighting conditions, as well as the development of a root algorithm capable of detecting and quantifying corrosion using the captured photographs. The work carried out is a contribution to the development of a norm. The algorithm developed using image processing techniques was optimized, making it possible to quickly determine the maximum and average penetration of corrosion from the edges, the number and density of corrosion spots and the respective area occupied by corrosion from an image. However, it still has limitations - in automatic mode, if there are shadows on the image or flaking on the sample, the detection of the limits of the sample fails, and it cannot detect 100% of the sample. On the other hand, both modes are unable to identify corrosion that is present near the edges as spots. Keywords: Concentrated Solar Power, solar reflector, corrosion detection, image processing.
Globally, there has been an increase in energy needs as a result of the economic, social and technological development experienced over the last few decades. Renewable energies have been widely adopted as a solution to meet these growing needs, and solar energy is one of them. One of the ways of harnessing this energy is by using reflective mirrors to concentrate sunlight on a receiver, producing electricity in a Concentrated Solar Power (CSP) plant. The cost associated with implementing a CSP plant is considerable, and one of the main components is the solar reflectors. Depending on the quality of the material and the atmospheric conditions at the plant's location, they can suffer degradation in the form of corrosion, which has an impact on the system's profitability. To choose the best reflector for the location, solar reflector samples are subjected to a series of corrosion tests to assess the reliability of the materials over the lifetime of a power station. One of the tests to which the samples are subjected is the accelerated ageing test which, in a way, reproduces, in cycles of hours, the impact that outdoor atmospheric conditions would have on the reflectors over a period of years. During the lifetime of a power station, as well as in laboratory tests, it is necessary to monitor the degradation of solar reflectors, given the implications that corrosion has on the loss of solar reflectance and consequently on the efficiency of a CSP plant. However, this monitoring must be done quickly and reliably. Thus, the need arose to create an efficient and automated method for quantifying the corrosion present in solar reflector samples. This need was met with the construction of the experimental apparatus (darkroom), in which it was possible to capture photographs of solar reflectors under controlled lighting conditions, as well as the development of a root algorithm capable of detecting and quantifying corrosion using the captured photographs. The work carried out is a contribution to the development of a norm. The algorithm developed using image processing techniques was optimized, making it possible to quickly determine the maximum and average penetration of corrosion from the edges, the number and density of corrosion spots and the respective area occupied by corrosion from an image. However, it still has limitations - in automatic mode, if there are shadows on the image or flaking on the sample, the detection of the limits of the sample fails, and it cannot detect 100% of the sample. On the other hand, both modes are unable to identify corrosion that is present near the edges as spots. Keywords: Concentrated Solar Power, solar reflector, corrosion detection, image processing.
Descrição
Palavras-chave
Energia de concentração solar refletor solar deteção da corrosão processamento de imagem