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Circunsolar radiation effect on the measurement of diffuse solar irradiance monitored by MEO shading ring method


Diffuse solar irradiance is an important meteorological parameter for several sectors of knowledge, with applications in weather forecasting models, in plasticulture and in ambient luminance studies. In the area of thermal engineering, for financial reasons, diffuse solar irradiance is used to estimate the direct solar irradiance. The direct solar irradiance, used in the validation of energy efficiency models of solar collectors and photovoltaic modules, requires a high financial contribution in the acquisition of the sensor and the solar tracking system, making it impossible to measure routine measurements in many meteorological stations. One solution, then, is to measure the global and diffuse solar irradiances, which do not require high financial investment, and to estimate direct solar irradiance by difference. The most cost-effective method for diffuse irradiance measurement is the shading ring method. However, its disadvantage is the application of correction factors as a function of the portion of the celestial hemisphere obstructed by the ring. There are two corrections: a geometric one, which depends on constructive aspects (width and radius of the ring) and geospatial (latitude and solar declination) and other atmospheric, which depends on the sky cover. Therefore, the project aims to verify the impact that different dimensions for the width and radius of the ring can cause in the atmospheric corrections, since it is expected that the circunsolar radiation, obstructed by the ring, can present different values for different widths of the ring. In this way, it is expected to improve the accuracy of the diffuse solar irradiance method. (AU)

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