Effect of Solar Position Calculations on Filtering and Analysis of Solar Radiation Measurements

An important step in the analysis and aggregation of solar radiation measurements is quality filtering of the measured values, and most of these tests rely on calculations of the solar position. Such calculations can be performed at different degrees of precision by using algorithms of various complexities. In this work, two solar position calculation methods are used to process one-minute measurements of direct, global and diffuse irradiances from two different locations, and the resulting aggregated and derived quantities at various time scales are compared in order to look for variations in the final products. The differences are found to be mostly irrelevant, except for clearness indices, which are useful in models deriving solar data from satellite observations, so the higher precision calculations are still recommended for such applications. In any case, the differences against non-filtered data can be quite large, stressing the importance of quality checks.