Automatic Detection of Clear-sky Periods Using Ground and Satellite Based Solar Resource Data

Solar resource availability and variability are important aspects of monitoring performance of photovoltaic installations. For example, recent degradation studies have highlighted the importance of considering cloud cover when calculation degradation rates. With this in mind, we present a method for optimizing clear sky detection algorithms given only modeled clear sky irradiance and ground-measured irradiance values. This method is tested on global horizontal irradiance (GHI) data from ground collectors at six sites across the US and was trained against clear sky classifications determined from satellite data. Thirty models were optimized on each individual site at GHI data frequencies of 1, 5, 10, 15, and 30 minutes. The models had an average F
_0.5
score of 0.945 ±.021 on a holdout test set. In comparison, the un-optimized clear sky detection algorithm produced F
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score that averaged to 0.707 ± 0.187.