Identifies times when GHI is consistent with clear sky conditions.
Uses the function pvlib.clearsky.detect_clearsky. Assumes ghi data with regular (constant) time intervals which must be 15 minutes or less.
- ghi (Series) – Global horizontal irradiance in W/m^2
- ghi_clearsky (Series) – Global horizontal irradiance in W/m^2 under clear sky conditions
flags (Series) – True when clear sky conditions are indicated.
Clear-sky conditions are inferred when each of six criteria are met; see pvlib.clearsky.detect_clearsky for references and details. Threshold values for each criterion were originally developed for ten minute windows containing one-minute data . As indicated in , the algorithm also works for longer windows and data at different intervals, if threshold criteria are roughly scaled to the window length. Here, the threshold values are based on  with the scaling indicated in .
Warns: RuntimeWarning – If pvlib.clearsky.detect_clearsky cannot be applied to the input.
 Reno, M.J. and C.W. Hansen, “Identification of periods of clear sky irradiance in time series of GHI measurements” Renewable Energy, v90, p. 520-531, 2016.
 B. H. Ellis, M. Deceglie and A. Jain, “Automatic Detection of Clear-Sky Periods From Irradiance Data,” in IEEE Journal of Photovoltaics, vol. 9, no. 4, pp. 998-1005, July 2019. doi: 10.1109/JPHOTOV.2019.2914444