Identification of periods of clear sky irradiance in time series of GHI measurements


We present an algorithm to identify clear periods in a GHI time series.

The method uses only measured GHI and a clear-sky model.

We validate our algorithm and compare its results to other algorithms.


We present a simple algorithm for identifying periods of time with broadband global horizontal irradiance (GHI) similar to that occurring during clear sky conditions from a time series of GHI measurements. Other available methods to identify these periods do so by identifying periods with clear sky conditions using additional measurements, such as direct or diffuse irradiance. Our algorithm compares characteristics of the time series of measured GHI with the output of a clear sky model without requiring additional measurements. We validate our algorithm using data from several locations by comparing our results with those obtained from a clear sky detection algorithm, and with satellite and ground-based sky imagery.


  • Solar resource;
  • Global horizontal irradiance;
  • Clear sky

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