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Horizontal Irradiance Processing models prepare input irradiance data (measured or modeled) for use in energy production calculations. These models handle component separation and clear-sky estimation required for downstream calculations.

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Models in This Section

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Horizontal Irradiance Components Validation

Validates input irradiance data using the (GHI = DHI + DNI × cos θz) and applies quality control checks to ensure physical consistency.

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Diffuse-Direct

Estimates DHI from GHI, then calculates DNI using the . This step is applied when DHI or DNI measurements are unavailable or when the user chooses to override measured values. Three model options:
  • Erbs: Simplest model; uses only GHI and extraterrestrial irradiance via a correlation
  • Reindl: Adds air temperature and optionally relative humidity for improved accuracy under varying atmospheric conditions
  • DIRINT: Uses adjacent timesteps to detect rapid irradiance changes (e.g., cloud transients), providing better accuracy for variable sky conditions

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Bird Clear Sky Model

Calculates theoretical clear-sky irradiance components using atmospheric transmittance factors. Used for spectral correction calculations.

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Processing Workflow

When DNI and DHI are provided: Values used directly with quality control checks. When only GHI is provided: Diffuse-direct estimates DNI and DHI using the selected model. Clear-sky calculation: Bird model provides reference irradiance for spectral corrections (regardless of input data availability).