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Transposition models convert irradiance components (, , ) to plane-of-array () irradiance on the tilted module surface. The transposed irradiance consists of three components: beam, sky diffuse, and ground-reflected.

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Models in This Section

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Hay-Davies Model

- hybrid model that splits diffuse irradiance into two components: an isotropic background uniformly distributed across the sky dome, and a component concentrated near the sun. The model uses an —the ratio of to extraterrestrial DNI—to weight the circumsolar fraction based on atmospheric clarity.

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Perez Model

Advanced anisotropic model that decomposes sky diffuse into three components: isotropic background, circumsolar brightening near the solar disk, and near the horizon. Sky clearness and brightness indices determine which empirical coefficient set is applied. Multiple coefficient sets available:
  • PlantPredict (default)
  • All Sites Composite 1988 and 1990
  • Sandia Composite 1988
  • Location-specific sets (USA, France, Phoenix, Elmonte, Osage, Albuquerque, Cape Canaveral, Albany)

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3D Transposition

-specific transposition for 3D scenes. Calculates individual bay orientations accounting for terrain slopes and eventual terrain-aware backtracking and applies the Perez model for each unique orientation. 3D transposition is automatically applied when the 3D scene is enabled.