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

Models in This Section

Hay-Davies Model

Isotropic-anisotropic hybrid model that splits diffuse irradiance into isotropic sky and circumsolar components using an anisotropy index.

Perez Model

Advanced anisotropic model with circumsolar and horizon brightening components. Multiple coefficient sets available:
  • PlantPredict (default)
  • All Sites Composite 1990
  • All Sites Composite 1988
  • Sandia Composite 1988
  • Location-specific sets (USA, France, Phoenix, Elmonte, Osage, Albuquerque, Cape Canaveral, Albany)

3D Transposition

Row-specific transposition for 3D scenes with Terrain-Aware Backtracking (TABT). Calculates individual bay orientations accounting for terrain slopes and applies the Perez model via pvlib for each unique orientation.

Model Selection

  • Hay-Davies: Simpler model, suitable when Perez coefficients are uncertain
  • Perez: More accurate for most locations, especially with appropriate regional coefficients
  • 3D Transposition: Automatically applied when 3D scene is loaded with TABT enabled