> ## Documentation Index
> Fetch the complete documentation index at: https://docs.plantpredict.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Transposition Models Overview

export const BayCap = () => <Tooltip tip="Section of a tracker where modules share the same tilt and rotation angle, receiving uniform irradiance.">
    Bay
  </Tooltip>;

export const Bay = () => <Tooltip tip="Section of a tracker where modules share the same tilt and rotation angle, receiving uniform irradiance.">
    bay
  </Tooltip>;

export const HorizonBrightening = () => <Tooltip tip="Enhanced diffuse irradiance near the horizon due to atmospheric scattering at low angles.">
    horizon brightening
  </Tooltip>;

export const AnisotropyIndex = () => <Tooltip tip="Ratio of DNI to extraterrestrial DNI; quantifies the directional fraction of diffuse irradiance.">
    anisotropy index
  </Tooltip>;

export const Circumsolar = () => <Tooltip tip="Diffuse irradiance concentrated in a bright ring around the solar disk.">
    circumsolar
  </Tooltip>;

export const Anisotropic = () => <Tooltip tip="Varying with direction; describes diffuse irradiance with directional components (e.g., circumsolar, horizon brightening).">
    anisotropic
  </Tooltip>;

export const IsotropicCap = () => <Tooltip tip="Uniform in all directions; describes diffuse irradiance distributed evenly across the sky dome.">
    Isotropic
  </Tooltip>;

export const Isotropic = () => <Tooltip tip="Uniform in all directions; describes diffuse irradiance distributed evenly across the sky dome.">
    isotropic
  </Tooltip>;

export const POA = () => <Tooltip tip="Plane-of-Array: solar irradiance on the tilted module surface (beam + diffuse + reflected).">
    POA
  </Tooltip>;

export const GHI = () => <Tooltip tip="Global Horizontal Irradiance: total solar radiation on a horizontal surface (direct + diffuse).">
    GHI
  </Tooltip>;

export const DHI = () => <Tooltip tip="Diffuse Horizontal Irradiance: solar radiation from the sky dome (excluding direct beam) on a horizontal surface.">
    DHI
  </Tooltip>;

export const DNI = () => <Tooltip tip="Direct Normal Irradiance: solar radiation received perpendicular to the sun's rays (direct beam only).">
    DNI
  </Tooltip>;

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

## Models in This Section

### [Hay-Davies Model](hay_davies)

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

### [Perez Model](perez)

Advanced anisotropic model that decomposes sky diffuse into three components: isotropic background, circumsolar brightening near the solar disk, and <HorizonBrightening /> 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)

### [3D Transposition](3d_transposition)

<BayCap />-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.