# pvl_grounddiffuse

Estimate diffuse irradiance from ground reflections given irradiance, albedo, and surface tilt.

## Contents

- Syntax
- Description
- Inputs
- Outputs
- Example 1
- Example 2
- References
- See Also

## Syntax

`GR = pvl_grounddiffuse(SurfTilt, GHI, Albedo)`

## Description

Function to determine the portion of irradiance on a tilted surface due to ground reflections. Any of the inputs may be vectors or scalars, as long as all vectors are of the same size.

## Inputs

- `SurfTilt` - a scalar or vector of surface tilt angles in decimal degrees. If `SurfTilt` is a vector it must be of the same size as all other vector inputs. `SurfTilt` must be >=0 and <=180. The tilt angle is defined as degrees from horizontal (e.g. surface facing up = 0, surface facing horizon = 90).
- `GHI` - a scalar or vector of global horizontal irradiance in W/m^2. If `GHI` is a vector it must be of the same size as all other vector inputs. `GHI` must be >=0.
- `Albedo` - a scalar or vector for ground reflectance, typically 0.1-0.4 for surfaces on Earth (land), may increase over snow, ice, etc. May also be known as the reflection coefficient. If `Albedo` is a vector it must be of the same size as all other vector inputs. Must be >=0 and <=1.

## Outputs

- `GR` - a column vector of ground reflected irradiances in W/m^2. The vector has the same number of elements as the input vector(s).

## Example 1

Calculate the ground reflected diffuse irradiance on an array tilted at 30 degrees from horizontal when GHI = 1,000 W/m^2 and albedo = 0.2.

    GR = pvl_grounddiffuse(30, 1000, 0.2)

    GR =

       13.3975

## Example 2

Calculate the ground reflected diffuse irradiance on an array tilted at 30 degrees from horizontal when GHI = 1,000 W/m^2 and albedo = 0.8 (typical of fresh snow).

    GR = pvl_grounddiffuse(30, 1000, 0.8)

    GR =

       53.5898

## References

[1] Loutzenhiser P.G. et al., 2007. Empirical validation of models to compute solar irradiance on inclined surfaces for building energy simulation, Solar Energy vol. 81. pp. 254-267.

## See Also

`pvl_perez`, `pvl_reindl1990`, `pvl_klucher1979`, `pvl_haydavies1980`, `pvl_isotropicsky`, `pvl_kingdiffuse`

Copyright 2014 Sandia National Laboratories