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