Estimate diffuse irradiance on a tilted surface from ground reflections.

Ground diffuse irradiance is calculated as

$G_{ground} = GHI \times \rho \times \frac{1 - \cos\beta}{2}$

where $$\rho$$ is albedo and $$\beta$$ is surface_tilt.

Parameters
• surface_tilt (numeric) – Surface tilt angles in decimal degrees. Tilt 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 (numeric) – Global horizontal irradiance. $$W/m^2$$

• albedo (numeric, default 0.25) – 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. Must be >=0 and <=1. Will be overridden if surface_type is supplied.

• surface_type (string, optional) – If supplied, overrides albedo. surface_type can be one of ‘urban’, ‘grass’, ‘fresh grass’, ‘snow’, ‘fresh snow’, ‘asphalt’, ‘concrete’, ‘aluminum’, ‘copper’, ‘fresh steel’, ‘dirty steel’, ‘sea’.

Returns

grounddiffuse (numeric) – Ground reflected irradiance. $$W/m^2$$

Notes

Table of albedo values by surface_type are from 2, 3, 4; see SURFACE_ALBEDOS.

References

1

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

2

https://www.pvsyst.com/help/albedo.htm Accessed January, 2024.

3

http://en.wikipedia.org/wiki/Albedo Accessed January, 2024.

4

Payne, R. E. “Albedo of the Sea Surface”. J. Atmos. Sci., 29, pp. 959–970, 1972. DOI: 10.1175/1520-0469(1972)029<0959:AOTSS>2.0.CO;2