pvlib.irradiance.isotropic(surface_tilt, dhi)[source]#

Determine diffuse irradiance from the sky on a tilted surface using the isotropic sky model.

\[I_{d} = DHI \frac{1 + \cos\beta}{2}\]

Hottel and Woertz’s model treats the sky as a uniform source of diffuse irradiance. Thus, the diffuse irradiance from the sky (ground reflected irradiance is not included in this algorithm) on a tilted surface can be found from the diffuse horizontal irradiance and the tilt angle of the surface. A discussion of the origin of the isotropic model can be found in 2.

  • surface_tilt (numeric) – Surface tilt angle 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)

  • dhi (numeric) – Diffuse horizontal irradiance in W/m^2. DHI must be >=0.


diffuse (numeric) – The sky diffuse component of the solar radiation.



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 DOI: 10.1016/j.solener.2006.03.009


Kamphuis, N.R. et al. “Perspectives on the origin, derivation, meaning, and significance of the isotropic sky model” 2020, Solar Energy vol. 201. pp. 8-12 DOI: 10.1016/j.solener.2020.02.067

Examples using pvlib.irradiance.isotropic#

Diffuse Self-Shading

Diffuse Self-Shading