pvlib.irradiance.isotropic

pvlib.irradiance.isotropic(surface_tilt, dhi)

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.

Parameters:

surface_tilt : float or Series

Surface tilt angle in decimal degrees. surface_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 : float or Series

Diffuse horizontal irradiance in W/m^2. DHI must be >=0.

Returns:

float or Series

The diffuse component of the solar radiation on an

arbitrarily tilted surface defined by the isotropic sky model as

given in Loutzenhiser et. al (2007) equation 3.

SkyDiffuse is the diffuse component ONLY and does not include the ground

reflected irradiance or the irradiance due to the beam.

SkyDiffuse is a column vector vector with a number of elements equal to

the input vector(s).

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] Hottel, H.C., Woertz, B.B., 1942. Evaluation of flat-plate solar heat collector. Trans. ASME 64, 91.