pvlib.irradiance.klucher

pvlib.irradiance.klucher(surface_tilt, surface_azimuth, dhi, ghi, solar_zenith, solar_azimuth)

Determine diffuse irradiance from the sky on a tilted surface using Klucher’s 1979 model

\[I_{d} = DHI \frac{1 + \cos\beta}{2} (1 + F' \sin^3(\beta/2)) (1 + F' \cos^2\theta\sin^3\theta_z)\]

where

\[F' = 1 - (I_{d0} / GHI)\]

Klucher’s 1979 model determines the diffuse irradiance from the sky (ground reflected irradiance is not included in this algorithm) on a tilted surface using the surface tilt angle, surface azimuth angle, diffuse horizontal irradiance, direct normal irradiance, global horizontal irradiance, extraterrestrial irradiance, sun zenith angle, and sun azimuth angle.

Parameters:

surface_tilt : float or Series

Surface tilt angles 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)

surface_azimuth : float or Series

Surface azimuth angles in decimal degrees. surface_azimuth must be >=0 and <=360. The Azimuth convention is defined as degrees east of north (e.g. North = 0, South=180 East = 90, West = 270).

dhi : float or Series

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

ghi : float or Series

Global irradiance in W/m^2. DNI must be >=0.

solar_zenith : float or Series

apparent (refraction-corrected) zenith angles in decimal degrees. solar_zenith must be >=0 and <=180.

solar_azimuth : float or Series

Sun azimuth angles in decimal degrees. solar_azimuth must be >=0 and <=360. The Azimuth convention is defined as degrees east of north (e.g. North = 0, East = 90, West = 270).

Returns:

float or Series.

The diffuse component of the solar radiation on an

arbitrarily tilted surface defined by the Klucher model as given in

Loutzenhiser et. al (2007) equation 4.

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] Klucher, T.M., 1979. Evaluation of models to predict insolation on tilted surfaces. Solar Energy 23 (2), 111-114.