pvlib.irradiance.klucher#

pvlib.irradiance.klucher(surface_tilt, surface_azimuth, dhi, ghi, solar_zenith, solar_azimuth)[source]#

Determine diffuse irradiance from the sky on a tilted surface using the Klucher (1979) model.

Parameters:

surface_tilt (numeric) – 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 (numeric) – 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 (numeric) – Diffuse horizontal irradiance, must be >=0. [Wm⁻²]
ghi (numeric) – Global horizontal irradiance, must be >=0. [Wm⁻²]
solar_zenith (numeric) – Apparent (refraction-corrected) zenith angles in decimal degrees. solar_zenith must be >=0 and <=180.
solar_azimuth (numeric) – 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:

diffuse (numeric) – The sky diffuse component of the solar radiation. [Wm⁻²]

Notes

The Klucher (1979) model [1] [2] 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, global horizontal irradiance, sun zenith angle, and sun azimuth angle. The expression for the sky diffuse irradiance, \(I_d\), is as follows:

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

DHI is the diffuse horizontal irradiance, \(\beta\) is the surface tilt angle, \(\theta_z\) is the solar zenith angle, and \(\theta\) is the angle of incidence. \(F'\) is a modulating function to account for when the sky changes from clear to overcast, and is defined as follows:

\[F' = 1 - (DHI / GHI)^2,\]

where GHI is the global horiztonal irradiance.

References