pvlib.irradiance.diffuse_par_spitters#
- pvlib.irradiance.diffuse_par_spitters(daily_solar_zenith, global_diffuse_fraction)[source]#
Derive daily diffuse fraction of Photosynthetically Active Radiation (PAR) from daily average solar zenith and diffuse fraction of daily insolation.
The relationship is based on the work of Spitters et al. (1986) 1. The resulting value is the fraction of daily PAR that is diffuse.
Note
The diffuse fraction is defined as the ratio of diffuse to global daily insolation, in J m⁻² day⁻¹ or equivalent.
- Parameters
daily_solar_zenith (numeric) – Average daily solar zenith angle. In degrees [°].
global_diffuse_fraction (numeric) – Fraction of daily global broadband insolation that is diffuse. Unitless [0, 1].
- Returns
par_diffuse_fraction (numeric) – Fraction of daily photosynthetically active radiation (PAR) that is diffuse. Unitless [0, 1].
Notes
The relationship is given by equations (9) & (10) in 1 and (1) in 2:
\[k_{diffuse\_PAR}^{model} = \frac{PAR_{diffuse}}{PAR_{total}} = \frac{\left[1 + 0.3 \left(1 - \left(k_d\right) ^2\right)\right] k_d} {1 + \left(1 - \left(k_d\right)^2\right) \cos ^2 (90 - \beta) \cos ^3 \beta}\]where \(k_d\) is the diffuse fraction of the global insolation, and \(\beta\) is the daily average of the solar elevation angle in degrees.
A comparison using different models for the diffuse fraction of the global insolation can be found in 2 in the context of Sweden.
References
- 1(1,2)
C. J. T. Spitters, H. A. J. M. Toussaint, and J. Goudriaan, ‘Separating the diffuse and direct component of global radiation and its implications for modeling canopy photosynthesis Part I. Components of incoming radiation’, Agricultural and Forest Meteorology, vol. 38, no. 1, pp. 217-229, Oct. 1986, DOI: 10.1016/0168-1923(86)90060-2.
- 2(1,2)
S. Ma Lu et al., ‘Photosynthetically active radiation decomposition models for agrivoltaic systems applications’, Solar Energy, vol. 244, pp. 536-549, Sep. 2022, DOI: 10.1016/j.solener.2022.05.046.
Examples using pvlib.irradiance.diffuse_par_spitters#
Calculating daily diffuse PAR using Spitter’s relationship