Source code for src.functions.SOLWEIGpython.UTIL.diffusefraction

from __future__ import division
import numpy as np



def diffusefraction(radG,altitude,Kt,Ta,RH):
    """
    Unchanged function: Estimate diffuse and direct beam solar radiation using the Reindl et al. (1990) model.

    Parameters:
        radG (float):     Global horizontal irradiance [W/m²].
        altitude (float): Solar altitude angle [degrees].
        Kt (float):       Clearness index (ratio of global radiation at surface to that at the top of atmosphere).
        Ta (float):       Air temperature [°C].
        RH (float):       Relative humidity [%].

    Returns
    -------
    radI : float
        Direct beam radiation [W/m²].
    radD : float
        Diffuse radiation [W/m²].
    """
    alfa = altitude*(np.pi/180)

    if Ta <= -999.00 or RH <= -999.00 or np.isnan(Ta) or np.isnan(RH):
        if Kt <= 0.3:
            radD = radG*(1.020-0.248*Kt)
        elif Kt > 0.3 and Kt < 0.78:
            radD = radG*(1.45-1.67*Kt)
        else:
            radD = radG*0.147
    else:
        RH = RH/100
        if Kt <= 0.3:
            radD = radG*(1 - 0.232 * Kt + 0.0239 * np.sin(alfa) - 0.000682 * Ta + 0.0195 * RH)
        elif Kt > 0.3 and Kt < 0.78:
            radD = radG*(1.329- 1.716 * Kt + 0.267 * np.sin(alfa) - 0.00357 * Ta + 0.106 * RH)
        else:
            radD = radG*(0.426 * Kt - 0.256 * np.sin(alfa) + 0.00349 * Ta + 0.0734 * RH)

    radI = (radG - radD)/(np.sin(alfa))

    # Corrections for low sun altitudes (20130307)
    if radI < 0:
        radI = 0

    if altitude < 1 and radI > radG:
        radI=radG

    if radD > radG:
        radD = radG

    return radI, radD