diffusefraction.py

from __future__ import division
import numpy as np

def diffusefraction(radG,altitude,Kt,Ta,RH):
    """
    This function estimates diffuse and directbeam radiation according to
    Reindl et al (1990), Solar Energy 45:1

    :param radG:
    :param altitude:
    :param Kt:
    :param Ta:
    :param RH:
    :return:
    """

    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