def net_in_sol_rad(sol_rad, albedo=0.23):
    """
    Calculate net incoming solar (or shortwave) radiation from gross
    incoming solar radiation, assuming a grass reference crop.
    Net incoming solar radiation is the net shortwave radiation resulting
    from the balance between incoming and reflected solar radiation. The
    output can be converted to equivalent evaporation [mm day-1] using
    ``energy2evap()``.
    Based on FAO equation 38 in Allen et al (1998).
    :param sol_rad: Gross incoming solar radiation [MJ m-2 day-1]. If
        necessary this can be estimated using functions whose name
        begins with 'sol_rad_from'.
    :param albedo: Albedo of the crop as the proportion of gross incoming solar
        radiation that is reflected by the surface. Default value is 0.23,
        which is the value used by the FAO for a short grass reference crop.
        Albedo can be as high as 0.95 for freshly fallen snow and as low as
        0.05 for wet bare soil. A green vegetation over has an albedo of
        about 0.20-0.25 (Allen et al, 1998).
    :return: Net incoming solar (or shortwave) radiation [MJ m-2 day-1].
    :rtype: float
    """
    return (1 - albedo) * sol_rad
