def watt_to_MJ(watt_m2):
    """
    Transform watt per m² to MJ per m² per day
    """
    joule_m2_s = watt_m2
    joule_m2_day = joule_m2_s * 86400
    mjoule_m2_day = joule_m2_day / 1000000
    return mjoule_m2_day