def _resolution_to_timedelta(res_text):
    """
    Convert an Entsoe resolution to something that pandas can understand

    Parameters
    ----------
    res_text : str

    Returns
    -------
    str
    """
    if res_text == 'PT60M':
        delta = '60min'
    elif res_text == 'P1Y':
        delta = '12M'
    elif res_text == "PT15M":
        delta = '15min'
    else:
        raise NotImplementedError("Sorry, I don't know what to do with the "
                                  "resolution '{}', because there was no "
                                  "documentation to be found of this format. "
                                  "Everything is hard coded. Please open an "
                                  "issue.".format(res_text))
    return delta