def persistence_model(latest_ghi):
    """
    Creates a persistence forecast when the software fails to receive a valid
    GHI observation. Can also be used if one simply desires a persistence
    forecast.
    Parameters
    ----------
    latest_ghi: 'Pandas Series object'
        Current time. Usually contains a year, month, day, hour, and minute.

    Returns
    -------
    persist_ghi: 'Pandas Series object'
        Persistence forecast for inputed date time.
    """
    persist_ghi = latest_ghi.copy()
    return persist_ghi