def _count_hours_gt_threshold(utilization, threshold):
    """Calculate number of hours above a given utilization threshold.

    :param pandas.DataFrame utilization: normalized power flow data frame as returned
        by :func:`get_utilization`.
    :param float threshold: utilization threshold ([0,1]).
    :return: (*pandas.Series*) -- number of hours above utilization threshold.
    """
    return (utilization > threshold).sum()