def curtailment(self):
        """
        Get curtailment time series of dispatchable generators (only active
        power)

        Parameters
        ----------
        curtailment : list or :pandas:`pandas.DataFrame<dataframe>`
            See class definition for details.

        Returns
        -------
        :pandas:`pandas.DataFrame<dataframe>`
            In the case curtailment is applied to all solar and wind generators
            curtailment time series either aggregated by technology type or by
            type and weather cell ID are returnded. In the first case columns
            of the DataFrame are 'solar' and 'wind'; in the second case columns
            need to be a :pandas:`pandas.MultiIndex<multiindex>` with the
            first level containing the type and the second level the weather
            cell ID.
            In the case curtailment is only applied to specific generators,
            curtailment time series of all curtailed generators, specified in
            by the column name are returned.

        """
        if self._curtailment is not None:
            if isinstance(self._curtailment, pd.DataFrame):
                try:
                    return self._curtailment.loc[[self.timeindex], :]
                except:
                    return self._curtailment.loc[self.timeindex, :]
            elif isinstance(self._curtailment, list):
                try:
                    curtailment = pd.DataFrame()
                    for gen in self._curtailment:
                        curtailment[gen] = gen.curtailment
                    return curtailment
                except:
                    raise
        else:
            return None