code: def peak_load(self):
          
          if self._peak_load is None:
              self._peak_load = sum(
                  [_.peak_load.sum()
                   for _ in self.graph.nodes_by_attribute('load')])
  
          return self._peak_load
docs: Cumulative peak load capacity of generators of this grid
  
          Returns
          -------
          float
              Ad-hoc calculated or cached peak load capacity