code: def add_aggregated_peak_demand(self):
          
          peak_load_aggregated = 0
          for lv_load_area in self.lv_load_areas():
              if lv_load_area.is_aggregated:
                  peak_load_aggregated += lv_load_area.peak_load
          self.peak_load_aggregated = peak_load_aggregated
docs: Summarizes peak loads of underlying aggregated load_areas