Add check if network components are connected

syfop/network.py

@@ -89,12 +89,23 @@ def __init__(
         self.time_coords = time_coords
 
         self._check_consistent_time_coords(nodes, time_coords)
+        self._check_all_nodes_connected(nodes)
 
         self.nodes = nodes
         self.nodes_dict = {node.name: node for node in nodes}
 
         self.model = self._generate_optimization_model(nodes, solver_dir)
 
+    def _check_all_nodes_connected(self, nodes):
+        """Check if graph of node forms a connected network."""
+        graph = self._create_graph(nodes)
+        components = list(nx.weakly_connected_components(graph))
+        if len(components) > 1:
+            raise ValueError(
+                "network is not connected, there are multiple components: "
+                f"{', '.join(str(component) for component in components)}"
+            )
+
     def _check_consistent_time_coords(self, nodes, time_coords):
         # all time series need to be defined on the same coordinates otherwise vector comparison
         # will lead to empty constraints

tests/test_network.py

@@ -499,6 +499,31 @@ def test_empty_network():
         Network([])
 
 
+def test_unconnected_nodes():
+    """Nodes that are not connected should raise an error."""
+    wind = NodeScalableInput(
+        name="wind",
+        input_profile=const_time_series(0.5),
+        costs=1,
+        output_unit="MW",
+    )
+    demand = NodeFixOutput(
+        name="demand",
+        inputs=[],
+        input_commodities="electricity",
+        output_flow=const_time_series(5.0),
+        costs=0,
+        output_unit="MW",
+    )
+
+    # is the order of components deterministic here? would need to know how networkx checks it, but
+    # I guess it should be fine... if the test fails because it sais "demand", "wind" instead of
+    # "wind", "demand", then just remove the rest of the error_msg stating the nodes
+    error_msg = "network is not connected, there are multiple components: {'wind'}, {'demand'}"
+    with pytest.raises(ValueError, match=error_msg):
+        Network([wind, demand])
+
+
 def test_node_with_same_name():
     """Nodes with the same name should raise an error."""
     wind = NodeScalableInput(