some small adjustments to run as single node model (PyPSA#1183)

* some small adjustments to run as single node model

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

scripts/cluster_gas_network.py

@@ -58,6 +58,9 @@ def build_clustered_gas_network(df, bus_regions, length_factor=1.25):
     # drop pipes within the same region
     df = df.loc[df.bus1 != df.bus0]
 
+    if df.empty:
+        return df
+
     # recalculate lengths as center to center * length factor
     df["length"] = df.apply(
         lambda p: length_factor

scripts/prepare_sector_network.py

@@ -2775,10 +2775,11 @@ def add_industry(n, costs):
         )
 
     domestic_navigation = pop_weighted_energy_totals.loc[
-        nodes, "total domestic navigation"
+        nodes, ["total domestic navigation"]
     ].squeeze()
     international_navigation = (
-        pd.read_csv(snakemake.input.shipping_demand, index_col=0).squeeze() * nyears
+        pd.read_csv(snakemake.input.shipping_demand, index_col=0).squeeze(axis=1)
+        * nyears
     )
     all_navigation = domestic_navigation + international_navigation
     p_set = all_navigation * 1e6 / nhours
@@ -3946,12 +3947,11 @@ def add_enhanced_geothermal(n, egs_potentials, egs_overlap, costs):
 
         snakemake = mock_snakemake(
             "prepare_sector_network",
-            # configfiles="test/config.overnight.yaml",
             simpl="",
             opts="",
-            clusters="37",
-            ll="v1.0",
-            sector_opts="730H-T-H-B-I-A-dist1",
+            clusters="1",
+            ll="vopt",
+            sector_opts="",
             planning_horizons="2050",
         )