Raise ValueError if PVSystem constructed with 0 Arrays (#1224)

Author: wfvining

pvlib/pvsystem.py

@@ -98,8 +98,9 @@ class PVSystem:
     arrays : iterable of Array, optional
         List of arrays that are part of the system. If not specified
         a single array is created from the other parameters (e.g.
-        `surface_tilt`, `surface_azimuth`). If `arrays` is specified
-        the following parameters are ignored:
+        `surface_tilt`, `surface_azimuth`). Must contain at least one Array,
+        if length of arrays is 0 a ValueError is raised. If `arrays` is
+        specified the following parameters are ignored:
 
         - `surface_tilt`
         - `surface_azimuth`
@@ -173,6 +174,11 @@ class PVSystem:
         Arbitrary keyword arguments.
         Included for compatibility, but not used.
 
+    Raises
+    ------
+    ValueError
+        If `arrays` is not None and has length 0.
+
     See also
     --------
     pvlib.location.Location
@@ -210,6 +216,12 @@ def __init__(self,
                 racking_model,
                 array_losses_parameters,
             ),)
+        elif len(arrays) == 0:
+            raise ValueError("PVSystem must have at least one Array. "
+                             "If you want to create a PVSystem instance "
+                             "with a single Array pass `arrays=None` and pass "
+                             "values directly to PVSystem attributes, e.g., "
+                             "`surface_tilt=30`")
         else:
             self.arrays = tuple(arrays)
 

pvlib/tests/test_pvsystem.py

@@ -2067,6 +2067,12 @@ def test_PVSystem_num_arrays():
     assert system_two.num_arrays == 2
 
 
+def test_PVSystem_at_least_one_array():
+    with pytest.raises(ValueError,
+                       match="PVSystem must have at least one Array"):
+        pvsystem.PVSystem(arrays=[])
+
+
 def test_combine_loss_factors():
     test_index = pd.date_range(start='1990/01/01T12:00', periods=365, freq='D')
     loss_1 = pd.Series(.10, index=test_index)