Raise ValueError if PVSystem constructed with 0 Arrays

Provides a useful error message directing users to the solution they are most likely to want (construct a PVSystem with an arbitrary default Array).
pvlib · wholmgren · May 17, 2021 · May 10, 2021 · May 17, 2021 · May 17, 2021
commit e2add9442071d49e60de479e85268e05eba78075
diff --git a/pvlib/pvsystem.py b/pvlib/pvsystem.py
@@ -98,7 +98,8 @@ 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
+        `surface_tilt`, `surface_azimuth`). Must contain at least one Array,
+        if empty a ValueError is raised. If `arrays` is specified
         the following parameters are ignored:
 
         - `surface_tilt`
@@ -210,6 +211,11 @@ 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 arbitrary default Array pass "
+                             "`arrays=None`.")
         else:
             self.arrays = tuple(arrays)
 

diff --git a/pvlib/tests/test_pvsystem.py b/pvlib/tests/test_pvsystem.py
@@ -2084,6 +2084,12 @@ 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)