Allow PVSystems to be created with single Arrays (#1854)

* allow single Arrays

* whatsnew

Author: kandersolar

docs/sphinx/source/whatsnew/v0.10.2.rst

@@ -22,6 +22,9 @@ Enhancements
 * Added :py:func:`~pvlib.iam.interp` option as AOI losses model in
   :py:class:`pvlib.modelchain.ModelChain` and
   :py:class:`pvlib.pvsystem.PVSystem`. (:issue:`1742`, :pull:`1832`)
+* :py:class:`~pvlib.pvsystem.PVSystem` objects with a single
+  :py:class:`~pvlib.pvsystem.Array` can now be created without wrapping the
+  ``Array`` in a list first. (:issue:`1831`, :pull:`1854`)
 
 Bug fixes
 ~~~~~~~~~

pvlib/pvsystem.py

@@ -101,10 +101,11 @@ class PVSystem:
 
     Parameters
     ----------
-    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`). Must contain at least one Array,
+    arrays : Array or iterable of Array, optional
+        An Array or 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 specified as a list, the list
+        must contain at least one Array;
         if length of arrays is 0 a ValueError is raised. If `arrays` is
         specified the following PVSystem parameters are ignored:
 
@@ -220,6 +221,8 @@ def __init__(self,
                 strings_per_inverter,
                 array_losses_parameters,
             ),)
+        elif isinstance(arrays, Array):
+            self.arrays = (arrays,)
         elif len(arrays) == 0:
             raise ValueError("PVSystem must have at least one Array. "
                              "If you want to create a PVSystem instance "

pvlib/tests/test_pvsystem.py

@@ -1887,8 +1887,6 @@ def test_PVSystem_multiple_array_creation():
     assert pv_system.arrays[0].module_parameters == {}
     assert pv_system.arrays[1].module_parameters == {'pdc0': 1}
     assert pv_system.arrays == (array_one, array_two)
-    with pytest.raises(TypeError):
-        pvsystem.PVSystem(arrays=array_one)
 
 
 def test_PVSystem_get_aoi():
@@ -2362,6 +2360,14 @@ def test_PVSystem_at_least_one_array():
         pvsystem.PVSystem(arrays=[])
 
 
+def test_PVSystem_single_array():
+    # GH 1831
+    single_array = pvsystem.Array(pvsystem.FixedMount())
+    system = pvsystem.PVSystem(arrays=single_array)
+    assert isinstance(system.arrays, tuple)
+    assert system.arrays[0] is single_array
+
+
 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)