From 1ee16e1e8b2b176161b313c905a58043c062719c Mon Sep 17 00:00:00 2001
From: Kevin Anderson <kevin.anderson@nrel.gov>
Date: Sat, 13 Mar 2021 12:36:21 -0700
Subject: [PATCH 01/15] add and apply decorator

---
 pvlib/pvsystem.py | 44 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/pvlib/pvsystem.py b/pvlib/pvsystem.py
index a727673265..0ab6cbe3e7 100644
--- a/pvlib/pvsystem.py
+++ b/pvlib/pvsystem.py
@@ -64,6 +64,36 @@ def f(*args, **kwargs):
     return f
 
 
+def _check_deprecated_passthrough(func):
+    """
+    Decorator to warn or error when getting and setting the "pass-through"
+    PVSystem properties that have been moved to Array.  Emits a warning for
+    PVSystems with only one Array and raises an error for PVSystems with
+    more than one Array.
+    """
+
+    @functools.wraps(func)
+    def wrapper(self, *args, **kwargs):
+        pvsystem_attr = func.__name__
+        class_name = self.__class__.__name__  # PVSystem or SingleAxisTracker
+        overrides = {  # some Array attrs aren't the same as PVSystem
+            'strings_per_inverter': 'strings',
+        }
+        array_attr = overrides.get(pvsystem_attr, pvsystem_attr)
+        alternative = f'{class_name}.arrays[i].{array_attr}'
+
+        if len(self.arrays) > 1:
+            raise AttributeError(
+                f'{class_name}.{pvsystem_attr} not supported for multi-array '
+                f'systems. Use {alternative} instead.')
+
+        wrapped = deprecated('0.9', alternative=alternative, removal='0.10',
+                             name=f"{class_name}.{pvsystem_attr}")(func)
+        return wrapped(self, *args, **kwargs)
+
+    return wrapper
+
+
 # not sure if this belongs in the pvsystem module.
 # maybe something more like core.py? It may eventually grow to
 # import a lot more functionality from other modules.
@@ -1019,72 +1049,86 @@ def pvwatts_ac(self, pdc):
 
     @property
     @_unwrap_single_value
+    @_check_deprecated_passthrough
     def module_parameters(self):
         return tuple(array.module_parameters for array in self.arrays)
 
     @property
     @_unwrap_single_value
+    @_check_deprecated_passthrough
     def module(self):
         return tuple(array.module for array in self.arrays)
 
     @property
     @_unwrap_single_value
+    @_check_deprecated_passthrough
     def module_type(self):
         return tuple(array.module_type for array in self.arrays)
 
     @property
     @_unwrap_single_value
+    @_check_deprecated_passthrough
     def temperature_model_parameters(self):
         return tuple(array.temperature_model_parameters
                      for array in self.arrays)
 
     @temperature_model_parameters.setter
+    @_check_deprecated_passthrough
     def temperature_model_parameters(self, value):
         for array in self.arrays:
             array.temperature_model_parameters = value
 
     @property
     @_unwrap_single_value
+    @_check_deprecated_passthrough
     def surface_tilt(self):
         return tuple(array.surface_tilt for array in self.arrays)
 
     @surface_tilt.setter
+    @_check_deprecated_passthrough
     def surface_tilt(self, value):
         for array in self.arrays:
             array.surface_tilt = value
 
     @property
     @_unwrap_single_value
+    @_check_deprecated_passthrough
     def surface_azimuth(self):
         return tuple(array.surface_azimuth for array in self.arrays)
 
     @surface_azimuth.setter
+    @_check_deprecated_passthrough
     def surface_azimuth(self, value):
         for array in self.arrays:
             array.surface_azimuth = value
 
     @property
     @_unwrap_single_value
+    @_check_deprecated_passthrough
     def albedo(self):
         return tuple(array.albedo for array in self.arrays)
 
     @property
     @_unwrap_single_value
+    @_check_deprecated_passthrough
     def racking_model(self):
         return tuple(array.racking_model for array in self.arrays)
 
     @racking_model.setter
+    @_check_deprecated_passthrough
     def racking_model(self, value):
         for array in self.arrays:
             array.racking_model = value
 
     @property
     @_unwrap_single_value
+    @_check_deprecated_passthrough
     def modules_per_string(self):
         return tuple(array.modules_per_string for array in self.arrays)
 
     @property
     @_unwrap_single_value
+    @_check_deprecated_passthrough
     def strings_per_inverter(self):
         return tuple(array.strings for array in self.arrays)
 

From 4d27febd1bfad1e72c60025299f69653b5ce299e Mon Sep 17 00:00:00 2001
From: Kevin Anderson <kevin.anderson@nrel.gov>
Date: Sat, 13 Mar 2021 12:36:31 -0700
Subject: [PATCH 02/15] fix everything that broke

---
 pvlib/modelchain.py            | 57 +++++++++++++++++++-------------
 pvlib/tests/test_modelchain.py | 52 +++++++++++++++++-------------
 pvlib/tests/test_pvsystem.py   | 59 +++++++++++++++++++++-------------
 pvlib/tests/test_tracking.py   |  4 +--
 pvlib/tracking.py              |  2 +-
 5 files changed, 102 insertions(+), 72 deletions(-)

diff --git a/pvlib/modelchain.py b/pvlib/modelchain.py
index 990598ae1e..8f43d3616b 100644
--- a/pvlib/modelchain.py
+++ b/pvlib/modelchain.py
@@ -328,26 +328,26 @@ class ModelChain:
 
     dc_model: None, str, or function, default None
         If None, the model will be inferred from the contents of
-        system.module_parameters. Valid strings are 'sapm',
+        system.arrays[i].module_parameters. Valid strings are 'sapm',
         'desoto', 'cec', 'pvsyst', 'pvwatts'. The ModelChain instance will
         be passed as the first argument to a user-defined function.
 
     ac_model: None, str, or function, default None
         If None, the model will be inferred from the contents of
-        system.inverter_parameters and system.module_parameters. Valid
-        strings are 'sandia', 'adr', 'pvwatts'. The
+        system.inverter_parameters and system.arrays[i].module_parameters.
+        Valid strings are 'sandia', 'adr', 'pvwatts'. The
         ModelChain instance will be passed as the first argument to a
         user-defined function.
 
     aoi_model: None, str, or function, default None
         If None, the model will be inferred from the contents of
-        system.module_parameters. Valid strings are 'physical',
+        system.arrays[i].module_parameters. Valid strings are 'physical',
         'ashrae', 'sapm', 'martin_ruiz', 'no_loss'. The ModelChain instance
         will be passed as the first argument to a user-defined function.
 
     spectral_model: None, str, or function, default None
         If None, the model will be inferred from the contents of
-        system.module_parameters. Valid strings are 'sapm',
+        system.arrays[i].module_parameters. Valid strings are 'sapm',
         'first_solar', 'no_loss'. The ModelChain instance will be passed
         as the first argument to a user-defined function.
 
@@ -605,9 +605,10 @@ def dc_model(self, model):
             model = model.lower()
             if model in _DC_MODEL_PARAMS.keys():
                 # validate module parameters
+                module_parameters = tuple(
+                    array.module_parameters for array in self.system.arrays)
                 missing_params = (
-                    _DC_MODEL_PARAMS[model] -
-                    _common_keys(self.system.module_parameters))
+                    _DC_MODEL_PARAMS[model] - _common_keys(module_parameters))
                 if missing_params:  # some parameters are not in module.keys()
                     raise ValueError(model + ' selected for the DC model but '
                                      'one or more Arrays are missing '
@@ -630,7 +631,8 @@ def dc_model(self, model):
 
     def infer_dc_model(self):
         """Infer DC power model from Array module parameters."""
-        params = _common_keys(self.system.module_parameters)
+        params = _common_keys(
+            tuple(array.module_parameters for array in self.system.arrays))
         if {'A0', 'A1', 'C7'} <= params:
             return self.sapm, 'sapm'
         elif {'a_ref', 'I_L_ref', 'I_o_ref', 'R_sh_ref', 'R_s',
@@ -645,9 +647,10 @@ def infer_dc_model(self):
             return self.pvwatts_dc, 'pvwatts'
         else:
             raise ValueError('could not infer DC model from '
-                             'system.module_parameters. Check '
-                             'system.module_parameters or explicitly '
-                             'set the model with the dc_model kwarg.')
+                             'system.arrays[i].module_parameters. Check '
+                             'system.arrays[i].module_parameters or '
+                             'explicitly set the model with the dc_model '
+                             'kwarg.')
 
     def sapm(self):
         dc = self.system.sapm(self.results.effective_irradiance,
@@ -696,7 +699,7 @@ def pvwatts_dc(self):
         """Calculate DC power using the PVWatts model.
 
         Results are stored in ModelChain.results.dc. DC power is computed
-        from PVSystem.module_parameters['pdc0'] and then scaled by
+        from PVSystem.arrays[i].module_parameters['pdc0'] and then scaled by
         PVSystem.modules_per_string and PVSystem.strings_per_inverter.
 
         Returns
@@ -805,7 +808,9 @@ def aoi_model(self, model):
             self._aoi_model = partial(model, self)
 
     def infer_aoi_model(self):
-        params = _common_keys(self.system.module_parameters)
+        module_parameters = tuple(
+            array.module_parameters for array in self.system.arrays)
+        params = _common_keys(module_parameters)
         if {'K', 'L', 'n'} <= params:
             return self.physical_aoi_loss
         elif {'B5', 'B4', 'B3', 'B2', 'B1', 'B0'} <= params:
@@ -816,8 +821,8 @@ def infer_aoi_model(self):
             return self.martin_ruiz_aoi_loss
         else:
             raise ValueError('could not infer AOI model from '
-                             'system.module_parameters. Check that the '
-                             'module_parameters for all Arrays in '
+                             'system.arrays[i].module_parameters. Check that '
+                             'the module_parameters for all Arrays in '
                              'system.arrays contain parameters for '
                              'the physical, aoi, ashrae or martin_ruiz model; '
                              'explicitly set the model with the aoi_model '
@@ -880,7 +885,9 @@ def spectral_model(self, model):
 
     def infer_spectral_model(self):
         """Infer spectral model from system attributes."""
-        params = _common_keys(self.system.module_parameters)
+        module_parameters = tuple(
+            array.module_parameters for array in self.system.arrays)
+        params = _common_keys(module_parameters)
         if {'A4', 'A3', 'A2', 'A1', 'A0'} <= params:
             return self.sapm_spectral_loss
         elif ((('Technology' in params or
@@ -890,8 +897,8 @@ def infer_spectral_model(self):
             return self.first_solar_spectral_loss
         else:
             raise ValueError('could not infer spectral model from '
-                             'system.module_parameters. Check that the '
-                             'module_parameters for all Arrays in '
+                             'system.arrays[i].module_parameters. Check that '
+                             'the module_parameters for all Arrays in '
                              'system.arrays contain valid '
                              'first_solar_spectral_coefficients, a valid '
                              'Material or Technology value, or set '
@@ -940,20 +947,24 @@ def temperature_model(self, model):
             # check system.temperature_model_parameters for consistency
             name_from_params = self.infer_temperature_model().__name__
             if self._temperature_model.__name__ != name_from_params:
+                common_params = _common_keys(tuple(
+                    array.temperature_model_parameters
+                    for array in self.system.arrays))
                 raise ValueError(
                     f'Temperature model {self._temperature_model.__name__} is '
                     f'inconsistent with PVSystem temperature model '
                     f'parameters. All Arrays in system.arrays must have '
                     f'consistent parameters. Common temperature model '
-                    f'parameters: '
-                    f'{_common_keys(self.system.temperature_model_parameters)}'
+                    f'parameters: {common_params}'
                 )
         else:
             self._temperature_model = partial(model, self)
 
     def infer_temperature_model(self):
         """Infer temperature model from system attributes."""
-        params = _common_keys(self.system.temperature_model_parameters)
+        temperature_model_parameters = tuple(
+            array.temperature_model_parameters for array in self.system.arrays)
+        params = _common_keys(temperature_model_parameters)
         # remove or statement in v0.9
         if {'a', 'b', 'deltaT'} <= params or (
                 not params and self.system.racking_model is None
@@ -1057,7 +1068,7 @@ def _eff_irrad(module_parameters, total_irrad, spect_mod, aoi_mod):
                     self.results.spectral_modifier, self.results.aoi_modifier))
         else:
             self.results.effective_irradiance = _eff_irrad(
-                self.system.module_parameters,
+                self.system.arrays[0].module_parameters,
                 self.results.total_irrad,
                 self.results.spectral_modifier,
                 self.results.aoi_modifier
@@ -1481,7 +1492,7 @@ def _prepare_temperature_single_array(self, data, poa):
         self.results.cell_temperature = self._get_cell_temperature(
             data,
             poa,
-            self.system.temperature_model_parameters
+            self.system.arrays[0].temperature_model_parameters
         )
         if self.results.cell_temperature is None:
             self.temperature_model()
diff --git a/pvlib/tests/test_modelchain.py b/pvlib/tests/test_modelchain.py
index d4cb14814e..c7471d81c9 100644
--- a/pvlib/tests/test_modelchain.py
+++ b/pvlib/tests/test_modelchain.py
@@ -645,8 +645,8 @@ def test_run_model_with_weather_pvsyst_temp(sapm_dc_snl_ac_system, location,
     # test with pvsyst cell temperature model
     weather['wind_speed'] = 5
     weather['temp_air'] = 10
-    sapm_dc_snl_ac_system.racking_model = 'freestanding'
-    sapm_dc_snl_ac_system.temperature_model_parameters = \
+    sapm_dc_snl_ac_system.arrays[0].racking_model = 'freestanding'
+    sapm_dc_snl_ac_system.arrays[0].temperature_model_parameters = \
         temperature._temperature_model_params('pvsyst', 'freestanding')
     mc = ModelChain(sapm_dc_snl_ac_system, location)
     mc.temperature_model = 'pvsyst'
@@ -663,7 +663,7 @@ def test_run_model_with_weather_faiman_temp(sapm_dc_snl_ac_system, location,
     # test with faiman cell temperature model
     weather['wind_speed'] = 5
     weather['temp_air'] = 10
-    sapm_dc_snl_ac_system.temperature_model_parameters = {
+    sapm_dc_snl_ac_system.arrays[0].temperature_model_parameters = {
         'u0': 25.0, 'u1': 6.84
     }
     mc = ModelChain(sapm_dc_snl_ac_system, location)
@@ -680,7 +680,7 @@ def test_run_model_with_weather_fuentes_temp(sapm_dc_snl_ac_system, location,
                                              weather, mocker):
     weather['wind_speed'] = 5
     weather['temp_air'] = 10
-    sapm_dc_snl_ac_system.temperature_model_parameters = {
+    sapm_dc_snl_ac_system.arrays[0].temperature_model_parameters = {
         'noct_installed': 45
     }
     mc = ModelChain(sapm_dc_snl_ac_system, location)
@@ -695,9 +695,9 @@ def test_run_model_with_weather_fuentes_temp(sapm_dc_snl_ac_system, location,
 
 def test_run_model_tracker(sapm_dc_snl_ac_system, location, weather, mocker):
     system = SingleAxisTracker(
-        module_parameters=sapm_dc_snl_ac_system.module_parameters,
+        module_parameters=sapm_dc_snl_ac_system.arrays[0].module_parameters,
         temperature_model_parameters=(
-            sapm_dc_snl_ac_system.temperature_model_parameters
+            sapm_dc_snl_ac_system.arrays[0].temperature_model_parameters
         ),
         inverter_parameters=sapm_dc_snl_ac_system.inverter_parameters)
     mocker.spy(system, 'singleaxis')
@@ -716,9 +716,9 @@ def test_run_model_tracker(sapm_dc_snl_ac_system, location, weather, mocker):
 def test_run_model_tracker_list(
         sapm_dc_snl_ac_system, location, weather, mocker):
     system = SingleAxisTracker(
-        module_parameters=sapm_dc_snl_ac_system.module_parameters,
+        module_parameters=sapm_dc_snl_ac_system.arrays[0].module_parameters,
         temperature_model_parameters=(
-            sapm_dc_snl_ac_system.temperature_model_parameters
+            sapm_dc_snl_ac_system.arrays[0].temperature_model_parameters
         ),
         inverter_parameters=sapm_dc_snl_ac_system.inverter_parameters)
     mocker.spy(system, 'singleaxis')
@@ -912,8 +912,8 @@ def test_temperature_models_arrays_multi_weather(
         temp_params, temp_model,
         sapm_dc_snl_ac_system_same_arrays,
         location, weather, total_irrad):
-    sapm_dc_snl_ac_system_same_arrays.temperature_model_parameters = \
-        temp_params
+    for array in sapm_dc_snl_ac_system_same_arrays.arrays:
+        array.temperature_model_parameters = temp_params
     # set air temp so it does not default to the same value for both arrays
     weather['temp_air'] = 25
     weather_one = weather
@@ -984,9 +984,9 @@ def test_run_model_from_poa_arrays_solar_position_weather(
 def test_run_model_from_poa_tracking(sapm_dc_snl_ac_system, location,
                                      total_irrad):
     system = SingleAxisTracker(
-        module_parameters=sapm_dc_snl_ac_system.module_parameters,
+        module_parameters=sapm_dc_snl_ac_system.arrays[0].module_parameters,
         temperature_model_parameters=(
-            sapm_dc_snl_ac_system.temperature_model_parameters
+            sapm_dc_snl_ac_system.arrays[0].temperature_model_parameters
         ),
         inverter_parameters=sapm_dc_snl_ac_system.inverter_parameters)
     mc = ModelChain(system, location, aoi_model='no_loss',
@@ -1200,11 +1200,13 @@ def test_infer_dc_model(sapm_dc_snl_ac_system, cec_dc_snl_ac_system,
     temp_model_params = {'sapm': {'a': -3.40641, 'b': -0.0842075, 'deltaT': 3},
                          'pvsyst': {'u_c': 29.0, 'u_v': 0}}
     system = dc_systems[dc_model]
-    system.temperature_model_parameters = temp_model_params[
-        temp_model_function[dc_model]]
+    for array in system.arrays:
+        array.temperature_model_parameters = temp_model_params[
+            temp_model_function[dc_model]]
     # remove Adjust from model parameters for desoto, singlediode
     if dc_model in ['desoto', 'singlediode']:
-        system.module_parameters.pop('Adjust')
+        for array in system.arrays:
+            array.module_parameters.pop('Adjust')
     m = mocker.spy(pvsystem, dc_model_function[dc_model])
     mc = ModelChain(system, location,
                     aoi_model='no_loss', spectral_model='no_loss',
@@ -1229,10 +1231,11 @@ def test_singlediode_dc_arrays(location, dc_model,
                          'pvsyst': temp_pvsyst}
     temp_model = {'cec': 'sapm', 'desoto': 'sapm', 'pvsyst': 'pvsyst'}
     system = systems[dc_model]
-    system.temperature_model_parameters = temp_model_params[dc_model]
+    for array in system.arrays:
+        array.temperature_model_parameters = temp_model_params[dc_model]
     if dc_model == 'desoto':
-        for module_parameters in system.module_parameters:
-            module_parameters.pop('Adjust')
+        for array in system.arrays:
+            array.module_parameters.pop('Adjust')
     mc = ModelChain(system, location,
                     aoi_model='no_loss', spectral_model='no_loss',
                     temperature_model=temp_model[dc_model])
@@ -1274,7 +1277,7 @@ def test_infer_temp_model(location, sapm_dc_snl_ac_system,
 
 
 def test_infer_temp_model_invalid(location, sapm_dc_snl_ac_system):
-    sapm_dc_snl_ac_system.temperature_model_parameters.pop('a')
+    sapm_dc_snl_ac_system.arrays[0].temperature_model_parameters.pop('a')
     with pytest.raises(ValueError):
         ModelChain(sapm_dc_snl_ac_system, location,
                    aoi_model='physical', spectral_model='no_loss')
@@ -1452,7 +1455,7 @@ def test_aoi_model_user_func(sapm_dc_snl_ac_system, location, weather, mocker):
 ])
 def test_infer_aoi_model(location, system_no_aoi, aoi_model):
     for k in iam._IAM_MODEL_PARAMS[aoi_model]:
-        system_no_aoi.module_parameters.update({k: 1.0})
+        system_no_aoi.arrays[0].module_parameters.update({k: 1.0})
     mc = ModelChain(system_no_aoi, location, spectral_model='no_loss')
     assert isinstance(mc, ModelChain)
 
@@ -1572,18 +1575,21 @@ def test_invalid_dc_model_params(sapm_dc_snl_ac_system, cec_dc_snl_ac_system,
     kwargs = {'dc_model': 'sapm', 'ac_model': 'sandia',
               'aoi_model': 'no_loss', 'spectral_model': 'no_loss',
               'temperature_model': 'sapm', 'losses_model': 'no_loss'}
-    sapm_dc_snl_ac_system.module_parameters.pop('A0')  # remove a parameter
+    for array in sapm_dc_snl_ac_system.arrays:
+        array.module_parameters.pop('A0')  # remove a parameter
     with pytest.raises(ValueError):
         ModelChain(sapm_dc_snl_ac_system, location, **kwargs)
 
     kwargs['dc_model'] = 'singlediode'
-    cec_dc_snl_ac_system.module_parameters.pop('a_ref')  # remove a parameter
+    for array in cec_dc_snl_ac_system.arrays:
+        array.module_parameters.pop('a_ref')  # remove a parameter
     with pytest.raises(ValueError):
         ModelChain(cec_dc_snl_ac_system, location, **kwargs)
 
     kwargs['dc_model'] = 'pvwatts'
     kwargs['ac_model'] = 'pvwatts'
-    pvwatts_dc_pvwatts_ac_system.module_parameters.pop('pdc0')
+    for array in pvwatts_dc_pvwatts_ac_system.arrays:
+        array.module_parameters.pop('pdc0')
     with pytest.raises(ValueError):
         ModelChain(pvwatts_dc_pvwatts_ac_system, location, **kwargs)
 
diff --git a/pvlib/tests/test_pvsystem.py b/pvlib/tests/test_pvsystem.py
index 5c0ef7b4a2..7b04ffc0ed 100644
--- a/pvlib/tests/test_pvsystem.py
+++ b/pvlib/tests/test_pvsystem.py
@@ -1543,7 +1543,9 @@ def test_PVSystem_get_ac_invalid(cec_inverter_parameters):
 def test_PVSystem_creation():
     pv_system = pvsystem.PVSystem(module='blah', inverter='blarg')
     # ensure that parameter attributes are dict-like. GH 294
-    pv_system.module_parameters['pdc0'] = 1
+    with pytest.warns(pvlibDeprecationWarning):
+        pv_system.module_parameters['pdc0'] = 1
+
     pv_system.inverter_parameters['Paco'] = 1
 
 
@@ -1551,9 +1553,6 @@ def test_PVSystem_multiple_array_creation():
     array_one = pvsystem.Array(surface_tilt=32)
     array_two = pvsystem.Array(surface_tilt=15, module_parameters={'pdc0': 1})
     pv_system = pvsystem.PVSystem(arrays=[array_one, array_two])
-    assert pv_system.surface_tilt == (32, 15)
-    assert pv_system.surface_azimuth == (180, 180)
-    assert pv_system.module_parameters == ({}, {'pdc0': 1})
     assert pv_system.arrays == (array_one, array_two)
     with pytest.raises(TypeError):
         pvsystem.PVSystem(arrays=array_one)
@@ -1732,41 +1731,54 @@ def test_PVSystem_multi_array_get_irradiance_multi_irrad():
 
 def test_PVSystem_change_surface_azimuth():
     system = pvsystem.PVSystem(surface_azimuth=180)
-    assert system.surface_azimuth == 180
-    system.surface_azimuth = 90
-    assert system.surface_azimuth == 90
+    with pytest.warns(pvlibDeprecationWarning):
+        assert system.surface_azimuth == 180
+    with pytest.warns(pvlibDeprecationWarning):
+        system.surface_azimuth = 90
+    with pytest.warns(pvlibDeprecationWarning):
+        assert system.surface_azimuth == 90
 
 
 def test_PVSystem_get_albedo(two_array_system):
     system = pvsystem.PVSystem(
         arrays=[pvsystem.Array(albedo=0.5)]
     )
-    assert system.albedo == 0.5
-    assert two_array_system.albedo == (0.25, 0.25)
+    with pytest.warns(pvlibDeprecationWarning):
+        assert system.albedo == 0.5
 
 
 def test_PVSystem_modules_per_string():
-    system = pvsystem.PVSystem(
-        arrays=[pvsystem.Array(modules_per_string=1),
-                pvsystem.Array(modules_per_string=2)]
-    )
-    assert system.modules_per_string == (1, 2)
     system = pvsystem.PVSystem(
         arrays=[pvsystem.Array(modules_per_string=5)]
     )
-    assert system.modules_per_string == 5
+    with pytest.warns(pvlibDeprecationWarning):
+        assert system.modules_per_string == 5
 
 
 def test_PVSystem_strings_per_inverter():
-    system = pvsystem.PVSystem(
-        arrays=[pvsystem.Array(strings=2),
-                pvsystem.Array(strings=1)]
-    )
-    assert system.strings_per_inverter == (2, 1)
     system = pvsystem.PVSystem(
         arrays=[pvsystem.Array(strings=5)]
     )
-    assert system.strings_per_inverter == 5
+    with pytest.warns(pvlibDeprecationWarning):
+        assert system.strings_per_inverter == 5
+
+
+@fail_on_pvlib_version('0.10')
+@pytest.mark.parametrize('attr', ['module_parameters', 'module', 'module_type',
+                                  'temperature_model_parameters', 'albedo',
+                                  'surface_tilt', 'surface_azimuth',
+                                  'racking_model', 'modules_per_string',
+                                  'strings_per_inverter'])
+def test_PVSystem_multi_array_attributes(attr):
+    array_one = pvsystem.Array()
+    array_two = pvsystem.Array()
+    system = pvsystem.PVSystem(arrays=[array_one, array_two])
+    with pytest.raises(AttributeError):
+        getattr(system, attr)
+
+    system = pvsystem.PVSystem()
+    with pytest.warns(pvlibDeprecationWarning):
+        getattr(system, attr)
 
 
 def test_PVSystem___repr__():
@@ -1921,7 +1933,8 @@ def test_PVSystem_pvwatts_dc(pvwatts_system_defaults, mocker):
     expected = 90
     out = pvwatts_system_defaults.pvwatts_dc(irrad, temp_cell)
     pvsystem.pvwatts_dc.assert_called_once_with(
-        irrad, temp_cell, **pvwatts_system_defaults.module_parameters)
+        irrad, temp_cell,
+        **pvwatts_system_defaults.arrays[0].module_parameters)
     assert_allclose(expected, out, atol=10)
 
 
@@ -1932,7 +1945,7 @@ def test_PVSystem_pvwatts_dc_kwargs(pvwatts_system_kwargs, mocker):
     expected = 90
     out = pvwatts_system_kwargs.pvwatts_dc(irrad, temp_cell)
     pvsystem.pvwatts_dc.assert_called_once_with(
-        irrad, temp_cell, **pvwatts_system_kwargs.module_parameters)
+        irrad, temp_cell, **pvwatts_system_kwargs.arrays[0].module_parameters)
     assert_allclose(expected, out, atol=10)
 
 
diff --git a/pvlib/tests/test_tracking.py b/pvlib/tests/test_tracking.py
index 248e3e3d53..75aa58dcfd 100644
--- a/pvlib/tests/test_tracking.py
+++ b/pvlib/tests/test_tracking.py
@@ -297,7 +297,7 @@ def test_SingleAxisTracker_creation():
 
     assert system.max_angle == 45
     assert system.gcr == .25
-    assert system.module == 'blah'
+    assert system.arrays[0].module == 'blah'
     assert system.inverter == 'blarg'
 
 
@@ -309,7 +309,7 @@ def test_SingleAxisTracker_one_array_only():
             surface_azimuth=None
         )]
     )
-    assert system.module == 'foo'
+    assert system.arrays[0].module == 'foo'
     with pytest.raises(ValueError,
                        match="SingleAxisTracker does not support "
                              r"multiple arrays\."):
diff --git a/pvlib/tracking.py b/pvlib/tracking.py
index 8dd9e43461..9aa4919198 100644
--- a/pvlib/tracking.py
+++ b/pvlib/tracking.py
@@ -239,7 +239,7 @@ def get_irradiance(self, surface_tilt, surface_azimuth,
                 dni_extra=dni_extra,
                 airmass=airmass,
                 model=model,
-                albedo=self.albedo,
+                albedo=self.arrays[0].albedo,
                 **kwargs)
             for array, dni, ghi, dhi in zip(
                 self.arrays, dni, ghi, dhi

From f5494aa291583cff8642b9341950dbc3951dba49 Mon Sep 17 00:00:00 2001
From: Kevin Anderson <kevin.anderson@nrel.gov>
Date: Sat, 13 Mar 2021 13:25:18 -0700
Subject: [PATCH 03/15] whatsnew

---
 docs/sphinx/source/whatsnew/v0.9.0.rst | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/docs/sphinx/source/whatsnew/v0.9.0.rst b/docs/sphinx/source/whatsnew/v0.9.0.rst
index cb8a34756e..71fd67321d 100644
--- a/docs/sphinx/source/whatsnew/v0.9.0.rst
+++ b/docs/sphinx/source/whatsnew/v0.9.0.rst
@@ -65,6 +65,22 @@ Deprecations
   * ``ModelChain.total_irrad``
   * ``ModelChain.tracking``
 
+* The following attributes of :py:class:`pvlib.pvsystem.PVSystem` and
+  :py:class:`pvlib.tracking.SingleAxisTracker` have been deprecated in
+  favor of the corresponding :py:class:`pvlib.pvsystem.Array` attributes:
+
+  * ``PVSystem.module_parameters``
+  * ``PVSystem.module``
+  * ``PVSystem.module_type``
+  * ``PVSystem.albedo``
+  * ``PVSystem.temperature_model_parameters``
+  * ``PVSystem.surface_tilt``
+  * ``PVSystem.surface_azimuth``
+  * ``PVSystem.racking_model``
+  * ``PVSystem.modules_per_string``
+  * ``PVSystem.strings_per_inverter``
+
+
 Enhancements
 ~~~~~~~~~~~~
 * Add :func:`~pvlib.iotools.read_bsrn` for reading BSRN solar radiation data

From 9852c1616700a3f07fb996c3004111c8f2f12b32 Mon Sep 17 00:00:00 2001
From: Kevin Anderson <kevin.anderson@nrel.gov>
Date: Sun, 28 Mar 2021 15:56:13 -0600
Subject: [PATCH 04/15] remove unnecessary fixture, on the correct branch this
 time

---
 pvlib/tests/test_pvsystem.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pvlib/tests/test_pvsystem.py b/pvlib/tests/test_pvsystem.py
index 7b04ffc0ed..4a4f4220ec 100644
--- a/pvlib/tests/test_pvsystem.py
+++ b/pvlib/tests/test_pvsystem.py
@@ -1739,7 +1739,7 @@ def test_PVSystem_change_surface_azimuth():
         assert system.surface_azimuth == 90
 
 
-def test_PVSystem_get_albedo(two_array_system):
+def test_PVSystem_get_albedo():
     system = pvsystem.PVSystem(
         arrays=[pvsystem.Array(albedo=0.5)]
     )

From 49635f4b37541684081d5fa812216cabe91d13c0 Mon Sep 17 00:00:00 2001
From: Kevin Anderson <57452607+kanderso-nrel@users.noreply.github.com>
Date: Tue, 11 May 2021 20:59:54 -0600
Subject: [PATCH 05/15] Update pvlib/modelchain.py

Co-authored-by: Cliff Hansen <cwhanse@sandia.gov>
---
 pvlib/modelchain.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/pvlib/modelchain.py b/pvlib/modelchain.py
index 8f43d3616b..ae5962da50 100644
--- a/pvlib/modelchain.py
+++ b/pvlib/modelchain.py
@@ -328,7 +328,9 @@ class ModelChain:
 
     dc_model: None, str, or function, default None
         If None, the model will be inferred from the contents of
-        system.arrays[i].module_parameters. Valid strings are 'sapm',
+        If None, the model will be inferred from the parameters that
+        are common to all of system.arrays[i].module_parameters. 
+        Valid strings are 'sapm',
         'desoto', 'cec', 'pvsyst', 'pvwatts'. The ModelChain instance will
         be passed as the first argument to a user-defined function.
 

From 7588a813ebb8596d510a0baf24a069b248ecbd30 Mon Sep 17 00:00:00 2001
From: Kevin Anderson <kevin.anderson@nrel.gov>
Date: Tue, 11 May 2021 21:00:48 -0600
Subject: [PATCH 06/15] reflow docstring

---
 pvlib/modelchain.py | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/pvlib/modelchain.py b/pvlib/modelchain.py
index ae5962da50..f817b5e4b6 100644
--- a/pvlib/modelchain.py
+++ b/pvlib/modelchain.py
@@ -327,12 +327,11 @@ class ModelChain:
         Passed to location.get_airmass.
 
     dc_model: None, str, or function, default None
-        If None, the model will be inferred from the contents of
         If None, the model will be inferred from the parameters that
-        are common to all of system.arrays[i].module_parameters. 
-        Valid strings are 'sapm',
-        'desoto', 'cec', 'pvsyst', 'pvwatts'. The ModelChain instance will
-        be passed as the first argument to a user-defined function.
+        are common to all of system.arrays[i].module_parameters.
+        Valid strings are 'sapm', 'desoto', 'cec', 'pvsyst', 'pvwatts'.
+        The ModelChain instance will be passed as the first argument
+        to a user-defined function.
 
     ac_model: None, str, or function, default None
         If None, the model will be inferred from the contents of

From 1824bd60fd7334513e0496c66e6d36c564a1677f Mon Sep 17 00:00:00 2001
From: Kevin Anderson <kevin.anderson@nrel.gov>
Date: Tue, 11 May 2021 21:04:51 -0600
Subject: [PATCH 07/15] more docstring updates

---
 pvlib/modelchain.py | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/pvlib/modelchain.py b/pvlib/modelchain.py
index f817b5e4b6..91d7d9d55e 100644
--- a/pvlib/modelchain.py
+++ b/pvlib/modelchain.py
@@ -334,23 +334,25 @@ class ModelChain:
         to a user-defined function.
 
     ac_model: None, str, or function, default None
-        If None, the model will be inferred from the contents of
-        system.inverter_parameters and system.arrays[i].module_parameters.
+        If None, the model will be inferred from the parameters that
+        are common to all of system.inverter_parameters.
         Valid strings are 'sandia', 'adr', 'pvwatts'. The
         ModelChain instance will be passed as the first argument to a
         user-defined function.
 
     aoi_model: None, str, or function, default None
-        If None, the model will be inferred from the contents of
-        system.arrays[i].module_parameters. Valid strings are 'physical',
-        'ashrae', 'sapm', 'martin_ruiz', 'no_loss'. The ModelChain instance
-        will be passed as the first argument to a user-defined function.
+        If None, the model will be inferred from the parameters that
+        are common to all of system.arrays[i].module_parameters.
+        Valid strings are 'physical', 'ashrae', 'sapm', 'martin_ruiz',
+        'no_loss'. The ModelChain instance will be passed as the
+        first argument to a user-defined function.
 
     spectral_model: None, str, or function, default None
-        If None, the model will be inferred from the contents of
-        system.arrays[i].module_parameters. Valid strings are 'sapm',
-        'first_solar', 'no_loss'. The ModelChain instance will be passed
-        as the first argument to a user-defined function.
+        If None, the model will be inferred from the parameters that
+        are common to all of system.arrays[i].module_parameters.
+        Valid strings are 'sapm', 'first_solar', 'no_loss'.
+        The ModelChain instance will be passed as the first argument to
+        a user-defined function.
 
     temperature_model: None, str or function, default None
         Valid strings are 'sapm', 'pvsyst', 'faiman', and 'fuentes'.

From 01099eda962aa648fac272d29c67287cf30ca77d Mon Sep 17 00:00:00 2001
From: Kevin Anderson <kevin.anderson@nrel.gov>
Date: Wed, 19 May 2021 13:38:40 -0600
Subject: [PATCH 08/15] alphabetize

---
 docs/sphinx/source/whatsnew/v0.9.0.rst | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/docs/sphinx/source/whatsnew/v0.9.0.rst b/docs/sphinx/source/whatsnew/v0.9.0.rst
index 67c07a1aa6..43b49a33a2 100644
--- a/docs/sphinx/source/whatsnew/v0.9.0.rst
+++ b/docs/sphinx/source/whatsnew/v0.9.0.rst
@@ -89,16 +89,16 @@ Deprecations
   :py:class:`pvlib.tracking.SingleAxisTracker` have been deprecated in
   favor of the corresponding :py:class:`pvlib.pvsystem.Array` attributes:
 
-  * ``PVSystem.module_parameters``
+  * ``PVSystem.albedo``
   * ``PVSystem.module``
+  * ``PVSystem.module_parameters``
   * ``PVSystem.module_type``
-  * ``PVSystem.albedo``
-  * ``PVSystem.temperature_model_parameters``
-  * ``PVSystem.surface_tilt``
-  * ``PVSystem.surface_azimuth``
-  * ``PVSystem.racking_model``
   * ``PVSystem.modules_per_string``
+  * ``PVSystem.racking_model``
   * ``PVSystem.strings_per_inverter``
+  * ``PVSystem.surface_tilt``
+  * ``PVSystem.surface_azimuth``
+  * ``PVSystem.temperature_model_parameters``
 
 
 Enhancements

From a29acaeaa2c8645d5794c0cc1dd206a30eda9ec9 Mon Sep 17 00:00:00 2001
From: Kevin Anderson <kevin.anderson@nrel.gov>
Date: Wed, 19 May 2021 13:57:51 -0600
Subject: [PATCH 09/15] rephrase error message

---
 pvlib/modelchain.py | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/pvlib/modelchain.py b/pvlib/modelchain.py
index f1b42e5e2c..eb0db817fd 100644
--- a/pvlib/modelchain.py
+++ b/pvlib/modelchain.py
@@ -735,11 +735,11 @@ def infer_dc_model(self):
         elif {'pdc0', 'gamma_pdc'} <= params:
             return self.pvwatts_dc, 'pvwatts'
         else:
-            raise ValueError('could not infer DC model from '
-                             'system.arrays[i].module_parameters. Check '
-                             'system.arrays[i].module_parameters or '
-                             'explicitly set the model with the dc_model '
-                             'kwarg.')
+            raise ValueError(
+                'Could not infer DC model from the module_parameters '
+                'attributes of system.arrays. Check the module_parameters '
+                'attributes or explicitly set the model with the dc_model '
+                'keyword argument.')
 
     def sapm(self):
         dc = self.system.sapm(self.results.effective_irradiance,

From c775bc0fc9796f46ba366ea3e28b06ca69872e74 Mon Sep 17 00:00:00 2001
From: Kevin Anderson <kevin.anderson@nrel.gov>
Date: Wed, 19 May 2021 14:32:30 -0600
Subject: [PATCH 10/15] pvsystem.rst edits

---
 docs/sphinx/source/pvsystem.rst | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/docs/sphinx/source/pvsystem.rst b/docs/sphinx/source/pvsystem.rst
index 58d943ac79..782680c40c 100644
--- a/docs/sphinx/source/pvsystem.rst
+++ b/docs/sphinx/source/pvsystem.rst
@@ -97,7 +97,7 @@ default value may be overridden by specifying the `temp_ref` key in the
 
 .. ipython:: python
 
-    system.module_parameters['temp_ref'] = 0
+    system.arrays[0].module_parameters['temp_ref'] = 0
     # lower temp_ref should lead to lower DC power than calculated above
     pdc = system.pvwatts_dc(1000, 30)
     print(pdc)
@@ -124,7 +124,7 @@ passed to `PVSystem.module_parameters`:
     inverter_parameters = {'pdc0': 5000, 'eta_inv_nom': 0.96}
     system = pvsystem.PVSystem(module_parameters=module_parameters,
                                inverter_parameters=inverter_parameters)
-    print(system.module_parameters)
+    print(system.arrays[0].module_parameters)
     print(system.inverter_parameters)
 
 
@@ -142,12 +142,9 @@ provided for each array, and the arrays are provided to
     array_two = pvsystem.Array(module_parameters=module_parameters)
     system_two_arrays = pvsystem.PVSystem(arrays=[array_one, array_two],
                                           inverter_parameters=inverter_parameters)
-    print(system_two_arrays.module_parameters)
+    print([array.module_parameters for array in system_two_arrays.arrays])
     print(system_two_arrays.inverter_parameters)
 
-Note that in the case of a PV system with multiple arrays, the
-:py:class:`~pvlib.pvsystem.PVSystem` attribute `module_parameters` contains
-a tuple with the `module_parameters` for each array.
 
 The :py:class:`~pvlib.pvsystem.Array` class includes those 
 :py:class:`~pvlib.pvsystem.PVSystem` attributes that may vary from array
@@ -188,7 +185,8 @@ these parameters can be specified using the `PVSystem.surface_tilt` and
 
     # single south-facing array at 20 deg tilt
     system_one_array = pvsystem.PVSystem(surface_tilt=20, surface_azimuth=180)
-    print(system_one_array.surface_tilt, system_one_array.surface_azimuth)
+    print(system_one_array.arrays[0].surface_tilt,
+          system_one_array.arrays[0].surface_azimuth)
 
 
 In the case of a PV system with several arrays, the parameters are specified
@@ -201,8 +199,7 @@ for each array using the attributes `Array.surface_tilt` and `Array.surface_azim
     array_two = pvsystem.Array(surface_tilt=30, surface_azimuth=220)
     system = pvsystem.PVSystem(arrays=[array_one, array_two])
     system.num_arrays
-    system.surface_tilt
-    system.surface_azimuth
+    [array.surface_tilt, array.surface_azimuth for array in system.arrays]
 
 
 The `surface_tilt` and `surface_azimuth` attributes are used in PVSystem
@@ -218,7 +215,8 @@ and `solar_azimuth` as arguments.
 
     # single south-facing array at 20 deg tilt
     system_one_array = pvsystem.PVSystem(surface_tilt=20, surface_azimuth=180)
-    print(system_one_array.surface_tilt, system_one_array.surface_azimuth)
+    print(system_one_array.arrays[0].surface_tilt,
+          system_one_array.arrays[0].surface_azimuth)
 
     # call get_aoi with solar_zenith, solar_azimuth
     aoi = system_one_array.get_aoi(solar_zenith=30, solar_azimuth=180)

From 7b963953bba50a12a680862493b37e9f35493940 Mon Sep 17 00:00:00 2001
From: Kevin Anderson <kevin.anderson@nrel.gov>
Date: Wed, 19 May 2021 14:40:41 -0600
Subject: [PATCH 11/15] create missing PVSystem setters

---
 pvlib/pvsystem.py | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/pvlib/pvsystem.py b/pvlib/pvsystem.py
index 05fa5d2aab..f2d07caa2b 100644
--- a/pvlib/pvsystem.py
+++ b/pvlib/pvsystem.py
@@ -1117,18 +1117,36 @@ def dc_ohms_from_percent(self):
     def module_parameters(self):
         return tuple(array.module_parameters for array in self.arrays)
 
+    @module_parameters.setter
+    @_check_deprecated_passthrough
+    def module_parameters(self, value):
+        for array in self.arrays:
+            array.module_parameters = value
+
     @property
     @_unwrap_single_value
     @_check_deprecated_passthrough
     def module(self):
         return tuple(array.module for array in self.arrays)
 
+    @module.setter
+    @_check_deprecated_passthrough
+    def module(self, value):
+        for array in self.arrays:
+            array.module = value
+
     @property
     @_unwrap_single_value
     @_check_deprecated_passthrough
     def module_type(self):
         return tuple(array.module_type for array in self.arrays)
 
+    @module_type.setter
+    @_check_deprecated_passthrough
+    def module_type(self, value):
+        for array in self.arrays:
+            array.module_type = value
+
     @property
     @_unwrap_single_value
     @_check_deprecated_passthrough
@@ -1172,6 +1190,12 @@ def surface_azimuth(self, value):
     def albedo(self):
         return tuple(array.albedo for array in self.arrays)
 
+    @albedo.setter
+    @_check_deprecated_passthrough
+    def albedo(self, value):
+        for array in self.arrays:
+            array.albedo = value
+
     @property
     @_unwrap_single_value
     @_check_deprecated_passthrough
@@ -1190,12 +1214,24 @@ def racking_model(self, value):
     def modules_per_string(self):
         return tuple(array.modules_per_string for array in self.arrays)
 
+    @modules_per_string.setter
+    @_check_deprecated_passthrough
+    def modules_per_string(self, value):
+        for array in self.arrays:
+            array.modules_per_string = value
+
     @property
     @_unwrap_single_value
     @_check_deprecated_passthrough
     def strings_per_inverter(self):
         return tuple(array.strings for array in self.arrays)
 
+    @strings_per_inverter.setter
+    @_check_deprecated_passthrough
+    def strings_per_inverter(self, value):
+        for array in self.arrays:
+            array.strings = value
+
     @property
     def num_arrays(self):
         """The number of Arrays in the system."""

From 71b07da40c08aa66a92bbba0c14ebea2de355628 Mon Sep 17 00:00:00 2001
From: Kevin Anderson <kevin.anderson@nrel.gov>
Date: Wed, 19 May 2021 14:41:59 -0600
Subject: [PATCH 12/15] rephrase error message

---
 pvlib/pvsystem.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/pvlib/pvsystem.py b/pvlib/pvsystem.py
index f2d07caa2b..43b856b903 100644
--- a/pvlib/pvsystem.py
+++ b/pvlib/pvsystem.py
@@ -85,7 +85,8 @@ def wrapper(self, *args, **kwargs):
         if len(self.arrays) > 1:
             raise AttributeError(
                 f'{class_name}.{pvsystem_attr} not supported for multi-array '
-                f'systems. Use {alternative} instead.')
+                f'systems. Set {array_attr} for each Array in '
+                f'{class_name}.arrays instead.')
 
         wrapped = deprecated('0.9', alternative=alternative, removal='0.10',
                              name=f"{class_name}.{pvsystem_attr}")(func)

From 53ea45d11e6bf15cca918eb07591cd25259464df Mon Sep 17 00:00:00 2001
From: Kevin Anderson <kevin.anderson@nrel.gov>
Date: Wed, 19 May 2021 14:47:28 -0600
Subject: [PATCH 13/15] another pvsystem.rst edit

---
 docs/sphinx/source/pvsystem.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/docs/sphinx/source/pvsystem.rst b/docs/sphinx/source/pvsystem.rst
index 782680c40c..25b9a1c9e6 100644
--- a/docs/sphinx/source/pvsystem.rst
+++ b/docs/sphinx/source/pvsystem.rst
@@ -199,7 +199,7 @@ for each array using the attributes `Array.surface_tilt` and `Array.surface_azim
     array_two = pvsystem.Array(surface_tilt=30, surface_azimuth=220)
     system = pvsystem.PVSystem(arrays=[array_one, array_two])
     system.num_arrays
-    [array.surface_tilt, array.surface_azimuth for array in system.arrays]
+    [(array.surface_tilt, array.surface_azimuth) for array in system.arrays]
 
 
 The `surface_tilt` and `surface_azimuth` attributes are used in PVSystem

From 4619a1eceb3c228fb27a6c2303f1f4793f1b0502 Mon Sep 17 00:00:00 2001
From: Kevin Anderson <kevin.anderson@nrel.gov>
Date: Wed, 19 May 2021 15:03:27 -0600
Subject: [PATCH 14/15] fix coverage drop

---
 pvlib/tests/test_pvsystem.py | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/pvlib/tests/test_pvsystem.py b/pvlib/tests/test_pvsystem.py
index 0f092744c4..d0abdefd4b 100644
--- a/pvlib/tests/test_pvsystem.py
+++ b/pvlib/tests/test_pvsystem.py
@@ -1814,10 +1814,16 @@ def test_PVSystem_multi_array_attributes(attr):
     with pytest.raises(AttributeError):
         getattr(system, attr)
 
+    with pytest.raises(AttributeError):
+        setattr(system, attr, 'dummy')
+
     system = pvsystem.PVSystem()
     with pytest.warns(pvlibDeprecationWarning):
         getattr(system, attr)
 
+    with pytest.warns(pvlibDeprecationWarning):
+        setattr(system, attr, 'dummy')
+
 
 def test_PVSystem___repr__():
     system = pvsystem.PVSystem(

From 62a549e01b39b3c0713f35a7c5130b31dd89ea38 Mon Sep 17 00:00:00 2001
From: Kevin Anderson <kevin.anderson@nrel.gov>
Date: Thu, 20 May 2021 15:22:13 -0600
Subject: [PATCH 15/15] add missing test

---
 pvlib/tests/test_modelchain.py | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/pvlib/tests/test_modelchain.py b/pvlib/tests/test_modelchain.py
index fc4b8162d1..4d2edbccae 100644
--- a/pvlib/tests/test_modelchain.py
+++ b/pvlib/tests/test_modelchain.py
@@ -1259,6 +1259,15 @@ def test_infer_dc_model(sapm_dc_snl_ac_system, cec_dc_snl_ac_system,
     assert isinstance(mc.results.dc, (pd.Series, pd.DataFrame))
 
 
+def test_infer_dc_model_incomplete(multi_array_sapm_dc_snl_ac_system,
+                                   location):
+    match = 'Could not infer DC model from the module_parameters attributes '
+    system = multi_array_sapm_dc_snl_ac_system['two_array_system']
+    system.arrays[0].module_parameters.pop('A0')
+    with pytest.raises(ValueError, match=match):
+        ModelChain(system, location)
+
+
 @pytest.mark.parametrize('dc_model', ['cec', 'desoto', 'pvsyst'])
 def test_singlediode_dc_arrays(location, dc_model,
                                cec_dc_snl_ac_arrays,
@@ -1721,7 +1730,9 @@ def test_invalid_dc_model_params(sapm_dc_snl_ac_system, cec_dc_snl_ac_system,
     kwargs['ac_model'] = 'pvwatts'
     for array in pvwatts_dc_pvwatts_ac_system.arrays:
         array.module_parameters.pop('pdc0')
-    with pytest.raises(ValueError):
+
+    match = 'one or more Arrays are missing one or more required parameters'
+    with pytest.raises(ValueError, match=match):
         ModelChain(pvwatts_dc_pvwatts_ac_system, location, **kwargs)