Handle poa_global and effective_irradiance for cell temperature models

docs/sphinx/source/whatsnew/v0.9.0.rst

@@ -46,6 +46,10 @@ Enhancements
   :py:class:`~pvlib.pvsystem.PVSystem` and
   :py:class:`~pvlib.modelchain.ModelChain` (as ``ac_model='sandia_multi'``).
   (:pull:`1076`, :issue:`1067`)
+* :py:class:`~pvlib.modelchain.ModelChain` 'run_model' methods now
+  automatically switch to using 'effective_irradiance' (if available) for
+  cell temperature models, when 'poa_global' is not provided in input weather
+  or calculated from input weather data.
 
 Bug fixes
 ~~~~~~~~~

pvlib/modelchain.py

@@ -1023,7 +1023,9 @@ def _set_celltemp(self, model):
         -------
         self
         """
-        poa = _tuple_from_dfs(self.results.total_irrad, 'poa_global')
+
+        poa = self._irrad_for_celltemp(self.results.total_irrad,
+                                       self.results.effective_irradiance)
         temp_air = _tuple_from_dfs(self.weather, 'temp_air')
         wind_speed = _tuple_from_dfs(self.weather, 'wind_speed')
         self.results.cell_temperature = model(poa, temp_air, wind_speed)
@@ -1041,6 +1043,28 @@ def faiman_temp(self):
     def fuentes_temp(self):
         return self._set_celltemp(self.system.fuentes_celltemp)
 
+    @staticmethod
+    def _irrad_for_celltemp(total_irrad, effective_irradiance):
+        """
+        Determine irradiance to use for cell temperature models, in order
+        of preference 'poa_global' or 'effective_irradiance'
+
+        Returns
+        -------
+        None.
+
+        """
+        if isinstance(total_irrad, tuple):
+            if all(['poa_global' in df for df in total_irrad]):
+                return _tuple_from_dfs(total_irrad, 'poa_global')
+            else:
+                return effective_irradiance
+        else:
+            if 'poa_global' in total_irrad:
+                return total_irrad['poa_global']
+            else:
+                return effective_irradiance
+
     @property
     def losses_model(self):
         return self._losses_model
@@ -1464,13 +1488,22 @@ def prepare_inputs_from_poa(self, data):
         return self
 
     def _get_cell_temperature(self, data,
-                              total_irrad, temperature_model_parameters):
+                              poa, temperature_model_parameters):
         """Extract the cell temperature data from a DataFrame.
 
-        If 'cell_temperature' column exists then it is returned. If
-        'module_temperature' column exists then it is used to calculate
-        the cell temperature. If neither column exists then None is
+        If 'cell_temperature' column exists in data then it is returned. If
+        'module_temperature' column exists in data, then it is used with poa to
+        calculate the cell temperature. If neither column exists then None is
         returned.
+
+        Parameters
+        ----------
+        data : DataFrame (not a tuple of DataFrame)
+        poa : Series (not a tuple of Series)
+
+        Returns
+        -------
+        Series
         """
         if 'cell_temperature' in data:
             return data['cell_temperature']
@@ -1483,14 +1516,14 @@ def _get_cell_temperature(self, data,
             # use SAPM cell temperature model only
             return pvlib.temperature.sapm_cell_from_module(
                 module_temperature=data['module_temperature'],
-                poa_global=total_irrad['poa_global'],
+                poa_global=poa,
                 deltaT=temperature_model_parameters['deltaT'])
 
-    def _prepare_temperature_single_array(self, data):
-        """Set cell_temperature using a single weather data frame."""
+    def _prepare_temperature_single_array(self, data, poa):
+        """Set cell_temperature using a single data frame."""
         self.results.cell_temperature = self._get_cell_temperature(
             data,
-            self.results.total_irrad,
+            poa,
             self.system.temperature_model_parameters
         )
         if self.results.cell_temperature is None:
@@ -1505,7 +1538,7 @@ def _prepare_temperature(self, data=None):
         If 'data' contains 'cell_temperature', these values are assigned to
         attribute ``cell_temperature``. If 'data' contains 'module_temperature`
         and `temperature_model' is 'sapm', cell temperature is calculated using
-        :py:func:`pvlib.temperature.sapm_celL_from_module`. Otherwise, cell
+        :py:func:`pvlib.temperature.sapm_cell_from_module`. Otherwise, cell
         temperature is calculated by 'temperature_model'.
 
         Parameters
@@ -1521,14 +1554,16 @@ def _prepare_temperature(self, data=None):
         Assigns attribute ``results.cell_temperature``.
 
         """
+        poa = self._irrad_for_celltemp(self.results.total_irrad,
+                                       self.results.effective_irradiance)
         if not isinstance(data, tuple) and self.system.num_arrays > 1:
+            # broadcast data to all arrays
             data = (data,) * self.system.num_arrays
         elif not isinstance(data, tuple):
-            return self._prepare_temperature_single_array(data)
+            return self._prepare_temperature_single_array(data, poa)
         given_cell_temperature = tuple(itertools.starmap(
             self._get_cell_temperature,
-            zip(data, self.results.total_irrad,
-                self.system.temperature_model_parameters)
+            zip(data, poa, self.system.temperature_model_parameters)
         ))
         # If cell temperature has been specified for all arrays return
         # immediately and do not try to compute it.

pvlib/temperature.py

@@ -49,7 +49,7 @@ def _temperature_model_params(model, parameter_set):
 
 
 def sapm_cell(poa_global, temp_air, wind_speed, a, b, deltaT,
-              irrad_ref=1000):
+              irrad_ref=1000.):
     r'''
     Calculate cell temperature per the Sandia Array Performance Model.
 
@@ -215,7 +215,7 @@ def sapm_module(poa_global, temp_air, wind_speed, a, b):
 
 
 def sapm_cell_from_module(module_temperature, poa_global, deltaT,
-                          irrad_ref=1000):
+                          irrad_ref=1000.):
     r'''
     Calculate cell temperature from module temperature using the Sandia Array
     Performance Model.

pvlib/tests/test_modelchain.py

@@ -918,6 +918,18 @@ def test_run_model_from_effective_irradiance(sapm_dc_snl_ac_system, location,
     assert_series_equal(ac, expected)
 
 
+def test_run_model_from_effective_irradiance_no_poa_global(
+        sapm_dc_snl_ac_system, location, weather, total_irrad):
+    data = weather.copy()
+    data['effective_irradiance'] = total_irrad['poa_global']
+    mc = ModelChain(sapm_dc_snl_ac_system, location, aoi_model='no_loss',
+                    spectral_model='no_loss')
+    ac = mc.run_model_from_effective_irradiance(data).results.ac
+    expected = pd.Series(np.array([149.280238, 96.678385]),
+                         index=data.index)
+    assert_series_equal(ac, expected)
+
+
 @pytest.mark.parametrize("input_type", [tuple, list])
 def test_run_model_from_effective_irradiance_arrays_error(
         sapm_dc_snl_ac_system_Array, location, weather, total_irrad,