refactor ModelChain._prep_inputs_solar_pos for wx in poa solpos (#1140)

* refactor ModelChain._prep_inputs_solar_pos for wx in poa solpos

* pr number

* add tests

* compat with py 3.6 and 3.7

Author: wholmgren

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

@@ -90,6 +90,9 @@ Enhancements
 
 Bug fixes
 ~~~~~~~~~
+* Pass weather data to solar position calculations in
+  :ref:meth:`~pvlib.modelchain.ModelChain.prepare_inputs_from_poa`.
+  (:issue:`1065`, :pull:`1140`)
 
 Testing
 ~~~~~~~

pvlib/modelchain.py

@@ -1210,10 +1210,19 @@ def _complete_irradiance(self, weather):
                 weather.ghi - weather.dni *
                 tools.cosd(self.results.solar_position.zenith))
 
-    def _prep_inputs_solar_pos(self, kwargs={}):
+    def _prep_inputs_solar_pos(self, weather):
         """
         Assign solar position
         """
+        # build weather kwargs for solar position calculation
+        kwargs = _build_kwargs(['pressure', 'temp_air'],
+                               weather[0] if isinstance(weather, tuple)
+                               else weather)
+        try:
+            kwargs['temperature'] = kwargs.pop('temp_air')
+        except KeyError:
+            pass
+
         self.results.solar_position = self.location.get_solarposition(
             self.times, method=self.solar_position_method,
             **kwargs)
@@ -1363,16 +1372,7 @@ def prepare_inputs(self, weather):
         self._assign_weather(weather)
         self._assign_times()
 
-        # build kwargs for solar position calculation
-        try:
-            press_temp = _build_kwargs(['pressure', 'temp_air'],
-                                       weather[0] if isinstance(weather, tuple)
-                                       else weather)
-            press_temp['temperature'] = press_temp.pop('temp_air')
-        except KeyError:
-            pass
-
-        self._prep_inputs_solar_pos(press_temp)
+        self._prep_inputs_solar_pos(weather)
         self._prep_inputs_airmass()
 
         # PVSystem.get_irradiance and SingleAxisTracker.get_irradiance
@@ -1470,7 +1470,7 @@ def prepare_inputs_from_poa(self, data):
                                         'poa_diffuse'])
         self._assign_total_irrad(data)
 
-        self._prep_inputs_solar_pos()
+        self._prep_inputs_solar_pos(data)
         self._prep_inputs_airmass()
 
         if isinstance(self.system, SingleAxisTracker):

pvlib/tests/test_modelchain.py

@@ -886,6 +886,20 @@ def test_temperature_models_arrays_multi_weather(
             != mc.results.cell_temperature[1]).all()
 
 
+def test_run_model_solar_position_weather(
+        pvwatts_dc_pvwatts_ac_system, location, weather, mocker):
+    mc = ModelChain(pvwatts_dc_pvwatts_ac_system, location,
+                    aoi_model='no_loss', spectral_model='no_loss')
+    weather['pressure'] = 90000
+    weather['temp_air'] = 25
+    m = mocker.spy(location, 'get_solarposition')
+    mc.run_model(weather)
+    # assert_called_once_with cannot be used with series, so need to use
+    # assert_series_equal on call_args
+    assert_series_equal(m.call_args[1]['temperature'], weather['temp_air'])
+    assert_series_equal(m.call_args[1]['pressure'], weather['pressure'])
+
+
 def test_run_model_from_poa(sapm_dc_snl_ac_system, location, total_irrad):
     mc = ModelChain(sapm_dc_snl_ac_system, location, aoi_model='no_loss',
                     spectral_model='no_loss')
@@ -909,6 +923,24 @@ def test_run_model_from_poa_arrays(sapm_dc_snl_ac_system_Array, location,
     assert_frame_equal(mc.results.dc[0], mc.results.dc[1])
 
 
+def test_run_model_from_poa_arrays_solar_position_weather(
+        sapm_dc_snl_ac_system_Array, location, weather, total_irrad, mocker):
+    data = weather.copy()
+    data[['poa_global', 'poa_diffuse', 'poa_direct']] = total_irrad
+    data['pressure'] = 90000
+    data['temp_air'] = 25
+    data2 = data.copy()
+    data2['pressure'] = 95000
+    data2['temp_air'] = 30
+    mc = ModelChain(sapm_dc_snl_ac_system_Array, location, aoi_model='no_loss',
+                    spectral_model='no_loss')
+    m = mocker.spy(location, 'get_solarposition')
+    mc.run_model_from_poa((data, data2))
+    # mc uses only the first weather data for solar position corrections
+    assert_series_equal(m.call_args[1]['temperature'], data['temp_air'])
+    assert_series_equal(m.call_args[1]['pressure'], data['pressure'])
+
+
 def test_run_model_from_poa_tracking(sapm_dc_snl_ac_system, location,
                                      total_irrad):
     system = SingleAxisTracker(