Updated modelchain.py #893 (#936)

This PR handles, the case where pressure or temp_air is not in weather, using the pvlib.tools._build_kwargs method, as keyword arguments. #893

Author: Ahanmr

pvlib/modelchain.py

@@ -16,7 +16,7 @@
 import pvlib.irradiance  # avoid name conflict with full import
 from pvlib.pvsystem import _DC_MODEL_PARAMS
 from pvlib._deprecation import pvlibDeprecationWarning
-
+from pvlib.tools import _build_kwargs
 
 def basic_chain(times, latitude, longitude,
                 module_parameters, temperature_model_parameters,
@@ -870,9 +870,15 @@ def prepare_inputs(self, weather, times=None):
                           'is used for times.', pvlibDeprecationWarning)
 
         self.times = self.weather.index
+        try:
+            kwargs = _build_kwargs(['pressure', 'temp_air'], weather)
+            kwargs['temperature'] = kwargs.pop('temp_air')
+        except KeyError:
+            pass
 
         self.solar_position = self.location.get_solarposition(
-            self.weather.index, method=self.solar_position_method)
+            self.weather.index, method=self.solar_position_method,
+            **kwargs)
 
         self.airmass = self.location.get_airmass(
             solar_position=self.solar_position, model=self.airmass_model)