add optional surface_tilt parameter to PVSystem.fuentes_celltemp

Author: kandersolar

pvlib/pvsystem.py

@@ -729,7 +729,8 @@ def faiman_celltemp(self, poa_global, temp_air, wind_speed=1.0):
         )
 
     @_unwrap_single_value
-    def fuentes_celltemp(self, poa_global, temp_air, wind_speed):
+    def fuentes_celltemp(self, poa_global, temp_air, wind_speed,
+                         surface_tilt=None):
         """
         Use :py:func:`temperature.fuentes` to calculate cell temperature.
 
@@ -744,6 +745,11 @@ def fuentes_celltemp(self, poa_global, temp_air, wind_speed):
         wind_speed : pandas Series or tuple of Series
             Wind speed [m/s]
 
+        surface_tilt : pandas Series or tuple of Series, optional
+            Panel tilt from horizontal. Superseded by ``surface_tilt``
+            values in ``self.arrays[i].temperature_model_parameters``
+            (see Notes). [degrees]
+
         Returns
         -------
         temperature_cell : Series or tuple of Series
@@ -754,11 +760,11 @@ def fuentes_celltemp(self, poa_global, temp_air, wind_speed):
         The Fuentes thermal model uses the module surface tilt for convection
         modeling. The SAM implementation of PVWatts hardcodes the surface tilt
         value at 30 degrees, ignoring whatever value is used for irradiance
-        transposition. This method defaults to using ``self.surface_tilt``, but
-        if you want to match the PVWatts behavior, you can override it by
-        including a ``surface_tilt`` value in ``temperature_model_parameters``.
+        transposition.  If you want to match the PVWatts behavior, specify a
+        ``surface_tilt`` value in the Array's ``temperature_model_parameters``.
 
-        The `temp_air` and `wind_speed` parameters may be passed as tuples
+        The `temp_air`, `wind_speed`, and `surface_tilt` parameters may be
+        passed as tuples
         to provide different values for each Array in the system. If not
         passed as a tuple then the same value is used for input to each Array.
         If passed as a tuple the length must be the same as the number of
@@ -769,12 +775,10 @@ def fuentes_celltemp(self, poa_global, temp_air, wind_speed):
         poa_global = self._validate_per_array(poa_global)
         temp_air = self._validate_per_array(temp_air, system_wide=True)
         wind_speed = self._validate_per_array(wind_speed, system_wide=True)
+        surface_tilt = self._validate_per_array(wind_speed, system_wide=True)
 
-        def _build_kwargs_fuentes(array):
-            # TODO: I think there should be an interface function so that
-            # directly accessing surface_tilt isn't necessary. Doesn't this
-            # break for SAT?
-            kwargs = {'surface_tilt': array.mount.surface_tilt}
+        def _build_kwargs_fuentes(array, user_tilt):
+            kwargs = {'surface_tilt': user_tilt}
             temp_model_kwargs = _build_kwargs([
                 'noct_installed', 'module_height', 'wind_height', 'emissivity',
                 'absorption', 'surface_tilt', 'module_width', 'module_length'],
@@ -784,9 +788,9 @@ def _build_kwargs_fuentes(array):
         return tuple(
             temperature.fuentes(
                 poa_global, temp_air, wind_speed,
-                **_build_kwargs_fuentes(array))
-            for array, poa_global, temp_air, wind_speed in zip(
-                self.arrays, poa_global, temp_air, wind_speed
+                **_build_kwargs_fuentes(array, user_tilt))
+            for array, poa_global, temp_air, wind_speed, user_tilt in zip(
+                self.arrays, poa_global, temp_air, wind_speed, surface_tilt
             )
         )