add SingleAxisTracker support to ModelChain

* add SingleAxisTracker support to ModelChain

* whitespace

* add mc.tracking assertion

* add note to whatsnew

Author: wholmgren

docs/sphinx/source/whatsnew/v0.3.3.txt

@@ -12,6 +12,8 @@ Enhancements
 * Adds the Erbs model. (:issue:`2`)
 * Adds the ``scale_voltage_current_power`` function and ``PVSystem`` method
   to support simple array modeling. (:issue:`159`)
+* Adds support for ``SingleAxisTracker`` objects in ``ModelChain``.
+  (:issue:`169`)
 
 
 Bug fixes

pvlib/modelchain.py

@@ -6,9 +6,12 @@
 the time to read the source code for the module.
 """
 
+from functools import partial
+
 import pandas as pd
 
 from pvlib import solarposition, pvsystem, clearsky, atmosphere
+from pvlib.tracking import SingleAxisTracker
 import pvlib.irradiance  # avoid name conflict with full import
 
 
@@ -317,9 +320,32 @@ def run_model(self, times, irradiance=None, weather=None):
                 airmass_data=self.airmass['airmass_absolute'])
         self.irradiance = irradiance
 
-        self.total_irrad = self.system.get_irradiance(
-            self.solar_position['apparent_zenith'],
-            self.solar_position['azimuth'],
+        # PVSystem.get_irradiance and SingleAxisTracker.get_irradiance
+        # have different method signatures, so use partial to handle
+        # the differences.
+        if isinstance(self.system, SingleAxisTracker):
+            self.tracking = self.system.singleaxis(
+                self.solar_position['apparent_zenith'],
+                self.solar_position['azimuth'])
+            self.tracking['surface_tilt'] = (
+                self.tracking['surface_tilt']
+                    .fillna(self.system.axis_tilt))
+            self.tracking['surface_azimuth'] = (
+                self.tracking['surface_azimuth']
+                    .fillna(self.system.axis_azimuth))
+            get_irradiance = partial(
+                self.system.get_irradiance,
+                surface_tilt=self.tracking['surface_tilt'],
+                surface_azimuth=self.tracking['surface_azimuth'],
+                solar_zenith=self.solar_position['apparent_zenith'],
+                solar_azimuth=self.solar_position['azimuth'])
+        else:
+            get_irradiance = partial(
+                self.system.get_irradiance,
+                self.solar_position['apparent_zenith'],
+                self.solar_position['azimuth'])
+
+        self.total_irrad = get_irradiance(
             self.irradiance['dni'],
             self.irradiance['ghi'],
             self.irradiance['dhi'],

pvlib/test/test_modelchain.py

@@ -1,9 +1,11 @@
 import numpy as np
 import pandas as pd
+from numpy import nan
 
 from pvlib import modelchain, pvsystem
 from pvlib.modelchain import ModelChain
 from pvlib.pvsystem import PVSystem
+from pvlib.tracking import SingleAxisTracker
 from pvlib.location import Location
 
 from pandas.util.testing import assert_series_equal, assert_frame_equal
@@ -100,6 +102,26 @@ def test_run_model_with_weather():
     assert_series_equal(ac, expected)
 
 
+def test_run_model_tracker():
+    system, location = mc_setup()
+    system = SingleAxisTracker(module_parameters=system.module_parameters,
+                               inverter_parameters=system.inverter_parameters)
+    mc = ModelChain(system, location)
+    times = pd.date_range('20160101 1200-0700', periods=2, freq='6H')
+    ac = mc.run_model(times).ac
+
+    expected = pd.Series(np.array([  121.421719,  -2.00000000e-02]),
+                         index=times)
+    assert_series_equal(ac, expected)
+
+    expected = pd.DataFrame(np.
+        array([[ 54.82513187,  90.        ,  11.0039221 ,  11.0039221 ],
+               [         nan,   0.        ,   0.        ,          nan]]),
+        columns=['aoi', 'surface_azimuth', 'surface_tilt', 'tracker_theta'],
+        index=times)
+    assert_frame_equal(mc.tracking, expected)
+
+
 @raises(ValueError)
 def test_bad_get_orientation():
     modelchain.get_orientation('bad value')