Accept albedo in weather input to ModelChain.run_model method

docs/sphinx/source/whatsnew/v0.9.2.rst

@@ -8,15 +8,17 @@ Deprecations
 
 Enhancements
 ~~~~~~~~~~~~
+* albedo can now be provided as a column in the `weather` DataFrame input to
+  :py:method:`pvlib.modelchain.ModelChain.run_model`. (:issue:`1387`, :pull:`1469`)
 
 Bug fixes
 ~~~~~~~~~
 * :py:func:`pvlib.irradiance.get_total_irradiance` and
   :py:func:`pvlib.solarposition.spa_python` now raise an error instead
-  of silently ignoring unknown parameters (:pull:`1437`)
+  of silently ignoring unknown parameters. (:pull:`1437`)
 * Fix a bug in :py:func:`pvlib.solarposition.sun_rise_set_transit_ephem`
   where passing localized timezones with large UTC offsets could return
-  rise/set/transit times for the wrong day in recent versions of ``ephem``
+  rise/set/transit times for the wrong day in recent versions of ``ephem``.
   (:issue:`1449`, :pull:`1448`)
 
 
@@ -41,3 +43,4 @@ Contributors
 * Naman Priyadarshi (:ghuser:`Naman-Priyadarshi`)
 * Chencheng Luo (:ghuser:`roger-lcc`)
 * Prajwal Borkar (:ghuser:`PrajwalBorkar`) 
+* Cliff Hansen (:ghuser:`cwhanse`)

pvlib/clearsky.py

@@ -960,8 +960,8 @@ def bird(zenith, airmass_relative, aod380, aod500, precipitable_water,
         Extraterrestrial radiation [W/m^2], defaults to 1364[W/m^2]
     asymmetry : numeric
         Asymmetry factor, defaults to 0.85
-    albedo : numeric
-        Albedo, defaults to 0.2
+    albedo : numeric, default 0.2
+        Ground surface albedo. [unitless]
 
     Returns
     -------

pvlib/irradiance.py

@@ -344,7 +344,7 @@ def get_total_irradiance(surface_tilt, surface_azimuth,
     airmass : None or numeric, default None
         Relative airmass (not adjusted for pressure). [unitless]
     albedo : numeric, default 0.25
-        Surface albedo. [unitless]
+        Ground surface albedo. [unitless]
     surface_type : None or str, default None
         Surface type. See :py:func:`~pvlib.irradiance.get_ground_diffuse` for
         the list of accepted values.
@@ -1872,7 +1872,7 @@ def gti_dirint(poa_global, aoi, solar_zenith, solar_azimuth, times,
         applied.
 
     albedo : numeric, default 0.25
-        Surface albedo
+        Gound surface albedo. [unitless]
 
     model : String, default 'perez'
         Irradiance model.  See :py:func:`get_sky_diffuse` for allowed values.

pvlib/modelchain.py

@@ -1471,11 +1471,14 @@ def prepare_inputs(self, weather):
 
         Parameters
         ----------
-        weather : DataFrame, or tuple or list of DataFrame
+        weather : tuple or list of DataFrames
             Required column names include ``'dni'``, ``'ghi'``, ``'dhi'``.
-            Optional column names are ``'wind_speed'``, ``'temp_air'``; if not
+            Optional column names are ``'wind_speed'``, ``'temp_air'``,
+            ``'albedo'``.
+
+            If optional columns ``'wind_speed'``, ``'temp_air'`` are not
             provided, air temperature of 20 C and wind speed
-            of 0 m/s will be added to the DataFrame.
+            of 0 m/s will be added to the `weather` DataFrame.
 
             If `weather` is a tuple or list, it must be of the same length and
             order as the Arrays of the ModelChain's PVSystem.
@@ -1490,6 +1493,9 @@ def prepare_inputs(self, weather):
         ValueError
             If `weather` is a tuple or list with a different length than the
             number of Arrays in the system.
+        ValueError
+            If ``'albedo'`` is a column in `weather` and is also an attribute
+            of the ModelChain's PVSystem.Arrays.
 
         Notes
         -----
@@ -1500,6 +1506,24 @@ def prepare_inputs(self, weather):
         --------
         ModelChain.complete_irradiance
         """
+        # transfer albedo from weather to mc.system.arrays if needed
+        if isinstance(weather, pd.DataFrame):  # single weather, many arrays
+            if 'albedo' in weather.columns:
+                for array in self.system.arrays:
+                    if hasattr(array, 'albedo'):
+                        raise ValueError('albedo found in both weather and on'
+                                         ' PVsystem.Array Provide albedo on'
+                                         ' one or on neither, but not both.')
+                    array.albedo = weather['albedo']
+        else:  # multiple weather and arrays
+            for w, array in zip(weather, self.system.arrays):
+                if 'albedo' in w.columns:
+                    if hasattr(array, 'albedo'):
+                        raise ValueError('albedo found in both weather and on'
+                                         ' PVsystem.Array Provide albedo on'
+                                         ' one or on neither, but not both.')
+                    array.albedo = w['albedo']
+
         weather = _to_tuple(weather)
         self._check_multiple_input(weather, strict=False)
         self._verify_df(weather, required=['ghi', 'dni', 'dhi'])
@@ -1724,16 +1748,32 @@ def run_model(self, weather):
         Parameters
         ----------
         weather : DataFrame, or tuple or list of DataFrame
-            Irradiance column names must include ``'dni'``, ``'ghi'``, and
-            ``'dhi'``. If optional columns ``'temp_air'`` and ``'wind_speed'``
+            Column names must include:
+
+            - ``'dni'``
+            - ``'ghi'``
+            - ``'dhi'``
+
+            Optional columns are:
+
+            - ``'temp_air'``
+            - ``'cell_temperature'``
+            - ``'module_temperature'``
+            - ``'wind_speed'``
+            - ``'albedo'``
+
+            If optional columns ``'temp_air'`` and ``'wind_speed'``
             are not provided, air temperature of 20 C and wind speed of 0 m/s
             are added to the DataFrame. If optional column
             ``'cell_temperature'`` is provided, these values are used instead
-            of `temperature_model`. If optional column `module_temperature`
+            of `temperature_model`. If optional column ``'module_temperature'``
             is provided, `temperature_model` must be ``'sapm'``.
 
-            If list or tuple, must be of the same length and order as the
-            Arrays of the ModelChain's PVSystem.
+            If optional column ``'albedo'`` is provided, ``'albedo'`` may not
+            be present on the ModelChain's PVSystem or PVSystem.Arrays.
+
+            If weather is a list or tuple, it must be of the same length and
+            order as the Arrays of the ModelChain's PVSystem.
 
         Returns
         -------

pvlib/pvsystem.py

@@ -134,7 +134,7 @@ class PVSystem:
         a single array is created from the other parameters (e.g.
         `surface_tilt`, `surface_azimuth`). Must contain at least one Array,
         if length of arrays is 0 a ValueError is raised. If `arrays` is
-        specified the following parameters are ignored:
+        specified the following PVSystem parameters are ignored:
 
         - `surface_tilt`
         - `surface_azimuth`
@@ -157,13 +157,16 @@ class PVSystem:
         North=0, East=90, South=180, West=270.
 
     albedo : None or float, default None
-        The ground albedo. If ``None``, will attempt to use
-        ``surface_type`` and ``irradiance.SURFACE_ALBEDOS``
-        to lookup albedo.
+        Ground surface albedo. If ``None``, then ``surface_type`` is used
+        to look up a value in ``irradiance.SURFACE_ALBEDOS``.
+        If ``surface_type`` is also None then a ground surface albedo
+        of 0.25 is used. For time-dependent albedos, add ``'albedo'`` to
+        the input ``'weather'`` DataFrame for
+        :py:class:`pvlib.modelchain.ModelChain` methods.
 
     surface_type : None or string, default None
-        The ground surface type. See ``irradiance.SURFACE_ALBEDOS``
-        for valid values.
+        The ground surface type. Required if ``albedo`` is None.
+        See ``irradiance.SURFACE_ALBEDOS`` for valid values.
 
     module : None or string, default None
         The model name of the modules.
@@ -1258,14 +1261,14 @@ class Array:
         If not provided, a FixedMount with zero tilt is used.
 
     albedo : None or float, default None
-        The ground albedo. If ``None``, will attempt to use
-        ``surface_type`` to look up an albedo value in
-        ``irradiance.SURFACE_ALBEDOS``. If a surface albedo
-        cannot be found then 0.25 is used.
+        Ground surface albedo. If ``None``, then ``surface_type`` is used
+        to look up a value in ``irradiance.SURFACE_ALBEDOS``.
+        If ``surface_type`` is also None then a ground surface albedo
+        of 0.25 is used.
 
     surface_type : None or string, default None
-        The ground surface type. See ``irradiance.SURFACE_ALBEDOS``
-        for valid values.
+        The ground surface type. Required if ``albedo`` is None.
+        See ``irradiance.SURFACE_ALBEDOS`` for valid values.
 
     module : None or string, default None
         The model name of the modules.

pvlib/tests/test_clearsky.py

@@ -756,6 +756,18 @@ def test_bird():
     assert np.allclose(
         testdata['Dif Hz'].where(dusk, 0.), diffuse_horz[1:48], rtol=1e-3
     )
+    # repeat test with albedo as a Series
+    alb_series = pd.Series(0.2, index=times)
+    irrads = clearsky.bird(
+        zenith, airmass, aod_380nm, aod_500nm, h2o_cm, o3_cm, press_mB * 100.,
+        etr, b_a, alb_series
+    )
+    Eb, Ebh, Gh, Dh = (irrads[_] for _ in field_names)
+    assert np.allclose(testdata['DEC'], np.rad2deg(declination[1:48]))
+    assert np.allclose(testdata['EQT'], eot[1:48], rtol=1e-4)
+    assert np.allclose(testdata['Hour Angle'], hour_angle[1:48])
+    assert np.allclose(testdata['Zenith Ang'], zenith[1:48])
+
     # test keyword parameters
     irrads2 = clearsky.bird(
         zenith, airmass, aod_380nm, aod_500nm, h2o_cm, dni_extra=etr

pvlib/tests/test_irradiance.py

@@ -120,29 +120,38 @@ def test_get_extra_radiation_invalid():
         irradiance.get_extra_radiation(300, method='invalid')
 
 
-def test_grounddiffuse_simple_float():
+def test_get_ground_diffuse_simple_float():
     result = irradiance.get_ground_diffuse(40, 900)
     assert_allclose(result, 26.32000014911496)
 
 
-def test_grounddiffuse_simple_series(irrad_data):
+def test_get_ground_diffuse_simple_series(irrad_data):
     ground_irrad = irradiance.get_ground_diffuse(40, irrad_data['ghi'])
     assert ground_irrad.name == 'diffuse_ground'
 
 
-def test_grounddiffuse_albedo_0(irrad_data):
+def test_get_ground_diffuse_albedo_0(irrad_data):
     ground_irrad = irradiance.get_ground_diffuse(
         40, irrad_data['ghi'], albedo=0)
     assert 0 == ground_irrad.all()
 
 
+def test_get_ground_diffuse_albedo_series(times):
+    albedo = pd.Series(0.2, index=times)
+    ground_irrad = irradiance.get_ground_diffuse(
+        45, pd.Series(1000, index=times), albedo)
+    expected = albedo * 0.5 * (1 - np.sqrt(2) / 2.) * 1000
+    expected.name = 'diffuse_ground'
+    assert_series_equal(ground_irrad, expected)
+
+
 def test_grounddiffuse_albedo_invalid_surface(irrad_data):
     with pytest.raises(KeyError):
         irradiance.get_ground_diffuse(
             40, irrad_data['ghi'], surface_type='invalid')
 
 
-def test_grounddiffuse_albedo_surface(irrad_data):
+def test_get_ground_diffuse_albedo_surface(irrad_data):
     result = irradiance.get_ground_diffuse(40, irrad_data['ghi'],
                                            surface_type='sand')
     assert_allclose(result, [0, 3.731058, 48.778813, 12.035025], atol=1e-4)
@@ -387,6 +396,26 @@ def test_get_total_irradiance(irrad_data, ephem_data, dni_et,
                                           'poa_ground_diffuse']
 
 
+def test_get_total_irradiance_albedo(
+        irrad_data, ephem_data, dni_et, relative_airmass):
+    models = ['isotropic', 'klucher',
+              'haydavies', 'reindl', 'king', 'perez']
+    albedo = pd.Series(0.2, index=ephem_data.index)
+    for model in models:
+        total = irradiance.get_total_irradiance(
+            32, 180,
+            ephem_data['apparent_zenith'], ephem_data['azimuth'],
+            dni=irrad_data['dni'], ghi=irrad_data['ghi'],
+            dhi=irrad_data['dhi'],
+            dni_extra=dni_et, airmass=relative_airmass,
+            model=model,
+            albedo=albedo)
+
+        assert total.columns.tolist() == ['poa_global', 'poa_direct',
+                                          'poa_diffuse', 'poa_sky_diffuse',
+                                          'poa_ground_diffuse']
+
+
 @pytest.mark.parametrize('model', ['isotropic', 'klucher',
                                    'haydavies', 'reindl', 'king', 'perez'])
 def test_get_total_irradiance_scalars(model):
@@ -698,6 +727,14 @@ def test_gti_dirint():
 
     assert_frame_equal(output, expected)
 
+    # test with albedo as a Series
+    albedo = pd.Series(0.05, index=times)
+    output = irradiance.gti_dirint(
+        poa_global, aoi, zenith, azimuth, times, surface_tilt, surface_azimuth,
+        albedo=albedo)
+
+    assert_frame_equal(output, expected)
+
     # test temp_dew input
     temp_dew = np.array([70, 80, 20])
     output = irradiance.gti_dirint(

pvlib/tests/test_modelchain.py

@@ -497,6 +497,45 @@ def test_prepare_inputs_multi_weather(
     assert len(mc.results.total_irrad) == num_arrays
 
 
+@pytest.mark.parametrize("input_type", [tuple, list])
+def test_prepare_inputs_transfer_albedo(
+        sapm_dc_snl_ac_system_Array, location, input_type):
+    times = pd.date_range(start='20160101 1200-0700',
+                          end='20160101 1800-0700', freq='6H')
+    mc = ModelChain(sapm_dc_snl_ac_system_Array, location)
+    # albedo on pvsystem but not in weather
+    weather = pd.DataFrame({'ghi': 1, 'dhi': 1, 'dni': 1},
+                           index=times)
+    # weather as a single DataFrame
+    mc.prepare_inputs(weather)
+    num_arrays = sapm_dc_snl_ac_system_Array.num_arrays
+    assert len(mc.results.total_irrad) == num_arrays
+    # repeat with tuple of weather
+    mc.prepare_inputs(input_type((weather, weather)))
+    num_arrays = sapm_dc_snl_ac_system_Array.num_arrays
+    assert len(mc.results.total_irrad) == num_arrays
+    # albedo on both weather and system
+    weather['albedo'] = 0.5
+    with pytest.raises(ValueError, match='albedo found in both weather'):
+        mc.prepare_inputs(weather)
+    with pytest.raises(ValueError, match='albedo found in both weather'):
+        mc.prepare_inputs(input_type((weather, weather)))
+    # albedo on weather but not system
+    pvsystem = sapm_dc_snl_ac_system_Array
+    for a in pvsystem.arrays:
+        del a.albedo
+    mc = ModelChain(pvsystem, location)
+    mc = mc.prepare_inputs(weather)
+    assert (mc.system.arrays[0].albedo.values == 0.5).all()
+    # again with weather as a tuple
+    for a in pvsystem.arrays:
+        del a.albedo
+    mc = ModelChain(pvsystem, location)
+    mc = mc.prepare_inputs(input_type((weather, weather)))
+    for a in mc.system.arrays:
+        assert (a.albedo.values == 0.5).all()
+
+
 def test_prepare_inputs_no_irradiance(sapm_dc_snl_ac_system, location):
     mc = ModelChain(sapm_dc_snl_ac_system, location)
     weather = pd.DataFrame()