Add support for iam.schlick to ModelChain

docs/sphinx/source/whatsnew/v0.16.0.rst

@@ -48,6 +48,9 @@ Enhancements
 * Map beam horizontal irradiance to ``bhi`` when
   :py:func:`~pvlib.iotools.get_era5` is called with ``map_variables=True``.
   (:pull:`2819`)
+* Add support for :py:func:`pvlib.iam.schlick` to :py:class:`pvlib.modelchain.ModelChain`,
+  :py:meth:`pvlib.pvsystem.PVSystem.get_iam`, and :py:meth:`pvlib.pvsystem.Array.get_iam`.
+  (:issue:`2828`, :pull:`2832`)
 * Allow variables from multiple datasets to be requested at once in
   :py:func:`~pvlib.iotools.get_merra2`. (:pull:`2839`)
 

pvlib/iam.py

@@ -816,6 +816,10 @@ def schlick(aoi):
     integrable alternative to the Fresnel equations for estimating IAM
     for diffuse irradiance [2]_ (see :py:func:`schlick_diffuse`).
 
+    .. warning:: The Schlick IAM model has not been validated for PV
+        performance modeling and is not commonly used in PV applications.
+        Users should consider these limitations when selecting models.
+
     Parameters
     ----------
     aoi : numeric
@@ -874,6 +878,10 @@ def schlick_diffuse(surface_tilt):
     This function implements the integration of the
     Schlick approximation provided by Xie et al. [2]_.
 
+    .. warning:: The Schlick IAM model has not been validated for PV
+        performance modeling and is not commonly used in PV applications.
+        Users should consider these limitations when selecting models.
+
     Parameters
     ----------
     surface_tilt : numeric

pvlib/modelchain.py

@@ -336,8 +336,8 @@ class ModelChain:
         If not specified, the model will be inferred from the parameters that
         are common to all of system.arrays[i].module_parameters.
         Valid strings are 'physical', 'ashrae', 'sapm', 'martin_ruiz',
-        'interp' and 'no_loss'. The ModelChain instance will be passed as the
-        first argument to a user-defined function.
+        'schlick', 'interp' and 'no_loss'. The ModelChain instance will be
+        passed as the first argument to a user-defined function.
 
     spectral_model : str or function, optional
         Valid strings are:
@@ -787,6 +787,8 @@ def aoi_model(self, model):
                 self._aoi_model = self.sapm_aoi_loss
             elif model == 'martin_ruiz':
                 self._aoi_model = self.martin_ruiz_aoi_loss
+            elif model == 'schlick':
+                self._aoi_model = self.schlick_aoi_loss
             elif model == 'interp':
                 self._aoi_model = self.interp_aoi_loss
             elif model == 'no_loss':
@@ -810,6 +812,10 @@ def infer_aoi_model(self):
             return self.martin_ruiz_aoi_loss
         elif iam._IAM_MODEL_PARAMS['interp'] <= params:
             return self.interp_aoi_loss
+        # 'schlick' is intentionally excluded from inference. Since it
+        # requires no parameters, it would always match and effectively
+        # become the default, which is undesirable because it is not
+        # commonly used for PV applications.
         else:
             raise ValueError('could not infer AOI model from '
                              'system.arrays[i].module_parameters. Check that '
@@ -846,6 +852,12 @@ def martin_ruiz_aoi_loss(self):
         )
         return self
 
+    def schlick_aoi_loss(self):
+        self.results.aoi_modifier = self.system.get_iam(
+            self.results.aoi, iam_model='schlick'
+        )
+        return self
+
     def interp_aoi_loss(self):
         self.results.aoi_modifier = self.system.get_iam(
             self.results.aoi,

pvlib/pvsystem.py

@@ -396,7 +396,7 @@ def get_iam(self, aoi, iam_model='physical'):
 
         iam_model : string, default 'physical'
             The IAM model to be used. Valid strings are 'physical', 'ashrae',
-            'martin_ruiz', 'sapm' and 'interp'.
+            'martin_ruiz', 'sapm', 'interp', and 'schlick'.
         Returns
         -------
         iam : numeric or tuple of numeric
@@ -1187,7 +1187,7 @@ def get_iam(self, aoi, iam_model='physical'):
 
         iam_model : string, default 'physical'
             The IAM model to be used. Valid strings are 'physical', 'ashrae',
-            'martin_ruiz', 'sapm' and 'interp'.
+            'martin_ruiz', 'sapm', 'interp' and 'schlick'.
 
         Returns
         -------
@@ -1200,7 +1200,7 @@ def get_iam(self, aoi, iam_model='physical'):
             if `iam_model` is not a valid model name.
         """
         model = iam_model.lower()
-        if model in ['ashrae', 'physical', 'martin_ruiz', 'interp']:
+        if model in ['ashrae', 'physical', 'martin_ruiz', 'interp', 'schlick']:
             func = getattr(iam, model)  # get function at pvlib.iam
             # get all parameters from function signature to retrieve them from
             # module_parameters if present

tests/test_modelchain.py

@@ -1451,7 +1451,7 @@ def constant_aoi_loss(mc):
 
 
 @pytest.mark.parametrize('aoi_model', [
-    'sapm', 'ashrae', 'physical', 'martin_ruiz'
+    'sapm', 'ashrae', 'physical', 'martin_ruiz', 'schlick'
 ])
 def test_aoi_models(sapm_dc_snl_ac_system, location, aoi_model,
                     weather, mocker):
@@ -1467,7 +1467,7 @@ def test_aoi_models(sapm_dc_snl_ac_system, location, aoi_model,
 
 
 @pytest.mark.parametrize('aoi_model', [
-    'sapm', 'ashrae', 'physical', 'martin_ruiz'
+    'sapm', 'ashrae', 'physical', 'martin_ruiz', 'schlick'
 ])
 def test_aoi_models_singleon_weather_single_array(
         sapm_dc_snl_ac_system, location, aoi_model, weather):

tests/test_pvsystem.py

@@ -75,9 +75,18 @@
     spy.assert_called_once_with(aoi[0], **interp_module_params)
 
 
+def test_PVSystem_get_iam_schlick(mocker):
+    system = pvsystem.PVSystem()
+    mocker.spy(_iam, 'schlick')
+    aoi = 0
+    out = system.get_iam(aoi, 'schlick')
+    _iam.schlick.assert_called_once_with(aoi)
+    assert_allclose(out, 1.0, atol=0.01)
+
+
 def test__normalize_sam_product_names():
 
     BAD_NAMES  = [' -.()[]:+/",', 'Module[1]']
     NORM_NAMES = ['____________', 'Module_1_']
 
     norm_names = pvsystem._normalize_sam_product_names(BAD_NAMES)