Verify weather includes 'dhi' in ModelChain.prepare_inputs() (#1093)

* Verify `weather` include 'dhi' in ModelChain.prepare_inputs()

* Fix whitespace

* Add entry to whatsnew under Bug Fixes

Author: wfvining

docs/sphinx/source/whatsnew/v0.8.1.rst

@@ -24,6 +24,8 @@ Bug fixes
 ~~~~~~~~~
 * Fix issue with :py:func:`pvlib.temperature.fuentes` with timezone-aware
   inputs. (:issue:`1071`, :pull:`1072`)
+* Raise ``ValueError`` from  :py:meth:`pvlib.modelchain.ModelChain.prepare_inputs`
+  when input does not have a 'dhi' column. (:issue:`1092`, :pull:`1093`)
 
 Testing
 ~~~~~~~
@@ -46,3 +48,4 @@ Contributors
 * Siyan (Veronica) Guo (:ghuser:`veronicaguo`)
 * Will Holmgren (:ghuser:`wholmgren`)
 * Cliff Hansen (:ghuser:`cwhanse`)
+* Will Vining (:ghuser:`wfvining`)

pvlib/modelchain.py

@@ -1133,7 +1133,7 @@ def prepare_inputs(self, weather):
         ModelChain.complete_irradiance
         """
 
-        self._verify_df(weather, required=['ghi', 'dni', 'ghi'])
+        self._verify_df(weather, required=['ghi', 'dni', 'dhi'])
         self._assign_weather(weather)
 
         self.times = self.weather.index

pvlib/tests/test_modelchain.py

@@ -249,6 +249,16 @@ def test_prepare_inputs_no_irradiance(sapm_dc_snl_ac_system, location):
         mc.prepare_inputs(weather)
 
 
+@pytest.mark.parametrize("missing", ['dhi', 'ghi', 'dni'])
+def test_prepare_inputs_missing_irrad_component(
+        sapm_dc_snl_ac_system, location, missing):
+    mc = ModelChain(sapm_dc_snl_ac_system, location)
+    weather = pd.DataFrame({'dhi': [1, 2], 'dni': [1, 2], 'ghi': [1, 2]})
+    weather.drop(columns=missing, inplace=True)
+    with pytest.raises(ValueError):
+        mc.prepare_inputs(weather)
+
+
 def test_run_model_perez(sapm_dc_snl_ac_system, location):
     mc = ModelChain(sapm_dc_snl_ac_system, location,
                     transposition_model='perez')