Add dc_ohmic_model to model chain

pvlib · ncroft-b4 · Oct 26, 2020 · Oct 30, 2020 · Oct 30, 2020 · Nov 16, 2020
commit 6860cdf97e186e7e36f2fdb4978f798615e47861
diff --git a/pvlib/modelchain.py b/pvlib/modelchain.py
@@ -327,6 +327,11 @@ class ModelChain:
         The ModelChain instance will be passed as the first argument to a
         user-defined function.
 
+    dc_ohmic_model: None, str or function, default None
+        Valid strings are 'dc_ohms_from_percent', 'no_loss'. The ModelChain
+        instance will be passed as the first argument to a user-defined
+        function.
+
     losses_model: str or function, default 'no_loss'
         Valid strings are 'pvwatts', 'no_loss'. The ModelChain instance
         will be passed as the first argument to a user-defined function.
@@ -343,6 +348,7 @@ def __init__(self, system, location,
                  airmass_model='kastenyoung1989',
                  dc_model=None, ac_model=None, aoi_model=None,
                  spectral_model=None, temperature_model=None,
+                 dc_ohmic_model=None,
                  losses_model='no_loss', name=None, **kwargs):
 
         self.name = name
@@ -361,7 +367,10 @@ def __init__(self, system, location,
         self.spectral_model = spectral_model
         self.temperature_model = temperature_model
 
+        # losses
+        self.dc_ohmic_model = dc_ohmic_model
         self.losses_model = losses_model
+
         self.orientation_strategy = orientation_strategy
 
         self.weather = None
@@ -924,6 +933,41 @@ def fuentes_temp(self):
             self.weather['wind_speed'])
         return self
 
+    @property
+    def dc_ohmic_model(self):
+        return self._dc_ohmic_model
+
+    @dc_ohmic_model.setter
+    def dc_ohmic_model(self, model):
+        if model is None:
+            self._dc_ohmic_model = self.no_dc_ohmic_loss
+        elif isinstance(model, str):
+            model = model.lower()
+            if model == 'dc_ohms_from_percent':
+                self._dc_ohmic_model = self.dc_ohms_from_percent
+            elif model == 'no_loss':
+                self._dc_ohmic_model = self.no_dc_ohmic_loss
+            else:
+                raise ValueError(model + ' is not a valid losses model')
+        else:
+            self._dc_ohmic_model = partial(model, self)
+
+    def dc_ohms_from_percent(self):
+        """
+        Calculate time series of ohmic losses and apply those to the mpp power
+        output of the `dc_model` based on the pvsyst equivalent resistance
+        method. Uses a `dc_ohmic_percent` parameter in the `losses_parameters`
+        of the PVsystem.
+        """
+        Rw = self.system.dc_ohms_from_percent()
+        ohmic_loss_fraction = Rw * self.dc['i_mp'] / self.dc['v_mp']
+        self.dc_ohmic_losses = ohmic_loss_fraction * self.dc['p_mp']
+        self.dc['p_mp'] = self.dc['p_mp'] - self.dc_ohmic_losses
+        return self
+
+    def no_dc_ohmic_loss(self):
+        return self
+
     @property
     def losses_model(self):
         return self._losses_model
@@ -1374,6 +1418,7 @@ def _run_from_effective_irrad(self, data=None):
         """
         self._prepare_temperature(data)
         self.dc_model()
+        self.dc_ohmic_model()
         self.losses_model()
         self.ac_model()