Adds functionality for 'pvsyst' to be used as a losses_model. Adds a function for calculating dc losses from a loss percentage at stc based on the method employed by pvsyst.

ncroft-b4 · ncroft-b4 · commit 56e1597b20d6 · 2020-10-30T14:56:20.000-07:00
diff --git a/pvlib/modelchain.py b/pvlib/modelchain.py
@@ -328,8 +328,8 @@ class ModelChain:
         user-defined function.
 
     losses_model: str, default 'no_loss'
-        Valid strings are 'pvwatts', 'no_loss'. The loss functions will
-        be set according to this parameter.
+        Valid strings are 'pvwatts', 'no_loss', 'pvsyst'. The loss functions
+        will be set according to this parameter.
 
     name: None or str, default None
         Name of ModelChain instance.
@@ -940,6 +940,9 @@ def losses_model(self, model):
             elif model == 'no_loss':
                 self._losses_model = model
                 self._dc_losses = self.no_extra_losses
+            elif model == 'pvsyst':
+                self._losses_model = model
+                self._dc_losses = self.pvsyst_dc_losses
             else:
                 raise ValueError(model + ' is not a valid losses model')
         else:
@@ -957,6 +960,19 @@ def no_extra_losses(self):
         self.losses = 1
         return self
 
+    def pvsyst_dc_losses(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.pvsyst_dc_losses_eq_ohms()
+        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 effective_irradiance_model(self):
         fd = self.system.module_parameters.get('FD', 1.)
         self.effective_irradiance = self.spectral_modifier * (
