change gamma_pdc to units of %/C (#125)

* change gamma_pdc to units of %/C

closes #106

* Update api/solarperformanceinsight_api/models.py

Co-authored-by: Will Holmgren <[email protected]>

* line lenght

Co-authored-by: Will Holmgren <[email protected]>

Author: alorenzo175

api/solarperformanceinsight_api/models.py

@@ -90,6 +90,15 @@ def UserString(default: Any = Undefined, *, title: str = None, description: str
     )
 
 
+class PVLibBase(BaseModel):
+    """Provide a `pvlib_dict` method to convert parameters if needed
+    for using in pvlib. Child classes may implement model-specific conversions
+    as needed."""
+
+    def pvlib_dict(self):
+        return self.dict()
+
+
 class FixedTracking(BaseModel):
     """Parameters for a fixed tilt array"""
 
@@ -135,7 +144,7 @@ class SingleAxisTracking(BaseModel):
     )
 
 
-class PVsystModuleParameters(BaseModel):
+class PVsystModuleParameters(PVLibBase):
     """Parameters for the modules that make up an array in a PVsyst-like model"""
 
     alpha_sc: float = Field(
@@ -191,7 +200,7 @@ class PVsystModuleParameters(BaseModel):
     _modelchain_dc_model: str = PrivateAttr("pvsyst")
 
 
-class PVWattsModuleParameters(BaseModel):
+class PVWattsModuleParameters(PVLibBase):
     """Parameters for the modules that make up an array in a PVWatts-like model"""
 
     pdc0: float = Field(
@@ -201,12 +210,17 @@ class PVWattsModuleParameters(BaseModel):
     gamma_pdc: float = Field(
         ...,
         description=(
-            "Temperature coefficient of power in units of 1/C. "
-            "Typically -0.002 to -0.005 per degree C"
+            "Temperature coefficient of power in units of %/C. "
+            "Typically -0.2 to -0.5 % per degree C"
         ),
     )
     _modelchain_dc_model: str = PrivateAttr("pvwatts")
 
+    def pvlib_dict(self):
+        """Convert to a dict pvlib understands for `module_parameters`
+        i.e. scale gamma_pdc to 1/C"""
+        return {k: v / 100 if k == "gamma_pdc" else v for k, v in self.dict().items()}
+
 
 class PVsystTemperatureParameters(BaseModel):
     """Parameters for the cell temperature model of the modules in a

api/solarperformanceinsight_api/pvmodeling.py

@@ -41,7 +41,7 @@ def construct_pvsystem(inverter: models.Inverter) -> Union[PVSystem, SingleAxisT
             dict(
                 albedo=array.albedo,
                 module=array.make_model,
-                module_parameters=array.module_parameters.dict(),
+                module_parameters=array.module_parameters.pvlib_dict(),
                 temperature_model_parameters=array.temperature_model_parameters.dict(),
                 modules_per_string=array.modules_per_string,
                 strings=array.strings,

api/solarperformanceinsight_api/tests/test_models.py

@@ -429,3 +429,9 @@ def test_inverter_multiple_arrays(system_def):
         arrays=[track0],
         inverter_parameters=system_def.inverters[0].inverter_parameters,
     )
+
+
+def test_pvwatts_module_temp_scaling():
+    mod = models.PVWattsModuleParameters(pdc0=100, gamma_pdc=-0.2)
+    assert mod.dict() == {"pdc0": 100, "gamma_pdc": -0.2}
+    assert mod.pvlib_dict() == {"pdc0": 100, "gamma_pdc": -0.002}