Add deprecation warning

Author: AdamRJensen

pvlib/pvsystem.py

@@ -845,6 +845,8 @@ def scale_voltage_current_power(self, data):
             for array, data in zip(self.arrays, data)
         )
 
+
+    @renamed_kwarg_warning("0.13.0", "g_poa_effective", "effective_irradiance", "0.14.0")
     @_unwrap_single_value
     def pvwatts_dc(self, effective_irradiance, temp_cell):
         """
@@ -2799,6 +2801,8 @@ def scale_voltage_current_power(data, voltage=1, current=1):
     return df_sorted
 
 
+from pvlib._deprecation import renamed_kwarg_warning
+@renamed_kwarg_warning("0.12.0", "g_poa_effective", "effective_irradiance", "0.13.0")
 def pvwatts_dc(effective_irradiance, temp_cell, pdc0, gamma_pdc, temp_ref=25.):
     r"""
     Implements NREL's PVWatts DC power model. The PVWatts DC model [1]_ is: