add ref irr/t as optional args, rename

Author: RDaxini

pvlib/pvsystem.py

@@ -2195,7 +2195,8 @@ def _parse_raw_sam_df(csvdata):
     return df
 
 
-def sapm(effective_irradiance, temp_cell, module):
+def sapm(effective_irradiance, temp_cell, module, reference_temperature = 25,
+         reference_irradiance = 1000):
     '''
     The Sandia PV Array Performance Model (SAPM) generates 5 points on a
     PV module's I-V curve (Voc, Isc, Ix, Ixx, Vmp/Imp) according to
@@ -2284,16 +2285,11 @@ def sapm(effective_irradiance, temp_cell, module):
     pvlib.temperature.sapm_module
     '''
 
-    # TODO: someday, change temp_ref and irrad_ref to reference_temperature and
-    # reference_irradiance and expose
-    temp_ref = 25
-    irrad_ref = 1000
-
     q = constants.e  # Elementary charge in units of coulombs
     kb = constants.k  # Boltzmann's constant in units of J/K
 
     # avoid problem with integer input
-    Ee = np.array(effective_irradiance, dtype='float64') / irrad_ref
+    Ee = np.array(effective_irradiance, dtype='float64') / reference_irradiance
 
     # set up masking for 0, positive, and nan inputs
     Ee_gt_0 = np.full_like(Ee, False, dtype='bool')
@@ -2316,31 +2312,31 @@ def sapm(effective_irradiance, temp_cell, module):
     out = OrderedDict()
 
     out['i_sc'] = (
-        module['Isco'] * Ee * (1 + module['Aisc']*(temp_cell - temp_ref)))
+        module['Isco'] * Ee * (1 + module['Aisc']*(temp_cell - reference_temperature)))
 
     out['i_mp'] = (
         module['Impo'] * (module['C0']*Ee + module['C1']*(Ee**2)) *
-        (1 + module['Aimp']*(temp_cell - temp_ref)))
+        (1 + module['Aimp']*(temp_cell - reference_temperature)))
 
     out['v_oc'] = np.maximum(0, (
         module['Voco'] + cells_in_series * delta * logEe +
-        Bvoco*(temp_cell - temp_ref)))
+        Bvoco*(temp_cell - reference_temperature)))
 
     out['v_mp'] = np.maximum(0, (
         module['Vmpo'] +
         module['C2'] * cells_in_series * delta * logEe +
         module['C3'] * cells_in_series * ((delta * logEe) ** 2) +
-        Bvmpo*(temp_cell - temp_ref)))
+        Bvmpo*(temp_cell - reference_temperature)))
 
     out['p_mp'] = out['i_mp'] * out['v_mp']
 
     out['i_x'] = (
         module['IXO'] * (module['C4']*Ee + module['C5']*(Ee**2)) *
-        (1 + module['Aisc']*(temp_cell - temp_ref)))
+        (1 + module['Aisc']*(temp_cell - reference_temperature)))
 
     out['i_xx'] = (
         module['IXXO'] * (module['C6']*Ee + module['C7']*(Ee**2)) *
-        (1 + module['Aimp']*(temp_cell - temp_ref)))
+        (1 + module['Aimp']*(temp_cell - reference_temperature)))
 
     if isinstance(out['i_sc'], pd.Series):
         out = pd.DataFrame(out)