make IXO and IXXO optional too

Author: kandersolar

pvlib/pvsystem.py

@@ -27,10 +27,10 @@
 # a dict of required parameter names for each DC power model
 _DC_MODEL_PARAMS = {
     'sapm': {
-        'C0', 'C1', 'C2', 'C3',  # C4-C7 (i_x and i_xx params) not required
+        # i_x and i_xx params (IXO, IXXO, C4-C7) not required
+        'C0', 'C1', 'C2', 'C3',
         'Isco', 'Impo', 'Voco', 'Vmpo', 'Aisc', 'Aimp', 'Bvoco',
-        'Mbvoc', 'Bvmpo', 'Mbvmp', 'N', 'Cells_in_Series',
-        'IXO', 'IXXO'},
+        'Mbvoc', 'Bvmpo', 'Mbvmp', 'N', 'Cells_in_Series'},
     'desoto': {
         'alpha_sc', 'a_ref', 'I_L_ref', 'I_o_ref',
         'R_sh_ref', 'R_s'},
@@ -2222,11 +2222,11 @@ def sapm(effective_irradiance, temp_cell, module):
         * v_mp : Voltage at maximum-power point (V)
         * p_mp : Power at maximum-power point (W)
         * i_x : Current at module V = 0.5Voc, defines 4th point on I-V
-          curve for modeling curve shape.  Omitted if ``C4`` and ``C5``
-          parameters are not supplied.
+          curve for modeling curve shape.  Omitted if ``IXO``, ``C4``, and
+          ``C5`` parameters are not supplied.
         * i_xx : Current at module V = 0.5(Voc+Vmp), defines 5th point on
-          I-V curve for modeling curve shape.  Omitted if ``C6`` and ``C7``
-          parameters are not supplied.
+          I-V curve for modeling curve shape.  Omitted if ``IXXO``, ``C6``,
+          and ``C7`` parameters are not supplied.
 
     Notes
     -----
@@ -2334,12 +2334,12 @@ def sapm(effective_irradiance, temp_cell, module):
 
     out['p_mp'] = out['i_mp'] * out['v_mp']
 
-    if 'C4' in module and 'C5' in module:
+    if 'IXO' in module and 'C4' in module and 'C5' in module:
         out['i_x'] = (
             module['IXO'] * (module['C4']*Ee + module['C5']*(Ee**2)) *
             (1 + module['Aisc']*(temp_cell - temp_ref)))
 
-    if 'C6' in module and 'C7' in module:
+    if 'IXXO' in module and 'C6' in module and 'C7' in module:
         out['i_xx'] = (
             module['IXXO'] * (module['C6']*Ee + module['C7']*(Ee**2)) *
             (1 + module['Aimp']*(temp_cell - temp_ref)))

tests/test_modelchain.py

@@ -1765,7 +1765,7 @@ def test_invalid_dc_model_params(sapm_dc_snl_ac_system, cec_dc_snl_ac_system,
 def test_sapm_optional_params(sapm_dc_snl_ac_system, location):
     # inference works when the optional (i_x, i_xx) SAPM parameters are missing
     for array in sapm_dc_snl_ac_system.arrays:
-        for key in ['C4', 'C5', 'C6', 'C7']:
+        for key in ['IXO', 'IXXO', 'C4', 'C5', 'C6', 'C7']:
             array.module_parameters.pop(key)
 
     # no error:

tests/test_pvsystem.py

@@ -197,7 +197,7 @@ def test_sapm(sapm_module_params):
                   pd.Series(sapm_module_params))
 
     # ensure C4-C7 are optional
-    optional_keys = ['C4', 'C5', 'C6', 'C7']
+    optional_keys = ['IXO', 'IXXO', 'C4', 'C5', 'C6', 'C7']
     params_no_c4c7 = {
         k: v for k, v in sapm_module_params.items() if k not in optional_keys
     }