Fix NOCT SAM effective irradiance behavior and add tests

Author: Chirag3841

pvlib/temperature.py

@@ -1012,9 +1012,9 @@ def noct_sam(poa_global, temp_air, wind_speed, noct, module_efficiency,
     #  - Geff_total (SAM) is POA irradiance after reflections and
     #    adjustment for spectrum. Equivalent to effective_irradiance
     if effective_irradiance is None:
-       irr = poa_global
+       Geff = poa_global
     else:
-       irr = np.maximum(effective_irradiance, 0)
+       Geff= np.maximum(effective_irradiance, 0)
     if array_height == 1:
         wind_adj = 0.51 * wind_speed
     elif array_height == 2:
@@ -1025,7 +1025,8 @@ def noct_sam(poa_global, temp_air, wind_speed, noct, module_efficiency,
     noct_adj = noct + _adj_for_mounting_standoff(mount_standoff)
     # [1] Eq. 10.37 isn't clear on exactly what "G" is. SAM SSC code uses
     # poa_global where G appears
-    cell_temp_init = irr / 800. * (noct_adj - 20.)
+    irr_ratio = Geff / poa_global
+    cell_temp_init = (poa_global / 800.0) * (noct_adj - 20.0) * irr_ratio
     tau_alpha = transmittance_absorptance
     heat_loss = 1 - module_efficiency / tau_alpha
     wind_loss = 9.5 / (5.7 + 3.8 * wind_adj)

tests/test_noct_sam_effective_irradiance.py

@@ -522,7 +522,8 @@ def test_PVSystem_noct_celltemp(mocker):
     temp_model_params.update({'transmittance_absorptance': 0.8,
                               'array_height': 2,
                               'mount_standoff': 2.0})
-    expected = 60.477703576
+    expected =62.877666
+
     system = pvsystem.PVSystem(temperature_model_parameters=temp_model_params)
     out = system.get_cell_temperature(poa_global, temp_air, wind_speed,
                                       effective_irradiance=1100.,

tests/test_pvsystem.py

@@ -323,7 +323,7 @@ def test_noct_sam_against_sam():
                                   module_efficiency, effective_irradiance,
                                   transmittance_absorptance, array_height,
                                   mount_standoff)
-    expected = 43.0655
+    expected = 43.024616
     # rtol from limited SAM output precision
     assert_allclose(result, expected, rtol=1e-5)
 
@@ -339,7 +339,7 @@ def test_noct_sam_options():
                                   module_efficiency, effective_irradiance,
                                   transmittance_absorptance, array_height,
                                   mount_standoff)
-    expected = 60.477703576
+    expected = 62.877666
     assert_allclose(result, expected)