Fix noct_sam()

pvlib/temperature.py

@@ -713,7 +713,8 @@ def ross(poa_global, temp_air, noct=None, k=None):
         return temp_air + k * poa_global
 
 
-def _fuentes_hconv(tave, windmod, temp_delta, xlen, tilt, check_reynold):
+def _fuentes_hconv(tave, windmod, tinoct, temp_delta, xlen, tilt,
+                   check_reynold):
     # Calculate the convective coefficient as in Fuentes 1987 -- a mixture of
     # free, laminar, and turbulent convection.
     densair = 0.003484 * 101325.0 / tave  # density
@@ -835,7 +836,7 @@ def fuentes(poa_global, temp_air, wind_speed, noct_installed, module_height=5,
     # convective coefficient of top surface of module at NOCT
     windmod = 1.0
     tave = (tinoct + 293.15) / 2
-    hconv = _fuentes_hconv(tave, windmod, tinoct - 293.15, xlen,
+    hconv = _fuentes_hconv(tave, windmod, tinoct, tinoct - 293.15, xlen,
                            surface_tilt, False)
 
     # determine the ground temperature ratio and the ratio of the total
@@ -895,7 +896,7 @@ def fuentes(poa_global, temp_air, wind_speed, noct_installed, module_height=5,
         for j in range(10):
             # overall convective coefficient
             tave = (tmod + tamb) / 2
-            hconv = convrat * _fuentes_hconv(tave, windmod,
+            hconv = convrat * _fuentes_hconv(tave, windmod, tinoct,
                                              abs(tmod-tamb), xlen,
                                              surface_tilt, True)
             # sky radiation coefficient (Equation 3)
@@ -1011,24 +1012,22 @@ 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_ratio = 1.
+       Geff = poa_global
     else:
-        irr_ratio = effective_irradiance / poa_global
-
+       Geff= np.maximum(effective_irradiance, 0)
     if array_height == 1:
         wind_adj = 0.51 * wind_speed
     elif array_height == 2:
         wind_adj = 0.61 * wind_speed
     else:
         raise ValueError(
             f'array_height must be 1 or 2, {array_height} was given')
-
     noct_adj = noct + _adj_for_mounting_standoff(mount_standoff)
-    tau_alpha = transmittance_absorptance * irr_ratio
-
     # [1] Eq. 10.37 isn't clear on exactly what "G" is. SAM SSC code uses
     # poa_global where G appears
-    cell_temp_init = poa_global / 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)
     return temp_air + cell_temp_init * heat_loss * wind_loss

tests/test_noct_sam_eff_irradiance.py

@@ -0,0 +1,51 @@
+import numpy as np
+from pvlib.temperature import noct_sam
+
+def test_noct_sam_effective_irr_reduces_temp():
+    # Effective irradiance should lower predicted module temp
+    t_full = noct_sam(
+        poa_global=800, temp_air=20, wind_speed=2,
+        noct=45, module_efficiency=0.20
+    )
+
+    t_eff_600 = noct_sam(
+        poa_global=800, temp_air=20, wind_speed=2,
+        noct=45, module_efficiency=0.20,
+        effective_irradiance=600
+    )
+
+    t_eff_200 = noct_sam(
+        poa_global=800, temp_air=20, wind_speed=2,
+        noct=45, module_efficiency=0.20,
+        effective_irradiance=200
+    )
+
+    assert t_eff_600 < t_full
+    assert t_eff_200 < t_eff_600
+
+
+def test_noct_sam_oc_case_reduces_temp():
+    # Open-circuit (efficiency=0) should still respond to effective irradiance
+    t_oc_full = noct_sam(
+        poa_global=800, temp_air=20, wind_speed=2,
+        noct=45, module_efficiency=0.0
+    )
+
+    t_oc_eff = noct_sam(
+        poa_global=800, temp_air=20, wind_speed=2,
+        noct=45, module_efficiency=0.0,
+        effective_irradiance=300
+    )
+
+    assert t_oc_eff < t_oc_full
+
+
+def test_noct_sam_not_below_ambient_for_small_eff():
+    # Very small effective irradiance should not predict cooling below ambient
+    t_small = noct_sam(
+        poa_global=800, temp_air=20, wind_speed=2,
+        noct=45, module_efficiency=0.20,
+        effective_irradiance=1.0
+    )
+
+    assert t_small >= 20.0 - 1e-6  # small numerical tolerance

tests/test_pvsystem.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_temperature.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)