From 4143e2ae93ee6f4970c566c7823c141cc42a4cf0 Mon Sep 17 00:00:00 2001
From: ramaroesilva <rasilva@fc.ul.pt>
Date: Thu, 18 Dec 2025 23:11:55 +0000
Subject: [PATCH 01/27] Adds faiman_rad and ross models to
 get_cell_temperature().

---
 pvlib/pvsystem.py | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/pvlib/pvsystem.py b/pvlib/pvsystem.py
index fe85359b99..76f53b3e74 100644
--- a/pvlib/pvsystem.py
+++ b/pvlib/pvsystem.py
@@ -1217,11 +1217,12 @@ def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
             Ambient dry bulb temperature [C]
 
         wind_speed : numeric
-            Wind speed [m/s]
+            Wind speed [m/s], although can be ``None`` for ``'ross'`` model
 
         model : str
             Supported models include ``'sapm'``, ``'pvsyst'``,
-            ``'faiman'``, ``'fuentes'``, and ``'noct_sam'``
+            ``'faiman'``, ``'faiman_rad'``, ``'fuentes'``, ``'noct_sam'``,
+            and ``'ross'``
 
         effective_irradiance : numeric, optional
             The irradiance that is converted to photocurrent in W/m^2.
@@ -1267,6 +1268,12 @@ def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
             required = tuple()
             optional = _build_kwargs(['u0', 'u1'],
                                      self.temperature_model_parameters)
+        elif model == 'faiman_rad':
+            func = temperature.faiman_rad
+            required = ()
+            optional = _build_kwargs(['ir_down','u0','u1',
+                                      'sky_view','emissivity'],
+                                     self.temperature_model_parameters)
         elif model == 'fuentes':
             func = temperature.fuentes
             required = _build_tcell_args(['noct_installed'])
@@ -1283,11 +1290,21 @@ def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
             optional = _build_kwargs(['transmittance_absorptance',
                                       'array_height', 'mount_standoff'],
                                      self.temperature_model_parameters)
+        elif model == 'ross':
+            func = temperature.ross
+            required = ()
+            # either noct or k must be defined
+            optional = _build_kwargs(['noct','k'],
+                                      self.temperature_model_parameters)
         else:
             raise ValueError(f'{model} is not a valid cell temperature model')
 
-        temperature_cell = func(poa_global, temp_air, wind_speed,
-                                *required, **optional)
+        if model == 'ross':
+            temperature_cell = func(poa_global, temp_air,
+                                    *required, **optional)
+        else:
+            temperature_cell = func(poa_global, temp_air,  wind_speed,
+                                    *required, **optional)
         return temperature_cell
 
     def dc_ohms_from_percent(self):

From 70bb9483bb890433b3afb2142d84258afaaf5f2e Mon Sep 17 00:00:00 2001
From: ramaroesilva <rasilva@fc.ul.pt>
Date: Thu, 18 Dec 2025 23:24:47 +0000
Subject: [PATCH 02/27] Addresses flake8 formatting issues.

---
 pvlib/pvsystem.py | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/pvlib/pvsystem.py b/pvlib/pvsystem.py
index 76f53b3e74..98e30a168a 100644
--- a/pvlib/pvsystem.py
+++ b/pvlib/pvsystem.py
@@ -1271,8 +1271,8 @@ def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
         elif model == 'faiman_rad':
             func = temperature.faiman_rad
             required = ()
-            optional = _build_kwargs(['ir_down','u0','u1',
-                                      'sky_view','emissivity'],
+            optional = _build_kwargs(['ir_down', 'u0', 'u1',
+                                      'sky_view', 'emissivity'],
                                      self.temperature_model_parameters)
         elif model == 'fuentes':
             func = temperature.fuentes
@@ -1294,8 +1294,8 @@ def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
             func = temperature.ross
             required = ()
             # either noct or k must be defined
-            optional = _build_kwargs(['noct','k'],
-                                      self.temperature_model_parameters)
+            optional = _build_kwargs(['noct', 'k'],
+                                     self.temperature_model_parameters)
         else:
             raise ValueError(f'{model} is not a valid cell temperature model')
 

From acc43b45c60bade542ee36c53418c846468e5434 Mon Sep 17 00:00:00 2001
From: ramaroesilva <rasilva@fc.ul.pt>
Date: Sun, 21 Dec 2025 10:44:12 +0000
Subject: [PATCH 03/27] Updates contribution md file.

---
 docs/sphinx/source/whatsnew/v0.13.2.rst | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/docs/sphinx/source/whatsnew/v0.13.2.rst b/docs/sphinx/source/whatsnew/v0.13.2.rst
index b6170a6053..85aab28275 100644
--- a/docs/sphinx/source/whatsnew/v0.13.2.rst
+++ b/docs/sphinx/source/whatsnew/v0.13.2.rst
@@ -46,6 +46,8 @@ Enhancements
   MERRA-2 reanalysis data. (:pull:`2572`)
 * Add :py:func:`~pvlib.spectrum.spectral_factor_polo`, a function for estimating
   spectral mismatch factors for vertical PV façades. (:issue:`2406`, :pull:`2491`)
+* Includes `ross` and `faiman_rad` in the allowed models within 
+  `pvlib.pvsystem.PVSystem.get_cell_temperature` (:issue:`2625`, :pull:`2631`)
 
 Documentation
 ~~~~~~~~~~~~~
@@ -87,3 +89,4 @@ Contributors
 * Anton Driesse (:ghuser:`adriesse`)
 * Rajiv Daxini (:ghuser:`RDaxini`)
 * Kevin Anderson (:ghuser:`kandersolar`)
+* Rodrigo Amaro e Silva (:ghuser:`ramaroesilva`)
\ No newline at end of file

From 69c7f434a207d17972795e930aeeed8c72d06f59 Mon Sep 17 00:00:00 2001
From: ramaroesilva <rasilva@fc.ul.pt>
Date: Sun, 21 Dec 2025 13:52:52 +0000
Subject: [PATCH 04/27] Adds test for ross option, placeholder for faiman_rad.

---
 tests/test_pvsystem.py | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/tests/test_pvsystem.py b/tests/test_pvsystem.py
index 4fbd782e65..852e84d602 100644
--- a/tests/test_pvsystem.py
+++ b/tests/test_pvsystem.py
@@ -494,6 +494,40 @@ def test_PVSystem_faiman_celltemp(mocker):
     assert_allclose(out, 56.4, atol=1e-1)
 
 
+def test_PVSystem_faiman_rad_celltemp(mocker):
+    # default values (need to account for a certain ir_down and adjust u0, u1)
+    ir_down = None
+    u0, u1 = 25.0, 6.84
+    sky_view = 1.0
+    emissivity = 0.88
+    
+    temp_model_params = {'ir_down': ir_down, 'u0': u0, 'u1': u1,
+                         'sky_view': sky_view, 'emissivity': emissivity}
+    system = pvsystem.PVSystem(temperature_model_parameters=temp_model_params)
+    mocker.spy(temperature, 'faiman_rad')
+    temps = 25
+    irrads = 1000
+    winds = 1
+    out = system.get_cell_temperature(irrads, temps, winds, model='faiman_rad')
+    temperature.faiman_rad.assert_called_once_with(irrads, temps, winds, u0, u1,
+                                                   sky_view, emissivity)
+    assert_allclose(out, 56.4, atol=1e-1)
+
+
+def test_PVSystem_ross_celltemp(mocker):
+    # example value
+    k = 0.0208 # free-standing system
+    
+    temp_model_params = {'k': k}
+    system = pvsystem.PVSystem(temperature_model_parameters=temp_model_params)
+    mocker.spy(temperature, 'ross')
+    temps = 25
+    irrads = 1000
+    out = system.get_cell_temperature(irrads, temps, model='ross')
+    temperature.faiman_rad.assert_called_once_with(irrads, temps, k)
+    assert_allclose(out, 45.8, atol=1e-1)
+
+
 def test_PVSystem_noct_celltemp(mocker):
     poa_global, temp_air, wind_speed, noct, module_efficiency = (
         1000., 25., 1., 45., 0.2)

From 5998725732f7af84c7778f41d483604f6155c837 Mon Sep 17 00:00:00 2001
From: ramaroesilva <rasilva@fc.ul.pt>
Date: Sun, 21 Dec 2025 13:55:57 +0000
Subject: [PATCH 05/27] Corrects flake8 issues.

---
 tests/test_pvsystem.py | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/tests/test_pvsystem.py b/tests/test_pvsystem.py
index 852e84d602..c103f9cff5 100644
--- a/tests/test_pvsystem.py
+++ b/tests/test_pvsystem.py
@@ -500,7 +500,7 @@ def test_PVSystem_faiman_rad_celltemp(mocker):
     u0, u1 = 25.0, 6.84
     sky_view = 1.0
     emissivity = 0.88
-    
+
     temp_model_params = {'ir_down': ir_down, 'u0': u0, 'u1': u1,
                          'sky_view': sky_view, 'emissivity': emissivity}
     system = pvsystem.PVSystem(temperature_model_parameters=temp_model_params)
@@ -509,15 +509,16 @@ def test_PVSystem_faiman_rad_celltemp(mocker):
     irrads = 1000
     winds = 1
     out = system.get_cell_temperature(irrads, temps, winds, model='faiman_rad')
-    temperature.faiman_rad.assert_called_once_with(irrads, temps, winds, u0, u1,
+    temperature.faiman_rad.assert_called_once_with(irrads, temps, winds,
+                                                   u0, u1,
                                                    sky_view, emissivity)
     assert_allclose(out, 56.4, atol=1e-1)
 
 
 def test_PVSystem_ross_celltemp(mocker):
     # example value
-    k = 0.0208 # free-standing system
-    
+    k = 0.0208  # free-standing system
+
     temp_model_params = {'k': k}
     system = pvsystem.PVSystem(temperature_model_parameters=temp_model_params)
     mocker.spy(temperature, 'ross')

From 61e8163be1a86c9bd455eedff6b040be242e6b83 Mon Sep 17 00:00:00 2001
From: ramaroesilva <rasilva@fc.ul.pt>
Date: Sun, 21 Dec 2025 14:06:06 +0000
Subject: [PATCH 06/27] Adds missing wind_speed=None when testing
 get_cell_temperature for ross.

---
 tests/test_pvsystem.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tests/test_pvsystem.py b/tests/test_pvsystem.py
index c103f9cff5..a135932631 100644
--- a/tests/test_pvsystem.py
+++ b/tests/test_pvsystem.py
@@ -524,7 +524,8 @@ def test_PVSystem_ross_celltemp(mocker):
     mocker.spy(temperature, 'ross')
     temps = 25
     irrads = 1000
-    out = system.get_cell_temperature(irrads, temps, model='ross')
+    winds = None
+    out = system.get_cell_temperature(irrads, temps, winds, model='ross')
     temperature.faiman_rad.assert_called_once_with(irrads, temps, k)
     assert_allclose(out, 45.8, atol=1e-1)
 

From 22f94a786d8b0056d1e6839bbaafd2359f1d09b6 Mon Sep 17 00:00:00 2001
From: ramaroesilva <rasilva@fc.ul.pt>
Date: Sun, 21 Dec 2025 15:34:56 +0000
Subject: [PATCH 07/27] Corrects wrong function naming.

---
 tests/test_pvsystem.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/test_pvsystem.py b/tests/test_pvsystem.py
index a135932631..a4e7dcc285 100644
--- a/tests/test_pvsystem.py
+++ b/tests/test_pvsystem.py
@@ -526,7 +526,7 @@ def test_PVSystem_ross_celltemp(mocker):
     irrads = 1000
     winds = None
     out = system.get_cell_temperature(irrads, temps, winds, model='ross')
-    temperature.faiman_rad.assert_called_once_with(irrads, temps, k)
+    temperature.ross.assert_called_once_with(irrads, temps, k)
     assert_allclose(out, 45.8, atol=1e-1)
 
 

From aaa52e32255b7e004c4dffca22aebd51b6226ce9 Mon Sep 17 00:00:00 2001
From: ramaroesilva <rasilva@fc.ul.pt>
Date: Sun, 21 Dec 2025 15:45:58 +0000
Subject: [PATCH 08/27] Adds missing input to functions within tests.

---
 tests/test_pvsystem.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tests/test_pvsystem.py b/tests/test_pvsystem.py
index a4e7dcc285..f9619b79db 100644
--- a/tests/test_pvsystem.py
+++ b/tests/test_pvsystem.py
@@ -510,7 +510,7 @@ def test_PVSystem_faiman_rad_celltemp(mocker):
     winds = 1
     out = system.get_cell_temperature(irrads, temps, winds, model='faiman_rad')
     temperature.faiman_rad.assert_called_once_with(irrads, temps, winds,
-                                                   u0, u1,
+                                                   ir_down, u0, u1,
                                                    sky_view, emissivity)
     assert_allclose(out, 56.4, atol=1e-1)
 
@@ -518,6 +518,7 @@ def test_PVSystem_faiman_rad_celltemp(mocker):
 def test_PVSystem_ross_celltemp(mocker):
     # example value
     k = 0.0208  # free-standing system
+    noct = None # function expects only one of two, the other as None
 
     temp_model_params = {'k': k}
     system = pvsystem.PVSystem(temperature_model_parameters=temp_model_params)
@@ -526,7 +527,7 @@ def test_PVSystem_ross_celltemp(mocker):
     irrads = 1000
     winds = None
     out = system.get_cell_temperature(irrads, temps, winds, model='ross')
-    temperature.ross.assert_called_once_with(irrads, temps, k)
+    temperature.ross.assert_called_once_with(irrads, temps, noct, k)
     assert_allclose(out, 45.8, atol=1e-1)
 
 

From c6d8ab9601cee7cb1cb579f652452d81d73b6368 Mon Sep 17 00:00:00 2001
From: ramaroesilva <rasilva@fc.ul.pt>
Date: Sun, 21 Dec 2025 15:53:25 +0000
Subject: [PATCH 09/27] Corrects test + flake8 issue.

---
 tests/test_pvsystem.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tests/test_pvsystem.py b/tests/test_pvsystem.py
index f9619b79db..54a7b3759b 100644
--- a/tests/test_pvsystem.py
+++ b/tests/test_pvsystem.py
@@ -518,7 +518,7 @@ def test_PVSystem_faiman_rad_celltemp(mocker):
 def test_PVSystem_ross_celltemp(mocker):
     # example value
     k = 0.0208  # free-standing system
-    noct = None # function expects only one of two, the other as None
+    noct = None  # function expects only one of two, the other as None
 
     temp_model_params = {'k': k}
     system = pvsystem.PVSystem(temperature_model_parameters=temp_model_params)
@@ -527,7 +527,7 @@ def test_PVSystem_ross_celltemp(mocker):
     irrads = 1000
     winds = None
     out = system.get_cell_temperature(irrads, temps, winds, model='ross')
-    temperature.ross.assert_called_once_with(irrads, temps, noct, k)
+    temperature.ross.assert_called_once_with(irrads, temps, k=k)
     assert_allclose(out, 45.8, atol=1e-1)
 
 

From 78eb4c3e64a0f2ae8beb012212c462074ab828a9 Mon Sep 17 00:00:00 2001
From: ramaroesilva <rasilva@fc.ul.pt>
Date: Sun, 21 Dec 2025 15:56:00 +0000
Subject: [PATCH 10/27] Minor update in documentation + flake8 issue.

---
 tests/test_pvsystem.py | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/tests/test_pvsystem.py b/tests/test_pvsystem.py
index 54a7b3759b..c373216c43 100644
--- a/tests/test_pvsystem.py
+++ b/tests/test_pvsystem.py
@@ -516,10 +516,9 @@ def test_PVSystem_faiman_rad_celltemp(mocker):
 
 
 def test_PVSystem_ross_celltemp(mocker):
-    # example value
+    # example value (could use equivalent noct as alternative input)
     k = 0.0208  # free-standing system
-    noct = None  # function expects only one of two, the other as None
-
+  
     temp_model_params = {'k': k}
     system = pvsystem.PVSystem(temperature_model_parameters=temp_model_params)
     mocker.spy(temperature, 'ross')

From 402b53caab321d11e0d68d2764c54b0e2b063568 Mon Sep 17 00:00:00 2001
From: ramaroesilva <rasilva@fc.ul.pt>
Date: Sun, 21 Dec 2025 15:57:12 +0000
Subject: [PATCH 11/27] Another flake8 issue handled.

---
 tests/test_pvsystem.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/test_pvsystem.py b/tests/test_pvsystem.py
index c373216c43..3445253370 100644
--- a/tests/test_pvsystem.py
+++ b/tests/test_pvsystem.py
@@ -518,7 +518,7 @@ def test_PVSystem_faiman_rad_celltemp(mocker):
 def test_PVSystem_ross_celltemp(mocker):
     # example value (could use equivalent noct as alternative input)
     k = 0.0208  # free-standing system
-  
+
     temp_model_params = {'k': k}
     system = pvsystem.PVSystem(temperature_model_parameters=temp_model_params)
     mocker.spy(temperature, 'ross')

From 9461e013af32d00cab0aa3d23df609e111111344 Mon Sep 17 00:00:00 2001
From: ramaroesilva <rasilva@fc.ul.pt>
Date: Mon, 22 Dec 2025 08:09:02 +0000
Subject: [PATCH 12/27] Improve faiman_rad test and completes
 get_cell_temperature doc.

---
 pvlib/pvsystem.py      | 8 +++++---
 tests/test_pvsystem.py | 9 +++++----
 2 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/pvlib/pvsystem.py b/pvlib/pvsystem.py
index 98e30a168a..22da2f5f2a 100644
--- a/pvlib/pvsystem.py
+++ b/pvlib/pvsystem.py
@@ -431,7 +431,8 @@ def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
 
         model : str
             Supported models include ``'sapm'``, ``'pvsyst'``,
-            ``'faiman'``, ``'fuentes'``, and ``'noct_sam'``
+            ``'faiman'``, ``'faiman_rad'``, ``'fuentes'``, ``'noct_sam'``,
+            and ``'ross'``
 
         effective_irradiance : numeric or tuple of numeric, optional
             The irradiance that is converted to photocurrent in W/m^2.
@@ -1236,8 +1237,9 @@ def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
         See Also
         --------
         pvlib.temperature.sapm_cell, pvlib.temperature.pvsyst_cell,
-        pvlib.temperature.faiman, pvlib.temperature.fuentes,
-        pvlib.temperature.noct_sam
+        pvlib.temperature.faiman, pvlib.temperature.faiman_rad,
+        pvlib.temperature.fuentes, pvlib.temperature.noct_sam,
+        pvlib.temperature.ross
 
         Notes
         -----
diff --git a/tests/test_pvsystem.py b/tests/test_pvsystem.py
index 3445253370..1cf4f87ed3 100644
--- a/tests/test_pvsystem.py
+++ b/tests/test_pvsystem.py
@@ -495,9 +495,10 @@ def test_PVSystem_faiman_celltemp(mocker):
 
 
 def test_PVSystem_faiman_rad_celltemp(mocker):
-    # default values (need to account for a certain ir_down and adjust u0, u1)
-    ir_down = None
-    u0, u1 = 25.0, 6.84
+    ir_down = 50  # arbitrary value
+    # default values, u0 and u1 being adjusted in same proportion as in
+    # https://www.osti.gov/servlets/purl/1884890/ (not suggested, just example)
+    u0,u1 = 25.0*0.86, 6.84*0.88 
     sky_view = 1.0
     emissivity = 0.88
 
@@ -512,7 +513,7 @@ def test_PVSystem_faiman_rad_celltemp(mocker):
     temperature.faiman_rad.assert_called_once_with(irrads, temps, winds,
                                                    ir_down, u0, u1,
                                                    sky_view, emissivity)
-    assert_allclose(out, 56.4, atol=1e-1)
+    assert_allclose(out, 48.6, atol=1e-1)
 
 
 def test_PVSystem_ross_celltemp(mocker):

From 90350669fb02d0b7fe64394169c8cb25bb4a9427 Mon Sep 17 00:00:00 2001
From: ramaroesilva <rasilva@fc.ul.pt>
Date: Mon, 22 Dec 2025 08:12:05 +0000
Subject: [PATCH 13/27] Addresses flake8.

---
 tests/test_pvsystem.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/test_pvsystem.py b/tests/test_pvsystem.py
index 1cf4f87ed3..109db1859c 100644
--- a/tests/test_pvsystem.py
+++ b/tests/test_pvsystem.py
@@ -498,7 +498,7 @@ def test_PVSystem_faiman_rad_celltemp(mocker):
     ir_down = 50  # arbitrary value
     # default values, u0 and u1 being adjusted in same proportion as in
     # https://www.osti.gov/servlets/purl/1884890/ (not suggested, just example)
-    u0,u1 = 25.0*0.86, 6.84*0.88 
+    u0, u1 = 25.0*0.86, 6.84*0.88
     sky_view = 1.0
     emissivity = 0.88
 

From 6f5bc0d1efdb54bea50e146369ea2c970078cb45 Mon Sep 17 00:00:00 2001
From: ramaroesilva <rasilva@fc.ul.pt>
Date: Mon, 22 Dec 2025 16:04:44 +0000
Subject: [PATCH 14/27] Update whatsnew doc.

---
 docs/sphinx/source/whatsnew/v0.13.2.rst | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/docs/sphinx/source/whatsnew/v0.13.2.rst b/docs/sphinx/source/whatsnew/v0.13.2.rst
index 85aab28275..72dce0efb0 100644
--- a/docs/sphinx/source/whatsnew/v0.13.2.rst
+++ b/docs/sphinx/source/whatsnew/v0.13.2.rst
@@ -46,8 +46,8 @@ Enhancements
   MERRA-2 reanalysis data. (:pull:`2572`)
 * Add :py:func:`~pvlib.spectrum.spectral_factor_polo`, a function for estimating
   spectral mismatch factors for vertical PV façades. (:issue:`2406`, :pull:`2491`)
-* Includes `ross` and `faiman_rad` in the allowed models within 
-  `pvlib.pvsystem.PVSystem.get_cell_temperature` (:issue:`2625`, :pull:`2631`)
+* Include `ross` and `faiman_rad` in the allowed models within 
+  :py:meth:`pvlib.pvsystem.PVSystem.get_cell_temperature` (:issue:`2625`, :pull:`2631`)
 
 Documentation
 ~~~~~~~~~~~~~

From a536cb27745f38047bbd4d613a6c192c42166bc7 Mon Sep 17 00:00:00 2001
From: ramaroesilva <rasilva@fc.ul.pt>
Date: Mon, 22 Dec 2025 16:23:47 +0000
Subject: [PATCH 15/27] Defines ir_down as weather variable Within faiman_rad.

---
 pvlib/pvsystem.py      | 23 +++++++++++++++++------
 tests/test_pvsystem.py |  7 ++++---
 2 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/pvlib/pvsystem.py b/pvlib/pvsystem.py
index 22da2f5f2a..cfc4f0d6b4 100644
--- a/pvlib/pvsystem.py
+++ b/pvlib/pvsystem.py
@@ -414,7 +414,7 @@ def get_iam(self, aoi, iam_model='physical'):
 
     @_unwrap_single_value
     def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
-                             effective_irradiance=None):
+                             effective_irradiance=None, ir_down=None):
         """
         Determine cell temperature using the method specified by ``model``.
 
@@ -437,6 +437,10 @@ def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
         effective_irradiance : numeric or tuple of numeric, optional
             The irradiance that is converted to photocurrent in W/m^2.
             Only used for some models.
+            
+        ir_down: numeric, optional
+            Downwelling infrared radiation from the sky, measured on a 
+            horizontal surface in W/m^2. Only used in ``'faiman_rad'`` model.
 
         Returns
         -------
@@ -460,14 +464,16 @@ def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
         # Not used for all models, but Array.get_cell_temperature handles it
         effective_irradiance = self._validate_per_array(effective_irradiance,
                                                         system_wide=True)
+        ir_down = self._validate_per_array(ir_down, system_wide=True)
 
         return tuple(
             array.get_cell_temperature(poa_global, temp_air, wind_speed,
-                                       model, effective_irradiance)
-            for array, poa_global, temp_air, wind_speed, effective_irradiance
+                                       model, effective_irradiance, ir_down)
+            for array, poa_global, temp_air, wind_speed, effective_irradiance,
+            ir_down
             in zip(
                 self.arrays, poa_global, temp_air, wind_speed,
-                effective_irradiance
+                effective_irradiance, ir_down
             )
         )
 
@@ -1205,7 +1211,7 @@ def get_iam(self, aoi, iam_model='physical'):
             raise ValueError(model + ' is not a valid IAM model')
 
     def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
-                             effective_irradiance=None):
+                             effective_irradiance=None, ir_down=None):
         """
         Determine cell temperature using the method specified by ``model``.
 
@@ -1229,6 +1235,10 @@ def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
             The irradiance that is converted to photocurrent in W/m^2.
             Only used for some models.
 
+        ir_down: numeric, optional
+            Downwelling infrared radiation from the sky, measured on a 
+            horizontal surface in W/m^2. Only used in ``'faiman_rad'`` model.
+
         Returns
         -------
         numeric
@@ -1271,7 +1281,8 @@ def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
             optional = _build_kwargs(['u0', 'u1'],
                                      self.temperature_model_parameters)
         elif model == 'faiman_rad':
-            func = temperature.faiman_rad
+            func = functools.partial(temperature.faiman_rad,
+                                     ir_down=ir_down)
             required = ()
             optional = _build_kwargs(['ir_down', 'u0', 'u1',
                                       'sky_view', 'emissivity'],
diff --git a/tests/test_pvsystem.py b/tests/test_pvsystem.py
index 109db1859c..50e338fa00 100644
--- a/tests/test_pvsystem.py
+++ b/tests/test_pvsystem.py
@@ -502,14 +502,15 @@ def test_PVSystem_faiman_rad_celltemp(mocker):
     sky_view = 1.0
     emissivity = 0.88
 
-    temp_model_params = {'ir_down': ir_down, 'u0': u0, 'u1': u1,
-                         'sky_view': sky_view, 'emissivity': emissivity}
+    temp_model_params = {'u0': u0, 'u1': u1, 'sky_view': sky_view,
+                         'emissivity': emissivity}
     system = pvsystem.PVSystem(temperature_model_parameters=temp_model_params)
     mocker.spy(temperature, 'faiman_rad')
     temps = 25
     irrads = 1000
     winds = 1
-    out = system.get_cell_temperature(irrads, temps, winds, model='faiman_rad')
+    out = system.get_cell_temperature(irrads, temps, winds, ir_down,
+                                      model='faiman_rad')
     temperature.faiman_rad.assert_called_once_with(irrads, temps, winds,
                                                    ir_down, u0, u1,
                                                    sky_view, emissivity)

From bc625789412e211ab1a1ec7d28e75fd22d736777 Mon Sep 17 00:00:00 2001
From: ramaroesilva <rasilva@fc.ul.pt>
Date: Mon, 22 Dec 2025 16:29:06 +0000
Subject: [PATCH 16/27] Handles flake8 issues.

---
 pvlib/pvsystem.py | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/pvlib/pvsystem.py b/pvlib/pvsystem.py
index cfc4f0d6b4..d307c57613 100644
--- a/pvlib/pvsystem.py
+++ b/pvlib/pvsystem.py
@@ -437,9 +437,9 @@ def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
         effective_irradiance : numeric or tuple of numeric, optional
             The irradiance that is converted to photocurrent in W/m^2.
             Only used for some models.
-            
+   
         ir_down: numeric, optional
-            Downwelling infrared radiation from the sky, measured on a 
+            Downwelling infrared radiation from the sky, measured on a
             horizontal surface in W/m^2. Only used in ``'faiman_rad'`` model.
 
         Returns
@@ -1236,7 +1236,7 @@ def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
             Only used for some models.
 
         ir_down: numeric, optional
-            Downwelling infrared radiation from the sky, measured on a 
+            Downwelling infrared radiation from the sky, measured on a
             horizontal surface in W/m^2. Only used in ``'faiman_rad'`` model.
 
         Returns

From 7612e56f9a5b28ab82fb5b909241de26f77923e2 Mon Sep 17 00:00:00 2001
From: ramaroesilva <rasilva@fc.ul.pt>
Date: Mon, 22 Dec 2025 22:55:29 +0000
Subject: [PATCH 17/27] Corrects bug in test.

---
 tests/test_pvsystem.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/test_pvsystem.py b/tests/test_pvsystem.py
index 50e338fa00..ab74566c92 100644
--- a/tests/test_pvsystem.py
+++ b/tests/test_pvsystem.py
@@ -509,7 +509,7 @@ def test_PVSystem_faiman_rad_celltemp(mocker):
     temps = 25
     irrads = 1000
     winds = 1
-    out = system.get_cell_temperature(irrads, temps, winds, ir_down,
+    out = system.get_cell_temperature(irrads, temps, winds, ir_down=ir_down,
                                       model='faiman_rad')
     temperature.faiman_rad.assert_called_once_with(irrads, temps, winds,
                                                    ir_down, u0, u1,

From 534e2f6f43cd825ffce5d03993d9af2123667acd Mon Sep 17 00:00:00 2001
From: ramaroesilva <rasilva@fc.ul.pt>
Date: Mon, 22 Dec 2025 23:00:26 +0000
Subject: [PATCH 18/27] Handles flake8.

---
 pvlib/pvsystem.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pvlib/pvsystem.py b/pvlib/pvsystem.py
index d307c57613..bf4dcb685a 100644
--- a/pvlib/pvsystem.py
+++ b/pvlib/pvsystem.py
@@ -437,7 +437,7 @@ def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
         effective_irradiance : numeric or tuple of numeric, optional
             The irradiance that is converted to photocurrent in W/m^2.
             Only used for some models.
-   
+
         ir_down: numeric, optional
             Downwelling infrared radiation from the sky, measured on a
             horizontal surface in W/m^2. Only used in ``'faiman_rad'`` model.

From 628c15b419da483d7a1ab520cdbd17acba588223 Mon Sep 17 00:00:00 2001
From: Cliff Hansen <cwhanse@sandia.gov>
Date: Tue, 31 Mar 2026 15:53:23 -0700
Subject: [PATCH 19/27] move whatsnew note

---
 docs/sphinx/source/whatsnew/v0.15.1.rst | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/docs/sphinx/source/whatsnew/v0.15.1.rst b/docs/sphinx/source/whatsnew/v0.15.1.rst
index 75ab242c94..d6d5625405 100644
--- a/docs/sphinx/source/whatsnew/v0.15.1.rst
+++ b/docs/sphinx/source/whatsnew/v0.15.1.rst
@@ -29,7 +29,8 @@ Enhancements
 ~~~~~~~~~~~~
 * Use ``k`` and ``cap_adjustment`` from :py:func:`pvlib.pvsystem.Array.module_parameters` in :py:func:`pvlib.pvsystem.PVSystem.pvwatts_dc`
   (:issue:`2714`, :pull:`2715`)
-  
+* Include `ross` and `faiman_rad` in the allowed models within 
+  :py:meth:`pvlib.pvsystem.PVSystem.get_cell_temperature` (:issue:`2625`, :pull:`2631`)  
 
 Documentation
 ~~~~~~~~~~~~~
@@ -84,4 +85,4 @@ Contributors
 * Rohan Saxena (:ghuser:`r0hansaxena`)
 * Marco Fumagalli (:ghuser:`fuma900`)
 * Jean-Baptiste Pasquier (:ghuser:`pasquierjb`)
-
+* Rodrigo Amaro e Silva (:ghuser:`ramaroesilva`)

From 747f7b993e9191cbea939ffc0660510fa0e5b266 Mon Sep 17 00:00:00 2001
From: Cliff Hansen <cwhanse@sandia.gov>
Date: Tue, 31 Mar 2026 15:54:27 -0700
Subject: [PATCH 20/27] undo edit to v0.14.0.rst

---
 docs/sphinx/source/whatsnew/v0.14.0.rst | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/docs/sphinx/source/whatsnew/v0.14.0.rst b/docs/sphinx/source/whatsnew/v0.14.0.rst
index ab29570360..4d7c4b1a50 100644
--- a/docs/sphinx/source/whatsnew/v0.14.0.rst
+++ b/docs/sphinx/source/whatsnew/v0.14.0.rst
@@ -41,8 +41,6 @@ Enhancements
   MERRA-2 reanalysis data. (:pull:`2572`)
 * Add :py:func:`~pvlib.spectrum.spectral_factor_polo`, a function for estimating
   spectral mismatch factors for vertical PV façades. (:issue:`2406`, :pull:`2491`)
-* Include `ross` and `faiman_rad` in the allowed models within 
-  :py:meth:`pvlib.pvsystem.PVSystem.get_cell_temperature` (:issue:`2625`, :pull:`2631`)
 
 Documentation
 ~~~~~~~~~~~~~
@@ -74,7 +72,6 @@ Contributors
 * Anton Driesse (:ghuser:`adriesse`)
 * Rajiv Daxini (:ghuser:`RDaxini`)
 * Kevin Anderson (:ghuser:`kandersolar`)
-* Rodrigo Amaro e Silva (:ghuser:`ramaroesilva`)
 * Mark Mikofski (:ghuser:`mikofski`)
 * Will Holmgren (:ghuser:`wholmgren`)
 * Ioannis Sifnaios (:ghuser:`IoannisSifnaios`)

From 080a84b2323d5653bc4e5a3f585043f8fa27b61b Mon Sep 17 00:00:00 2001
From: Cliff Hansen <cwhanse@sandia.gov>
Date: Tue, 31 Mar 2026 15:55:50 -0700
Subject: [PATCH 21/27] Apply suggestions from code review

Co-authored-by: Echedey Luis <80125792+echedey-ls@users.noreply.github.com>
Co-authored-by: Kevin Anderson <kevin.anderso@gmail.com>
---
 pvlib/pvsystem.py | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/pvlib/pvsystem.py b/pvlib/pvsystem.py
index 33878ff85f..54bfc1bdde 100644
--- a/pvlib/pvsystem.py
+++ b/pvlib/pvsystem.py
@@ -438,7 +438,7 @@ def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
             The irradiance that is converted to photocurrent in W/m^2.
             Only used for some models.
 
-        ir_down: numeric, optional
+        ir_down: numeric or tuple of numeric, optional
             Downwelling infrared radiation from the sky, measured on a
             horizontal surface in W/m^2. Only used in ``'faiman_rad'`` model.
 
@@ -1228,7 +1228,8 @@ def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
             Ambient dry bulb temperature [C]
 
         wind_speed : numeric
-            Wind speed [m/s], although can be ``None`` for ``'ross'`` model
+            Wind speed [m/s]
+            When ``model='ross'``, this input is ignored
 
         model : str
             Supported models include ``'sapm'``, ``'pvsyst'``,
@@ -1288,7 +1289,7 @@ def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
             func = functools.partial(temperature.faiman_rad,
                                      ir_down=ir_down)
             required = ()
-            optional = _build_kwargs(['ir_down', 'u0', 'u1',
+            optional = _build_kwargs(['u0', 'u1',
                                       'sky_view', 'emissivity'],
                                      self.temperature_model_parameters)
         elif model == 'fuentes':

From d55cf78b3980f85af089b10773fe3695c08c9461 Mon Sep 17 00:00:00 2001
From: Cliff Hansen <cwhanse@sandia.gov>
Date: Wed, 1 Apr 2026 09:45:35 -0700
Subject: [PATCH 22/27] replace ir_down with longwave_down

---
 pvlib/pvsystem.py      | 20 +++++++++++---------
 tests/test_pvsystem.py |  7 ++++---
 2 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/pvlib/pvsystem.py b/pvlib/pvsystem.py
index 54bfc1bdde..465b7d83dc 100644
--- a/pvlib/pvsystem.py
+++ b/pvlib/pvsystem.py
@@ -414,7 +414,7 @@ def get_iam(self, aoi, iam_model='physical'):
 
     @_unwrap_single_value
     def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
-                             effective_irradiance=None, ir_down=None):
+                             effective_irradiance=None, longwave_down=None):
         """
         Determine cell temperature using the method specified by ``model``.
 
@@ -438,7 +438,7 @@ def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
             The irradiance that is converted to photocurrent in W/m^2.
             Only used for some models.
 
-        ir_down: numeric or tuple of numeric, optional
+        longwave_down: numeric or tuple of numeric, optional
             Downwelling infrared radiation from the sky, measured on a
             horizontal surface in W/m^2. Only used in ``'faiman_rad'`` model.
 
@@ -464,16 +464,18 @@ def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
         # Not used for all models, but Array.get_cell_temperature handles it
         effective_irradiance = self._validate_per_array(effective_irradiance,
                                                         system_wide=True)
-        ir_down = self._validate_per_array(ir_down, system_wide=True)
+        longwave_down = self._validate_per_array(longwave_down,
+                                                 system_wide=True)
 
         return tuple(
             array.get_cell_temperature(poa_global, temp_air, wind_speed,
-                                       model, effective_irradiance, ir_down)
+                                       model, effective_irradiance,
+                                       longwave_down)
             for array, poa_global, temp_air, wind_speed, effective_irradiance,
-            ir_down
+            longwave_down
             in zip(
                 self.arrays, poa_global, temp_air, wind_speed,
-                effective_irradiance, ir_down
+                effective_irradiance, longwave_down
             )
         )
 
@@ -1215,7 +1217,7 @@ def get_iam(self, aoi, iam_model='physical'):
             raise ValueError(model + ' is not a valid IAM model')
 
     def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
-                             effective_irradiance=None, ir_down=None):
+                             effective_irradiance=None, longwave_down=None):
         """
         Determine cell temperature using the method specified by ``model``.
 
@@ -1240,7 +1242,7 @@ def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
             The irradiance that is converted to photocurrent in W/m^2.
             Only used for some models.
 
-        ir_down: numeric, optional
+        longwave_down: numeric, optional
             Downwelling infrared radiation from the sky, measured on a
             horizontal surface in W/m^2. Only used in ``'faiman_rad'`` model.
 
@@ -1287,7 +1289,7 @@ def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
                                      self.temperature_model_parameters)
         elif model == 'faiman_rad':
             func = functools.partial(temperature.faiman_rad,
-                                     ir_down=ir_down)
+                                     longwave_down=longwave_down)
             required = ()
             optional = _build_kwargs(['u0', 'u1',
                                       'sky_view', 'emissivity'],
diff --git a/tests/test_pvsystem.py b/tests/test_pvsystem.py
index 48b7504bcd..cdd21d17e3 100644
--- a/tests/test_pvsystem.py
+++ b/tests/test_pvsystem.py
@@ -495,7 +495,7 @@ def test_PVSystem_faiman_celltemp(mocker):
 
 
 def test_PVSystem_faiman_rad_celltemp(mocker):
-    ir_down = 50  # arbitrary value
+    longwave_down = 50  # arbitrary value
     # default values, u0 and u1 being adjusted in same proportion as in
     # https://www.osti.gov/servlets/purl/1884890/ (not suggested, just example)
     u0, u1 = 25.0*0.86, 6.84*0.88
@@ -509,10 +509,11 @@ def test_PVSystem_faiman_rad_celltemp(mocker):
     temps = 25
     irrads = 1000
     winds = 1
-    out = system.get_cell_temperature(irrads, temps, winds, ir_down=ir_down,
+    out = system.get_cell_temperature(irrads, temps, winds,
+                                      longwave_down=longwave_down,
                                       model='faiman_rad')
     temperature.faiman_rad.assert_called_once_with(irrads, temps, winds,
-                                                   ir_down, u0, u1,
+                                                   longwave_down, u0, u1,
                                                    sky_view, emissivity)
     assert_allclose(out, 48.6, atol=1e-1)
 

From 1398207dbd5fe8ad254f9f82f05d1473c08d1838 Mon Sep 17 00:00:00 2001
From: Cliff Hansen <cwhanse@sandia.gov>
Date: Wed, 1 Apr 2026 11:41:24 -0700
Subject: [PATCH 23/27] finish replacing ir_down with longwave_down

---
 pvlib/temperature.py   | 18 +++++++++---------
 tests/test_pvsystem.py |  4 ++--
 2 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/pvlib/temperature.py b/pvlib/temperature.py
index cb487ee77b..c601590e96 100644
--- a/pvlib/temperature.py
+++ b/pvlib/temperature.py
@@ -509,7 +509,7 @@ def faiman(poa_global, temp_air, wind_speed=1.0, u0=25.0, u1=6.84):
     return temp_air + temp_difference
 
 
-def faiman_rad(poa_global, temp_air, wind_speed=1.0, ir_down=None,
+def faiman_rad(poa_global, temp_air, wind_speed=1.0, longwave_down=None,
                u0=25.0, u1=6.84, sky_view=1.0, emissivity=0.88):
     r'''
     Calculate cell or module temperature using the Faiman model augmented
@@ -534,7 +534,7 @@ def faiman_rad(poa_global, temp_air, wind_speed=1.0, ir_down=None,
         factor was determined.  The default value 1.0 m/s is the wind
         speed at module height used to determine NOCT. [m/s]
 
-    ir_down : numeric, default 0.0
+    longwave_down : numeric, default 0.0
         Downwelling infrared radiation from the sky, measured on a horizontal
         surface. [W/m^2]
 
@@ -572,11 +572,11 @@ def faiman_rad(poa_global, temp_air, wind_speed=1.0, ir_down=None,
     are vectors they must be the same length.
 
     When only irradiance, air temperature and wind speed inputs are provided
-    (`ir_down` is `None`) this function calculates the same device temperature
-    as the original faiman model. When down-welling long-wave radiation data
-    are provided as well (`ir_down` is not None) the default u0 and u1 values
-    from the original model should not be used because a portion of the
-    radiative losses would be double-counted.
+    (`longwave_down` is `None`) this function calculates the same device
+    temperature as the original faiman model. When downwelling long-wave
+    radiation data are provided (`longwave_down` is not None) the
+    default `u0` and `u1` values from the original model should not be used
+    because a portion of the radiative losses would be double-counted.
 
     References
     ----------
@@ -606,11 +606,11 @@ def faiman_rad(poa_global, temp_air, wind_speed=1.0, ir_down=None,
     abs_zero = -273.15
     sigma = scipy.constants.Stefan_Boltzmann
 
-    if ir_down is None:
+    if longwave_down is None:
         qrad_sky = 0.0
     else:
         ir_up = sigma * ((temp_air - abs_zero)**4)
-        qrad_sky = emissivity * sky_view * (ir_up - ir_down)
+        qrad_sky = emissivity * sky_view * (ir_up - longwave_down)
 
     heat_input = poa_global - qrad_sky
     total_loss_factor = u0 + u1 * wind_speed
diff --git a/tests/test_pvsystem.py b/tests/test_pvsystem.py
index cdd21d17e3..46c07d5b81 100644
--- a/tests/test_pvsystem.py
+++ b/tests/test_pvsystem.py
@@ -510,8 +510,8 @@ def test_PVSystem_faiman_rad_celltemp(mocker):
     irrads = 1000
     winds = 1
     out = system.get_cell_temperature(irrads, temps, winds,
-                                      longwave_down=longwave_down,
-                                      model='faiman_rad')
+                                      model='faiman_rad',
+                                      longwave_down=longwave_down)
     temperature.faiman_rad.assert_called_once_with(irrads, temps, winds,
                                                    longwave_down, u0, u1,
                                                    sky_view, emissivity)

From 72b983918db8a3a80f26e5c8a4af7add7d448dac Mon Sep 17 00:00:00 2001
From: Cliff Hansen <cwhanse@sandia.gov>
Date: Wed, 1 Apr 2026 11:52:35 -0700
Subject: [PATCH 24/27] undo edits to temperature.py

---
 pvlib/temperature.py | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/pvlib/temperature.py b/pvlib/temperature.py
index c601590e96..cb487ee77b 100644
--- a/pvlib/temperature.py
+++ b/pvlib/temperature.py
@@ -509,7 +509,7 @@ def faiman(poa_global, temp_air, wind_speed=1.0, u0=25.0, u1=6.84):
     return temp_air + temp_difference
 
 
-def faiman_rad(poa_global, temp_air, wind_speed=1.0, longwave_down=None,
+def faiman_rad(poa_global, temp_air, wind_speed=1.0, ir_down=None,
                u0=25.0, u1=6.84, sky_view=1.0, emissivity=0.88):
     r'''
     Calculate cell or module temperature using the Faiman model augmented
@@ -534,7 +534,7 @@ def faiman_rad(poa_global, temp_air, wind_speed=1.0, longwave_down=None,
         factor was determined.  The default value 1.0 m/s is the wind
         speed at module height used to determine NOCT. [m/s]
 
-    longwave_down : numeric, default 0.0
+    ir_down : numeric, default 0.0
         Downwelling infrared radiation from the sky, measured on a horizontal
         surface. [W/m^2]
 
@@ -572,11 +572,11 @@ def faiman_rad(poa_global, temp_air, wind_speed=1.0, longwave_down=None,
     are vectors they must be the same length.
 
     When only irradiance, air temperature and wind speed inputs are provided
-    (`longwave_down` is `None`) this function calculates the same device
-    temperature as the original faiman model. When downwelling long-wave
-    radiation data are provided (`longwave_down` is not None) the
-    default `u0` and `u1` values from the original model should not be used
-    because a portion of the radiative losses would be double-counted.
+    (`ir_down` is `None`) this function calculates the same device temperature
+    as the original faiman model. When down-welling long-wave radiation data
+    are provided as well (`ir_down` is not None) the default u0 and u1 values
+    from the original model should not be used because a portion of the
+    radiative losses would be double-counted.
 
     References
     ----------
@@ -606,11 +606,11 @@ def faiman_rad(poa_global, temp_air, wind_speed=1.0, longwave_down=None,
     abs_zero = -273.15
     sigma = scipy.constants.Stefan_Boltzmann
 
-    if longwave_down is None:
+    if ir_down is None:
         qrad_sky = 0.0
     else:
         ir_up = sigma * ((temp_air - abs_zero)**4)
-        qrad_sky = emissivity * sky_view * (ir_up - longwave_down)
+        qrad_sky = emissivity * sky_view * (ir_up - ir_down)
 
     heat_input = poa_global - qrad_sky
     total_loss_factor = u0 + u1 * wind_speed

From d9a808de4f0023d7177f66c0a5b7c1bc1b83dd64 Mon Sep 17 00:00:00 2001
From: Cliff Hansen <cwhanse@sandia.gov>
Date: Wed, 1 Apr 2026 11:55:12 -0700
Subject: [PATCH 25/27] temperature.faiman_rad doesn't use longwave_down yet

---
 pvlib/pvsystem.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pvlib/pvsystem.py b/pvlib/pvsystem.py
index 465b7d83dc..f839126da5 100644
--- a/pvlib/pvsystem.py
+++ b/pvlib/pvsystem.py
@@ -1289,7 +1289,7 @@ def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
                                      self.temperature_model_parameters)
         elif model == 'faiman_rad':
             func = functools.partial(temperature.faiman_rad,
-                                     longwave_down=longwave_down)
+                                     ir_down=longwave_down)
             required = ()
             optional = _build_kwargs(['u0', 'u1',
                                       'sky_view', 'emissivity'],

From 82fa5030ec714c5b2c5c2e18e27e958933146b80 Mon Sep 17 00:00:00 2001
From: Cliff Hansen <cwhanse@sandia.gov>
Date: Wed, 1 Apr 2026 12:46:27 -0700
Subject: [PATCH 26/27] Apply suggestions from code review

Co-authored-by: Anton Driesse <anton.driesse@pvperformancelabs.com>
---
 pvlib/pvsystem.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pvlib/pvsystem.py b/pvlib/pvsystem.py
index f839126da5..e8d3c1d6e9 100644
--- a/pvlib/pvsystem.py
+++ b/pvlib/pvsystem.py
@@ -439,7 +439,7 @@ def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
             Only used for some models.
 
         longwave_down: numeric or tuple of numeric, optional
-            Downwelling infrared radiation from the sky, measured on a
+            Downwelling long-wave radiation from the sky, measured on a
             horizontal surface in W/m^2. Only used in ``'faiman_rad'`` model.
 
         Returns
@@ -1243,7 +1243,7 @@ def get_cell_temperature(self, poa_global, temp_air, wind_speed, model,
             Only used for some models.
 
         longwave_down: numeric, optional
-            Downwelling infrared radiation from the sky, measured on a
+            Downwelling long-wave radiation from the sky, measured on a
             horizontal surface in W/m^2. Only used in ``'faiman_rad'`` model.
 
         Returns

From 12e27ffb15a28375d8ba5d133fd7ee2516d0d64b Mon Sep 17 00:00:00 2001
From: Cliff Hansen <cwhanse@sandia.gov>
Date: Thu, 2 Apr 2026 08:08:51 -0700
Subject: [PATCH 27/27] Update tests/test_pvsystem.py

Co-authored-by: Echedey Luis <80125792+echedey-ls@users.noreply.github.com>
---
 tests/test_pvsystem.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tests/test_pvsystem.py b/tests/test_pvsystem.py
index 46c07d5b81..9257b769f3 100644
--- a/tests/test_pvsystem.py
+++ b/tests/test_pvsystem.py
@@ -524,12 +524,12 @@ def test_PVSystem_ross_celltemp(mocker):
 
     temp_model_params = {'k': k}
     system = pvsystem.PVSystem(temperature_model_parameters=temp_model_params)
-    mocker.spy(temperature, 'ross')
+    m = mocker.spy(temperature, 'ross')
     temps = 25
     irrads = 1000
     winds = None
     out = system.get_cell_temperature(irrads, temps, winds, model='ross')
-    temperature.ross.assert_called_once_with(irrads, temps, k=k)
+    m.assert_called_once_with(irrads, temps, k=k)
     assert_allclose(out, 45.8, atol=1e-1)