Improve faiman_rad test and completes get_cell_temperature doc.

Author: ramaroesilva

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
         -----

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):