Clarify which SAPM parameters are required by module in pvsystem.sapm

docs/sphinx/source/whatsnew/v0.12.1.rst

@@ -20,8 +20,10 @@ Enhancements
 Documentation
 ~~~~~~~~~~~~~
 * Add a supporting reference to :py:func:`pvlib.atmosphere.get_relative_airmass` (:issue:`2390`, :pull:`2424`)
-* Documented how `np.nan` values are handled by :py:func:`~pvlib.spectrum.average_photon_energy`
+* Document how ``np.nan`` values are handled by :py:func:`~pvlib.spectrum.average_photon_energy`
   (:issue:`2423`, :pull:`2426`)
+* Clarify which SAPM coefficients are required by the ``module`` parameter in
+  :py:func:`~pvlib.pvsystem.sapm` (:issue:`2392`, :pull:`2435`)
 
 Testing
 ~~~~~~~

pvlib/pvsystem.py

@@ -2199,16 +2199,16 @@ def sapm(effective_irradiance, temp_cell, module):
     '''
     The Sandia PV Array Performance Model (SAPM) generates 5 points on a
     PV module's I-V curve (Voc, Isc, Ix, Ixx, Vmp/Imp) according to
-    SAND2004-3535. Assumes a reference cell temperature of 25 C.
+    SAND2004-3535. Assumes a reference cell temperature of 25°C.
 
     Parameters
     ----------
     effective_irradiance : numeric
         Irradiance reaching the module's cells, after reflections and
-        adjustment for spectrum. [W/m2]
+        adjustment for spectrum. [Wm⁻²]
 
     temp_cell : numeric
-        Cell temperature [C].
+        Cell temperature [°C].
 
     module : dict-like
         A dict or Series defining the SAPM parameters. See the notes section
@@ -2230,12 +2230,12 @@ def sapm(effective_irradiance, temp_cell, module):
 
     Notes
     -----
-    The SAPM parameters which are required in ``module`` are
-    listed in the following table.
-
     The Sandia module database contains parameter values for a limited set
     of modules. The CEC module database does not contain these parameters.
-    Both databases can be accessed using :py:func:`retrieve_sam`.
+    Both databases can be accessed using :py:func:`retrieve_sam`. The full list
+    of SAPM parameters is presented in the table below. All but ``A0`` to
+    ``A4``, ``B0`` to ``B5``, ``C4`` to ``C7``, ``IXO``, and ``IXXO`` are
+    required in the ``module`` parameter.
 
     ================   ========================================================
     Key                Description
@@ -2251,19 +2251,19 @@ def sapm(effective_irradiance, temp_cell, module):
     Voco               Open circuit voltage at reference condition (amps)
     Vmpo               Maximum power voltage at reference condition (amps)
     Aisc               Short circuit current temperature coefficient at
-                       reference condition (1/C)
+                       reference condition (1/°C)
     Aimp               Maximum power current temperature coefficient at
-                       reference condition (1/C)
+                       reference condition (1/°C)
     Bvoco              Open circuit voltage temperature coefficient at
-                       reference condition (V/C)
+                       reference condition (V/°C)
     Mbvoc              Coefficient providing the irradiance dependence for the
                        BetaVoc temperature coefficient at reference irradiance
-                       (V/C)
+                       (V/°C)
     Bvmpo              Maximum power voltage temperature coefficient at
                        reference condition
     Mbvmp              Coefficient providing the irradiance dependence for the
                        BetaVmp temperature coefficient at reference irradiance
-                       (V/C)
+                       (V/°C)
     N                  Empirically determined "diode factor" (dimensionless)
     Cells_in_Series    Number of cells in series in a module's cell string(s)
     IXO                Ix at reference conditions