Drop DataFrame as option for module input to pvsystem.sapm (#811)

* update docstring for pvsystem.sapm

* update whatsnew

* minor edit

Author: cwhanse

docs/sphinx/source/whatsnew/v0.7.0.rst

@@ -142,6 +142,9 @@ Documentation
 ~~~~~~~~~~~~~
 * Corrected docstring for `pvsystem.PVSystem.sapm`
 * Fixed broken ipython examples from CEC data updates
+* Edited docstring for `pvsystem.sapm` to remove DataFrame option for input
+  `module`. The DataFrame option was never tested and would cause an error if
+  used. (:issue:`785`)
 
 Removal of prior version deprecations
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

pvlib/pvsystem.py

@@ -1586,8 +1586,8 @@ def sapm(effective_irradiance, temp_cell, module):
         The cell temperature (degrees C).
 
     module : dict-like
-        A dict, Series, or DataFrame defining the SAPM performance
-        parameters. See the notes section for more details.
+        A dict or Series defining the SAPM parameters. See the notes section
+        for more details.
 
     Returns
     -------
@@ -1605,11 +1605,11 @@ def sapm(effective_irradiance, temp_cell, module):
 
     Notes
     -----
-    The coefficients from SAPM which are required in ``module`` are
+    The SAPM parameters which are required in ``module`` are
     listed in the following table.
 
-    The modules in the Sandia module database contain these
-    coefficients, but the modules in the CEC module database do not.
+    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`.
 
     ================   ========================================================