Fix PVSystem module_type docstring default

Author: r0hansaxena

docs/sphinx/source/whatsnew/v0.15.1.rst

@@ -38,6 +38,9 @@ Documentation
 * Add AI checkbox to PR template, and auto-generate a comment on PRs
   from first-time contributors regarding AI and contributing guidelines.
   (:issue:`2617`, :pull:`2624`)
+* Fix :py:class:`pvlib.pvsystem.PVSystem` docstring incorrectly stating
+  ``module_type`` defaults to ``'glass_polymer'`` instead of ``None``.
+  (:issue:`2634`)
 * Fix a broken docstring reference to ``grounddiffuse`` in
   :py:func:`pvlib.irradiance.poa_components`
   (:issue:`2089`, :pull:`2708`)

pvlib/pvsystem.py

@@ -140,7 +140,7 @@ class PVSystem:
     module : string, optional
         The model name of the modules.
 
-    module_type : string, default 'glass_polymer'
+    module_type : string, default None
          Describes the module's construction. Valid strings are 'glass_polymer'
          and 'glass_glass'. Used for cell and module temperature calculations.