BUG: fix kimber cleaning threshold and grace period off-by-one

- rainfall equal to cleaning_threshold now triggers cleaning
- grace_period window now correctly includes the rain day itself
- regenerated greensboro nowash/manwash expected test data
- added tests for both cases

Fixes #2796

Author: dgowdaan-cmyk

docs/sphinx/source/whatsnew/v0.15.3.rst

@@ -14,6 +14,9 @@ Deprecations
 
 Bug fixes
 ~~~~~~~~~
+* Fixed :py:func:`pvlib.soiling.kimber` so that rainfall equal to
+  ``cleaning_threshold`` triggers cleaning, and fixed an off-by-one
+  error in the grace period window. (:issue:`2796`)
 
 
 Enhancements

pvlib/soiling.py

@@ -205,10 +205,10 @@ def kimber(rainfall, cleaning_threshold=6, soiling_loss_rate=0.0015,
     soiling = pd.Series(soiling, index=rainfall.index, name='soiling')
 
     # rainfall events that clean the panels
-    rain_events = accumulated_rainfall > cleaning_threshold
+    rain_events = accumulated_rainfall >= cleaning_threshold
 
     # grace periods windows during which ground is assumed damp, so no soiling
-    grace_windows = rain_events.rolling(grace_period, closed='right').sum() > 0
+    grace_windows = rain_events.rolling(grace_period, closed='both').sum() > 0
 
     # clean panels by subtracting soiling for indices in grace period windows
     cleaning = pd.Series(float('NaN'), index=rainfall.index)