update whats new v0.8.0

* with new side_slope arg in SingleAxisTracker class
* add fix for low sun angle tracker rotation calculations (issue 824)
* add links to pr 823
* ignore invalid warnings for nan > x and nan % x in tracking.py

Author: mikofski

docs/sphinx/source/whatsnew/v0.8.0.rst

@@ -95,17 +95,19 @@ Enhancements
   :py:func:`~pvlib.tracking.calc_system_tracker_side_slope` to calculate the
   tracker axes tilt and the side-slope angle, which is perpendicular to the
   tracker axes for trackers on sloped terrain that is not parallel to the axes,
-  such as a north-south tracker on an south-east slope.
-* Added `side_slope` argument to :py:func:`~pvlib.tracking.singleaxis` which
-  defaults to zero, for use with
-  :py:func:`~pvlib.tracking.calc_system_tracker_side_slope`
+  such as a north-south tracker on an south-east slope. (:pull:`823`)
+* Added ``side_slope`` argument to :py:func:`~pvlib.tracking.singleaxis` and
+  :py:func:`~pvlib.tracking.SingleAxisTracker` which defaults to zero. Use
+  :py:func:`~pvlib.tracking.calc_system_tracker_side_slope` to calculate the
+  side-slope angle if necessary. (:pull:`823`)
 * Added ability for :py:func:`pvlib.soiling.hsu` to accept arbitrary time intervals. (:pull:`980`)
 
 Bug fixes
 ~~~~~~~~~
 * Fixed unit and default value errors in :py:func:`pvlib.soiling.hsu`. (:pull:`977`, :pull:`980`)
 * Handle NUL characters and fix version column dtype in
   :py:func:`~pvlib.iotools.crn.read_crn`. (:issue:`1025`)
+* Fix low sun angle tracker rotation calculation. (:issue:`824`)
 
 Testing
 ~~~~~~~

pvlib/tracking.py

@@ -489,7 +489,8 @@ def singleaxis(apparent_zenith, apparent_azimuth,
         # NOTE: in the middle of the day, arccos(temp) is out of range because
         # there's no row-to-row shade to avoid, & backtracking is unnecessary
         # Equations 15-16, ref [2]
-        tracker_theta = wid + np.where(temp < 1, wc, 0)
+        with np.errstate(invalid='ignore'):
+            tracker_theta = wid + np.where(temp < 1, wc, 0)
     else:
         tracker_theta = wid
 
@@ -604,7 +605,8 @@ def singleaxis(apparent_zenith, apparent_azimuth,
     # 5. Map azimuth into [0,360) domain.
     # surface_azimuth[surface_azimuth < 0] += 360
     # surface_azimuth[surface_azimuth >= 360] -= 360
-    surface_azimuth = surface_azimuth % 360
+    with np.errstate(invalid='ignore'):
+        surface_azimuth = surface_azimuth % 360
 
     # Calculate surface_tilt
     dotproduct = (panel_norm_earth * projected_normal).sum(axis=1)