pvlib · echedey-ls · Jan 8, 2025 · Jan 8, 2025 · Jan 8, 2025 · Jan 8, 2025
diff --git a/benchmarks/benchmarks/infinite_sheds.py b/benchmarks/benchmarks/infinite_sheds.py
@@ -35,7 +35,7 @@ def setup(self, vectorize):
             self.tracking = tracking.singleaxis(
                 self.solar_position['apparent_zenith'],
                 self.solar_position['azimuth'],
-                axis_tilt=0,
+                axis_slope=0,
                 axis_azimuth=0,
                 max_angle=60,
                 backtrack=True,

diff --git a/benchmarks/benchmarks/tracking.py b/benchmarks/benchmarks/tracking.py
@@ -22,7 +22,7 @@ def time_singleaxis(self):
         with np.errstate(invalid='ignore'):
             tracking.singleaxis(self.solar_position.apparent_zenith,
                                 self.solar_position.azimuth,
-                                axis_tilt=0,
+                                axis_slope=0,
                                 axis_azimuth=0,
                                 max_angle=60,
                                 backtrack=True,

diff --git a/docs/examples/bifacial/plot_bifi_model_mc.py b/docs/examples/bifacial/plot_bifi_model_mc.py
@@ -43,7 +43,7 @@
 times = pd.date_range('2021-06-21', '2021-6-22', freq='1T', tz=tz)
 
 # create site system characteristics
-axis_tilt = 0
+axis_slope = 0
 axis_azimuth = 180
 gcr = 0.35
 max_angle = 60
@@ -65,7 +65,7 @@
 cs = site_location.get_clearsky(times)
 
 # load solar position and tracker orientation for use in pvsystem object
-sat_mount = pvsystem.SingleAxisTrackerMount(axis_tilt=axis_tilt,
+sat_mount = pvsystem.SingleAxisTrackerMount(axis_slope=axis_slope,
                                             axis_azimuth=axis_azimuth,
                                             max_angle=max_angle,
                                             backtrack=True,

diff --git a/docs/examples/irradiance-transposition/plot_transposition_gain.py b/docs/examples/irradiance-transposition/plot_transposition_gain.py
@@ -85,7 +85,7 @@ def calculate_poa(tmy, solar_position, surface_tilt, surface_azimuth):
 # single-axis tracking:
 orientation = tracking.singleaxis(solar_position['apparent_zenith'],
                                   solar_position['azimuth'],
-                                  axis_tilt=0,  # flat array
+                                  axis_slope=0,  # flat array
                                   axis_azimuth=180,  # south-facing azimuth
                                   max_angle=60,  # a common maximum rotation
                                   backtrack=True,  # backtrack for a c-Si array

diff --git a/docs/examples/shading/plot_martinez_shade_loss.py b/docs/examples/shading/plot_martinez_shade_loss.py
@@ -54,8 +54,8 @@
 gcr = width / pitch  # ground coverage ratio
 N_modules_per_row = 6
 axis_azimuth = 180  # N-S axis
-axis_tilt = 0  # flat because the axis is perpendicular to the slope
-cross_axis_tilt = -7  # 7 degrees downward to the east
+axis_slope = 0  # flat because the axis is perpendicular to the slope
+cross_axis_slope = -7  # 7 degrees downward to the east
 
 latitude, longitude = 40.2712, -3.7277
 locus = pvlib.location.Location(
@@ -91,12 +91,12 @@
 tracking_result = pvlib.tracking.singleaxis(
     apparent_zenith=solar_apparent_zenith,
     solar_azimuth=solar_azimuth,
-    axis_tilt=axis_tilt,
+    axis_slope=axis_slope,
     axis_azimuth=axis_azimuth,
-    max_angle=(-90 + cross_axis_tilt, 90 + cross_axis_tilt),  # (min, max)
+    max_angle=(-90 + cross_axis_slope, 90 + cross_axis_slope),  # (min, max)
     backtrack=False,
     gcr=gcr,
-    cross_axis_tilt=cross_axis_tilt,
+    cross_axis_slope=cross_axis_slope,
 )
 
 tracker_theta, aoi, surface_tilt, surface_azimuth = (
@@ -111,12 +111,12 @@
     solar_apparent_zenith,
     solar_azimuth,
     axis_azimuth,
-    axis_tilt=axis_tilt,
+    axis_slope=axis_slope,
     shaded_row_rotation=tracker_theta,
     shading_row_rotation=tracker_theta,
     collector_width=width,
     pitch=pitch,
-    cross_axis_slope=cross_axis_tilt,
+    cross_axis_slope=cross_axis_slope,
 )
 
 # %%

diff --git a/docs/examples/shading/plot_shaded_fraction1d_ns_hsat_example.py b/docs/examples/shading/plot_shaded_fraction1d_ns_hsat_example.py
@@ -44,7 +44,7 @@
 latitude, longitude = 28.51, -13.89
 altitude = pvlib.location.lookup_altitude(latitude, longitude)
 
-axis_tilt = 3  # degrees, positive is upwards in the axis_azimuth direction
+axis_slope = 3  # degrees, positive is upwards in the axis_azimuth direction
 axis_azimuth = 180  # degrees, N-S tracking axis
 collector_width = 3.2  # m
 pitch = 4.15  # m
@@ -71,12 +71,12 @@
 rotation_angle = pvlib.tracking.singleaxis(
     solar_zenith,
     solar_azimuth,
-    axis_tilt,
+    axis_slope,
     axis_azimuth,
     max_angle=(-50, 50),  # (min, max) degrees
     backtrack=False,
     gcr=gcr,
-    cross_axis_tilt=cross_axis_slope,
+    cross_axis_slope=cross_axis_slope,
 )["tracker_theta"]
 
 # %%
@@ -95,7 +95,7 @@
 # failure or with a different system configuration.
 
 psza = pvlib.shading.projected_solar_zenith_angle(
-    solar_zenith, solar_azimuth, axis_tilt, axis_azimuth
+    solar_zenith, solar_azimuth, axis_slope, axis_azimuth
 )
 
 # Calculate the shaded fraction for the eastmost row
@@ -108,7 +108,7 @@
         solar_azimuth,
         axis_azimuth,
         shaded_row_rotation=rotation_angle,
-        axis_tilt=axis_tilt,
+        axis_slope=axis_slope,
         collector_width=collector_width,
         pitch=pitch,
         surface_to_axis_offset=surface_to_axis_offset,
@@ -126,7 +126,7 @@
         solar_azimuth,
         axis_azimuth,
         shaded_row_rotation=rotation_angle,
-        axis_tilt=axis_tilt,
+        axis_slope=axis_slope,
         collector_width=collector_width,
         pitch=pitch,
         surface_to_axis_offset=surface_to_axis_offset,
@@ -139,7 +139,7 @@
         solar_azimuth,
         axis_azimuth,
         shaded_row_rotation=rotation_angle,
-        axis_tilt=axis_tilt,
+        axis_slope=axis_slope,
         collector_width=collector_width,
         pitch=pitch,
         surface_to_axis_offset=surface_to_axis_offset,
@@ -157,7 +157,7 @@
         solar_azimuth,
         axis_azimuth,
         shaded_row_rotation=rotation_angle,
-        axis_tilt=axis_tilt,
+        axis_slope=axis_slope,
         collector_width=collector_width,
         pitch=pitch,
         surface_to_axis_offset=surface_to_axis_offset,

diff --git a/docs/examples/solar-tracking/plot_discontinuous_tracking.py b/docs/examples/solar-tracking/plot_discontinuous_tracking.py
@@ -26,7 +26,7 @@
 
 class DiscontinuousTrackerMount(pvsystem.SingleAxisTrackerMount):
     # inherit from SingleAxisTrackerMount so that we get the
-    # constructor and tracking attributes (axis_tilt etc) automatically
+    # constructor and tracking attributes (axis_slope etc) automatically
 
     def get_orientation(self, solar_zenith, solar_azimuth):
         # Different trackers update at different rates; in this example we'll
@@ -37,9 +37,9 @@ def get_orientation(self, solar_zenith, solar_azimuth):
 
         tracking_data_15min = tracking.singleaxis(
             zenith_subset, azimuth_subset,
-            self.axis_tilt, self.axis_azimuth,
+            self.axis_slope, self.axis_azimuth,
             self.max_angle, self.backtrack,
-            self.gcr, self.cross_axis_tilt
+            self.gcr, self.cross_axis_slope
         )
         # propagate the 15-minute positions to 1-minute stair-stepped values:
         tracking_data_1min = tracking_data_15min.reindex(solar_zenith.index,

diff --git a/docs/examples/solar-tracking/plot_single_axis_tracking.py b/docs/examples/solar-tracking/plot_single_axis_tracking.py
@@ -34,7 +34,7 @@
 truetracking_angles = tracking.singleaxis(
     apparent_zenith=solpos['apparent_zenith'],
     solar_azimuth=solpos['azimuth'],
-    axis_tilt=0,
+    axis_slope=0,
     axis_azimuth=180,
     max_angle=90,
     backtrack=False,  # for true-tracking
@@ -62,7 +62,7 @@
     backtracking_angles = tracking.singleaxis(
         apparent_zenith=solpos['apparent_zenith'],
         solar_azimuth=solpos['azimuth'],
-        axis_tilt=0,
+        axis_slope=0,
         axis_azimuth=180,
         max_angle=90,
         backtrack=True,

diff --git a/docs/examples/solar-tracking/plot_single_axis_tracking_on_sloped_terrain.py b/docs/examples/solar-tracking/plot_single_axis_tracking_on_sloped_terrain.py
@@ -14,8 +14,8 @@
 # calculating the backtracking angle requires knowledge of the relative spacing
 # of adjacent tracker rows. This example shows how the backtracking angle
 # changes based on a vertical offset between rows caused by sloped terrain.
-# It uses :py:func:`pvlib.tracking.calc_axis_tilt` and
-# :py:func:`pvlib.tracking.calc_cross_axis_tilt` to calculate the necessary
+# It uses :py:func:`pvlib.tracking.calc_axis_slope` and
+# :py:func:`pvlib.tracking.calc_cross_axis_slope` to calculate the necessary
 # array geometry parameters and :py:func:`pvlib.tracking.singleaxis` to
 # calculate the backtracking angles.
 #
@@ -97,20 +97,20 @@
 
 # compare the backtracking angle at various terrain slopes
 fig, ax = plt.subplots()
-for cross_axis_tilt in [0, 5, 10]:
+for cross_axis_slope in [0, 5, 10]:
     tracker_data = tracking.singleaxis(
         apparent_zenith=solpos['apparent_zenith'],
         solar_azimuth=solpos['azimuth'],
-        axis_tilt=0,  # flat because the axis is perpendicular to the slope
+        axis_slope=0,  # flat because the axis is perpendicular to the slope
         axis_azimuth=180,  # N-S axis, azimuth facing south
         max_angle=90,
         backtrack=True,
         gcr=gcr,
-        cross_axis_tilt=cross_axis_tilt)
+        cross_axis_slope=cross_axis_slope)
 
     # tracker rotation is undefined at night
     backtracking_position = tracker_data['tracker_theta'].fillna(0)
-    label = 'cross-axis tilt: {}°'.format(cross_axis_tilt)
+    label = 'cross-axis tilt: {}°'.format(cross_axis_slope)
     backtracking_position.plot(label=label, ax=ax)
 
 plt.legend()
@@ -141,14 +141,14 @@
 axis_azimuth = 180  # tracker axis is still N-S
 
 # calculate the tracker axis tilt, assuming that the axis follows the terrain:
-axis_tilt = tracking.calc_axis_tilt(slope_azimuth, slope_tilt, axis_azimuth)
+axis_slope = tracking.calc_axis_slope(slope_azimuth, slope_tilt, axis_azimuth)
 
 # calculate the cross-axis tilt:
-cross_axis_tilt = tracking.calc_cross_axis_tilt(slope_azimuth, slope_tilt,
-                                                axis_azimuth, axis_tilt)
+cross_axis_slope = tracking.calc_cross_axis_slope(slope_azimuth, slope_tilt,
+                                                  axis_azimuth, axis_slope)
 
-print('Axis tilt:', '{:0.01f}°'.format(axis_tilt))
-print('Cross-axis tilt:', '{:0.01f}°'.format(cross_axis_tilt))
+print('Axis tilt:', '{:0.01f}°'.format(axis_slope))
+print('Cross-axis tilt:', '{:0.01f}°'.format(cross_axis_slope))
 
 # %%
 # And now we can pass use these values to generate the tracker curve as
@@ -157,18 +157,18 @@
 tracker_data = tracking.singleaxis(
     apparent_zenith=solpos['apparent_zenith'],
     solar_azimuth=solpos['azimuth'],
-    axis_tilt=axis_tilt,  # no longer flat because the terrain imparts a tilt
+    axis_slope=axis_slope,  # no longer flat because the terrain imparts a tilt
     axis_azimuth=axis_azimuth,
     max_angle=90,
     backtrack=True,
     gcr=gcr,
-    cross_axis_tilt=cross_axis_tilt)
+    cross_axis_slope=cross_axis_slope)
 
 backtracking_position = tracker_data['tracker_theta'].fillna(0)
 backtracking_position.plot()
 
 title_template = 'Axis tilt: {:0.01f}°   Cross-axis tilt: {:0.01f}°'
-plt.title(title_template.format(axis_tilt, cross_axis_tilt))
+plt.title(title_template.format(axis_slope, cross_axis_slope))
 plt.show()
 
 # %%

diff --git a/docs/sphinx/source/_images/Anderson_Mikofski_2020_Fig4.png b/docs/sphinx/source/_images/Anderson_Mikofski_2020_Fig4.png
diff --git a/docs/sphinx/source/reference/tracking.rst b/docs/sphinx/source/reference/tracking.rst
@@ -7,6 +7,6 @@ Tracking
    :toctree: generated/
 
    tracking.singleaxis
-   tracking.calc_axis_tilt
-   tracking.calc_cross_axis_tilt
+   tracking.calc_axis_slope
+   tracking.calc_cross_axis_slope
    tracking.calc_surface_orientation
diff --git a/docs/sphinx/source/user_guide/extras/nomenclature.rst b/docs/sphinx/source/user_guide/extras/nomenclature.rst
@@ -41,9 +41,38 @@ There is a convention on consistent variable names throughout the library:
         Refraction-corrected solar elevation angle. This is the complement of
         :term:`apparent_zenith` (90 - apparent_zenith). [°]
 
+    axis_slope
+        Angle of a tracker axis with respect to horizontal.
+        This is, left-hand rotation angle of :math:`t_y` around :math:`t_x` in Fig. [4] of [Anderson2020]_.
+        See figure in :term:`cross_axis_slope`.
+
     bhi
         Beam/direct horizontal irradiance
 
+    cross_axis_slope
+        Cross-axis slope angle. [°]
+        The angle, relative to horizontal, of the line formed by the
+        intersection between the slope containing the tracker axes and a plane
+        perpendicular to the tracker axes. Cross-axis slope should be specified
+        using a right-handed convention.
+
+        For example, trackers with axis azimuth of 180° (N-S rotation axis)
+        will have a negative cross-axis slope if the tracker axes plane slopes
+        down to the east and positive cross-axis slope if the tracker axes plane
+        slopes up to the east.
+
+        .. figure:: ../../_images/Anderson_Mikofski_2020_Fig4.png
+            :alt: Two rows of modules, tracker coordinate system and cross-axis slope of the second row w.r.t. the leftmost.
+            :align: center
+            :scale: 50 %
+
+        Fig. 4, [Anderson2020]_: Cross-axis slope angle :math:`\beta_C` relative to the tracker coordinate system.
+
+        Use :py::func:`pvlib.tracking.calc_cross_axis_slope` to calculate
+        ``cross_axis_slope``.
+
+        See also :term:`axis_slope`.
+
     dhi
         Diffuse horizontal irradiance
 
@@ -215,3 +244,9 @@ units, refer to the following sources from `SoDa Service <http://www.soda-pro.co
 
 .. note:: These further references might not use the same terminology as
           *pvlib*. But the physical process referred to is the same.
+
+References
+----------
+.. [Anderson2020] K. Anderson and M. Mikofski, 'Slope-Aware Backtracking for
+    Single-Axis Trackers', National Renewable Energy Lab. (NREL), Golden, CO (United States);
+    NREL/TP-5K00-76626, Jul. 2020. :doi:`10.2172/1660126`.
diff --git a/docs/sphinx/source/whatsnew/v0.13.2.rst b/docs/sphinx/source/whatsnew/v0.13.2.rst
@@ -13,7 +13,17 @@ Breaking Changes
 
 Deprecations
 ~~~~~~~~~~~~
+* Rename ``axis_tilt`` and ``cross_axis_tilt`` to ``axis_slope`` and ``cross_axis_slope`` all through the project, while keeping backwards-compatibility. Affects:
 
+  - :py:func:`pvlib.shading.shaded_fraction1d` parameters ``cross_axis_tilt`` and ``axis_tilt``
+  - :py:func:`pvlib.shading.projected_solar_zenith_angle` parameter ``axis_tilt``
+  - :py:func:`pvlib.tracking.singleaxis` parameters ``cross_axis_tilt`` and ``axis_tilt``
+  - :py:func:`pvlib.tracking.calc_surface_orientation` parameter ``axis_tilt``
+  - :py:func:`!pvlib.tracking.calc_axis_tilt` function is renamed to :py:func:`~pvlib.tracking.calc_axis_slope`
+  - :py:func:`!pvlib.tracking.calc_cross_axis_tilt` function is renamed to :py:func:`~pvlib.tracking.calc_cross_axis_slope`, and its parameter ``axis_tilt``
+  - :py:class:`pvlib.pvsystem.SingleAxisTrackerMount` dataclass fields ``axis_tilt`` and ``cross_axis_tilt``
+
+  (:issue:`2334`, :pull:`2543`)
 
 Bug fixes
 ~~~~~~~~~

diff --git a/docs/sphinx/source/whatsnew/v0.8.0.rst b/docs/sphinx/source/whatsnew/v0.8.0.rst
@@ -110,14 +110,14 @@ Enhancements
 * Added ``racking_model``, ``module_type``, and ``temperature_model_parameters`` to
   :py:class:`~pvlib.pvsystem.PVSystem` and :py:class:`~pvlib.tracking.SingleAxisTracker`
   repr methods. (:issue:`1027`)
-* Added :py:func:`~pvlib.tracking.calc_axis_tilt` to calculate the
-  tracker axes tilt and :py:func:`~pvlib.tracking.calc_cross_axis_tilt` to
+* Added :py:func:`!pvlib.tracking.calc_axis_tilt` to calculate the
+  tracker axes tilt and :py:func:`!pvlib.tracking.calc_cross_axis_tilt` to
   calculate the cross-axis tilt, which is the angle, relative to horizontal, of
   the line formed by the intersection between the slope containing the tracker
   axes and a plane perpendicular to the tracker axes. (:pull:`823`)
 * Added ``cross_axis_tilt`` argument to :py:func:`~pvlib.tracking.singleaxis`
   and :py:func:`~pvlib.tracking.SingleAxisTracker` which defaults to zero. Use
-  :py:func:`~pvlib.tracking.calc_cross_axis_tilt` to calculate the cross-axis
+  :py:func:`!pvlib.tracking.calc_cross_axis_tilt` to calculate the cross-axis
   tilt angle if necessary. (:pull:`823`)
 * Added ability for :py:func:`pvlib.soiling.hsu` to accept arbitrary time intervals. (:pull:`980`)
 * Added :py:func:`pvlib.temperature.fuentes` for cell temperature modeling. (:pull:`1037`)

diff --git a/pvlib/_deprecation.py b/pvlib/_deprecation.py
@@ -334,7 +334,7 @@ def renamed_kwarg_warning(since, old_param_name, new_param_name, removal=""):
         Not compatible with positional-only arguments.
 
     .. note::
-        Documentation for the function may updated to reflect the new parameter
+        Affected function docstring may be updated to reflect the new parameter
         name; it is suggested to add a |.. versionchanged::| directive.
 
     Parameters

diff --git a/pvlib/modelchain.py b/pvlib/modelchain.py
@@ -1257,7 +1257,7 @@ def _prep_inputs_tracking(self):
             self.results.solar_position['azimuth'])
         self.results.tracking['surface_tilt'] = (
             self.results.tracking['surface_tilt']
-                .fillna(self.system.axis_tilt))
+                .fillna(self.system.axis_slope))
         self.results.tracking['surface_azimuth'] = (
             self.results.tracking['surface_azimuth']
                 .fillna(self.system.axis_azimuth))