Allow asymmetrical rotation limits in pvlib.tracking.singleaxis

pvlib/pvsystem.py

@@ -1410,12 +1410,17 @@ class SingleAxisTrackerMount(AbstractMount):
         A value denoting the compass direction along which the axis of
         rotation lies, measured east of north. [degrees]
 
-    max_angle : float, default 90
-        A value denoting the maximum rotation angle
+    max_angle : float or tuple, default 90
+        A value denoting the maximum rotation angle, in decimal degrees,
         of the one-axis tracker from its horizontal position (horizontal
-        if axis_tilt = 0). A max_angle of 90 degrees allows the tracker
-        to rotate to a vertical position to point the panel towards a
-        horizon. max_angle of 180 degrees allows for full rotation. [degrees]
+        if axis_tilt = 0). If a float is provided, it represents the maximum
+        rotation angle, and the minimum rotation angle is assumed to be the
+        opposite of the maximum angle. If a tuple of (min_angle, max_angle)
+        is provided, it represents both the minimum and maximum rotation angles.
+
+        A max_angle of 90 degrees allows the tracker to rotate to a vertical
+        position to point the panel towards a horizon. A max_angle of 180 degrees
+        allows for full rotation.
 
     backtrack : bool, default True
         Controls whether the tracker has the capability to "backtrack"

pvlib/tests/test_tracking.py

@@ -151,6 +151,22 @@ def test_max_angle():
     assert_frame_equal(expect, tracker_data)
 
 
+def test_min_angle():
+    apparent_zenith = pd.Series([60])
+    apparent_azimuth = pd.Series([270])
+    tracker_data = tracking.singleaxis(apparent_zenith, apparent_azimuth,
+                                       axis_tilt=0, axis_azimuth=0,
+                                       max_angle=(-45, 50), backtrack=True,
+                                       gcr=2.0/7.0)
+
+    expect = pd.DataFrame({'aoi': 15, 'surface_azimuth': 270,
+                           'surface_tilt': 45, 'tracker_theta': -45},
+                          index=[0], dtype=np.float64)
+    expect = expect[SINGLEAXIS_COL_ORDER]
+
+    assert_frame_equal(expect, tracker_data)
+
+
 def test_backtrack():
     apparent_zenith = pd.Series([80])
     apparent_azimuth = pd.Series([90])

pvlib/tracking.py

@@ -44,12 +44,17 @@ def singleaxis(apparent_zenith, apparent_azimuth,
         A value denoting the compass direction along which the axis of
         rotation lies. Measured in decimal degrees east of north.
 
-    max_angle : float, default 90
+    max_angle : float or tuple, default 90
         A value denoting the maximum rotation angle, in decimal degrees,
         of the one-axis tracker from its horizontal position (horizontal
-        if axis_tilt = 0). A max_angle of 90 degrees allows the tracker
-        to rotate to a vertical position to point the panel towards a
-        horizon. max_angle of 180 degrees allows for full rotation.
+        if axis_tilt = 0). If a float is provided, it represents the maximum
+        rotation angle, and the minimum rotation angle is assumed to be the
+        opposite of the maximum angle. If a tuple of (min_angle, max_angle)
+        is provided, it represents both the minimum and maximum rotation angles.
+
+        A max_angle of 90 degrees allows the tracker to rotate to a vertical
+        position to point the panel towards a horizon. A max_angle of 180 degrees
+        allows for full rotation.
 
     backtrack : bool, default True
         Controls whether the tracker has the capability to "backtrack"
@@ -190,7 +195,17 @@ def singleaxis(apparent_zenith, apparent_azimuth,
 
     # NOTE: max_angle defined relative to zero-point rotation, not the
     # system-plane normal
-    tracker_theta = np.clip(tracker_theta, -max_angle, max_angle)
+
+
+    # Determine minimum and maximum rotation angles for the tracker based on max_angle.
+    # If max_angle is a single value, assume min_angle is the negative of max_angle.
+    if np.array(max_angle).size == 1:
+        min_angle = -max_angle
+    else: 
+        min_angle, max_angle = max_angle
+
+    # Clip tracker_theta between the minimum and maximum angles.
+    tracker_theta = np.clip(tracker_theta, min_angle, max_angle)
 
     # Calculate auxiliary angles
     surface = calc_surface_orientation(tracker_theta, axis_tilt, axis_azimuth)