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Add is_backtracking and is_at_limit outputs to singleaxis #2709

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3 changes: 3 additions & 0 deletions docs/sphinx/source/whatsnew/v0.15.1.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,9 @@ Bug fixes

Enhancements
~~~~~~~~~~~~
* Add ``is_backtracking`` and ``is_at_limit`` boolean outputs to
:py:func:`pvlib.tracking.singleaxis`
(:issue:`2672`, :ghuser:`r0hansaxena`)


Documentation
Expand Down
20 changes: 16 additions & 4 deletions pvlib/tracking.py
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Expand Up @@ -103,6 +103,10 @@ def singleaxis(apparent_zenith, solar_azimuth,
* `surface_azimuth`: The azimuth of the rotated panel, determined by
projecting the vector normal to the panel's surface to the earth's
surface. [degrees]
* `is_backtracking`: Boolean indicator of whether the tracker is
in backtracking mode to avoid row-to-row shading.
* `is_at_limit`: Boolean indicator of whether the rotation angle
has been clipped to ``max_angle`` or its opposite.

See also
--------
Expand Down Expand Up @@ -172,11 +176,14 @@ def singleaxis(apparent_zenith, solar_azimuth,
# there's no row-to-row shade to avoid, & backtracking is unnecessary
# [1], Eqs. 15-16
with np.errstate(invalid='ignore'):
_backtracking_mask = temp < 1
tracker_theta = omega_ideal + np.where(
temp < 1, omega_correction,
_backtracking_mask, omega_correction,
0)
is_backtracking = _backtracking_mask
else:
tracker_theta = omega_ideal
is_backtracking = np.full_like(omega_ideal, False, dtype=bool)

# NOTE: max_angle defined relative to zero-point rotation, not the
# system-plane normal
Expand All @@ -189,7 +196,9 @@ def singleaxis(apparent_zenith, solar_azimuth,
min_angle, max_angle = max_angle

# Clip tracker_theta between the minimum and maximum angles.
tracker_theta_unclipped = tracker_theta.copy()
tracker_theta = np.clip(tracker_theta, min_angle, max_angle)
is_at_limit = tracker_theta_unclipped != tracker_theta

# Calculate auxiliary angles
surface = calc_surface_orientation(tracker_theta, axis_tilt, axis_azimuth)
Expand All @@ -200,12 +209,15 @@ def singleaxis(apparent_zenith, solar_azimuth,

# Bundle DataFrame for return values and filter for sun below horizon.
out = {'tracker_theta': tracker_theta, 'aoi': aoi,
'surface_azimuth': surface_azimuth, 'surface_tilt': surface_tilt}
'surface_azimuth': surface_azimuth, 'surface_tilt': surface_tilt,
'is_backtracking': is_backtracking, 'is_at_limit': is_at_limit}
if index is not None:
out = pd.DataFrame(out, index=index)
out[zen_gt_90] = np.nan
out.loc[zen_gt_90, ['tracker_theta', 'aoi',
'surface_azimuth', 'surface_tilt']] = np.nan
else:
out = {k: np.where(zen_gt_90, np.nan, v) for k, v in out.items()}
for k in ['tracker_theta', 'aoi', 'surface_azimuth', 'surface_tilt']:
out[k] = np.where(zen_gt_90, np.nan, out[k])

return out

Expand Down
83 changes: 67 additions & 16 deletions tests/test_tracking.py
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Expand Up @@ -27,7 +27,7 @@ def test_solar_noon():
index=index, dtype=np.float64)
expect = expect[SINGLEAXIS_COL_ORDER]

assert_frame_equal(expect, tracker_data)
assert_frame_equal(expect, tracker_data[SINGLEAXIS_COL_ORDER])


def test_scalars():
Expand Down Expand Up @@ -86,7 +86,7 @@ def test_nans():
[nan, nan, nan, nan],
[nan, nan, nan, nan]]),
columns=['tracker_theta', 'aoi', 'surface_azimuth', 'surface_tilt'])
assert_frame_equal(tracker_data, expect)
assert_frame_equal(tracker_data[SINGLEAXIS_COL_ORDER], expect)


def test_arrays_multi():
Expand Down Expand Up @@ -122,7 +122,7 @@ def test_azimuth_north_south():
index=[0], dtype=np.float64)
expect = expect[SINGLEAXIS_COL_ORDER]

assert_frame_equal(expect, tracker_data)
assert_frame_equal(expect, tracker_data[SINGLEAXIS_COL_ORDER])

tracker_data = tracking.singleaxis(apparent_zenith, apparent_azimuth,
axis_tilt=0, axis_azimuth=0,
Expand All @@ -131,7 +131,7 @@ def test_azimuth_north_south():

expect['tracker_theta'] *= -1

assert_frame_equal(expect, tracker_data)
assert_frame_equal(expect, tracker_data[SINGLEAXIS_COL_ORDER])


def test_max_angle():
Expand All @@ -147,7 +147,7 @@ def test_max_angle():
index=[0], dtype=np.float64)
expect = expect[SINGLEAXIS_COL_ORDER]

assert_frame_equal(expect, tracker_data)
assert_frame_equal(expect, tracker_data[SINGLEAXIS_COL_ORDER])


def test_min_angle():
Expand All @@ -163,7 +163,7 @@ def test_min_angle():
index=[0], dtype=np.float64)
expect = expect[SINGLEAXIS_COL_ORDER]

assert_frame_equal(expect, tracker_data)
assert_frame_equal(expect, tracker_data[SINGLEAXIS_COL_ORDER])


def test_backtrack():
Expand All @@ -180,7 +180,7 @@ def test_backtrack():
index=[0], dtype=np.float64)
expect = expect[SINGLEAXIS_COL_ORDER]

assert_frame_equal(expect, tracker_data)
assert_frame_equal(expect, tracker_data[SINGLEAXIS_COL_ORDER])

tracker_data = tracking.singleaxis(apparent_zenith, apparent_azimuth,
axis_tilt=0, axis_azimuth=0,
Expand All @@ -192,7 +192,7 @@ def test_backtrack():
index=[0], dtype=np.float64)
expect = expect[SINGLEAXIS_COL_ORDER]

assert_frame_equal(expect, tracker_data)
assert_frame_equal(expect, tracker_data[SINGLEAXIS_COL_ORDER])


def test_axis_tilt():
Expand All @@ -210,7 +210,7 @@ def test_axis_tilt():
index=[0], dtype=np.float64)
expect = expect[SINGLEAXIS_COL_ORDER]

assert_frame_equal(expect, tracker_data)
assert_frame_equal(expect, tracker_data[SINGLEAXIS_COL_ORDER])

tracker_data = tracking.singleaxis(apparent_zenith, apparent_azimuth,
axis_tilt=30, axis_azimuth=0,
Expand All @@ -222,7 +222,7 @@ def test_axis_tilt():
index=[0], dtype=np.float64)
expect = expect[SINGLEAXIS_COL_ORDER]

assert_frame_equal(expect, tracker_data)
assert_frame_equal(expect, tracker_data[SINGLEAXIS_COL_ORDER])


def test_axis_azimuth():
Expand All @@ -239,7 +239,7 @@ def test_axis_azimuth():
index=[0], dtype=np.float64)
expect = expect[SINGLEAXIS_COL_ORDER]

assert_frame_equal(expect, tracker_data)
assert_frame_equal(expect, tracker_data[SINGLEAXIS_COL_ORDER])

apparent_zenith = pd.Series([30])
apparent_azimuth = pd.Series([180])
Expand All @@ -254,7 +254,7 @@ def test_axis_azimuth():
index=[0], dtype=np.float64)
expect = expect[SINGLEAXIS_COL_ORDER]

assert_frame_equal(expect, tracker_data)
assert_frame_equal(expect, tracker_data[SINGLEAXIS_COL_ORDER])


def test_horizon_flat():
Expand All @@ -272,7 +272,7 @@ def test_horizon_flat():
[ 0., 45., 270., 0.],
[ nan, nan, nan, nan]]),
columns=['tracker_theta', 'aoi', 'surface_azimuth', 'surface_tilt'])
assert_frame_equal(out, expected)
assert_frame_equal(out[SINGLEAXIS_COL_ORDER], expected)


def test_horizon_tilted():
Expand All @@ -288,7 +288,7 @@ def test_horizon_tilted():
[ 0., 45., 180., 90.],
[ 179., 45., 359., 90.]]),
columns=['tracker_theta', 'aoi', 'surface_azimuth', 'surface_tilt'])
assert_frame_equal(out, expected)
assert_frame_equal(out[SINGLEAXIS_COL_ORDER], expected)


def test_low_sun_angles():
Expand All @@ -301,8 +301,8 @@ def test_low_sun_angles():
'aoi': np.array([80.420987]),
'surface_azimuth': np.array([253.897886]),
'surface_tilt': np.array([64.341094])}
for k, v in result.items():
assert_allclose(expected[k], v)
for k, v in expected.items():
assert_allclose(v, result[k])


def test_calc_axis_tilt():
Expand Down Expand Up @@ -389,6 +389,57 @@ def test_slope_aware_backtracking():
check_less_precise=True)


def test_singleaxis_backtracking_flag():
"""Test that is_backtracking is True when backtracking is active."""
# low sun angle that triggers backtracking
apparent_zenith = pd.Series([80])
apparent_azimuth = pd.Series([90])

# with backtrack=True and a low sun angle, backtracking should be active
tracker_data = tracking.singleaxis(apparent_zenith, apparent_azimuth,
axis_tilt=0, axis_azimuth=0,
max_angle=90, backtrack=True,
gcr=2.0/7.0)
assert tracker_data['is_backtracking'].iloc[0] is np.bool_(True)

# with backtrack=False, is_backtracking should always be False
tracker_data = tracking.singleaxis(apparent_zenith, apparent_azimuth,
axis_tilt=0, axis_azimuth=0,
max_angle=90, backtrack=False,
gcr=2.0/7.0)
assert tracker_data['is_backtracking'].iloc[0] is np.bool_(False)

# at solar noon (small zenith), backtracking should not be active
index = pd.date_range(start='20180701T1200', freq='1s', periods=1)
apparent_zenith_noon = pd.Series([10], index=index)
apparent_azimuth_noon = pd.Series([180], index=index)
tracker_data = tracking.singleaxis(apparent_zenith_noon,
apparent_azimuth_noon,
axis_tilt=0, axis_azimuth=0,
max_angle=90, backtrack=True,
gcr=2.0/7.0)
assert tracker_data['is_backtracking'].iloc[0] is np.bool_(False)


def test_singleaxis_at_limit_flag():
"""Test that is_at_limit is True when angle is clipped."""
# 60 degree ideal angle clipped to 45 degree max
apparent_zenith = pd.Series([60])
apparent_azimuth = pd.Series([90])
tracker_data = tracking.singleaxis(apparent_zenith, apparent_azimuth,
axis_tilt=0, axis_azimuth=0,
max_angle=45, backtrack=True,
gcr=2.0/7.0)
assert tracker_data['is_at_limit'].iloc[0] is np.bool_(True)

# 60 degree ideal angle within 90 degree max — should not be clipped
tracker_data = tracking.singleaxis(apparent_zenith, apparent_azimuth,
axis_tilt=0, axis_azimuth=0,
max_angle=90, backtrack=True,
gcr=2.0/7.0)
assert tracker_data['is_at_limit'].iloc[0] is np.bool_(False)


def test_singleaxis_aoi_gh1221():
# vertical tracker
loc = pvlib.location.Location(40.1134, -88.3695)
Expand Down