8000 better nan handling in singleaxis by wholmgren · Pull Request #697 · pvlib/pvlib-python · GitHub
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May 3, 2019
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better nan handling in singleaxis #697

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94e4db2
better nan handling in singleaxis
wholmgren May 2, 2019
c1e1c9e
a couple of comments
wholmgren May 2, 2019
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9 changes: 7 additions & 2 deletions docs/sphinx/source/whatsnew/v0.6.2.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -40,7 +40,11 @@ Bug fixes
* Fixed :py:func:`~pvlib.irradiance.erbs` behavior when zenith is
near 90 degrees. (:issue:`681`)
* :py:func:`~pvlib.irradiance.dni` now referenced in API under
Decomposing and Combining irradiance header. (:issue:`686`)
Decomposing and Combining irradiance header. (:issue:`686`)
* Fixed NaN output from :py:func:`~pvlib.tracking.singleaxis` when sun
near horizon. (:issue:`656`)
* Fixed numpy warnings in :py:func:`~pvlib.tracking.singleaxis` when
comparing NaN values to limits. (:issue:`622`)


Testing
Expand All @@ -53,4 +57,5 @@ Contributors
* Will Holmgren (:ghuser:`wholmgren`)
* Roel Loonen (:ghuser:`roelloonen`)
* Todd Hendricks (:ghuser:`tahentx`)

* Kevin Anderson (:ghuser:`kevinsa5`)
* :ghuser:`bentomlinson`
60 changes: 35 additions & 25 deletions pvlib/test/test_tracking.py
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Original file line number Diff line number Diff line change
@@ -1,5 +1,3 @@
import datetime

import numpy as np
from numpy import nan
import pandas as pd
Expand Down Expand Up @@ -96,10 +94,10 @@ def test_arrays_multi():
apparent_azimuth = np.array([[180, 180], [180, 180]])
# singleaxis should fail for num dim > 1
with pytest.raises(ValueError):
tracker_data = tracking.singleaxis(apparent_zenith, apparent_azimuth,
axis_tilt=0, axis_azimuth=0,
max_angle=90, backtrack=True,
gcr=2.0/7.0)
tracking.singleaxis(apparent_zenith, apparent_azimuth,
axis_tilt=0, axis_azimuth=0,
max_angle=90, backtrack=True,
gcr=2.0/7.0)
# uncomment if we ever get singleaxis to support num dim > 1 arrays
# assert isinstance(tracker_data, dict)
# expect = {'tracker_theta': np.full_like(apparent_zenith, 0),
Expand All @@ -121,7 +119,7 @@ def test_azimuth_north_south():

expect = pd.DataFrame({'tracker_theta': -60, 'aoi': 0,
'surface_azimuth': 90, 'surface_tilt': 60},
index=[0], dtype=np.float64)
index=[0], dtype=np.float64)
expect = expect[SINGLEAXIS_COL_ORDER]

assert_frame_equal(expect, tracker_data)
Expand All @@ -146,7 +144,7 @@ def test_max_angle():

expect = pd.DataFrame({'aoi': 15, 'surface_azimuth': 90,
'surface_tilt': 45, 'tracker_theta': 45},
index=[0], dtype=np.float64)
index=[0], dtype=np.float64)
expect = expect[SINGLEAXIS_COL_ORDER]

assert_frame_equal(expect, tracker_data)
Expand All @@ -163,7 +161,7 @@ def test_backtrack():

expect = pd.DataFrame({'aoi': 0, 'surface_azimuth': 90,
'surface_tilt': 80, 'tracker_theta': 80},
index=[0], dtype=np.float64)
index=[0], dtype=np.float64)
expect = expect[SINGLEAXIS_COL_ORDER]

assert_frame_equal(expect, tracker_data)
Expand All @@ -175,7 +173,7 @@ def test_backtrack():

expect = pd.DataFrame({'aoi': 52.5716, 'surface_azimuth': 90,
'surface_tilt': 27.42833, 'tracker_theta': 27.4283},
index=[0], dtype=np.float64)
index=[0], dtype=np.float64)
expect = expect[SINGLEAXIS_COL_ORDER]

assert_frame_equal(expect, tracker_data)
Expand All @@ -193,7 +191,7 @@ def test_axis_tilt():
expect = pd.DataFrame({'aoi': 7.286245, 'surface_azimuth': 142.65730,
'surface_tilt': 35.98741,
'tracker_theta': -20.88121},
index=[0], dtype=np.float64)
index=[0], dtype=np.float64)
expect = expect[SINGLEAXIS_COL_ORDER]

assert_frame_equal(expect, tracker_data)
Expand All @@ -205,7 +203,7 @@ def test_axis_tilt():

expect = pd.DataFrame({'aoi': 47.6632, 'surface_azimuth': 50.96969,
'surface_tilt': 42.5152, 'tracker_theta': 31.6655},
index=[0], dtype=np.float64)
index=[0], dtype=np.float64)
expect = expect[SINGLEAXIS_COL_ORDER]

assert_frame_equal(expect, tracker_data)
Expand All @@ -222,7 +220,7 @@ def test_axis_azimuth():

expect = pd.DataFrame({'aoi': 30, 'surface_azimuth': 180,
'surface_tilt': 0, 'tracker_theta': 0},
index=[0], dtype=np.float64)
index=[0], dtype=np.float64)
expect = expect[SINGLEAXIS_COL_ORDER]

assert_frame_equal(expect, tracker_data)
Expand All @@ -237,7 +235,7 @@ def test_axis_azimuth():

expect = pd.DataFrame({'aoi': 0, 'surface_azimuth': 180,
'surface_tilt': 30, 'tracker_theta': 30},
index=[0], dtype=np.float64)
index=[0], dtype=np.float64)
expect = expect[SINGLEAXIS_COL_ORDER]

assert_frame_equal(expect, tracker_data)
Expand Down Expand Up @@ -277,6 +275,20 @@ def test_horizon_tilted():
assert_frame_equal(out, expected)


def test_low_sun_angles():
# GH 656
result = tracking.singleaxis(
apparent_zenith=80, apparent_azimuth=338, axis_tilt=30,
axis_azimuth=180, max_angle=60, backtrack=True, gcr=0.35)
expected = {
'tracker_theta': np.array([-50.31051385]),
'aoi': np.array([61.35300178]),
'surface_azimuth': np.array([112.53615425]),
'surface_tilt': np.array([56.42233095])}
for k, v in result.items():
assert_allclose(expected[k], v)


def test_SingleAxisTracker_creation():
system = tracking.SingleAxisTracker(max_angle=45,
gcr=.25,
Expand All @@ -299,37 +311,35 @@ def test_SingleAxisTracker_tracking():

tracker_data = system.singleaxis(apparent_zenith, apparent_azimuth)

expect = pd.DataFrame({'aoi': 7.286245, 'surface_azimuth': 142.65730 ,
expect = pd.DataFrame({'aoi': 7.286245, 'surface_azimuth': 142.65730,
'surface_tilt': 35.98741,
'tracker_theta': -20.88121},
index=[0], dtype=np.float64)
index=[0], dtype=np.float64)
expect = expect[SINGLEAXIS_COL_ORDER]

assert_frame_equal(expect, tracker_data)

### results calculated using PVsyst
# results calculated using PVsyst
pvsyst_solar_azimuth = 7.1609
pvsyst_solar_height = 27.315
pvsyst_axis_tilt = 20.
pvsyst_axis_azimuth = 20.
pvsyst_system = tracking.SingleAxisTracker(max_angle=60.,
axis_tilt=pvsyst_axis_tilt,
axis_azimuth=180+pvsyst_axis_azimuth,
backtrack=False)
pvsyst_system = tracking.SingleAxisTracker(
max_angle=60., axis_tilt=pvsyst_axis_tilt,
axis_azimuth=180+pvsyst_axis_azimuth, backtrack=False)
# the definition of azimuth is different from PYsyst
apparent_azimuth = pd.Series([180+pvsyst_solar_azimuth])
apparent_zenith = pd.Series([90-pvsyst_solar_height])
tracker_data = pvsyst_system.singleaxis(apparent_zenith, apparent_azimuth)
expect = pd.DataFrame({'aoi': 41.07852 , 'surface_azimuth': 180-18.432,
'surface_tilt': 24.92122 ,
expect = pd.DataFrame({'aoi': 41.07852, 'surface_azimuth': 180-18.432,
'surface_tilt': 24.92122,
'tracker_theta': -15.18391},
index=[0], dtype=np.float64)
index=[0], dtype=np.float64)
expect = expect[SINGLEAXIS_COL_ORDER]

assert_frame_equal(expect, tracker_data)



def test_LocalizedSingleAxisTracker_creation():
localized_system = tracking.LocalizedSingleAxisTracker(latitude=32,
longitude=-111,
Expand Down
16 changes: 10 additions & 6 deletions pvlib/tracking.py
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Expand Up @@ -441,19 +441,22 @@ def singleaxis(apparent_zenith, apparent_azimuth,
# angle convention being used here.
if backtrack:
axes_distance = 1/gcr
temp = np.minimum(axes_distance*cosd(wid), 1)
# clip needed for low angles. GH 656
temp = np.clip(axes_distance*cosd(wid), -1, 1)

# backtrack angle
# (always positive b/c acosd returns values between 0 and 180)
wc = np.degrees(np.arccos(temp))

# Eq 4 applied when wid in QIV (wid < 0 evalulates True), QI
tracker_theta = np.where(wid < 0, wid + wc, wid - wc)
with np.errstate(invalid='ignore'):
# errstate for GH 622
tracker_theta = np.where(wid < 0, wid + wc, wid - wc)
else:
tracker_theta = wid

tracker_theta[tracker_theta > max_angle] = max_angle
tracker_theta[tracker_theta < -max_angle] = -max_angle
tracker_theta = np.minimum(tracker_theta, max_angle)
tracker_theta = np.maximum(tracker_theta, -max_angle)

# calculate panel normal vector in panel-oriented x, y, z coordinates.
# y-axis is axis of tracker rotation. tracker_theta is a compass angle
Expand Down Expand Up @@ -560,8 +563,9 @@ def singleaxis(apparent_zenith, apparent_azimuth,
surface_azimuth = 90 - surface_azimuth + axis_azimuth

# 5. Map azimuth into [0,360) domain.
surface_azimuth[surface_azimuth < 0] += 360
surface_azimuth[surface_azimuth >= 360] -= 360
# surface_azimuth[surface_azimuth < 0] += 360
# surface_azimuth[surface_azimuth >= 360] -= 360
surface_azimuth = surface_azimuth % 360

# Calculate surface_tilt
dotproduct = (panel_norm_earth * projected_normal).sum(axis=1)
Expand Down
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