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Sep 9, 2024
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Add reference to tracking.singleaxis #2198

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Update tracking.py
RDaxini Sep 5, 2024
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Update pvlib/tracking.py
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72 changes: 37 additions & 35 deletions pvlib/tracking.py
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Original file line number Diff line number Diff line change
Expand Up @@ -13,20 +13,20 @@ def singleaxis(apparent_zenith, apparent_azimuth,
Determine the rotation angle of a single-axis tracker when given particular
solar zenith and azimuth angles.

See [1]_ for details about the equations. Backtracking may be specified,
and if so, a ground coverage ratio is required.
See [1]_ and [2]_ for details about the equations. Backtracking may be
specified, in which case a ground coverage ratio is required.

Rotation angle is determined in a right-handed coordinate system. The
tracker `axis_azimuth` defines the positive y-axis, the positive x-axis is
90 degrees clockwise from the y-axis and parallel to the Earth's surface,
and the positive z-axis is normal to both x & y-axes and oriented skyward.
Rotation angle `tracker_theta` is a right-handed rotation around the y-axis
in the x, y, z coordinate system and indicates tracker position relative to
horizontal. For example, if tracker `axis_azimuth` is 180 (oriented south)
and `axis_tilt` is zero, then a `tracker_theta` of zero is horizontal, a
`tracker_theta` of 30 degrees is a rotation of 30 degrees towards the west,
and a `tracker_theta` of -90 degrees is a rotation to the vertical plane
facing east.
tracker ``axis_azimuth`` defines the positive y-axis, the positive x-axis
is 90 degrees clockwise from the y-axis and parallel to the Earth's
surface, and the positive z-axis is normal to both x and y-axes and
oriented skyward. Rotation angle ``tracker_theta`` is a right-handed
rotation around the y-axis in the x, y, z coordinate system and indicates
tracker position relative to horizontal. For example, if tracker
``axis_azimuth`` is 180 (oriented south) and ``axis_tilt`` is zero, then a
``tracker_theta`` of zero is horizontal, a ``tracker_theta`` of 30 degrees
is a rotation of 30 degrees towards the west, and a ``tracker_theta`` of
-90 degrees is a rotation to the vertical plane facing east.

Parameters
----------
Expand All @@ -39,7 +39,7 @@ def singleaxis(apparent_zenith, apparent_azimuth,
axis_tilt : float, default 0
The tilt of the axis of rotation (i.e, the y-axis defined by
``axis_azimuth``) with respect to horizontal.
``axis_tilt`` must be >= 0 and <= 90. [degree]
``axis_tilt`` must be >= 0 and <= 90. [degrees]

axis_azimuth : float, default 0
A value denoting the compass direction along which the axis of
Expand All @@ -53,37 +53,37 @@ def singleaxis(apparent_zenith, apparent_azimuth,
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 rotation to 'max_angle' is a counter-clockwise rotation about the
A rotation to ``max_angle`` is a counter-clockwise rotation about the
y-axis of the tracker coordinate system. For example, for a tracker
with 'axis_azimuth' oriented to the south, a rotation to 'max_angle'
is towards the west, and a rotation toward 'min_angle' is in the
opposite direction, toward the east. Hence a max_angle of 180 degrees
(equivalent to max_angle = (-180, 180)) allows the tracker to achieve
its full rotation capability.
with ``axis_azimuth`` oriented to the south, a rotation to
``max_angle`` is towards the west, and a rotation toward ``-max_angle``
is in the opposite direction, toward the east. Hence, a ``max_angle``
of 180 degrees (equivalent to max_angle = (-180, 180)) allows the
tracker to achieve its full rotation capability.

backtrack : bool, default True
Controls whether the tracker has the capability to "backtrack"
to avoid row-to-row shading. False denotes no backtrack
capability. True denotes backtrack capability.

gcr : float, default 2.0/7.0
A value denoting the ground coverage ratio of a tracker system
which utilizes backtracking; i.e. the ratio between the PV array
surface area to total ground area. A tracker system with modules
2 meters wide, centered on the tracking axis, with 6 meters
between the tracking axes has a gcr of 2/6=0.333. If gcr is not
provided, a gcr of 2/7 is default. gcr must be <=1.
A value denoting the ground coverage ratio of a tracker system that
utilizes backtracking; i.e. the ratio between the PV array surface area
to the total ground area. A tracker system with modules 2 meters wide,
centered on the tracking axis, with 6 meters between the tracking axes
has a ``gcr`` of 2/6=0.333. If ``gcr`` is not provided, a ``gcr`` of
2/7 is default. ``gcr`` must be <=1.

cross_axis_tilt : float, default 0.0
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 tilt should be specified
using a right-handed convention. For example, trackers with axis
azimuth of 180 degrees (heading south) will have a negative cross-axis
tilt if the tracker axes plane slopes down to the east and positive
cross-axis tilt if the tracker axes plane slopes down to the west. Use
:func:`~pvlib.tracking.calc_cross_axis_tilt` to calculate
`cross_axis_tilt`. [degrees]
perpendicular to the tracker axes. The cross-axis tilt should be
specified using a right-handed convention. For example, trackers with
axis azimuth of 180 degrees (heading south) will have a negative
cross-axis tilt if the tracker axes plane slopes down to the east and
positive cross-axis tilt if the tracker axes plane slopes down to the
west. Use :func:`~pvlib.tracking.calc_cross_axis_tilt` to calculate
``cross_axis_tilt``. [degrees]

Returns
-------
Expand All @@ -107,9 +107,11 @@ def singleaxis(apparent_zenith, apparent_azimuth,

References
----------
.. [1] Kevin Anderson and Mark Mikofski, "Slope-Aware Backtracking for
.. [1] Anderson, K., and Mikofski, M., "Slope-Aware Backtracking for
Single-Axis Trackers", Technical Report NREL/TP-5K00-76626, July 2020.
https://www.nrel.gov/docs/fy20osti/76626.pdf
.. [2] Lorenzo, E., Narvarte, L., and Muñoz, J. (2011). Tracking and
back-tracking 19(6), 747–753. :doi:`10.1002/pip.1085`
"""

# MATLAB to Python conversion by
Expand All @@ -127,9 +129,9 @@ def singleaxis(apparent_zenith, apparent_azimuth,
if apparent_azimuth.ndim > 1 or apparent_zenith.ndim > 1:
raise ValueError('Input dimensions must not exceed 1')

# The ideal tracking angle omega_ideal is the rotation to place the sun
# The ideal tracking angle, omega_ideal, is the rotation to place the sun
# position vector (xp, yp, zp) in the (x, z) plane, which is normal to
# the panel and contains the axis of rotation. omega_ideal= 0 indicates
# the panel and contains the axis of rotation. omega_ideal=0 indicates
# that the panel is horizontal. Here, our convention is that a clockwise
# rotation is positive, to view rotation angles in the same frame of
# reference as azimuth. For example, for a system with tracking
Expand Down
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