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Add aod and clearsky_index to glossary, link terms in spectrum.rst #2663

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eae7536
add aod, clearsky index
RDaxini Jan 21, 2026
83089aa
line length of various definitions
RDaxini Jan 21, 2026
ff24b9e
Update spectrum.rst
RDaxini Jan 21, 2026
296831e
add clarification for numbers eg aod500
RDaxini Jan 21, 2026
62e1a9b
link aod500 in spectrum.rst
RDaxini Jan 21, 2026
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57 changes: 37 additions & 20 deletions docs/sphinx/source/user_guide/extras/nomenclature.rst
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Expand Up @@ -19,7 +19,16 @@ There is a convention on consistent variable names throughout the library:
albedo
Ratio of reflected solar irradiance to global horizontal irradiance
[unitless]


aod
aod500
aerosol optical depth. Measure of aerosols (e.g., smoke
particles, desert dust) distributed within a column of air from the
instrument (Earth's surface) to the top of the atmosphere. The AOD
value indicates the level of extinction of sunlight in this column, and
when followed by a number (e.g. AOD500), indicates the extinction at
this wavelength (500nm). [unitless]

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@echedey-ls echedey-ls Jan 21, 2026 •
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Is it described by these equations? https://en.wikipedia.org/wiki/Optical_depth#Spectral_optical_depth

I have trouble finding PV specific information on a mathematical relationship. At least that is the only missing piece for me.

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@cwhanse cwhanse Jan 21, 2026

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Suggest moving [unitless] to follow aerosol optical depth [unitless].

aoi
Angle of incidence. Angle between the surface normal vector and the
vector pointing towards the sun's center. [°]
Expand All @@ -33,17 +42,21 @@ There is a convention on consistent variable names throughout the library:

apparent_zenith
Refraction-corrected solar zenith angle. The solar
zenith angle describes the position of the sun relative to the vertical and is
defined as the angle between a vector pointed straight up and a vector pointed
at the sun, from the observer. [°]
zenith angle describes the position of the sun relative to the vertical
and is defined as the angle between a vector pointed straight up and a
vector pointed at the sun, from the observer. [°]

apparent_elevation
Refraction-corrected solar elevation angle. This is the complement of
:term:`apparent_zenith` (90 - apparent_zenith). [°]

bhi
Beam/direct horizontal irradiance


clearsky_index
clearsky index. Ratio of actual global irradiance to modeled clearsky
global irradiance
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@echedey-ls echedey-ls Jan 21, 2026

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Various ideas:

  1. Citing https://ebrary.net/183058/environment/clear_index:

    The clear-sky index is sometimes called cloud modification factor. It is dimensionless. Kc varies between 0 and 1. The greater the attenuation of the radiation by the clouds, the smaller Kc.

    I find it interesting this naming variant (I think it's uncommon in PV but may be of interest for newcomers from other engineering areas).

  2. Maybe the formula? :math:`K_C = \frac{GHI_\text{actual}}{GHI_\text{clear-sky}}`

  3. Maybe note that can either be used with irradiation too?

  4. An admonition to distinguish it from clearness index?

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@cwhanse cwhanse Jan 21, 2026

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+1 for "An admonition to distinguish it from clearness index"


dhi
Diffuse horizontal irradiance

Expand Down Expand Up @@ -95,10 +108,12 @@ There is a convention on consistent variable names throughout the library:
Sandia Array Performance Model IV curve parameters

latitude
Latitude in decimal degrees. Positive north of equator, negative to south.
Latitude in decimal degrees. Positive north of equator, negative to
south.

longitude
Longitude in decimal degrees. Positive east of prime meridian, negative to west.
Longitude in decimal degrees. Positive east of prime meridian, negative
to west.

pac, ac
AC power
Expand Down Expand Up @@ -149,15 +164,16 @@ There is a convention on consistent variable names throughout the library:
Diode saturation current

solar_azimuth
Azimuth angle of the sun in degrees East of North. The solar azimuth angle
describes the sun’s position along the horizon relative to the observer.
The pvlib-python convention is defined as degrees East of North, so
North = 0°, East = 90°, South = 180°, West = 270°.
Azimuth angle of the sun in degrees East of North. The solar azimuth
angle describes the sun’s position along the horizon relative to the
observer. The pvlib-python convention is defined as degrees East of
North, so North = 0°, East = 90°, South = 180°, West = 270°.
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@cwhanse cwhanse Jan 21, 2026

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Suggested change
observer. The pvlib-python convention is defined as degrees East of
North, so North = 0°, East = 90°, South = 180°, West = 270°.
observer. Azimuth is defined as degrees East of
North, so North = 0°, East = 90°, South = 180°, West = 270°.


solar_zenith
Zenith angle of the sun in degrees. This is the angle between is between a
vector pointed straight up and a vector pointed at the sun, from the observer.
This is the complement of solar elevation (90 - elevation). [°]
Zenith angle of the sun in degrees. This is the angle between is
between a vector pointed straight up and a vector pointed at the sun,
from the observer. This is the complement of solar elevation
90 - elevation). [°]
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@cwhanse cwhanse Jan 21, 2026

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Suggested change
Zenith angle of the sun in degrees. This is the angle between is
between a vector pointed straight up and a vector pointed at the sun,
from the observer. This is the complement of solar elevation
90 - elevation). [°]
Zenith angle of the sun in degrees [°]. Zenith is the angle between is
between a vector pointed straight up and a vector pointed at the sun,
from the observer. Zenith is the complement of solar elevation, i.e.,
zenith = 90 - elevation.

Since we're editing this definition.


spectra
spectra_components
Expand All @@ -167,16 +183,17 @@ There is a convention on consistent variable names throughout the library:
is composed of direct and diffuse components.

surface_azimuth
Azimuth angle of the surface in degrees East of North. This angle describes the
horizontal projection of the normal vector from the surface. The pvlib-python
convention is defined as degrees East (clockwise) of North, so North = 0°,
East = 90°, South = 180°, West = 270°.
Azimuth angle of the surface in degrees East of North. This angle
describes the horizontal projection of the normal vector from the
surface. The pvlib-python convention is defined as degrees East
(clockwise) of North, so North = 0°, East = 90°, South = 180°,
West = 270°.
Comment on lines +186 to +190
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Suggested change
Azimuth angle of the surface in degrees East of North. This angle
describes the horizontal projection of the normal vector from the
surface. The pvlib-python convention is defined as degrees East
(clockwise) of North, so North = 0°, East = 90°, South = 180°,
West = 270°.
Azimuth angle of the surface in degrees East of North. Surface azimuth
is specified by the horizontal projection of the normal vector from
the surface. Azimuth is defined as degrees East
(clockwise) of North, so North = 0°, East = 90°, South = 180°,
West = 270°.


surface_tilt
Tilt from horizontal [°]. The surface tilt angle
is defined as degrees from the horizontal
such that a surface facing up would have a surface tilt of 0°, and one facing
the horizon would be 90°. [°]
such that a surface facing up would have a surface tilt of 0°, and one
facing the horizon would be 90°. [°]

temp_air
Temperature of the air
Expand Down
6 changes: 3 additions & 3 deletions docs/sphinx/source/user_guide/modeling_topics/spectrum.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -51,21 +51,21 @@ Reference [2]_.
| +-----------------------------+ | | | | | | |
| |:term:`precipitable_water`, | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | [2]_ |
| +-----------------------------+ | | | | | | |
| | aod | | | | | | | |
| | :term:`aod` | | | | | | | |
+-----------------------------------------------------+-----------------------------+---------+---------+------+------+------+------------+-----------+
| :py:func:`First Solar <spectral_factor_firstsolar>` | :term:`airmass_absolute`, | | | | | | | |
| +-----------------------------+ | ✓ | ✓ | | | | [3]_ |
| | :term:`precipitable_water` | | | | | | | |
+-----------------------------------------------------+-----------------------------+---------+---------+------+------+------+------------+-----------+
| :py:func:`JRC <spectral_factor_jrc>` | :term:`airmass_relative`, | | | | | | | |
| +-----------------------------+ | ✓ | ✓ | | | + [4]_ |
| | clearsky_index | | | | | | | |
| | :term:`clearsky_index` | | | | | | | |
+-----------------------------------------------------+-----------------------------+---------+---------+------+------+------+------------+-----------+
| :py:func:`Polo <spectral_factor_polo>` | :term:`precipitable_water`, | | | | | | | |
| +-----------------------------+ ✓ | | ✓ | ✓ | ✓ | + [5]_ |
| | :term:`airmass_absolute`, | | | | | | | |
| +-----------------------------+ | | | | | | |
| | aod500, | | | | | | | |
| | :term:`aod500` | | | | | | | |
| +-----------------------------+ | | | | | | |
| | :term:`aoi`, | | | | | | | |
| +-----------------------------+ | | | | | | |
Expand Down
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