There is a convention on consistent variable names throughout the library:
.. glossary::
airmass
Airmass
airmass_absolute
Absolute airmass
airmass_relative
Relative airmass
albedo
Ratio of reflected solar irradiance to global horizontal irradiance
[unitless]
aoi
Angle of incidence. Angle between the surface normal vector and the
vector pointing towards the sun's center. [°]
aoi_projection
cos(aoi). When the sun is behind the surface, the value is negative.
For many uses, negative values must be set to zero.
ape
Average photon energy
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. [°]
apparent_elevation
Refraction-corrected solar elevation angle. This is the complement of
:term:`apparent_zenith` (90 - apparent_zenith). [°]
axis_slope
Angle of a tracker axis with respect to horizontal.
This is, left-hand rotation angle of :math:`t_y` around :math:`t_x` in Fig. [4] of [Anderson2020]_.
See figure in :term:`cross_axis_slope`.
bhi
Beam/direct horizontal irradiance
cross_axis_slope
Cross-axis slope angle. [°]
The angle, relative to horizontal, of the line between the axes of two
adjacent trackers, in the plane perpendicular to the tracker axes.
Cross-axis slope should be specified using a right-handed convention.
For example, trackers with axis azimuth of 180° (N-S rotation axis)
will have a negative cross-axis slope if the tracker axes plane slopes
down to the east and positive cross-axis slope if the tracker axes plane
slopes up to the east.
.. figure:: ../../_images/Anderson_Mikofski_2020_Fig4.png
:alt: Two rows of modules, tracker coordinate system and cross-axis slope of the second row w.r.t. the leftmost.
:align: center
:scale: 50 %
Fig. 4, [Anderson2020]_: Cross-axis slope angle :math:`\beta_C` relative to the tracker coordinate system.
Use :py::func:`pvlib.tracking.calc_cross_axis_slope` to calculate
``cross_axis_slope``.
See also :term:`axis_slope`.
dhi
Diffuse horizontal irradiance
dni
Direct normal irradiance [Wm⁻²]. Irradiance received per unit area by a
surface perpendicular (normal) to the sun's rays that propagate in a
straight line from the sun.
dni_clear
Clear sky direct normal irradiance
dni_extra
Direct normal irradiance at top of atmosphere (extraterrestrial)
effective_irradiance
Effective irradiance
eta_inv
Inverter efficiency
eta_inv_nom
Nominal inverter efficiency
eta_inv_ref
Reference inverter efficiency
g_poa_effective
Broadband plane of array effective irradiance
gamma_pdc
Module temperature coefficient. Typically in units of 1/C.
ghi
Global horizontal irradiance
ghi_clear
Clearsky global horizontal irradiance [Wm⁻²]
ghi_extra
Horizontal irradiance at top of atmosphere (extraterrestrial)
gri
Ground-reflected irradiance
i_sc
Short circuit module current
i_x, i_xx
Sandia Array Performance Model IV curve parameters
latitude
Latitude in decimal degrees. Positive north of equator, negative to south.
longitude
Longitude in decimal degrees. Positive east of prime meridian, negative to west.
pac, ac
AC power
pdc, dc
DC power
pdc0
Nameplate DC rating
photocurrent
Photocurrent
poa_diffuse
Total diffuse irradiance in plane [Wm⁻²]. Sum of ground and sky diffuse
components of global irradiance.
poa_direct
Direct/beam irradiance in plane [Wm⁻²].
poa_global
Global irradiance in plane. Sum of diffuse and beam projection [Wm⁻²].
poa_ground_diffuse
In plane ground reflected irradiance [Wm⁻²].
poa_sky_diffuse
Diffuse irradiance in plane from scattered light in the atmosphere
(without ground reflected irradiance) [Wm⁻²].
precipitable_water
Total precipitable water contained in a column of unit cross section
from earth to top of atmosphere
pressure
Atmospheric pressure
relative_humidity
Relative humidity
resistance_series
Series resistance
resistance_shunt
Shunt resistance
saturation_current
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°.
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). [°]
spectra
spectra_components
Spectral irradiance (components) [Wm⁻²nm⁻¹]. The amount of energy
incident on a unit area per unit time and per unit
wavelength. As with broadband irradiance, global spectral irradiance
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°.
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°. [°]
temp_air
Temperature of the air
temp_cell
Temperature of the cell
temp_dew
Dewpoint temperature
temp_module
Temperature of the module
tz
Timezone
v_mp, i_mp, p_mp
Module voltage, current, power at the maximum power point
v_oc
Open circuit module voltage
wind_direction
Wind direction
wind_speed
Wind speed
For further explanation of the variables, common symbols, and units, refer to the following sources from SoDa Service:
Note
These further references might not use the same terminology as pvlib. But the physical process referred to is the same.
| [Anderson2020] | K. Anderson and M. Mikofski, 'Slope-Aware Backtracking for Single-Axis Trackers', National Renewable Energy Lab. (NREL), Golden, CO (United States); NREL/TP-5K00-76626, Jul. 2020. :doi:`10.2172/1660126`. |