Nomenclature#

There is a convention on consistent variable names throughout the library:

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 apparent_zenith (90 - apparent_zenith). [°]
bhi#: Beam/direct horizontal irradiance
cross_axis_slope#: Cross-axis tilt angle. [°] Consider two parallel rows of modules at different height; cross_axis_slope is the angle formed the line formed by the intersection between the slope containing the tracker axes and a plane perpendicular to the tracker axes, and the horizontal plane. Cross-axis tilt is measured by using a right-handed convention. For example, trackers with axis azimuth of 180° (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 up to the east. Use calc_cross_axis_slope() to calculate cross_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:

Acronyms, Terminology and Units

Plane orientations and radiation components

Time references

Note

These further references might not use the same terminology as pvlib. But the physical process referred to is the same.