# Variables and Symbols¶

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

List of used Variables and Parameters
variable description
tz timezone
latitude latitude
longitude longitude
dni_extra direct normal irradiance at top of atmosphere (extraterrestrial)
aoi angle of incidence between $$90\deg$$ and $$90\deg$$
aoi_projection cos(aoi)
airmass airmass
airmass_relative relative airmass
airmass_absolute absolute airmass
poa_ground_diffuse in plane ground reflected irradiation
poa_diffuse total diffuse irradiation in plane. sum of ground and sky diffuse.
poa_global global irradiation in plane. sum of diffuse and beam projection.
poa_sky_diffuse diffuse irradiation in plane from scattered light in the atmosphere (without ground reflected irradiation)
surface_tilt tilt angle of the surface
surface_azimuth azimuth angle of the surface
solar_zenith zenith angle of the sun in degrees
apparent_zenith refraction-corrected solar zenith angle in degrees
solar_azimuth azimuth angle of the sun in degrees East of North
temp_cell temperature of the cell
temp_module temperature of the module
temp_air temperature of the air
temp_dew dewpoint temperature
relative_humidity relative humidity
v_mp, i_mp, p_mp module voltage, current, power at the maximum power point
v_oc open circuit module voltage
i_sc short circuit module current
i_x, i_xx Sandia Array Performance Model IV curve parameters
photocurrent photocurrent
saturation_current diode saturation current
resistance_series series resistance
resistance_shunt shunt resistance
transposition_factor the gain ratio of the radiation on inclined plane to global horizontal irradiation: $$\frac{poa\_global}{ghi}$$
pdc0 nameplate DC rating
pdc, dc dc power
gamma_pdc module temperature coefficient. Typically in units of 1/C.
pac, ac ac powe.
eta_inv inverter efficiency
eta_inv_ref reference inverter efficiency
eta_inv_nom nominal inverter efficiency

For a definition and further explanation on the variables, common symbols and units refer to the following sources:

Note

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