Variables and Symbols#
There is a convention on consistent variable names throughout the library:
variable |
description |
---|---|
tz |
timezone |
latitude |
latitude |
longitude |
longitude |
dni |
direct normal irradiance |
dni_extra |
direct normal irradiance at top of atmosphere (extraterrestrial) |
dni_clear |
clear sky direct normal irradiance |
dhi |
diffuse horizontal irradiance |
bhi |
beam/direct horizontal irradiance |
ghi |
global horizontal irradiance |
ghi_extra |
horizontal irradiance at top of atmosphere (extraterrestrial) |
gri |
ground-reflected irradiance |
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_direct |
direct/beam irradiation in plane |
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) |
g_poa_effective |
broadband plane of array effective irradiance. |
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 |
wind_speed |
wind speed |
wind_direction |
wind direction |
pressure |
atmospheric pressure |
albedo |
ratio of reflected solar irradiance to global horizontal irradiance, unitless |
precipitable_water |
total precipitable water contained in a column of unit cross section from earth to top of atmosphere |
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 |
effective_irradiance |
effective irradiance |
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:
IEC 61724-1:2017 – Photovoltaic system performance - Part 1: Monitoring section: 3 – Terms and definitions; the Indian Standard referencing the withdrawn earlier global IEC standard IEC 61724:1998 is available online: IS/IEC 61724 (1998) and can provide relevant contents.
Explanation of Solar irradiation and solar geometry by SoDa Service
Note
These further references might not use the same terminology as pvlib. But the physical process referred to is the same.