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) |
dhi | diffuse horizontal irradiance |
ghi | global horizontal irradiance |
aoi | angle of incidence |
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) |
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 |
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: \(\frac{poa\_global}{ghi}\) |
For a definition and further explanation on the variables, common symbols and units refer to the following sources:
IEC 61724:1998 – Photovoltaic system performance monitoring - Guidelines for measurement, data exchange and analysis ; the Indian Standard referencing the global IEC standard is available online: IS/IEC 61724 (1998)
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.