API field
Precipitable water
Optional water-vapour column, the preferred spectral input
Unit cm
What it is
The depth of water the atmosphere would produce if all its vapour condensed, per interval, in centimetres. It is optional and is the preferred input of the spectral correction. Values are held between 0.1 and 8 cm inside the model.
Typical values and how to get it
From about 0.5 cm in dry climates to 5 cm in the humid tropics. Include it when the file has it; NSRDB files carry it. Without this column and without relative humidity the Lee and Panchula correction cannot run; the air-mass modifier does not need it. If not given: derived from the temperature and the relative humidity by Gueymard 1994 when the file has humidity; without either, the Lee and Panchula spectral correction is skipped.
References
- Lee & Panchula 2016, Spectral correction for photovoltaic module performance based on air mass and precipitable water, IEEE 43rd Photovoltaic Specialists Conference
API
weather.precipitable_water