Spectral coefficients

What it is

The six coefficients of the Lee and Panchula formula, in the order $c_0$ to $c_5$ below. Empty uses the published set for the module's technology. The air-mass modifier does not use them.

Typical values and how to get it

Empty unless a manufacturer publishes a set for the module.

How it is applied

$$M = c_0 + c_1\,\text{AM}_a + c_2\,P_w + c_3\sqrt{\text{AM}_a} + c_4\sqrt{P_w} + c_5\,\frac{\text{AM}_a}{\sqrt{P_w}}$$

where

Symbol	Meaning	Unit
$M$	the spectral modifier of the timestep, a factor near 1	—
$c_0 \ldots c_5$	this input, the six coefficients in order	—
$\text{AM}_a$	the air mass corrected for the site elevation or the air pressure, from the Spectral air mass formula	—
$P_w$	the precipitable water	cm

References

1. Lee & Panchula 2016, Spectral correction for photovoltaic module performance based on air mass and precipitable water, IEEE 43rd Photovoltaic Specialists Conference

API

spectral.coefficients

Symbols follow the symbol registry.