Temperature impact on reported Irradiation

[mathieucarbou]

Irradiation seems to be calculated as a % of the current DC power by the configured max power Wp).

The problem is that the maximum power is given by a lab test of the panels at 25C and this value changes over time based on the temperature of the cells.

Example:

In Winter for example, my 400Wp DMEGC panels were each able to produce more than 425 W DC.
But in summer, with the increased temperatures, the maximum value could easily drop to 380W.

And all that is fo the same irradiation value.

So in winter, the reported irradiation value can be higher than reality while in summer, it will be lower than reality.

For exemple, today, no clouds, blue sky, hot sun (20C shade). Cells are probably at more than 40C and inverters are reaching more than 50C. I got a 400W DC production spike in the morning, but then with the heat they decrease to 380-380W, at about 95% of 400 Wp.

And in both case, the irradiation should be close to 100%. But because it is calculated on a maximum Wp at 25C, it does not take in consideration the variation of this maximum based on cell temperature.

I know cell temp is not an information we can get from the DTU. So I know there is no easy solution to this.

I was wondering if someone has already though about that and some (even partial) solutions.

Should we instead put in this configuration a value that is lower than the Wp at 25C, knowing well that in summer most of the time the panels won't be able to product that because of the heat ?

Thanks!