Power AC STC

[JavierGV]

Once the system is defined, you can see the Nominal PV power and the nominal AC power (Global System Summary) and while you introduce parameters for the calculation of Detailed losses -> Ohmin Losses -> AC circuit, you can see "STC: P ac".

This parameter, P ac at STC, is used at the external transformer iron loss calculation: when you introduce a percentage value for the iron loss, a value in kW appears beside it. This value in kW is the percentage value * (P ac at STC).

How is this value (P ac at STC) calculated?

[André Mermoud]

This value is simply the Pnom array, multiplied by the efficiency of the inverter at this power.

This is not a very sensitive value.

In a future version (not the next one), we will change this way of estimationg the Transformer losses and propose a more understandable procedure based on "real" transformers properties.

[JavierGV]

Do you mean that the program takes the efficiency of the inverter from the Efficency curve defined in the inverter OND file to relate it with the transformer losses?

:shock:

[André Mermoud]

Yes if you want.

But this has a very weak significance: the STC PnomAC value is just here for a definition of a Reference Power.

[jammyc]

Unless I haven't understood this and related threads correctly, this value is used for calculating transformer losses, which on a larger solar park are not insignificant! Granted they are (one hopes) small compared to generation, but they do reflect large sums of money, and it can be quite relevant when assessing proposals from manufacturers with differently rated inverters and transformers.

So I take issue with the assertion that it of "weak significance"!

[André Mermoud]

I didn's say that the transformer loss is not significant of course.

What I meant is that the choice of the STC PnomAC has not a significant effect on the evaluation of the transformer loss.