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Transformer losses


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I have noticed that PVsyst appears to take transformer losses as a % of the array (DC) STC output rating, rather than a % of the park AC rating as implied by the documentation.

As an aside, as well as clarifying this situation, since the value is stored as a % it would helpful if it had sufficient accuracy to translate values specified in Watts back to their original figure. For example, when basing losses on generic transformers sized to EN50464 loss classes, we get questioned when instead of P0=3,500W, we see P0=3,424W in the report.


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  • 2 months later...

Hi Andre,

That would be useful; I look forward to that update.

In the meantime I've just come across a clear example illustrating the problem, which I thought I'd share to help you along:


Transformer loss example


Here we have exactly the same AC system; the only changes have been a reduction in quantity of module strings and reconfiguring the DC combiner boxes. The inverters and AC loss definitions have not been touched. However, the transformer iron losses have changed by 225W (or 1.9MWh/yr), which should not be the case since they will obviously be the same spec as before so the losses should be the same (and I would expect Pnom,AC to be the same too).

Even if this is the expected behavious in terms of how you have defined the loss, it is quite counter-intuitive that the DC rating should have any bearing on this loss.

Kind regards,


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