Defining system losses based on the DC System Size

I was wondering how would one adjust the "system losses" PVWatts v5 uses, based on the initial DC System Size.

By default PVWatts v5 uses 4kW system, which is about 20 modules of 200 Watts DC.

But what if I would like to calculate the annual AC Energy for only two modules or just a single module (400 Watts or 200 Watts DC)?
How do initially defined "system losses" have to be changed in that case?

By setting the "Wiring" and "Connections" both to 0 %?
Or just to set the "Wiring" to 0%, and leave "Connections" its default value of 0.5%?

Thank you for the reply.

Hello,

I do not have specific advice on how to change the system losses in PVWatts for different system designs. You can find some discussion of the default loss values in SAM's Help topic on the PVWatts system design page. The losses are generally appropriate for a rooftop system.

You might also want to do some parametric studies to see how much of an impact the losses have on your output metric of interest. For example, if you are interested in the project net present value (NPV), you could run a few simulations to determine how much the NPV is affected by a 2% change in the wiring loss assumption.

I did a web search for "PVWatts losses" and found a few articles and white papers that might be helpful. For example, the Enphase inverter company has a technical brief on losses (or derate factors) that they consider appropriate for systems that use their inverters.

Best regards,
Paul.

Thank you Paul.
I did not succeed in finding PVWatts system design page at SAM's Help.
Do you mind sharing the link?

Also, the Enphase derate factors recommendations you mentioned are these:
enphase.com/sites/default/files/Enphase_PVWatts_Derate_Guide_ModSolar_06-2014.pdf
?

Once again thank you for the informative reply and new pdf files Paul!

I guess the reason why I can't PVWatts System Design Help page is due to an older version of SAM (2013.1.15). Looks like that page started being shipped with later versions of SAM.

Interestingly that "PVWatts System Desing" page can not be found in an online version of SAM Help, which I guess should correspond to the one shipped with SAM application itself:
www.nrel.gov/analysis/sam/help/html-php/index.html?pvwatts.htm