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Ohmic Losses - Dc cables

Michalis Angeli

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I would like to ask if there is a different in the way I definede the DC cables in Ohmic Losses dialog.

Actually, i have an inverter with 9 mppt inputs. Should I define seperate the length of dc cables for each individual mppt (for ex. 23 panels for one String)

Or can I define the length of dc cable as the average length of all strings?
What differents may have in simulation that scenario.

I attach some pictures to be more specific.



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Dear Michalis Angeli,
In the Wiring layout you should define the average length for one string (blue) and the distance to the main box to the inverter (green). If you have multiple strings and/or inverters this will be reflected in the Global array and the Field global wiring resistance. See example below. It is this number that will be used in the simulation. 


If you wish to simulate a more pessimistic scenario, to be on the safe side, you can artificially increase the Loss fraction at STC  to, for instance 0.8%, compared to the calculated values of 0.65 from the example. 

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In this example, you have 7 inverters with 9 Mppt inputs and therefore overall 63 strings. The Field global wiring resistance is the whole resistance for all strings and inverters?

I would like you to calrify me, if is necessary to create differents subbarays in define system dialog in order to define one by one the lengths of each string and mppt input?
Or i can define a value (cable length) for all strings.

In our projects we don't use Main so I don't define any value there I keep it equal to 0.

Thank you!

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Dear Michalis, 

In your case you must define the average length of a string.

Then PVsyst will calculate the resistance of the DC circuit taking into account the number of strings in your system.

At this location, the number of MPPTs is not taken into account in the calculation of DC losses. We will take into account the number of inverters and strings


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