# Detailed losses Ohmin Losses Tab

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Hi all,

I have a questions about the detailed losses that can be defined in PVSyst. And than special the Ohmic Losses tab.

I have studied the available PV Tutorials and read several articles about it. I can't find a in detail explained version in

PVSyst manual.

I would like to explain my question by a real live case.

See the SLD below

Capacity 940,680 Watt

13 x Huawei SUN2000 KTL 60 KW

2808 x Seraphim 335 Wp Poly

156 Strings

AC Side

All Inverters are connected with an ACDP by NYY Cable 4C x 35mm2  N L1 L2 L3

All inverters are grounded by NYA Cable 1C x 16mm2 from inverter to grounding bus bar in the ACDP

Average distance from Inverter to ACDP 15 Meter

The ACDP is connected with a MDP Distance from ACDP to MDP 60 Meters

NYY Cable 4 x (3 x 1 C x 300mm2) N L1 L2 L3

NYA Cable 2 x (1C x 240mm2) Grounding between ACDP and Grounding Bus Bar of the MDP

DC Side

156 Strings Average string length between string and inverter 150 meter

H1Z2Z2-K Solar cable 2 x (1C x 4mm2)

I think that's all information we need.

The question is how to adapt this info to the Ohmic Losses Tab in PV Syst

First DC Side

First we must make the choice between a general number for losses or a calculated number for losses.

I want to define calculated number for losses. Global Wiring resistance.

The number of 18.49 shows up automatically. Where does it come from? How is it calculated?

After clicking Detailed Computation the following screen pops up

What is meant here by String module connections / Average Length m / circuit? Is this the average String length 150 meter? Or? That is just not clear to me.

What is meant here by Main box to inverter / Average Length m / circuit? Is this the length in case we use a combiner box for strings and then here define the lengths

between the combiner box and the inverter?  That is just not clear to me.

Second AC Side

If I don't activate "Uses AC circuit ohmic loss"  I guess there will be no AC losses included in the simulation results, is that correct?

So I activate "Uses AC circuit ohmic loss"

I can make a choice per inverter or whole system. I guess for a bigger system with more than one inverter we must activate Whole system. Is that correct?

If I activate "Whole system"  what will be the " Length inverter to injection" In my example I guess the distance between the ACDP and the MDP ? Is that correct?

If I choose for wire section 400mm2 PVSyst gives an error message "This wire section is undersized for this current, with respect to IEC standards)

I do understand that that number of square mm2 is to small. But when I choose 500mm2 in the wire section PVSyst says that is ok?

I don't understand that. 500 mm2 in total is not enough to connect the ACDP with the MDP

What exactly is meant by wire section? Is that meant per Phase and neutral?  So 500mm2 for L1 500mm2 for L2 500 mm2 for L3 and 500 mm2 for Neutral?

Than the official design that I posted is heavenly oversized with 3 x 1c x 300mm2 That's 900mm2 per Phase and Neutral?

In my example I guess here stops defining the detailed losses for Ohmic losses because no

I do realize that I ask a lot of questions, just want to make sure I understand PVSyst.

It's a great programm

Kind regards

Ben

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• 2 weeks later...

Hi,

The ohmic resistance of the wiring circuit induces losses ( ELoss =  Rw · I² ) between the power available from the modules and the power at the terminals of the sub-array.

The relevant parameter for the simulation is the Rw value, which is an  equivalent resistance of the wires, as "seen" from the input of the global sub-array  (i.e. the set of MPPT inputs defined in this sub-array). You should define one Rw value for each sub-array in your system.

Basically, the  AC wiring losses are calculated from the resistivity, i.e. the wire lenght, section and metal.  During simulation, at each time step, the power loss is calculated as NWire * Rwire · I².

However in practice, as a first step of the design, people often use the relative ohmic loss. This relative loss should be referred to a specified Power.

Thank you for your questions, if you still have some, don't hesitate to ask us.

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• 3 months later...
On 7/11/2022 at 12:59 PM, Lazare Fesnien said:

Hi,

The ohmic resistance of the wiring circuit induces losses ( ELoss =  Rw · I² ) between the power available from the modules and the power at the terminals of the sub-array.

The relevant parameter for the simulation is the Rw value, which is an  equivalent resistance of the wires, as "seen" from the input of the global sub-array  (i.e. the set of MPPT inputs defined in this sub-array). You should define one Rw value for each sub-array in your system.

Basically, the  AC wiring losses are calculated from the resistivity, i.e. the wire lenght, section and metal.  During simulation, at each time step, the power loss is calculated as NWire * Rwire · I².

However in practice, as a first step of the design, people often use the relative ohmic loss. This relative loss should be referred to a specified Power.

Thank you for your questions, if you still have some, don't hesitate to ask us.

Hi,

i had the same question (regarding the DC part of the instalation) and i just read the links you  suggested.

So just to be clear. If for exapmle there was  an instalation with 15 strings with 15 modules each...the length in the string module connections (AVG length m./ciruit) is  an average length of all the strings and not the sum of them.

is that right?

George

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Hi,

For the DC part: there is indeed a tool for a quick evaluation of the array's resistance in rather simple cases.

This may involve combiner boxes. Please see "Detailed losses > Ohmic losses > Detailed computation".

But if this is a complex layout, you can also calculate the wires resistance by yourself, see the help  "Project design > Array and system losses > Array ohmic wiring loss".

For the AC losses after the inverters, you have to define wire lengths and sections between inverter, transformers and injection points. You can do approximations if you have more complex circuits with combiner boxes.

NB: we are preparing a tool for drawing the shema of the installation, which should be available soon.