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Summary

DC wiring resistance represents the combined ohmic resistance of the cables connecting modules in series and parallel strings to the inverter. Rather than modeling wiring losses as a separate derating factor, PlantPredict converts a user-specified wiring loss percentage into an equivalent module-level that is added to each module’s series resistance before the equation is solved. This approach captures the voltage- and current-dependent nature of resistive losses within the .

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Inputs

NameSymbolUnitsDescription
DC Wiring Loss PercentageLwireL_{wire}%User-specified wiring loss at reference conditions
Module Maximum PowerPmp,refP_{mp,ref}WModule maximum power at reference conditions
Number of Parallel StringsNpN_p—Parallel strings in the DC field
Number of Modules in SeriesNsN_s—Modules in series per string

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Outputs

NameSymbolUnitsDescription
Field-Level Wiring ResistanceRDC,fieldR_{DC,field}ΩDC-field-level effective resistance
Per-Module Wiring ResistanceRDC,moduleR_{DC,module}ΩModule-level equivalent series resistance

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Detailed Description

The user specifies DC wiring losses as a percentage of power at reference conditions. PlantPredict converts this into a per-module equivalent resistance so that wiring losses are modeled as part of the single-diode circuit rather than as an external derating. This conversion is performed once during prediction initialization.

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Reference MPP Current

To convert a loss percentage into a resistance, the current at under reference conditions is needed. PlantPredict obtains this by running a preliminary 5-parameter or 7-parameter single-diode equation solve at:
  • Reference irradiance (GrefG_{ref}, typically 1000 W/m²) with the combined DC system loss coefficient applied
  • Reference temperature (TrefT_{ref}, typically 25 °C)
  • Zero wiring resistance
  • Zero back irradiance
The resulting maximum power point current is denoted Imp∗I_{mp}^*. Because both irradiance and temperature are at reference values, this represents the operating point at which the user-specified loss percentage applies.

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DC-Field-Level Effective Resistance

The total DC-field-level resistance that would produce the specified wiring loss at the reference operating point is: RDC,field=Lwire×Pmp,ref×Np×Ns(Imp∗×Np)2R_{DC,field} = \frac{L_{wire} \times P_{mp,ref} \times N_p \times N_s}{(I_{mp}^* \times N_p)^2} where LwireL_{wire} is the wiring loss fraction (percentage / 100). This field-level resistance is used for ohmic loss reporting in the loss tree.

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Per-Module Equivalent Resistance

The field-level resistance is distributed equally across all modules as a per-module series resistance: RDC,module=RDC,field×NpNs=Lwire×Pmp,refImp∗2R_{DC,module} = \frac{R_{DC,field} \times N_p}{N_s} = \frac{L_{wire} \times P_{mp,ref}}{I_{mp}^{*2}} This resistance is added to the module series resistance RsR_s during parameter translation: Rs←Rs+RDC,moduleR_s \leftarrow R_s + R_{DC,module}