DC Wiring Resistance

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 .

Inputs

Name	Symbol	Units	Description
DC Wiring Loss Percentage	$L_{wire}$	%	User-specified wiring loss at reference conditions
Module Maximum Power	$P_{mp,ref}$	W	Module maximum power at reference conditions
Number of Parallel Strings	$N_p$	—	Parallel strings in the DC field
Number of Modules in Series	$N_s$	—	Modules in series per string
Reference Irradiance	$G_{ref}$	W/m²	Reference irradiance (typically 1000 W/m²)
Reference Temperature	$T_{ref}$	°C	Reference cell temperature (typically 25 °C)

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Outputs

Name	Symbol	Units	Description
Field-Level Wiring Resistance	$R_{DC,field}$	Ω	DC-field-level effective resistance
Per-Module Wiring Resistance	$R_{DC,module}$	Ω	Module-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.

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 ($G_{ref}$, typically 1000 W/m²) with the combined DC system loss coefficient applied
• Reference temperature ($T_{ref}$, typically 25 °C)
• Zero wiring resistance
• Zero back irradiance

The resulting maximum power point current is denoted $I_{mp}^*$. Because both irradiance and temperature are at reference values, this represents the operating point at which the user-specified loss percentage applies.

DC-Field-Level Effective Resistance

The total DC-field-level resistance that would produce the specified wiring loss at the reference operating point is:

$$R_{DC,field} = \frac{L_{wire} \times P_{mp,ref} \times N_p \times N_s}{(I_{mp}^* \times N_p)^2}$$

where $L_{wire}$ is the wiring loss fraction (percentage / 100). This field-level resistance is used for ohmic loss reporting in the loss tree.

Per-Module Equivalent Resistance

The field-level resistance is distributed equally across all modules as a per-module series resistance:

$$R_{DC,module} = \frac{R_{DC,field} \times N_p}{N_s} = \frac{L_{wire} \times P_{mp,ref}}{I_{mp}^{*2}}$$

This resistance is added to the module series resistance $R_s$ during parameter translation:

$$R_s \leftarrow R_s + R_{DC,module}$$