> ## Documentation Index
> Fetch the complete documentation index at: https://docs.plantpredict.com/llms.txt
> Use this file to discover all available pages before exploring further.

# DC Wiring Resistance

export const IVCurve = () => <Tooltip tip="Current-voltage characteristic of a PV cell or module; the operating point on this curve determines power output.">
    I-V curve
  </Tooltip>;

export const MaximumPowerPoint = () => <Tooltip tip="Operating point on a PV module's I-V curve where the product of voltage and current is maximized.">
    maximum power point
  </Tooltip>;

export const SingleDiode = () => <Tooltip tip="Equivalent circuit representing a PV cell as a current source, diode, and resistances to predict I-V behavior.">
    single-diode
  </Tooltip>;

export const SeriesResistance = () => <Tooltip tip="Combined ohmic resistance of cell metallization, interconnects, and wiring in the module current path; causes I²R losses.">
    series resistance
  </Tooltip>;

## 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 <SeriesResistance /> that is added to each module's series resistance before the <SingleDiode /> equation is solved. This approach captures the voltage- and current-dependent nature of resistive losses within the <IVCurve />.

## 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)       |

***

## 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 |

***

## 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 <MaximumPowerPoint /> under reference conditions is needed. PlantPredict obtains this by running a preliminary [5-parameter](/models/dc-performance/5_parameter_model) or [7-parameter](/models/dc-performance/7_parameter_model) single-diode equation solve at:

* Reference irradiance ($G_{ref}$, typically 1000 W/m²) with the combined [DC system loss](/models/dc-performance/dc_system_losses) 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](/models/dc-performance/parameter_translation):

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