> ## 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 System Losses

export const Mismatch = () => <Tooltip tip="Power loss when series-connected cells or modules operate at mismatched levels due to shading, manufacturing variation, soiling, or temperature differences.">
    mismatch
  </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 STC = () => <Tooltip tip="Standard Test Conditions: 1000 W/m² irradiance, 25 °C cell temperature, AM1.5G spectrum; the reference conditions for rating PV modules.">
    STC
  </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>;

export const LightInducedDegradation = () => <Tooltip tip="Initial power loss from light exposure, primarily due to boron-oxygen defects in p-type silicon.">
    light-induced degradation
  </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>;

## Summary

DC System Losses account for non-ideal effects—module <Mismatch />, <LightInducedDegradation />, module quality variation, and DC health—by reducing the effective irradiance before the <SingleDiode /> conversion. PlantPredict applies these losses as a combined coefficient that scales the effective POA irradiance.

DC wiring losses are applied downstream in the <SingleDiode /> model, accounted for as additional <SeriesResistance />. Time-dependent degradation is applied downstream of the single-diode conversion and is documented separately in the [Degradation Losses (DC Applied)](../inverter-models/degradation_dc_applied) and [Degradation Losses (AC Applied)](../ac-losses/degradation_ac_applied) pages.

## Inputs

| Name                               | Symbol              | Units | Description                                                                                                                                    |
| ---------------------------------- | ------------------- | ----- | ---------------------------------------------------------------------------------------------------------------------------------------------- |
| **Effective POA Irradiance**       | $G_{POA,tot,eff}$   | W/m²  | Combined front and rear POA irradiance from the [irradiance calculation](/models/poa-irradiance/overview)                                      |
| **Module Mismatch Coefficient**    | $f_{MM}$            | %     | Module-to-module mismatch loss percentage                                                                                                      |
| **Light-Induced Degradation**      | $f_{LID}$           | %     | Light-induced degradation loss                                                                                                                 |
| **Module Quality Factor**          | $f_{MQ}$            | %     | Power deviation from nameplate due to module binning and manufacturing tolerances                                                              |
| **DC Health Factor**               | $f_{DCH}$           | %     | User-defined DC system loss to account for factors such as connection degradation                                                              |
| **Backside Mismatch**              | $f_{MM,rear}$       | %     | Rear-side irradiance mismatch loss                                                                                                             |
| **Average Rear Irradiance**        | $G_{POA,rear}$      | W/m²  | Average rear irradiance after structure shading, before bifaciality weighting (from [rear irradiance](/models/poa-irradiance/rear_irradiance)) |
| **Effective Front POA Irradiance** | $G_{POA,front,eff}$ | W/m²  | Front-side effective POA irradiance                                                                                                            |

***

## Outputs

| Name                            | Symbol             | Units | Description                                     |
| ------------------------------- | ------------------ | ----- | ----------------------------------------------- |
| **Scaled Effective Irradiance** | $G'_{POA,tot,eff}$ | W/m²  | Effective POA irradiance after DC system losses |

***

## Detailed Description

PlantPredict applies module mismatch, LID, module quality, and DC health losses as a single combined coefficient that uniformly scales the effective POA irradiance before the single-diode conversion. Each input percentage is converted to a fraction (divided by 100) before use:

$$
G'_{POA,tot,eff} = G_{POA,tot,eff} \times C_{comb}
$$

where $G_{POA,tot,eff}$ is the total effective POA irradiance from the [irradiance calculation](/models/poa-irradiance/overview), including all front-side components and bifaciality-weighted rear irradiance. The composition of $C_{comb}$ depends on the prediction version.

### Version 10 and Later

The combined coefficient includes module mismatch, module quality, LID, and DC health:

$$
C_{comb} = (1 - f_{MM}) \times (1 - f_{MQ}) \times (1 - f_{LID}) \times (1 - f_{DCH})
$$

For bifacial modules, backside mismatch $f_{MM,rear}$ is applied directly to the rear irradiance in the [rear irradiance](/models/poa-irradiance/rear_irradiance) calculation and is not part of the combined coefficient.

When SunSolve-calibrated parameters are used, $f_{MM}$ should be supplied from the SunSolve simulation output—a single combined mismatch value accounting for non-uniform illumination on both the front and rear of the module. The separate backside mismatch term is set to zero in [rear irradiance](/models/poa-irradiance/rear_irradiance) to avoid double-counting. This is physically more accurate, since electrical mismatch arises from imbalanced photocurrents between series-connected cells regardless of which side of the module the light arrives from.

### Version 9 and Earlier

In Version 9 and earlier, the combined coefficient also includes rear-side mismatch for bifacial modules. Because the combined coefficient is applied uniformly to all irradiance components, the backside mismatch fraction is approximated as an effective value weighted by the rear-to-front irradiance ratio:

$$
f_{MM,rear,eff} = f_{MM,rear} \cdot \frac{G_{POA,rear}}{G_{POA,front,eff}}
$$

where $G_{POA,rear}$ is the average rear irradiance after structure shading (see [Rear Irradiance](/models/poa-irradiance/rear_irradiance)) and $G_{POA,front,eff}$ is the front-side effective POA irradiance. The full combined coefficient becomes:

$$
C_{comb} = (1 - f_{MM}) \times (1 - f_{MQ}) \times (1 - f_{LID}) \times (1 - f_{DCH}) \times (1 - f_{MM,rear,eff})
$$

Because the coefficient is applied uniformly to both front and rear irradiance, this approach slightly overestimates the backside mismatch loss compared to applying it directly to the rear irradiance. Version 10 eliminates this by moving backside mismatch upstream into the [rear irradiance](/models/poa-irradiance/rear_irradiance) calculation.

For monofacial modules, $G_{POA,rear} = 0$ so $f_{MM,rear,eff} = 0$ and the combined coefficient reduces to the Version 10+ form.

### Loss Reporting

For reporting (loss tree), each individual loss component is approximated as $L_i = P_{mp} \times f_i$, where $P_{mp}$ is the maximum power point power from the single-diode equation and $f_i$ is the corresponding loss fraction.