DC System Losses

Summary

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

DC wiring losses are applied downstream in the model, accounted for as additional . Time-dependent degradation is applied downstream of the single-diode conversion and is documented separately in the Degradation Losses (DC Applied) and Degradation Losses (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
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)
Effective Front POA Irradiance	$G_{POA,front,eff}$	W/m²	Front-side effective POA irradiance

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Outputs

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

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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, 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 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 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) 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 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.