P50 Loss Tree

Understanding the P50 loss tree and how each loss factor is calculated in PlantPredict

The P50 Loss Tree provides a comprehensive breakdown of energy losses throughout the PV system, from incident solar resource to final AC energy delivered at the point of interconnection. Each loss factor is calculated as a percentage and represents the energy reduction attributable to that specific mechanism. The calculations reference specific parameters from the Nodal Data exports, allowing users to trace and verify each loss.

About Loss Aggregation

The Loss Tree displays annual percentage values aggregated across all timesteps and DC fields. To calculate these from Nodal Data exports, you must sum the values across all timesteps for each DC field, then aggregate across all DC fields weighted by module area. The formulas below show the conceptual relationships using Nodal Data parameter names.

Detailed Description of Losses

Irradiance Losses

These losses affect the solar resource before it is converted to electrical energy. They are derived from DC Field Nodal Data parameters.

Loss Parameter	Description	Calculation
Transposition on Plane	The change in irradiance from horizontal to the tilted module plane, which can be positive (gain) or negative (loss) depending on array orientation and location	$L_{trans} = \frac{100 \cdot \sum (\text{Global POAI} - \text{GHI})}{\sum \text{GHI}}$
3D Corrected Transposition	Adjustment to transposition calculation when using 3D transposition model to account for site-specific geometry effects	$L_{3D} = \frac{100 \cdot \sum (\text{3D Corrected Global POAI} - \text{Global POAI})}{\sum \text{Global POAI}}$
Far (Horizon) Shading	Irradiance loss from distant objects blocking the sun, such as mountains or buildings on the horizon	$L_{horizon} = \frac{100 \cdot \sum (\text{Horizon Shaded Global POAI} - \text{3D Corrected Global POAI})}{\sum \text{Global POAI}}$
Near Shading	Irradiance loss from inter-row shading and nearby obstructions within the array field	$L_{near} = \frac{100 \cdot \sum (\text{Near Shaded Global POAI} - \text{Horizon Shaded Global POAI})}{\sum \text{Global POAI}}$
Soiling	Irradiance loss from dust, dirt, snow, or other materials accumulating on the module surface	$L_{soil} = \frac{100 \cdot \sum (\text{Global POAI After Soiling} - \text{Near Shaded Global POAI})}{\sum \text{Global POAI}}$
IAM Factor	Irradiance loss due to increased reflection at non-normal incidence angles (Incidence Angle Modifier)	$L_{IAM} = \frac{100 \cdot \sum (\text{Global POAI After IAM} - \text{Global POAI After Soiling})}{\sum \text{Global POAI}}$
Spectral	Irradiance loss or gain from atmospheric spectral variations compared to the reference AM1.5 spectrum	$L_{spec} = \frac{100 \cdot \sum (\text{Effective Global POAI} - \text{Global POAI After IAM})}{\sum \text{Global POAI}}$
Bifaciality	Effective irradiance reduction when applying the bifaciality factor to rear-side irradiance	$L_{bifi} = \frac{-100 \cdot \sum \text{Effective Back POAI Lost due to BiFaciality}}{\sum \text{Global POAI}}$
Structure Shading	Rear-side irradiance loss from mounting structure shadows on bifacial modules	$L_{struct} = \frac{-100 \cdot \sum \text{Structure Shading Loss}}{\sum \text{Global POAI} \cdot A_{module}}$
Backside Irradiance	Effective irradiance gain from rear-side illumination of bifacial modules	$L_{back} = \frac{100 \cdot \sum (\text{Backside Irradiance} / A_{module})}{\sum \text{3D Corrected Global POAI}}$
Back Mismatch	Power loss from non-uniform rear-side irradiance distribution across bifacial modules	$L_{back\_mis} = \frac{-100 \cdot \sum \text{DC Power Lost due to Back Mismatch}}{\sum \text{Global POAI} \cdot A_{module}}$

Unit Considerations for Structure Shading, Backside Irradiance, and Back Mismatch

Some DC Field Nodal Data parameters are reported in Watts (W) while irradiance values are in W/m²:

• Structure Shading Loss (W) - power
• Backside Irradiance (W) - power
• DC Power Lost due to Back Mismatch (W) - power

To maintain dimensional consistency when using these with irradiance denominators, the calculation must account for module area ($A_{module}$). The prediction engine performs this area-weighting internally during aggregation.

Sign Convention

All formulas use a consistent sign convention where losses are negative and gains are positive:

• For subtractions: 100 · (After - Before) — when After < Before (a loss), result is negative
• For named loss values: -100 · Loss — loss values are positive in Nodal Data, so negation yields negative result
• For gains (e.g., Backside Irradiance): 100 · Gain — yields positive result

DC Performance Losses

These losses occur during DC power generation. They are derived from DC Field Nodal Data parameters and normalized by DC Power at STC.

Loss Parameter	Description	Calculation
Electrical Shading	DC power loss from partial shading causing electrical mismatch and bypass diode activation	$L_{elec} = \frac{-100 \cdot \sum \text{DC Power Lost due to Electrical Shading}}{\sum \text{DC Power at STC}}$
Module Irradiance	Power deviation from STC due to operating at irradiance levels different from 1000 W/m²	$L_{irr} = \frac{-100 \cdot \sum \text{Module Irradiance}}{\sum \text{DC Power at STC}}$
Module Temperature	Power loss from module operating temperatures above the 25°C STC reference	$L_{temp} = \frac{100 \cdot \sum (\text{DC Power at MPP} + \text{DC Power Lost due to Electrical Shading} - \text{DC Power at 25C})}{\sum \text{DC Power at STC}}$
Module Mismatch	Power loss from electrical parameter variations between modules in a string or array	$L_{mis} = \frac{-100 \cdot \sum \text{DC Power Lost due to Module Mismatch}}{\sum \text{DC Power at STC}}$
LID (Light Induced Degradation)	Initial power loss occurring in the first hours of light exposure, primarily in crystalline silicon modules	$L_{LID} = \frac{-100 \cdot \sum \text{DC Power Lost due to LID}}{\sum \text{DC Power at STC}}$
Module Quality	Power deviation from nameplate due to module binning and manufacturing tolerances	$L_{qual} = \frac{-100 \cdot \sum \text{DC Power Lost due to Module Quality}}{\sum \text{DC Power at STC}}$
DC Health	User-defined DC system losses to account for factors such as module soiling non-uniformity or connection degradation	$L_{DC\_health} = -\text{avg}(\text{DC Power Lost due to DC Health (\%)})$
DC Wiring	Resistive losses in DC cables between modules and inverter inputs	$L_{wire} = \frac{-100 \cdot \sum \text{Ohmic Power Loss}}{\sum \text{DC Power at STC}}$
Degradation (if applied to DC)	Annual module power degradation applied to DC power at the inverter level before the DC-to-AC conversion. Appears here when the prediction uses a DC degradation model (Linear DC or Non-Linear DC).	$L_{deg\_DC} = \frac{-100 \cdot \sum (\text{DC Power at MPP} - \text{DC Power} - \text{Inverter Limitation})}{\sum \text{DC Power at STC}}$
Inverter Limitation	Power loss when the inverter operates off the maximum power point due to voltage window or power clipping constraints	$L_{inv\_lim} = \frac{-100 \cdot \sum \text{Inverter Limitation}}{\sum \text{DC Power at STC}}$
Inverter Efficiency	Power loss in the DC-to-AC conversion process based on the inverter efficiency curve	$L_{inv\_eff} = \frac{100 \cdot \sum (\text{AC Power} - \text{DC Power})}{\sum \text{DC Power at STC}}$

Inverter Parameters

DC Power at MPP, Inverter Limitation, DC Power, and AC Power are from Inverter Nodal Data, while other DC performance parameters are from DC Field Nodal Data.

Degradation Model Placement

The Degradation loss appears in different sections of the loss tree depending on the degradation model selected in the prediction:

• DC degradation models (Linear DC, Non-Linear DC): Degradation appears in the DC Performance Losses section, normalized by DC Power at STC. The degradation is applied to DC power at the inverter level before the inverter operating point and DC-to-AC conversion are calculated.
• AC degradation models (Linear AC, Stepped AC): Degradation appears in the AC System Losses section, normalized by Total AC Power from Inverters. The degradation is applied to AC power at the array level after the inverter output.

AC System Losses

These losses occur in the AC system after the inverter. They are derived from Array Nodal Data parameters and normalized by Total AC Power from Inverters.

Loss Parameter	Description	Calculation
Inverter Cooling	Auxiliary power consumption for inverter thermal management systems	$L_{cool} = \frac{-100 \cdot \sum \text{Shelter Cooling Loss}}{\sum \text{Total AC Power from Inverters}}$
Tracker Motor	Auxiliary power consumption for single-axis tracker motor operation	$L_{track} = \frac{-100 \cdot \sum \text{Tracker Motor Loss}}{\sum \text{Total AC Power from Inverters}}$
Data Acquisition	Auxiliary power consumption for monitoring and data acquisition systems	$L_{DAS} = \frac{-100 \cdot \sum \text{Data Acquisition System Loss}}{\sum \text{Total AC Power from Inverters}}$
MV Transformers	Power losses in medium-voltage transformers at the array level	$L_{MV} = \frac{-100 \cdot \sum \text{Transformer Losses}}{\sum \text{Total AC Power from Inverters}}$
AC Collection Lines	Resistive losses in the medium-voltage collection system between arrays and the plant substation	$L_{coll} = \frac{-100 \cdot \sum \text{AC Collection Loss}}{\sum \text{Total AC Power from Inverters}}$
Degradation (if applied to AC)	Annual module power degradation applied at the array level after the DC-to-AC conversion. Appears here when the prediction uses an AC degradation model (Linear AC or Stepped AC).	$L_{deg\_AC} = \frac{100 \cdot \sum (\text{AC Power After Degradation} - \text{Total AC Power from Inverters})}{\sum \text{Total AC Power from Inverters}}$

Plant-Level Losses

These losses occur at the plant level and affect the final energy delivered to the grid. They are derived from System Nodal Data parameters.

Loss Parameter	Description	Calculation
HV Transformers	Power losses in high-voltage transformers at the plant substation	$L_{HV} = \frac{-100 \cdot \sum \text{AC Power Lost due to HV Transformer(s)}}{\sum \text{HV Transformer and Transmission Line Input}}$
Transmission Lines	Power losses in transmission lines between the plant and point of interconnection	$L_{TL} = \frac{-100 \cdot \sum \text{AC Power Lost due to Transmission Line(s)}}{\sum \text{HV Transformer and Transmission Line Input}}$
LGIA Limitation	Energy curtailment when plant output exceeds the interconnection agreement limit	$L_{LGIA} = \frac{-100 \cdot \sum \text{AC Power Lost due to Plant Output Limit}}{\sum \text{HV Transformer and Transmission Line Input}}$
Availability	Energy loss from planned and unplanned system downtime	$L_{avail} = \frac{100 \cdot \sum (\text{AC Power after Availability} - \text{Transformer and Transmission Line Output})}{\sum \text{Transformer and Transmission Line Output}}$

Parameter Reference by Nodal Data Level

Nodal Data Level	Parameters Used in Loss Calculations
DC Field	GHI (from System), Global POAI (W/m²), 3D Corrected Global POAI (W/m²), Horizon Shaded Global POAI (W/m²), Near Shaded Global POAI (W/m²), Global POAI After Soiling (W/m²), Global POAI After IAM (W/m²), Effective Global POAI (W/m²), Effective Global Back POAI (W/m²), Effective Back POAI Lost due to BiFaciality (W/m²), Structure Shading Loss (W), Backside Irradiance (W), DC Power Lost due to Back Mismatch (W), DC Power Lost due to Electrical Shading (W), DC Power at STC (W), DC Power at 25C (W), Module Irradiance (W), DC Power at MPP (W), DC Power Lost due to Module Mismatch (W), DC Power Lost due to LID (W), DC Power Lost due to Module Quality (W), DC Power Lost due to DC Health (%), Ohmic Power Loss (W)
Inverter	DC Power at MPP (W), Inverter Limitation (W), DC Power (W), AC Power (W)
Array	Shelter Cooling Loss (W), Tracker Motor Loss (W), Data Acquisition System Loss (W), Transformer Losses (W), AC Collection Loss (W), Total AC Power from Inverters (W), Degradation, AC Power After Degradation (W)
System	GHI (W/m²), POAI (W/m²), HV Transformer and Transmission Line Input (W), AC Power Lost due to HV Transformer(s) (W), AC Power Lost due to Transmission Line(s) (W), Transformer and Transmission Line Output (W), AC Power after Availability (W), Plant Output Limit (W), AC Power Lost due to Plant Output Limit (W)