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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.
Example Loss Tree
About Loss AggregationThe 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.

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Detailed Description of Losses

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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 ParameterDescriptionCalculation
Transposition on PlaneThe change in irradiance from horizontal to the tilted module plane, which can be positive (gain) or negative (loss) depending on array orientation and locationLtrans=100⋅∑(Global POAI−GHI)∑GHIL_{trans} = \frac{100 \cdot \sum (\text{Global POAI} - \text{GHI})}{\sum \text{GHI}}
3D Corrected TranspositionAdjustment to transposition calculation when using 3D transposition model to account for site-specific geometry effectsL3D=100⋅∑(3D Corrected Global POAI−Global POAI)∑Global POAIL_{3D} = \frac{100 \cdot \sum (\text{3D Corrected Global POAI} - \text{Global POAI})}{\sum \text{Global POAI}}
Far (Horizon) ShadingIrradiance loss from distant objects blocking the sun, such as mountains or buildings on the horizonLhorizon=100⋅∑(Horizon Shaded Global POAI−3D Corrected Global POAI)∑Global POAIL_{horizon} = \frac{100 \cdot \sum (\text{Horizon Shaded Global POAI} - \text{3D Corrected Global POAI})}{\sum \text{Global POAI}}
Near ShadingIrradiance loss from inter-row shading and nearby obstructions within the array fieldLnear=100⋅∑(Near Shaded Global POAI−Horizon Shaded Global POAI)∑Global POAIL_{near} = \frac{100 \cdot \sum (\text{Near Shaded Global POAI} - \text{Horizon Shaded Global POAI})}{\sum \text{Global POAI}}
SoilingIrradiance loss from dust, dirt, snow, or other materials accumulating on the module surfaceLsoil=100⋅∑(Global POAI After Soiling−Near Shaded Global POAI)∑Global POAIL_{soil} = \frac{100 \cdot \sum (\text{Global POAI After Soiling} - \text{Near Shaded Global POAI})}{\sum \text{Global POAI}}
IAM FactorIrradiance loss due to increased reflection at non-normal incidence angles (Incidence Angle Modifier)LIAM=100⋅∑(Global POAI After IAM−Global POAI After Soiling)∑Global POAIL_{IAM} = \frac{100 \cdot \sum (\text{Global POAI After IAM} - \text{Global POAI After Soiling})}{\sum \text{Global POAI}}
SpectralIrradiance loss or gain from atmospheric spectral variations compared to the reference AM1.5 spectrumLspec=100⋅∑(Effective Global POAI−Global POAI After IAM)∑Global POAIL_{spec} = \frac{100 \cdot \sum (\text{Effective Global POAI} - \text{Global POAI After IAM})}{\sum \text{Global POAI}}
BifacialityEffective irradiance reduction when applying the bifaciality factor to rear-side irradianceLbifi=−100⋅∑Effective Back POAI Lost due to BiFaciality∑Global POAIL_{bifi} = \frac{-100 \cdot \sum \text{Effective Back POAI Lost due to BiFaciality}}{\sum \text{Global POAI}}
Structure ShadingRear-side irradiance loss from mounting structure shadows on bifacial modulesLstruct=−100⋅∑Structure Shading Loss∑Global POAI⋅AmoduleL_{struct} = \frac{-100 \cdot \sum \text{Structure Shading Loss}}{\sum \text{Global POAI} \cdot A_{module}}
Backside IrradianceEffective irradiance gain from rear-side illumination of bifacial modulesLback=100⋅∑(Backside Irradiance/Amodule)∑3D Corrected Global POAIL_{back} = \frac{100 \cdot \sum (\text{Backside Irradiance} / A_{module})}{\sum \text{3D Corrected Global POAI}}
Back MismatchPower loss from non-uniform rear-side irradiance distribution across bifacial modulesLback_mis=−100⋅∑DC Power Lost due to Back Mismatch∑Global POAI⋅AmoduleL_{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 MismatchSome 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 (AmoduleA_{module}). The prediction engine performs this area-weighting internally during aggregation.
Sign ConventionAll 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

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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 ParameterDescriptionCalculation
Electrical ShadingDC power loss from partial shading causing electrical mismatch and bypass diode activationLelec=−100⋅∑DC Power Lost due to Electrical Shading∑DC Power at STCL_{elec} = \frac{-100 \cdot \sum \text{DC Power Lost due to Electrical Shading}}{\sum \text{DC Power at STC}}
Module IrradiancePower deviation from STC due to operating at irradiance levels different from 1000 W/m²Lirr=−100⋅∑Module Irradiance∑DC Power at STCL_{irr} = \frac{-100 \cdot \sum \text{Module Irradiance}}{\sum \text{DC Power at STC}}
Module TemperaturePower loss from module operating temperatures above the 25°C STC referenceLtemp=100⋅∑(DC Power at MPP+DC Power Lost due to Electrical Shading−DC Power at 25C)∑DC Power at STCL_{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 MismatchPower loss from electrical parameter variations between modules in a string or arrayLmis=−100⋅∑DC Power Lost due to Module Mismatch∑DC Power at STCL_{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 modulesLLID=−100⋅∑DC Power Lost due to LID∑DC Power at STCL_{LID} = \frac{-100 \cdot \sum \text{DC Power Lost due to LID}}{\sum \text{DC Power at STC}}
Module QualityPower deviation from nameplate due to module binning and manufacturing tolerancesLqual=−100⋅∑DC Power Lost due to Module Quality∑DC Power at STCL_{qual} = \frac{-100 \cdot \sum \text{DC Power Lost due to Module Quality}}{\sum \text{DC Power at STC}}
DC HealthUser-defined DC system losses to account for factors such as module soiling non-uniformity or connection degradationLDC_health=−avg(DC Power Lost due to DC Health (%))L_{DC\_health} = -\text{avg}(\text{DC Power Lost due to DC Health (\%)})
DC WiringResistive losses in DC cables between modules and inverter inputsLwire=−100⋅∑Ohmic Power Loss∑DC Power at STCL_{wire} = \frac{-100 \cdot \sum \text{Ohmic Power Loss}}{\sum \text{DC Power at STC}}
Inverter LimitationPower loss when the inverter operates off the maximum power point due to voltage window or power clipping constraintsLinv_lim=−100⋅∑Inverter Limitation∑DC Power at STCL_{inv\_lim} = \frac{-100 \cdot \sum \text{Inverter Limitation}}{\sum \text{DC Power at STC}}
Inverter EfficiencyPower loss in the DC-to-AC conversion process based on the inverter efficiency curveLinv_eff=100⋅∑(AC Power−DC Power)∑DC Power at STCL_{inv\_eff} = \frac{100 \cdot \sum (\text{AC Power} - \text{DC Power})}{\sum \text{DC Power at STC}}
Inverter ParametersInverter Limitation, DC Power, and AC Power are from Inverter Nodal Data, while other DC performance parameters are from DC Field Nodal Data.

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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 ParameterDescriptionCalculation
Inverter CoolingAuxiliary power consumption for inverter thermal management systemsLcool=−100⋅∑Shelter Cooling Loss∑Total AC Power from InvertersL_{cool} = \frac{-100 \cdot \sum \text{Shelter Cooling Loss}}{\sum \text{Total AC Power from Inverters}}
Tracker MotorAuxiliary power consumption for single-axis tracker motor operationLtrack=−100⋅∑Tracker Motor Loss∑Total AC Power from InvertersL_{track} = \frac{-100 \cdot \sum \text{Tracker Motor Loss}}{\sum \text{Total AC Power from Inverters}}
Data AcquisitionAuxiliary power consumption for monitoring and data acquisition systemsLDAS=−100⋅∑Data Acquisition System Loss∑Total AC Power from InvertersL_{DAS} = \frac{-100 \cdot \sum \text{Data Acquisition System Loss}}{\sum \text{Total AC Power from Inverters}}
MV TransformersPower losses in medium-voltage transformers at the array levelLMV=−100⋅∑Transformer Losses∑Total AC Power from InvertersL_{MV} = \frac{-100 \cdot \sum \text{Transformer Losses}}{\sum \text{Total AC Power from Inverters}}
AC Collection LinesResistive losses in the medium-voltage collection system between arrays and the plant substationLcoll=−100⋅∑AC Collection Loss∑Total AC Power from InvertersL_{coll} = \frac{-100 \cdot \sum \text{AC Collection Loss}}{\sum \text{Total AC Power from Inverters}}
DegradationAnnual module power degradation applied at the array levelLdeg=100⋅∑(AC Power After Degradation−Total AC Power from Inverters)∑Total AC Power from InvertersL_{deg} = \frac{100 \cdot \sum (\text{AC Power After Degradation} - \text{Total AC Power from Inverters})}{\sum \text{Total AC Power from Inverters}}

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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 ParameterDescriptionCalculation
HV TransformersPower losses in high-voltage transformers at the plant substationLHV=−100⋅∑AC Power Lost due to HV Transformer(s)∑HV Transformer and Transmission Line InputL_{HV} = \frac{-100 \cdot \sum \text{AC Power Lost due to HV Transformer(s)}}{\sum \text{HV Transformer and Transmission Line Input}}
Transmission LinesPower losses in transmission lines between the plant and point of interconnectionLTL=−100⋅∑AC Power Lost due to Transmission Line(s)∑HV Transformer and Transmission Line InputL_{TL} = \frac{-100 \cdot \sum \text{AC Power Lost due to Transmission Line(s)}}{\sum \text{HV Transformer and Transmission Line Input}}
LGIA LimitationEnergy curtailment when plant output exceeds the interconnection agreement limitLLGIA=−100⋅∑AC Power Lost due to Plant Output Limit∑HV Transformer and Transmission Line InputL_{LGIA} = \frac{-100 \cdot \sum \text{AC Power Lost due to Plant Output Limit}}{\sum \text{HV Transformer and Transmission Line Input}}
AvailabilityEnergy loss from planned and unplanned system downtimeLavail=100⋅∑(AC Power after Availability−Transformer and Transmission Line Output)∑Transformer and Transmission Line OutputL_{avail} = \frac{100 \cdot \sum (\text{AC Power after Availability} - \text{Transformer and Transmission Line Output})}{\sum \text{Transformer and Transmission Line Output}}

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Parameter Reference by Nodal Data Level

Nodal Data LevelParameters Used in Loss Calculations
DC FieldGHI (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)
InverterInverter Limitation (W), DC Power (W), AC Power (W)
ArrayShelter 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)
SystemGHI (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)