> ## 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.
# 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) |