> ## 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.

# Simulation Settings

> Configure prediction timeframe, irradiance models, module models, shading models, and degradation parameters

The Simulation Settings page allows you to configure the prediction timeframe and select the sub-models used for irradiance calculation, module performance, shading analysis, and degradation. These settings control the algorithms applied during the energy prediction simulation.

<Frame caption="Simulation Settings">
  <img src="https://mintcdn.com/terabaseenergy/NaTzh7AscdffXqcV/images/simulation-settings-ui.png?fit=max&auto=format&n=NaTzh7AscdffXqcV&q=85&s=168193751927f44e7dbc3210c8235d2a" alt="Simulation Settings" width="2048" height="1618" data-path="images/simulation-settings-ui.png" />
</Frame>

## Overview

The Simulation Settings page is organized into the following sections:

1. **Timeframe** — Set the prediction start and end dates, and access uncertainty analysis configuration. Weather file summary information is displayed for reference.
2. **Irradiance Models** — Select decomposition, transposition, and circumsolar treatment algorithms, plus toggle options for using weather file DNI and pre-calculated POAI values.
3. **Module Related Models** — Choose incidence angle modifier (IAM) and module temperature calculation methods.
4. **Shading Models** — Configure direct and diffuse shading calculation approaches.
5. **Degradation** — Define long-term degradation parameters including annual rates and LeTID modeling.

***

## User Inputs (Timeframe)

<table>
  <colgroup>
    <col style={{width: "4%"}} />

    <col style={{width: "18%"}} />

    <col style={{width: "10%"}} />

    <col style={{width: "6%"}} />

    <col style={{width: "44%"}} />

    <col style={{width: "18%"}} />
  </colgroup>

  <thead>
    <tr>
      <th>#</th>
      <th>Input</th>
      <th>Type</th>
      <th>Units</th>
      <th>Description</th>
      <th>Related Documentation</th>
    </tr>
  </thead>

  <tbody>
    <tr>
      <td>**1**</td>
      <td>**Start Date**</td>
      <td>Date Picker</td>
      <td>—</td>
      <td>Beginning date and time for the prediction simulation. Must fall within the weather file date range shown in the summary panel.</td>
      <td>—</td>
    </tr>

    <tr>
      <td>**2**</td>
      <td>**End Date**</td>
      <td>Date Picker</td>
      <td>—</td>
      <td>Ending date and time for the prediction simulation. Must fall within the weather file date range shown in the summary panel.</td>
      <td>—</td>
    </tr>

    <tr>
      <td>**3**</td>
      <td>**Show Uncertainty Analysis**</td>
      <td>Button</td>
      <td>—</td>
      <td>Opens the [Uncertainty Analysis](/user-guide/ui/uncertainty-analysis) configuration panel to define P-value selections and uncertainty parameters for probabilistic energy estimates (P50/P90/P99).</td>
      <td>[Uncertainty Analysis](/user-guide/ui/uncertainty-analysis)</td>
    </tr>
  </tbody>
</table>

The Timeframe section also displays **Weather File Summary** information (read-only):

* **Weather File Name** — Name and location coordinates of the loaded weather file
* **Start Date / End Date** — Date range available in the weather file
* **Time Step** — Temporal resolution of weather data (e.g., 60 min)
* **Duration** — Total years of weather data

***

## User Inputs (Irradiance Models)

<table>
  <colgroup>
    <col style={{width: "4%"}} />

    <col style={{width: "18%"}} />

    <col style={{width: "10%"}} />

    <col style={{width: "6%"}} />

    <col style={{width: "44%"}} />

    <col style={{width: "18%"}} />
  </colgroup>

  <thead>
    <tr>
      <th>#</th>
      <th>Input</th>
      <th>Type</th>
      <th>Units</th>
      <th>Description</th>
      <th>Related Documentation</th>
    </tr>
  </thead>

  <tbody>
    <tr>
      <td>**4**</td>
      <td>**Weather File DNI**</td>
      <td>Toggle</td>
      <td>—</td>
      <td>When **ON**, uses Direct Normal Irradiance (DNI) values directly from the weather file. When **OFF**, DNI is calculated from GHI using the selected decomposition model.</td>
      <td>[Horizontal Irradiance](/models/horizontal-irradiance/horizontal_irradiance_components)</td>
    </tr>

    <tr>
      <td>**5**</td>
      <td>**Frontside POAI**</td>
      <td>Toggle</td>
      <td>—</td>
      <td>When **ON**, uses pre-calculated frontside Plane-of-Array Irradiance from the weather file instead of calculating via transposition models. Horizontal components (GHI, DNI, DHI) are reverse-decomposed from POAI using the GTI-DIRINT algorithm.</td>
      <td>[POAI Decomposition](/models/horizontal-irradiance/poai_diffuse_direct_decomposition)</td>
    </tr>

    <tr>
      <td>**6**</td>
      <td>**Backside POAI**</td>
      <td>Toggle</td>
      <td>—</td>
      <td>When **ON**, uses pre-calculated backside irradiance from the weather file for bifacial modules instead of calculating via the bifacial model.</td>
      <td>[Bifacial](/models/poa-irradiance/rear_irradiance)</td>
    </tr>

    <tr>
      <td>**7**</td>
      <td>**Decomposition**</td>
      <td>Dropdown</td>
      <td>—</td>
      <td>Select the algorithm for decomposing GHI into direct and diffuse components. Options: **None**, **DIRINT**, **Erbs**, **Reindl**.</td>
      <td>[Decomposition](/models/horizontal-irradiance/diffuse_direct_decomposition)</td>
    </tr>

    <tr>
      <td>**8**</td>
      <td>**Circumsolar Treatment**</td>
      <td>Dropdown</td>
      <td>—</td>
      <td>Select how circumsolar radiation is handled in transposition. **Diffuse** treats circumsolar as part of diffuse; **Direct** treats it as part of beam irradiance.</td>
      <td>[Transposition](/models/transposition/perez)</td>
    </tr>

    <tr>
      <td>**9**</td>
      <td>**Transposition**</td>
      <td>Dropdown</td>
      <td>—</td>
      <td>Select the transposition model for calculating plane-of-array irradiance from horizontal components. Options: **Perez**, **Hay-Davies**.</td>
      <td>[Transposition Models](/models/transposition/overview)</td>
    </tr>

    <tr>
      <td>**10**</td>
      <td>**Perez Coefficients**</td>
      <td>Dropdown</td>
      <td>—</td>
      <td>Select the coefficient set for the Perez transposition model. Options: **PlantPredict**, **All Sites Composite 1990**, **All Sites Composite 1988**, **Sandia Composite 1988**, or location-specific sets (USA, France, Phoenix, Elmonte, Osage, Albuquerque, Cape Canaveral, Albany).</td>
      <td>[Perez Model](/models/transposition/perez)</td>
    </tr>
  </tbody>
</table>

***

## User Inputs (Module Related Models)

<table>
  <colgroup>
    <col style={{width: "4%"}} />

    <col style={{width: "18%"}} />

    <col style={{width: "10%"}} />

    <col style={{width: "6%"}} />

    <col style={{width: "44%"}} />

    <col style={{width: "18%"}} />
  </colgroup>

  <thead>
    <tr>
      <th>#</th>
      <th>Input</th>
      <th>Type</th>
      <th>Units</th>
      <th>Description</th>
      <th>Related Documentation</th>
    </tr>
  </thead>

  <tbody>
    <tr>
      <td>**11**</td>
      <td>**Incidence Angle**</td>
      <td>Dropdown</td>
      <td>—</td>
      <td>Select the Incidence Angle Modifier (IAM) model. Options: **None**, **Tabular IAM**, **Physical IAM**, **Sandia**, **ASHRAE**.</td>
      <td>[Incidence Angle Modifier](/models/poa-irradiance/iam)</td>
    </tr>

    <tr>
      <td>**12**</td>
      <td>**Module Temperature**</td>
      <td>Dropdown</td>
      <td>—</td>
      <td>Select the module temperature calculation method. Options: **Heat Balance**, **NOCT**, **Sandia**, **DC Field Defined**.</td>
      <td>[Module Temperature](/models/dc-performance/overview#cell-temperature-models)</td>
    </tr>
  </tbody>
</table>

***

## User Inputs (Shading Models)

<table>
  <colgroup>
    <col style={{width: "4%"}} />

    <col style={{width: "18%"}} />

    <col style={{width: "10%"}} />

    <col style={{width: "6%"}} />

    <col style={{width: "44%"}} />

    <col style={{width: "18%"}} />
  </colgroup>

  <thead>
    <tr>
      <th>#</th>
      <th>Input</th>
      <th>Type</th>
      <th>Units</th>
      <th>Description</th>
      <th>Related Documentation</th>
    </tr>
  </thead>

  <tbody>
    <tr>
      <td>**13**</td>
      <td>**Direct Shading**</td>
      <td>Dropdown</td>
      <td>—</td>
      <td>Select the direct beam shading calculation method. Options: **Module File Defined Shading**, **None**, **Linear**, **Fractional Electrical Shading**. **Note:** This field is **disabled** when a 3D scene has been configured; shading settings are controlled via the [3D Scene Overview](/user-guide/ui/3d-scene-overview) page.</td>
      <td>[Row-to-Row Beam Shading](/models/shading/row_to_row_beam_shading)</td>
    </tr>

    <tr>
      <td>**14**</td>
      <td>**Diffuse Shading**</td>
      <td>Toggle</td>
      <td>—</td>
      <td>When **ON**, applies diffuse sky shading factors to account for horizon obstruction and row-to-row diffuse blocking. When **OFF**, no diffuse shading is applied.</td>
      <td>[Diffuse Shading](/models/shading/sky_diffuse_shading)</td>
    </tr>
  </tbody>
</table>

<Note>
  When a **3D Scene** is configured for the prediction, the Direct Shading dropdown is disabled. Shading calculations are controlled by the settings in the [3D Scene Overview](/user-guide/ui/3d-scene-overview) page, which provides more advanced shading analysis options.
</Note>

***

## User Inputs (Degradation)

<table>
  <colgroup>
    <col style={{width: "4%"}} />

    <col style={{width: "18%"}} />

    <col style={{width: "10%"}} />

    <col style={{width: "6%"}} />

    <col style={{width: "44%"}} />

    <col style={{width: "18%"}} />
  </colgroup>

  <thead>
    <tr>
      <th>#</th>
      <th>Input</th>
      <th>Type</th>
      <th>Units</th>
      <th>Description</th>
      <th>Related Documentation</th>
    </tr>
  </thead>

  <tbody>
    <tr>
      <td>**15**</td>
      <td>**Number of Years**</td>
      <td>Text Field</td>
      <td>years</td>
      <td>Total project lifetime for degradation calculations. Determines how many years of degraded energy output are calculated.</td>
      <td>—</td>
    </tr>

    <tr>
      <td>**16**</td>
      <td>**Degradation Model**</td>
      <td>Dropdown</td>
      <td>—</td>
      <td>Select the degradation calculation method. Options: **Linear DC**, **Non-Linear DC**, **Linear AC**, **Stepped AC**.</td>
      <td>[Degradation](/models/inverter-models/degradation_dc_applied)</td>
    </tr>

    <tr>
      <td>**17**</td>
      <td>**Degradation Rate**</td>
      <td>Text Field</td>
      <td>% Per Year</td>
      <td>Annual degradation rate applied according to the selected model. Typical values range from 0.25% to 0.7% per year for crystalline silicon modules.</td>
      <td>[Degradation](/models/inverter-models/degradation_dc_applied)</td>
    </tr>

    <tr>
      <td>**18**</td>
      <td>**First Year Degradation**</td>
      <td>Toggle</td>
      <td>—</td>
      <td>When **ON**, applies degradation starting from Year 1. When **OFF**, Year 1 energy is calculated at full capacity with degradation beginning in Year 2.</td>
      <td>—</td>
    </tr>

    <tr>
      <td>**19**</td>
      <td>**Use Leap Years**</td>
      <td>Toggle</td>
      <td>—</td>
      <td>When **ON**, accounts for leap years (366 days) in multi-year degradation calculations. When **OFF**, all years are treated as 365 days.</td>
      <td>—</td>
    </tr>

    <tr>
      <td>**20**</td>
      <td>**LeTID**</td>
      <td>Toggle</td>
      <td>—</td>
      <td>Enable Light and Elevated Temperature Induced Degradation modeling. When **ON**, applies additional degradation in early years that recovers over time, typical of PERC cells.</td>
      <td>—</td>
    </tr>

    <tr>
      <td>**21**</td>
      <td>**LeTID Rates**</td>
      <td>Table</td>
      <td>%</td>
      <td>Year-by-year LeTID degradation rates. Typically shows elevated degradation in Years 1-3 followed by recovery. Values are editable for each year.</td>
      <td>—</td>
    </tr>

    <tr>
      <td>**22**</td>
      <td>**Add More Years**</td>
      <td>Button</td>
      <td>—</td>
      <td>Extends the LeTID Rates table with additional years beyond the default 25-year period.</td>
      <td>—</td>
    </tr>

    <tr>
      <td>**23**</td>
      <td>**Apply LeTID Defaults**</td>
      <td>Button</td>
      <td>—</td>
      <td>Populates the LeTID Rates table with default values based on typical PERC cell degradation and recovery curves.</td>
      <td>—</td>
    </tr>
  </tbody>
</table>

***

## Saving Changes

Click **Save + Close Simulation Settings** to save all configuration changes and return to the prediction. Click **Save Progress** to save without closing. Click **Cancel** to close without saving.