> ## 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.

# NOCT-SAM Model

export const IEC61215 = () => <Tooltip tip="International standard defining design qualification and type approval tests for PV modules, including the NOCT measurement procedure.">
    IEC 61215
  </Tooltip>;

export const Transposition = () => <Tooltip tip="Converting horizontal irradiance components to plane-of-array (tilted surface) irradiance.">
    transposition
  </Tooltip>;

export const SpectralMismatch = () => <Tooltip tip="Difference between actual solar spectrum and reference spectrum (AM1.5G), affecting module performance vs. rated efficiency.">
    spectral mismatch
  </Tooltip>;

export const Soiling = () => <Tooltip tip="Accumulation of dust, dirt, and debris on module surfaces, reducing light transmission and energy production.">
    soiling
  </Tooltip>;

export const IAM = () => <Tooltip tip="Incidence Angle Modifier: correction factor for optical losses at non-perpendicular light angles.">
    IAM
  </Tooltip>;

export const POAIrradiance = () => <Tooltip tip="Solar irradiance on the tilted module surface (beam + diffuse + reflected); drives PV power generation.">
    POA irradiance
  </Tooltip>;

export const STC = () => <Tooltip tip="Standard Test Conditions: 1000 W/m² irradiance, 25 °C cell temperature, AM1.5G spectrum; the reference conditions for rating PV modules.">
    STC
  </Tooltip>;

export const NominalOperatingCellTemperatureCap = () => <Tooltip tip="Cell temperature measured at 800 W/m² irradiance, 20 °C ambient temperature, and 1 m/s wind speed.">
    Nominal Operating Cell Temperature
  </Tooltip>;

## Summary

The NOCT-SAM model estimates cell temperature from a module's <NominalOperatingCellTemperatureCap />, typically determined according to <IEC61215 />, applying corrections for irradiance level, module-level optical losses, electrical conversion efficiency, and conductive and convective heat dissipation. This model is based on the System Advisor Model (SAM) implementation (Gilman et al., 2018).

## Inputs

| Name                                      | Symbol              | Units | Description                                                                                                                                   |
| ----------------------------------------- | ------------------- | ----- | --------------------------------------------------------------------------------------------------------------------------------------------- |
| **Front POA Irradiance**                  | $G_{POA,front}$     | W/m²  | Front POA irradiance after transposition, before optical adjustments (from [irradiance calculation](/models/poa-irradiance/overview))         |
| **Effective Front POA Irradiance**        | $G_{POA,front,eff}$ | W/m²  | Front-side POA irradiance after optical adjustments, before DC system losses (from [irradiance calculation](/models/poa-irradiance/overview)) |
| **Ambient Air Temperature**               | $T_a$               | °C    | Ambient air temperature                                                                                                                       |
| **Wind Speed**                            | $v_w$               | m/s   | Wind velocity                                                                                                                                 |
| **Module STC Efficiency**                 | $\eta_{STC}$        | —     | Module efficiency at standard test conditions                                                                                                 |
| **Nominal Operating Cell Temp**           | $NOCT$              | °C    | Nominal operating cell temperature, as defined by IEC 61215                                                                                   |
| **Transmittance-Absorptance**             | $\tau\alpha$        | —     | Fraction of incident light absorbed by the PV cell at normal incidence                                                                        |
| **Cell-to-Module Temperature Difference** | $\Delta T_{c-m}$    | °C    | Temperature difference between cell and module surface                                                                                        |
| **Reference Irradiance**                  | $G_{ref}$           | W/m²  | Reference irradiance for cell-to-module temperature difference (typically 1000 W/m²)                                                          |

***

## Outputs

| Name                           | Symbol | Units | Description                        |
| ------------------------------ | ------ | ----- | ---------------------------------- |
| **Cell Temperature**           | $T_c$  | °C    | Operating temperature of PV cells  |
| **Module Surface Temperature** | $T_m$  | °C    | Back-of-module surface temperature |

***

## Detailed Description

The NOCT-SAM model takes as its starting point the Nominal Operating Cell Temperature (NOCT), measured under the standardized conditions defined in IEC 61215, and adjusts it to estimate cell temperature under actual operating conditions.

Unlike the Heat Balance and Sandia models, which use only the effective front-side POA irradiance ($G_{POA,front,eff}$), the NOCT-SAM model uses both the front-side POA irradiance ($G_{POA,front}$)—before module-level optical adjustments—and the effective front-side POA irradiance ($G_{POA,front,eff}$)—after module-level optical adjustments. This allows explicit separation between thermal and optical contributions.

The model starts from the temperature difference $(NOCT - 20)$ between the nominal operating cell temperature and its reference ambient temperature (20 °C), then applies three scaling factors:

### Irradiance Scaling

$$
\frac{G_{POA,front}}{800}
$$

This factor scales the temperature rise by the ratio of actual to NOCT reference irradiance (800 W/m²).

### Absorptance and Efficiency Correction

$$
1 - \frac{\eta_{STC}}{\tau\alpha} \cdot \frac{G_{POA,front}}{G_{POA,front,eff}}
$$

This factor reduces the temperature rise to account for the fraction of absorbed light converted to electricity rather than heat.

The transmittance-absorptance product $\tau\alpha$ represents the fraction of incoming light absorbed by the solar cell at normal incidence—accounting for transmittance through the front layers (glass, encapsulant), absorptance in the solar cell, and internal reflections at layer interfaces—while the ratio $G_{POA,front,eff}/G_{POA,front}$ adjusts for time-dependent optical effects (<IAM />, <Soiling />, <SpectralMismatch />).

### Heat Dissipation

$$
\frac{9.5}{5.7 + 3.8 \cdot 0.51 \cdot v_w}
$$

This factor scales thermal losses relative to the NOCT reference wind conditions.

The 0.51 factor accounts for the reduced air flow in PV power plants—compared to the open-rack configuration used for NOCT measurement—due to row-to-row shielding and other systemic effects. In PlantPredict, this parameter is hard-coded to 0.51, corresponding to ground-mount systems.

### Cell Temperature Equation

$$
T_c = T_a + \frac{G_{POA,front}}{800} \cdot (NOCT - 20) \cdot \left(1 - \frac{\eta_{STC}}{\tau\alpha} \cdot \frac{G_{POA,front}}{G_{POA,front,eff}}\right) \cdot \frac{9.5}{5.7 + 1.938 \cdot v_w}
$$

where:

* $T_a$ is the ambient air temperature in °C (from weather data)
* $NOCT$ is the nominal operating cell temperature in °C (from DC field definition)
* $G_{POA,front}$ is the front-side <POAIrradiance /> before module-level optical adjustments in W/m² (from [irradiance calculation](/models/poa-irradiance/overview))
* $G_{POA,front,eff}$ is the front-side POA irradiance after module-level optical adjustments in W/m² (from [irradiance calculation](/models/poa-irradiance/overview))
* $\eta_{STC}$ is the module efficiency at <STC /> (from module definition)
* $\tau\alpha$ is the transmittance-absorptance product at normal incidence, without soiling or spectral correction (from DC field definition)
* $\tau\alpha \cdot G_{POA,front,eff} / G_{POA,front}$ is the effective absorptance under actual operating conditions (including soiling, IAM, and spectral effects)
* $v_w$ is the wind speed in m/s (from weather data)

The constants 800 W/m² and 20 °C are the NOCT reference irradiance and ambient temperature conditions. The general NOCT-SAM model also includes a modification to the base NOCT for roof-mounted systems with reduced standoff distance. PlantPredict does not include this adjustment, as it only models utility-scale PV power plants where the module's NOCT value is used directly.

### Module Surface Temperature

$$
T_m = T_c - \frac{G_{POA,front,eff}}{G_{ref}} \cdot \Delta T_{c-m}
$$

where:

* $G_{ref}$ is the reference irradiance in W/m² (from module definition, typically 1000 W/m²)
* $\Delta T_{c-m}$ is the cell-to-module temperature difference at the reference irradiance, in °C (from DC field definition)

***

## References

* Gilman, P., Dobos, A., DiOrio, N., Freeman, J., Janzou, S., & Ryberg, D. (2018). *SAM photovoltaic model technical reference update.* NREL/TP-6A20-67399, National Renewable Energy Laboratory, Golden, CO. DOI: [10.2172/1495693](https://doi.org/10.2172/1495693)