> ## 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.

# Measured Surface Temperature

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

## Summary

When measured back-of-module surface temperature data is available as a time series, it can be used directly in place of a temperature model. This option overrides the selected temperature model (Heat Balance, Sandia, or NOCT-SAM) and derives cell temperature from the measured back-of-module surface temperature using the standard irradiance-proportional offset.

## Inputs

| Name                                      | Symbol              | Units | Description                                                                                                                                   |
| ----------------------------------------- | ------------------- | ----- | --------------------------------------------------------------------------------------------------------------------------------------------- |
| **Measured Surface Temperature**          | $T_{m,measured}$    | °C    | Back-of-module surface temperature from time-series data                                                                                      |
| **Effective Front POA Irradiance**        | $G_{POA,front,eff}$ | W/m²  | Front-side POA irradiance after optical corrections, before DC system losses (from [irradiance calculation](/models/poa-irradiance/overview)) |
| **Cell-to-Module Temperature Difference** | $\Delta T_{c-m}$    | °C    | Temperature difference between cell and module surface at reference irradiance                                                                |
| **Reference Irradiance**                  | $G_{ref}$           | W/m²  | Reference irradiance (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 (from time series) |

***

## Detailed Description

The measured back-of-module surface temperature is used directly. For each time step:

$$
T_m = T_{m,measured}
$$

Cell temperature is derived by adding the standard irradiance-proportional offset:

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

where:

* $T_m$ is the measured back-of-module surface temperature (from time-series data)
* $G_{POA,front,eff}$ is the front-side <POAIrradiance /> after optical corrections, before DC losses, in W/m² (from [irradiance calculation](/models/poa-irradiance/overview))
* $G_{ref}$ 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)

This cell-temperature derivation uses the same formula as the [Sandia model](temperature_sandia). To use this model, the user must both upload surface temperature time series and assign these time series to their respective DC fields.