> ## 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.

# Inverter Temperature Derating

export const Clipping = () => <Tooltip tip="Condition where DC power exceeds the inverter's rated AC capacity; the inverter moves off the maximum power point to limit output.">
    clipping
  </Tooltip>;

export const Inverter = () => <Tooltip tip="Power electronics device that sets the operating point on the DC array's I-V curve and converts DC to AC for grid injection.">
    inverter
  </Tooltip>;

## Summary

The maximum AC power $P_{AC,derated}$ sets the upper bound for the <Inverter /> operating region logic, determining the <Clipping /> threshold. The AC power setpoint $P_{AC,set}$ is defined in the inverter configuration from the nameplate rating and the design derate factor. Alternatively, the setpoint or the derate factor can be set per timestep using a user-uploaded time series. When manufacturer derate curves are provided, the setpoint may be further reduced depending on ambient temperature and site elevation.

## Inputs

| Name                        | Symbol                   | Units   | Description                                             |
| --------------------------- | ------------------------ | ------- | ------------------------------------------------------- |
| **Rated AC Power**          | $P_{AC,rated}$           | kVA     | Inverter nameplate AC power rating                      |
| **Design Derate**           | $d$                      | —       | Fractional multiplier on rated power (0 to 1)           |
| **AC Power Setpoint**       | $P_{AC,set}$             | kVA     | Effective AC power limit                                |
| **Altitude**                | $h$                      | m       | Elevation above sea level                               |
| **Ambient Air Temperature** | $T_a$                    | °C      | Ambient air temperature                                 |
| **Inverter Derate Curves**  | $P_{AC,derate,h_k}(T_j)$ | °C, kVA | Temperature-power data points at rated elevations $h_k$ |

***

## Outputs

| Name                                | Symbol           | Units | Description               |
| ----------------------------------- | ---------------- | ----- | ------------------------- |
| **Temperature-Corrected Max Power** | $P_{AC,derated}$ | W     | Derated AC power capacity |

***

## Detailed Description

### Setpoint Determination

The AC power setpoint is the baseline upper bound on inverter output. It is derived from the inverter nameplate rating and the user-configured design derate:

$$
P_{AC,set} = d \times P_{AC,rated}
$$

A design derate of $d = 1.0$ uses the full nameplate; lower values curtail the inverter (e.g., $d = 0.95$ limits output to 95% of rated capacity). The user can set either the design derate $d$ or the absolute setpoint $P_{AC,set}$; the other value is adjusted automatically to satisfy the equation above.

Both values can also be overridden on a per-timestep basis by uploading a time series. A setpoint time series provides $P_{AC,set}$ directly in kVA, while a derate time series provides $d$ as a ratio (0 to 1). If both are configured, the setpoint time series takes priority.

### Curve Selection by Elevation

<Frame caption="Example Inverter Temperature / Elevation Derate Curves">
  <img src="https://mintcdn.com/terabaseenergy/KfoZBRK09Qv1HDiz/images/elevation-derate.jpg?fit=max&auto=format&n=KfoZBRK09Qv1HDiz&q=85&s=b493e9b3d3641326c3daab249132a158" alt="Example Inverter Temperature / Elevation Derate Curve" width="1227" height="549" data-path="images/elevation-derate.jpg" />
</Frame>

Inverter manufacturers may provide multiple derate curves at different elevation ratings $h_1 < h_2 < \cdots < h_K$. If these curves are available, PlantPredict selects the curve whose elevation is the smallest value still strictly above the site altitude:

$$
h^* = \min \{ h_k : h_k > h \}
$$

If the site altitude exceeds all available curve elevations ($h > h_K$), the highest curve is used:

$$
h^* = h_K
$$

### Temperature Interpolation

Once the curve $P_{AC,derate,h^*}$ is selected, the ambient temperature $T_a$ is linearly interpolated against its data points to obtain $P_{AC,derate,h^*}(T_a)$. If $T_a$ falls outside the curve's temperature range, the inverter is derated to zero ($P_{AC,derated} = 0$).

### Final Output

The final AC power limit is the lesser of the setpoint and the temperature-derated capacity:

$$
P_{AC,derated} = \min\bigl(P_{AC,set},\, P_{AC,derate,h^*}(T_a)\bigr)
$$

The prediction engine converts $P_{AC,derated}$ from kVA to W ($\times\,1000$) before passing it to the [inverter operating region](/models/inverter-models/inverter_operating_regions) logic.

When derate curves are not enabled, the temperature derating step is skipped and $P_{AC,derated} = P_{AC,set}$.