> ## 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.

# Array-Level Aggregation & AC Losses

export const LeTID = () => <Tooltip tip="Light and Elevated Temperature Induced Degradation: partially reversible efficiency loss from carrier-induced defects at elevated temperatures.">
    LeTID
  </Tooltip>;

export const EnergizationDate = () => <Tooltip tip="Date when a PV system block is first connected to the grid; reference point for degradation calculations.">
    energization date
  </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>;

export const NighttimeDisconnectCap = () => <Tooltip tip="Operational mode that disconnects transformers and zeroes plant output when inverters are in shutdown or low-power regions.">
    Nighttime Disconnect
  </Tooltip>;

export const NighttimeDisconnect = () => <Tooltip tip="Operational mode that disconnects transformers and zeroes plant output when inverters are in shutdown or low-power regions.">
    nighttime disconnect
  </Tooltip>;

export const Transformer = () => <Tooltip tip="Device connecting two AC circuits at different voltages; losses comprise constant no-load (core) and load-dependent (winding) components.">
    transformer
  </Tooltip>;

export const MV = () => <Tooltip tip="Medium Voltage: electrical infrastructure between inverter output and the plant collection point, including step-up transformers and AC cabling.">
    MV
  </Tooltip>;

## Summary

Array-level calculations aggregate individual <Inverter /> outputs, apply AC losses in sequence—auxiliary load deductions, <MV /> <Transformer /> losses, and AC collection system losses—then aggregate array outputs to the block level. Each array is calculated independently using repeater counts at both the inverter and array levels.

## Inputs

| Name                        | Symbol          | Units | Description                                                                                           |
| --------------------------- | --------------- | ----- | ----------------------------------------------------------------------------------------------------- |
| **Inverter AC Power**       | $P_{AC,inv}$    | W     | AC power output of each inverter (from [Inverter Efficiency](../inverter-models/inverter_efficiency)) |
| **Inverter Rated AC Power** | $P_{AC,rated}$  | kVA   | Inverter nameplate AC power rating                                                                    |
| **Inverter Repeater Count** | $n_{rep,inv}$   | —     | Number of identical inverters represented                                                             |
| **DAS Load**                | $L_{DAS}$       | W     | Data acquisition system power consumption                                                             |
| **Cooling Load**            | $L_{cool}$      | W     | Inverter/equipment cooling power consumption                                                          |
| **Tracker Motor Load**      | $L_{track}$     | W     | Tracker motor power consumption                                                                       |
| **MV Transformer Rating**   | $P_{MV,rated}$  | kVA   | Array-level MV transformer nameplate capacity                                                         |
| **MV No-Load Loss**         | $L_{NL,MV}$     | %     | MV transformer no-load loss as a percentage of $P_{MV,rated}$                                         |
| **MV Full-Load Loss**       | $L_{FL,MV}$     | %     | MV transformer full-load loss as a percentage of $P_{MV,rated}$                                       |
| **AC Collection Loss**      | $f_{coll}$      | %     | AC collection system loss percentage at max power                                                     |
| **Array Repeater Count**    | $n_{rep,array}$ | —     | Number of identical arrays represented in the block                                                   |

***

## Outputs

| Name            | Symbol      | Units | Description                                                      |
| --------------- | ----------- | ----- | ---------------------------------------------------------------- |
| **Block Power** | $P_{block}$ | W     | Aggregated AC power at block level, after all array-level losses |

***

## Detailed Description

### Inverter Aggregation

Each array may contain multiple inverters (with repeater counts). Because all inverters in an array operate at the same AC voltage and frequency, they are connected in parallel upstream of the MV transformer and their powers add directly. The total array-level AC power is:

$$
P_{AC,array} = \sum_{inverters} P_{AC,inv} \times n_{rep,inv}
$$

This aggregated power is the input to AC degradation (see [Degradation Losses (AC Applied)](degradation_ac_applied)), which produces $P_{AC,deg}$, accounting for both standard degradation and <LeTID /> losses.

### Auxiliary Loads

Auxiliary loads are constant power deductions subtracted from the degraded AC power before transformer losses. The tracker motor load ($L_{track}$) is aggregated from per-DC-field "Tracker Actuator Load" inputs (specified in MWh/MWp/year), scaled by each field's DC capacity and repeater counts on DC fields and inverters; it is zero for fixed-tilt systems.

$$
P_{aux} = P_{AC,deg} - L_{DAS} - L_{cool} - L_{track}
$$

Before the <EnergizationDate />, all auxiliary loads are zero (the system is not yet commissioned). After energization:

* **DAS load** is applied regardless of whether the array is producing power.
* **Cooling and tracker motor loads** are applied only when the total inverter output is positive ($P_{AC,array} > 0$); otherwise they are zero.
* **<NighttimeDisconnectCap />** overrides all of the above: when triggered, all three auxiliary loads are set to zero (see [Inverter Operating Regions](../inverter-models/inverter_operating_regions) for trigger conditions).

### MV Transformer

If an MV transformer is defined for the array, the [Transformer Loss Model](transformer_loss_model) is applied to $P_{aux}$:

$$
P_{MV} = P_{aux} - L_{MV,trans}
$$

where $L_{MV,trans}$ is computed from the quadratic loss equation using $P_{MV,rated}$, $L_{NL,MV}$, and $L_{FL,MV}$. When Nighttime Disconnect is enabled and triggered, the transformer no-load loss is set to zero, eliminating standby core losses.

If no MV transformer is defined, there is no loss: $L_{MV,trans} = 0$ and $P_{MV} = P_{aux}$.

### AC Collection System

AC collection losses represent resistive losses in the medium-voltage cabling between the MV transformer and the plant-level collection point. The input loss percentage $f_{coll}$ is converted to a fraction before use.

**Versions 3–11 (Flat Percentage Model):**

During daytime operation ($P_{MV} > 0$):

$$
L_{coll} = P_{MV} \times f_{coll}
$$

$$
P_{coll} = P_{MV} - L_{coll} = P_{MV} \times (1 - f_{coll})
$$

During nighttime operation ($P_{MV} \leq 0$), power flows in reverse—the grid supplies current through the collection system to keep transformers energized. The collection line losses compound: the grid must supply extra power to cover the losses, and that extra power itself incurs additional losses. The effective loss fraction becomes $(1 + f_{coll})^2 - 1 \approx 2 f_{coll}$ for small $f_{coll}$:

$$
L_{coll} = |P_{MV}| \times \left[ (1 + f_{coll})^2 - 1 \right] \geq 0
$$

$$
P_{coll} = P_{MV} - L_{coll} = P_{MV} \times (1 + f_{coll})^2 \leq 0
$$

**Version 12+ (Quadratic Model):**

Loss scales quadratically with power flow, reflecting the I²R characteristic of conductor losses:

$$
L_{coll} = \left| \frac{P_{MV}^2}{P_{AC,rated,array}} \times f_{coll} \right|
$$

where $P_{AC,rated,array}$ is the total inverter rated capacity for the array (scaled from kVA to VA):

$$
P_{AC,rated,array} = \sum_{inverters} P_{AC,rated} \times n_{rep,inv}
$$

The collection output is:

$$
P_{coll} = P_{MV} - L_{coll}
$$

### Block Aggregation

Array outputs are aggregated to the block level using repeater counts:

$$
P_{block} = \sum_{arrays} P_{coll} \times n_{rep,array}
$$