Array-Level Aggregation & AC Losses

Summary

Array-level calculations aggregate individual outputs, apply AC losses in sequence—auxiliary load deductions, 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 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

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Outputs

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

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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)), which produces $P_{AC,deg}$, accounting for both standard degradation and 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 , 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.
• overrides all of the above: when triggered, all three auxiliary loads are set to zero (see Inverter Operating Regions for trigger conditions).

MV Transformer

If an MV transformer is defined for the array, the 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:

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