Unused energy (grid limitation)

What this step does

The energy the grid power limitation removes, shown on its own row when the limitation is accounted as a separate loss (Losses tab). The inverters lower their ceiling so that the grid connection stays within the limit, and the row is the inverter output without that ceiling minus the output with it. Without the separate row, the same energy counts in Inverter Loss over nominal inv. power.

The math

1. Running total
2. Loss at a timestep

$$E_{after} = E_{before} - E_{row},\qquad E_{row} = \frac{\Delta t}{1000\,P_{DC}}\sum_i L_i \tag{1}$$ $$L_i = N_{inv}\,\left(P^{u}_{inv,i} - P_{inv,i}\right) \tag{2}$$

where

Symbol	Meaning	Unit
$E_{before}$	the running total of the loss diagram before this row	kWh/kWp
$E_{after}$	the running total after this row	kWh/kWp
$E_{row}$	the row taken as a loss	kWh/kWp
$\Delta t$	the length of one timestep	hours
$P_{DC}$	the DC nameplate of the system	kWp
$L_i$	the power lost at timestep $i$ over the whole system	W
$N_{inv}$	the number of inverters	—
$P^{u}_{inv,i}$	the output one inverter would deliver at timestep $i$ without the grid ceiling	W
$P_{inv,i}$	the output of one inverter at timestep $i$ with the ceiling	W

Reading the number

A loss, negative. Zero without a limit; a limit well below the inverters' nameplate on a utility system can cost several percent, and a rooftop system with an export limit loses in the same way. The limit relative to the system's peak AC output sets it.

API

loss.grid_limit

Symbols follow the symbol registry.