Inverter Loss during operation (efficiency)

What this step does

The energy lost inside the inverter when it converts DC to AC: at every timestep, the DC power the inverter draws minus the AC power it delivers at the operating power and voltage. The Model tab's Inverter efficiency step sets the inverter's output for a given input.

The math

1. Running total
2. Loss at a timestep

$$E_{after} = E_{before} - E_{row},\qquad E_{row} = \frac{\Delta t}{1000\,P_{DC}}\sum_i L_i \tag{1}$$ $$L_i = N_{inv}\left[P_{dc,i} - P_{out}(P_{dc,i}, U_i)\right] \tag{2}$$

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	—
$P_{dc,i}$	the DC power one inverter draws at timestep $i$	W
$P_{out}(P, U)$	the AC output of one inverter at DC input $P$ and DC voltage $U$	W
$U_i$	the DC voltage at timestep $i$	V

Reading the number

A loss, negative. Modern inverters lose 1.5 to 2.5 % over a year, on utility and rooftop systems alike. Long hours far below rated power and DC voltages far from the inverter's best voltage raise it.

References

1. King, Gonzalez, Galbraith & Boyson 2007, Performance Model for Grid-Connected Photovoltaic Inverters, Sandia report SAND2007-5036
2. Driesse, Jain & Harrison 2008, Beyond the curves: modeling the electrical efficiency of photovoltaic inverters, IEEE 33rd Photovoltaic Specialists Conference

API

loss.inv_efficiency

Symbols follow the symbol registry.