Sandia, no voltage terms

Method

The method is the Sandia inverter model of King and co-workers with its curvature and voltage coefficients set to zero. The AC output then rises on a straight line in the DC input, from zero at the self-consumption $P_{so}$ to the AC nameplate at the DC input $P_{dc0} = P_{ac0}/\eta_{nom}$, and continues on that line above it until the operating limits cut it. The nominal efficiency $\eta_{nom}$ is the inverter's maximum efficiency from the Inverter tab. The measured efficiency curves, the power threshold and the DC voltage are not used. The self-consumption is 0.4931 % of the AC nameplate for an array of 1 kW DC or more, 0.2478 % from 10 W to 1 kW, and 0.2246 % below 10 W. At or below the self-consumption the output is zero.

Settings

Setting	Value
Nominal efficiency $\eta_{nom}$	the inverter's maximum efficiency (Inverter tab)
Self-consumption $P_{so}$	0.4931 % of $P_{ac0}$ from 1 kW DC; 0.2478 % from 10 W; 0.2246 % below
Curvature and voltage coefficients	0

The math

$$P_{out} = \begin{cases} P_{ac0}\,\dfrac{P_{dc} - P_{so}}{P_{dc0} - P_{so}} & P_{dc} > P_{so} \\ 0 & P_{dc} \le P_{so} \end{cases},\qquad P_{dc0} = \frac{P_{ac0}}{\eta_{nom}} \tag{1}$$

where

Symbol	Meaning	Unit
$P_{out}$	the AC output before the operating limits	W
$P_{ac0}$	the inverter's AC nameplate	W
$P_{dc}$	the DC input	W
$P_{so}$	the self-consumption, the DC input below which the output is zero	W
$P_{dc0}$	the DC input at which the output reaches the nameplate	W
$\eta_{nom}$	the nominal efficiency	—

References

1. King, Gonzalez, Galbraith & Boyson 2007, Performance Model for Grid-Connected Photovoltaic Inverters, Sandia report SAND2007-5036
2. NREL SAM Simulation Core (SSC) source code, release 2026.7.3, github.com/NatLabRockies/ssc: shared/lib_sandia.cpp, sandia_inverter_t::acpower(); ssc/cmod_pvwattsv8.cpp, the inverter parameters and the clipping

API

inverter.efficiency_interpolation = sandia

Symbols follow the symbol registry.