Metrel PQA: measuring PV inverter efficiency

Amongst the many applications our power quality analysers (PQAs) are suitable for, is also measurement of power efficiency of 1- and 3-phase inverters in photovoltaic (PV) electrical installations. Supported analysers include the MI 2893 Power Master XT, MI 2892 Power Master and MI 2885 Master Q4, all with appropriate current clamps (list down below).

Current clamps for measurements in DC systems:

A 1391 PQA Current clamp 40/300 A / 1 V (currents up to 300 A)
A 1636 Current clamp DC 2000 A, AC 1000 A (currents up to 1000 A)
A 1717 Current clamp AC/DC 100/1000A / 1V (currents up to 2000 A)

Measurement setup: on AC side a 3-wire connection and on the DC side, the voltage is measured between neutral and ground, while the current terminal is connected to neutral. The analyser will therefore record signal data on both the AC and DC side. The recorded data includes:

Current and voltage (RMS, AC and DC values).
Inverter power (import/export: DC import/export, apparent import/export).
Inverter efficiency.
For exceptionally large PV installations with multiple strings we recommend the use of as many analysers as there are strings with an addition of A 1355 GPS receiver for time synchronisation.
The inverter efficiency (PV/DC – AC inverter) is calculated using the following formula:

η = Pac/Pinv

Where Pac is the AC power measured on the AC inverter output (point connected to the grid) and Pinv is the DC power measured on the PV inverter input (voltage and current from the PV panels).