How to calculate inverter efficiency and loss
An inverter loses power to switching and conduction every time it converts DC to AC or changes frequency. Measure input and output at the same instant and efficiency is simply output divided by input times 100, while the difference between the two readings is the loss.
That loss leaves as heat, so it drives your cooling design. One kW of loss equals about 3,412 BTU/hr, and the heat figure here feeds straight into enclosure ventilation or panel air-conditioner sizing. Add run hours and your electricity rate and you also see what the loss costs over a year.
Catalog peak efficiency is usually measured near full load. Real installations spend most of their hours at part load, which is why the industry compares units by a load-weighted number such as CEC weighted efficiency or European weighted efficiency rather than the single peak value. When measuring, use a true-RMS power meter that accounts for power factor and harmonics, and read input and output simultaneously. If your measured loss is well above the data sheet, check cooling airflow, terminal torque and contact resistance, and whether input voltage sits inside the rated MPPT or DC window.
Frequently Asked Questions
Part-load operation, high ambient temperature, and input voltage outside the rated window all reduce efficiency. Also check whether filters or long cable runs fall inside the section you are measuring.
It is the basis for enclosure temperature rise and for sizing ventilation fans or panel coolers. When several drives share one enclosure, add the heat from every unit before sizing the cooling.