Types of inverter efficiency
It’s important to note that inverter efficiency is not a fixed number. Inverter’s have what is called an ‘efficiency curve’, usually displayed in a chart that shows how efficiency fluctuates with the input power or voltage fed into it. Each brand and model of inverter has its own efficiency curve.
You may encounter the following terms referring to efficiency when shopping around for an inverter: peak efficiency, Euro (η) efficiency, and CEC efficiency. The difference between these is explained below.
The nominal rating for an inverter is usually its ‘peak efficiency’. For example, a 3kW inverter’s peak efficiency is reached when it is receiving 3kVA (essentially 3kW in DC electricity parlance) from the solar panel array. Throughout the day your solar array output does not remain constant; it’s lower in the morning and evening, and higher in the afternoon when the sun is shining.
Simply put, peak efficiency is calculated as DC input to AC output when the inverter is operating at (usually) its rated capacity. Peak efficiency for some of the best inverters can get up to 99%. That sounds pretty impressive, but remember that although this is a noteworthy number, it is not the final word on inverter efficiency. Your inverter may only operate in its peak efficiency range for a very small part of the day or not at all. This is why the CEC and Euro weighted efficiencies have been developed. They recognize that inverters don’t always operate in optimal conditions, and instead these measurements offer an indication of how an inverter might perform throughout the day.