European or CEC Efficiency

Inverters and power converters do not always operate at maximum efficiency; instead, they operate according to an efficiency profile that is a function of power.

The "European Efficiency" is an averaged operating efficiency over a yearly power distribution corresponding to middle-Europe climate. This was proposed by the Joint Research Center (JRC/Ispra), based on the Ispra climate (Italy), and is now referenced on almost any inverter datasheet.

The value of this weighted efficiency is obtained by assigning a percentage of time the inverter resides in a given operating range.

If we denote by "Eff50%" the efficiency at 50% of nominal power, the weighted average is defined as:

Euro Efficiency = 0.03 x Eff5% + 0.06 x Eff10% + 0.13 x Eff20% + 0.1 x Eff30% + 0.48 x Eff50% + 0.2 x Eff100%.

Now for climates of higher insolations like US south-west regions, the California Energy Commission (CEC) has proposed another weighting, which is now specified for some inverters used in the US.

CEC Efficiency = 0.04 x Eff10% + 0.05 x Eff20% + 0.12 x Eff30% + 0.21 x Eff50% + 0.53 x Eff75%. + 0.05 x Eff100%.

as defined in the Sandia_Guideline_2005.pdf document, p17.

See also the construction of automatic efficiency profiles.