# CEC vs EUR

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Hello,

I'm getting a far different efficiency profile when calculating with CEC (98.0%) and EUR (98.3).

In my understanding, CEC/EUR efficiencies are merely a way of standardizing inverters efficiency, as all they do is to weight the efficiencies at different load levels to represent different climates.

From PVsyst help:

"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%."

From this, I understand that ii shouldn't matter if I use EUR or CEC efficiency to build my profile, I should arrive in the same Eff10% / Eff20% / Eff30% and so on.

Is that correct?

If it is, any clue on why my profiles are so different?

Cheers.

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I don't understand well what you mean when you say "different efficiency profile when calculating with CEC (98.0%) and EUR (98.3)".   A profile is defined as a set of values, not one only; what is 98 or 98.3 %?

The EURO or CEC efficiencies are indeed a way of evaluating a yearly average of the effective efficiency, based on the expressions you gave above. This average is a weighted average of a supposed power distribution along the year,  If these data powers distributions are different, the weighted result is different.

The EURO efficiency is a weighted average calculated on a "reference" energy distribution corresponding to meteo data chosen as those of ISPRA  (location of the JRC - Joint Research Center - at North of Italy, in the years 1990), when the CEC efficiency is based on a climate corresponding to the californian climate.

Now in absence of an explicitly defined efficiency profile, PVsyst tries to reconstruct a  "supposed" efficiency profile reproducing these very simplist data  "Max efficiency" and "EURO efficiency" (or "CEC" efficiency). This reconstruction uses reasonable hypothesis, but cannot obviously be absolute.

These hypothesis are described in the Help  "Physical models used > Grid inverter > Inverter model: efficiency"

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• 3 months later...

Hi,

I have a question regarding the weighting of each efficiency for each normalized power.

For instance, we have the standard Euro efficiency below:

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%.

It assumes that under the standard conditions, only 3% of the time do I have a normalized power of 5%. What if the weather conditions raise it in such a way that 10% of the year limits the inverter power to 5% of the Peak Power?

Should I modify the weights in PVsyst to get more realistic results?

Or would that be incorrect?

BR

Esma

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This "Euro efficiency" weighted average was proposed by the "Joint Research Center" (center of the European Communities) in the years 1990.

These weighting parameters were evaluated from the weather data of their location (Ispra, north of Italy).

Another weithing is proposed by the US (CEC), based on the californian climate.

It doesn't make sense to redefine these weighting parameters, as this is a "standard" distribution which defines the behaviour of many inverters.

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I would like to raise another question. I would like to know, what is the process that Pvsyst uses to calculate the Inverter efficiency losses and consequently the PR loss due to the inverter efficiency.

I mean, does PVsyst tries to use the inverter efficiency losses based on DC power at each timestamp (hourly, 10 minutes or ...) To calculate the losses and then aggregate them to get a yearly value, or Euro/CEC efficiency at the yearly level to get a yearly losses?

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The inverter efficiency depend on a certain extent on the DC power. In the .OND file, in the Efficiency curve tab you can see the relation between the inverter efficiency and the Power in the DC circuit. The efficiency is then calculated in hourly time steps in the simulation and monthly averages of the total production is shown in the report. The PR is also calculated in hourly timesteps and monthly and yearly averages are shown in the report.