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PR calculation

Ahmad Elghobashy

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Hi All,

I am running a simulation with PVsol and it is required to calculate the performance ratio for the system to compare between different systems,

in the result screen I got a PR equal to 79.6%

Although in the energy balance I got a rated PV energy= 139,303 kWh

And AC output minus standby = 114,960 kWh

when manually divide both I got a PR= 82.5%

IS this formula correct? and how the program calculate the PR in the result screen?

and how can that be justified by the numbers in the energy balance sheet?

see attached pictures for illustration



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Hi Ahmad Elghobashy,

the performance ratio is the ratio between the actual pv energy and the theoretical maximum pv energy. The actual pv energy is, as you have already mentioned, the "PV energy (AC) minus standby use", but the theoretical maximum is not the "Rated PV Energy", because there are already some influences on the radiation like soiling and reflection.

The correct formula for the performace ratio (PR) is:

PR  = ("PV energy (AC) minus standby use") / ("Global Radiation at the Module" - "Reflection on the Module Interface") * module area * module efficiency ))

In your case, that would be:

PR = 114,960.40 kWh /[(2,041.7 kWh/m² - (- 33.13 kWh/m²)) * 414.11 m² * 0.1681]

PR = 0.79594 = 79.6 %


Kind regards,



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  • 5 months later...

Dear Marcel, how we can get all information about each parameter in Energy Balance?   with this dictionary (Glossary with explanation), we can understand how read this result.  For example, when we will to oversized the inverter, how we can understand  what happened with all PV System. i have clipping..etc.   Thanks for you valuable information

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Dear Hotline_sf,  the help about "Energy Balance" is very little, and understand this report is very import.   What parameter say about if the inverter is making clipping?  and what percent is good and what is bad?  do you know url or document for understand better.  Thanks

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Dear Soler,

The clipping percentage can be found under "Down-regulation on account of the max. DC Power" and "Down-regulation on account of the max. AC Power/cos phi". In most of the cases you only will find some values under "Down-regulation on account of the max. AC Power/cos phi" because normally the maximum AC power is lower than the maximum DC power of the inverter. Then the simulation clipps the power directly to the AC value because it has to be cut to this amount anyway. But if you simulate a pv system with a battery system which is DC intermediate coupled then also "Down-regulation on account of the max. DC Power" can appear in addition because it matters if DC has to be cut off or not for the charging of the battery.


Which percentages is good or bad is nothing which we can tell. Of course the red ones are basically bad because you loose some energy. But the values of course depend from the shading situation the characteristics of the modules, inverters etc. we cannot say which value you will find acceptable and which not. At least it depend on the costs of the system, what energy is delivered from the system and how much money you get from the pv production.

Best regards



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