Effective Energy at output of array doesn't match sum of losses

[nico7904]

Dear All,

When I run the simulation for a stand alone system in PVsyst version 5.74, the Effective Energy at output of array, displayed in loss diagram in the report, doesn't match with the parameter EArUfix (Array nominal energy (at STC effic.) after remove all losses.

For example for this project, I have 1165 kWh for the Array nominal Energy at STC.

Here is the link for the screenshot of the Loss Diagram :

https://photos.google.com/share/AF1QipNmgDl5SX7Q4J7SvH_rsFXStJQfwRAVO4Hy_9cTzWZX6Yfb6LX7BO0vFVlCkYwl0Q?key=T2ttUEpVd2xvYWxyWkRCMVpSOHFLSTJJTkM1YTRB

If I recalculate losses following percentages displayed on the loss diagram attached, I get :

1165 - 0.037x1165 = 1122 kWh - After PV loss due to irradiance level

1122 - 0.107x1122 = 1002 kWh - After PV loss due to temperature

1002 - 0.019x1002 = 983 kWh - After module quality loss

983 - 0.015x983 = 968 kWh - After module array mismatch loss

968 - 0.012x968 = 956 kWh - After ohmic wiring loss

956 - 0.186x956 = 779 kWh - After loss by respect to the MPP running

779 - 0.015x779 = 767 kWh - After Unused energy (full battery) loss

...which is different of the Effective energy at the output of the array : 757 kWh.

Could anyone explain that difference ?

Thanks for your help

[André Mermoud]

The difference represents 1.3% ...

There may be some rounding uncertainty in the percentages, and the simulation procedure for stand-alone systems was not quite optimal in this old version 5.74 (there is some retro-action between the direct-coupled PVarray and the real battery voltage).

With the next version 6.40 (to be released beginning of January 2016), the simulation of stand-alone systems has been deeply revised, and this balance is now quite correct (within 0.1 to 0.2%).