Energy Production Discrepancy -- V6.32 to V6.33

[Dan Nicksy]

Good afternoon all,

Some time ago I created a PVsyst model for a site using PVsyst V6.30. The model uses string inverters, and a number of the string inverters have modules in two different orientations. Where necessary, the Orientation "Mixed #1 and #2" was used in the System parameter definition. The calculated specific production was 1190 kWh/kWp/yr. Recently I re-ran the model using PVsyst V6.33. I used the same files (PAN, OND, SIT, MET) and the same variant, but the calculated production was lower: 1178 kWh/kWp/yr.

In order to isolate the problem, I ran the variant in different PVsyst versions. PVsyst V6.30 through V6.32 calculate a specific production of 1190 kWh/kWp/yr, whereas PVsyst V6.33 and V6.34 calculate a specific production of 1178 kWh/kWp/yr. In the Loss Diagram (see attached), the changes from V6.32 to V6.33 are shown: DC ohmic wiring loss increases, mixed orientation mismatch loss increases (from zero), and inverter loss during operation (efficiency) decreases. I reviewed the PVsyst Software Development change-log, and to my understanding nothing there explains this discrepancy.

Can anyone help me understand this change between versions? And, most importantly, which version is more accurate? Thanks in advance for any and all help,

-Dan

[André Mermoud]

We discovered indeed an error in the simulation of systems with Mixed Orientations in the versions 6.33 and 6.34.

This will be corrected in the next version 6.35, to be released very soon.

[Dan Nicksy]

Thanks for the clarification. I look forward to the next updated version.

Cheers,

Dan