Independence of subarrays

[laurahin]

PVsyst allows us to define individual subarrays that include, for example, different module types or different ILRs at the inverter.  To what extent are the calculations performed independently for these subarrays, i.e., are the calculations independent all the way through the inverter output, as is the case with actual PV plants, or combined at some earlier point?  It's difficult to say because some parameters, such as bifaciality, are shown as averages in the PVsyst report and the waterfall diagram lumps together losses over the entire array.

Thanks.

Edited December 12, 2023 by laurahin
Clarification

[Michele Oliosi]

Hi @laurahin, the transposition calculation is lumped together *if* the orientation is the same. From there onwards, however, the calculations are done independently per sub-array. This is because most parameters are defined on a sub-array basis.

The most notable exception is the bifacial modeling, which is defined globally for the whole system. If two sub-arrays have different bifaciality factors, PVsyst will define an “average” bifaciality factor, by weighing by the respective DC nominal powers. In general this works well, but can be incorrect if one sub-array has very different irradiance conditions (or IAM factors for example) than the other, by which the weighing based on DC nominal powers is not really correct.

A second exception is shadings, which is done orientation by orientation (which may therefore lump together multiple sub-arrays), if you are using the “according to strings” aka partition model. If you use the “module layout” model, then we are accounting for the sub-array differences in shadings as well.