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Treatment of POI clipping in v. 7.3


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Could someone explain what changes were made to the treatment of POI clipping in going from v. 7.2 to 7.3?  We are running a set of simulations varying the inverter count and the POI limit and have been using v. 7.3.2.  We have found instances where POI clipping is diagnosed even though the total inverter capacity is lower than the POI limit.  We noticed the following version notes about changes to POI clipping in different revisions of v. 7.3  

PVsyst 7.3 - 19/12/2022

- Simulation: complete revision of the grid-limitation treatment in the simulation.

Patch 7.3.2 - 08/02/2023

- System, grid limitation: the sharing between inverter overload loss and EUnused energy loss (grid limitation) is now correct

but they suggest that whatever problem was introduced has been resolved.  Here are some examples of waterfall diagrams with and without POI limits.  DC capacity is 388 MW; inverter capacity is 300 MW (ILR 1.28); POI limit, when included, is 344 MW (DC/AC 1.128).  Note that both systems give the same final output, but some of the inverter clipping is shifted to POI clipping when the (meaningless) POI limit is added.  For comparison, a run using v. 7.2.21 that includes the grid limit is provided last.  It shows no clipping at the POI.  (Final output is not the same due to a slight difference in electrical shading loss.)  We have similar examples for other ILR values, input resource files, etc., and find this behavior completely counterintuitive.




v. 7.3.2, no POI limit  


v. 7.3.2 with 344 MW grid limit


v 7.2.21 with 344 MW grid limit


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We have deeply reviewed the treatment of the Grid limitation in the version 7.3.2. The result is now more correct for some special configurations.

However there is indeed a bug when calculating the repartition between the inverter’s loss and the loss due to grid limitation in some particular cases. The loss due to the grid limit is fully reported on the inverter’s overload loss. This corresponds to the situation when you uncheck the case “account as separate loss”.

However, this doesn’t affect the global loss, the final yield E_Grid is correct.

We have corrected this balance between losses in the latest version 7.3.3.

NB: you have indeed a little difference bwtween V 7.3.2 and 7.2.21  (-0.08% ! ). As I wrote previously, the calculation was not quite correct before V 7.3.2, this was the reason of the update.

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