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For Generalities and principles, see Storage: Power peak shaving

 

Many big PV installations with peak shaving include a DC bus collecting the power of the whole PV array, with Inverters (DC:AC) for the direct grid injections, and DC:DC converters for  feeding a battery pack (BESS) when the power exceeds the grid injection limit.

NB: it is not possible to define sub-arrays with DC:AC inverters, and other sub-arrays feeding DC-DC converters. Because the overpower will be a global feature: you cannot have a sub-array dedicated to a given "base" power, and another sub-array for the overpower.

Therefore such a configuration necessarily works with a fully centralized DC bus for the whole PV array, mixing the AC and DC inputs. This means a behavior similar to the "Master/Slave": one device decides the operating point for the whole array (MPPT), and controls the operating input voltage for all other converters connected on this DC bus.  This means that all the strings of this Array are connected in parallel !

Implementation in PVsyst

This configuration of  DC:DC converters connected in parallel with DC:AC inverters is not yet implemented in PVsyst.

However in the meantime, you can use the present configuration for your calculations with storage.

You should define inverters for a total power ensuring the whole possible production   (AC inverter => grid + DC converter => batteries).

The fact that the power is transferred in AC or DC is not significant: we can admit that the extra-inverters represent exactly your DC converters. From an energetic point of view, these will have about the same efficiency profile.

Then the DC converter at the input of the battery pack may be configured with a very high efficiency profile (ideally 100%),  or it can compensate if your DC converters have efficiencies lower than the Solar inverters.    

The calculation of PVsyst    (Inverter DC:AC +  converterAC:DC)  will be quite equivalent to an explicit definition of DC:DC  converters directly feeding the Battery pack.  

The Power Grid limitation is no more defined at the inverter level:  this is the  “grid power limit”  parameter defined in the grid storage dialog.