Modeling two different module using One central Inverter

[mohsinsanaullah]

I want to simulate using two different manufacturers with different wattage using one central inverter having one MPPT. Can we model it in PVSYST. I know for two different modules we need to make two subarray. I cannot make two subarray because I have one central inverter.

Your help is appercated.

Thanks

[dtarin]

Add "dummy" mppt inputs by modifying the OND file of the inverter. You can add for example two (2) mppt inputs if it is a 50-50 split, add one subarray with (1) mppt and the second subarray with (1) mppt, which will be equivalent to one inverter. Go into power sharing and allocate it evenly. If it is a non equal split, for example module A is 70% and module B is 30%, then add ten (10) mppt inputs to the OND file, and allocate seven (7) to subarray A and three (3) to subarray B. There looks like a bug though, I am not seeing the information being generated in latest version.

 

Should there be something displayed @Michele Oliosi? I have an unequal number of strings for each subarray and different ratios, but when I click enable power sharing, nothing really happens.  

[Michele Oliosi]

Hi !

We have changed the interface for this tool (because it was starting to show limitations for large systems). Now you need to drag and drop sub-arrays from the right hand panel into configurations.

The procedure is described and shown here:

 

https://www.pvsyst.com/help/powersharing.htm

Btw, the trick of setting dummy MPPTs is quite correct.

[dtarin]

Thank you for the link, haven't needed to use this in a few years. 

[jonipa]

Hello, wouldn't this trick increase value of the parameters EOutInv, EArrayMPP and EArray among others?

Since now the inverter has more MPPTs, does it affect in any way PV field or inverter production?

Thank you.

[Michele Oliosi]

No in principle the total inverter power is maintained.

[sauld]

Reviving old thread, but I don't think this would be a very accurate way of modeling this issue. As I'm getting higher production total with less total DC nameplate(assuming due to the virtue of multi mppts helping with mismatch between shaded/unshaded sections)

In reality the string/s of different wattage module would negatively impact a combiner due to the mismatch of overall Vmp.

Unless there is something I'm not thinking about.

 

[Michele Oliosi]

@sauld no you are right, there could be some losses that would be missed by this approximation. Unfortunately this is a compromise, because currently MPPTs can only receive identical strings in the System definition in PVsyst. 

However for most cases these losses are rather small. The most important is the string to string mismatch (usually shading effects are even smaller because you need a very specific shading pattern for the multi-MPPT to help). You could add an estimate of these losses to the mismatch losses manually. You can estimate them using a tool found from Home window > Tools. There is a similar discussion here (see the last answer by my colleague Luca):