Multiple MPPTs

[Mattheos80]

Hi all,

Can someone explain in more detail (and maybe a worked example) how to use the Multiple MPPT feature on PVsyst. I have spent all afternoon at work trying to figure it out to no success, unless the system size is matched by the inverter size. I want to simulate a 100 kW system with 2 MPPT inverters having two different string sizes. Is there a a limit on the size of the system that can be simulated with the Multiple MPPT solution described in PVsyst help file.

Thanks

[André Mermoud]

In the "System" definition dialog:

Top left, please define "2 kinds of Subfields".

After that you can define 2 kinds of Array dispositions, i.e. use different MPPT inputs of the same inverter in both sub-arrays.

If you have for example 2 inverters with 2 MPPT inputs each, as you mention, you can define a first sub-array of 2 MPPT inputs with a given string length (number of modules in series), and a second sub-array with 2 MPPT inputs and another number of modules in series.

Now if your problem is that the Inverter has unbalanced MPPT inputs, please have a look on How to use the inverters with very different inputs like SMA Tripower?

[traj123]

Hi Andre,

Could you please clarify exactly what you mean with the following example:

Scenario 1:

Inverter A - 1 MPPT

2 strings of 11 modules in parallel to the input

Scenario 2:

Inverter B - 2 MPPT

1 string of 10 modules to first input

1 string of 12 modules to second input

How would I model these two scenarios in PVsyst? Also, as far as I understand, inverters with multiple MPPTs can be have different string configurations connected to them. So what is the difference between a regular inverter with 2 MPPTs and an "unbalanced inverter" with 2 MPPTs?

Thanks,

Taran

[traj123]

Hi Marvin,

Thanks for your response.

So, per your explanation the nominal power gets split evenly between the MPPTs in multiple MPPT inverters. You also state that, "If you are using the same rating modules in both strings you will have more power from one string than the other and if this results in one MPPT input being overpowered or underpowered it will effect the results since PVsyst is going to split the power 50/50."

I have a couple of follow up questions based on that:

1) So if the 12 module string overpowers its respective MPPT, its (ONLY that MPPT) output gets clipped to 50% of the nominal rating of the inverter. However, this seems like the correct response expected. Am I correct?

2) If multiple MPPT systems require 2 subfields defined, then would you happen to know why PVsyst 5 has the entry for number of MPPTs in the inverter file? Since it appears that each MPPT needs to be modeled separately.

3) Can you direct me to a data sheet of an inverter with asymmetric power ratings for its MPPTs. I looked at the SMA Tripower series and didn't see anything different relating to this.

4) Lastly, could you please clarify this point "If you have multiple inverters with multiple MPPT inputs you have to assign the number of MPPT inputs to the subfield that is equal to the power output of that subfield. The fewer inverters you have the closer to a 50/50 power split the subfields have to be"

Thank you very much!!

Taran