very small PV system with parallel modules and microinverter

Dear SAM team and forum members,

I am trying to simulate a very small PV system with 4 modules (~400 Wp, 2 south, 2 west) and 1 microinverter (800 W) with 2 MPPTs.
To tackle the complex partial shading situation, each MPPT shall be connected to 1 south-side module and 1 west-side module in parallel arrangement.

After reading the manual and several forum threads, I understand that it is usually recommended to simulate a microinverter by specifying one inverter per module. But somehow, I have difficulties to apply this recommendation to my use case.

Am I supposed to define 4 subarrays and set the number of inverters to 4? If so, wouldn't I have to adapt the technical specifications of the inverter, because using 4x800W inverter would not reflect the real setup at all. However, reducing the inverter power limit to 400 W or 200 W seems wrong, too.

Wouldn't it be better to simulate the system by specifying only one 800W Inverter with 4 MPPTs? In that case, I would simply approximate the parallel connection of modules with a pair of separate MPPTs.

Hi Ulrich,

You should be able to model your system in SAM with 4 modules, 1 inverter, and 2 MPPT inputs. This requires enabling 2 subarrays (1 for each inverter input), which allows the model to calculate the operating voltage of each inverter input separately.

Feel free to attach a copy of your .sam file if you would like me to review your design.

Best regards,
Paul.

Hi Paul!

Thanks for the quick reply. I think I know what you mean: For each of the two subarrays I could set the number of parallel strings to 2 and it would automatically simulate 2 modules (each of them representing a 1-module-substring) in parallel for the one MPPT of this subarray.

However, this will not work for my usecase, as SAM only allows one single orientation for an MPPT. And the system I want to simulate has two different orientations for an MPPT: An MPPT shall be connected to one south-side module in parallel to one west-side module.

Do you agree that in this case it would be more reasonable to approximate the desired system by speciying 4 instead of 2 MPPTs?

Hi Ulrich,

If each of the four modules have different orientations, then you could model the system with 1 inverter, 4 MPPT inputs, and 4 subarrays with 1 module per subarray. This would represent an array with 4 modules that are allowed to operate at 4 different voltages.

Best regards,
Paul.

Thank you. Do you think that a SAM simulation with 4 MPPTs would be an acceptable approximation for the following real system?

 

Hi Ulrich,

I would assign two west-facing modules to Subarray 1, connected to MPPT 1, and two south-facing modules to Subarray 2, connected to MPPT 2:



Inputs on the System Design page would look like this:



Best regards,
Paul.