Modeling a large scale PV with multiple inverter and MPPT inputs

Hi, I am Behine and I am new to the SAM environment. I have done a couple of searches about this topic but couldn't find related ones. I have started modeling a large scale utility PV facility (100 MW). This system, by nature, has multiple inverters which each one of them has multiple MPPT inputs. When I enter my inverter specs and try to proceed to the next step (system design) I get this warning:
"Multiple MPPT Input Error!

Multiple MPPT is only supported for systems with one inverter.

Set number of inverters to one. Or, to model a system with more than one inverter, temporarily set the number of inverters to one, then on the Inverter page set the number of MPPT inputs to one before changing the number of inverters to more than one."
I am a bit confused and required assistance on this because I don't know how should I model this system. The instructions says that I have to either set the number of inverters to one or set the number of MPPT inputs to one which in my case neither is correct.

Hi Behine,

The multiple MPPT input feature allows you to model an array with up to four sections (called subarrays in SAM) that operate at different voltages. This may be the case when subarrays have different string lengths, tilt and azimuth angle, shading, etc.

If the system you are modeling is designed so that all sections of the array operate at the same voltage, then you can model the inverter with a single MPPT input even if the actual inverter has multiple MPPT inputs.

If you are modeling a complex system with different sections that operate at different voltages, then you are limited to four MPPT inputs.

Best regards,
Paul.

Hello Paul, taking advantage of this thread, I also have a question about how to proceed with my system design.

I am developing a PV system aimed at 500 kWp, located in a company's parking lot to supply power to a new administrative building. 

Our situation is as follows: Since it is a sizable array that will likely use around 1,000 PV panels, we will need at least 3 inverters to cover the project. The inverters we plan to adopt have multiple MPPTs. Additionally, about 30% of the area experiences shading from local trees and the new building itself. Naturally, this shading profile shifts throughout the day as the sun moves.

Given this, and as discussed in previous comments, SAM's limitations restrict us to modeling either 1 inverter with multiple MPPTs or multiple inverters with a single MPPT. Because of the moving shade, we will certainly have voltage mismatches across the arrays during generation.

What would be the best approach to model this scenario accurately in SAM? Thanks in advance,

Hi Arthur,

If you choose to model the system as multiple inverters with a single MPPT, you could account for the voltage mismatch losses by adjusting the DC losses on the Losses page. This would require estimating the DC losses outside of SAM. You could use parametric simulations to see how much these losses affect your output metrics of interest. (See  samrepo.nrelcloud.org/help/parametrics.html .)

If you model the system as a single inverter with up to four MPPTs, you can divide the array into subarrays (each connected to a different MPPT), which would allow the subarrays to operate at different voltages. You could then model shading of one or more of the subarrays using the inputs on the Shading and Layout page.

Both of these approaches would provide an estimate of the effect of shading on your system. You can try both approaches to see how well they work.

Best regards,
Paul.