How to configure multiple string lengths on same inverter type without detailed stringing design

[Allison]

Hello, I'm working on a community solar site that will be 4950kWac (QTY 18 275kW string inverters). I'm utilizing string lengths of 24, 22 and 20 modules. I have total number of strings for each string length based on the preliminary site design however, I do not have stringing configuration per inverter yet. I'm trying to figure out the best way to utilize the multi-MPPT function to model the differing string lengths without knowing exactly how the strings will be allocated to the 18 inverters. 

So far, I've created three different subarrays to represent each string length. For totals I've got the following:

• 376 strings of 24 modules
• 46 strings of 22 modules
• 48 strings of 20 modules

I know the total number of inverters is 18 which equals 216 total MPPT inputs to be utilized. Is best practice to manually allocate the 216 MPPT inputs between the three configurations targeting a similar Pnom ratio between all three subarrays? After allocating the strings, do I use the power sharing function to balance the strings onsite within one configuration? Screenshots below show what I've done so far, I just want to make sure that this is the most accurate way to model without detailed stringing being completed.

 

 

Thank you!

[Linda Thoren]

Hello Allison,

When using the multiple MPPT feature, it is important that the numbers of strings is a multiple of the numbers of MPPT inputs, or PVsyst cannot evenly distribute the strings over the MPPTs and you risk increased inverter loss over nominal inverter power. For instance, 46 strings over 18 MPPTs results in 2,5 strings per MPPT.

In general, if you have multiple inverters with the same configuration, the number of strings and MPPTs can be multiplied with the number of inverters and be assigned to the same configuration in the Power sharing window. 

If you think this is not the case, you should define several configurations in Power sharing window, thus also additional sub-arrays.

The following youtube tutorial show additional examples of how to use the Multi-MPPT and Power Sharing

Kind regards