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MPPT current limit


Abdel Rahman
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Hello,

First of all, sorry for much details in my question but it is necessary to describe the problem.    

I have solar residential  PV system in Germany, I am facing a problem and I hope to get help . The DC power of the system is 9430 W (9.4 KWp) with 23 luxor 410W PV modules connected with SMA Sunny Tripower 10.0KW. The inverter has 2 MPPTs (A:2/B:1). The inverter has Max. input current input A (20A) / input B (12A), and Max. DC short-circuit current input A (30A) / input B (18A). The PV module Impp is 12.9A and the short circuit current of the module is 13.72A  

Now the problem as follows:

At the beginning we had 24 modules divided into 2 strings, each string consist of 12 PV modules connected to the name MPPT (Input A). During the installation we forced to remove one module from the system. Then we modified the system to be two strings one with 12 Module and another one with 11 modules. each string has been connected to separate MPPTs since they different with the number of PV modules. 

After that I returned to PVsol to update the plan and make it two strings , one with 12 modules and another one with 11 modules  but the program gives an warning message which prevent me to complete the design as shown the figure . Actually I know the reason why I got this message ( the PV module current Impp at STC (12.9A) is greater than the Max. input current of input B (12A) of the inverter, but the system was installed in September and it is working without any problems but we don't know if will be any problem in the future.

Now, We need to update the plan because it is necessary step as a part of PV system installation process for the customer. 

What can I do since we must update the plan?

Please any suggestions that could help me to complete the design and solve the problem. 

Also, here I am wondering in the beginning (before removing one PV module) with the case of two PV strings (each 12) connected to same MPPT (Input A), where the max input current for tracker A is 20A but the current of the two strings that entering into the tracker is 25.8A, and that's mean the limitation of the inverter has been exceeded but PVsol has been accept the design!   

I attached the Inverter and PV module specifications. 

Final question, do you think that the modules currently don't produce the nominal current for that reason the system is working properly, but the modules might produce higher current in summer for example which can cause problem for the inverter ? 

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Dear Abdel,

thank you for your detailed question. The more information we get, the easier it is for us to answer, so no need to apologize for detail :)

First, you do not have to worry about the system that you installed. The only current that must not be exceeded is the max short circuit current. Exceeding it might be harmful to the inverter. If you exceed only the max input current, the inverter will not be able to handle the full current and some clipping will occur. But it is not harmful to the inverter.

As you wrote, the max. short circuit current of the inverter is 30A input A and 18A on input B, and you only have connected one string on each input, with 12.9 A short circuit current at STC (1000 W/m²). So I'd say, you are safe there.

The whole configuration check is overhauled for the new major version PV*SOL premium 2023 R1 (coming around the end of November), including the check for the max short circuit current. It should be less confusing in the future.

 

13 hours ago, Abdel Rahman said:

What can I do since we must update the plan?

For now, you can put in a larger value for the input current tolerance. Click on "configuration limits" and enter a higher value for the current tolerance:

image.png

Hope that helps, kind regards,

Martin

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