I’m working to design an off-grid DC coupled system. I see online that you sell two Schneider MPPT charge controllers. What is the main difference between the two? This is a larger system with approximately 6kW of PV.

Comments

I assume you are looking at the following two charge controllers:

MPPT 60 150 

MPPT 80 600

The main difference between these two is the maximum DC input voltage. The 600 Vdc unit will allow you to string in a similar fashion as a standard residential grid-tied string inverter, while the 150 Vdc unit will keep your strings short.

 

Using your project as an example, the 150 Vdc charge controller will limit you to a max string length of 2-3 modules (depending on your climate and orientation). Assuming you are using a 290W module, a 6kW system will be comprised of approximately 20 modules. Using the 150 Vdc charge controller will result in at least 7 strings of modules. This configuration will require additional wire, combiner box(es) and OCPD. You will also need a 2nd charge controller to handle the current produced in parallel by these strings.

 

By comparison, the 600 Vdc unit would allow you to run 2 strings of 10 on a single charge controller.  

 

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