6000XP Single unit vs add second

[WS6-4467]

Hello,

I have (2) EG4 6000XP units and 30 Canadian Solar 355W panels. I was thinking about only setting up one inverter initially - and trying to figure out the best configuration of panels. They are 355W units - VOC 46.8V and ISC 9.59A. 8 panels in series to each MPPT is comfortable but I feel like I am not maximizing the input wattage that way for a single unit. Hooking up the second unit would give plenty of room on the PV inputs - but doubles the idle consumption. Any suggestions how to maximize with a single unit?

 

[Rednecktek]

I think 9s3p would max out your 6500, or 9s2p on one MPPT and 9s on the other. 10s will be too high a voltage.

 

[WS6-4467]

8S puts me at 374.4 volts * 9.59 amps = 3590 watts per MPPT x 2 = 7180 watts total.

But they are 355W panels x 16 = 5680 watts - I guess I don't understand the difference between the two calculations.

Not sure what I am missing...

 

[Rednecktek]

They calculate wattage by Vmp and you calculate string voltage from Voc. They're a few volts difference but to your SCC it's a REALLY important difference.

 

[WS6-4467]

I think 9s3p would max out your 6500, or 9s2p on one MPPT and 9s on the other. 10s will be too high a voltage.

9S2P would seem too high at 421 volts not allowing for cold also would be over wattage on one MPP.

I must not be calculating correctly - do I only use VOC and ISC to make sure the MPP can handle the absolute limit?

Otherwise I use the operating voltage VMP 39.4V and IMP 9.02 operating amps to calculate the string?

 

[EG4_Jared]

To maximize the MPPT with a single inverter, you could configure a 7s2p setup, which would result in 327.6VDC and 19.18A. This configuration would enable 4,970W per MPPT, slightly exceeding the usable wattage of 4,000W per MPPT, while remaining well under the 480V maximum input.

 

[Rednecktek]

It's pretty much impossible to match up maximum inputs on a unit like that because the designs are something like "Will take up to 5000w*!!"

*500w limit is calculated at 500v @ 10a @ 25c lab test conditions...

Which of course you can NEVER get in reality because Voc is higher than the Vmp, and temperature changes. Nobody lives in lab conditions. So the best you can do is get a little over paneled, get the voltage as high as you safely can, and leave a few theoretical watts on the table in the best weather hoping you can still get something usable in the worst weather.

TL;DR - Don't fixate on getting exact perfect numbers to maximize the limits of the unit. Get as close as the math and weather allow and hope for a little bit of energy left over.

 

[WS6-4467]

It's pretty much impossible to match up maximum inputs on a unit like that because the designs are something like "Will take up to 5000w*!!"

*500w limit is calculated at 500v @ 10a @ 25c lab test conditions...

Which of course you can NEVER get in reality because Voc is higher than the Vmp, and temperature changes. Nobody lives in lab conditions. So the best you can do is get a little over paneled, get the voltage as high as you safely can, and leave a few theoretical watts on the table in the best weather hoping you can still get something usable in the worst weather.

TL;DR - Don't fixate on getting exact perfect numbers to maximize the limits of the unit. Get as close as the math and weather allow and hope for a little bit of energy left over.

Thank you for the info - that makes perfect sense

 

[WS6-4467]

To maximize the MPPT with a single inverter, you could configure a 7s2p setup, which would result in 327.6VDC and 19.18A. This configuration would enable 4,970W per MPPT, slightly exceeding the usable wattage of 4,000W per MPPT, while remaining well under the 480V maximum input.

Thank you - I think I will go this direction. It means lower gauge wire vs just wiring 8S and using the second inverter, but if I can do everything with a single unit I can keep the second for expansion when I get more panels.