Sizing my MPPT charge controller

[Troubleshooter]

My plan is to install 20 JA Solar 405W on the roof of my barn,
(VMPP) 41.60 V
(IMPP) 9.74 A
(VOC) 49.86 V
(ISC) 10.39 A

I am trying to size the charge controllers I'll need. I am going with Victron stuff, as I can get a very good deal through a friend.

According to Victron Calculator I need 2 150/70 controllers if I connected each to a 10 panel string in 2 series, 5 parallel config. I guess where I am getting confused is that charge controller is said to support up to 4000W of solar with 48v battery, but I am at 4050W and the calculator didn't tell me to go with 150/85 units.

 

[snoobler]

20 * 405W = 8100W

8100W/48V = 169A (max)
8100W/54.4V = 149A (typical)

Victron commonly specifies up to something like 20-30% over-paneling on their MPPT. This is because the chances that you'll actually deliver the true 100% rated power of your panels is pretty unlikely MOST of the time, i.e., almost all the time, you'll produce less than 140A out of the two MMPT.

You can always opt for the 150/85.