Monofacial vs Bifacial - Are they calculated the same and how does the rear ISC impact the total ISC of 2 strings in parallel

[Cmiller]

Instead of 3x 8S strings set your panels to 2 strings of 12 panels. Still within 18K voltage limits and you have the input 1 mppt free for future use?

VOC- 41.5V x 12S = 498VOC, but you have to add an additional 25% for cold condition overvoltage (unless OP is somewhere that he won't ever see 40F or colder). 498 x 1.25 = 622.5VOC. I would definitely not do more than 9 or absolute max 10 panels in series on this voltage rated mppt!

Hitting that voltage level (600+ volts) even once will very likely destroy the mppts!

 

[MattiFin]

VOC- 41.5V x 12S = 498VOC, but you have to add an additional 25% for cold condition overvoltage (unless OP is somewhere that he won't ever see 40F or colder). 498 x 1.25 = 622.5VOC. I would definitely not do more than 9 or absolute max 10 panels in series on this voltage rated mppt!

Hitting that voltage level (600+ volts) even once will very likely destroy the mppts!

Fair enough, 12S might be tad high. IIRC 1.25 factor for VOC is the easy "rule of thumb" but rules* allows you to also calculate it from panel specs and lowest temperature on building site. OP's panels have -0.27%/K voltage coefficent so anything warmer than -49Cel/-56F would be ok.

*)Literally far from any sort of expert on North American standards but this should be from NEC 2017:
(A) Photovoltaic Source and Output Circuits. In a dc PV source circuit or output circuit, the maximum PV system voltage for that circuit shall be calculated in accordance with one of the following methods:

(1) Instructions in listing or labeling of the module: The sum of the PV module–rated open-circuit voltage of the series connected modules corrected for the lowest expected ambient temperature using the open-circuit voltage temperature coefficients in accordance with the instructions included in the listing or labeling of the module

 

[sunshine_eggo]

NEC 2017 table:

PV array temperature correction table (NEC 2017)

There are calculators like this one made by @upnorthandpersonal which help you calculate PV array voltage and power for low temperatures based on the specific specifications of your panels. These are great tools and will give more precise...

diysolarforum.com

 

[zanydroid]

MULTIcrystalline?

 

[garybryan33]

Instead of 3x 8S strings set your panels to 2 strings of 12 panels. Still within 18K voltage limits and you have the input 1 mppt free for future use?

At the moment the plan is if after collecting data, input 1 cannot be paralleled, I will be adding panels as you suggested to open the 3rd input for further expansion.