MMPT Max PV Input Voltage - Voc or Vmp?

[dsaint1884]

I ordered the Renogy 400w solar kit. It comes with a 40a MMPT that has a max PV Input Voltage of 100w. It also comes with 4x100 watt 12v panels. I'm trying to determine the wiring for the solar panels (4p, 4s, 2s2p). Depending on what numbers I use from the website I'm not sure the MMPT can handle a 4s wiring setup.

Link to Kit with Specs on what I'm working with:

New 400 Watt 12 Volt Solar Premium Kit W/MPPT or REGO Solar Charge Controller

4* 100W Eclipse Monocrystalline Solar Panels totaling 400 Watt, 1* 40 Amp MPPT Charge Controller, 2* 20' Solar Extension Cables, 1* Solar Adapter Kit 9'' in length, and 4 Sets of Z brackets for Mounting

renogy.com

Open-Circuit Voltage 24.3 (Voc)
Optimum Operating Voltage 20.4 (Vmp)
(These are 12v panels so I'm not sure why it says the open circuit voltage is 24.3, just to have enough volts to charge a 12v system I assume)

Anyway...when I calculate the total voltage created do I use Open Circuit Voltage or Optimum Operating Voltage? In 4s configuration one way I get 97.2 volts, the other 81.6 volts. The 97.2 is probably too close to the 100v max when I consider any cold temp voltage increases. The 81.6 seems like it would potentially be ok but still uncomfortable. Alternatively I could just run this in 2s2p and be well within voltage capacity of the MMPT.

My question is, which voltage should I be using to see if I can run 4s with the MMPT I've purchased within the kit?

 

[Cyanlite]

Use VOC

 

[dsaint1884]

Use VOC

Awesome, thank you. That's what I thought but didn't want to rule out 4s if I didn't need to. It seems like 4s would be too close to the volt max (100v) for my MMPT at 97.2voc (24.3x4 panels) and I will need to either use 4p or 2s2p for this setup. Thank you again!

 

[Cyanlite]

4s would probably be fine at 97.2 VOC, but I'd still go 2s2p to help with any shading issues. It only takes a small amount of shading to reduce the majority of your solar generation.

 

[rmaddy]

Definitely too close. Voc goes up as the temperature goes down. The 97.2Voc would exceed the 100V limit at about 60ºF/16ºC.

 

[dsaint1884]

Definitely too close. Voc goes up as the temperature goes down. The 97.2Voc would exceed the 100V limit at about 60ºF/16ºC.

Thanks for confirming and helping out. Appreciate your help and this forum! I'll likely go with a 2s2p configuration which I believe puts me at 48.6Voc and should leave enough room.

 

[dsaint1884]

4s would probably be fine at 97.2 VOC, but I'd still go 2s2p to help with any shading issues. It only takes a small amount of shading to reduce the majority of your solar generation.

Thank you, 2s2p seems like the way to go for a number of reasons then.

 

[ericfx1984]

4s would probably be fine at 97.2 VOC, but I'd still go 2s2p to help with any shading issues. It only takes a small amount of shading to reduce the majority of your solar generation.

You beat me to it

 

[rmaddy]

I'll likely go with a 2s2p configuration which I believe puts me at 48.6Voc and should leave enough room.

At 48.6V it can't get cold enough to exceed 100V. Seriously, the cold of space isn't cold enough. You'll be fine.

If you get 2 more panels you can also go with 3S2P and still be under 100V under any temperature.

 

[dsaint1884]

At 48.6V it can't get cold enough to exceed 100V. Seriously, the cold of space isn't cold enough. You'll be fine.

If you get 2 more panels you can also go with 3S2P and still be under 100V under any temperature.

Perfect, that's what I figured. That works great and gives me room to add if I need it. Thank you!