Selecting the "best" solar panel voltage for my new 24v battery / inverter

[georgiadawg]

Good day all!

I have a question that I wanted to put out to the group. I've studied this, read what I could, pondered, and I think I know what to do, but I wanted to be sure that I don't miss anything.

Here are the factors that I'm considering:

1. After much consideration (and after getting great feedback from SolarPoweredRV), I am installing a 24v system and have already purchased two (2) EG4 LifePower 24v 200ah rack-mount batteries.
2. I have priced 24v components - especially the 24v Victron Multi-plus II.
3. The roof of our Reflection has a lot of "things" (two A/C, two sunlights, two vents, plumbing vents, etc.) that make locating solar panels a bit complicated. I have already moved the huge, useless Winegard (useless because we use Starlink), and that freed up some space. I can only use relatively narrow solar panels, and, no matter what I do, I can only get six (6) panels on the roof. (I might be able to get a seventh, but it would be tough).
4. I've searched and searched for narrow panels and there aren't many options that work. Rich Solar has three that I'm considering: 250w 24v, 200w 24v and a 250w 12v. The best option (250w 24v) is out of stock, so, as of now, I'm considering the remaining two while I wait to hear back from Rich about the availability of the 250w/24v. Either way, and even if I get the 250w 24v, I'm going to wire them 3S2P.

So, my question boils down to the following: if my only choices are six (6) 200w 24v panels or six (6) 250w 12v, which option is "best", considering differing MPPT controller requirements, wire size, battery charging, etc.?

I ran calculations for both options and the results are as follows:

250 (3) series x (2) parallel
Max power output 1500w
Maximum Power Voltage(Vmp): 56.7v
Maximum Power Current(Imp): 26.4a
Max Voc 76.6v
200 (3) series x (2) parallel
Max power output 1200w
Maximum Power Voltage(Vmp): 113v
Maximum Power Current(Imp): 10.64a
Max Voc 152.5v



Any feedback or tips would be MOST appreciated.

Jeff

 

[Second Chance]

Thread moved to Solar Systems and Generators.

Rob

 

[wireslv]

I ran calculations for both options and the results are as follows:

250 (3) series x (2) parallel
Max power output 1500w
Maximum Power Voltage(Vmp): 56.7v
Maximum Power Current(Imp): 26.4a
Max Voc 76.6v
200 (3) series x (2) parallel
Max power output 1200w
Maximum Power Voltage(Vmp): 113v
Maximum Power Current(Imp): 10.64a
Max Voc 152.5v



Any feedback or tips would be MOST appreciated.

Jeff

Jeff,

Given your two options I personally would go 3S2P with the 250W panels. Your 26.4A current is reasonable so there is no compelling reason to move to a higher voltage. With the other option, your VOC will be much higher that the stated 152V VOC in colder temperatures, requiring the purchase of a more expensive higher voltage MPPT controller. Also, the MPPT efficiency drops as the delta between the input voltage and battery voltage increases.

For reference, I have a 24V Victron system and I'm running four 400W panels 39.7V 7.7A in a 1S4P configuration.

 

[kb0zke]

Jeff, we have a 2022 Reflection 315 RLTS. I don't climb ladders anymore, so I "measured" from inside. I figured I could get six panels on the roof. Panels are ~ 40 x 70 inches. Got the six panels, the installer said one, maybe two, would fit. Found another installer who actually went up on the roof and measured. He said he could fit four panels, so I sold the other two at Q. Got back to the installer and we lacked 2" of putting the four on. I now have three 365W residential panels up there charging my two 24V 200AH Redodo batteries. The panels are in series, so max of 120V, 10A.

No one wanted to buy the fourth panel, so I put it on the roof of the casita, where it will power a small security system.