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Help with panels

El Guapo

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Joined
Jan 7, 2021
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13
Hello everyone,

I posted the message below in the marine forum a few days ago and haven't had a response. Just hoping I might find some help/expertise here.

Kindly,

Good afternoon everyone,

We recently (last week) upgraded our 680ah of AGM to 780ah of LifePo4 and are now turning our attention to our panels as they don't seem to be keeping up/charging sufficiently.

The existing panel configuration is:
  • 2 - 165watt panels
  • 4 - 100 watt panels
I'm considering upgrading the panels by replacing the 4 - 100watt panels with 4 - 380 watt LG NeON 2 panels and keeping the 2 - 165watt panels.

I have an existing FlexMax 80 MPPT and it is new, with less than 1 yr of operations. If I didn't purchase an additional MPPT, I assume I would be forced to config as follows but am concerned that the panels will exceed MPPT ratings (I believe I have the option of wiring in parallel and then series but don't know how stepping up voltage at pv array effects 12v operating system):
1638217438646.png


If I elect to purchase an additional FlexMax 80, I could split the panels as follows, but I don't know if the added cost is worth the output received. (to be clear, I'm okay with spending money to get this setup optimized. I'm lacking the technical expertise.)
1638217566508.png



Any recommendations for research or other areas I can educate myself on the best way to configure our system, it would be greatly appreciated.

As a side note, given the limitations of wind and hydro power generation, I've concluded that it would be best to size the pv array so that I can primarily depend on that system for charging and fall back on the Balmar on my stbd engine if we run into multiple overcast days or for running energy hogs such as the water maker, A/C, water heater, etc.

Thank you in advance and I'm happy to provide any additional details needed.

Kindly,

Kevin Fort
 
Maybe I’m dumb (and I didn’t like ok up the specs) but I don’t think you need to have a second flexmax to arrange 3S2P like you are suggesting. I can see advantages to that. I’m assuming the single flexmax are parallel panels?
assume I would be forced to config as follows but am concerned that the panels will exceed MPPT ratings (I believe I have the option of wiring in parallel and then series but don't know how stepping up voltage at pv array effects 12v operating system):
In series volts get added, amps stay the same.
So each of the two series strings would sum the voltage, and the amps would be double the single string amps.

As long as the sum VOC doesn’t exceed 75-80% of the SCC max volts it should be fine. Just need to know the SCC max volts… guessing it is 150 (80A) but not sure

Runnng dissimilar panels, however, could reduce your panels effectiveness. If the specs are right, though, it may not matter. You may have calculated this already- dunno.
 
they don't seem to be keeping up/charging sufficiently.

How close is the existing setup to meeting needs?

Have you tested the 400w and 160w panels separately on the 80A controller to see if they make more significantly more power separately than combined? If they do and the existing setup is very close to meeting needs it's possible that just splitting the 2x 165w off to their own 30A MPPT could get the job done.

If the existing setup isn't close to meeting needs I'd consider 2x 160w on a 30A MPPT and 3x 380w (1140w) on the existing 80A controller, which should ~double the harvest you are seeing now.

Full disclosure: the manual for the maxflex series (pdf) suggests they don't like to be overpaneled (page 100 shows a panel max of 1000w for the 80A at 12v. ), but this thread suggests overpaneling is fine. And Page 12 of the manual says:

The largest PV array must have a rated short-circuit current of 64 amps or less under STC (Standard Test Conditions).

I'm guessing 3x 380w 24v panels will have Isc of ~30A, well under the 64A limit.
 
How close is the existing setup to meeting needs?

Have you tested the 400w and 160w panels separately on the 80A controller to see if they make more significantly more power separately than combined? If they do and the existing setup is very close to meeting needs it's possible that just splitting the 2x 165w off to their own 30A MPPT could get the job done.

If the existing setup isn't close to meeting needs I'd consider 2x 160w on a 30A MPPT and 3x 380w (1140w) on the existing 80A controller, which should ~double the harvest you are seeing now.

Full disclosure: the manual for the maxflex series (pdf) suggests they don't like to be overpaneled (page 100 shows a panel max of 1000w for the 80A at 12v. ), but this thread suggests overpaneling is fine. And Page 12 of the manual says:



I'm guessing 3x 380w 24v panels will have Isc of ~30A, well under the 64A limit.
I tested each panel with my multimeter and was able to determine good voltage on each. My meter doesn't test DC current so I wasn't able to get a reading on that.

I tested my system by pulling up the batteries on my BMS app with a standard load on the system. For us this included:
  • 12v Fridge
  • 12v Freezer
  • Xantrex Freedom XC 2000w
  • Starboard 120 outlets charging two laptops and a couple cell phones
  • Port 120 outlets with no load
  • 120v water heater
With this, I was able to see that each battery was in a discharge state and there was about a 2 amp negative draw reading on the BMSs. I switched off the water heater (which shouldn't have been making hot water at the time as no one was using any water) and that only reduced the amp draw by 1 amp. I switched off the port side 120 outlets with no change as expected. I then switched off the starboard outlets and this was enough to change the battery status to charging. Please keep in mind that I had disconnected shore power so we were on solar only. I know this is a very rudimentary testing method but it was enough to convince me that my existing setup is not sufficient for our needs.

I didn't know that mismatching panels can cause less than optimal performance. I know that I definitely want to increase our production capacity given that we are headed offshore for an extended period. I will look to add a 30A MPPT for the two 165W panels. That seems like a great idea that would allow me to add some wiring to charge starting batteries if needed.

I would like to stay with 4 380 panels as this will help balance the weight on the boat. I gues what remains is figuring out how to wire them so as to not exceed the capacity of the FlexMax 80.
 
Maybe I’m dumb (and I didn’t like ok up the specs) but I don’t think you need to have a second flexmax to arrange 3S2P like you are suggesting. I can see advantages to that. I’m assuming the single flexmax are parallel panels?

In series volts get added, amps stay the same.
So each of the two series strings would sum the voltage, and the amps would be double the single string amps.

As long as the sum VOC doesn’t exceed 75-80% of the SCC max volts it should be fine. Just need to know the SCC max volts… guessing it is 150 (80A) but not sure

Runnng dissimilar panels, however, could reduce your panels effectiveness. If the specs are right, though, it may not matter. You may have calculated this already- dunno.
Correct, the single panels are currently wired in parallel.
 
I would like to stay with 4 380 panels as this will help balance the weight on the boat. I gues what remains is figuring out how to wire them so as to not exceed the capacity of the FlexMax 80.
I'm the local overpaneling zealot, and I have definitely overpaneled a controller that aggressively before. Of course, I was in no danger of being eaten by offshore sharks so I had less skin in the game. :)

The specs say the FM80 has a 150V input max, so maybe we hold that to 120V input as a safety margin. Some of the 380w panels I looked up had Vmp ~40v and Voc ~49v. In a 2P2S configuration that would result in Vmp ~80v and Voc ~98v, well within our input voltage limits.

I look forward to reading the input from others.
 
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