Suggestions for New Array with (2) FM100s

[shoot24p]

I'm looking into replacing my aging and miss-matched solar array. I'd like to max out what our system can safely handle without making any other upgrades other than the modules and rewiring strings as needed. I have an off-grid 48v system with (2) FM100s, (2) GS8048 Radians and 600ah of Relion LiFePO4 batteries.

We have a south-facing garage roof where we can easily replace our 28 panels, but no room for any more. We could also add more panels elsewhere on the house roof, but would like to avoid for now.

My installer is suggesting 440w Qcells. Does this seem like a good option? That would give us about 12.3kW. Looks like the (2) FM100s are rated for 14kW @48v. But I'm doubting the extra cost of building and wiring a second array would be worth the additional 2kW.

Also, our garage gets HOT in the summer, so I'm sure I'd be bumping into the output temperature limits anyway.

Any suggestions for how the strings should be configured? Matched and split equally between the two? I think this should be possible as long as it's OK to run the strings close to the 300v limit.

Any other specific modules I should be looking at? My installer is pretty solid with standard residential installations, (and they did ours originally) but they definitely don't specialize in Outback systems, so I want to do as much research as I can.

[raysun]

440W is a good form factor and cost point. Qcells have a good track record.
Yes, I'd split what can fit on one roof between the two FM100.
You will need to do some careful temperature calculations for cold weather V(oc).
A 7S at 40V(oc) = 280V - uncomfortably close to thd 300V limit which cannot be exceeded without damage to the FM100.
6S3P is 18 per array.

[chrisski]

Record cold in your area will drive how many in series. 5 x 400 watt panels use my area in super hot phoenix.

Six would exceed or be more nvomfirtanly close to the record cold limits with VOC.

My first array with 10 kW with 2 x FM 100s 4s3p to each controller.

[raysun]

6S @ 40V(oc) is 240V. Is there a possibility of a 60V excursion? Most of my North European friends are pretty comfortable with 20% headroom.

[shoot24p]

Thanks for the info. I live in North County San Diego, so we get a few frosty mornings, but rarely below 35F, record cold is somewhere around 10F.

I see…Splitting 28 panels evenly between the two controllers doesn’t leave many options for how to run them. Could I split it 12/16? Series of 4 on each? That would be just a hair over 7000w on one controller. I could just get 430w panels to be safe?

Definitely not room for any more, and I think if I get any less it wouldn’t be worth the effort.

[raysun]

From a pragmatic standpoint two arrays: 4S4P and 4S3P would make the best use of the 28 panel real estate.

[Specialist]

Use the outback excell for pv sizing.

I have 5s3p of qcell 410w on 2x fm100.

You can match 6S3P in first fm100 and 5s3P on 2nd fm100

[shoot24p]

According to the sizing tool, looks like 5s3p is the sweet spot for 440w panels to safely max out the FM100. I'm going to see if there is a way to squeeze another two modules up there (30 total) so we can just run that to each charge controller.

If not, we'll go with 430w and use 4s4p and 4s3p. Thanks.