DIY residential 24v off-grid system -- sanity check please

[x98myers7]

Hi all... need a sanity check on my system planning at a component level. i'm in Michigan, so definitely have to contend with winter temps.

all-in-one inverter/mppt:
Growatt spf-3000tl-lvm-24p

Best Price 24V Growatt SPF 3000TL LVM – 3kW 120Vac Stackable Inverter 2kW MPPT Charge Controller Split Phase 120V/240V capable with two or more units – Special – Watts247 Wholesale

watts247.com

max PV voc=145
PV input= 30-115

panels:
10x 200w (likely RichSolar at this point) 12v = 20.4voc/20.4vmp/9.8a for "2000watts" total.... which is right at the "2000 watt" PV input limit on the growatt... check good

I was originally going for a 48v system, but I have a partial shading issue on one panel (d'oh!). so, with that, I am needing to drop array voltage to have 5 panels in series on two parallel strings so I can at least get 1kw on one string.


here's my basic math:
5 panels @ 24.3voc= 121.5voc which is less than the 145voc limit on the growatt....check good

so.... need help with winter temps. I recall reading somewhere on here needing to account for a winter temperature "spike", and suggesting a calculation factor of 1.2 for planning.

121.5 * 1.2 temp coefficient = 145.8voc which is right at the 145voc on the growatt... yikes?... not good? << help here please
------

5 panels @ 20.4v operating= 102v which is in range 30-115v for the growatt....check good
two 5 panel series strings is 9.8a per string * 2 strings = 19.6amps... plenty safe for typical wiring/breakers/disconnects. nothing fancy needed.


for reference, this system is being sized to support two freezers and a refrigerator estimated at 4166watts/day. at a solar factor of 4.1hours per day here in Michigan, i should be generating approx 6500watts per day at 80% efficiency. i'll have 200ah at 24v for ~5kwh of storage, which is enough for 24hours of no PV input. not ideal, but I plan to expand the battery bank to 400ah as funds allow.

 

[DThames]

Any reason that you wouldn't get normal panels, 300+ watts? Get some real panels that have Voc of 48-49v with 3 in series if you want that less than 150v input. Doesn't the 48v Growatt have a higher input voltage? That would be an advantage with normal large panels.

 

[x98myers7]

physical space constraints on where i'm placing the array. I have 60x288" to work with. need to keep the panels around 55" long.

 

[DThames]

physical space constraints on where i'm placing the array. I have 60x288" to work with. need to keep the panels around 55" long.

Okay. No ground mount option?

The Growatt uses about 50-60watts just being on, which is a notable overnight load on the size battery system that you plan.

Expect less and hope for more when it comes to panel production.

 

[x98myers7]

unfortunately, no ground mount option. we live on a lake and only have 1/2 acre. i have other roof options, but am leaving all of those open for future expansion as budget allows. i'm open to suggestions on separate components that are more efficient; but as always; I am measuring value versus return.

i'm not worried about production, as much. I know that solar in MI is exceptionally bad. in the winter we regularly go for an entire week without sun.

 

[DThames]

unfortunately, no ground mount option. we live on a lake and only have 1/2 acre. i have other roof options, but am leaving all of those open for future expansion as budget allows. i'm open to suggestions on separate components that are more efficient; but as always; I am measuring value versus return.

i'm not worried about production, as much. I know that solar in MI is exceptionally bad. in the winter we regularly go for an entire week without sun.

The subject says "off grid" but do grid AC to supplement when you are a week without sun? Hmm, never seen a floating solar array but it should work

 

[x98myers7]

The subject says "off grid" but do grid AC to supplement when you are a week without sun?

yes, so... is that technically a "hybrid" system then?

 

[DThames]

yes, so... is that technically a "hybrid" system then?

Hybrid might be closer, unless one thinks hybrid means grid tied with back feed. I was not picking at the subject, just trying to confirm that you have AC grid power when you don't have solar/battery.

 

[DThames]

The Growatt has a setting for max AC charge current. You might consider setting that value at some low value so that at night you are getting an amp or two from the grid so to keep your battery from discharging as deeply. If you see the battery at a lower SOC than you want in the morning, you could tweak that number so to not take it down as far. If you have solar charging priority set, as soon as you had sun, the AC charging would drop off.