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Combiner Box question

cdunham

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Aug 15, 2020
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I have a Growatt 3000 48v unit 145VDC 80A
I have many 260 Watt 60 cell 8.50A 37.8V VOC solar panels

Would I be able to do the following with the panels and Growatt unit I have?
3S5P 260 Watt 60 cell 8.50A 37.8V VOC

If so, is there a combiner box that anyone can suggest and the breakers that I should get?
 
You should check the Growatt documentation. The 3000-s datasheet says 70-550V PV voltage 230V output, but the regular 3000 says 145V PV voltage, 110V output. Is your battery 24V like the Growatt 3000 for sale on Amazon?

Let's assume it is the 145V PV, 80A battery, 24V battery one on Amazon. I haven't read the specifications in detail but here's my calculations:

3 series panels @ 37.8V ~= 3 * 42V when cold = 126V so you're ok there. However, this is too much power for the Growatt3000, which handles 80A of charge current at 24V, depending on the model you have. For example: 3S5P = 15 panels @ 260W is 3.9kW which exceeds the 3kW of the Growatt 3000. More to the point it appears to be an 80A battery charger so if you're talking a 24V battery that's only 24V * 80A = 1920W that you can pump into the battery when it's empty, or about half of what your 15 panels can generate. You would have to verify what the Growatt does when fed too much solar: does it just not use it (basically detuning its MPPT point?) or does it explode in a fiery wreck? Does it blow a fuse?

Anyway, 15x 260W panels seems like too much for this unit.
 
You should check the Growatt documentation. The 3000-s datasheet says 70-550V PV voltage 230V output, but the regular 3000 says 145V PV voltage, 110V output. Is your battery 24V like the Growatt 3000 for sale on Amazon?

Let's assume it is the 145V PV, 80A battery, 24V battery one on Amazon. I haven't read the specifications in detail but here's my calculations:

3 series panels @ 37.8V ~= 3 * 42V when cold = 126V so you're ok there. However, this is too much power for the Growatt3000, which handles 80A of charge current at 24V, depending on the model you have. For example: 3S5P = 15 panels @ 260W is 3.9kW which exceeds the 3kW of the Growatt 3000. More to the point it appears to be an 80A battery charger so if you're talking a 24V battery that's only 24V * 80A = 1920W that you can pump into the battery when it's empty, or about half of what your 15 panels can generate. You would have to verify what the Growatt does when fed too much solar: does it just not use it (basically detuning its MPPT point?) or does it explode in a fiery wreck? Does it blow a fuse?

Anyway, 15x 260W panels seems like too much for this unit.
His GW is 48v. 3S5P PV array would be under 80 amps also. The 3000 for GW is inverter size, not capacity. Slightly overpaneled with 3S5P but doable, if input amps exceed 80a, then it will just accept the 80a.
 
I have the 48V 3000W 120/240V Solar Inverter Growatt SPF LVM 4KW-80A MPPT
 
I see "SPF 3000TL LVM-48P" on their website (http://www.growatt-america.com/show-9-589.html) so if yours is the same as that and you are using a 48V battery then I think you should be right at the margin: you have 3.9kW and it is designed for 4.5kW, safely above what you could generate. If you have a 48V battery then charge current is nominally 81.25A, but probably that's close enough to 80A and other MPPTs I have seen don't get ruined they just don't take advantage of the extra power. In general the battery voltage will be a bit higher and you will be right at 80A in peak conditions. In all likelihood you won't see the full 3.9kW very often if ever. I'd say go for it as long as you wire it as 5 parallel strings of 3 panels! Let us know how it goes!
 
thank you, I was hoping for some direction on a combiner box with breakers :)
 
I am a newbie but I like MidNite Solar's breaker / box offerings. Here are their pre-wired ones with breakers:


They are sold at several online stores; I just bought some MidNite Solar breakers from Solarflexion.
 
Thank you, I just didn't know if anyone had any suggestions. I know a lot of combiner boxes come without the breakers as well.

Like, should I have a breaker for each string? I would assume so, but wanted to make sure
 
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Yes, you should have a breaker for each series string if you want to do it right. In normal operation it makes no difference since they're connected in parallel after the breakers, but if one string has a short which causes a bunch of current, this configuration keeps the rest of the array from dumping its power into the shorted string because that string's breaker would [hopefully] trip.
 
okay, that is what I was thinking, just needed to make sure. Is there a preference with the breaker Amps I should be getting?
 
Yes, there is a rule for it; don't quote me on it but I think you want to aim for 1.56x the nominal short-circuit current. So if each panel has Isc = 10A you would want 15A breakers per series string. You should read up on this before you buy the box + breakers as you may be able to find a Midnite box (or other vendor's) which comes with the breakers you need already installed.
 
okay, thanks Paul, that is really helpful information. Each panel is 9.01A short circuit current.

Having the panels in series and parallel was throwing me off on what amp breakers I would need.
 
I don't know what your panel short circuit current is (you could just read the sticker and tell us), but this box has 6 connections with 15A breakers installed, 80A maximum. Easy peasy.


I didn't shop around, I just clicked one of the top results on Google so you may be able to find it cheaper. Midnite solar knows what they're doing with DC circuit breakers and they are rated to 150V, perfect for your series strings.
 
Great, so that's 9A short circuit current. The breakers should be 1.56x that, which is 14A. In my opinion 15A would be close enough as that's a standard breaker value. If you want to be picky about it, on that Amazon page the seller says "contact us if you need a different breaker value", so it might be available but if it were me I would just use 15A. Double check their wiring though before you hook it up, per the one review on that page.
 
Oh yeah actually it says "Maximum Series Fuse" = 15A so just do that.
 
Ok well good luck and post again if you have questions while hooking it up or you want to share some photos!
 
You should check the Growatt documentation. The 3000-s datasheet says 70-550V PV voltage 230V output, but the regular 3000 says 145V PV voltage, 110V output. Is your battery 24V like the Growatt 3000 for sale on Amazon?

Let's assume it is the 145V PV, 80A battery, 24V battery one on Amazon. I haven't read the specifications in detail but here's my calculations:

3 series panels @ 37.8V ~= 3 * 42V when cold = 126V so you're ok there. However, this is too much power for the Growatt3000, which handles 80A of charge current at 24V, depending on the model you have. For example: 3S5P = 15 panels @ 260W is 3.9kW which exceeds the 3kW of the Growatt 3000. More to the point it appears to be an 80A battery charger so if you're talking a 24V battery that's only 24V * 80A = 1920W that you can pump into the battery when it's empty, or about half of what your 15 panels can generate. You would have to verify what the Growatt does when fed too much solar: does it just not use it (basically detuning its MPPT point?) or does it explode in a fiery wreck? Does it blow a fuse?

Anyway, 15x 260W panels seems like too much for this unit.
he said 48v not 24v.... 15 panels is not bad, but its depend on the battery power he may use.
 
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