Wire sizing for 1.3kW 24V system - 4x320W panels

[Colorado_Al]

Hi there. I'm trying to design a system for an off grid house of 900sq ft.
I'm planning on using 4 LONGi 320W Solar Panel 120 cell LR6-60HPH Modules, wired 2x2 so as not to exceed the limits of the Growatt SPF 3000TL LVM-24P.
Batteries are expected to be 2x 12V 200Ah AGM in series. I might need more battery, but not sure at this time.
After wiring the panels 2 each in series and those in parallel, I'll have 81.2V & 15.8A.
The run to the Growatt is about 45'.
Will this 8 AWG 50' set be sufficient or do I need to go bigger?

Amazon.com

Thanks for your advice, and any other advice you might offer instead of my proposed plan.
Thanks!
Al

These are the expected loads:
10 single light fixtures with 10w LED bulbs
1 Cellular to WiFi router
1 wireless home controller
2-4 laptop computers (depending on occupancy)
1 clothes washer
2-4 cell phones (depending on occupancy)
3 oscillating fans (that we haven't bought yet)

Current refrigerator is propane, but it is old and crappy. Thinking of replacing it with a 13 cu ft AC one, if I have enough power/battery.
Normal occupancy will be 2 people, with occasional use of up to 6 people.
Thanks!

 

[mopat]

Will this 8 AWG 50' set be sufficient

Yes.

 

[MichaelK]

Here is an ampicity chart that you might find valuable.

My gut feeling is that you'll need both more panels, and more battery. Don't design your system to work in the middle of summer. Design it to work in the middle of winter. I would say that 8 gauge is fine for the system as it is designed NOW. But, if you decide to upgrade panels later, you might find 8 gauge to be limiting. Better to go overboard on gauge now, then having to rip out wire and starting over if you need to upgrade later. I personally used 4 gauge from the combiner to my controller.

Your total storage is 24V x 200Ah= 4800Wh. That's not much. If you want to add a refrigerator, I'd expect you to use about 2400Wh per day. Running your batteries down 50% every single day is not going to be good. I have 48V x 375Ah = 18000Wh, and I consider it on the small side. And my cabin is only 2/3 your size. I'm upgrading to 730Ah next year.

Let's say you target 15% depletion of the batteries each day. That would give you three days of autonomy before hitting 50% charge. So, I'd say you'd need 2400W/0.15 =16000Wh. That would be a battery bank about 3X bigger than what you are planning. Feel free though to plug in your own consumption numbers to update the calculations. The values may change, but the math stays the same.

 

[Colorado_Al]

Here is an ampicity chart that you might find valuable.

My gut feeling is that you'll need both more panels, and more battery. Don't design your system to work in the middle of summer. Design it to work in the middle of winter. I would say that 8 gauge is fine for the system as it is designed NOW. But, if you decide to upgrade panels later, you might find 8 gauge to be limiting. Better to go overboard on gauge now, then having to rip out wire and starting over if you need to upgrade later. I personally used 4 gauge from the combiner to my controller.

Your total storage is 24V x 200Ah= 4800Wh. That's not much. If you want to add a refrigerator, I'd expect you to use about 2400Wh per day. Running your batteries down 50% every single day is not going to be good. I have 48V x 375Ah = 18000Wh, and I consider it on the small side. And my cabin is only 2/3 your size. I'm upgrading to 730Ah next year.

Let's say you target 15% depletion of the batteries each day. That would give you three days of autonomy before hitting 50% charge. So, I'd say you'd need 2400W/0.15 =16000Wh. That would be a battery bank about 3X bigger than what you are planning. Feel free though to plug in your own consumption numbers to update the calculations. The values may change, but the math stays the same.

Thanks so much for this.
I'm taking your advice and upping the wire size and system size.
I think I actually found a local source for panels and batteries and since they don't have to be shipped the cost is much better.
My current plan is 6 Hanwha Q-Cell QPEAK DUO BLK G5 315w Mono Half-Cell Solar Panel that I can buy for $150 each. 40.29V Open Circuit Voltage, 9.89A Short Circuit Current.
And 4x 12v 195Ah AGM batteries.
I think I will have to wire the panels 3s2p and have max of 121V 20A. The Growatt specs say max DC input of 145V & 80A, if I'm reading everything correctly.
Since I'll have 4 batteries, my question now is do I go with a 48V or 24V system? Cost of the Growatt 48 vs 24 is negligible. It seems most here go with a 48v system. As I understand it, the advantage of a 24V system with 4 batteries is that if one goes bad, I will still have one active battery bank. The advantage of the 48V system is less resistive loss between controller and batteries. Are there other pro/con for either? What do you recommend? My main concern of 48v is that the location is quite remote and getting a replacement battery could take weeks.
(Or do I just pony up the cash and go with 8 batteries? I'm actually pretty sure I don't have room for that many.)
The location is near the Tropic of Cancer so still decent sun in winter, though as anywhere, clouds are unpredictable.
Thanks!!!

Location info and panel specs:

 

[MichaelK]

Since you are close to the tropics, I'll assume your winter lows are not below freezing? You're not up in the mountains where it can get cold are you? The voltage of solar panel goes up as the temperature goes down. At 0 degrees C your panels would be putting out 130.8Voc, so that's still within the safe limit. I determined this using Midnight Solar's string calculator.

You can use it yourself by going to http://www.midnightsolar.com/ and first clicking on "PRODUCTS" in the main menu, then clicking on "Charge Controllers - Classics". Select and run their "Classic Sizing Tool", where you plug in the specifications of your panels, your string design, and the seasonal temperatures. It will spit out the highest voltage your system is ever likely to produce and will let you know if your electronics are in danger.

I am not a big fan of parallel battery connections. As they go up, each battery string gets harder and harder to charge properly. I'm also not a fan of AGM batteries. They cost twice as much and last half as long. I much prefer regular lead-acid batteries where you can check the specific gravity of the acid, and equalize charge them. With standard off-grid lead acid batteries, you could put together a single string from 100 to 1500Ah of power. Just be ready to do the lifting.

I've never seen a series battery failure, so I don't worry about that much. I would much more prefer the higher system voltage simply because of the extra power potential, so my vote would be for 48V. That is what I myself am using, though mostly because I use my solar system to power my 240VAC well pump. Everything is just easier to do at higher voltage. I do though have a 24V system for my one-room workshop, and it runs my power tools just fine, but it doesn't have 24/7 demands on it like my whole-cabin system.

 

[Colorado_Al]

Thanks for that.
No. Never freezing. Coldest temps are 50°F in Jan.
Though I'd like to use standard lead-acid batteries, I travel often and need something that is low maintenance and doesn't need to be topped up.
Thanks for the advice. I'll go with 4 12v 195Ah in series and see how that goes. I'm not in a rush to swap the propane fridge for electric at this time. I'll take it one step at a time. Thanks for the advice!

 

[Colorado_Al]

Batteries that I was going to buy were not as good a source as I'd hoped.
Looking into GYLL LiFePo4 48v batteries. Might go with them instead. Maybe 2. Anyone with experience using them with the Growatt?
Thx!