Gathering info for initial components.

[Jimmynik1]

I'm constructing a system to be used purely for emergency backup. Not grid tied, not used as a main source ran through a hybrid inverter ats. Just a bank of batteries hooked to an inverter, charged by sun for when/if shtf and there is no grid. The whole power audit thing really doesn't apply to me as I am making this for solely emergency use so in an actual emergency I could just reduce use if I had to, but for sake of argument lets say I want to comfortably run 10a of ac and have the system be ok with it. 10a ac or 55a dc on my idyllic 24v system. 10a ac in my home is every light I could want on, both recirculating pumps for heat, my fridge, my tankless water heater and whatever other small items I would want.

What i've got to work with as far as roof space is a 600sq ft 12x25 brand new roof at a 6/12 pitch. So plenty of space there. The sun passes over in an east to west fashion and both sides get a decent amount of sun throughout the day.

I've decided to go for the 3.2v cells, 300ah (or 271s or 310s if the 300s aren't available), 16 of them in parallel and then series. Giving me a 24v system @ 600ah. From Basen tech though alibaba. Several friends used them and had good results as well as good reviews online show them as one of the more reputable vendors.

I've chosen to use an all in one hybrid inverter. 24v- to 110v 3k. Specifically the LV2424, Growatt 24v-110v 3k, or one if its clones. I like them because from what I've read i can change the way it charges, making it use solar mainly but then if its plugged in to ac itself, switch to ac if the batteries are not charged enough when the solar input gets too low.

Where I would love some input is deciding on the arrangement and way to feed my bank with solar.
I understand if I am drawing a max of 10a ac or 55a dc I should have a system that allows for that much and more to be put bank into my bank. So I think that's around 1200-1400 watts of panels. If the LV2424 has a max input of 145vdc at 80a for example, what would be the best way/panels to use. I understand the difference, pros/cons of wiring panels in series vs parallel. But when wiring in series to increase voltage with the main benefit being using thinner wire, to me it doesn't seem that the loss of potential amperage is worth it unless there is more I don't understand yet. Should I find individual panels that can charge a 24v system on their own and put as many of them in parallel as I can while staying under the inverters dc input rating? I also know almost next to nothing about bms other than that they monitor the battery bank. So I will certainly need recommendations for a decent 24v bms that I will get two of for each string in my bank.

So thats basically it, a 24v system that is just for emergency, that'll have approx 600ah wired to a hybrid inverter. Looking for advice and suggestions on the array.
Greatly appreciate any and all advice.
Jim

 

[iamrich]

I am running the Hybrid LV2424 and using x9 250w panels (3S3P) which comes out to ~100vdc, ~25a for at max output. Assuming you are never going to back feed the grid (mine is not UL listed), I would just source used panels and build a bigger array than you need. You want to be able to charge more than you use in case you have some cloudy/rainy days in a row.

Santan solar or similar can sell you used 250w panels in the $50 range + shipping (~$200 per pallet). Obviously the more panels you buy, the cheaper the overall shipping is per panel. I bought 12 and ended up spending $584 (snail trail panels, $33.50 each on sale).

 

[iamrich]

What i've got to work with as far as roof space is a 600sq ft 12x25 brand new roof at a 6/12 pitch. So plenty of space there. The sun passes over in an east to west fashion and both sides get a decent amount of sun throughout the day.

Didn't see this on the first pass read. I have a 12'x36' roof so I just ran a single run of 9 panels but that was ~30 feet, so you would have to get creative. Maybe six and three, or you could run less panels at a higher wattage maybe. You have a ton of options.

 

[Jimmynik1]

I am running the Hybrid LV2424 and using x9 250w panels (3S3P) which comes out to ~100vdc, ~25a for at max output.

Awesome thank you, that is what I was looking for. So with those 9 panels @ 250w each, you said 3s3p so 3 sets of 3 in series then those 3 sets in parallel?
Of the snail trail panel specs "Max power voltage (VMP): 30.3 V" and "Max power current: 8.27 A" Is the 30.3v x 3 the around 100vdc you have and the 25adc the 3 x 8.27?
I'm just not following the benefit of putting panels in series to increase voltage if the voltage of one panel individually is enough to charge a 24v bank on its own.
And I dont plan for this ever to be on grid for any other purpose than using the built in charger of the 2424 if i wanted/needed.
On santans site and have an estimate for $635 for 6 of your panels to my door. If i put those in a 2s3p configuration would that increase amperage going in to my bank while still keeping my input voltage around 60?
Thanks again

 

[iamrich]

Awesome thank you, that is what I was looking for. So with those 9 panels @ 250w each, you said 3s3p so 3 sets of 3 in series then those 3 sets in parallel?
Of the snail trail panel specs "Max power voltage (VMP): 30.3 V" and "Max power current: 8.27 A" Is the 30.3v x 3 the around 100vdc you have and the 25adc the 3 x 8.27?

Yep

I'm just not following the benefit of putting panels in series to increase voltage if the voltage of one panel individually is enough to charge a 24v bank on its own.

You want the voltage as high as possible (but low enough you don't get close to the max vdc rating) because you can use smaller and less wires. If you run all the panels parallel, you have to use 9 sets of wires. You can do it that way if you want. The input would be ~33vdc at ~72amps which still works, but you will have spaghetti wires all over the place and will need a hell of a combiner box hopefully as close as possible to the inverter because at 72 amps the wires to connect will be big.

On Santan's site and have an estimate for $635 for 6 of your panels to my door. If i put those in a 2s3p configuration would that increase amperage going in to my bank while still keeping my input voltage around 60?
Thanks again

That work work as well. I was trying to max my array (I am actually over-paneled). It is critical you don't exceed the max voltage, but most SCCs will just clip if you push too much total power into them.

 

[snoobler]

Awesome thank you, that is what I was looking for. So with those 9 panels @ 250w each, you said 3s3p so 3 sets of 3 in series then those 3 sets in parallel?
Of the snail trail panel specs "Max power voltage (VMP): 30.3 V" and "Max power current: 8.27 A" Is the 30.3v x 3 the around 100vdc you have and the 25adc the 3 x 8.27?
I'm just not following the benefit of putting panels in series to increase voltage if the voltage of one panel individually is enough to charge a 24v bank on its own.
And I dont plan for this ever to be on grid for any other purpose than using the built in charger of the 2424 if i wanted/needed.

MPPT charge controllers are the most efficient. They are the only solar charging technology that enables one to extract near 100% rated from a panel. They are tolerant of "over-paneling" where your array can be larger than the output power supported to allow for higher outputs for longer periods even if you don't get the peak power.

PWM is the prior charging technology and is limited to about 80% of a panel's potential. It REQUIRES you use the correct nominal voltage panel, and they must all be in parallel. The output current of your array MUST NOT exceed the rated charge current of the controller.

The panels in question are NOT suitable for 24V systems in a PWM application. They are basically an 18V nominal panel. When selecting panels for PWM charge controllers, they will typically have a Vmp of around 36V. If you use these with a 24V system, you need at least 2 in series on an MPPT controlers.

On santans site and have an estimate for $635 for 6 of your panels to my door. If i put those in a 2s3p configuration would that increase amperage going in to my bank while still keeping my input voltage around 60?

Array current is independent from battery current on an MPPT controller. On a PWM controller, they are identical.

With MPPT:

V_array * I_array = V_batt * I_batt

This enables a higher panel voltage and lower panel current as input. Higher voltage and lower current in a circuit has less resistive losses due to voltage drop.

MPPT controllers are rated based on peak Voc and BATTERY charge current, e.g., Victron 100/50 = 100Voc maximum series voltage (also need to allow for cold weather voltage spikes) and 50A of peak battery charge current. Can handle a 50A * 28.8V = 1440W array @ peak 24V charge voltage.

With PWM:

V_array = V_batt (okay, a V_array is a tiny bit higher to get current to flow)
I_array = I_batt

 

[Jimmynik1]

MPPT charge controllers are the most efficient. They are the only solar charging technology that enables one to extract near 100% rated from a panel. They are tolerant of "over-paneling" where your array can be larger than the output power supported to allow for higher outputs for longer periods even if you don't get the peak power.

PWM is the prior charging technology and is limited to about 80% of a panel's potential. It REQUIRES you use the correct nominal voltage panel, and they must all be in parallel. The output current of your array MUST NOT exceed the rated charge current of the controller.

The panels in question are NOT suitable for 24V systems in a PWM application. They are basically an 18V nominal panel. When selecting panels for PWM charge controllers, they will typically have a Vmp of around 36V. If you use these with a 24V system, you need at least 2 in series on an MPPT controlers.

Need to be honest and say I don't understand a good portion if not all of that or the second portion.
If I use a lv2424 like the other guy that basically did what I want to do, will 6 of those panels work in a 2s3p configuration and be alright?

 

[snoobler]

Need to be honest and say I don't understand a good portion if not all of that or the second portion.
If I use a lv2424 like the other guy that basically did what I want to do, will 6 of those panels work in a 2s3p configuration and be alright?

Was trying to educate a bit.

2S3P or 3S2P will work. They should almost perform identically. if you have a long run between your panels and the MPPT, 3S2P will likely be better.

 

[Jimmynik1]

Ok so thats good thanks.
In regards to bms's for my two individual 24v batteries. Would the daly 8s 100a 24v bms, two of them suit my needs? Ive read they each can handle 100a or 2400 watts which seems to go well with my lv2424. Regardless whether they would work or i have to go with a different one, since im going for two 24v 300ah in parallel, i will have two main pos and two main negs off both infividual bms's right? Do those just get put in parallel like anything else would and hooked to my inverter? Then two 8s that can carry 100a dc on their own paralleled giving me 200adc.?

 

[snoobler]

Ok so thats good thanks.
In regards to bms's for my two individual 24v batteries. Would the daly 8s 100a 24v bms, two of them suit my needs? Ive read they each can handle 100a or 2400 watts which seems to go well with my lv2424. Regardless whether they would work or i have to go with a different one, since im going for two 24v 300ah in parallel, i will have two main pos and two main negs off both infividual bms's right? Do those just get put in parallel like anything else would and hooked to my inverter?

BMS should work. I have a personal preference for overkillsolar units.

You would parallel the batteries only at the main terminal.

Consulting the document at "wiring" in link #2 in my signature. Good general wiring info + best practices on bank configuration.

 

[Jimmynik1]

I also have two of overkills in my cart as well. Since i would go with two 8 cell bms that carry 100a each and then parallel them it would give me 200adc available?
And parallel the batts only on the main terminal to make them one big battery and then draw off the far opposites?
It makes sense when in my head when i look at my crude drawing.
- to + on each set of 8 then + to + on the top, bms modules on the sides attaching to both main negatives and both main positives coming down just above them.

 

[snoobler]

Your diagram is not clear. Looks like you'd have 7 unused cells in each battery.



main terminals circled.

 

[Jimmynik1]

Yea I saw it after, my little hast marks were meant to show them being connected in series, not a negative sign, but yours is nicer.
You cleared it up for me, I was stuggling to figure out where my two main - wires from both bms's would meet and it looks like they'd become one and go to my inverter.

So do my numbers look ok on paper?

16 3.2v cells in s/p making a 24v 600ah bank, with 2 8s 100a bms's. charged by 6 250w panels in 2/3 or 3/2, feeding into a lv2424 or some similar hybrid inverter?

 

[snoobler]

Yea I saw it after, my little hast marks were meant to show them being connected in series, not a negative sign, but yours is nicer.
You cleared it up for me, I was stuggling to figure out where my two main - wires from both bms's would meet and it looks like they'd become one and go to my inverter.

So do my numbers look ok on paper?

16 3.2v cells in s/p making a 24v 600ah bank, with 2 8s 100a bms's. charged by 6 250w panels in 2/3 or 3/2, feeding into a lv2424 or some similar hybrid inverter?

Yep.

 

[Jimmynik1]

My man, ty very much.
When doing my panels in either the 2s3p or 3p2s config would i be fine with typical 10 wire as in one config im potentially running 8a x 3 for a 24a max and the other way im at 8a x 2 for 16, both well under the 10 wire 30a rating?
Additionally when i go to hook my inverter to my bank, since whatever inverter i will use will have only one - & + terminal i would of course go from a main positive to the inverter + but then i will have 2 - from both my bms's would i just make those into one and put that one now main - onto the inverter - terminal or put both on there if they reached or either way?
Also confirming 8s2p is fine for my 16 cell total with an end goal of 560ah or so. I read another thread that suggested 2s8p but would be unsure how to do that one.
Also also, on the hybrid all in one types, the unit charges the battery bank off the same line that it draws from? When looking at them i only see one set of +/- going from the unit to the bank but wanted to confirm.
Lastly did some digging and if 8s2p is fine, i found someone who did what I want to do and offered this picture as reference.

 

[iamrich]

When doing my panels in either the 2s3p or 3p2s config

These are the same. I assume a typo?

When doing my panels in either the 2s3p or 3s2P config would I be fine with typical 10 wire as in one config I'm potentially running 8a x 3 for a 24a max and the other way I'm at 8a x 2 for 16, both well under the 10 wire 30a rating?

10awg would be fine as long as the distance isn't insane. I am using 12awg (30') on my three sets of 3 panels in series to the combiner box (`30')

Also confirming 8s2p is fine for my 16 cell total with an end goal of 560ah or so. I read another thread that suggested 2s8p but would be unsure how to do that one.

8S2P = 24v X 2, 2S8P = 6v x 8 One makes a good 24v pack, the other makes a oddly powerful 6v battery

Also also, on the hybrid all in one types, the unit charges the battery bank off the same line that it draws from? When looking at them i only see one set of +/- going from the unit to the bank but wanted to confirm.

Yes the same lines feed the battery from the solar, and feed the inverter in all in ones. Also the solar feeds the inverter directly in most all in ones.

 

[Jimmynik1]

These are the same. I assume a typo?

yes lol meant 2s3p or 3s2p

10awg would be fine as long as the distance isn't insane. I am using 12awg (30') on my three sets of 3 panels in series to the combiner box (`30')

ok good, is typical panel wire that most sell with the pre attached connecters 12 or 10?

8S2P = 24v X 2, 2S8P = 6v x 8 One makes a good 24v pack, the other makes a oddly powerful 6v battery

yea i didnt get that either, just saw it on another thread and was confused
so im good with 8s2p?

Yes the same lines feed the battery from the solar, and feed the inverter in all in ones. Also the solar feeds the inverter directly in most all in ones.

ok awesome thanks

 

[Jimmynik1]

24volt 560 amp lifepo4 2bms or 1 large bms??

already ordered but may make another. bank is it better to have 2 24v280ah batteries and connect parallel to get 560 amh will the 2 bms interfere with each other? or get a 16s bms??

diysolarforum.com

this was the thread i was talking about

 

[iamrich]

ok good, is typical panel wire that most sell with the pre attached connecters 12 or 10?

You can get 10 or 12awg with MC4 connectors. I think you will be more than fine with 12 unless your run is really long. I actually got a 100' set and cut them down to ~33' each and added MC4's

 

[Jimmynik1]

Ok great thanks. Im not going far at all. Maybe 30' 35' max depending if i put my bank in my garage or detached garage. If the bank goes in the detached where the panels are on the roof of then im looking at 15' or so.