Matching Batteries to a system and array

[Friggs]

This is my first post shortly after registering.
I recently obtained four Power Safe SBS190F 12v AGM 190ah batteries that were used as a back up system and were hardly used. I want to used them along with a solar system at my cabin.
I presently use propane lights, refrigerator and also use a generator at times.
I was thinking of matching these batteries to a 24v SCC and use used 250w solar panels. I was thinking about a Growatt or Mpp Solar 5 in 1 system. I like the option of AC input with my generator and the lower price.
Just wondering what size SCC I need and how many panels to match the batteries.

Thanx friggs

 

[pollenface]

4x190 = @ 50% depth of discharge is 4.56kwh

As a general rule of thumb one might size their array to 4.56/4 (4 sun hours) which gives an array size of 1140w

in 24v a 40a amp SCC would be sufficient

 

[Friggs]

Thanks for the quick response Pollenface. I got my eye on 5 panels at 240w 37.2voc each giving me 1.2kw. I guess I should string them in parallel because I have some shady spots or how should I string them ?
I’m placing them on a south facing roof and could buy one or two more if it would help.

 

[pollenface]

with a bit of shading, you'd probably do best to run them in parallel, you could even get away with a big PWM unit without too much efficiency loss with the lower voltage panels (37voc pv & 24v battery bank). If you do select a PWM, it's a general rule of thumb to oversize it by 125% of your array's short circuit current (Isc) in which case a 60'ish PWM would be in the ballpark.

 

[MichaelK]

As a general rule of thumb, most lead-acid batteries get optimal charging at around 1/8th of C, though some AGMs can go higher, up to about 1/5th C. Assuming you wire your batteries 2S2P, you'll make a 380Ah 24V battery bank. One thing to think about though is that some batteries designed for backup useage, don't do well with daily cycling. If they don't potentially last that long, you might be looking at a battery replacement in just a few years.

Five panels is an odd prime number, so hard to wire for solar. Assuming you want to charge at 1/8th C that works out to be... (380Ah/8) X 25Vcharging X 1.175fudgefactor = 1395W of panels. Call that 6 of the 250W panels and call it done. Those 6 panels will max out at (1500W/25V charging) X 0.85fudgefactor = 51A, so a 60A charge controller would be appropriate.

Keep in mind though that AiO units like growatt and MPP have a charge controller built-in, so you need to check the CC specs of that particular unit. Let's say you wire those six panels in a 3S2P configuration. That most likely will be a Voc of ~114-116V at room temperature, with ~7-8amps of current per string, or a max of 14-16A. How low do your winters get? At freezing, those panels will put out around 120Voc. I believe that most of the MPP units have a Volts maximum of 145V, so pay close attention to the Voc of what you put together. Use this string calculator to check your max voltage.

MidNite Solar - Classic Sizing Tool.

MidNite Solar is the industry leader and manufacture of quality Renewable Energy System electrical components and E-Panels.

www.midnitesolar.com

 

[Friggs]

Thanks Michael for the response. I’m building this solar system for my cabin in central Ontario Canada. We only use it mostly in the spring and fall for 3-4 days. The winters can get very cold just like your upper Michigan. I’ve decided to go with 6 Trina Solar panels 240w, 37.2 voc 7.89a 3S2P on the roof top.
I think your right about these AGM batteries being used as a backup bank but I got them for very cheap plus I’m a novice at all this solar stuff. I found that calculator you linked me to very informative and tried it on 3S2P. I’m assuming those settings from the string calculator are for me to implement into the settings on the SCC especially during the winter.
Also, I’m not certain if I should take these four AGM batteries home for the winter and keep them in the basement till spring or leave them at the cabin as is or is there anything or suggestions I should do.

 

[MichaelK]

Also, I’m not certain if I should take these four AGM batteries home for the winter and keep them in the basement till spring or leave them at the cabin as is or is there anything or suggestions I should do.

I think your best option is just leave the system in place over the winter. Fully charged batteries are good to at least -40F, and I've read, but can't confirm down to -70F.

The one issue to deal with is winter snow cover? How much snow will you be expecting to cover the panels in winter? I think you can assume if your panels get snowed in, and there's no charging at all, then the batteries will start draining. How far they have to drain before they are ready to freeze at your place I can't say. If the panels get snowed in, it might be the better option to bring them home.