Four batteries or eight?

706jim
706jim Solar Expert Posts: 521 ✭✭✭✭
in Off Grid Solar & Battery Systems #1
After 19 seasons, I replaced my 12 GC's with 8 Trojan L16's, the 370 A-h version. Now after 9 seasons, I have one battery with a dead cell and another reading higher charging voltage than the rest which sort of indicates this one may be on its way out. My bank has a marine splitter switch where I can run either bank (of four L16's) separately or combine them both. After discovering the failing batteries, one string is still working fine and I'm wondering when the eventual replacing is done if I should go with a single bank of four L16's or two like I have now. My array is about 2300 watts at 24 volts and usual power consumption is about 6 Kw-hr/day.

More batteries = more capacity but slower recharging and higher cost.

Fewer batteries = less capacity but faster recharging and lower cost.

My array generates 40-60 amps on a sunny day which would be within the suggested 13% rated charge current for four batteries, but a little shy for 8 of them. 

Since my batteries have to endure winter temperatures for at least 3 months, well below freezing FLA is my only real option.

Yes I did equalize the batteries regularly check and add water and avoided extreme discharges.

As many are aware, batteries now make up the most expensive component of an off grid system. L16's have more than doubled in price since 2015.

I've been at this for 30 years now, kinda figured I knew it all, but am interested in suggestions from others who've been down this path.
Island cottage solar system with appriximately 2500 watts of panels, 1kw facing southeast 1.3kw facing southwest 170watt ancient Arco's facing due south. All panels in parallel for a 24 volt system. Trace DR1524 MSW inverter which has performed flawlessly since 1994. Outback Flexmax 80 MPPT charge controller four 467A-h AGM batteries. Insignia 11.5 cubic foot electric fridge 1/4hp GSW piston pump. My 31st year.
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  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,174 ✭✭✭✭
    #2
    A customer just replaced his 24v 800 ah, 11-year-old L16 off-grid battery bank in Wrangell, Alaska. He went with a single string of twelve 2v 900 ah GC2-tall AGM batteries because L16s have gone up so much. 
    Not cheap at around $400 each, but 12 of them were essentially the same cost as 8 L16s of the same type that he had - and he gained 100 ah. He prefers a single string and he wanted to stick with AGMs because the system is unattended when he is out of town working. 
    With your long history and experience, you can judge if the 4 batteries will have enough autonomy to meet your needs.



    I always have more questions than answers. That's the nature of life.
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