Battery Dilemma- advice needed

SDCacti

As part of a work assignment I was tasked with replacing our off grid system’s battery bank which was 6 x 210ah 12v batteries in series parallel making 24v. Long story short a sales person determined we should get a 300ah 24v LifePo4 battery and all would be fine. Well 3 months later we are notified the manufacturer cannot fulfill this order and recommended they provide us with 3x100ah batteries ( in parallel as an alternative ). From research I’ve done this isn’t recommended if avoidable and if so- to do this with a BMS. Below I’ve listed the equipment we have. Can anyone recommend a comparable battery that will meet or exceed the battery storage we had? And is Lithium a good alternative with this equipment or should we just go back to SLA batteries?  Thank you!

(6) 190j PV modules wire 2 in series by 3 in parallel - 15.0A @ 76.0VDC

(6) Deka 8G4D, 210AH 12vdc nominal battery. 100 hour rate wired 2 in series by 3 in parallel, 630AH @ 24vdc nominal

24vdc 1500 watt inverter

Morningstar ProStar MPPT 40M controller 

mike95490

It depends on the batteries, many drop-in replacements have a primitive BMS, some scale well with more batteries, some not.

BB.

A few questions.... Where is the system located (nearest major city)? What are you daily loads? Is this a backup system, or daily use?

More or less, a daily use system would suggest a 10% to 13%+ rate of charge... I.e., 630 AH would be ~63 amps suggested minimum rate of charge:

• Solar Panel Watts, minimum: 63 Amps * 29.0 volts charging * 1/0.77 panel+controller deratings = 2,373 Watt array (10% rate of charge)
• 2,373 Watt array / 190 Watt panels  = 12.5 ~ 12 or 14+ panels
• 190 Watt panels * 6 = 1,140 Watts (closer to 5% rate of charge--Lightly used system)

For batteries--I like to reduce the number of cells (less to check/water), and reduce the number of series strings... For example:

https://www.solar-electric.com/deka-8l16-pro-master-deep-cycle-battery.html

6 volt @ 370 AH --- 4x in series (24 volts) and 2x parallel (740 AH)--If you want to stay with Deka batteries.

If you want a sealed battery--AGMs are a possibility--For example, Full River has several sizes that are lower voltage (6 volt and 2 volt), and higher AH capacity too...

https://www.solar-electric.com/residential/batteries-battery-storage/deep-cycle-batteries.html?manufacturer=540

I like to size the battery bank for the loads (say 2 days of storage, 50% nominal max planned discharge or 4x daily loads) as a good starint point. And look at 5% to 13% rate of charge--with 10%+ rate of charge for daily use (and also double check loads against hours of sun per day by season for location of use).

More or less, keep the battery bank on the "smaller side" (batteries are heavy, expensive, and somewhat easy to damage through under charging/over discharging), and add more solar panels (panels are historically cheap, and have a 20+ year life)... Basically, keep the battery bank "happy".

In times past, when batteries were "cheap" and solar panels were expensive--Then people thought that adding more batteries to a system gave them more power--But unless you have a generator for times of bad weather/winter loads, too small of solar array would usually under charge and give poor battery life.

If you are using much of the 1,500 Watt inverter's capacity--Then a ~300 AH @ 24 volt battery bank (flooded cell lead acid) minimum suggested (to support inverter's current/surge current requirements).

But without knowing your daily loads--Still flying blind here.

-Bill

SDCacti

I really appreciate you guys taking the time to educate me on these solar ins and outs. One last question to the community. Is anyone of the belief that LifePO4 batteries can be placed in series and in parallel? The battery we originally were sold on was a single unit with basically 1 battery. Has to be 24v volt and about 300ah for this application,.currently we have a1500wt inverter a pro-star 40m mppt controller. budget is around $45oo.  Ive read that with these types of batteries using 12 volt in series parallel is not a good idea/may create issues. Lastly any brand you guys recommend over any other? thx

Raj174

From what I've read, all of this type battery can be paralleled, but only recommend placing them in series if it is approved by the manufacturer. These batteries balance at the top of the charge, but they have to be fully charged before the bank is assembled. I have a friend who has been using 4 Battle Born 12V 100AH batteries arranged in a series parallel configuration with out issue for about 2 years.

My own LFP bank is DIY composed of 32 180AH cells arranged in series parallel. The configuration is called 2P16S for 51.2V 360AH and cost about $4000. They were from China through Alibaba. Needless to say DIY is less than half the price, but one would need to be willing to invest the time and patients to learn how to balance and configure them properly. And although I don't use one, a BMS is recommended.

Rick

SDCacti

Raj174 said:

From what I've read, all of this type battery can be paralleled, but only recommend placing them in series if it is approved by the manufacturer. These batteries balance at the top of the charge, but they have to be fully charged before the bank is assembled. I have a friend who has been using 4 Battle Born 12V 100AH batteries arranged in a series parallel configuration with out issue for about 2 years.

My own LFP bank is DIY composed of 32 180AH cells arranged in series parallel. The configuration is called 2P16S for 51.2V 360AH and cost about $4000. They were from China through Alibaba. Needless to say DIY is less than half the price, but one would need to be willing to invest the time and patients to learn how to balance and configure them properly. And although I don't use one, a BMS is recommended.

Rick

Rick,

Thank you for your input. That's exactly what I did, was contact the manufacturer of these batteries (Allied). They told me they do not recommend placing their batteries in series. Parallel as much as you want- But series parallel for an off grid system is not recommended. If this was my own offgrid system at my house I would be more willing to experiment but this system has to be reliable 24/7 to actuate a valve to distribute reclaimed water. Failures would be frowned upon. What I would like for this system is simplicity. 24v batteries- just 1 or 2. Now its a matter of convincing the vendor for these batteries that this is not going to meet our needs. Are Battle Born Batteries a good option high quality Lithium iron phosphate?

Raj174

I bought my first set of LFP cells 5 years ago from Electric Car Parts Co. in Utah. They now sell a range of preconfigured LFP storage batteries such as this 24v 300ah battery with built-in BMS and 10 year warranty that's easily within your budget.

https://www.electriccarpartscompany.com/7500wh-24v-300ah-lifepo4-lithium-battery-solar-energy-storage-system

The company has been in business since 2007, and Carl, one of the owners, is very knowledgeable with the tech. If interested, email him for more information. Here's the link.

https://www.electriccarpartscompany.com/About-Us

Rick

SDCacti

Raj174 said:

I bought my first set of LFP cells 5 years ago from Electric Car Parts Co. in Utah. They now sell a range of preconfigured LFP storage batteries such as this 24v 300ah battery with built-in BMS and 10 year warranty that's easily within your budget.

https://www.electriccarpartscompany.com/7500wh-24v-300ah-lifepo4-lithium-battery-solar-energy-storage-system

The company has been in business since 2007, and Carl, one of the owners, is very knowledgeable with the tech. If interested, email him for more information. Here's the link.

https://www.electriccarpartscompany.com/About-Us

Rick

Awesome. I sent him an email for a quote. great pricing and warranty! Have a great day!