Need Battery Advice

[TC McClure]

I've been off grid since 1985 and, of course, started and continued with flooded lead acid batteries. My 24V system currently produces 4-5 KWH per day which is stored in 20 6 volt golf cart batteries and supplies our need with minimum back up generator operation during the winter months. At current prices, my battery bank costs about $110 for each battery and a bit over $2200 for total replacement. I have always replaced the batteries individually as the cells lose specific gravity numbers. The batteries generally last about 7 years.
I'm giving some thought to upgrading to the new lithium batteries that so many of you use.

Two questions: What would be the approximate cost of replacement of my current batteries? Would the summer heat in my PV shed (100+ degrees occasionally) be a deterrent to using the new batteries?

 

[timselectric]

Two questions: What would be the approximate cost of replacement of my current batteries? Would the summer heat in my PV shed (100+ degrees occasionally) be a deterrent to using the new batteries?

Would need to know what size your current batteries are. (amp hours)
And while they will operate at that temperature. I wouldn't recommend it. You should add some type of cooling.

 

[BentleyJ]

Cost varies a lot between battery brands. For example a 5.1kWh rack battery, EG4 brand, is $1,500 Plus or Minus. That's $300 per kWh for an off the shelf ready to go battery. There may be some misc. hardware cost of changing lugs or some cables depending on how the connections are made.

The temp is going to be a problem. Most Battery Management Systems will cut out at 100 to 105F. Is it possible to add an evaporative cooler to the shed and/or insulate it. In those situations a heavy block wall construction with fully grouted cells and insulation is the best way to create a passive temp stable environment.

 

[Rocketman]

Also, does it freeze where you are? You can’t charge a lithium battery below 32deg F without ruining it.

Insulation the building with the batteries can solve both issues. (Or putting them in a conditioned space - basement).

Also, does your solar charge controllers have a lithium setting or can they be programmed for a lithium setting.

The GC batteries I have used were about 220ah - so is your system about 1100ah at 24v. That would be four or five of the EG4 rack systems above.

Good luck

 

[TC McClure]

Thanks for the advice. Due to the concerns you raised about heat, I will stay "old school" and keep my lead acid batteries.

 

[DIYrich]

I have always replaced the batteries individually as the cells lose specific gravity numbers.

I was under the impression you don't want to mix old and new lead acid batteries.

 

[TC McClure]

The battery producers probably agree with you. At the beginning of my off grid journey I would replace the entire bank (24 at that time). As I got older, the task of replacing the batteries was too much work so I experimented with just replacing those batteries that were diminishing. I have not noticed any issues with doing this and it's a lot easier on the body. I even take it a step further. I have a stand alone 24V swamp cooler that I power with my old panels and the worst batteries. That also works fine. In the interest of full disclosure, I live in Southern California which is PV paradise. My batteries are usually full and floating by 11AM. I measured the specific gravity in my batteries yesterday. Only one was diminishing. It was purchased in 10/2015 and the cells measured 1300, 1175, 1300. Not bad for almost 8 years.

 

[Steve_S]

A 24V/100AH LFP has 2560Wh of usable energy.
LFP can discharge from -20C/-4F to +55C/131F
LFP can take Charge from 0C/32F up to 55C/131F.
LFP Battery Packs can be built with warmers or can be purchased with built-in warmers.
LFP Battery Packs do not require venting (no off gassing) and can be stored within an insulated warmed container if desired.

Unlike Lead Acid, LFP has no aging issues like lead, you can add packs in parallel overtime without any losses. This allows you to grow your battery bank without losing capacity due to one weak battery pack in the bank.

There are many commercial producers that do make 24V Battery Packs that range from 50AH to 300AH and the costs can vary a great deal. It is NOT Suggested to use 12V Batteries in series to make 24V, it is best to stay at the Native Voltage. Will has reviewed several and the video's are posted.