Maximum battery capacity

[asdex]

Hi, I have the opportunity to get some 100 AH 12 volt batteries and was wondering what the maximum AH capacity I should have with a 2kW PV array. The batteries will need to be two in series then all paralleled up for a 24 volt bank. Not ideal I know but they are near new and a $1 each. I was thinking 20 batteries for a 1000AH bank??
I don't remember the battery type at the moment as they are in service but they are sealed, 12 year lifespan types.
Thanks,

[Sunking]

You should pass on using parallel batteries. Just asking for trouble.

Anyway depends on controller type being PWM or MPPT.

PWM assuming you use 76 cell panels (You must use 76 cell panels for PWM at 24 volt battery) range is 400 to 660 AH

For range is 660 to 1000 AH

[inetdog]

If they are GEL type sealed batteries, they are probably not right for your application, as their maximum charging rate is probably quite low. (~C/20)
A very simple rule of thumb for AGM type sealed cells is not to exceed C/2 charging and to be able to provide at least C/4.
Based on that you could have a battery bank of between 160AH and 320AH at 24V.
You can go larger as long as you make sure that the batteries get fully charged (100%SOC) regularly.
If you want to go to 300AH with the batteries you describe you will have to put three strings in parallel. That is not very good design and you will have trouble keeping the batteries balanced as you charge and discharge them.
Finally, the fact that they have a nominal 12 year lifespan (in float service, never being used?) does not tell you what kind of remaining useful life they have, since that will depend on how they have been treated.
Still, at $1.00 per battery it is hard to go too far wrong. Except by designing a system around batteries you may not be able to inexpensively replace down the road.

[asdex]

Thanks, I just looked at the batteries and they are HAZE HZB12-100 AGM batteries. 12v 106AH (C20 To 1.75VPC). I have 72 available. The Blub says: 12 year design life for stand by power applications. They are 2 years old and in a UPS. I think I'll always have to have batteries in parallel unless I get 2 volt cells but they are much too expensive. Otherwise it would be four say 660AH batteries if I can find them. My controller is a Midnite Classic 150 so MPPT.
Cheers,

[Logan005]

It is likely those batteries were swapped out because there are a few bad units in the bunch, you would need to do testing to weed them out and to re pair them into balanced banks.

[asdex]

No, these are the original batteries when replaced two years ago. I purchased them and oversaw they fitting.
Cheers,

[inetdog]

My biggest concern is that the battery data sheet lists them as for standby (UPS) use. It gives charging voltages for both float and cyclic use, but gives no information at all about the battery life (number of cycles) in cyclic (RE) use.
It also gives no indication of the maximum charging current (just the charging voltage).

[Logan005]

No, these are the original batteries when replaced two years ago. I purchased them and oversaw they fitting.
Cheers,

so they were cycled for 2 years? or just standby? or reserve replacements?

[asdex]

Hi, they have been standyby batteries, just kept charged. I don't think the UPS has ever need to supply power directly from the batteries ie a power outage.

[Logan005]

If you charge and take some standing voltage readings you can match them into banks. but how do you plan to use them? cyclical? Standby? How do you plan to maintain them?> is Grid avail for maintenance? you would be much better off building a 48 volt with the best of the batteries and get a new inverter. not sure what you wish to accomplish with old batteries?

[Logan005]

those batteries were mildly cycled during periodic system testing and every time the grid lapsed. depending on what was connected depends on what level of discharge. hence level of damage they have, you should load test each of them as well. simple carbon pile heater and VU meter,.

[asdex]

Hi, thanks for your reply. We use our bank mainly for lights, water pump, fridge and freezer. We have no grid power. The inverter, an Outback FX2420 was expensive and we don't want to replace it. So will be cycling the batteries daily. Our existing bank is 440AH and discharges to about 95% each night. They are budging quite a bit at the ends and sides.
The AGM batteries won't have been discharged much at all.I can load test them.

[Logan005]

What is your current set up? 12v or 6v batteries. size? how old? charge controller? old gel stand by batteries may have some life left in them, you will only know after standing volt and load tests. Bulging batteries sound like over charging, are you sure your Charge controller is set correctly? The reason I mention going to 48 volts, based on your chosen used 12v batteries, 48 would give you the most Amp hrs with out paralleling batteries is not recommended

[Sunking]

No, these are the original batteries when replaced two years ago. I purchased them and oversaw they fitting.
Cheers,

OK you fell for Telecom Tricks and games. I know I used to do it all the time especially around Xmas.

First those are not Deep Cycle batteries for daily cycling. They are made for Emergency Standby use. When new they have about 150 to 200 cycles. The data center turned a liability into a asset of not having to pay someone to haul them off to the junk yard into some pocket cash by selling you used spent junk batteries.

[asdex]

Yes my batteries were over charged for a couple of weeks due to using incorrect voltage settings in the controller. They are 8 x 6 volt. 220AH 2007 vintage so they are about out anyway.
It sounds like the HAZE batteries are the wrong sort so will scrap them.
Thanks for your comments.
Cheers,