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bajapedro
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[*] posted on 4-13-2018 at 04:06 PM
what batteries to use


Putting in new solar system in new casa. Putting up 2300w array with outback controller (MPPT 80 amp) and considering going with 2v 672AH AGM batteries. will need 12 for 24v system. Have used lead acid in past, but have to water then in summer time when not there. Anyone using a similar system or (dare I ask) have an opinion here?
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Bob and Susan
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[*] posted on 4-13-2018 at 05:02 PM


why use a 24v system?
why not a 12v system?

why not use 12v batteries?
why 2v batteries

there are lots of 12v batteries in baja
all cars use 12v batteries
how many 2v batteries can you buy in baja?

what if ONE 2v battery dies?
isn't your system DEAD?


you should read about "amp hours" and how they are figured
its not 70 degrees in the summer
i think the amp hour numbers the battery manufactures give you are NOT REAL



[Edited on 4-14-2018 by Bob and Susan]




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willardguy
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[*] posted on 4-13-2018 at 05:05 PM


:lol:you knew that was coming!
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Bob and Susan
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[*] posted on 4-13-2018 at 05:07 PM


yup...I hate batteries




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rts551
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[*] posted on 4-13-2018 at 06:53 PM


I know you said you did not want to use flooded acid batteries, but we finally switched over to 8D batteries because they can easily be purchased in Mexico and are very happy. Getting harder and more expensive to bring batteries across the border.
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bajapedro
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[*] posted on 4-13-2018 at 06:58 PM


Bob, clearly you are not off grig. 24v allows me to have more array to controller and the higher the voltage, the presumptive higher efficiency.
the advantage, I see to a 2v battery is the amp/hr capacity. Yes, 2v system requires 12 batteries in series, (for 24v system) and yes I would assume if one fails your voltage will drop by 2 volts. But 12 2v batteries at 648 AH each is about 7700 AH of storage, which means less deep cycling from battery, which I am hoping means less sulphide build up on plates, which I hope means longer battery life. AGM batteries are maintenance free, and I would not need to water them. (which is an issue for me)The question I was hoping to get opinions on is if anyone uses this type of system, and how it works, or is my head in the clouds on this, not whether to use solar or grid tie, as this in not an option where I am. And, yes Bob, you Can get 2v batteries in Baja, or can bring them down.
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[*] posted on 4-13-2018 at 07:22 PM


open a 12v inverter then open a 24v inverter
circuit boards inside...not much difference

if you lose 2v out of your 24v bank you have 22v
at 22v your inverter WILL NOT work

7700 ah of storage is a made up number
read how they figure this number

if you use higher wattage your batteries voltage lowers
then shut down the inverter

the reason to have many batteries is not storage but the ability to handle large loads

rethink your system
don't believe the solar salesman

think "battery failure" and replacement
think like a survivalist
you're not in Kansas anymore




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willardguy
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[*] posted on 4-13-2018 at 07:52 PM


my advice would be to throw that question out to the folks over at Northern Arizona Wind and Sun.....not someone with a room full of paralleled group 27's.
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[*] posted on 4-13-2018 at 08:16 PM


Putting batteries in series does not increase the amp-hours of the battery bank. It does increase the kW-hours (amps x volts) so the total amount of stored energy goes up. Higher voltage can increase efficiency since the system's voltage drop will potentially be less and you can use smaller cables. Also it is bad practice to parallel more than two sets of batteries as the batteries will not charge evenly.

I think you're on the right track. Just be sure to set your charge controller for AGM type batteries and the battery mfg recommended charge parameters.

BTW, all normal lead-acid batteries are made up of 2-volt cells. A 12-volt battery just has six small cells contained within a single case.
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[*] posted on 4-14-2018 at 06:26 AM


I use the large 2v cells like you are thinking about and am very happy with them. Get good ones and you won't go wrong.



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[*] posted on 4-14-2018 at 06:48 AM


Not exactly your size, but I've come to a similar conclusion. AGMs for me.
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[*] posted on 4-14-2018 at 04:54 PM


I'm with Bob & Susan, - sort of.

With 24V system if one 2V unit dies, you're up the creek without paddle.

AGM is a good choice for maintenance-free winter-only home, yes.

Edit-PS:

one more thing. Your cycle will not be shallower with these units.

This is 2V unit, so 672 AH (or was it 648?) equals to 112 AH in normal 12V lingo. So, you don't get 7-something thousand of AH, but only 1-something thousand AH @12V.

This is easier to understand if you convert capacity into WH.

[Edited on 4-15-2018 by Alm]
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[*] posted on 4-14-2018 at 05:34 PM


the reality is...

if you don't have enough batteries

you'll get up in the morning turn on the coffee pot
...pop in the toast...
wash your cup and the water pump will pressurize
and...
the inverter will shut OFF

also the OP is putting up a 2300w solar panel array
doesn't he need 2 charge controllers?
whats the limit on an mx80 without burning it up?

does someone sell 2v batteries in BCS?
or do they just buy them up north... import...ship them down...and mark them up?








[Edited on 4-15-2018 by Bob and Susan]




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[*] posted on 4-14-2018 at 06:47 PM


Quote: Originally posted by bajapedro  
Bob, clearly you are not off grig. .


what are you talking about. he is running more stuff off grid than anyone I know. and he will give good practical advice if you care to listen.




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[*] posted on 4-14-2018 at 07:07 PM


Quote: Originally posted by Bob and Susan  
the reality is...

if you don't have enough batteries

you'll get up in the morning turn on the coffee pot
...pop in the toast...
wash your cup and the water pump will pressurize
and...
the inverter will shut OFF

also the OP is putting up a 2300w solar panel array
doesn't he need 2 charge controllers?
whats the limit on an mx80 without burning it up?

does someone sell 2v batteries in BCS?
or do they just buy them up north... import...ship them down...and mark them up?








[Edited on 4-15-2018 by Bob and Susan]


If he is using the flexmax 80, input max is 2500 watts.

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rts551
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[*] posted on 4-14-2018 at 07:13 PM


BajaPedro is correct when he says that by running a 24 volt system it allows him to run a larger panel array 2500 watts as apposed to 1250 for a 12 volt system...

but his calculation on AH is totally wrong. He will still only have a maximum of 672 AH because the batteries are run in series.
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4-14-2018 at 08:47 PM
Alm
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[*] posted on 4-14-2018 at 10:40 PM


rts551, in terms of 12V he will have 1,344 AH bank. Or 672 AH @24V, but it's confusing talking AH for anything but 12V.

More universal measure is Watt-Hours, it's used for all other voltages like 48V e-scooters or 120V grid power.

"whats the limit on an mx80 without burning it up?" - it depends, Bob ;)...
Outback 80 is rated to max 2,000W array at 24V bank. MPPT controllers can handle panel wattage a little over its rated input without going up in smoke. 10% more maybe. Input voltage limit 150V is not to be exceeded, this is a no-no.

[Edited on 4-15-2018 by Alm]
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[*] posted on 4-15-2018 at 06:12 AM


Quote: Originally posted by bajapedro  
Putting in new solar system in new casa. Putting up 2300w array with outback controller (MPPT 80 amp) and considering going with 2v 672AH AGM batteries. will need 12 for 24v system. Have used lead acid in past, but have to water then in summer time when not there. Anyone using a similar system or (dare I ask) have an opinion here?


Try asking your question on solarpaneltalk.com. The site has forum for off grid solar

And remember that sometimes it is best to hire a specialist and let a pro do it right :light:





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[*] posted on 4-15-2018 at 06:24 AM


One more opinion......
I’ve been using AGM batteries for 20+ years. I feel, especially if you have a part time residence, AGM is the way to go. Now that I’m full time, I still use them. I hate maintaining batteries. For a part time home, they can sit for up to 9 months without loosing significant charge, and you don’t need to hire someone to take care of them. I’m getting about 8 years out of Concorde AGM’s.

In my opinion, I think Bob is correct about 2 volt batteries. I’d go with a couple banks of 6 or 12 volt batteries. When your batteries get older and are near failure, you may not recognize until it’s too late that a battery is failing. Recently I lost a battery and was able to eliminate one bank of batteries while limping along on the other bank (keeping my refrigerators full of food running) until I was able to buy new batteries. If you use two volt batteries, and one fails, your entire system will be useless. If you do use 2 volt batteries, as they get older, you will have to be very diligent about monitoring them so you can replace the system BEFORE it fails.

I also have two parallel inverters. Which has saved me twice. Two times I’ve had an inverter fail and was able to continue running on the remaining inverter until the failed inverter could be repaired/replaced. It takes an average of 4 weeks to get an inverter repaired (Outback).

In a new system, I would go with 24 or 48 volts. I had a 12 volt system for years and recently upgraded to 48 volts. The main advantage I see is that the inverter runs MUCH cooler, and heavy loads don’t cause any dimming/flickering of lights, or draw down on the AC side. The conversion from DC to AC is more efficient with higher DC voltages. Also, higher voltage systems allow you to combine more panel amps on one charge controller, so future expansion may be possible without buying a second charge controller.

Don’t scrimp on panels and batteries. Calculate what you think you need and add 20-25 percent. You ALWAYS, ALWAYS use more power than you think you will. Also, as Bob mentioned, summer heat decreases the efficiency of your batteries/panels.

Now…if you want to get something much less expensive batteries and available in Mexico, many homes in our neighborhood are using LTH deep cycle batteries. They are not AGM and do require maintenance, but they are readily available and everyone I know that uses them say they perform better and last longer than the Trojan wet cell batteries.
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[*] posted on 4-15-2018 at 08:26 AM


Looks like there is more than one way to skin a cat here. There is more than one right answer so no need to get your back up. I would like to throw Lithium ion in to the mix. Some interesting things are being done in this area with recycling to bring down costs. If I were considering an off grid system, which I am, I would be doing some serious investigation in this area, which I am. I am gathering up and maintaining all the 18650's I can at the moment. This is "fun" project for me but you may want to just throw money at is and buy a Tesla powerwall. Despite the increased cost it is the future in energy storage. Errr. except that some people are doing really interesting stuff with capacitors. When all is said and done, more will be said and more will be done.



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