What size / type my next battery bank should be?

Discussion about the OutBack Energy Cell Batteries
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papapanda
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Posts: 3
Joined: Wed Jun 21, 2017 1:43 pm
My RE system: VFX3048E/FM80/Mate3 1.2KW solar cells 4x220Ahx12V battery bank.

What size / type my next battery bank should be?

Post by papapanda » Sun Jun 10, 2018 2:21 am

Hi,

What size / type my next battery bank should be ?


14 months ago i've bought an off-grid solar system (Outback VFX3048E + 6x190W Amerisolar mono panel + FM80 solar charger). 8 months ago (as the winter was coming) i've bought 10 more Amerisolar 200W mono solar panels. Now I have 16 solar panels(grouped by 2) . My battery bank is composed of 4 Newmax Gel batteries (220Ah(C20)) http://www.e-solare.com/documents/attri ... 5545_4.pdf, having a total of 10,560 Kwh stored.

My mean daily consumption is ~ 6-8 KWh
During this 14 months the Diesel Generator was started ~ 400 hours (in the first period when the system was reaching 48V it autostarted the generator. Daily in the winter period, and in the last 2 weeks, also for 1h in the night.)
The configuration for the batteries is: 57.6 Absorb time (2 hours), Float Voltage 52.8V
The max current limit was set to 40A

Current status : 1.my batteries are reaching daily the 50C (protection stops the charging until they cool down)
2.the volage drops bellow 42V in the night and the systems shuts down.

I am thinking on replacing the battery bank with a 3 x 4 x CROWN CR 12V - 265 Ah/C100 ( 215 Ah/C20 ) acid lead battery, this would mean a stored capacity of 30KwH, taking into account my mean consumption of 8kW, this mean I should not reach 50% DOD, so it's feasible to say that the batteries should last 4-5 years.

Do you think my proposed battery bank is large enough? Are there any good alternatives?

sparksalot
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Re: What size / type my next battery bank should be?

Post by sparksalot » Sun Jun 10, 2018 5:07 am

Buy the biggest single ahr at the lowest single voltage...eg 2 volt each X 24 for a single string of 48 volt batteries.
A reconditioned 48 volt tow motor or fork truck battery is such, but only if it is practical to move the large heavy single unit into location . These can weigh in excess of 2000 lbs but have only 2 connections. Otherwiise 24 single 2 volt cells to move but have 25 connections after moving all to location.
Either choice has 20% DOD, 24 vent caps total for SG readings and water addition...not 72 vent caps total like 3 x 4 x 12volt that you are considering..

Parallel battery strings are difficult to get charged equally and much more problems and work then having one large series string.

My next battery bank will be Lithium... Zero caps, zero SG readings, zero water, 2 connection, smaller footprint, 80-100% DOD and 15+ year life. :cool:

papapanda
Forum Junior Member
Posts: 3
Joined: Wed Jun 21, 2017 1:43 pm
My RE system: VFX3048E/FM80/Mate3 1.2KW solar cells 4x220Ahx12V battery bank.

Re: What size / type my next battery bank should be?

Post by papapanda » Sun Jun 10, 2018 12:08 pm

thanks sparksalot for your answer.

what I've understood that I should do : go with a lower voltage per battery, and put all the batteries in a single series to reach 48 V.

Lithium is not an option for me, not at the current price. (I'll wait for Tesla & others to force the drop of prices. :smile: )

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Kurt Lundquist
Alpha Energy Engineering
Posts: 1389
Joined: Tue May 31, 2011 7:23 am
My RE system: VFX3524, Mate3, 200Ah 24V AGM Battery Bank
Location: Arlington, WA

Re: What size / type my next battery bank should be?

Post by Kurt Lundquist » Mon Jun 11, 2018 3:18 pm

Have you thought about adding move PV? With your current array, I estimate you need at least 4 sun hours per day to charge batteries for an 8kWh load (based on 75% PV harvest vs STC and 80% battery charge efficiency). PV is cheap compared to batteries. Either way, it is time for a new bank. 625Ah (C/20) gives you almost 2 days of autonomy at 50% DoD so it is a big improvement on your current bank. I agree with Sparksalot that minimum string size is the best chance for long battery life. Keep in mind flooded batteries are like a pet. If you give them constant love they will love you back. If you neglect them they will neglect you. Where do I come up with this stuff?? Anyway, it is important to be dedicated to checking specific gravity and running the generator for extended periods to equalize charge the cells. I couldn't do it but I am grid-tied so AGM's make sense for me.

-Kurt
Kurt Lundquist
Renewable Energy Project Engineer
http://alphaenergy.us/

papapanda
Forum Junior Member
Posts: 3
Joined: Wed Jun 21, 2017 1:43 pm
My RE system: VFX3048E/FM80/Mate3 1.2KW solar cells 4x220Ahx12V battery bank.

Re: What size / type my next battery bank should be?

Post by papapanda » Mon Jun 18, 2018 9:28 am

Hi Kurt and thanks for the answer.

Adding more PV is not needed for the moment in my opinion , i have now a 3.1KW total PV power. Even with half of the array size I was reaching daily the float stage for the batteries, and they would stay in float for several hours.

My dilemma on the battery bank is now if : 1. I should go one more year with 4 new 12V batteries, 1.2 k in price, and after 1 year to have them dead again, but maybe the lithium price will go by magic down. or invest now 5-6 k in a properly sized battery bank made of 24 pieces of 2V wet battery (and hope to last for 5-6 years).

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