Best Battery Value

SolarJohnSolarJohn Solar Expert Posts: 202 ✭✭✭✭✭
If I were going to purchase and install a battery bank with new batteries, which type/brand would give me the most value for my money? This would be for a PV system where the SOC rarely drops below 80%. I would probably be considering a bank in the range of 800 to 1600ah. The load would seldom exceed 20 amps, except for short durations. Also, I wouldn't want to use batteries that are hard to handle, meaning the very heavy ones. I'm leaning toward the Surrette-Rolls, partly because of their long life expectancy.

John

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Best Battery Value

    When you are thinking about batteries--State of Charge and your discharge depth you are will not go to will also greatly affect the cost of your installation...

    80% SOC = 1,000 AmpHour battery bank (just for discussion)
    60% SOC = 500 AH battery bank
    50% SOC = 400 AH battery bank
    20% SOC = 250 AH battery bank

    Now, in reality, you could probably use a cheap battery for the 1,000 AH bank because of the little amount of discharge. The 250 AH bank would probably be a AGM battery rated for 80% depth of discharge.

    Also, if you have wet cell battery bank--the 80% SOC should have about 4x larger charge current requirement for equalization current (possibly a few more solar panels required).

    Part of sizing a bank is how long you want to go without charging (poor weather, etc.). I like the idea of having an oversized bank--but that does add lots of issues besides cost of batteries:
    • Larger battery bank, more shipping/installation costs
    • Larger Battery Box/building
    • more cables to install maintain
    • Using cheaper wet cell batteries in a larger bank will require monthly watering and cleaning of terminals
    • If a smaller bank, you may be able to justify AGM batteries which require less cleaning/venting/mount in any orientation
    • AGM's also have lower energy losses (estimated 90% eff vs 80% eff for wet cell--just like getting 10% more solar panels)

    I am not the battery expert here--but try not to limit your options until you have looked at all of the available solutions.

    I would suggest that you also look at AGM batteries (Wind-Sun's store has them too) at 50% usage level and see if you can find any advantages for your application (smaller size, reduced maintenance, etc.).

    If you are going to build a large bank, I would suggest looking at large cell batteries (sometimes available even as a single cell per battery)--My suggestion would be to install all the cells in series (instead of a bank of parallel or series/parallel). Some places have reported better life (balancing power draw/charge for parallel batteries is not always easy)--and it is easier to find/replace a bad cell (cell voltage is cell voltage, not the voltage of several cells in parallel).

    Wind-Sun themselves (IIRC--not wanting to place words in his mouth) has not see any (major) issues with life of parallel for their installations/customers (reported on another thread here)... Different people have different experiences.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Best Battery Value

    SolarJohn,

    Rolls/Surrette flooded-cell models are apparently quite good, but their warranty / life expectancy specs vary by series. For example, while the 5000 Series batteries have a 10 year warranty, a 15 year life expectancy and are rated for 3300 cycles (@ 20% DoD?). the 4000 Series batteries – which includes the very popular S-430 and S-530 models – have a seven year warranty, a 10 year life expectancy, and are rated for 1,300 cycles. The big Rolls / Surrette batteries can be pretty heavy, and make sure you confirm their prices.

    See: http://www.rollsbattery.com/pdf/6cs25ps.pdf
    and: http://www.rollsbattery.com/pdf/s460.pdf
    and: http://www.rollsbattery.com/pdf/s530.pdf

    It’s my understanding that Trojan is now warranting their solar application batteries (i.e., the L-16P and -H) for seven years. See: http://www.trojanbattery.com/Tech-Support/SolarWarranty.aspx

    Ain’t competition great!

    Unfortunately, the batteries above are all flooded-cell models that require considerable maintenance. They require equalization, an operational maintenance; they require physical inspection, testing and watering; and they require active ventilation to the outside while they’re in absorb- or EQ charge modes. For a 12 V x 1200 Ah bank built from six S-530’s or L-16’s, that would be 18 cells to maintain.

    I switched from flooded-cell to VRLA (AGM or gel) batteries in late 2005. They’ve so far been essentially no maintenance, and, because they typically don't vent, I could keep them in my house if I so chose. My experiment is chronicled below, and I doubt I’ll ever look back. However, in the spirit of full disclosure, I did have a problem with individual battery voltages after I converted from a parallel-only configuration (12 V bank) to a series/parallel configuration (24 V). That problem, and its resolution, is also discussed below.

    See: http://www.outbackpower.com/forum/viewtopic.php?t=848
    and: http://www.outbackpower.com/forum/viewtopic.php?t=1750

    You could build a 12 v x ~800 Ah bank from four side 4D VRLA batteries, or a 12 V x ~1,000 Ah bank from four size 8D batteries. Connected correctly, I doubt that the parallel batteries would be a problem. Brock built a 12 v x ~2,000 AH bank from eight size 8D batteries wired in parallel, and so far, so good.

    See: http://www.trojanbattery.com/Products/RenewableEnergy.aspx
    and: http://www.eastpenn-deka.com/assets/base/0919.pdf
    and: http://www.mkbattery.com/images/lagm.pdf

    Concorde makes very good AGM batteries. Check their “Sun Xtender” and “Lifeline” batteries. See: http://www.concordebattery.com

    Finally, Exide/GNB makes apparently very good AGM batteries, their Absolyte IIP, rated for 5000 cycles at 20% DoD. See: http://industrialenergy.exide.com/exidepdfs/Absolyte_62_61.pdf

    As Bill mentioned, don’t forget VRLA batteries’ superior coulombic efficiency (Ah out / Ah in). Flooded-cell batteries run ~90%, and get worse as they age, while VRLA run ~99%. In fact, I think this issue deserves more attention than it gets. Flooded-cell batteries, with their high absorb voltage and low coulombic efficiency, have a recharge energy efficiency (Wh out / Wh in) of 80% or less. The the other extreme, VRLA gel batteries, with their low absorb voltage and high coulombic efficiency, deliver a recharge energy efficiency of >90%. That feature translates directly into a smaller PV array and/or larger loads.

    Ultimately, it’ll be your decision. I’d look at “best value” as sunk cost (cabinet, ventilation, maintenance tools), battery cost per cycle, an efficiency factor, and the least (and safest) amount of maintenance. To get really fancy, you could throw in opportunity cost of the money required to buy the batteries.

    Enough… I hope this helps.
    Jim / crewzer
  • System2System2 Posts: 6,290 admin
    Re: Best Battery Value

    My application is for backup power.  I have worked a deal with a local battery company where I can buy Hawker 6VF11 batteries for $42.  These are 12 volts, 100 AH @ the c8 rate and weigh 105 #.  20 of these cost $840, gives me 500 AH @ 48 volts @ the c8 rate.  If any go bad, I can trade them in for free and the cost of a lunch for the guy.  You can read about them here http://www.enersys-japan.com/documents/telecom.pdf.  These are very high end AGM batteries and were $700 each new and are supper reliable.  They were pulled out of service from a local phone company who keeps them in a float charged state.  When I got them they were fully charged.  I just got a Trimetric from NAWS and I want to load test them down to 1.75 vpc to see the actual capacity. 

    They also have Lucent 4VR125e that are very nice too.  They are 2 - 2 volt cells bussed together with copper buss bars.  They are 115 AH @ c8 rate, 125 @ c10, or 150 @ c20 rate and VRLA type.  So both are practically no maint.  The Lucent have the advantage of being 2 volt cells and spares could be purchased right at the beginning that would be the same type, age, and be great for replacing any that might go bad.  The cost for 4 volt units (4VR125e) is $21.20 and I can trade these in for free, plus lunch. 

    These are available, and it breaks my heart when they go to the smelter before I can buy any more.  I suppose you can't save ALL of them..  Haha

    Right now they have a pallet of Hawker cyclon units in 12 volt, with copper buss bars attaching the cells.  I thought about scrounging the copper, there is a fair amount of it!  They are 2 volt cells 25 AH @ c8 and great for replacing UPS batteries or something like dedicated outdoor lighting for walkways etc. 

    Skip
  • System2System2 Posts: 6,290 admin
    Re: Best Battery Value

    I would suggest that you also look at AGM batteries (Wind-Sun's store has them too) at 50% usage level and see if you can find any advantages for your application (smaller size, reduced maintenance, etc.).

    If you are going to build a large bank, I would suggest looking at large cell batteries (sometimes available even as a single cell per batter)--My suggestion would be to install all the cells in series (instead of a bank of parallel or series/parallel). Some places have reported better life (balancing power draw/charge for parallel batteries is not always easy)--and it is easier to find/replace a bad cell (cell voltage is cell voltage, not the voltage of several cells in parallel).
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