need help with batteries.

burrow_87
burrow_87 Registered Users Posts: 10
So due to the VA's request I have moved to a location that's very remote. Now I have to install solar for power. I have already purchased an Outback FM 80 controller. So my next step is batteries. This is where I get confused. I have two options but I .am not sure which is better for storage. I can afford either 16 Trojan l16-h for a 48 volt system or I can afford 12 trojan l16 re-b 2volt for a 24v system. Either way it will be an Outback vfx inverter. I just do not understand the math behind amp hour calculations. Any help is appreciated.

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: need help with batteries.

    Welcome to the forum.

    You'll want to read this thread: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power

    You've sort of put the cart before the horse buying charge controller without first determining power needs, but fortunately an FM80 is a very flexible unit. At the top end it can handle 80 Amps to a 48 Volt system which would be enough for 800 Amp hours @ 48 Volts or up to 19kW hours of stored power. That's quite a lot.

    It will also work with 24 or 12 Volt systems and also with less Amp hour capacity.
  • burrow_87
    burrow_87 Registered Users Posts: 10
    Re: need help with batteries.

    I bought it because it was flexible enough to use on a temp system. Which is currently 12x t-150 hooked to a cheap Chinese inverter and 2x 235 renolog pv panels. I live totally off grid so I need the best storage I can afford. I am just unsure how to crunch numbers. I would think that 16x l16-h's at 420 ah would be more storage than the 12x trojan l16re-b's 2volt at 1110 but I just not positive which equals more storage. Either way I have to buy more pv.
  • Mountain Don
    Mountain Don Solar Expert Posts: 494 ✭✭✭
    Re: need help with batteries.

    amp-hours x battery bank volts = watt-hours

    16 L16; two series strings of 8, in parallel to get 48 volts
    420 amp hours x 48 = 20160 watt hrs
    X2 that by two (parallel strings); 20160 x 2 = 40320

    12 L12 2volt; one series string for 24 volts
    1110 x 24 = 26640 watt hours


    That said the single series string would be best for the batteries.


    But how much capacity is required??
    Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
  • burrow_87
    burrow_87 Registered Users Posts: 10
    Re: need help with batteries.

    Currently I am using about 2.5 kw per day total. So I figured off grid with winter coming I need at least 4 to 5 days reserve. I was told that using the built in charger on the vfx is too sensitive to the 60 htz drop and that generators are useless with them so I need a larger reserve.

    That being said. Let me ask this. The FM-80 can take 4000 watts of pv in 48v configuration and 2000 watts of pv in 24v. Does that mean 48v system will charge faster?
  • Mountain Don
    Mountain Don Solar Expert Posts: 494 ✭✭✭
    Re: need help with batteries.
    burrow_87 wrote: »
    I was told that using the built in charger on the vfx is too sensitive to the 60 htz drop and that generators are useless with them so I need a larger reserve.

    Hmmm. We had a VFX for 5+ years* and never had any issues charging or EQ'ing with it using the Yamaha inverter generator. Maybe it depends on the generator, as in cheapy and loud 'run-full-speed-all-the-time' ones may produce power that is too dirty. ??? I'm guessing on that.


    *(5+ years until lightning struck. I have some boards coming to repair it. The generator OTOH may not be work the cost of the control box considering the number of hours on the engine. )
    Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: need help with batteries.
    burrow_87 wrote: »
    Currently I am using about 2.5 kw per day total. So I figured off grid with winter coming I need at least 4 to 5 days reserve. I was told that using the built in charger on the vfx is too sensitive to the 60 htz drop and that generators are useless with them so I need a larger reserve.

    That being said. Let me ask this. The FM-80 can take 4000 watts of pv in 48v configuration and 2000 watts of pv in 24v. Does that mean 48v system will charge faster?

    It is time to look at your total system!

    Will your loads continue at 2.5Kwh? what were they last winter?
    What will you be charging the batteries with? a 20kwh battery bank will like around 3200 watt array (off the cuff).
    What are your winters like? What is your location?
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: need help with batteries.
    burrow_87 wrote: »
    That being said. Let me ask this. The FM-80 can take 4000 watts of pv in 48v configuration and 2000 watts of pv in 24v. Does that mean 48v system will charge faster?

    Not in any real sense, charge controllers are rated for the amperage they can pass along to the battery bank, in a 48 volt system it can handle 4000 watts since 4000/48 = 83.333 Amps and it can handle 2000 watts at 24 volts 2000/24=83.333 Amps. That said it can deliver more wattage(power) at 48 volts.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: need help with batteries.
    burrow_87 wrote: »
    That being said. Let me ask this. The FM-80 can take 4000 watts of pv in 48v configuration and 2000 watts of pv in 24v. Does that mean 48v system will charge faster?
    Compare two systems with the same energy capacity, say 24V at 200AH and 48V at 100AH. Each of the two has a nominal energy storage capacity of 4.8kWh. (V times Ah = Wh)
    With the same controller but twice the number of panels you could pump twice a much power into the 48V bank and you would be recharging it twice as fast.
    But if you compare a 24V 200Ah bank and a 48V 200Ah bank, the second bank will hold twice as much energy and so by charging it at twice the power you would bring it from 80% SOC to 90% SOC in exactly the same time as the first bank.
    The key is that you need twice as much panel power (double the array size) to take advantage of the extra capability of the CC at the higher voltage. :)
    SMA SB 3000, old BP panels.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: need help with batteries.
    burrow_87 wrote: »
    I was told that using the built in charger on the vfx is too sensitive to the 60 htz drop and that generators are useless with them so I need a larger reserve.

    Nonsense (unless your generator is really horrible).

    What you heard is true for the GVFX inverters. These are bidirectional grid interactive inverters. They have to be very sensitive to the quality of the AC from the grid because if the grid starts to go down the inverter must quickly disconnect from it. Many folks have found that you can use a GVFX inverter with an inverter type generator because the output of an inverter generator is better than the grid.

    The VFX inverters are designed for generators... they can't "sell" power to the generator and they don't need to sync to the generator waveform. When the generator turns on, the VFX waits until the generator is stable (you can set that amount of time). When it's ready to use the generator power it stops inverting and switches your AC loads to the generator. If the generator is still stable it then begins to ramp up the battery charging. You can set the VFX to not draw more than your generator can handle.

    --vtMaps

    EDIT: If you do have an inverter generator, you might want to consider a GVFX inverter. A GVFX inverter can do some neat tricks with AC coupling (generator support). Forum member 'blackcherry04' has written quite a bit on this forum about using GVFX gen support with a GVFX inverter.
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: need help with batteries.
    burrow_87 wrote: »
    So my next step is batteries. This is where I get confused.

    Best practice is a single string of batteries. Avoid parallel.
    short discussion here: http://www.wind-sun.com/ForumVB/showthread.php?14674

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • burrow_87
    burrow_87 Registered Users Posts: 10
    Re: need help with batteries.

    Well this is what I am thinking as of right now.
    1x Outback FM-80 controller
    12x trojan l16re-b 2volt batteries
    1x Outback VFX 3524 inverters
    8x Renolgy 235 watt pv
    Currently using Generac GP3300 but thinking of going with the eu2000 or larger 11 kw Genera c propane generator.

    I live in northern arizona. Show Low area so I do have snow to deal from time to time. My energy needs will be stable throughout the winter. Thi s is my first winter so I have no numbers for comparison
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: need help with batteries.
    burrow_87 wrote: »
    Currently I am using about 2.5 kw per day total. So I figured off grid with winter coming I need at least 4 to 5 days reserve.
    burrow_87 wrote: »
    Well this is what I am thinking as of right now.

    12x trojan l16re-b 2volt batteries

    Having so many days autonomy is usually not cost effective.
    First of all, when you have such a large battery with such small loads, you will have very shallow cycling when you have multiple sunny days in a row. This is not good for batteries... they get lead-dioxide clumping on the positive plates.

    Having a larger battery means you have more invested in batteries, but the battery is unlikely to last proportionately longer. Having larger battery also means you need more invested in solar or generator to charge the larger bank.

    There are some applications where autonomy is critical, but 5 days of autonomy is very expensive compared to 2 days auonomy with occasional use of generator.

    If you do decide to get such a large bank, your decision to go with 2 volt batteries is wise, but I would avoid those particular trojans. Those trojans are actually three 2-volt cells in parallel... there are three caps per battery to maintain... add water, measure SG. Find a 2 volt battery that is one large 2 volt cell.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: need help with batteries.
    burrow_87 wrote: »
    12x trojan l16re-b 2volt batteries

    Are those the 1 cap batteries, or 3 caps ? If 3 caps, they are 3, 2V cells in parallel, not an ideal way to start, and you have many cells to check/add water to.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,