choosing the right AGM battery

krisman
krisman Solar Expert Posts: 57 ✭✭✭✭
I have a small 50 watt panel, and a 1500 watt inverter. I am going to try to max it out every night to get the most out of it. but i need an indoor battery. Could you please post me a link or some stats on the right AGM battery to get? i have heard it is better than a gel battery

Comments

  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: choosing the right AGM battery

    if you plan on maxing out the inverter then you better rethink it because it can only give what is delivered to it plus losses. also remember solar energy is not a constant every day as some days are longer and some shorter and some are rainy/cloudy. if your pv is delivering 90% of its rating for losses this is 45w(optimistically). if it does this 5 days of the week with 5 hrs each of those days (also optimistically) your battery will be afforded about 64ah over the week or about 9.1ah per day. for a 12v battery this is about 110wh per day. i would not use all of the 110wh available or risk the battery slowly going down to its death.
    the only way to max out the solar panel is to use the power directly and as fast as it is delivered. this can be done with a pure resistance and the net result is heat and very little of it. because batteries and loads don't act quite like that and are handicapped with voltage and current requirements you won't use all of the pv's power.
    if you meant to use all of the power delivered to the battery and thus drain it until dead each time, you will find your battery soon to be dead.
    can you spell out more specifically what it is you want solar to do?
  • krisman
    krisman Solar Expert Posts: 57 ✭✭✭✭
    Re: choosing the right AGM battery

    i meant runnning the battery down or close to it every night, thats not a good idea even for a deep cycle agm?
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: choosing the right AGM battery

    no. no battery should be drawn down that far unless it is of the li ion design and those should be drawn down to about 40%, but not 0%.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: choosing the right AGM battery

    Why?

    Generally, for long battery life you want to only discharge by 50% -- You can take them to 80% discharge (20% state of charge), any further and you will destroy the battery by "reverse charging" a cell.

    A 50 watt panel averaging 5 hours of sun per day (depending on where you are and what season/weather conditions):

    50 watts panel * 5 hours of sun * 52% sys efficiency = 130 Watt*Hours per day of useful power

    Say you load your 1,500 watt inverter to 50% load (750 Watts--note actual numbers will vary--but this is a good middle of the road estimate):

    130 Watt*Hours / 750 Watts = 0.173 hours = 10.4 minutes per average day

    If you are recharging the battery from another power source during the day--you can size the battery to your load... But you should use a Kill-A-Watt meter to measure your actual loads.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bryanl
    bryanl Solar Expert Posts: 175 ✭✭✭✭✭
    Re: choosing the right AGM battery

    The 50% DoD goal for lead acid batteries is a cost benefit conclusion. It balances between number of batteries needed versus how long they will last to determine lowest long term costs.

    If you place any batteries indoors, they should always be properly ventilated. There are guidelines that indicate you can be reasonably safe with a large enough room and a small enough battery bank, but it is still a good idea to use a proper battery box with outside ventilation.

    In a nutshell: Gels are best for standby, float service. AGM's are good when high current in or out is anticipated or you have unusual storage requirements. Wet cell is the most cost effective for usual use.
  • krisman
    krisman Solar Expert Posts: 57 ✭✭✭✭
    Re: choosing the right AGM battery

    I am forced to have an indoor battery or else drill up my floor which i dont want to do. AGM's are not supposed to emit any fumes or anything that can harm you, at least that is what they say. So what would be the most output that my system would produce nightly or every other night? 100-200 watts without destroying the battery life? i think i could handle that, but i have to know what amp size battery and everything to ask for first. and with a system that small, is an agm or gel recommended? i may eventually go to a second panel, so that would require a pretty good size battery right?
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: choosing the right AGM battery

    backup a bit there and tell us what the loads you will require of it will be and about for how long.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: choosing the right AGM battery

    AGM's are still lead acid batteries. And while in NORMAL OPERATION they will not out-gas hydrogen or sulfuric acid fumes. Even if you crack a case, they are not supposed to let electrolyte out... During ABNORMAL OPERATION they can fail like any other battery type (vent hydrogen/electrolyte/etc.).

    Typical abnormal operations: Overcharging (failed/miss-programed charge controller); over current (short circuit); fire caused by shorted wire/sparks/tools falling on battery; and/or end of life failure (typically battery on charge for several years, case expanding from oxidation of the positive electrodes, sudden use of current, etc.).

    In the end, at least install the battery bank in some sort of plastic or heavy metal container that can contain any reasonable failures. Keep the acid contained and prevent tools/metal items from falling across the top of the batteries and shorting them out.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bryanl
    bryanl Solar Expert Posts: 175 ✭✭✭✭✭
    Re: choosing the right AGM battery

    watts are the rate of energy draw. 200 watts steady for a fifteen hour night would be 3,000 watt hours of energy. Using a reasonable rule of thumb, that means you'd need 300 pounds of battery to supply that amount of energy.

    As for venting, your problem is more corrosion and explosive gases than it is poisonous gases like CO or CO2. If you take care with charging to not get too vigorous, you might get by without too much of a problem but you need to consider the risks. There are other batteries besides AGM's that are sealed but I don't think that factor should be the major factor in choosing battery type in regards to venting needs.

    Also keep in mind that it can take 12 hours or more to fully charge lead acid batteries. That is one reason why daily cycling can be rather hard on batteries in off grid use as it is usually rather difficult to get a full charge.
  • krisman
    krisman Solar Expert Posts: 57 ✭✭✭✭
    Re: choosing the right AGM battery

    i have a battery box, it is plastic though. wouldnt acid eat through it if it did leak? and i guess for my needs, it would be just little stuff like laptops, charging batteries, nothing major. maybe run a tv or cd player or something. it wouldnt even have to be daily, just every other day or every few days. for a few hours of the evening. i think i can live with that. a few people have mentioned to me that gel batteries would work just as well for this, but i dont know
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: choosing the right AGM battery
    krisman wrote: »
    i have a battery box, it is plastic though. wouldnt acid eat through it if it did leak? and i guess for my needs, it would be just little stuff like laptops, charging batteries, nothing major. maybe run a tv or cd player or something. it wouldnt even have to be daily, just every other day or every few days. for a few hours of the evening. i think i can live with that. a few people have mentioned to me that gel batteries would work just as well for this, but i dont know

    All acids aren't the same; some that will eat through metal will leave certain plastics alone. If this battery box is made to hold flooded cells, it is logical to assume it's made out of a plastic that can take the sulphuric acid in batteries.

    Funny thing about "little stuff"; it adds up. It's not just the current draw but the time that factors into battery capacity. Using 100 Watts for one hour would require approximately 9 Amp/hrs. Using it for ten hours and you need 90 Amp/hrs.

    Trouble is, it's hard to predict how much TV you're going to watch in advance. :p
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: choosing the right AGM battery

    Sulfuric Acid (10%-75%) chemical resistance chart:
    Material Compatibility
    =======================================
    304 stainless steel D-Severe Effect
    316 stainless steel D-Severe Effect
    ABS plastic B-Good
    Acetal (Delrinr) D-Severe Effect
    Aluminum D-Severe Effect
    Brass N/A
    Bronze B-Good
    Buna N (Nitrile) B-Good
    Carbon graphite A-Excellent
    Carbon Steel D-Severe Effect
    Carpenter 20 A-Excellent
    Cast iron D-Severe Effect
    Ceramic Al203 A-Excellent
    Ceramic magnet N/A
    ChemRaz (FFKM) A-Excellent
    Copper N/A
    CPVC A-Excellent
    EPDM B-Good
    Epoxy A-Excellent
    Fluorocarbon (FKM) A-Excellent
    Hastelloy-Cr B-Good
    Hypalonr B-Good
    Hytrelr
    N/A
    Kalrez
    A-Excellent
    Kel-Fr
    A-Excellent
    LDPE
    A-Excellent
    Natural rubber
    C-Fair
    Neoprene
    B-Good
    NORYLr
    A-Excellent
    Nylon
    D-Severe Effect
    Polycarbonate
    B-Good
    Polyetherether Ketone (PEEK) D-Severe Effect
    Polypropylene
    A-Excellent
    Polyurethane
    D-Severe Effect
    PPS (Ryton®)
    A-Excellent
    PTFE
    A-Excellent
    PVC
    A-Excellent
    PVDF (Kynar®)
    A-Excellent
    Silicone
    D-Severe Effect
    Titanium
    D-Severe Effect
    Tygonr
    N/A
    Vitonr
    A-Excellent
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: choosing the right AGM battery
    krisman wrote: »
    i have a battery box, it is plastic though. wouldnt acid eat through it if it did leak? and i guess for my needs, it would be just little stuff like laptops, charging batteries, nothing major. maybe run a tv or cd player or something. it wouldnt even have to be daily, just every other day or every few days. for a few hours of the evening. i think i can live with that. a few people have mentioned to me that gel batteries would work just as well for this, but i dont know

    Yes, there are gel deep cycle batteries that will work just fine. These are very different than the Optima sort of gel batteries that you would use in a car.

    Gels are MUCH more sensitive to charging voltage, so for a beginner system, you should stick with AGM.

    Both are sealed...well, sealed UNTIL you blow the seal by some sort of abuse as Bill described in a previous post.

    There won't be any acid or hydrogen gas to worry about unless you blow the seal.

    For the most part, running a TV is not a "little load". The laptop, maybe not too bad - it depends. Mine draws 60w @ 120v which is .5a, so at 12v that would be 5a. That would mean that I could theoretically run it from a 100ah 12v battery for 10 hours and the battery would be at 50% - which is as low as you want to go if you want your battery to survive a goodly number of charge/discharge cycles (the deeper you discharge, the less cycles your battery will do before it dies).

    But then, figure with the inverter inefficiency and whatnot, I could actually only run the laptop for 5 hours. Then figure I want my battery to live a good long while so I want to limit the drain to 25% - now that 100ah battery can probably only run my laptop for about 2.5 hours before I need to recharge the battery.

    To put back 25ah into the battery with a 50w panel, you would almost certainly need over 6 hours of good sunlight (direct full sunlight - anything less and the PV panel will put out almost nothing). If you got 4 hours a day on that panel, then you could figure that your rig would run my laptop for 2.5 hours every other day.