48 volt off grid system

bundy
bundy Registered Users Posts: 10 ✭
in Off Grid Solar & Battery Systems #1
hi all just looking for some input i was installing a 4448 inverter, nine 240 watt panels for a small hous. going to have propane fridge and stove led lights and and water pump.im undecided on which way to go on battery bank size. 2 banks of 8 6volts surrette s then parrelel them to make 48 volt or 24 2volt batterys.which would u prefer.thanks
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: 48 volt off grid system

    Welcome to the forum.

    All other factors being equal (which they never are) I would pick the one series string of twenty-four 2 Volt cells. Reason? No parallel battery wiring = guaranteed equal current through all batteries.

    But Surrettes come in many sizes and the 2 Volt cells tend to be "big" only. Since your array is 2160 Watts (three strings of three in series I presume) it can support about 279 Amp hours @ 48 Volts. About the smallest 2 Volt cell you can get is the Crown 500 Amp hour, which those panels would not really be adequate for recharging.

    That leads to the inevitable question: have you sized your battery bank capacity according to your Watt hour use?
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  • bundy
    bundy Registered Users Posts: 10 ✭
    #3
    Re: 48 volt off grid system

    Thanks for your response I bought the panels but I didn't buy the batterys or the inverter yet but I would like to stick with forty eight volt inverter so what yur saying is maybe just stick with eight six batterys
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  • bundy
    bundy Registered Users Posts: 10 ✭
    #4
    Re: 48 volt off grid system

    Thanks for replying I didn't buy the batterys yet or inverter but I would like to stay wih forty eight volts so I would be better to go with eight six volts like the surrette four sixty batterys would it be ok to have two strings of eight just trying to find what would work the best. Ya the panels will be three strings of three and I'm useing an ob80 thanks let me know what u think of my battery configuration or if u have a solution thanks again. I thought that lots of capacity would of been a goog idea but if my solar array is to small that doesn't help my batterys much down the road
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  • mikeo
    mikeo Solar Expert Posts: 386 ✭✭✭
    #5
    Re: 48 volt off grid system
    Since your array is 2160 Watts (three strings of three in series I presume) it can support about 279 Amp hours @ 48 Volts.
    I get 2160 watt panels/52 volts =~ 42 amps peak or can support a 420 amp hour battery OK. Eight L16 style batteries would fill that bill. That would match a 4kw inverter fairly well and with his FM80 he could nearly double the array capacity as well as the battery capacity. This of course does not speak to his loads so running the battery down to a max of 75% SOC daily, with 50% derate 57.5 amp hours or 2.7 kw on an annualized 4 hour day. What am I missing? He would of course need generator backup for those long cloudy stretches.
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  • solarvic
    solarvic Solar Expert Posts: 1,071 ✭✭✭✭
    #6
    Re: 48 volt off grid system
    mikeo wrote: »
    I get 2160 watt panels/52 volts =~ 42 amps peak or can support a 420 amp hour battery OK. Four L16 style batteries would fill that bill. That would match a 4kw inverter fairly well and with his FM80 he could nearly double the array capacity as well as the battery capacity. This of course does not speak to his loads so running the battery down to a max of 75% SOC daily, with 50% derate 57.5 amp hours or 2.7 kw on an annualized 4 hour day. What am I missing? He would of course need generator backup for those long cloudy stretches.
    Mike. L-!6 batterys are 6 volt so would need 8 of them for 48 volt. Solarvic
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  • mikeo
    mikeo Solar Expert Posts: 386 ✭✭✭
    #7
    Re: 48 volt off grid system
    Mike. L-!6 batterys are 6 volt so would need 8 of them for 48 volt. Solarvic
    Of course your are correct, yet another example of my CRS problem:confused:
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
    Re: 48 volt off grid system
    mikeo wrote: »
    I get 2160 watt panels/52 volts =~ 42 amps peak or can support a 420 amp hour battery OK. Eight L16 style batteries would fill that bill. That would match a 4kw inverter fairly well and with his FM80 he could nearly double the array capacity as well as the battery capacity. This of course does not speak to his loads so running the battery down to a max of 75% SOC daily, with 50% derate 57.5 amp hours or 2.7 kw on an annualized 4 hour day. What am I missing? He would of course need generator backup for those long cloudy stretches.

    What you're missing is that a 2160 Watt array doesn't put out 2160 Watts most of the time and the charge Voltage for a "48 Volt" system is closer to 60 Volts, not 52.

    2160 * 77% efficiency = 1663 Watts / 59.2 Volts (for Trojans anyway) = 28 Amps approximately.

    Whereas panels don't put out full power from the moment they turn on and you will probably never see 28 Amps @ 59.2 Volts the formula there is pretty good for coming up with an array & battery combination that will recharge completely on most days.

    Also remember that "L16" is a case size, not an Amp hour capacity. They can range from about 320 to 395 Amp hours, and due to the "tall case" design will want full 10% charge current (or better) to avoid electrolyte stratification.

    #1 problem with off-grid systems: too little panel for the battery, which leads to early battery death.
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  • bundy
    bundy Registered Users Posts: 10 ✭
    #9
    Re: 48 volt off grid system

    Thanks for the replys. Very interesting reading your posts. Iwas looking at some other batt
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  • bundy
    bundy Registered Users Posts: 10 ✭
    #10
    Re: 48 volt off grid system

    Thanks for the replys. Very interedtng reading the stuff. Now. U got me thing ab out those bbatters. What other size of battery would Suite me besides the l16. And the absolute biggest battery I could go with. Like the 4 volt ones.I think the lowest amp hour ones are 55o amp hour.the 6oo surrete which are 45o amp hour @2o hour but with lots more lead which also has less acid. So what's your thoughts on the 4 volt and the l16 battyers.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #11
    Re: 48 volt off grid system

    Effective charging for FLA's can be had with 5% to 13% of the battery's Amp hour capacity.
    The trouble is that should be net charge rate. If you try for the low-end 5% rate expecting it to support a larger battery then the loads that inevitably will be running at the same time will drag down the effective charge rate, leaving the batteries undercharged. Or you may not have enough power to recharge the batteries fully (including Absorb cycle) in the amount of daylight available. Or if you try to run 5% on tall case batteries the electrolyte will stratify.

    Hence my preference for targeting 10% on standard FLA's.
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