enlarging system, which comes first

uncledave
uncledave Registered Users Posts: 4
in Off Grid Solar & Battery Systems #1
Hello,
Our RV has 4 100 watt panels with 4 deep cycle 6volt batteries ( 12 volts 270ah ),, it was not quite enough at burning Man this year and I wonder if I should add a couple more Batteries or a couple more 100 watt panels first??? Obviously new to this so any insight would be welcome...
Thanks,
Dave
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: enlarging system, which comes first

    Welcome to the forum Dave.

    Are you sure about the size of those batteries? Not 270 Amp hours @ 6 Volt each? Because that would make a large difference in capacity and charging.

    Four 100 Watt panels should be (based on the Renogy 18.9 Vmp & a PWM controller) about 20 Amps max current under good insolation conditions. That would be a tad low for 270 Amp hours, and if what you really have is two parallel strings of such battery totaling 540 Amp hours it would be insufficient. So it is important to have the battery size right.

    Most people have too few panels. For example 'ideally' 270 Amp hours would have 27 Amps peak current, which would require two more of those panels and a charge controller that can handle more than 30 Amps.

    Can't say if you've got enough battery because we have no idea what the load demand is (Watt hours).
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  • uncledave
    uncledave Registered Users Posts: 4
    #3
    Re: enlarging system, which comes first

    Sorry ,, not clear enough,, each 6 volt is 135 ah, and connected so as give me 12volts and 270 ah,, (anyway that 's what I think that I did) during the day we were using between 6 and 9 amps all day and even after the sun went down for a while then just around three amps at night... using a 30 amp MTTP controller,,, seems that I need to add a couple more Renogy panels,, thanks for the in put,,,
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  • jcheil
    jcheil Solar Expert Posts: 722 ✭✭✭
    #4
    Re: enlarging system, which comes first
    uncledave wrote: »
    Sorry ,, not clear enough,, each 6 volt is 135 ah

    That's a rather small and strange size battery? Are you sure it is a deep cycle battery and that is the 20-hour rate on it? Would be interested in the brand/model of those batteries just so we could be sure. Most generic GC2-type 6v batteries in the PV world are around 215-230ah each.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
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  • Plowman
    Plowman Solar Expert Posts: 203 ✭✭✭✭✭
    #5
    Re: enlarging system, which comes first
    uncledave wrote: »
    during the day we were using between 6 and 9 amps all day and even after the sun went down for a while then just around three amps at night... using a 30 amp MTTP controller,

    Say average of (7.5 amps * 12 hrs) + (3 amps * 12 hrs) = 126 ah/day

    With Cariboocoot's figure of 20 amp max output and a generous 6 solar hours/day = 120 ah/day produced by panels on an ideal day.

    More panels are needed. A 10% charge rate with 77% derate would require ~700W of panels. Might be able to get by with fewer panels depending on how and when you use your system, but 400W definitely seems too low to me.
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