Proposed RV Solar Setup Comments?

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System
System Posts: 2,511 admin
in Solar Beginners Corner #1
Hello All,
I've read and learned a lot from this forum and appreciate all those who have contributed. I've put together a tentifive list of compnents that I think would fit my solar needs for my 5th Wheel. I'd welcome any suggestions anyone may have before I make my purchase. I estimate my usage is about 40 or 50 amps a day. The panels will be mounted toward the rear of the trailer. The controller will be mounted at the front of the trailer in the outside battery/storage compartment. The battery monitor will be inside the trialer. Also, I'd like to know if the panels in this setup would be more efficient wired in parallel or series with the mppt controller. Thanks.
BART
Propsed System:
2 - Kyocera KD135GX-LP 135 Watt Panels
1 - Morningstar SunSave MPPT Controller
1 - Trimetric TM2020 Batter Monitor
2 - Unirack RV Flush Mount Feet Set
2 - 30' MC4 Extender Cable Male/Female (for panel/controller)
2 - 6' 6 gage wire and lugs (for contoller/batteries)
2 - 6v batteries
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #2
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    Re: Proposed RV Solar Setup Comments?

    My general back of the napkin rule of thumb (others may disagree) is, taking into account all system efficiencies, if you take the name plate rating of the PV system,,, divide that number in 1/2,,, then multiply that number by the number of hours of good sun you expect. Rarely more than four. So in your case, your 270 watts of Pv divided by to = 135x 4 hours=540 wh/day.

    Your 50 ah/day would translate,, at 12vdc (I assume a 12volt system) would be 600 watt hours. So you are close,, but you have built in little or nothing for reserve, AND, I suspect that with an RV mount you are not likely to get optimal sun for those 4 hours,, so on quick first glance,, I think you are under paneled or over loaded.

    I am also assuming your 6volt batteries would be some where in the 225 ah range. Ideally you would never draw the battery down more than 50%,, and recharge that 50% within a couple of days. Some of us suggest a depth of discharge not to exceed 20% for maximum battery longevity. That is a calculation that you can look at,,, life cycles vs depth of discharge related to cost per cycle.

    Good luck and welcome to the forum,

    Tony

    PS,, The advantage of wiring the the Pv in series is you can use smaller wire gauge for less line loss. On the other hand,, in a array of this size,,I don't think it is going to make much difference.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,448 admin
    #3
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    Re: Proposed RV Solar Setup Comments?

    Probably wire the panels in series. Less wire to run from the rear to the front (two wires instead of four for parallel connection). All things being roughly equal--choose the easiest wiring method.

    Don't forget a Remote Battery Temperature Sensor for the Morning Star charge controller... It absolutely needs a RBTS to fully charge the batteries.

    -Bill

    PS: Appropriate wiring protection fuses too.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
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    Re: Proposed RV Solar Setup Comments?

    you don't necessarily need to run separate wires down for paralleled pvs as it can be tied and sent down with thicker wire and if shading is encountered the parallel arrangement may prove better.
    also note that during the summer solstice you may not notice much loss from flat mounted pvs, but as the sun angle changes with the other seasons the losses will become more apparent with the winter solstice as being nearly useless even if kept clear of snow(if applicable).
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  • System2
    System2 Posts: 6,290 admin
    #5
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    Re: Proposed RV Solar Setup Comments?

    Good comments! Do I need the battery sensor if the controller is next to the batteries? I thought it only might be needed if the controller was in another location like inside the trailer where the temperature is different. Also, where are fuses needed for proper protection; i.e. between the controller and panels, the controller and batteries, or both?

    Regarding the series/parallel question, I figured there were two scenarios: 1) Panels connected in parallel where I'd get 7.5 amps x 2 = 15 amps/hr, minus higher line loses, and 2) Panels connected in series where I'd get 7.5 amps/hr plus whatever I gained from the mppt and lower line loses. It's probably more complicated than this but wouldn't I get more power connecting the panels in parallel?
    BART
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #6
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    Re: Proposed RV Solar Setup Comments?
    blmhb wrote: »
    Regarding the series/parallel question, I figured there were two scenarios: 1) Panels connected in parallel where I'd get 7.5 amps x 2 = 15 amps/hr, minus higher line loses, and 2) Panels connected in series where I'd get 7.5 amps/hr plus whatever I gained from the mppt and lower line loses. It's probably more complicated than this but wouldn't I get more power connecting the panels in parallel?
    BART

    You are forgetting the voltage. In series you would get 7.5 amps yes, but at double the voltage. Works out to the same wattage either way.

    The parallel connection is not as sensitive to shade - if there is even a tiny corner of your panel in shade, it can reduce your panel's output to almost nothing. If you connect the panels in series, then the whole "string" puts out less.

    In parallel, only the panel in the shade puts out less, while the one in full sunlight still puts out full power.


    Oh, and the temp sensor - both the battery and the controller heat up a bit during use, but not the same amount. Even if they are "near" to each other they probably won't be exactly the same temp.

    The controller needs to know both the voltage of the battery and the temp so that it can optimize the charging as much as possible.

    So yes, get the battery temp sensor if the controller supports it.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,448 admin
    #7
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    Re: Proposed RV Solar Setup Comments?

    Past testing/use of the Morning Star MPPT controller shows that its internal temperature sensor reads "hot" (I don't know if this is because the control gets warm (normal operation) or because of a calibration issue--or a combination of the two. This will cause the controller to drop the battery charging voltage a bit. Placing the temp sensor directly on the battery prevents this problem.

    For the most part--think of the battery "+" / common positive bus at the center of a "Star". All the wires that leave this point should be protected by a fuse sized to protect the outgoing wire from short circuits/overloads.

    So, in your case, there should be a fuse, near the battery, that goes to the "positive battery" terminal on the solar charge controller.

    You can see the 25 Amp fuse they recommend on page 17 of the manual.

    On page 41, there is a charge of wire distances vs gauge recommendations... Unfortunately, the chart does not go up to 25 amp circuits.

    Using NEC ratings--25 amp fuse would require at least 10 AWG wire between the controller and the battery bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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