2 variations of the same installation question

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bmet
bmet Solar Expert Posts: 630 ✭✭
in Solar Beginners Corner #1
I am preparing to start the installation of my 1800 Watts of solar panels, for an RV. the location of the array is going to be about 75 feet away. I would like the opinion of the forum members, on which installation would make more sense.

1. Locate everything at the solar array and run the inverted AC the 75 feet to the RV

2. use the higher voltage from the combiner box, to span the distance to a charge controller at the RV.

The 24V, 225 watt solar panels would be configured in two strings of 4, with a VOC of approximately 104 volts each.
Another way of doing it, would be 4 strings of two into the combiner, avoiding need for a fuse, and having the charge controller and battery at the same spot.

I would like to use a 24 volt system but because of the 30 Amp requirement, not sure if that would be a wise idea.
I would appreciate any thoughts that readers have on these two variations of this installation. thank you
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #2
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    Re: 2 variations of the same installation question

    what Cc will you be using, that may impact what voltage you (can) run to the RV
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #3
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    Re: 2 variations of the same installation question
    bmet wrote: »
    The 24V, 225 watt solar panels would be configured in two strings of 4, with a VOC of approximately 104 volts each.
    Another way of doing it, would be 4 strings of two into the combiner, avoiding need for a fuse, and having the charge controller and battery at the same spot.
    four strings coming into the combiner will require fuses/breakers in each of the four strings. Two strings will not require fuses/breakers in each string.
    bmet wrote: »
    I would like to use a 24 volt system but because of the 30 Amp requirement, not sure if that would be a wise idea.
    I don't understand... what 30 amp requirement?

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #4
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    Re: 2 variations of the same installation question

    Hi bmet,

    First, the "24 Volt" PV modules are probably NOT really 24 V modules ... It is possible, but it is rare for real 24 V modules to have a power rating in this range. 24 V modules should have 72 Cells, and have a Vmp of about 35-ish volts. And with the stated Voc of 104 V nominal for four in series, something seems a bit off. Four 24 V PVs in series would have a Voc of about 175 volts or so.

    Some 220-ish PVs have 54 cells. A very common cell configuration for 220 - 250 watt PVs is 60 cells, but for either, four modules in series would yield a voc of at least 120 volts @ STC conditions.

    Exactly which PV module are you considering? -- Manufacturer and P/N please. Thanks, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #5
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    Re: 2 variations of the same installation question

    Well still palletized, I'm guessing you have ESE panels and perhaps your using the NOTC (normal operating temperature conditions)? That would still be 26.9V for 225 watt panels...

    Reguardless there are other questions, along with if this will be grid connected, though it looks like an off grid if your running an inverter to the RV, looks like your still in the planning stages for a charge controller.

    Since longevity of the batteries depends on them being kept as cool as possible, will the RV be shaded? Air conditioned? could you/would you be willing to build a berm shelter for the batteries near/under the array?

    I'm a fan of leaving the batteries near the array, for several reasons, it moves one potential hazzard away from another, I've cooked with gas in the past, if my place burns down I still have my solar system, if my inverter decides to freak out it doesn't fill my cabin with smoke or a potential fire. But I live in Missouri where typically we have 6 weeks of summer and the batteries living in the shade of my array stay reasonably cool. SW Texas is likely a harder place to do this, hence the berm shelter (earth around a structure, poured or concrete blocks allowing the earths temps to help cool the structure), which should keep them cooler...

    Not sure what 30 amp requirement your refering to either, there is a limited access for above 30 volts, but your panels exceed that either as ESE's or 24V nominal.
    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.
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  • bmet
    bmet Solar Expert Posts: 630 ✭✭
    #6
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    Re: 2 variations of the same installation question

    vtMaps,
    the 30A, 120VAC, is what the RV requires for utility hookup.
    thank you for clearing up my confusion on the series strings,
    i thought that more than 2 pvs connected in series needed a fuse, clearly i misunderstood.

    vic,
    off the top of my head i don't recall how many many cells, these have a voc of 36v, and a vmp of 29.5v.
    i was adding the voc of 4 in series to determine my charge controller needs. At this point i am leaning toward
    a midnight classic 200. it gets hot and humid here, not cold very often.

    photowhit,

    not sure of the exact model of evergreen, got to look it up and return.

    Thanks everyone, for your input. i'll be updating info later today
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #7
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    Re: 2 variations of the same installation question
    bmet wrote: »
    thank you for clearing up my confusion on the series strings,
    i thought that more than 2 pvs connected in series needed a fuse, clearly i misunderstood.

    It is 3 or more strings in parallel that need a fuse per string (1-20 cells in each series string--fusing does not matter--It is the # of parallel strings that drive the per string fusing requirement).

    The series protection fuse/breaker is usually listed on the data sheet and is around 1.56x Isc.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • bmet
    bmet Solar Expert Posts: 630 ✭✭
    #8
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    Re: 2 variations of the same installation question

    i looked up evergreen specs, these panels are from the FA series.
    Imp-7.65A
    Vmp-29.5V
    Isc-8.33A
    Voc-36.1V

    Photowhit, keeping heat from the batteries is a primary concern. The RV is a fifth wheel, so the batteries could be sheltered for most of the day.
    if I placed the batteries at the array, they would not be as well shielded from heat. not sure what the best solution is, maybe something unconventional could work.
    the location of the array is going to be in a pasture. maybe a cabinet constructed of cinder blocks filled with dirt might be good against heat.
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