12 v or 24?

RadiomanRadioman Registered Users Posts: 7
How do I know if I need a 12v system or 24? I have four 130 watt pannels .

Comments

  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: 12 v or 24?

    if you not looking to ever expand it very much and you keep the wire runs fairly short say less than 15 ft from panels to charge controller and about 6ft from controller to batteries and 4 ft from batteries to inverter 12 v is ok.. and it easy to connect many low voltage items. as most are 12v
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 12 v or 24?

    You figure it out by determining your intended loads. If your use is high, then the higher voltage system is better because it reduces the DC Amperage. Generally speaking, if you're under 2000 Watts then the advantages are with the 12V - including the ready availability of 12V parts and accessories (auto/RV equipment).

    Your (4) 130W panels are in the "less than 2000 Watt system" range, but that's not the starting point for design.
  • RadiomanRadioman Registered Users Posts: 7
    Re: 12 v or 24?

    I am planning on adding four more pannels at some time. Do I need a combiner box and what gage wire do I need from panels to combiner and from there to controller? I am about 15' from pannel to controller.
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: 12 v or 24?

    well even with 8 panels its only about 1000 real watts. so Iwould stay with 12v as your cable distance is ok.. I would run #6 cable from combiner box to controller.

    But really you need top know what your load and time usage of the system is going to be before deciding on the panel array size..
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 12 v or 24?

    And to really understand wire sizing

    http://forum.solar-electric.com/showthread.php?t=29

    Also, be sure and read the instruction manuals that come with your equipment. The better quality manufacturers are quite good about including info regarding proper wire/fuse sizing for their particular device in respect to different applications.

    Be sure to work out and plan all of your design before your start buying & building; it works better that way. Otherwise you end up with shortcomings due to unforeseen circumstances. They usually take the form of "out of money".

    As Icarus always says; "Avoid ready, fire, aim!"
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: 12 v or 24?

    system of what, pvs or batteries or both? many will use higher voltage pv systems to help keep voltage drop losses down. when the pv design voltage is higher than the battery design voltage (like 24v pv and 12v battery) then this needs a downconverting mppt controller to accomplish that. going 12v to 12v or 24v to 24v can take a standard pwm controller, but the mppt controller is also advantageous for larger systems by recovering some of the lost charge power.
    if you already have, say, a 12v inverter and 12v lights then this dictates what your battery system will be unless you desire or need to buy new stuff designed for 24v. sometimes the same voltage drops that influence a pv system voltage could also influence a battery system design voltage as huge amounts of current flowing can cause significant voltage drops if the wire isn't large enough or even short enough.
    that was fairly general and we can comment further if we know what all you have and what all you have in mind? btw, anytime there are more pv inputs than the controller can take, then combiners are needed. the output of that combiner will be of a larger sized wire to handle the combined pv currents for the distance it needs to travel and of course don't forget fuses or circuit breakers.
  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: 12 v or 24?

    With 1KW of panels, look at using an MPPT controller. Wire the panels for 24V to the charge controller. Then use an 12V battery(ies). Will cost more up front, but will have a better system in the end.
  • tallgirltallgirl Solar Expert Posts: 413 ✭✭
    Re: 12 v or 24?
    n3qik wrote: »
    With 1KW of panels, look at using an MPPT controller. Wire the panels for 24V to the charge controller. Then use an 12V battery(ies). Will cost more up front, but will have a better system in the end.

    Disagree -- go as high as possible on the DC voltages if there are any AC loads. Higher DC voltages means much smaller cables and power lossage.
  • Solar GuppySolar Guppy Solar Expert Posts: 1,962 ✭✭✭
    Re: 12 v or 24?
    tallgirl wrote: »
    Disagree -- go as high as possible on the DC voltages if there are any AC loads. Higher DC voltages means much smaller cables and power lossage.


    Losses on DC side is purely based on the wire size. This is something an owner/installer can configure to suit their needs or budget. Further most of the loss is only at the peak production, 2/3rd of the day the losses would be less than half as the peak hour or so of the day. The loss is current squared times resistance for the power loss.

    One can over look what can be a significant loss in the charge controllers, which can easily be 2-3% more losses and thermal stresses on the charge controller, The higher Voltage In, Voltage out differential, the less efficient the charge controller will operate at, regardless of which brand.

    So while using smaller wire for higher voltages can have less wire loss, its almost always negated by charge controller decrease in efficiency were as a larger wire with lower loss allows the charge controller to have a smaller Vin and operate more efficiently.
  • halfcrazyhalfcrazy Solar Expert Posts: 720 ✭✭✭
    Re: 12 v or 24?

    Beware of 48 volt You will be forced to buy in larger quantities to meet battery voltage.

    My rule of thumb is

    12vdc-small camp style system up to say 1kw of panels and 1500 watt inverter

    24vdc-large camp size or small to medium house around 2kw of panels and around a 4000 watt inverter

    48vdc- large house size system

    But like i said for the 3 examples if you wanted to add panels and they are 12vdc each you could buy 1 at a time for 12vdc but would need to buy 4 at a time for 48vdc
  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: 12 v or 24?
    tallgirl wrote: »
    Disagree -- go as high as possible on the DC voltages if there are any AC loads. Higher DC voltages means much smaller cables and power lossage.
    Losses on DC side is purely based on the wire size. This is something an owner/installer can configure to suit their needs or budget. Further most of the loss is only at the peak production, 2/3rd of the day the losses would be less than half as the peak hour or so of the day. The loss is current squared times resistance for the power loss.

    One can over look what can be a significant loss in the charge controllers, which can easily be 2-3% more losses and thermal stresses on the charge controller, The higher Voltage In, Voltage out differential, the less efficient the charge controller will operate at, regardless of which brand.


    So while using smaller wire for higher voltages can have less wire loss, its almost always negated by charge controller decrease in efficiency were as a larger wire with lower loss allows the charge controller to have a smaller Vin and operate more efficiently.

    I think TallGirl was looking at the battery voltage, not the array voltage. This is a valid point. At 1KW with a 12 volt system, it will work and gives the OP ability to use 12 volt devices. If OP is going to be using only 120 AC volts, then a 24/48 volt battery bank would be better.

    I have lots of stuff that run off of 12VDC, so that is my mindset when working/typing on this stuff.

    Plus, I agree to disagree :D
  • tallgirltallgirl Solar Expert Posts: 413 ✭✭
    Re: 12 v or 24?
    n3qik wrote: »
    I think TallGirl was looking at the battery voltage, not the array voltage. This is a valid point. At 1KW with a 12 volt system, it will work and gives the OP ability to use 12 volt devices. If OP is going to be using only 120 AC volts, then a 24/48 volt battery bank would be better.

    I have lots of stuff that run off of 12VDC, so that is my mindset when working/typing on this stuff.

    Plus, I agree to disagree :D

    Nah, talking about all possible voltages. High panel voltage and high battery voltage is my preferred.

    I also disagree with the poster who said it cost more to go higher -- that depends on a LOT. Battery banks still have to be kept of similar age and condition, so a higher voltage bank brings advantages in terms of fewer paralleled strings, which is its own reward.
  • nigtomdawnigtomdaw Solar Expert Posts: 705 ✭✭
    Re: 12 v or 24?

    I agree with Julie in the home,higher base voltage offers more inverter efficiency, no cost hit, on purchase price, more PV allotment to a charge controller, smaller amp carriage thus smaller wiring size thus less cost, and I really am enjoying Julies take to Naws

    A one bank string at 48v is always better than a 4 string 12 volt battery bank or is King Kanute here ?:p
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: 12 v or 24?

    As its only a 1000w system it would seem he does NOT have any heavy loads to power.. My guess is if he was using an inverter it would be well below 1000w so 12v is ok. not really much loss in 3ft of #4 wire from batteries to inverter.. also you have the advantage of using many available things that are cheap to buy on 12v.. ie lights..not too many LED ones work on 48v ??
    And there are quite often problems with series batteries as well .they not perfect solution and nor are parallel..
    and really using a MPPT controller is not very cost effective on a small system.
  • tallgirltallgirl Solar Expert Posts: 413 ✭✭
    Re: 12 v or 24?
    john p wrote: »
    As its only a 1000w system it would seem he does NOT have any heavy loads to power.. My guess is if he was using an inverter it would be well below 1000w so 12v is ok. not really much loss in 3ft of #4 wire from batteries to inverter.. also you have the advantage of using many available things that are cheap to buy on 12v.. ie lights..not too many LED ones work on 48v ??
    And there are quite often problems with series batteries as well .they not perfect solution and nor are parallel..
    and really using a MPPT controller is not very cost effective on a small system.

    Why? PV array size and peak demand aren't related. Consider an off-grid weekend cabin. Assuming batteries sized to avoid spillage on a weekly charge cycle basis, average power availability is 7/2's that of a structure that's occupied every day. 7 / 2 * 1000 = 3500 watts. Would you say a 3500 watt PV system is "small"? I provide a sizable fraction of power for my 3 bedroom, 2 bath, high-tech gadget filled house from Fall to Spring and I have 2800 watts DC. With a pair of GVFX3648 inverters providing the AC.
  • mike95490mike95490 Solar Expert Posts: 8,489 ✭✭✭✭✭
    Re: 12 v or 24?
    Beware of 48 volt You will be forced to buy in larger quantities to meet battery voltage.

    Well, yes, 32V of panels wont do it. There are some really high voltage (72?) panels I've heard of. Would only need 1 of those. But you do have to buy all the battery interconnects, and 48V fuses are harder to get then 12V fuses.

    And there are quite often problems with series batteries as well .they not perfect solution

    Can you expand on this ? Only "problems" I can think of is more battery caps (which would be present in a parallel system anyway) and the interconnect wires.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: 12 v or 24?

    tall girl Would you say a 3500 watt PV system is "small"? NO But your statement has to do with what??? he says he has or will have a 1000 watt system??
    And mabe all his devices are 12v dc..??????? As nowhere does he say he is using or about to buy an inverter,????

    this was his first post.. its hard to know how you got from this to a weekender with everyknown electrical device known to man in it.
    How do I know if I need a 12v system or 24? I have four 130 watt pannels .
    Problems with series batteries can be but not limited to"a cell failure in one battery ":grr
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 12 v or 24?

    Note to all:

    When designing a system for off-grid, economics, economics of scale, and technical efficiency aren't the only considerations. There are a lot of things to think about, including availability and "repairability" - if you're out in the middle of nowhere you can't always get parts to put a 48V system back together. Jerry-rigging a 12V back into operation is fairly easy because you can 'borrow' stuff from the automotive world.

    I think in general we need to pay more attention to OPs and regard what their particular situation is rather than explain what the best/most efficient/cheapest per kW set-up would be.

    The only problem with multiple batteries is that the more connections you have the greater number of possible wiring faults. In the real world this isn't much of a problem.

    Let's try to maintain perspective. Look at the set-ups some off-gridders have (like Tony and me) and see how small they can be. No sense getting more than you need.
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: 12 v or 24?

    Cariaboocoot.. hooray .it so nice to hear from someone that can see this problem of over the top system designing when only something simple is needed as is most users case..

    To give my set up its 12v with 3x80 w panels 4x truck batteries 1x 30a PWM controller 1x300 w modified sine wave inverter to run all lights permanent and 1x1000w sine wave inverter for on demand use sometimes reason being it all works perfect for the job and can run my many 12v things pump/and LED security lights. simple and relatively cheap and easy to replace parts or add 12v devices..:cool:
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: 12 v or 24?

    So many get carried away with overdesigned syatems.. with over the top costs and complexities.. usually with
    I not use something home made as it may not last 30 to 40 years.. and dont want to be climbing on to roof of building in blinding snow storm and then attacked by polar bears.. so I buy everything factory made..
    Most people that want to use something home made are just people having learning experience with solar.. not trying to build or make a system to power a 70 story building
    secondly they only want to build home made parts that are simple not MPPT controllers. like low voltage cutouts etc.
    Also most solar systems have only the panels mounted on roof,, so the usual crap "have to climb on roof" to fix something is crazy .. mabe some these people do mount the batteries and inverters onthe roof to show the neighbours"my system is bigger than yours"" ????
    Think about it..
    is that system really going to be ok in 30 to 40 years?? when even controller and inverter manufacturers say life should be for those parts about 15 years..
    solar panel output at 30 to 40 yrs?? hmm how much??

    Computer connected inverters and charge controllers at 30 to 40 years.. you really think the current interfaces are going to work with your 30 to 40 years in future computer????????
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 12 v or 24?

    I never worry about 30 or 40 years down the road, because I know I won't be here then. :roll:
  • nigtomdawnigtomdaw Solar Expert Posts: 705 ✭✭
    Re: 12 v or 24?

    Best advice, is what its about , failing to show going up to 24v or 48v and its advantages is being a luddite, if the guy has a PV system or around a 1000 watts at 12 volts then it excludes him from a MX FM or XW MPPT charge controller as a single option, yes 12 volts has its attractions but so does higher base voltages.


    Like

    Charge Controllers increased PV Capacity
    Thinner wiring costs
    Higher efficiency on inverters
    Lower strings on battery bank sizes

    Over designing is not a word I understand, correct fit for purpose designing I do understand:roll:


    These all add up to cost and efficiency savings so as 12 volt systems have there place dont disregard physics as it doesnt work. If you ask for advice then listen.

    As we all know we think Yes this is good for me I can cope with this system! Reality is heck this doesnt work I need a bigger system, been there done that, so have most of us, so listen to people that have paid out the money that you dont have to. Living with a small system is perfectly OK but expecting it to perform miracles is not, some guys/gals here function well on small systems and I applaud them, my system is modest to most US systems, but I very often nearly always go to customers who have illusions of grandure on what a 12 volt 1000 watt big system can achieve. Living off grid.

    In Spain my system is considered huge with the expats, but I dont have knackered (wasted batteries) and a $1000 to $3000 fuel bill for generators as most I know, Ive said it b4 there is not such thing as too much solar living off grid.

    Ranting again as I do ;)
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: 12 v or 24?

    NIGTOMDAWyour system for most of us would have a payback time measured in decades. And it most likely be all useless junk by then .
    Even my small lighting system will NEVER have a patback time.. its only used because where its in use has many typhoons each year and blackouts from 1 day to sometimes a week.
    I dont think its being a ludite not talking about 24 or 48v systems when we talking about a small system at or below 1000watts. I think its better to keep the talk at a level that informs the original poster asking for advice. And keeping in mind his uses and where its to be used rather than giving explanations to show ones expertise on the subject .. And if you notice its always advice that involves considerable expendature.
    keep it simple 12v is just fine for most users of small (below 100w) systems..
    savings in cable costs or effeciencies going to higher voltages in such systems is just about non existant.
  • BB.BB. Super Moderators, Administrators Posts: 29,797 admin
    Re: 12 v or 24?

    Ok guys and girl... Let Radioman digest the thread and direct it where he wants it to go next (if anywhere).

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