How to wire 7 12v panels to achieve 24v?

Hello...

Just discovered I need more panels to cover the load of my new graphic workstation. Currently I have 4 x 12v in parallel.

At a minimum I could add 2 more, and wire them to output 24v, as this would benefit me by not having to upgrade my 'buried' and amp limited combiner to controller wires.

But, ideal I want the 3rd additional panel for a total of 7, as this covers the new loads.

Can someone show me how to wire 7 panels and achieve 24v?

Thanks!

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,612 admin
    Re: How to wire 7 12v panels to achieve 24v?

    What kind of charge controller do you have?

    Are you planning on upgrading to a 24 volt battery bank?

    What is your existing/planned battery bank voltage/current?

    What charge controller do you have now?

    Is this an off-grid or on-grid system (emergency backup) or something else?

    What make/model/size (Vmp, Imp) of solar panels do you have?

    How cold does it get in your area (near the water or in the back country)?

    Basically, the only way you can efficiently use the extra voltage (say "24 volt" wired panels and a "12 volt" battery bank) is to use a MPPT type charge controller.

    And, depending on the exact panels and how cold it gets in your area and what type/brand/model of charge controller--there will be a current and voltage limit to the array and battery charging current... But you will either have to live with 7 panels in series and a high-end MPPT charge controller, or get more/less panels and figure out your series x parallel setup: 1x7, 2x4, 4x2, 2x3, or 3x2--etc.

    Usually we suggest:
    1. Conservation
    2. Measure your loads with a kill-a-watt and/or DC Amp*Hour/Watt*Hour meter
    3. Battery bank around 3 days of no-sun and 50% maximum discharge (3-6x daily load)
    4. Solar Array sized (based on where it is installed for available sunlight) to battery bank and to keep up with your daily load for at least 9 months of the year without need for a generator
    5. Pick Charge controllers, inverters, generators, solar panel setup that meets your needs.
    We have quite a few posters here who are up in Canada--And they can give you some information on what they do for off-grid power up there.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • OrioNOrioN Registered Users Posts: 13
    Re: How to wire 7 12v panels to achieve 24v?
    BB. wrote: »
    What kind of charge controller do you have?

    Are you planning on upgrading to a 24 volt battery bank?

    What is your existing/planned battery bank voltage/current?

    What charge controller do you have now?

    Is this an off-grid or on-grid system (emergency backup) or something else?

    What make/model/size (Vmp, Imp) of solar panels do you have?

    How cold does it get in your area (near the water or in the back country)?

    Basically, the only way you can efficiently use the extra voltage (say "24 volt" wired panels and a "12 volt" battery bank) is to use a MPPT type charge controller.

    And, depending on the exact panels and how cold it gets in your area and what type/brand/model of charge controller--there will be a current and voltage limit to the array and battery charging current... But you will either have to live with 7 panels in series and a high-end MPPT charge controller, or get more/less panels and figure out your series x parallel setup: 1x7, 2x4, 4x2, 2x3, or 3x2--etc.

    Usually we suggest:
    1. Conservation
    2. Measure your loads with a kill-a-watt and/or DC Amp*Hour/Watt*Hour meter
    3. Battery bank around 3 days of no-sun and 50% maximum discharge (3-6x daily load)
    4. Solar Array sized (based on where it is installed for available sunlight) to battery bank and to keep up with your daily load for at least 9 months of the year without need for a generator
    5. Pick Charge controllers, inverters, generators, solar panel setup that meets your needs.
    We have quite a few posters here who are up in Canada--And they can give you some information on what they do for off-grid power up there.

    -Bill

    Thanks Bill for the quick reply...

    What kind of charge controller do you have?
    Solar Boost 3024iL (Will be swapped for a Solar Boost 50)

    Are you planning on upgrading to a 24 volt battery bank?
    No... Inverters are both 12 volt.

    What is your existing/planned battery bank voltage/current?
    Existing bank is 4 x 4D Discover EV4DA-A - 980aH total / parallel 12V

    What charge controller do you have now?
    Solar Boost 3024iL (Will be swapped for a Solar Boost 50)

    Is this an off-grid or on-grid system (emergency backup) or something else?
    Off-grid... mobile design studio (custom rv). Backup system is a under carriage propane powered 2.5kW generator.

    What make/model/size (Vmp, Imp) of solar panels do you have?
    4 x Carmanah CTI-95(formerly Sunpower SPR90) 95W/ 380W total. Vmp: 17.6, Imp: 5.5

    How cold does it get in your area (near the water or in the back country)?
    I'm mobile... temperatures range from -20F to 105F. Batteries are inside RV and range from 40F to 110F. I spend winter in the AZ sun and summers in the Vancouver 'Sun'

    Basically, the only way you can efficiently use the extra voltage (say "24 volt" wired panels and a "12 volt" battery bank) is to use a MPPT type charge controller.
    Doing MPPT now...

    So just to re-iterate... and add more details...

    I only have room for 3 more and same panels on my rooftop. The current panels were selected for their excellent amp to sq. ft ratio, and foot print (length) for my narrow Sprinter roof and racking/awning/equipment setup.

    This is a mobile design studio with a computer workstation. Computer, monitor, modems, 5.1 speakers (do I see eyes rolling?) use 16-18aH (min.). Current setup can do 22aH, which doesn't leave me headroom to charge up for 'no solar' hrs. The past year I use my notebook, modems and 5.1's and used 7-9ah, and I was in the 'black'. So 2 additional panels would/could do and are easy to wire as a 24V PV, but at this point I have to option for the 3rd or 7 total panels.

    Also, I'm trying to avoid replacing the main 6g wire from my rooftop combiner to the controller (12 ft), for convenience purposes. Plus I hear having a 24v PV has some advantages?

    Thanks!
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: How to wire 7 12v panels to achieve 24v?

    If you are doing MPPT now, and going to do MPPT with the new controller, then it probably doesn't have to be 24v on the input - some can handle 150v or more - so why bother trying to stick with that restriction?

    Setting them up at a higher voltage would also help to keep the amperage down to something that that #6 can handle. If your MPPT controller can handle it, you could just wire the whole string of 7 in series and not need the combiner box.

    As for how to wire 7 panels to get 24v...I'd guess you'd have to setup 2 in series for 24v, then another 2 in series for 24v, then 2 in parallel for 12v and then series that with the remaining panel to get 24v. That would be 3 24v strings, which would then be paralleled.

    I dunno if that would work though - need to get an engineer's opinion.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: How to wire 7 12v panels to achieve 24v?

    orion,
    you'll need to wire them all in parallel with the odd number of pvs as it won't work for 24v. there is a slight advantage with a higher input voltage, but i think you will need to design the wiring for the current it'll have with all pvs paralleled.

    thanks for the info on an offbranded sunpower pv. is this the same as those with all of the wiring in the rear of the cell or does it have tracks on the face of the cell?
  • KamalaKamala Solar Expert Posts: 452 ✭✭
    Re: How to wire 7 12v panels to achieve 24v?

    I think that the max Vin for the 3024iL is 57V. Seven of the indicated panels will exceed this value if wired in series.

    K
  • OrioNOrioN Registered Users Posts: 13
    Re: How to wire 7 12v panels to achieve 24v?

    He's back...

    So I took the liberty of creating a wiring diagram based on dwh's method.

    Does anyone see how and where this wouldn't work?

    Thanks!
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: How to wire 7 12v panels to achieve 24v?

    it will not work as the added current from the 3rd pv will be limited by the pv those 2 paralleled pvs that they would be in series with. it will only pass the current of a single pv and being a prime number of pvs it will not work in any other configurations for a mppt controller except for all in series if the controller can handle that high of a voltage input or all in parallel. 24v output is then only available for 7 12v pvs with all in series as paralleled leaves only the 12v output.
  • mike95490mike95490 Solar Expert Posts: 9,572 ✭✭✭✭✭
    Re: How to wire 7 12v panels to achieve 24v?

    The last segment of 3 panels, just toss one of them away. There is no good way to wire an odd number of panels like this.
    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 ,

  • OrioNOrioN Registered Users Posts: 13
    Re: How to wire 7 12v panels to achieve 24v?

    UNCLE!!

    You guys win...

    So the big (new) questions is...

    Which MPPT controller do I now go with?
    What do you guys recommend?

    7 panels wired in series, I will now have:

    ~126 volts
    665 watts


    Thanks!
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: How to wire 7 12v panels to achieve 24v?

    at this point it looks like none of them will work all 7 in series as the voc is likely over the max limit for the controllers out there. i don't know if anybody else knows of one and they are welcome to chime in if they do know. midnight solar will have the classic some time in the future with 2 high voltage versions, but they are still all in beta right now. you could temporarily use them in a 12v configuration and make the batteries that way also with a pwm controller of sufficient current capacity until the classic comes out or find a way to add an 8th pv so that you could series/parallel the pvs for 24v and be able to use an mppt controller already available. 4 strings of 2 in parallel works for most mppt controllers out there, but read specs to be sure.
    it's your decision on which way to go with this as we can only make some suggestions.
  • OrioNOrioN Registered Users Posts: 13
    Re: How to wire 7 12v panels to achieve 24v?
    niel wrote: »
    at this point it looks like none of them will work all 7 in series as the voc is likely over the max limit for the controllers out there. i don't know if anybody else knows of one and they are welcome to chime in if they do know. midnight solar will have the classic some time in the future with 2 high voltage versions, but they are still all in beta right now. you could temporarily use them in a 12v configuration and make the batteries that way also with a pwm controller of sufficient current capacity until the classic comes out or find a way to add an 8th pv so that you could series/parallel the pvs for 24v and be able to use an mppt controller already available. 4 strings of 2 in parallel works for most mppt controllers out there, but read specs to be sure.
    it's your decision on which way to go with this as we can only make some suggestions.

    VOC is 150.5v (7 x 21.5).
    8th panel is not possible, absolutely no room left on the roof.

    :cry:
  • BB.BB. Super Moderators, Administrators Posts: 32,612 admin
    Re: How to wire 7 12v panels to achieve 24v?

    Not cheap, but two MPPT solar charge controllers. Once for 4 panels, the other for three...

    Short of placing two very expensive 45+ amp MorningStar or equivalent MPPT charge controllers in parallel to the battery bank... Could you add an "eight panel" and use it as a "porch roof" over your entry door (fold it against the side of the RV while traveling and fold it out flat near the roof line as a sun/rain roof)?

    Otherwise contact boB and Midnite Solar directly and see if you can get a high voltage controller from them in a useful time frame for you.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: How to wire 7 12v panels to achieve 24v?

    bb does bring up a valid option in the 2 controllers, but as he said it is expensive to go with 2 and you have few options at this point that are cheap or easy just so that odd 7th pv could be used. 150.5v is overvoltage i believe for all mppt controllers that i know of that are currently available, but i'm still holding out hope for somebody to chime in with one we may not be thinking of or aware of.
  • OrioNOrioN Registered Users Posts: 13
    Re: How to wire 7 12v panels to achieve 24v?
    niel wrote: »
    bb does bring up a valid option in the 2 controllers, but as he said it is expensive to go with 2 and you have few options at this point that are cheap or easy just so that odd 7th pv could be used. 150.5v is overvoltage i believe for all mppt controllers that i know of that are currently available, but i'm still holding out hope for somebody to chime in with one we may not be thinking of or aware of.


    Looks like for VOC:

    Outback Flexmx 60:
    150 VDC absolute maximum coldest conditions / 145 VDC start-up and operating maximum

    Xantrex XW 150 Voc

    Hmmm....

    Also, I'm also severly space limited, I can't add a second controller of the same sizing, I can barely swapout for a Xantex XW or Outback 60. It's a Sprinter RV with most space already alloted for.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: How to wire 7 12v panels to achieve 24v?
    OrioN wrote: »
    Looks like for VOC:

    Outback Flexmx 60:
    150 VDC absolute maximum coldest conditions / 145 VDC start-up and operating maximum

    Xantrex XW 150 Voc

    Hmmm....

    I remember seeing one that did I think 200v or 220v or some such. Apollo?
  • BB.BB. Super Moderators, Administrators Posts: 32,612 admin
    Re: How to wire 7 12v panels to achieve 24v?

    Looks like DWH is correct... There is an Apollo HV with Voc = 200 VDC.
    Model: T80HV
    200 Volt Input, 80 Amp MPPT Charge Controller
    200 V max PV input voltage (Voc)

    Do some reasearch about the Apollo reliability... (Windsun, our admin here from NAWS):
    Windsun wrote: »
    Just a heads up - we no longer carry the Apollo stuff for the simple reason that far too much was coming back on warranty.

    Although, price wise, the two 45 amp controllers are not that much more (size may be another issue). The Apollo does come with a Battery Monitor --may justify the extra costs.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: How to wire 7 12v panels to achieve 24v?

    looks like your options are growing, but will still be an expense.
  • OrioNOrioN Registered Users Posts: 13
    Re: How to wire 7 12v panels to achieve 24v?
    niel wrote: »
    looks like your options are growing, but will still be an expense.

    Still much less than rent up here in Vancouver! And I'm talking one month!
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