Wiring at a Distance - Series or Parallel?

Hey Solheads,

I got 4 x 275W panels (1100W) to install on my A-frame garden shed. 

This shed is about 200 feet from my house, in a pasture.

VOC for each module is 44.1V. 
IMP is 7.76A

A friend thinks I could just wire the panels in series and run the VDC 200' to the charge controller, inverter, and battery bank in the house. My concern is that the voltage will be so high that, yes, the wiring will be manageable, but it makes it trickier to find a controller to handle such a voltage.

I haven't arranged anything yet; perhaps the battery bank and other components could all be insulated and stored in the shed, thus a case can be made to wire in parallel. I know the wiring is contingent on the specifications of the charge controller.

All I know now is that I plan to run my system at 24V.

Any help is much appreciated.


  • BB.BB. Super Moderators, Administrators Posts: 32,226 admin
    Welcome to the forum Avacc,

    Yes, sending high(er) voltage and low(er) current is the way to go...

    You could put the panels+batteries+AC inverter in the shed, and send the 120/240 VAC long distances.

    Or you can get solar charge controllers that manage with higher array voltages (and lower current). In general, there are a lot of MPPT controllers with Vpanel max around 140-150 VDC... That typically works out to Vmp-array of ~100 VDC maximum. Since solar panel output varies with temperature (sub-freezing days, upwards of 20% higher output voltage), the exact Voc/Vmp of the array, many companies offer a website or similar to help you calculate the maximum working voltage/wattage for the array.

    And, there are other variations, for example Midnite MPPT controllers (generally) have a "hyper volt" protection against over voltage... Their controller will shut down at 150 VDC, but will "not be damaged at 150 VDC + Vbattt... Or 150+24 vdc batt = 174 Voc-panel max.

    Midnite also have controllers that have higher working voltages (up to 250 VDC max working voltage).

    There are also charge controllers that have upwards of 600 VDC max working voltage (Vmp-array~400 VDC max). Both Schneider and MorningStar have versions of these (tend to be pricey charge controllers).

    You can look through our host's store (they pay the fees and maintain our nice little forum here) and get an idea what is out there (as always, refer to the product manuals--I am not in the business and things change and/or I have forgotten stuff).


    You don't have to purchase from Northern Arizona Wind & Sun for support on the forum--We are open to all.

    So, roughly the minimum output of the MPPT charge controller would be:
    • 1,100 Watt array * 0.77 panel+controller derating * 1/29.0 volts charging = 29 Amps typical "maximum (best case)" charging current
    And when you pick your solar panels and have a long distance back to the charge controller... You may find that 2x of your panels end up with (2x 36 volts =) 72 VDC Vmp-array... So you end up with 2x series and 2x parallel panels (if you are in cold climate).

    However if you pick different panels (like Vmp~30 volts), you can put 3x of them in series. Higher Vmp-array, lower current, smaller copper cable from array to charge controller... However, your array can only be 3x series, or 2x 3x series parallel (for 6 panels, etc.)... You kind of get wrapped around the axel with different components, choices of charge controllers, etc.

    That is why paper designs before you purchase any hardware is important. Sometimes the h/w you got on sale/Craig's List, cannot be easily configured into your system needs.

    You have not talked about where your system will be installed (hours of sun per day, by season) and your battery bank (brand/model/number of batteries/connections) and your energy needs... So, really no idea if 1,100 Watt array is "enough" for your needs or not.

    Typically we like to:
    1. Pick loads that are highly efficient (laptop computer vs desktop, solar friendly well pump, LED lighting, etc.) and figure out working voltage (120 VAC, or 24 VDC or mix). Almost always cheaper to purchase energy efficient appliances that to build a "bigger" solar power system to run inefficient loads.
    2. Size the battery bank to run your loads for 2 days without sun (various reasons) and typical maximum discharge of 50% (longer flooded cell lead acid battery life). There are some other suggestions, like avoid a 12 volt battery bank at 1,400 AH. Next step up is 24 volts @ 700 AH (same stored energy, but current is 1/2--Smaller cables needed for battery bus and AC inverter connections, less voltage drop issues, etc. if you keep the battery bank below ~800 AH).
    3. Size the array to 5% to 13% or so rate of charge. 5% can work for summer/weekend system. 10%+ rate of charge suggested full time off grid system
    4. Also, check the size of the array for your daily loads by season... Array has to be large enough to supply your loads and keep the battery bank charged.
    5. Backup genset... Size genset+AC battery charger, if needed for winter/bad weather power. For many people in sunnier climates, they can go with a larger solar array and avoid generator runtime most of the year, or even never need to run the genset.
    Once you have a back of the envelope of your energy needs, then you can layout the system and see what components will meet your needs (and cost points).
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • EstragonEstragon Registered Users Posts: 4,495 ✭✭✭✭✭
    In locating bank et al:

    Pro-shed; run 120/240vac to house on smaller wire, could get away with a cheaper  controller, don't have to deal with hazards of batteries in the house

    Con-shed; batteries may not be happy if too hot (shortened life expectancy) or cold (lower effective capacity, can't charge lithium sub-freezing) though insulation would help, might be a PITA going to shed to (eg) reset inverter after overload just as the show on TV was getting good, sometimes stuff in sheds is more likely to "grow legs" and walk away :wink:

    The shed plan makes more sense to me just in terms of wiring, but other considerations might tip the balance back to house?
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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