Best array configuration for a 24 volt system

Hairfarm
Hairfarm Solar Expert Posts: 225 ✭✭✭
Greetings,

I'm considering upgrading to 24 volt when I add two new panels to my array.

In the end I'll have 8 panels. They are 135 watt Kyocera. 17.7 volts, 7.6A.  I'm thinking two strings of four panels each in parallel for 70.8 volts, 15.3 amps.  Is this array config still too high for a 24 volt system?

thanks

Comments

  • Raj174
    Raj174 Solar Expert Posts: 795 ✭✭✭✭
    No, it's not too high as long as the MPPT controller can handle the VOC voltage, 4 per string will work fine.
    4480W PV, MNE175DR-TR, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 360AH nominal LiFePO4, Kohler Pro 5.2E genset.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Hairfarm said:
    I'm considering upgrading to 24 volt when I add two new panels to my array.

    In the end I'll have 8 panels. They are 135 watt Kyocera. 17.7 volts, 7.6A.  I'm thinking two strings of four panels each in parallel for 70.8 volts, 15.3 amps.  Is this array config still too high for a 24 volt system?
    What controller are you using?  Many (most?) MPPT controllers will work OK with 4 of those panels to a string. 

    Do you have room for 9 panels?  If so, 3 strings of 3 panels per string (string Vmp = 53.1) would be ideal.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Hairfarm
    Hairfarm Solar Expert Posts: 225 ✭✭✭
    What controller are you using?  Many (most?) MPPT controllers will work OK with 4 of those panels to a string. 

    I'm using an Outback Flexmax 80. Max VOC for the CC is 150V I only have room to add two more panels for a total of eight.


    thanks!


  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    edited September 2016 #5
    vtmaps is saying use strings of 3 panels so you won't have a problem with VOC. You should use try to limit incoming voltage to about 2x the system voltage, 24 volt x 2 = 48 volts. This will keep the charge controller from working as hard down converting the higher voltage to a lower voltage and losing some of your energy in the process of aging your charge controller quicker.

    There is a string sizing tool for the Flex Max 80 here;

    http://www.outbackpower.com/outback-support/string-sizing-tool

    But in a 24 volt configuration, with an 80 amp output max, you should be able to handle 1900 watts of array minimum (1900 watts ÷ 24 volts = <80 amps) and cost effective to around 2500 (2500 x 75% normal output of array = 1875 watts), with the charge controller limiting output to 80 amps for those cool days.
    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.