12v or 24v in this situation

Hi there, I think this is a simple question but I am really having a hard time finding a simple answer! I am currently using a 12v system, 3 x 24v panels @ 280w and a 30A MPPT controller to fill 4 x 160Ah batteries at 12v. I then use a 1000w, 12v to 220 Inverter.

Simply put, is there any advantage of changing it up to a 24v system? ie. Recable the batteries so there are 2 banks of 24v, then use a 24v to 220v AC inverter? My MPPT controller accepts either 12v or 24v batteries. Will it charge the batteries "faster" or more efficiently if they are in 24v strings rather than 12v? Or am I already getting the same charging efficiency from 12v that I would from 24v by already having the MPPT?

Thanks

Comments

  • mike95490mike95490 Solar Expert Posts: 8,380 ✭✭✭✭✭
    Re: 12v or 24v in this situation

    Your gains are not in recharge time, but in savings of expensive copper wire, and less losses with a higher voltage system.
    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
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  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: 12v or 24v in this situation
    BigBrosMo wrote: »
    Hi there, I think this is a simple question but I am really having a hard time finding a simple answer! I am currently using a 12v system, 3 x 24v panels @ 280w and a 30A MPPT controller to fill 4 x 160Ah batteries at 12v. I then use a 1000w, 12v to 220 Inverter.

    Simply put, is there any advantage of changing it up to a 24v system? ie. Recable the batteries so there are 2 banks of 24v, then use a 24v to 220v AC inverter? My MPPT controller accepts either 12v or 24v batteries. Will it charge the batteries "faster" or more efficiently if they are in 24v strings rather than 12v? Or am I already getting the same charging efficiency from 12v that I would from 24v by already having the MPPT?

    Welcome to the forum,

    One of the main advantages of going 24 volts for you is that your batteries will be in two parallel strings, rather than four strings. That will be a huge advantage for your batteries because parallel battery banks are unstable. short discussion here:
    http://forum.solar-electric.com/showthread.php?14674

    How are your panels configured (three in series or in parallel?) What is the Vmp and Voc of the panels? What is the Vmax of your controller? The reason I ask is that depending on the Vmp of your panels, they may have to be in series to charge a 24 volt battery. If they are in series, the Voc of the string may exceed the Vmax of the controller.

    As far as charging efficiency is concerned, your MPPT controller will be most efficient when down converting from a string Vmp that is 15 - 20 volts above your nominal battery voltage.

    You asked about whether a 24 volt system would be better for your batteries. The answer is yes, but I wouldn't necessarily change your system just for the sake of your batteries... your batteries are ephemeral. (how old are they now?) More importantly, does a 12 volt system meet your needs? If so, save some money by not upgrading and put the money into your "next battery fund".

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • westbranchwestbranch Solar Expert Posts: 5,142 ✭✭✭✭
    Re: 12v or 24v in this situation

    What are the specs of those panels and which MPPT Cc is it?
    Reason I ask is you may be near the limitations of a 12 v setup, and may benefit from a change to 24v, but can't know without the specs of the equipment.
     
    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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