system design question

louielouie
louielouie Registered Users Posts: 18
Noob here.
My system will be off grid.
This will be an upgrade/expansion for me as I currently have two kyocera 235watt panels feeding a morningstar MPPT-45, feeding a 12vdc system.
I have only read 14 pages of the beginners forum, so I guess you could say I haven’t done all my research before asking this question(s). I have seen bits/pieces of what I want to do, but not something that addresses my specific question. Of course, this is where cariboocoot starts getting that déjà vu feeling.
My proposed system:
Did I mention my system will be off grid?
Two parallel pv arrays. The arrays will be identical twins, panels, power. All of the uncontrollables will be present, wire length, shading, etc. Each array will feed a charge controller. It will be up to me to insure no component is overloaded, connected properly, wiring properly sized, combiners, breakers, etc.
What I would like to do:
Did I mention my system will be off grid?
Each array will tie/feed their own charge controller. The two charge controllers will then combine/join to tie into the battery bank. The system will be 48vdc. I can sense I have just angered Neil(?) and his 12vdc system.
What I am asking/confused about is:
Did I mention my system is off grid?
Should both charge controllers be MPPT(morningstar)?
Should I instead arrange the battery bank in parallel as well? I.e., each array would feed an MPPT that would feed a battery bank. I would then make the battery bank 24vdc and the inverter as well.
I don't plan on violating more than half the NEC, and/or three of the commandments. Of course, after I start assembling the system, all bets are off.

Comments

  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: system design question

    You can have a single large battery bank (any voltage) fed by 2 different charge controllers. If I was to upgrade my system with a 2nd array, I'd aim the larger one 20 deg East for a boost of morning charge, and the smaller one, 10deg west, to improve my evening charge.
    Unless your charge controllers are networked together with a data cable, even if they have the same settings programmed, one will sense voltages 0.01 differently, and the other one will lag a few minutes. It should not be an issue worth worrying about.

    Keep all the proper fuses and such, and it should be OK.
    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 ,

  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: system design question

    You won't anger Neil with a 48V system, likely he'd recommend it if you need a fairly large system...

    ...but that's where your off on the wrong foot. We first need to know your energy needs. Do you have some idea of how many Kwh you'll need each day? This is where all sensible discussion of systems start.

    If you need help with this, if your plan on using all of the electrical items you currently use in the manner your currently are, How many Kwh a month do you use from your electric bill?

    We'll also need to know what your highest wattage items are to suggest an inverter size, and What area of the country you live in to figure out your solar isolation.

    Nearly impossible and sometimes impossible! to follow NEC code. In the last revision, they nearly required combiner boxes that had provision for all hidden connections(can't recall what this is called) but no one was making one yet!
    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.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: system design question

    Clear as mud. :roll:

    What 48 Volt system? How many batteries of what capacity arranged how?

    If you expect to use one array to charge half the bank and one array to charge the other half, don't. If they aren't oriented the same the charging won't be equal. If they are oriented the same there's no point in dividing it up like that.
    Those KD 235 panels have a Vmp around 30; two in series will not provide enough Voltage to charge a 48 Volt system. Also, if those are what the new panels will be also you must use an MPPT controller or else lose a lot of power as the Vmp isn't suitable for any standard system Voltage.

    You need to get a definition of what the power capacity of he new/upgraded system will be, then work out how best to charge it.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: system design question

    no anger on my part. if you can use a 48v system all the power to you. pun intended.:D