Basic question on mixing panels

HI Forum

I should know this really :blush:, but i've never mixed panels before as it's not ideal practice so i have to ask:

I wish to add a KC120 Kyocera panel to an existing very small installation with an A85P ATERSA. The system is at 12V, therefore the panels will be connected in parallel.

I know that the Vmp of the 2 panels must be within 10% of each other-- but my questions are:

1. Can i simply wire the positive of the new panel to the positive of the existing panel and the negative of the new panel to the negative of the existing panel? Thus requiring only two additional wires- or is this bad practice?

2. As there are only two parallel series, can I get away without putting any fuses between the strings?

Many thanks
Larry

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Basic question on mixing panels

    You already know Step 1: make sure the Vmp's are close for parallel connection.
    Step 2: there's only two panels, but they are quite different in power. What is the Isc of the Atersa? The Kyocera is 8.37. It is therefor possible for that panel to put 8 Amps into the other one should something go wrong: the smaller panel could burn up under such a circumstance. For safest results, fuse each according to its Isc. This is one of those "not absolutely necessary but a good idea just in case" scenarios.

    The big issue will be adding another 7 to 8 Amps to the circuit from where the two panels combine to where they connect to the charge controller. Is the wire heavy enough to take the combined current and keep the Voltage drop to a minimum? Again you need the current values for the small panel to determine this.
  • BB.BB. Super Moderators, Administrators Posts: 29,509 admin
    Re: Basic question on mixing panels

    I personally would aim at a fuse/breaker 1.25xIsc at a minimum... Fuses and breakers are really designed to operate at a maximum of 80% of rated capacity.

    If you run them ~100%, you will have nuisance trips (a real pain if the over current devices are on the roof/top of a pole).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • lazzalazza Solar Expert Posts: 330 ✭✭✭
    Re: Basic question on mixing panels

    Isc of the old Atersa is about 5A.

    Thanks for your answers. Yeah, i'll put a couple of inline fuses for each series before joining them, and think i'll put a separate pair of cables as the existing cables may not cope with the combined current.

    by the way, does anyone know if there a simple program for drawing circuits, for example simple PV setup with fuses, panels, cables etc?? It would greatly help in explaining things to clients and for my own purposes
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Basic question on mixing panels
    lazza wrote: »
    by the way, does anyone know if there a simple program for drawing circuits, for example simple PV setup with fuses, panels, cables etc?? It would greatly help in explaining things to clients and for my own purposes

    Very good question!

    If anyone does know, speak up! Something less complex than CAD but less time-consuming than the drawing programs, perhaps with a library of symbols that can be dropped and line-snapped?

    We'd be using it ten times a day on the forum if such a thing exists! ;)
  • BB.BB. Super Moderators, Administrators Posts: 29,509 admin
    Re: Basic question on mixing panels

    Outback has a nice set of pdf drawings for simple to complex setups in their support section.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 8,373 ✭✭✭✭✭
    Re: Basic question on mixing panels
    lazza wrote: »
    ...by the way, does anyone know if there a simple program for drawing circuits, for example simple PV setup with fuses, panels, cables etc?? It would greatly help in explaining things to clients and for my own purposes

    I use Visio, but I have it, others use Google Sketch Up. If it's really simple, Windows PAINT can work too. Visio:
    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 ,

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Basic question on mixing panels

    That's a beautiful drawing, Mike! How long did it take to do that?
  • mike95490mike95490 Solar Expert Posts: 8,373 ✭✭✭✭✭
    Re: Basic question on mixing panels

    The drawing, in Visio, took about 3 days, with making all the little parts, make one PV cell, clone it 20 times = panel, clone it 15 times = array....

    any future ones will be MUCH faster, working off the existing patterns.
    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 ,

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