Various Panel wattages?

andyrudandyrud Solar Expert Posts: 68 ✭✭
What is the result if a person hooks up various wattage panels in parallel, such as 4 100 watt panels and 4 120 watt panels, and 2 135 watt panels?  

Thanks in advance,
Andy R

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,924 admin
    More or less, the rule of thumb we use here are connect panels (or strings of panels) in parallel if their Vmp is within 10% of each other (i.e., 30 Vmp + or - 3 volts with other panels). The closer they are together, the better they will "share" their output current).

    If you have 12 volt and 24 volt panels in parallel--The 12 volt panel will not deliver any useful current.

    For series connected panels, match Imp within 10% too for series connections. The maximum series string current will be limited to the panel with the lowest Imp rating (i.e., 3 amp and 6 amp panels in series--Pretty much 3 amps for the array).

    There are bypass diodes in solar panels--So if there are a bunch of 6 amp Imp panels and one 3 amp panel in the string, the 3 amp panel will go into "bypass" and will be at "zero volts" output voltage (or even 1 diode drop negative voltage).

    The bypass diodes are there to protect each cell (or group of cells) from over current... Dark and shaded cells "go high resistance" and excessive voltage (over ~12 volts or so) and will ruin the "dark cells"--Over voltage the cell's diode blocking voltage rating).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • littleharbor2littleharbor2 Solar Expert Posts: 1,806 ✭✭✭✭✭
    As long as they're all 36 cell (12 volt) panels you should be fine

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

  • BB.BB. Super Moderators, Administrators Posts: 32,924 admin
    If you want to go deeper... When you parallel panels (espeiclaly 3 or more), you also need to look at the series fuse protection too...

    A 100 Watt panel (or string) in parallel with a 400 Watt panel, each will most likely require a different series fuse/breaker (i.e., 5 amp vs 15 or 20 amp).

    That is to present the 400 Watt panel back feeding too much current into a shorted 100 watt panel).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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