Different wattage/voltage panels connecting to an mppt controller

Fabian
Fabian Registered Users Posts: 131 ✭✭
Is there a rule for mixing different  size panels to connect to an mppt charge controller?
I have a set of 24V panels. (6) are 320 watt and (2) is 370watt. They are all canadian solar brand.

My 60A mppt controller can accept a total of (8) of these panels for charging my 48V battery bank. What i need to know is if the Vmp/Voc of the panels are off by say 1 or 2volts difference between them will this cause any operating issue from the mppt controller?
Will i still get optimum performance/tracking from it? I assume that the 370watt will decrease in wattage and perform at 320watt max will that be the case?

Please advise me as to how much difference you can have in terms of mixing panels with different open circuit voltage and optimum operating voltage and then connecting  them to an mppt charge controller and still expect excellent performance from it in regards to producing close to your overall wattage and excellent tracking ability with the different voltage strings.

Comments

  • jtdiesel65
    jtdiesel65 Solar Expert Posts: 242 ✭✭✭
    A rock hit two of my panels in one of my arrays. They were 170w. All I could find that matched appearance were 190w. They work fine with my midnite classic. That array actually produces slightly more than the other one with just the original 170w panels.

    I think the real issue would be if larger panels makes it so that the voltage exceeds the cc's capability.  I would think not with just a volt or two, but you really need the cc's specs to be sure.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    More or less, the rules are:
    • For panel strings connected in series, Imp of different panels must match to within 10% of high to low (i.e., 10 amp Imp panels mixed with 9 amp Imp panels in series).
    • For panels (and panel strings) connected in parallel, Vmp must match within 10% of hi to low (i.e., Vmp 30 volts and Vmp 33 volts in parallel is OK. Vmp 30 and Vmp 36 volt panels connected in parallel are not).
    For folks that have two groups of differing sets of panels--Either starting over with new panels that match, or match some of the old panels is a possibility... However, many times, the multiple year old panels cannot find/match new panels, or buying "older spec'ed panels" are much more expensive that simply starting over with the low cost/matched spec'ed panels of today.

    Another method is to split the two (for example) panel groups into two, and simply get two MPPT controllers--And make two array+controller sets. Connecting two (or more) controllers to a single battery bank works fine.

    Many times, it is just near impossible to mix and match panels with differing specifications. In some cases, it can be electrically damaging to mix the "wrong" panels (wrong Imp in series strings). And other cases, you cannot make "matching" parallel connections of panels/panel strings--The controller will work, but there is no "optimum" match of panels that will work together:

    Vmp = 30 Volts: Array options: 30/60/90/120 VDC
    Vmp = 36 volts: Array options: 36/72/108 VDC

    Just no "common" voltage matches available for a typical 150 VDC max input voltage MPPT controller. 

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