panel difference

erneerne Solar Expert Posts: 41
My neighbor has 24 - 120 watt Kyocera panels and just got 8 - Solarex 65 watt panels.
She has 16 - 120’s wired in pairs and those pared in the combiner box for 85 volts into an FX-60. She also has 8 - 120 watt Kyocera panels configured the same as the above running thru a separate FX 60, her intent is to combine the Solarex’s in the second FX system. Will running the smaller panels in series of 4 and parallel of two work or will it degragate the system. Both Voc’s are 21.5 Volts, Only the amps are less. Would it be better to reconfigure the panels to 120 and 65 pair’s times 4, instead of 120-120 pair times 2, and 65-65 pair times 2.
Thanks

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,698 admin
    Re: panel difference

    Do you have the Voc/Vmp/Imp ratings of those panels?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: panel difference

    if she were to add these to her system it may not add much if anything at all as 24 x 120w = 2880w. the controller at its 60a max current rating (assuming 48v battery bank) is 60a x 48v = 2880w. 2 notes here are that it would still be questionable if the pvs have retained their ratings and that there is no such thing as an fx60. it is either an mx60 or an fm60, but both have a 60a rating. in order to add these pvs i would recommend running them into another controller and then to the common battery bank.
  • erneerne Solar Expert Posts: 41
    Re: panel difference

    My bad--- the controllers are Outback fm-60’s, the controller in question has 8 Kyocera 120 watt panels installed, VOC 21.5 ISC 7.45 amps, the panels in question are Solerex
    sx 64u VOC 21.5 ISC 4.06 amps
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: panel difference

    very good on the clarification on the controller, but as i said it doesn't matter for either controller is a 60a controller and the system is maxed out already so any more pvs need to be added with another controller.
  • TnAndyTnAndy Solar Expert Posts: 249 ✭✭✭✭✭
    Re: panel difference
    niel wrote: »
    if she were to add these to her system it may not add much if anything at all as 24 x 120w = 2880w. the controller at its 60a max current rating (assuming 48v battery bank) is 60a x 48v = 2880w.

    Per the Outback manual, on the FM60:

    Max STC rating on the panels for a 48v system is: 3600w
    NEC STC rating recommended is: 3000w


    Would be nice to know WHAT her system battery voltage is, though......
  • TnAndyTnAndy Solar Expert Posts: 249 ✭✭✭✭✭
    Re: panel difference
    erne wrote: »
    My neighbor has 24 - 120 watt Kyocera panels and just got 8 - Solarex 65 watt panels.
    She has 16 - 120’s wired in pairs and those pared in the combiner box for 85 volts into an FX-60. She also has 8 - 120 watt Kyocera panels configured the same as the above running thru a separate FX 60, her intent is to combine the Solarex’s in the second FX system. Will running the smaller panels in series of 4 and parallel of two work or will it degragate the system. Both Voc’s are 21.5 Volts, Only the amps are less. Would it be better to reconfigure the panels to 120 and 65 pair’s times 4, instead of 120-120 pair times 2, and 65-65 pair times 2.
    Thanks

    Guess I'm confused. IF she has 85v at the combiner, sounds like she already has the Kyocera panels wired in strings of 4 ( in series ).

    The second FM60 that has 8--120w panels ( 960w ) on it could handle the 8--65w panels ( 520w ) by also wiring them in sets of 4 in series, for a total of 1480w. They would work OK because the VOC is the same. The amperage difference won't matter.

    She does know putting that many in strings of 4 means any shading on about any of the panels means serious loss in an individual string, right ? So watch out for shade !
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: panel difference
    TnAndy wrote: »
    Per the Outback manual, on the FM60:

    Max STC rating on the panels for a 48v system is: 3600w
    NEC STC rating recommended is: 3000w


    Would be nice to know WHAT her system battery voltage is, though......

    andy,
    offhand do you know how this is as 60a at 48v is 2880w? 3600w/48v=75a. does the fm60 handle 75a out just like the mx60 was modifiable to a higher current? if so does this mod apply to the fm80 as well and to what extent?

    edit to add: i did misread the original post as there are 2 controllers, but as andy pointed out, we don't know the battery voltage you are using.
  • TnAndyTnAndy Solar Expert Posts: 249 ✭✭✭✭✭
    Re: panel difference

    Niel,

    Nope....I don't know. My "guess" is Outback knows panel rating and real life output are two different things, but that IS what their online specs say......which, interestingly enough, IS different from the manual I have with mine....it says 3200w max panel on a 48v system....so they've upped that some since I bought my controllers several years back.

    When I set mine up, I had 2- 60amp controllers originally for two arrays of 6 x 175w ( 1050w ) on a 24v system. Manual says 1600w max on 24v output. I ordered 6 more panels about 6months after the orginal 12, and intended to put 3 on each array...putting them at 1575.....just under the 1600w limit.

    BUT after observing the output of mine, including cold, really BRIGHT winter days with sun reflecting off snow, I suspected I could "fudge" the numbers, so I ended up putting 10 on one array, and 8 on the other, just to try it and see what happened. Most I ever saw on the 10 panel array were brief spikes over 1600 ( like 1640-50 ) on those cold, bright, snowy days.....so later I upped the second array to 10 panels ( 1750w ) as well.....

    It's pushing the envelope a bit, I know. I sure wouldn't do it on anyone else's system, and I'm not saying anyone else should do it.......but what I've found is it does run my 2 at pretty much max capacity more of the time ( like yesterday....bright, cool day.....I was seeing 1500+ watts out of those arrays ). I also figure as my panels age, and degrade, the chances of running too much thru them lessens.
  • erneerne Solar Expert Posts: 41
    Re: panel difference

    she has a 24 volt system
    16 X 120 =1920 watts - looks like the system should have never worked. I will drop the controllers to 12 X 120 = 1440 watts. If this change does to her system the same as it did to mine she probably won’t need the added panels or another controller. She also has 24 batteries in the system. Her installer really got to her. Second set in 4 years. I will drop battery count to 10% charge (have her sell the balance) and lower the controller wattage. The batteries are new (4 Months old.)
  • hillbillyhillbilly Solar Expert Posts: 334 ✭✭
    Re: panel difference
    erne wrote: »
    she has a 24 volt system
    16 X 120 =1920 watts - looks like the system should have never worked. I will drop the controllers to 12 X 120 = 1440 watts. If this change does to her system the same as it did to mine she probably won’t need the added panels or another controller. She also has 24 batteries in the system. Her installer really got to her. Second set in 4 years. I will drop battery count to 10% charge (have her sell the balance) and lower the controller wattage. The batteries are new (4 Months old.)

    How "off" is the balance from her pv charging capability, and does she have a generator? I ask because it may not be worth it to sell some batteries at a huge loss. If she's not that far off on charging capability, and she has the ability to charge at higher currents from the generator I'd be inclined to keep the batteries if she already payed for them. If they are 24 individuals, what's the configuration? 12X2V (2 paralleled sets), 4X6V (6 parallel sets), etc... that would make a potentially big difference to me.
  • erneerne Solar Expert Posts: 41
    Re: panel difference

    24-6V batteries / 4ea. for 24V = 6 rows X 360 AH = 2160 X 10% = 216 amps X 24V = 5184 watts
    24 panels X 120 watt = 2880 watts, not enough panels. To many battery rows for good life. Wasn't she sold the wrong size of battery for that capacity?
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: panel difference

    i think she may be better off asking the people she bought from if she could exchange her inverter for a 48v model assuming she has and bought the inverter at the same time. upping the voltage does double the current ability and thus doubles the power ability of the cc.

    i can see she got bad advice from somebody. you are there and maybe you could evaluate her needs for her loads and start to work backwards on this and then determine a course of action rather than acting and then rework it from there?
  • BB.BB. Super Moderators, Administrators Posts: 29,698 admin
    Re: panel difference

    It is right on the bottom side of our generic rule of thumb (5% to 13% of Bank AH capacity for solar charging).

    I like to derate the solar panels+charge controller to 77% (more realistic average output of solar charging system):
    • 24 panels X 120 watt * 0.77 derating = 2,016 watts average peak solar power
    Or, using 5% minimum rate of charge:
    • 2,016 watts * 1/29 volts charging * 1/0.05 min rate of charge = 1,390 AH @ 24 volt battery bank maximum size
    Vs 2,160 AH battery bank... Yea, way too much battery.

    A couple of things to take into account with parallel battery strings. First, you should "balance" the parallel connections to equalize charging/discharging current:

    www.smartgauge.co.uk/batt_con.html

    And, second, I would suggest an inexpensive DC Current Clamp meter for the customer to check the peak heavy charging (and/or discharging) currents are shared among the strings. Check once a week to once a month to find any problems before there is damage to the batteries (over/under charging of various strings based on bad connections/open or sorted cells/etc.). Also use the DVM part to measure the batteries and ensure that no battery/cell has too high or too low of voltage (open/shorted cell, poor charging, etc.).

    Another set of tools--Hydrometer (if flooded cell). And a Battery Monitor highly recommended (and almost mandatory if this is a sealed/AGM battery bank). Makes day to day managing of the battery bank state of charge and loads a bunch easier--Can easily pay for itself if it saves a bank of batteries from "mistakes".

    Lastly, if there are parallel strings, it would be a good idea (and probably code) to place a circuit breaker/fuse in series with each string for safety... Fuse should be sized to the capacity of the wiring connecting the battery strings together (lots of parallel strings add costs of fuses/breakers per string too).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • hillbillyhillbilly Solar Expert Posts: 334 ✭✭
    Re: panel difference

    I'd second Niels suggestion to up the inverter to 48V (this would reduce the parallel batteries to 3 sets also). That would be a better system voltage for the size anyways.
  • TnAndyTnAndy Solar Expert Posts: 249 ✭✭✭✭✭
    Re: panel difference
    erne wrote: »
    she has a 24 volt system
    16 X 120 =1920 watts - looks like the system should have never worked.

    No, it shouldn't have. I don't really know what happens when you WAY overload the input.....maybe her's never did due to direction and angle of the panels....but by the manual, that's 320w too much on a 60amp controller.

    Be interesting to stand there and watch the controller screen on a bright, cold day, just to see how much it actually IS taking in......
  • BB.BB. Super Moderators, Administrators Posts: 29,698 admin
    Re: panel difference

    In general, a good quality MPPT controller should limit its output current to its rated maximum (and will cut back if controller is overheating)...

    So, the maximum amount of solar array becomes a cost/benefit ratio... Extra panels will generate more power during the day--but be lost at "peak sun"/optimum weather conditions (vs adding a second charge controller).

    A decent rule of thumb is to derate the system by 77% (1/0.7=1.30) or over panel by up to ~30%.

    If the system is in a cold/snowy region, then you might want to use a 80 or 82% derating (or even 100%) to account for winter production peaks (cold weather, snow reflections, etc.).

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