Mixing new with existing panel

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kikepr17
kikepr17 Registered Users Posts: 5 ✭✭
in Solar Beginners Corner #1
Hi. I have a Kyocera KC-120, 120 watts, 16.9 volts, 7.1 Amps, open circuit voltage 21.5, short circuit current 7.45 Amps. I want to get more panel to get at least 360 watts (combined). Of course, the easiest way will be to get two more 120 watts, but seen more choices of manufacturers and prices in other capacities I was wondering if it will be possible to, for example, combine four-30 watts panels in parallel and connect them to the existing panel using a combiner box? Also, if I combine the 30 watt panels in parallel, can I connect them in series to the 120 watts panel to make a 24 volts system and keep the current low, so there is no need to increase wire size?
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  • bsolar
    bsolar Solar Expert Posts: 103 ✭✭✭
    #2
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    with that few panels wire size wont be an issue if you use something reasonable like 12awg ... i would parallel them, series would probably be screwy with widely differing panels .. with vastly different types of panels they will have different characteristics that will hamper performance, but overall, throw a bunch of similarly rated voltage panels together and you'll get some increased output ..
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  • kikepr17
    kikepr17 Registered Users Posts: 5 ✭✭
    #3
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    Thanks bsolar, I agree I'm overthinking this too much. The thing is, I live in Puerto Rico and searching for info in the tiny screen of my phone and with intermittent signal is a little hard. We are going to be without power for a while, so I'm trying to setup a system for maybe two table fans, lights and at least a small tv. I'm attaching a diagram of what I'm planning. I know it could be over what I need. The thing is, I live at an urban area a couple of miles from the coast line. My brother who lives in NC wants to help me get the equipment because, if everything goes well, he want me to help with a system for his mother-in-law who lives in a rural area at the center of the island where they are expected to be months (maybe more than a year) without power. I apologize for the quality of the image. My laptop was running out of battery and didn't have another way to transfer it to my phone, but with a photo. So I have the following doubts: 1) Maybe the combiner box is not completely necessary due to the size of the array, but I feel better having a way to disconnect each string. I'm sizing the breakers multipling the short-circuit current by 1.25. Is that the correct way to do it? 2) The size of the fuse for the inverter is clearly indicated on it's documentation. But I'm having a hard time figuring the one for the controller. On it's manual indicates it should be sized according to the ampacity of the wire. So how I know the size of the wire? Should It be selected by the size of the controller? Or by the voltage/current at which the controller will charge the battery? Any input (comments, suggestions, corrections) will be appreciated. Thanks in advance.
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  • kikepr17
    kikepr17 Registered Users Posts: 5 ✭✭
    #4
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    I'm having some trouble posting the diagram..
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  • kikepr17
    kikepr17 Registered Users Posts: 5 ✭✭
    #5
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    https://1drv.ms/i/s!Ag2Z36-z4_j58iiwm1WhrQKxDiJP
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #6
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    Size of the pv string breakers is usually the max size specified by the panel maker (often 15a). You would use a wire with higher ampacity than that to minimize voltage drop. You could go as small as 14ga at 15a, but you,ll likely want to use 10-12ga.

    I would use the biggest wire that physically fits on the controller. I think the breaker would be sized to protect that wire, and at least the output of the controller x 1.25 if not specified by the manufacturer. Be sure to use DC rated breakers, and note they generally need to be connected with the '+' terminal connected to the source of current *in a fault condition*. In the case of the controller, for example, that would be the battery, not the controller.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • kikepr17
    kikepr17 Registered Users Posts: 5 ✭✭
    #7
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    Thanks Estragon. That makes a lot of sense, since they are mentioning the ampacity of the wire. I'll check the literature for the panels.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #8
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    Here is Kikepr17's photo:

    httpsekbkgg-sn3301files1drvcomy4m2L9bcVQeAfX2SAJ6-WK2LKyZnkBFCvVutr1Yt-P0lSJqr1z2_auEb4eqwnlrOBcpJvI_Srg-dO7EnHKy_J0sSQUAeE9Tl8YFWgTysOg2KYLLmp6tXscjOrPIigrjR7QarU5PgzoycBNcClKvBGub_OTnLzZbSljdnBkDDSXdfMs-MxbfuIbcdfnkAlttxt4uLttvhMTw57QOUy50N9xANw2017045726amjpgpsid1

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