Mixing Solar Panels?

sunpower33
sunpower33 Registered Users Posts: 4
in Solar Beginners Corner #1
Hi everyone, I am new to solar. So I buy the cheap 45watt panel system from Harbor Freight and swapped the charge controller with a Sunforce 10Amp Digital Charge Controller. Then connected to 4 each 35AH batteries wired in parallel. My question is... If I was to make my own solar panel panel using 6 each 5V 500mA Solar Cells wired in series and parallel to make a 15V 1A Panel, could I connect it to my current setup? The Harbor Freight Panels are rated at 17.5V (Vmp) and 23.5V Open Current (Voc).

Thank you in advance.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #2
    Re: Mixing Solar Panels?

    It would be better if your panel was 17.5 to 18.6 volts or so Vmp--15 volts is too low to fully/quickly charge a 12 volt battery through a charge controller (you need around 14.4 to 14.8 volts to fully/quickly recharge a flooded cell storage battery)... By the time you take Vmp reduction (as panels get hot, Vmp drops) and voltage drop due to wiring and controller--Vmp in the range of 17.5 to 18.6 volts is about the minimum you would want to design for.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • sunpower33
    sunpower33 Registered Users Posts: 4
    #3
    Re: Mixing Solar Panels?

    Thanks Bill! What if I use 8 of the cells to get 20V, would that be better?

    Thanks
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #4
    Re: Mixing Solar Panels?

    I am not sure which cells you are thinking of using--But the "typical" bare solar cell is 0.5 volts, not 5.0 volts... So, commercial panels would be around 18 cells in series to create a Vmp~17.5 volt array.

    You can go a bit higher--Will not give you more power with a PWM controller--They are simple "on/off" type switching, so the Imp-panel is what is the limiting factor here. You can go with Vmp~20 volts, it will not hurt anything and it will give you a bit more "head room" for voltage drop (for example, if you have long wire runs, hot panels/cold batteries, some batteries that require 15-16 volts for full charging, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • sunpower33
    sunpower33 Registered Users Posts: 4
    #5
    Re: Mixing Solar Panels?

    Thanks Bill, If you want to see what I am referring to they are sold on eBay as 2.5W 5V/500mA mini solar cell epoxy panels the link is
    http://www.ebay.com/itm/160924198563?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
    Let me know what you think of these. The price is too good to pass up.

    Thanks
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #6
    Re: Mixing Solar Panels?

    OK--those are "complete" panels--But they are epoxy and appear to be designed for yard lights/weather stations/portable chargers/etc. type usage... I would not count on them being good for more than a few years before they weather-check/delaminate.

    Also, these are very small panels and not really worth the money if you are attempting to add them to your existing array... $38/2.5 watts = $15.20 per watt.

    If you are after a small/portable system--perhaps they are worth the money.

    If you are after a larger system--Then larger solar panels are much more cost effective on a $/Watt basis:

    wind-sun_2239_12809186
    Power Up 10 Watt Multicrystalline 12 volt Solar Module
    Price: ~$50 (plus shipping and insurance)

    Or you can get larger panels (100-250+ watts per panel) in the $3 to $1.20 per Watt (plus shipping/insurance)

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #7
    Re: Mixing Solar Panels?
    BB. wrote: »
    Also, these are very small panels and not really worth the money if you are attempting to add them to your existing array... $38/2.5 watts = $15.20 per watt.

    The eBay price was for eight of them. $2.00/watt for small panels is not quite so far out of line. :-)
    SMA SB 3000, old BP panels.
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  • sunpower33
    sunpower33 Registered Users Posts: 4
    #8
    Re: Mixing Solar Panels?

    actually that price is for 8 panels so, 2.5 watts each X 8 = 20 Watts so $37.99/20 = $1.90 / watt

    using 4 sets of 2 in parallel, then wiring those in series = 20V @ 1Amp (20 Watts)
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #9
    Re: Mixing Solar Panels?

    Sorry, that makes more sense.

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