"small" project

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kylew
kylew Registered Users Posts: 15 ✭
in Solar Beginners Corner #1
Hello, I have searched these postings and several others, and the more I know the less I understand. I hope you can share some wisdom with me.
I am putting a small solar array on a small (27 ft) sailboat. it started out a simple concept. I have 2 group 27 AGM batteries in parallel (12 v). the needs of the boat are very small: I have no starter battery. only A few cabin lights, a GPS and VHS radio, maybe a 12v AA battery charger once in a while. in the slip she is plugged into 110 shore power with a good 3 phase marine charger to keep her charged up. Away from the slip for days/weeks at a time, I want to have a few solar panels. I have 1 55 watt monocrystaline panel, and a 65 watt amorphous flexible panel. The rigid panel will be mounted on a post on the stern, usually oriented flat, but I could angle it to face the sun if/when that ever made sense for max power (the boat moves around of course..) The flexible panel would be kept rolled up below desks in harsher conditions but rolled out on the foredeck and plugged into the system when possible. My thinking is that they both have their advantages in various conditions, the rigid one being up and out there all the time, and the amorphous could contribute when it can.(I know they are better on cloudy days, for example..)


I know I need a charge controller and I went from thinking of a simple shunt controller, then thinking to a PWM, and just this week thinking I need a MPPT. After a bit more research, and knowing that most of the conditions will be quite warm (So Cal and Mexico) , I am back to thinking a 3 phase PWM controller is the best overall. I was thinking I could just wire both panels together into the same charge controller and into the battery bank and the combined power would flow into the charger and charge the batteries. the more I think about that I am not so sure electricity works that way, and wonder what special stuff I might need to do to use these 2 types of panels together. Do I need 2 controllers? and do I need then to regulate which panel is pumping juice, or can I just combine them into one controller and let her rip?

I am assuming also that I need some sort of switch to shut off the panels when the 110V is doing the work, or are the charger/controllers smart enough to be able to keep it all connected and each would back off whenever the batteries are full, regardless of the source?

thanks so much. I hope you can share some wisdom with me.
Cheers
kyle
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #2
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    Re: "small" project

    I have 2 group 27 AGM batteries in parallel (12 v). the needs of the boat are very small: I have no starter battery. only A few cabin lights, a GPS and VHS radio, maybe a 12v AA battery charger once in a while. in the slip she is plugged into 110 shore power with a good 3 phase marine charger to keep her charged up. Away from the slip for days/weeks at a time, I want to have a few solar panels. I have 1 55 watt monocrystaline panel, and a 65 watt amorphous flexible panel.This is a bit hard to understand.You have 27 batteries wired in parallel?? what size batteries? It correct you have only 1 x65 w panel and 1x 55w panel?? A total of 120w???? How can that charge 27 batteries??? its a total of 10 amps under perfect conditions about 90 watts or a bit over 7 amps in real conditions??
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #3
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    Re: "small" project

    I believe that is 2 group 27 batteries.

    Tony
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  • kylew
    kylew Registered Users Posts: 15 ✭
    #4
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    Re: "small" project

    yes, I have 2 battreies, known as "group 27" type. they each have about 90 amp hours capacity
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #5
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    Re: "small" project

    ok.. my misunderstanding of the post. I obviously didnt read it properly before replying. :grrwill try harder next time:cool:
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  • tomba
    tomba Registered Users Posts: 21 ✭
    #6
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    Re: "small" project

    Hi. Not knowing the Vmp/Imp of the two panels, and since you happy with PWM charge controllers, I'd just run them to separate controllers charging the batteries in tandem.You can get a couple of 6 amp SunSavers for change. If you *really* want only one controller, run the panels in parallel and get a 10A 12V controller. Others could tell you better why you really might not want to go this route. And you should not have to disconnect the controller(s) from your batteries when docked, but you should use some marine breakers to make that possible anyway.
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  • Kamala
    Kamala Solar Expert Posts: 452 ✭✭
    #7
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    Re: "small" project

    I agree with everything tomba suggested, except the use one only one controller. It is very likely that the Vmp/Imp of the two panels are sufficiently dissimilar to make a parallel configuration less than ideal.
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  • kylew
    kylew Registered Users Posts: 15 ✭
    #8
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    Re: "small" project

    Hello, thanks again so much for your helps. I have gathered the needed data

    the rigid panel is 55W, Current @Pmax = 3.1 A, VOltage at Pmax is 18.18 V

    the amorphous panel is 68 watts, C@Pmax= 4.1 A, V@ Pmax = 16.5. it can be seen in full detail at http://www.affordable-solar.com/uni.solar.laminate.pvl.series.68.watt.htm.

    Are these too different to think about putting them on the same controller? And if I use 2 controllers, can I simply wire them (the controllers) both to the batteries and let them work as much as they are able, or do I need to separate the circuits somehow?

    thanks again.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #9
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    Re: "small" project
    kylew wrote: »
    the rigid panel is 55W, Current @Pmax = 3.1 A, VOltage at Pmax is 18.18 V

    the amorphous panel is 68 watts, C@Pmax= 4.1 A, V@ Pmax = 16.5

    If you use a PWM charge controller and put both panels in parallel--You will have no problem with the voltages...

    You can either use one PWM controller and parallel the panels on the PV input for the controller. Or use two PWM controllers (one charge controller on each panel string) and parallel them at the battery bank. Your choice.

    If you where to use a MPPT type charge controller--It is close, but you should be able to parallel the two panels too. With MPPT, if the Vmp voltages are within 10%, you will loose less than 10% of the power (the Vmp peaks are fairly flat)...

    You should not put the two panels in series for PWM or MPPT type charge controllers (not that you had plans to do that). The Imp current difference is too much for them to operate properly and give good output power.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • kylew
    kylew Registered Users Posts: 15 ✭
    #10
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    Re: "small" project

    good to hear! not that the controllers are too expensive, but I am trying to keep is all as simple as possible. (There is enough to go wrong on a boat as it is....

    To be crystal clear, when we talk of tying the 2 panels in parallel into the one controller, can I simply bring the 2 positive leads from the panels together and then run 1 wire to the appropriate input on the controller, and ditto for the negative? Can it be that simple?

    The runs are short, and I will make sure I use the proper guage wires and connectors.
    thanks
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  • mikeo
    mikeo Solar Expert Posts: 386 ✭✭✭
    #11
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    Re: "small" project
    To be crystal clear, when we talk of tying the 2 panels in parallel into the one controller, can I simply bring the 2 positive leads from the panels together and then run 1 wire to the appropriate input on the controller, and ditto for the negative? Can it be that simple?
    Yes this is correct, Your panels output will be around the 16.5 volts and 7.2 amps at peak power output wired in parallel. Just run #10 AWG marine grade wire from pos of one panel to the pos of the 2nd panel, then to the controller positive. Do the same from neg of each panel to neg of controller.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #12
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    Re: "small" project

    Also, make sure you use something that polarizes the panel plugs... You don't want to have to always match + to + ... mistakes happen.

    In this case, plugging the panels in + to - and connecting to a pwm controller could cause the reverse wired panel to fry (or damage the charge controller) in some conditions if the panels are miss-wired.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #13
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    Re: "small" project

    to add to bb's comments,
    there was a post some years back where 1 pv was reversed and it was fried by the power of the rest of the pvs. fuses were not in place on that system and if more than 2 pvs are paralleled then it is required to fuse each one of them before the combining point.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #14
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    Re: "small" project
    BB. wrote: »
    Also, make sure you use something that polarizes the panel plugs... You don't want to have to always match + to + ... mistakes happen.

    In this case, plugging the panels in + to - and connecting to a pwm controller could cause the reverse wired panel to fry (or damage the charge controller) in some conditions if the panels are miss-wired.

    -Bill

    Anderson Connectors,, see site host store for examples.

    Tony
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #15
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    Re: "small" project

    Anderson Connectors

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • kylew
    kylew Registered Users Posts: 15 ✭
    #16
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    Re: "small" project

    thanks for the suggestion. I have used these Anderson connectors when I wired up a trolling motor. Yes, they are bomb and idiot proof. it was good experience for me to solder them with a torch.
    cheers, and I hope to soon have some good experience to share with some newer newby.
    Kyle
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