Solar Afloat #3 60A One string or Two

Highland_Fling
Highland_Fling Solar Expert Posts: 37 ✭
in Solar Beginners Corner #1
I am going to put on four Kyocera 185W panels - in series they generate a scary voltage (On a Boat)

1 string with 4 panels 116V.

2 strings of 2 panels each obviously half that at 58V.

I intend to do a phased install with first two panels then about six months later when i next visit the boat add another two.

So should i put the four panels in two strings or one string?

If i leave them in one string to maximise the output early in the day and as the sun goes down - since four panels in series will obviously get into a charging output mode before two separate strings would - is that the best way to go and just stop worrying about the high voltages.

If i am worried should i connect all my panels in a secure area below deck in an enclosure with a High Voltage Warning Label

I was thinking i could join all of the panels together in a daisy chain manner above deck where they are installed on top of the Bimini. and lead only two conductors down to the controller rather than have two for each panel.

Have i got that wrong or is this marginal or a choice thing or what?

regards

David
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Solar Afloat #3 60A One string or Two

    This is a "your call" thing, but we can give you some general information that might help you make the decision.

    First off, 116 Volts isn't that dangerous. Unless you're uncomfortable with it. Panels are a current source, and the current here isn't that bad:
    4 * 185 Watts = 740 Watts
    4 * 23.6 Vmp = 94.4 Vmp for the string
    Maximum current = 7.8 Amps

    Does that sound a bit "friendlier"?

    If you parallel two panels the Imp will be 2 * 7.8, or 15.4 Amps. In reality it will be slightly less due to efficiency losses, and the 15 Amp controller should have no trouble with this.

    There is an issue with controller efficiency and large differences between system Voltage and array Voltage. Normally you don't have an array that's more than 2 times the system Voltage, or "the next step up" as in: 12 V system with 24 V array, 24 V system with 48 V array, 48 V system with 96 V array. This is not a rule, law, or mandatory application! It's just sort of a "usually we do it like this" thing.

    Were it me, I'd run two of these panels in series through the controller to start, and then parallel another set of two on later. You may find there's some over-all "harvest" advantage to not having all the panels "pointed the same way". I've no idea what the "roof real estate" is like on your boat so you'll have to decide this yourself.
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  • Highland_Fling
    Highland_Fling Solar Expert Posts: 37 ✭
    #3
    Re: Solar Afloat #3 60A One string or Two
    Cariboocoot wrote: »
    This is a "your call" thing, but we can give you some general information that might help you make the decision.


    If you parallel two panels the Imp will be 2 * 7.8, or 15.4 Amps. In reality it will be slightly less due to efficiency losses, and the 15 Amp controller should have no trouble with this.


    Were it me, I'd run two of these panels in series through the controller to start, and then parallel another set of two on later. You may find there's some over-all "harvest" advantage to not having all the panels "pointed the same way". I've no idea what the "roof real estate" is like on your boat so you'll have to decide this yourself.

    MORNINGSTAR say two of these KD-185 panels are too much for the the 15L controller if you look at their web site calculator http://www.morningstarcorp.com/en/strings/calc.php which is why i was looking at a cheaper first step into MORE Solar power that being two of the SunWize 100W panels.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Solar Afloat #3 60A One string or Two

    Are we talking about the same controller here?
    I'm looking at the specs on this 15 Amp Morningstar MPPT: http://store.solar-electric.com/mosumpsochco.html
    I do not see any reason why it will not work as I said.
    Maybe I'm missing something, or maybe it's that extra 0.4 Amps which causes Morningstar's program to disqualify it. Frankly I'd expect that difference to never show up in real world application.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,641 admin
    #5
    Re: Solar Afloat #3 60A One string or Two

    If I did the calcuations correctly.. the Kyocera 185 watt panels, two in series will be Voc=66volts at 14F ... The 15 amp MPPT controller max input is 75 volts.

    Assuming 14.5 volts and 15 amps with a 0.77 panel/controller derating (average peak power you will see on an average day):
    • 14.5 volts * 15 amps * 1/0.77 derating = 282 watts array power
    So, if you go above ~280 watts for your array, the controller will be OK, but you will hit the controller limit of 15 amps (no damage, controller limits to it maximum output current to keep everything fine). With 370 watts of panels on the 15 amp controller--there will probably many time in the middle of a sunny day where you are not collecting all the power you can...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Highland_Fling
    Highland_Fling Solar Expert Posts: 37 ✭
    #6
    Re: Solar Afloat #3 60A One string or Two
    Cariboocoot wrote: »
    Are we talking about the same controller here?
    I'm looking at the specs on this 15 Amp Morningstar MPPT: http://store.solar-electric.com/mosumpsochco.html
    I do not see any reason why it will not work as I said.
    Maybe I'm missing something, or maybe it's that extra 0.4 Amps which causes Morningstar's program to disqualify it. Frankly I'd expect that difference to never show up in real world application.

    Yes that was/is the controller i have. HOWEVER Today the string controller says two KD-185 panels are OK with it.....finger trouble by me i guess.
    BB. wrote: »
    If I did the calcuations correctly.. the Kyocera 185 watt panels, two in series will be Voc=66volts at 14F ... The 15 amp MPPT controller max input is 75 volts.

    Assuming 14.5 volts and 15 amps with a 0.77 panel/controller derating (average peak power you will see on an average day):
    • 14.5 volts * 15 amps * 1/0.77 derating = 282 watts array power
    So, if you go above ~280 watts for your array, the controller will be OK, but you will hit the controller limit of 15 amps (no damage, controller limits to it maximum output current to keep everything fine). With 370 watts of panels on the 15 amp controller--there will probably many time in the middle of a sunny day where you are not collecting all the power you can...

    -Bill

    OK that is good news in a way i cant blow up the Morningstar SunSaver 15 Amp MPPT Solar Charge Controller by feeding it too many watts :D However i am in the sunny Caribbean where it is HOT high 80's and mid 90's very hot for someone from Scotland i can jump in the water to cool down and hot for these panels too i assume they dont work under water :grr:-). So i will lose the top end and 'only' get 15 amps when or if the panels are producing more. BUT my understanding is that when things get marginal like early morning VERY Cloudy days and as dusk approaches my MPPT controller will then be working its butt off to give me every last drop the panels can produce. Having two panels is series will mean that less light will be needed to generate a charging voltage - so i will be charging my batteries for more hours in the day - Yes No Maybe or have i got that all wrong?

    Also these SunWiz 100W panels have a higher working voltage my MPPT controller is OK with that - BUT does this mean that these panels will produce more output will less sunlight early morning and late on in the day and in cloudy conditions than the Kyocera KD (12V style) panels? So the SW 100W panels will be more productive day in day out than two KD-135 which would give me a listed 270 watts or even KD-185 panels which give listed 370 watts some of which i cant collect and send to the batteries.

    Somewhat confused again so to asking the BIG question - since i will keep the Morningstar SunSaver 15 Amp MPPT Solar Charge Controller http://www.morningstarcorp.com/en/sunsavermppt no matter what - what is /which are the best two panels to connect to that to give me the best daily input to my batteries

    Morningstar says MAX 200W input - Yet when i run their string calculator it says two KD-185W panels in series with a listed output of 370W is an optimal configuration

    So you will understand my KUNFUSSION!!!

    thanks again for all your help here

    kindest regards

    David
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #7
    Re: Solar Afloat #3 60A One string or Two

    There is no limit to the input wattage on the SunSaver Mppt, the controller limits its Output to 15amps regardless of the input. In the development of this controller I ran 3-4 KC120's all the time to a single controller.

    In your hot location, three panels would be ideal for a single Sunsaver Mppt
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,917 ✭✭✭✭✭✭
    #8
    Re: Solar Afloat #3 60A One string or Two
    Solar Guppy wrote: »
    There is no limit to the input wattage on the SunSaver Mppt, the controller limits its Output to 15amps regardless of the input. In the development of this controller I ran 3-4 KC120's all the time to a single controller.

    In your hot location, three panels would be ideal for a single Sunsaver Mppt

    How did you get the panels to work at night;)
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • Highland_Fling
    Highland_Fling Solar Expert Posts: 37 ✭
    #9
    Re: Solar Afloat #3 60A One string or Two
    Solar Guppy wrote: »
    There is no limit to the input wattage on the SunSaver Mppt, the controller limits its Output to 15amps regardless of the input. In the development of this controller I ran 3-4 KC120's all the time to a single controller.

    In your hot location, three panels would be ideal for a single Sunsaver Mppt

    I want symmetry so two our four is best i doubt if i could mount three in an acceptable way but all things are possible - please explain why you say three would be ideal - three what size panels 120W like you used?
    Dave Sparks wrote: »
    How did you get the panels to work at night;)

    A BIG BIG BIG Mirror hung WAY UP HIGH in the Sky................however these KC-120's work great in moonlight too :-):-):-)
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #10
    Re: Solar Afloat #3 60A One string or Two
    Dave Sparks wrote: »
    How did you get the panels to work at night;)

    I made no mention of night , where did you dig that up from?, The control loop is always active if your somehow twisting the 15 amp regulation on the output into your silly statement
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