First time solar user

System
System Posts: 2,511 admin
in Solar Beginners Corner #1
I am in the process of installing solar panels on my sailboat. I am not clear on what items I will need to install a complete system that will charge three banks of batteries. Can someone point me in the right direction?
Robert
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
    Re: First time solar user

    welcome to the forum.

    3 banks of batteries?

    maybe you should start there by explaining what the capacity and voltage is for each bank.

    after that you can explain what your loads are that you need what you stated and we'll kick it around from there.
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  • System2
    System2 Posts: 6,290 admin
    #3
    Re: First time solar user

    Niel, Two of the banks are 12 volt deep cycle "house" batteries that support, lights, navigation, water maker, radios, various water pumps etc. The third bank is my engine start battery. I am in the process of doing a power inventory, so I am nor sure what size panels I will be purchasing. What i am trying to learn is what equipment I will need to deliver the energy from the panels to the batteries.

    Robert
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,591 admin
    #4
    Re: First time solar user

    In general, for smaller systems (less than 200 watts of solar panels), a PWM charge controller will usually work out well.

    For systems over 800 watts, look at MPPT.

    Most charge controllers can only charge 1 battery bank at a time...

    With many PWM controllers, you could have one set of panels and three PWM controllers, each charging its own bank by sharing the one solar array.

    And MorningStar does have a "Dual" PWM charge controller:

    Morningstar Dual Battery Charge Controller 25 Amp

    And you can select one bank as "critical" which will take most of the charging current until that bank is charged.

    A big thing with solar power systems is "balance"... Many times, people have large battery banks and a small solar array that is only really practical for trickle charging a battery bank (like boats which do not have room to mount 10 large solar panels).

    Basically know you loads and your batteries first... Then we can work on picking the panels and the rest of the hardware...

    Typically, a minimum rate solar PV charger would supply around 5-13% of the battery bank's 20 Hour Amp*Hour rating...

    For example, a 100 AH bank with minimum 5% rate of charge and assuming 77% efficient panels+charge controller:
    • 100 AH * 14.5 volts charging * 1/0.77 derating * 0.05 minimum charge rate = 94 watts recommended minimum
    If you are in a reasonably sunny area, you probably can get 4 hours of sun during 6-9 months of the year. Another rule of thumb is that a solar PV system is ~50% efficient from solar panel thru charger to battery to inverter to loads:
    • 94 watts panel * 4 hours per day * 0.50 = 188 Watt*Hours per day
    Or in Amp*Hours:
    • 188 WH per day * 1/12 volt battery bank = 15.6 AH @ 12 volts per sunny day
    Just some random calculations--I assume your battery banks are much larger... Then the question is how much room do you have to mount panels.

    Lastly, where will the boat spend most of its time--Out west of San Francisco, we would get 4 days of fog and 2 days of sun during the summer... Solar panels need no shadows and full sun to produce near rated output... Fog, clouds, shading (ropes, sails, masts, etc.) all serve to kill solar output.

    10 miles away, across some coastal hills, and we have clear skies and tons of sun with 80-90+F weather.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • System2
    System2 Posts: 6,290 admin
    #5
    Re: First time solar user

    Thank you Bill, that is a lot of good information, and a place for me to start. I am in the process of doing a power inventory to determine what my daily load is. I have enough space on my davit rack to hold two fairly large panels with no shadow obstructions (sails, mast etc). Since I am currenly in Mexico and plan to be here or farther south for a few years, I should think 4 to 6 hours of good direct sun can be expected. I will also start looking around for a multi-bank "smart" controller (if one exists). Thanks again for your help.

    Robert
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #6
    Re: First time solar user

    Yes, there are charge controllers that can do multiple banks. Also dc-dc chargers that will charge one bank from another so you run the solar to one bank, and charge the second bank off the first.

    As for what gear you need.

    Solar panels.
    Mounting for the solar panels.
    Possibly a combiner box for the solar panels.
    Charge controller.
    Wire, and fuses to protect the wire.
    Good battery monitor(s) if you don't already have them.
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