Newbe setting up solar on boat, layout ideas. comtrollers

I have such a tight schedule I have not posted much, would like to share more.

Project 1: rig new boat (2003) for Caribbean trip Dec 1.

  • New Batteries, 5 8Ds replacing the 48Ds, No more space.

  • 4 – 270 watt solar panels = 1080 watts =~77ah

  • 210 amp Idle pro Alternator/ Balmar regulator On hold mounting problems

  • A case of rum

I am a Newbe to solar, bought 4 370 watt panels for a boat. The panels wiil be mounted on a flat roof on the rear of boat. Set in a square, could be some shading on two at times. Silfab 370 watt 39.7 volt 9.39 amps. New boat batteries AGM or Gel 1250ah five 8Ds. 12 volt system.

QUESTON; suggestions on set up, I would prefer one MPPT, easier to set up. But I just bought 2 60amp MPPT. Really pushing a deadline.


  • BB.BB. Super Moderators, Administrators Posts: 30,050 admin
    Based on what I see here (and guessing), I would just run the 4 panels in parallel (Vmp-array~40 volts, Imp-array~40 amps).

    Solar electric panels just do not work well when shaded (the cells go "high resistance" when dark, need bypass diodes to pass current around the ~12 volt block of shaded cells--if just one block).

    Mount/orient the panels so that they have at least some chance during the day of running without shading (no lines crossing the panels either).

    Other question--are panels for when moored? Or for use at sea, or both?

    If use when moored, then if docked or prevailing winds/current (anchored)--Then mount panels favoring the direct of sun (south east through south west if north of the equator.

    You can use a solar panel hours of sun estimator to figure out angles and direction to point:

    If this is when under sail--Unless you have standard course and time of day (going north during the day, sailing south at night)--having 2 panels to port and 2 panels to starboard--With separate MPPT controllers (one for port, other for starboard)... But I would try with just one controller anyway (save space and keep a spare--sea water is tough on everything).

    Anyway some thoughts...

    Solar panels are difficult animals to get any large amount of power from them on a moving sailboat... Assuming you will get a minimal amount of power (10-30%) and make your minimum energy usage less than that (GPS, Autopilot, Radio, LED lighting/running lights)--That would be about all I would count on. Use a genset/boat generator for larger amounts of power (refrigeration, cooking, computers, etc.).

    We have had people try the solar only power for their trips (sailing competition from US to Hawaii, if I recall correctly), and they ran out of battery power before they completed the voyage.

    If a bit of speed loss is not a huge issue--A towed propeller and alternator may be more effective if you are under sail much of the time... (don't know anything about website or product--Just an example for discussion)

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 30,050 admin
    One thing I forgot to add, if you put all for panels in parallel, you should use a circuit breaker based combiner box--If one panel gets shorted, the other three panels can feed current to the short and start a fire--Each panel/string having its own circuit breaker (probably around 15-20 amps, check solar panel specifications) reduces the chances for short circuit fires (for 2 panels or less in an array, a combiner box is not needed).

    And some tools... If these are Flooded Cell Lead Acid batteries get a Hydrometer to monitor the state of charge of the bank:

    Rinse the hydrometer with distilled water prior to putting away (and glass hydrometers are always very easy to drop and break).

    And get a DC current clamp DMM (digital multimeter)... Makes debugging DC (and AC) power circuits much easier and safer: (cheap and good enough for our needs) (mid price/quality meter)


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SteveNashvilleSteveNashville Registered Users Posts: 2
    edited October 2018 #4

    This boat is a powerboat, it has a flybridge with a radar arch no telling what telling what direction the sun will hit the panels. Solar is for travel and for at anchor. When you anchor the boat swings around and faces the wind you are right hoping to topoff batteries have a 12kw Genset for real power needs.

    I just bought five 8D AGM today, 1250 ah thanks for the tip on the DC clamp. I had bought one and found out later it was AC only could not find a DC clamp so thanks again.

    If I setup the panels in parallel will I have a 160 volts and still 9.4amps? Do you think I should put a 15-20 amp fuse between each connection of the four panels? Open for anymore advice.  Just read about MC4 fuses on this forum, is that what you were talking about?

    Thanks for your response


  • EstragonEstragon Registered Users Posts: 4,451 ✭✭✭✭✭
    The max string fuse size should be listed in the panel specs, typically ~15a.  

    In parallel, total array voltage will be roughly that of a single panel, total current will be roughly panel amps * number of panels (so 9.4*4 in this case.
    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
  • BB.BB. Super Moderators, Administrators Posts: 30,050 admin
    As Estragon says... Solar panels are just like batteries... Connect them in parallel, current adds. Plug them in series, voltage adds.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mcgivormcgivor Solar Expert Posts: 3,274 ✭✭✭✭✭
    Since the boat has no static orientation to direction, mounted flat would probably be the only logical  position, the output may be less than than expected, unless you're at the equator.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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