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CaptainBlackCaptainBlack Registered Users Posts: 1
Hello everyone Im Captain Black. I have Charter and commercial boats in Florida and have toyed with the idea of solar on my commercial boat. I the roof on the boat is 18 feet wide and 50 feet long so the is an abundance of room up there. I run 6 8D lead acid batteries with 245 amp hours each. 2 batteries are for starting 2 for house and 2 for 12v electric fishing bandits. I have someone close that has  First solar FS-6440A panels rated at 440 watts. I have no real concept of what these panels are capable of and real world application. What would be a good amount of these panels to have a strong system. I have a large alternator on the boat but no generator. Thank you for indulging my question.


  • littleharbor2littleharbor2 Solar Expert Posts: 1,698 ✭✭✭✭
     These panels are Thin film tech. with strange output voltages. You will do much better seeking Monocrystalline or Polycrystalline cell technology. 
     Odd, high voltage 220 Voc. 180.xx Vmp.

     Odd, large size 48" x 80"

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    Welcome to the forum CapitanBlack,

    I know nothing about First Solar--And I have generally suggested to avoid thin film panels. But these do seem to have a good warranty (not sure what the 10 year material warranty vs the 25 year power warranty). And boats/water/salt water is hard on amost any metal and electrical components. And placing a "glass roof" on top of your boat--Kind of fragile.

    In general these days--It seems like the customer has a good chance of being their own warranty "bank" (solar companies do seem to come and go pretty often). But when you are looking at $0.50 a watt pricing now, vs $5.00 to $10.00 a watt pricing several decades ago--The "risk" to your bank account is much less today.

    And as LittleHarbor2 says--These panels are around Voc 220 Voc @ 25C (77F) or relatively high voltage compared to "Typical" solar controllers (typically max voltage is in the 100-150 VDC range).

    So, an MPPT charge controller--You will be looking at some less common "high voltage" controllers. I.e., more expensive.

    The first ~ dozen of these MPPT charge controllers are rated around 300 to 600 VDC max input voltage--And run around $1,200 to $2,000 (this link is to our host's website--There are lots of other controllers out there too):

    They have different output current ratings and all have many different features (networking, etc.), so you may want to look at a few to get an idea of what is available.

    You could get into some "configuration issues"... You don't say if everything is 12 volts or if some is 24 volts (for larger power systems, 24 or 48 volts means smaller wiring, more efficient use of MPPT solar charge controllers (i.e., a 60 amp controller can manage ~900 Watt array at 12 volts, or 1,800 Watts @ 24, or 3,600 Watts @ 48 volt bank--I.e., Power=Voltage*Current, double the working voltage, you have double the power at the same current).

    If you had both 24 volt bank and a 12 volt bank... Then you have to figure out the optimum (for you) solar configuration (we can discuss later).

    Guessing you have 8D @ 12 volts @ 245 AH (flooded cell) x 6 of them... That could be 6x batteries in parallel (12 @ 1,470 AH) or 4x parallel (house bank) and 2x in parallel for 12 volt starting bank, etc. Making several "different banks" of batteries does add some cost and complexity vs one "big" bank" for everything. Obviously, for a boat, you want some isolation/redundancy.

    The "typical" MPPT solar charge controller is going to have one Vbatt output. It is not designed to charge 3x different banks at the same time. And with "high voltage" solar panels--Finding "small/high voltage" solar charge controllers may be difficult. For the most part, going higher voltage with solar is for higher power systems.

    One other "issue" with solar panels is that the market is constantly changing/churning. The panels you get today with a "good price", may be almost impossible to get 5 years from now (new panels different size/voltage/current ratings may not fit with "existing array"). Somebody drops a wrench on one panel (or flips a fishing weight onto a panel--These are typically "single weight" tempered glass and not really "impact resistant". These panels (good or bad) are an "unsual" configration so may be difficult to get "spares/replacments down the road). And they require "high voltage" MPPT charge controllers.

    Anyway... Where we like to start is with your loads (voltage, current, Amp*Hours or Watt*Hours per day). And for typical lead acid battery banks, at least 10% rate of charge minimum for optimum charging (again, this is all standalone solar--You have a boat and does(do) the engine(s) run most of the trip--Or do you anchor out for a few days at time and want to limit engine runtime?).

    Just to do "some math" for one battery bank. Say minimum of 10% rate of charge for 2d batteries in parallel 12 volt @ 490 AH bank:
    • 14.5 volts charging * 490 AH bank * 1/0.77 panel+controller derating * 0.10 rate of charge = 923 Watt minimum "ideal" array 
    • 923 Watt array / 440 Watts per panel = 2.1 panels = 2 panels for 10% rate of charge.(i.e., 2x = 4 panels for 20% rate of charge)
    • 2x 440 Watt panels = 880 Watts
    • 2x panels in parallel = 185 Vmp * 2 parallel = 185 Volt Vmp-array
    • 2x panels in series = 185 Vmp * 2 series = 370 Volt Vmp-array
    You have to look at your local temperatures and the Vpanel input min/max for the MPPT charge controllers to figure out if 2x parallel or 2x series panels
    • 880 Watt array * 0.77 panel+controller deratings * 1/14.5 volts charging = 46.7 Amp typical "max charging" current to 12 volt battery bank from this array
    So a 45-60 Amp @ 12 volt MPPT charge controller would be "optimum" for this 2x panel array. A 100 "high voltage" controller would work--But would be "more expensive" typically than a 50 amp controller.

    Now--What would a 880 Watt array produce for south Florida... Using a "simple" solar irradiation website (close enough for our needs usually):

    Average Solar Insolation figures

    Measured in kWh/m2/day onto a horizontal surface:


    I don't know your "down time"... I will guess you have fewer charters from June through Novemeber. That leaves December as the minimum solar harvest month at 3.37 hours of sun per day (long term average). Making December "break even" month:
    • 880 Watt array * 0.52 off grid AC system eff * 3.37 Hours of sun per day (Dec average) = 1,542 WH per day (Dec)
    • 1,542 WH / 12 volts = 129 AH per day average harvest
    Of course, if you need more power or have a day of overcast, you have storage of the battery bank--Plus hour Alternator to charge when needed.

    For a Lead Acid batteries, typically use 25% to 50% of storage ampacity:
    • 490 AH * 0.25 discharge (25%) = 122.5 AH used
    • 122.5 AH * 12 volts = 1,470 WH used
    • 490 AH * 0.50 discharge (50%) = 245 AH used
    • 245 AH * 12 volts = 2,940 WH used
    Anyway--Lots of guesses on my part and some suggestions. Obviously, there are still lots of details to work out... But the above math is a good start for rough paper sizing/design of the system. And then you can start to look for hardware that may meet your needs.

    Does this help?

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