Recharging a marine battery with sun/wind?

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System
System Posts: 2,511 admin
in Solar Water Pumping #1
Hey, I'd like to start off by saying I don't really have a clue about any of this stuff, so if I'm talking nonsense then be kind!

Anyway, is it possible to charge a battery on a boat that is powering a pump with a 12v motor drawing 6Amps entirely by sun or wind? I've been looking at all the different products on google for the last few hours and I'm finding it hard to make sense of it all, so many different terminologies and amps and volts and watts etc. Any help appreciated, thanks.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
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    Re: Recharging a marine battery with sun/wind?

    Is your 6A pump running all the time, or only 2 minutes each hour. There is a VAST difference in the power needed to supply those 2 different conditions.

    Yes it is possible. Is this a power boat, or sailboat (mast & stays=shadows ) ?
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • System2
    System2 Posts: 6,290 admin
    #3
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    Re: Recharging a marine battery with sun/wind?

    Well it's not running constantly for sure, probably a couple of mins an hour at the max. And it's a powerboat, so only have clouds and the nighttime to contend with!
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,446 admin
    #4
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    Re: Recharging a marine battery with sun/wind?

    For example:

    6amps * 12 volts * 3 min / 60 min = 3.6 watt*hour average draw

    3.6 Wh * 24 hours per day = 86.4 watt*hours per day...

    Say your near Dublin, Ireland. Use this site to see how much sun you have.

    Ignoring the part about Grid Tied power generation, we see you get 0.98 kW/m^2 per day in December. Or 3+ kWr/m^2 per day in the "Boating" Months (nice weather)... Assume 50% derating factor (magic fudge factor):

    Panel Wattage = 86.4 WH per day/0.98 kW/m^2 per day * 1/0.50= 176 watt panel in December...

    Panel Wattage = 86.4 WH per day/3 kW/m^2 per day * 1/0.50= 58 watt solar panel for "sunnier" months of boating weather...

    The above assumes your boat is docked and you can point the solar panel south and at an angle of 53 degrees from horizontal... You can point it more vertical to better capture winter sun (+15 or more degrees).

    Or, if this boat is at anchor, you would do the same calculations with the solar array at zero degrees (flat) to account for anchor swing (you would also need to clean the panel much more often because of being flat... Mounting with a minimum of 15 degree tilt makes them, pretty much, self cleaning). As above, tilt set to zero...

    It appears to cut your sun capture by, roughly, 1/2. So, that would mean that the above panels sizes calculated before would have to be 2x larger with a flat panel mounted on a boat that swings at anchor...

    The numbers above are a bit on the conservative side. Also, you can work the numbers assuming that you run your boat, for example once every seven days for a Sunday cruise, but want to keep the batteries somewhat charged (say make up 50% of the pump power--so panels could be 1/2 of what I estimated above).

    Does this help?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,446 admin
    #5
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    Re: Recharging a marine battery with sun/wind?

    The above assumes the pump and solar panels are all using your battery as the power source...

    You could also get a very small DC pump and connect it directly to a smallish solar panel. Of course, it would only pump when the sun was shining--but you could use your battery powered pump as a backup (with the water level sensor set higher). Nice primary plus emergency backup system.

    -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
    #6
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    Re: Recharging a marine battery with sun/wind?

    That helps a really great deal, thank you very much.
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