Sailboat PV System

System
System Posts: 2,511 admin
in Off Grid Solar & Battery Systems #1
I am installing a PV system on my 43' sailboat. Here is what I have so far--a Kyocera 135 (polycrystalline) mounted to the dodger and a Morningstar MPPT 45W controller. Space is limited on the boat, but I plan to add two more 85W panels (ET monocrystalline). These will be mounted on the side rails, one port and one starboard. I plan on wiring the 3 panels up in parallel. The controller is wired to my 12V house bank which is about 750 AHrs. The first question I have concerns partial shading of the panels. With all the rigging of a ketch, there will always be some partial shading of 1 or more panels. With this in mind, is it better to wire the 3 panels in parallel or series? Also, has anyone heard anything about ET solar panel quality? I paid about $250 each for them. Is there a problem using different panels (the max power voltages are 17.7V for the Kyocera and 18.0V for the ET)? Does either mono or poly handle partial shading better than the other? Thanks in advance!
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: Sailboat PV System

    At this point--Can you try different connections yourself and see which gives you the most power? You will not damage anything.

    Personally, even though I normally recommend series connections of panels, I would connect in parallel.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: Sailboat PV System

    Welcome to the forum.

    You are not alone; these are questions often asked! :D
    For shading conditions it is better to have the panels in parallel.
    To that end, you are right that you can't just connect any two panels in parallel (or series for that matter). Your Kyocera 135 has a Vmp of 17.7, so any panels you want to parallel to it should have a Vmp close to this, about 16.8 to 18.5. If they are outside of this range you will not be able to get the maximum power from whatever panel(s) have the high Vmp. (For serial connections it is the Imp that matters.) An MPPT controller can not make up for this difference. The ET panels @ 18 Vmp fall within this range.
    That 45 Amp controller is overkill for this application, even with two 85 Watt panels added (305 Watts total). But if you've got it, use it!
    There's no practical difference between polycrystaline and monocrystaline panels as far as shading goes. Your biggest problem will be that the panels will rarely be pointed at that perfect angle to the sun.
    Don't expect 305 Watts of panel to do much charging of a 750 Amp hour battery bank. At best you will be delaying the inevitable generator charge. To totally charge that much battery from solar you'd need something like a 1200 Watt array, and you probably don't have room for that!
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  • System2
    System2 Posts: 6,290 admin
    #4
    Re: Sailboat PV System

    I'm just trying to supplement my system and be a little green. When going offshore, I will be consuming around 150AHrs/day to run my refrigeration, navigation equip, lights, etc. Since I don't want to discharge the house bank below 50%, I have 375AHrs to consume, or 2.5 days worth before running my engine (with a high output alternator). For my 300W PV system, I estimated about 85AHrs per day being added to my battery. This should make my daily consumption around 65AHrs (150-85) which would extend my days before running the engine from 2.5 days to 5.7 days.

    I hope the above analysis is correct. Please comment...
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Sailboat PV System

    That should be close.
    If you figure the array/wiring/controller loss to be 75% of the 305 Watt total that's roughly 228 Watts "usable" at the battery. Divide by 12 Volts nominal and you get around 19 Amps. If you get 5 hours of "equivalent good sun" on the panels that would end up being 95 Amp hours "harvest" per day under good conditions. That would be about a 2.5% charge rate on those batteries; barely a trickle charge.

    It certainly won't hurt, though.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #6
    Re: Sailboat PV System

    You might not get 65 AH per day--given all the shading/less than ideal sun angles...

    Also, check with your battery manufacturer... Generally, you don't want the bank to remain below ~75% state of charge for too long (i.e., days/weeks/months). That will increase battery sulphation rate.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: Sailboat PV System

    A little "ballpark math" on what Bill's referring to:

    75% of 750 Amp hours = 562.5 Amp hours. You don't want to be below that for long or you'll get the sulphation problem.

    Your usage is 150 Amp hours per day, less what you can get back from the panels (let's use your 85 Amp hours) so that's down to 65 Amp hours per day, providing the sun shines and you can use the power when you get it.

    25% of capacity is 187.5 Amp hours. Divide by 65 Amp hours per day and you get 2.8 days.

    That fits pretty well with your 2.5 days between engine charges you're using now, so it looks good for squeezing a couple more days out if the sun shines. A lot depends on what the battery (or batteries) are designed to do. A forklift battery meant to go to 80% DOD would be nice here, but probably impractical for the install.
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  • System2
    System2 Posts: 6,290 admin
    #8
    Re: Sailboat PV System

    My house batteries are 6-6V (connected in series & parallel to get 12V). They are Lifeline AGMs. Any idea what discharge percentage they are meant for to not have sulphation? I always assumed it was 50%, but am not sure. I've never taken them below 25% since I usually end up motoring some when there is no wind, or else plug into a dock. I'm just trying to get ready for offshore cruising where motoring will be kept to a minimum.

    I'll probably add a wind generator before going offshore to also supplement battery charging since I cannot fit more panels onto the boat. Speaking of wind generators, how would they fit in with the PV system? I was thinking of running the wind output directly to the battery bank and manually shut it down when the bank is nearly fully charged. I don't think it can interface with the solar MPPT controller, right?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: Sailboat PV System

    The sulphation problem is pretty much the same for all batteries; not a matter of how deeply discharged as how long they have to go between recharging. The panels will buy you some time, which is what you want.

    I wouldn't be too keen to spend money on a wind turbine. The sad truth is most of them aren't worth a dime. Then you have the whole problem of mounting them; hard enough on dry land, but raising one 50 feet above a boat ... you tell me how easy that would be. They do not like turbulent air, and they can be fairly heavy. Add to that the need to keep them under control when batteries are charged and/or wind is heavy and you really have to wonder if it would be worth the money. Normally a diversion controller is installed to shunt the surplus power to somewhere (like hot water heating). You really can't run it into the same controller as the PV, and the best controller available for them right now is probably the MidNite Classic which is $700+.

    Think that one through several times over before you get out the check book. :cool:
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  • System2
    System2 Posts: 6,290 admin
    #10
    Re: Sailboat PV System

    Good points. Since I have a mizzen mast, it would be easy to mount it about 12' off the deck. The one I looked at has an electronic break that can be activated from the cabin by throwing a switch (no need to physically tie off a rotor blade). It produces 4.4A with 5 knot wind, and 9A with 15 knot wind. Assuming 12 hours of wind, that would contribute 53AHrs @ 5 knots or 108AHrs @ 15 knots. It weighs 23 lbs. Adding this to my PV seems like a good idea. Cost is about $1200.
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  • Tricksailing
    Tricksailing Registered Users Posts: 25 ✭✭
    #11
    Re: Sailboat PV System
    Apropos wrote: »
    I'll probably add a wind generator before going offshore to also supplement battery charging since I cannot fit more panels onto the boat. Speaking of wind generators, how would they fit in with the PV system? I was thinking of running the wind output directly to the battery bank and manually shut it down when the bank is nearly fully charged. I don't think it can interface with the solar MPPT controller, right?
    The answer depends on where you'll be sailing and the conditions that you're comfortable with. Even 15 kts in an anchorage can produce some pretty uncomfortable swells. I'm in the Sea of Cortez and have an Air-X-Marine rated at 300W (~25A) in 28kts of wind. The turbine power output drops with the cube of windspeed change so in 14 kts, you get around 40W (3A) and at 7kts, you get 5W (<.5A). Generally windspeeds in anchorages are less than 7 kts. Everyone I've spoken to with a wind generator in the Sea of Cortez agrees that they aren't worth having. That probably changes when you get into the tradewinds and can rely on fairly constant 20 kt winds. People sailing the Caribbean seem to find them much more useful.

    Many cruisers erect some kind of stern arch with several solar panels and usually incorporating davits for a dinghy.

    However, new wind generators are coming onto the market, some with good output in low windspeeds, so do your research - on the turbine and the conditions you expect to encounter when you're out sailing.

    Also, the stop switch doesn't stop the blades completely. It's handy to be able to lasso the blades and tie them to something, so bear that in mind when siting up a mast. I've watched one blow off a mast in 70 kt winds. There's much more drag on a rotating turbine because the blades may not be stalled.
    5kW grid-tied SMA + 2kW grid-tied SMA (total 4kW emergency daytime power) + 2kW genset, 500W off-grid marine system. Baja Sur.
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