PV system on sailboat, what output possible?

Vronsky
Vronsky Registered Users Posts: 3
in Solar Beginners Corner #1
I'm considering a solar charger system on my sailboat.
On the forward deck in front of the mast, there is a total of 12ft2 of free surface available to mount 2 panels in combination.
Ideal would be one of these thin bendable marine PV systems with a durable, walkable surface.

What kind of performance can reasonably be possible in this situation with variable illumination?

Suggestions/pointers regarding controller, inverter and installation scheme are very welcome.

THANKS,
V.
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: PV system on sailboat, what output possible?

    Welcome to the forum.

    What kind of performance can be expected? Not good.
    Start with the panel type: thin, flexible panels will be far less efficient than rigid, monocrystaline panels.
    Factor in the varying illumination. Is that a 12' by 2' area? In other words 24 square feet? Rough calculation shows about 140 Watts.

    Probably the best you can hope for is to find some panels that suit your installation requirements and accept whatever power they produce as supplementing your battery time. This is not going to be a lot, so you have to evaluate whether it will be enough to be worth the money and effort. That will also depend on how large the battery is, which should be based on your power needs. Figure that out first, then see how the charging works out.
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  • Vronsky
    Vronsky Registered Users Posts: 3
    #3
    Re: PV system on sailboat, what output possible?

    I wish it could be 140W: it's actually only 12 square ft of deck space available for mounting two panels in a reasonable way :grr, so I have to do with whatever's possible.
    Yes, it would only serve as a supplemental charging system when grid electricity is not around, to reduce use of the engine's alternator, and as back up to run boat's most essential functions in case engine fails while offshore.
    I don't want to install these noisy turbine systems, and fuel cells are way to expensive.
    As standard, boat has a 70Ah starter battery, and a 70Ah service battery

    So would 70W be a good indication (based on best available panels and electronics) of what I can count on ?

    THANKS !
    V.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: PV system on sailboat, what output possible?
    Vronsky wrote: »
    I wish it could be 140W: it's actually only 12 square ft of deck space available for mounting two panels in a reasonable way :grr, so I have to do with whatever's possible.
    Yes, it would only serve as a supplemental charging system when grid electricity is not around, to reduce use of the engine's alternator, and as back up to run boat's most essential functions in case engine fails while offshore.
    I don't want to install these noisy turbine systems, and fuel cells are way to expensive.
    As standard, boat has a 70Ah starter battery, and a 70Ah service battery

    So would 70W be a good indication (based on best available panels and electronics) of what I can count on ?

    THANKS !
    V.

    Possibly. It is still a matter of "see what fits" and how much power that will put out. BTW you will be looking at Amps more so than Watts. For example a 12 Volt system uses a panel that actually has a Voltage rating of around 17-18. But what the battery needs is Amps in charging. So a 70 Watt '12 Volt' panel will put out about 4 Amps. That would be just the minimum current suited for a 70 Amp hour battery.

    This is where panel choice makes a big difference, as a monocrystaline panel will produce much more power from the same area (if you can find one that fits). But you are not going to want to walk on one and they are not flexible at all. They are also difficult to find in small panels, and expensive per Watt.
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  • LandKurt
    LandKurt Solar Expert Posts: 41 ✭
    #5
    Re: PV system on sailboat, what output possible?

    You might consider something like the Renogy 100W bendable monocrystalline panel. It's a laminated flexible plastic sheet. I don't know how much walking it would withstand but it is surely more durable than a glass panel and cheaper and more efficient than thin film. The RNG-100DB looks to be just over six square feet, so there's a chance you could fit two depending on the exact space you have available.
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  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    #6
    Re: PV system on sailboat, what output possible?

    What many of the marine guys do is put an mppt controller on each panel. Best to run the GTI voltages, and not the 12v nominal panels. Controllers run parallel on the house bank battery.

    For additional marine-specific tips, you may want to visit the electrical threads on Cruisersforum.
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  • Vronsky
    Vronsky Registered Users Posts: 3
    #7
    Re: PV system on sailboat, what output possible?

    Something like this one perhaps (2 units) >

    https://www.sunware.de/sunware/produkte/module_detail/SW-5066

    Why 2 MPPT controllers, instead of one unti for both ?

    MANY THANKS !
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  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    #8
    Re: PV system on sailboat, what output possible?

    I'm not really sure that is a bargain - I'd definitely keep shopping.

    The reason for individual controllers is that multiple panels in a marine environment may not encounter the same conditions as we would with a fixed array. Temporary shading of one panel is common, and with multiple controllers they can really optimize each panel's condition. Expensive, yes, but with limited mounting space, that means trying to extract the most from a small solar array in a short amount of time.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: PV system on sailboat, what output possible?

    If the panels are in parallel the varying insolation is not a problem regardless of whether you use a PWM or MPPT type controller. Multiple controllers are needed if: 1). there is more array than one controller can handle; 2). the arrays are of greatly (more than 10% variance) different Voltage; 3). the arrays are oriented differently.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #10
    Re: PV system on sailboat, what output possible?
    Cariboocoot wrote: »
    .... 3). the arrays are oriented differently.
    That is often not a problem either as long as neither array gets partial shade. Partial shade itself can be a problem even if the basic orientation of the two arrays is the same.
    And for 2 and 3 you do not necessarily need two CCs if one CC has two or more MPPT inputs. (Not as common a thing to find as with GTIs, but apparently some CCs may do this.)
    SMA SB 3000, old BP panels.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #11
    Re: PV system on sailboat, what output possible?
    inetdog wrote: »
    That is often not a problem either as long as neither array gets partial shade. Partial shade itself can be a problem even if the basic orientation of the two arrays is the same.
    And for 2 and 3 you do not necessarily need two CCs if one CC has two or more MPPT inputs. (Not as common a thing to find as with GTIs, but apparently some CCs may do this.)

    Actually I've just been testing this.
    The power issues comes not only with partial shading but also as a function of Voltage difference from non-shaded arrays. What I have found is that for arrays whose Vmp specs match it is not that severe of a problem (about 2% difference from optimum).

    Keep in mind that is on a particular old MX60 controller. I expect the issue is even less with a newer controller like a Classic.

    The worst case is with V difference and I difference where one array can pull the other "off spec": either V above Vmp causing Voltage loss or V below Vmp causing V*I loss. This is most likely to occur with either really different size arrays (2X Watts) or really different Vmp's (and this appears to be well above the 10% difference).

    Unfortunately smoke has halted the testing. It is now raining, which helps with the smoke but doesn't help produce any electricity.
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