Sunpower X21-345 Off grid installation Help Please

Holiday
Holiday Registered Users Posts: 1
in Off Grid Solar & Battery Systems #1
Well I think I am in over my head a bit on this one.

I found a really good deal on 8 new Sunpower X21-345w panels so I jumped on it and bought them. Well I come to find out that these panels might require a positive ground (apparently some Sunpower panels require this).

I also purchased 2 Midnite Classic 150 MPPT charge controllers and Midnites combiner box and all necessary breakers.

I have been researching this on the internet but have found no good solutions for an off grid 12v battery system that uses a Negative ground.

I have also not been able to determine if these panels are indeed positive ground or negative ground.

Does anyone out there have experience with a similar setup? I have seen posts in other forums referring to Sunpower panels on boats and RVs so there must be a safe way to accomplish a positive ground or are people just ignoring this. It does seem that if you hook them up normality they will still work but they might have a reduced output.

Any help or direction would be greatly appreciated.

Cheers,
CJ
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Sunpower X21-345 Off grid installation Help Please

    Welcome to the forum.

    Well boats and RV's don't really have ground in the sense they aren't tied to Earth. But negative is used as a common chassis connection.

    The new NEC regs require DC ground-fault protection which isolates both positive and negative from ground. So what we really have to ask is: do 'positive ground' panels really need to be? Looking at the data sheet I find no reference to positive grounding.

    These panels are actually not suitable for off-grid use. They have an odd Vmp of 57.3. On a 12 Volt system that will move the controller efficiency off the curve a few percentage points. You'd have all eight of these in parallel and have 48 Amps @ 57 Volts going from array to controller.

    On a grid-tie system none of this matters. Although for most central inverters you'd only have six in a string. Very odd configuration.

    So three things: contact the company to find out if negative grounding or fault isolation will be a problem, use them on a GT system instead, sell them and buy panels suited to the application.

    Sometimes a bargain is not a bargain.
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #3
    Re: Sunpower X21-345 Off grid installation Help Please

    I think Midnight makes Positive ground controllers, I'd give them a call and see if they can tell you what you might be able to do. You can PM member " boB " he for sure can or " Halfcrazy " . I think Midnight has swapped out controllers for people in the past as a accommodation . I agree with Coot, those are not the best panels to use, especially on a 12V off grid system.

    www.morningstarcorp.com/.../TS.APP.Positive_GND_Wiring.01.EN.pdf‎
    .
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  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    #4
    Re: Sunpower X21-345 Off grid installation Help Please

    Or just go 24v, use one controller, panels in parallel.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


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