Positive Ground vs. Negative Ground Solar Panels???

ywhic
ywhic Solar Expert Posts: 621 ✭✭
in Off Grid Solar & Battery Systems #1
1st.. I am not using this on a vehicle, but a cabin and the panels will not be directly on the buillding..

I have been looking at Home Depot 12v Grape 100watt panels $199 each for use, but read something about they are POSTIVE ground panels..

I'm going to assume most 12v panels are NEGATIVE ground.. (and someone noted RV safe.. again not applicable to me)..

Both types have 2 wires coming down off them with MC4 connectors (not that it matters) and all have aluminum framing..

Would there be any issues using them with a non-positive ground charge controller... I know they make 2 types of the Morningstar Pro 30 controller I was looking to use..

I was planning on grounding the panels to the ground with a steel rebar type rod outside...

Help or direction appreciated..
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #2
    Re: Positive Ground vs. Negative Ground Solar Panels???

    5.5 Amps X 14.5 volts = 100 watts?
    Max current listed does not say if it's under normal load, or under short circuit conditions. The latter would look better in promo info and is most likely what they're listing.
    Max OC voltage 18.
    Be aware that you may well not be getting what they would have you believe you're getting with these panels.
    Neighbor of mine got me to hook up 4 of these panels and to be truthful, I felt sorry for her. The frames of panels sold by big box stores are also usually very flimsy.
    The experience of others may vary.
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  • ywhic
    ywhic Solar Expert Posts: 621 ✭✭
    #3
    Re: Positive Ground vs. Negative Ground Solar Panels???
    waynefromnscanada wrote: »
    5.5 Amps X 14.5 volts = 100 watts?
    Max current listed does not say if it's under normal load, or under short circuit conditions. The latter would look better in promo info and is most likely what they're listing.
    Max OC voltage 18.
    Be aware that you may well not be getting what they would have you believe you're getting with these panels.
    Neighbor of mine got me to hook up 4 of these panels and to be truthful, I felt sorry for her. The frames of panels sold by big box stores are also usually very flimsy.
    The experience of others may vary.

    Think your on the wrong ones... http://www.homedepot.com/Grape-Solar/h_d1/N-5yc1vZ8p9/R-203336897/h_d2/ProductDisplay?catalogId=10053&langId=-1&storeId=10051

    Specs are 5.42 amp and 18.5 v... (100.27 watts)..

    Anyway.. I called MorningStar and got some info..

    IF I wanted to use the panels with a normal controller (neg ground) and NOT on a vehicle..

    1) I cannot have 1/2 + ground and 1/2 - ground panels.
    2) I can use the + ground panels with the normal controller IF I ground ONLY the + battery terminal..

    MS provided me a PDF link talking about a + ground panel setup using there TriStar controller.. http://www.morningstarcorp.com/en/support/item.cfm?ItemId=32

    I think i will avoid the + panels and stick with simple - systems otherwise I will be stuck..
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  • calbiker
    calbiker Banned Posts: 50 ✭✭✭✭
    #4
    Re: Positive Ground vs. Negative Ground Solar Panels???

    I haven't dealt with a positive ground for over 40 years. My MGA was a great car but had an interesting positive ground. For the life of me, I can't understand how a panel can have a positive ground. I googled Grape Solar with no mention of a positive ground. As I see it, a solar panel has two connections. The electrons come out of one connection and go back at the other connection. There isn't a defined ground.

    Cal
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  • ywhic
    ywhic Solar Expert Posts: 621 ✭✭
    #5
    Re: Positive Ground vs. Negative Ground Solar Panels???

    From TAB #1 on the panel listing at HD.. http://www.homedepot.com/buy/grape-solar-100-watt-monocrystalline-solar-panel-227164.html

    This panel works best when paired with a positive ground capable charge controller

    The MorningStar guy said maybe its NOT MANDATORY but recommended for a + ground system for better performance.. (which is wht the HD blurb is saying I think)..

    Found a linky to get in on Grape Site..

    http://www.grapesolar.com/index.php/products/modulesandkits/grounding/
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #6
    Re: Positive Ground vs. Negative Ground Solar Panels???

    Here is one discussion about positive grounding:

    when positive ground is used in pv

    And, in the above thread, I posted this that reference specifically why Sun Power panels (Germany--and they are very good solar panels) are sensitive to ground polarity:
    BB. wrote: »
    What do you mean by Positive Ground? Generally the panels are not grounded at all--and require you to make the ground connection...

    If you have the Sunpower panels, which require positive grounding (read this thread for technical details and links to Sunpower documents)--yes, you need to positive the ground the "+" terminal from the string. If you don't and use a "-" ground, you can lose multiple ten's of percent worth of output because the panel accumulates charge. The charge can be quickly removed by positive grounding (hours?).

    As far as I know, the other standard silicon panels can be positive or negative grounded without issue.

    You can positive ground some MPPT charge controllers (I think the MX-60 can be positive ground--but read the manual)--you have to be real careful--much "car type" DC equipment assumes negative ground and the sheet metal chassis will now be "hot"... Positive ground is used by telephone companies and for cathodic protection systems (to prevent, for example, buried metal gas pipes from corroding).

    I would avoid positive grounding and off-grid system unless you have no other option (or need positive ground reference for some reason) and have checked out each piece of equipment you plan to use and understand where chassis ground vs positive grounded battery bus are each referenced.

    -Bill

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • calbiker
    calbiker Banned Posts: 50 ✭✭✭✭
    #7
    Re: Positive Ground vs. Negative Ground Solar Panels???

    Thanks for all the links. Bill, you did a great job documenting positive ground panel issues. What I get out of it, in Sunpower's effort to maximize efficiency, they ran into an "uh-oh". Leakage currents and surface polarization cause the cell's surface transistor to conduct, resulting in lost efficiency. There's a static charge problem.

    The GrapeSolar link shows only parallel panel configurations. Can you use them in series?

    I would avoid positive ground panels at all cost.

    Cal
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #8
    Re: Positive Ground vs. Negative Ground Solar Panels???

    Yep... But for 98% of the people that use Grid Tied solar--Positive grounding is just a minor configuration issue on the GT inverter (note: The loss of power occures only with negative or floating ground systems over maybe 100's of hours of sun. And is "fixed" with something like 10's of hours of positive grounding when exposed to sunlight). For the people with battery systems--The issues are a bit more complex. Much of the 12 volt stuff out there assumes negative grounding for use in cars and such... So, if you choose to positive ground (like much of the telecom gear), you need to double check everything that they have +/- separate from "earth ground/case ground" connections. Otherwise you do run the risk of making the chassis "hot" with respect to ground (i.e., a car radio connected to a positive grounded solar PV system).

    Also, for most PWM solar charge controllers you can ground the panel "-" side and the battery "-" side without issues. But for some of the MPPT charge controllers, they measure current in the negative lead--and if you jumper the panel ground/battery ground around the charge controller, it will not allow it to properly do the MPPT function (cannot accurately measure array current).

    Most/all of the links to original source documents are dead now, and I could not find backup copies of them (PDF files on studies).

    Regarding placing any solar panels in series... Basically, there should be a maximum working voltage rating. For older panels, they frequently were around 70-75 VDC maximum working voltage (series connection) assuming PWM charge controllers and 48 volt battery banks.

    Today, the standard for larger panels is between 600 VDC (VAC?) and 1,000 VDC (European standard).

    If the panels are UL/NRTL approved, are >100 watts (in general)--They are usually intended for Grid Tied operation which, in the US would require 600 VAC minimum rating. So, they would be "safe" for connecting in series.

    A few people here purchased end of run 90 watt Sun Power panels and are very happy with them on there off grid systems.

    Remember that Sun Power (Germany) is (usually) different from other unrelated "Sun Power" company/brand names out there...

    -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 ✭✭✭
    #9
    Re: Positive Ground vs. Negative Ground Solar Panels???

    I was going to say that we've had both positive and negative input on Grape panels, but it might confuse people. :p
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  • RobW
    RobW Registered Users Posts: 23 ✭✭
    #10
    Re: Positive Ground vs. Negative Ground Solar Panels???

    Resurrecting this old thread with what I found in Grape's Connection Guide for their 100W MONO GS-S-100-FAB36.
    Grounding
    The inverters and panels have grounding terminals but grounding is not a requirement for operation. The systems in our test lab have been operated with and without grounding with no differences in performance.

    Positive Grounding
    The GS-S-100-TS panel uses an advanced, back contact cell. In grid-tied systems, these cells require positive grounding to prevent the build up of ions on the cell’s surface which reduce the panel’s efficiency. But, in low voltage battery charging systems, we have found that the reduced efficiency as a result of ion build-up with improper grounding is negligible. To minimize the effect of ion build up, Grape Solar recommends against connecting more than two of the GS-S-100-TS panels in series when not using a positive ground compatible charge controller. The buildup of ions does not harm the panel. When the sun sets the ions dissipate.
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  • GrapeSolar
    GrapeSolar Registered Users Posts: 1
    #11
    Re: Positive Ground vs. Negative Ground Solar Panels???
    ywhic wrote: »
    I have been looking at Home Depot 12v Grape 100watt panels $199 each for use, but read something about they are POSTIVE ground panels..

    No Grape Solar panels use or benefit from positive grounding.

    Do not use positive grounding on any Grape Solar panels.

    Anybody saying Grape Solar panels need positive grounding is misinformed.

    If you have questions on this, please call Grape Solar at 1-877-264-1014
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