cell PIV rating

SUNUP
SUNUP Registered Users Posts: 24 ✭✭
in Advanced Solar Electric Technical Forum #1
Hi
What is the PIV rating of each cell in a solar panel?

Thanks Charlie.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
    Re: cell PIV rating

    Since that is not a spec'd item, we should assume it's only a couple of volts. PV cells are not "diodes" although they sometimes seem to act that way.
    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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  • BB.
    BB. Super Moderators, Administrators Posts: 33,591 admin
    #3
    Re: cell PIV rating

    I believe the typical "safe" PIV (peak inverse voltage) would be ~12 volts (probably around 17-22 volts Voc). That is the normal maximum range of series cells (~36 cells in series) is bypassed with diodes (to protect cells that are shaded from being damaged in a panel/array).

    http://www.windsun.com/General/tech_tips.htm

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • SUNUP
    SUNUP Registered Users Posts: 24 ✭✭
    #4
    Re: cell PIV rating

    Hi, thanks for the reply. I am not referring to the bypass diode or the blocking diode. I was asking about the cells that make up the solar panel. I understand they are not diodes, but they are a PN junction so at some reverse voltage they will break down and conduct. I suppose it might not be an issue.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #5
    Re: cell PIV rating
    SUNUP wrote: »
    Hi, thanks for the reply. I am not referring to the bypass diode or the blocking diode. I was asking about the cells that make up the solar panel. I understand they are not diodes, but they are a PN junction so at some reverse voltage they will break down and conduct. I suppose it might not be an issue.

    you are correct that they are pn junctions and there is a similarity to diodes as they originated from diodes that were discovered to emit a small voltage under bright light. that is an interesting question that i don't have the answer for. and as all diodes would differ slightly then i would imagine that point of breakdown would vary considerably and that it would be so for pv cells as well. even identically manufactured diodes have some variance in the exact breakdown points.

    i am curious as to why you would need this info? just what is it that comes to your mind that this becomes an important factor?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,591 admin
    #6
    Re: cell PIV rating

    Found a chart of reverse voltage for a generic solar cell:

    http://www.mpi-halle.de/mpi/publi/pdf/8454_09.pdf

    Around 13 volts is the "hard" breakdown voltage range.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #7
    Re: cell PIV rating
    SUNUP wrote: »
    Hi, thanks for the reply. I am not referring to the bypass diode or the blocking diode. I was asking about the cells that make up the solar panel. I understand they are not diodes, but they are a PN junction so at some reverse voltage they will break down and conduct. I suppose it might not be an issue.


    I've heard that if you connect a PV backwards to a 12V battery, it blows the PV, (fries all the diodes).
    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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  • BB.
    BB. Super Moderators, Administrators Posts: 33,591 admin
    #8
    Re: cell PIV rating

    Yes, a solar panel connected backwards to a battery bank will be fried.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • SUNUP
    SUNUP Registered Users Posts: 24 ✭✭
    #9
    Re: cell PIV rating

    Hi,Thanks again for all the replies.
    niel wrote: »
    i am curious as to why you would need this info? just what is it that comes to your mind that this becomes an important factor?

    We were talking about solar panels with a group of Amateur Radio Operators and the question came up, as far as needing the info probably not.

    Thanks for the Link.

    This is a great Forum for Info, I spend a lot of time here reading and learning.

    Charlie.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,591 admin
    #10
    Re: cell PIV rating

    Just trying to be helpful.... Many times we get questions that are based on "different" uses of equipment/materials. Some of which are not very safe.

    For example, a 100+ DIY solar panel built with plastic and wood and mounted on a home/over brush. There is a very significant fire hazard and (for the most part) the panels will not last more than a few months in full sunlight before they fail (and the failures can become ignition points for fire).

    Also, many people build DIY solar panels from cells purchased on EBay--Many times, those cells are rejected from by panel vendors because of mfg. defects. One of which can include "current defects" where cells can overheat (again fire hazard) as in that last link I put up about breakdown voltage.

    The obvious "fix" for protecting a string of solar cells from reverse voltage is a blocking diode (or bypass diode for series strings)--But that was not what you were looking for--So "we" were just wondering what the application was. There are many "secondary" issues which can be hazardous--And we try to be very careful here that we don't lead people down a road where they can get hurt because of lack of knowledge on either party's side.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • SUNUP
    SUNUP Registered Users Posts: 24 ✭✭
    #11
    Re: cell PIV rating

    Hi
    Thanks bill I understand your concern about giving out information that could cause injury or worse. I do go down the wrong road sometimes. I am a retired Industrial Electrician and have been known to use a few things as they were not made for to get a job done. We learn along the way by making a few mistakes. I read a lot of forums and know the advice that is given by some can be very dangerous to some Individuals to say the least. Not all are as concerned about safety as you are. It would appear there is not an issue with peak inverse voltage within the panel, only outside the panel between the solar panel and the load. And using bypass diodes to bypass current around a low producing panel.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #12
    Re: cell PIV rating
    SUNUP wrote: »
    And using bypass diodes to bypass current around a low producing panel.
    Commercial panels will typically have three or more bypass diodes connected internally, basically so that each section with a voltage higher than ~18 volts will have its own bypass diode. That will allow some power output from the panel in a series string if it is only partially shaded. DIY panels should follow the same plan. If you have only one bypass diode, shading just one cell will cost you the full output of the panel.
    That takes care of the forward breakdown voltage, and a blocking diode or fuses will take care of reverse breakdown voltage (or maybe I have the two reversed. It is not really clear with a photodiode. :-))
    SMA SB 3000, old BP panels.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #13
    Re: cell PIV rating

    " It would appear there is not an issue with peak inverse voltage within the panel, only outside the panel between the solar panel and the load. And using bypass diodes to bypass current around a low producing panel."

    in the cases of higher voltages being pressed against that of a pv's voltage then a blocking diode comes into play there. this, as you know, would prevent power flow into the pv from external sources providing it is of the same polarity. be aware there is no protection by either diodes or fuses that stop things if you were to reverse the leads of 2 or more power sources with pv being at least one of them. sounds confusing, but it's simple. take two pvs with + to + and - to - in parallel through a fuse rated for the current of both pvs. all is well. put + to - and the pvs don't get damaged and no fuse blows because it is roughly the imp of 1 of the pvs that will flow as the 2 pvs are now a closed circuit unto themselves. put a battery into the mix as we normally do and the paralleled arrangement just allows the full benefit of both pvs charging the battery. with the pv leads reversed to each other going to the battery you will have the current of both the battery and 1 pv going to the pv that was placed in reverse. this could be blocked by the blocking diode from entering the reversed pv, but without that a fuse would pop from the high current being fed by the battery. if there's only pvs but 3 pvs without a battery the current can get high enough to damage the single pv that was reversed and still not blow a fuse unless a blocking diode is present.

    i can keep going on with the differing scenarios, but i think you get a bit of this picture. with 3 or more power sources paralleled with at least one of them as pv then fusing is a must for each pv or string of pvs. there was an incident long ago where an early member accidentally reversed the connections on one of his pvs (pre mc connection days) in a 3 pv array and it popped the one pv as it was being loaded with the power of the other 2 pvs. he had not fused each pv's output and there weren't any blocking diodes involved either. today's polarized pv connections do limit this reverse possibility and blocking diodes are rarely needed especially being most all controllers block any back flow of power from the battery to the pv.

    out of curiosity, was this on a net or particular band/freq that you guys get into these conversations as many of us are hams? if you don't want it publicaly known then you could withhold that info and you can optionally pm that info to me if you wish to answer me.
    73s n3ghx
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #14
    Re: cell PIV rating

    If the 'PIV' is referring to Peak Inverse Voltage rating then it could have two meanings. One of the cell itself, other for bypass diodes.

    Most panel manf. rate maximum system DC voltage (not PIV for a panel) which is the maximum overall voltage allowed for series stacking of panels, typically important to GT inverter setups. The typical number is 600 vdc. This is set by 'PIV' rating on bypass diodes.
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  • boB
    boB Solar Expert Posts: 1,032 ✭✭✭✭
    #15
    Re: cell PIV rating

    You will most likely never see or run into the PIV rating of module bypass diodes because the forward voltage (Voc) of the module will be
    hit way before that happens. They are kind of like 2 paralleled back to back diodes.
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