PV panels -- OC and SC ...

billybard
billybard Registered Users Posts: 7 ✭
in Solar Beginners Corner #1
Howdy:

I've read somewhere that the charge controller will either short a panel or open circuit it when power is no longer required.

However, I've not seen much about the damage or non-damage to a PV panel by doing either of the above (either short term
or long term).

I am planning on putting a PV system on my motorhome, but I rather infrequently boondock off the grid.
I am concerned that being plugged into power for long periods of time will maybe cause problems.

The converter will usually be charging the batteries while I am plugged in, and I am concerned about the
charge controller and the converter both trying to charge the batteries at the same time.

My ill-informed concern is that the charge controller will be "shutting off" the PV panels probably more than allowing them to function.

Sure would like some clarification from the gurus on the forum. (Yeah, I've got a lot to learn--thanks for your patience!)

Thanks.
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #2
    Re: PV panels -- OC and SC ...

    In theory, neither open circuiting (turning off the solar panel/array) or short circuiting ("crowbarring" the solar array) will cause damage. Solar panels do not experience any "extra stress" when their output is "open". There is some extra heat stress (I2R current flow causes some heating in the panel array)--But panels are supposed to be designed to carry the current (Isc short circuit current is a bit larger than Imp max power current--but the difference is not that great).

    However, for various reasons, I would stick with the normal method of using a standard solar charge controller that "turns off" the array when the battery bank is done charging. In normal usage, I cannot imagine the need to crowbar a solar array.

    If you have an RV with shore power--You can leave the solar array+charge controller turned on assuming you have a good quality charge controller with bulk/absorb/float settings.

    You can parallel charge controllers (solar plus converter/shore power charger)--The controller with the highest charging voltage will win.

    In many cases, simple RV converters may not have float charging mode and tend to overcharge/use battery water more than a good quality solar charger. Batteries should not have voltage higher than ~13.2-13.6 volts (12 volt bank) 24x7 for long term storage. if the batteries are >13.6 volts for long term storage, they may tend to "boil" the electrolyte down and need monthly (or so) distilled water replacement.

    What ever you do--make sure that the battery is also NOT subjected to being discharged to dead by loads left on (light in closet, water pump, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #3
    Re: PV panels -- OC and SC ...
    BB. wrote: »

    What ever you do--make sure that the battery is also NOT subjected to being discharged to dead by loads left on (light in closet, water pump, etc.).

    -Bill
    Haha Glad I'm not the only one who makes typo errors. Hahaha Left out a word there BB, or stuck in a wrong one. :D
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  • billybard
    billybard Registered Users Posts: 7 ✭
    #4
    Re: PV panels -- OC and SC ...

    Hey Wayne:

    Unless Bill snuck in and changed a word, his comment reads OK to me. What am I missing??

    Thanks BIll for the comments re the PV panels being able to handle the stress of OC (and maybe tolerate with some groans when SC'd).

    Cheers.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #5
    Re: PV panels -- OC and SC ...

    Yes, I did sneak in and added the word NOT. (a little moderator humor).

    -Bill 8)
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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