[RE-wrenches] Microfractures in PV Modules

Bill Hoffer sunengser at gmail.com
Sat Oct 4 11:20:48 PDT 2014


Christopher

There are some level of micro fractures that are always present in cells
and not visible to the naked eye.  Some of these will produce visible
fractures over time from loading and flexing of the module from weather and
temperature changes.  The micro fractures can be an issue with performance,
but may not show up until later, they are not necessarily an issue with
safety.  If the encapsulation is intact and the there is not a specific
internal fault caused by the separation the only issue would be loss of
conducting surface between the broken piece and the internal string wiring
resulting in a loss of performance.  Bottom line as long as there is not a
fault, your AHJ does not have much to say about performance, the NEC says
nothing about performance, only if the installation is safe.  All modules
are flash tested and sorted for performance and checked for faults (
insulation resistance tested at a voltage significantly higher than the
operational rating, 2x max voltage + 1000V).  This is required before a
module manufacturer can place a UL sticker on it.  IMHO as long as the
damage and is not causing leakage current during an insulation resistance
test at the factory the AHJ really cannot say anything about it legally, he
is not an inspector for UL and really only needs to be able to read the UL
sticker and certify it is being used according to the listing.

That being said some module manufacturers do add an additional
Electroluminescence test that does detect micro cracks by placing a small
reverse current through the module that causes the active material to act
as a Light Emitting Diode in the near infrared spectrum that it is possible
to detect with a special camera calibrated for that light spectrum.
Usually done in a lab, although there are expensive field units available
now.  These test will show micro-cracks, bad print screening and bad spots
on the cells from the doping process.  I have done tests were we purposely
damage cells in a module and we have been able to detect micro cracks that
did not necessarily result in a reduced flash test at the factory.  Over
time I assume that will not be the case and reduced output may be the.  So
IMHO your AHJ does not have the equipment nor does he have the expertise to
perform these tests, nor does the NEC or UL1703 require it!

Good Luck with the inspector, but I think he is way out of his league on
this one, until it becomes a safety issue, even a visible crack in a cell
is not an issue of his concern.

Bill

On Sat, Oct 4, 2014 at 8:20 AM, Christopher Warfel <
cwarfel at entech-engineering.com> wrote:

> Recently a inspector raised the issue of microfractures in pv modules, and
> that the existence of such fractures would require replacement of the
> modules and a failing of the system inspection. I found information from
> NREL confirming the existence of microfractures in poly crystalline.
> However, I have not seen any information on how to detect them (ie, what
> they look like).  Does anyone have a reference that shows this, and is this
> a valid concern for the industry?  Thank you, Chris
>
>
>
>
>
>
> --
> Christopher Warfel, President
> ENTECH Engineering, Inc.
> PO Box 871, Block Island, RI 02807
> 401-466-8978
>
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-- 
William Hoffer
161 SE Fourth Ave
P.O. Box 1823
White Salmon, WA 98672-1823
sunengser at gmail.com <bhoffer at sunergyengineeringservices.com>
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