[RE-wrenches] PID

[Bill Hoffer]

Drake

PID is caused by many factors, the capacitive nature of a solar panel and
materials ( cheaper, thinner encapsulants and backsheets and cell surface
treatments to get more efficiency to name a few).  The new marketing battle
cry for module manufacturers material vendors is PID resistant materials,
but we all have to take marketing claims with a grain of salt until we get
independent data to show that it is true!

A simplified explanation of PID is the build up of charged ions in a module
that cause a significant reduction in voltage output, dominated by a
complex interaction between materials within the module.  With a negative
grounded system there is a path to bleed off this charge .  The nature of
SunPowers module when negative grounding was used initially was the charge
build up was not bleed off the negative side, but needed to bleed off the
positive side.   This resulted in significantly reduced output, which is
irreversible after a period of time.  These were the first cases of PID in
the US.  That is why they solved it by specifying positive grounding to
bleed off this charge properly.  A transformerless inverter does not ( and
can not with fatal results) have a bond between negative and ground, so it
cannot bleed off this excess charge.  There may have already been PID, but
we never noticed with transformer based inverters and 600 VDC systems.  We
are seeing it predominately in Europe now where 1000VDC transformerless
inverters are more common, combined with cheaper modules ( ie materials) .

I am surprised that SMA knows nothing about this since I understand they
have a field fix  to add a switch, controlled by the inverter that allows a
bond connection between PV negative and ground when the inverter shuts down
over night to bleed off this excess charge and the switch is opened at
sunrise by the inverter before it makes it 's checks ( ground - negative
isolation and megging of the array for faults before startup).  Maybe this
is only available so far in Europe?

see http://files.sma.de/dl/7418/PID-TI-UEN113410.pdf
and http://files.sma.de/dl/7418/PID-PVOBox-TI-en-10.pdf

It can be a serious problem once it has reached an irreversible point!
 Some modules seem to be more susceptible to this issue. but it is not easy
to find which ones to avoid!

Bill


On Fri, Dec 27, 2013 at 8:39 AM, Drake <drake.chamberlin at redwoodalliance.org
> wrote:

>  Hello Wrenches,
>
> Attached is an article from Home Power that came in my email. It says
> module degradation is increased by PID (Potential Induced Degradation) by
> the use of transformerless inverters.  It says power degradation can occur
> over days or weeks and cause a 10% to 60% loss of efficiency.
>
> I called Power One and SMA and their tech support people have not had any
> reports of problems. Is this something we need to be concerned about?
>
>
> Thanks,
>
>
> Drake
>
>
> Drake Chamberlin
>
>
>
>
>
> *Athens Electric LLC OH License 44810 CO License 3773 NABCEP Certified
> Solar PV 740-448-7328 <740-448-7328> *http://athens-electric.com/
>
>
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-- 
Bill Hoffer
161 SE Fourth Ave
P.O. Box 1823
White Salmon, WA 98672
sunengser at gmail.com <bhoffer at sunergyengineeringservices.com>
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