[RE-wrenches] PID

[drake.chamberlin at redwoodalliance.org]

Bill,

Thank you. That is exactly the data needed.

Drake


> 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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