Bi-polar PV systems and Potential Induced Degradation (PID)

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John HSB

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When using a bi-polar systems with the midpoint grounded, half of the array is positive with respect to ground and the other half of the array is negative with respect to ground. PID is not a concern with systems that have the negative terminal grounded. With bi-polar systems will the positively grounded half of the array be vulnerable to the PID and the negatively grounded side not be affected by PID? How much help will it be to use PID resistant solar panels on the positively grounded half of the array with respect to eliminating concerns with PID in a bi-polar system?
 
You probably have take that question to module manufacturers' application engineers. PID seems to vary by module. Also by climate. And by system grounding. So I don't know that there is a one-size-fits all answer. I'm aware of one module manufacturer that will not honor its power warranty in a bi-polar application. But that could be an exception rather than a rule.
 
Are the old Grape Solar panels that required positive ground not crystalline?
As I understand it the problem there was not PID per set, but rather a reversible build up of stray charge resulting from the construction technique.

Tapatalk!
 
GoldDigger said:
Are the old Grape Solar panels that required positive ground not crystalline?
As I understand it the problem there was not PID per set, but rather a reversible build up of stray charge resulting from the construction technique.
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The only manufacture I am aware of it possible being a problem is SunPower. If you look at NREL white papers on the subject it appears to be a lot of worry about nothing and that weather has more to do with it than design. On the design side crystalline panels are not affected or so minimal it can be ignored.

My take is the problem is with thin film panels operating at high voltage. IMHO thin film should not be used for anything unless experimental or where you must have light weight or bendable like a experimental solar car. Otherwise they degrade and pretty much useless in 5 to 7 years. You see thin film being used in co generation plants, but IMO that is being done to minimize cost to enable the builder to sell the plant to a SUCKER. After completion, on line, and once government subsidies are received, the investment paid for by tax dollars. Profit comes from the sale of the plant.
 
dereckbc said:
Just use Crystaline panels and the problem goes away.
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It's more nuanced than that. There were a lot of PID study results presented as part of Solar Power International's "poster program" in Chicago. It's fair to say that there isn't any consensus RE: root causes of PID. But it is a real concern, and it definitely impacts c-Si PV modules.

Based on what I've read, PID impacts in the field will vary based on: module construction, system grounding, array voltage, module mounting, relative humidity (high humidity environments are worst), etc.

A colleague of mine noticed language in SunEdison's warranty restrictions that seemed to rule out using their modules in bi-polar arrays. When he contacted the manufacturer, an applications engineer confirmed that the power warranty would not apply if these particular modules were used in a bi-polar configuration. My impression is that PID was the reason for the warranty exclusion.

This white paper by AE is relevant:

http://solarenergy.advanced-energy.com/upload/File/White_Papers/ENG-PID-270-01 web.pdf

The AE white paper seems to suggest that PID effects are module specific. If so, you should be able to find a c-Si PV module manufacturer that is more than happy to give you a thumbs up to use their product in a bipolar application. I'd go that extra step before placing a PO.
 
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