PV degradation [RE-wrenches]

[Jim Duncan]

Bob-O Schultze wrote:
> 
> Hiya Gang,
> Mitsubishi claim that their "no lead" approach to module  
> interconnections will reduce degradation due to lead solder  
> oxidation. Maybe so.
> I'll let you know in 10 years or so, Buddha willing and the creek  
> don't rise.
> Merry Christmas to all.
> Bob-O
> On Dec 12, 2006, at 12:07 PM, Bruce Roush wrote:
> 
> >
> > Windy,
> > The figures used by BP are from 1/2 to 1% per year degradation. Of  
> > this
> > power loss, 1/2 is voltage and 1/2 current.
> > Most modules are warrantied to produce 80% power output after 25 years
> > (this equates to 0.8% per year).
> >
> > Significantly, the warranty is for the wattage adjusted to the stated
> > tolerance factor of the module. For a module with 9% power tolerance,
> > you would first multiply the wattage times .91, to adjust the  
> > rating to
> > the guaranteed minimum. Then the 80% would be applied.
> >
> > As to the reason for the loss, I have heard that is is a result of the
> > development of resistance in the cell junctions and between crystal
> > boundries within the cells.
> >
> > Bruce Roush
> >
> >
> >
> > Windy Dankoff wrote:
> >>
> >> Wrenches,
> >>
> >> Perhaps you can help  me answer a question for "Ask The Experts"
> >> column in Home Power. It regards degradation of PV modules.
> >>
> >> There seems to be some agreement on a norm of about 1/2% per year
> >> degradation (not due to dirt). This is a rough average, of course.Is
> >> there any general agreement on WHY this happens?
> >>
> >> I think it's the average of a variety of factors, but if you have
> >> data on this issue, it may be helpful.
> >>
> >> Also, if you have factual data on percentages of failures rates of PV
> >> over a long period, that will help too.
> >>
> >> Thanks!
> >> Windy


I recall that one problem that existed in 1993, according to Seimens 
Solar, is that nothing had been found that will "stick" to silicon and 
provide a solid solder-like electrical bond. The next best thing, and 
the process still used I suspect, is simply pressing the conducting 
ribbon against the surface of the cell and holding it tight as a part of 
the lamination. Even the most pristine surface to surface connection is 
going to be vulnerable to corrosion since air and water will always be 
present in tiny amounts. Is this still the same process or has something 
been discovered to improve the connection.
Jim Duncan
North Texas Renewable Energy Inc
Fort Worth, Texas


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