PV degradation [RE-wrenches]

[Bruce Roush]

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


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