[RE-wrenches] Module Degradation - voltage or current?

[Ray Walters]

I agree that Voc doesn't seem to degrade as much.  I've had a chance to 
measure several modules over 20 years old, and the Voc is only dropping 
about 1/2 the rate suggested by others here.   I think a more 
appropriate number might be 0.25% V drop/ year.

R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760

On 6/4/2014 11:36 AM, Nathan Charles wrote:
> So I read this paper, Smith, R. M., Jordan, D. C., & Kurtz, S. R. 
> (2012). Outdoor PV Module Degradation of Current-Voltage Parameters, 
> which seems to seems to suggest that Voc doesn't degrade like Isc 
> degrades. Based on that and other data I've seen it seems like panels 
> that degrade at 0.5%/year are outliers on the low side.
>
> Thoughts from other wrenches?
>
>
>
>
> On Tue, Jun 3, 2014 at 11:59 PM, Bill Hoffer <sunengser at gmail.com 
> <mailto:sunengser at gmail.com>> wrote:
>
>     Dana
>
>     Bill Brooks, passed on past data, ( correct me Bill if I am out of
>     date here) recommends 1% Power loss per year with approximately
>     0.5% current and 0.5%voltage.  That is also what Solar Energy
>     International Best Practices curriculum recommends.  Based on some
>     newer data from larger projects requiring testing to actually
>     determine those values for the Bankability requirements ( PVsyst
>     PAN files),  I believe we are seeing lower numbers than that now.
>      In general, quality of modules are higher than the older modules.
>      We of course are usually not privy to those results and may not
>     even be getting the same level of binning for small residential
>     projects as the MW projects do.   0.5% V loss per year seems like
>     a like a good conservative number to me, especially if you add a
>     little buffer (1-2%) in there.
>
>     Bill
>
>
>     On Tue, Jun 3, 2014 at 3:41 PM, Dana Brandt
>     <dana at ecotechenergy.com <mailto:dana at ecotechenergy.com>> wrote:
>
>         Hi Wrenches,
>
>         Does anyone know what percentage of module degradation over
>         time is voltage and what is current? I'm wanting to make sure
>         we give ourselves plenty of breathing room on the minimum Vmp
>         of the inverters over the long term so need to try to
>         anticipate how much voltage we'll lose on the array over 30
>         years.
>
>         Thanks,
>
>         Dana
>
>         Dana Brandt
>         Ecotech Energy Systems, LLC
>         www.ecotechenergy.com <http://www.ecotechenergy.com>
>         dana at ecotechenergy.com <mailto:dana at ecotechenergy.com>
>         360.318.7646 <tel:360.318.7646>
>
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>     William Hoffer
>     161 SE Fourth Ave
>     P.O. Box 1823
>     White Salmon, WA 98672-1823
>     sunengser at gmail.com <mailto:bhoffer at sunergyengineeringservices.com>
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> -- 
> Nathan Charles
> Engineer
> NABCEP Certified PV Installation Professional #042013-20
> Paradise Energy Solutions
> (717) 283-2021 direct
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