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 <[email protected]
<mailto:[email protected]>> 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Bill Brooks, passed on past data, ( correct me Bill if I am out of
date here) recommends 1% Power loss per year with approximately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
<[email protected] <mailto:[email protected]>> 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>
[email protected] <mailto:[email protected]>
360.318.7646 <tel:360.318.7646>
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