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

[Bill Brooks]

Bill and all,

 

Dana asked for good conservative data for long-term performance. This is not
necessarily what you would use when you are trying to make yourself look as
good as possible for a financier.

 

The real question is, where did this data come from confirming lower losses?
It takes about 7-10 years of data to establish a degradation rate. The newer
data is based on an NREL study that was released several years ago. This
means that the study was based on modules manufactured in the U.S., Japan,
and Germany with very few Chinese or other Asian origins. The numbers may
have improved-or they could be worse.

 

Ultimately, if you do not have long term data on any module (which you
clearly don't) any assumption about voltage or current degradation is a
guess at best.

 

Figures lie and liars figure.  Cynicism in this area is a positive character
trait.

 

Bill.

 

From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On
Behalf Of Bill Hoffer
Sent: Tuesday, June 03, 2014 9:00 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Module Degradation - voltage or current?

 

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Bill Brooks, passed on past data, ( correct me Bill if I am out of date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 

 



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