PV Module Degradation (was PV Inverters module strings) [RE-wrenches]

[Bill Brooks]

Pat,

It is not 1-2% module degradation. PVUSA proved that all system degrade 1-2%
per year as a system. This requires 6-8 years of constant monitoring to
actually detect. This is due to the fact that measurement uncertainties are
higher than the degradation rates.

How much of that is module, is hard to say. It is likely more than 0.5% for
most modules. The system degradation is likely 75% of the system degradation
if not more. This means that modules could be degrading slightly faster than
their warranties allow (0.75%-1.5% per year). For a 20-year warranty
degradation to 80% of rating, this allows for a 1.1% degradation. A 1.5%
degradation will result in a final performance of 74%. Looks like you're
entitled to 6% from the warranty.

However, have you ever tried to make a claim on a PV warranty from a power
point of view (not failure)? Module warranties are great for module failures
and very difficult for underperformance. It requires, removing the array and
shipping it back to the manufacturer for flash testing. Then you have to
live with their results.

Most people have the erroneous idea that if their array underperforms that
they'll either get a new array or automatically get some new modules. Not
so. These warranties are very carefully written and it will cost the
installer or system owner far more to collect on the warranty than the
warranty is worth. I went through the warranty process just to confirm this
fact.

Case in point as to why third party testing is so critical. We are at the
mercy of manufacturers information and there is very little muscle any one
customer (unless you buy Megawatts of PV) can bear to get satisfaction.

This is not to say that manufacturers are routinely dishonest or trying to
scam folks. They are trying to make money and until recently, this has not
been a major issue. When you operate on-grid PV systems, you can more
accurately measure the performance of the PV system and show good or bad
performance with a simple meter. Off-grid systems are a little more
challenging in that regard, so we overdesign for a variety of reasons
(phantom loads--both real and imaginary) and it all comes out in the wash.
Welcome to the real world of real-life performance.

Our industry needs to grow up, but it is going to take all our help. The
federal DOE program unknowingly contributes to the problem because they must
show continued improvement on costs and performance. To change the
performance metrics in mid-stream (kinda like Wag the Dog), this could cause
some problems with explaining why the numbers all of a sudden got worse
instead of better.

Bill.


> -----Original Message-----
> From: Pat Kiernan, Eco Electric, Inc. [mailto:ecoelec at rof.net]
> Sent: Monday, May 14, 2001 6:00 PM
> To: RE-wrenches at topica.com
> Subject: PV Module Degradation (was PV Inverters module strings)
> [RE-wrenches]
>
>
> Bill Brooks,
>
> I would really like to see the PVUSA documentation you mention if it is
> available. The reports I've seen indicate 0.5% power degradation per year
> with voltage degradation largely due to increasing resistance in
> connections
> and current degradation due to optical degradation in the
> encapsulant/lamination.
>
> If 1-2% module power degradation per year is real than most PV warranties
> are a hoax and RE is a little closer to snake oil than I would like.
>
>
> Pat Kiernan
>
> Eco Electric, Inc.
> PO Box 550
> Carbondale, CO 81623
> tel/fax (970) 963-3132
> e-mail: ecoelec at rof.net
> ----- Original Message -----
> From: Bill Brooks <billbrooks7 at earthlink.net>
> To: <RE-wrenches at topica.com>
> Sent: Thursday, May 10, 2001 1:40 PM
> Subject: RE: PV Inverters module strings (Last Call) [RE-wrenches]
>
>
> > Carl,
> >
> > No self-respecting PV manufacturer is going to share eventual
> > underperformance numbers. They are non-the-less very real and are fairly
> > consistent with all PV technologies available. No special conspiracy
> theory
> > for a-Si. All systems degrade at 1-2% per year and most of the
> degradation
> > seems to occur in voltage. Documented at PVUSA with over 20
> systems of all
> > types over 10 years.
> >
> > Initial overperformance is probably only an issue if you start a system
> > during the colder time of year. Most inverters, I believe this includes
> > Trace Tech (Kent please chime in) will stay offline with a DC
> overvoltage
> > condition should the Voc get over 600 Volts initially. As the
> array warms
> in
> > the sun and degrades, that voltage will settle into the proper range and
> the
> > inverter will start.
> >
> > Bill.
> >
>
>
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