Reality versus the "last" final stats. [RE-wrenches]

Fri Apr 25 21:10:29 PDT 2003

John,
You are the best inverter engineer/communicator in the world! Thank you for
putting it all on the table for everyone to see and plan accordingly.
Best regards,
Joel Davidson

John Berdner wrote:

> Wrenches:
>
> I have been out of town for a few days at, coincidentally, a DOE
> inverter reliability workshop.  Sorry I was not able to chime in here
> sooner.
>
> With all deference to Jeff, his experience is an anomaly which does not
> agree statistically with the installed base of inverters in the US.  I
> also disagree with his conclusions, his definitions, and his methodology
> for calculating reliability.  What I do know is that it is always the
> inverter's fault no matter the real root cause of the problem.
>
> I have not yet analyzed the data for 2003 yet but...  Other than the
> Firmware V8.65 / Vac_srr issue, which I think has been largely resolved,
> I do not see any patterns that would indicated that there is a
> significant change in the number of failures we are seeing.  What I can
> say, definitively, based on real data through the end of 2002 is:
>
> Our total return rate through 2002 for inverters sold in the US was
> 4.3%.  Of these, about 15% have no problems found after they are
> returned. Not including the "no problems found" units, our actual total
> failure rate for inverters is 3.8%.
>
> The largest number of failures to date is 1.4% for the dreaded Vac_Srr
> error message with which many of you are all too familiar.  I am sure
> this will also be our largest failure related issue when we do the
> numbers for 2003. Unfortunately, we did not fully understand the problem
> for a couple of weeks and so there were more units than I would have
> liked that made it into systems.  We retested and reworked many
> inverters here at SMA America and recalled all the ones we could track.
> We also did our best to get the word out to try to find the others we
> could not track in an effort to solve the problems as quickly and
> painlessly as possible for all concerned.
>
> For those not aware of this problem: 2500's with version 8.32 and 8.66
> firmware are fine.  Units with 8.65 firmware can trip off line at too
> low a voltage and will display a characteristic error message Vac_Srr.
> These units can be upgraded in the field with new firmware which we
> supply at no charge. We estimate that the firmware fix will solve the
> problem in about 80% of the cases but that some units will need to come
> back here for replacement of two small capacitors.  Contact Jason Mills
> if you have any questions or need help with Vac_Srr issues.
>
> This leaves a remaining failure rate of 2.37%.  Of this, the most common
> failures are:
> 0.50% - Unknown failure reported by the user - troubleshooting
> inconclusive.
> 0.51% - Vac_Bfr error message.  This related to a bad batch of ceramic
> surface mount capacitors that developed micro fractures typically after
> a few days or weeks of thermal cycling. We changed capacitor vendors and
> the problem has disappeared.
> 0.31% - Ground fault will not clear.  More than half of the "no problems
> found units" were returned for ground faults.  We believe this indicates
> a lack of understanding of ground faults and how to troubleshoot them.
> Some of these were caused by wires that were loose or could have been
> damaged during installation.  Others had dead current sensors that could
> have been defective or were destroyed by replacing the 1 amp fuse with a
> larger size before clearing the ground fault.
> 0.39% - EEPROMD This failure occurs when the end of day data is
> corrupted as it is written from the inverter's RAM into Non-volatile
> ROM. There is a simple in field reset procedure that solves the problem
> and once solved they do not appear to reoccur.  This cause of this issue
> is not well understood but the next version of the inverter firmware
> will automatically reset the error.
> 0.17% - Failed IGBT's/caps. Typically an over voltage failure caused by
> incorrect installation.  We have seen 3 units to date that look like
> failures due to lightning.
> 0.10% Broken cover screws.  All units now ship with greased screws and
> the case was reworked to make misalignment during initial assembly less
> likely.
> 0.09% - DOA  usually a power supply issue.  40% of these units had no
> problems found and were never powered up.  Probably caused by low PV
> voltage.
>
> The remaining failures (0.3% total) are all below 0.1% and are
> essentially random production related events.  K1 open, broken
> terminals, melted ac fuse holders, over current failure, noisy, bad temp
> sensor, etc.
>
> In much this failure analysis we did not differentiate if the failure
> was production related or likely precipitated by the installation.  The
> one notable exception is over voltage failures where the inverter is
> essentially destroyed. Another important thing to point out is there is
> a wide disparity of the failure rate depending on the installer.  We are
> in a newly emerging market and the installer's level of experience with
> our inverters clearly has an impact on the in-field failure rates.  Some
> wrenches out there have installed many sunny boys with very few problems
> others have seen a much higher failure rate on a much smaller sample
> size.  Some times the failures come in clusters and are, IMHO, an
> unfortunate bad luck of the draw issue.
>
> To close: Every inverter undergoes numerous quality tests during
> manufacture In addition, every inverter is functionally tested on an
> automatic burn in rack before it leaves the factory.  We take failures
> seriously and take corrective action to remedy the situation as quickly
> as possible.  We address problems openly and factually to the best of
> our knowledge and will continue to do so.  I encourage all of you to
> provide us with feed back so that we can continue to improve our
> products as we move forward.
>
> If you have any questions or if I may be of any further assistance,
> please do not hesitate to contact me.
>
> Best Regards,
>
> John Berdner
>
> SMA America, Inc.
> 12438-C Loma Rica Road
> Grass Valley, CA  95945
> 530.273.4595 - Tel
> 530.274.7271 - Fax
>
> -----Original Message-----
> From: Jeff Oldham [mailto:starpower4u at juno.com]
> Sent: Thursday, April 24, 2003 04:18 PM
> To: RE-wrenches at topica.com
> Subject: Re: Sunny Boy Stats "final" [RE-wrenches]
>
> Jeff,
>
> I counted every call back, DOA and reship. In other words "failures", it
> does not matter how small or trivial to me, if I'm going back to the job
> to deal with it and it was not caused by UPS, the client or acts of the
> Goddess then it is an equipment failure. I would consider a broken LED a
> failure unless it fixed itself! Even if the number is half of what this
> group came up with it is still too high in my book and triple that of
> the company line. I was really just trying to see if our experience was
> unique or not, it turns out it is not.
>
> -jeff
>
> >From the Solar, Wind and Hydro powered office of Jeff Oldham
>
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