Sunny Boy Stats final [RE-wrenches]

Fri Apr 25 08:39:50 PDT 2003

Robert,

Thank you for your detailed email. I hope SMA appreciates your efforts. SMA
makes good inverters and John Berdner is probably among the top 20
respected PV engineers, but...

Carrying a spare inverter should be like having a spare tire in your truck
or car. The spare is for emergency repairs, not a swap-out because your
regular inverter (or tires) are unreliable.

John remembers when I bought almost 300 Omnion 4 and 8 kW inverters in
1994-95 and 6% were DOA or failed in the first month. Call-backs were
killing our project budget. Turned out that Omnion's "burn-in" was running
an inverter overnight for around 8 hours on a bench supply at a fixed
voltage and current. This is not a very effective way to test PV inverters
that are subject to varying voltage and varying current and off/on
switching. I recommended that Onmion do a 3-day burn-in using a programed
power supply that randomly varies voltage, current and off/on switching.
Onmion engineers at Omnion agreed that factory testing and burn-in should
be at least 24 hours and variable, but they never changed their test
procedures.

The PV inverter company that has the best machine and the best QC will win
the market - and (listen up management) be able to charge a premium because
contractors will gladly pay more for a machine that does not require
call-backs.

Best regards,
Joel Davidson

Original Message:
-----------------
From: Robert Warren robertwarren at mail.com
Date: Fri, 25 Apr 2003 05:04:45 +0000
To: RE-wrenches at topica.com
Subject: RE: Sunny Boy Stats "final" [RE-wrenches]

Jeff, John Berdner, et al,
 I don't think this issue is dead yet.
 I have commissioned or installed around 300+ of the Sunnyboy inverters 
in the last 2-1/2 years, over here in England, in my work at Solar 
Century. We have a much greater variety of approved SMA inverters than 
you do in the States, so they are not precisely the same animals. 
 I would have to go back through my records, but I am pretty sure the 
failure rate I have seen is around 8 to 10%. This amounts to something 
like 25 to 30 inverters I have had to send back for various reasons. A 
couple of times, I have sent back a pallet with 8 or 10 of them. While 
this seems like an alarmingly high failure rate, quite a few of them 
were never installed. Before I install any of these inverters, I first 
hook them up to a regulated variable DC power supply in the shop and 
re-program them to the high and low voltage and frequency standards 
which are presently required in the UK, quite different than the German 
regs. SMA finally got around to providing a programming option for the 
UK, as they have for the US, but I still like to know that an inverter 
isn't DOA before taking it out to a job site a couple hundred miles 
away. 
 Furthermore, quite a few of these inverters I returned weren't dead, 
but I returned them because I found a huge variance on the spot value 
reaadings for AC voltage. After setting up the parameters, I would look 
at the "spot value" readings (using either a Sunnyboy controller or a 
desktop computer to communicate via either Powerline, RS-232 or RS-485 
as we use all types). If the inverter says its AC grid voltage is over 5 
volts different than what my calibrated True RMS meter says, I would 
reject it. This turned out to be a bit of a harsh practice, however, as 
I was haveing to reject so many that sometimes we didn't have enough 
stock to start a job. So I started letting them slide a bit, only 
rejecting ones that were 8 to 10 VAC too high. Then I would adjust the 
max VAC parameter a bit higher and note in my inverter log the 
difference in values observed.
  The main problem for me is that here in the UK, we are only allowed a 
maximum VAC output of 253 VAC against the nominal grid voltage of 240. I 
have personally visited most of our PV sites and routinely see grid 
voltage around 246-250. As the inverter may be reading the actual grid 
voltage of 248 as 253 if it has a 5 volt error, then it goes into high 
AC shutdown mode. I have had numerous installations where the inverter 
seldom or never ran, just because of this problem. All of my larger 
installations have modem and remote dial-in capabilties, so sometimes I 
have been able to dial in and remotely change the max AC parameter and 
get the inverter to work again, in situations where performance was 
spotty. I have complained numerous times about this to SMA, but never 
got them to respond with the answer I wanted. I have several times asked 
them to beef up their calibration Quality control, so I don't have to 
deal with such problems. What they would do instead, was to send me a 
new inverter promptly any time I sent one back, which was good. 
 Some of the inverter failures may have been due to electrical spikes 
(one installation had 7 failures out of 30 inverters, but the apartments 
were just a few blocks from a high voltage switching station. A couple 
were due to installer errors. I must admit that I have seen a huge 
improvement in inverter quality and lots of little detail improvements 
over this period, and all in all, I am very impressed with the product. 
I like them much more than anything I have used from US manufacturers, 
excepting for inverters made by UPS manufacturers (I am factory 
certified by Best and Toshiba). 
 What I would say to dealers, is, in addition to carrying a spare 
inverter (since for you it is likely to be a 2500, is to carry a 
Sunnyboy controller and spare Powerline modem to pop into the inverter 
so you can check the performance and read your error messages from the 
inverters on site. The self diagnostic features are quite helpful, and I 
am sure they will get better. 
 I hope this is helpful.
Robert Warren
robertwarren at amil.com 

Jeff Oldham wrote:
> 
> 
> It looks like this string has wound down. I've complied the numbers 
> given by all and the average is 12.75% failure rate. Two other 
> observations came from this - 1) a rather high DOA and 2)once fixed and 
> opperating for a week or two there are very few problems thereafter. I'm 
> sure we all would like to see inverters more reliable than this, but at 
> this time all agree (including me) that SMA has the best product around 
> and the service is hard to beat anywhere. We also have a manufacturer 
> here that makes very generous, valuable and consistant contributions to 
> this list, thank you John Berdner.
> 
> The moral of the story and as John @ SMA has always been telling me - 
> Always carry a spare inverter in your rig to the job sites.
> 
> Thank you all for the feedback, what a great group!
> 
> -jeff
> From the Solar, Wind and Hydro powered office of Jeff Oldham

What will we do if there is another fuel shortage? 
Did you know that there is a pollution free, completely
renewable fuel which you can use right now in your own car? 
Don't replace the engine, replace the fuel.
Check out my website on making your own fuel: 
http://running_on_alcohol.tripod.com 
robertwarren at mail.com

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