[RE-wrenches] trouble shooting system with Sun Tie

Thu Sep 11 21:04:27 PDT 2008

Randy and Dana,
Not sure here (never installed a SunTie, thanks to this list in the early
days), but I believe that Xantrex' swap program ended years ago.

I see from your website that you're in Bellingham, Washington. OK, that
explains your low expectations (1,123 kwh/yr from 1.44kW? Here in NewMex we
estimate around double that).

I copied some earlier (2001) saved Wrenches postings about the SunTie (then
deleted them). I hope you find them enjoyable and enlightening.

Allan at Positive Energy

-----Original Message-----

Dana, 
I thought Xantrex recalled all the ST1500s and replaced them with XR2500s.
Mine was, years ago.  You might check with them about this.
Good luck,
Randy Brooks

Brooks Solar, Inc.

Solar Power for People

140 Columbia View

Chelan, WA  98816

509-682-9646

Randy at BrooksSolar.com

www.BrooksSolar.com

On Sep 11, 2008, at 3:23 PM, Dana Brandt wrote:

Hi all,
I was called out this week to trouble shoot a system I didn't install.
It's a five year old 1.44kW system with the following: Sun Tie ST 1500
inverter and 12 Astro Power modules. It only produced 634kWh last
year. With our sun here, the shading, orientation, equipment, etc. it
should have produced around 1123kWh.

I've heard a lot about Sun Tie failures, but don't know the details.
What are the common failure modes? Is it likely that a failure of the
Sun Tie would leave it operating, but only producing half what it
should?

When I showed up the system was producing 950W on a relatively sunny
day - seemed pretty reasonable. After restarting the inverter it only
produced around 150W. Is the MPPT very, very slow to find that sweet
spot, or what was going on there?

The system is comprised of three strings of 4 modules each. When I was
there all three strings were producing about the same current, so that
leads me to believe it's not a module failure.

To make things more fun, the modules were installed at two different
orientations. One string is at 38d slope, 30d east of true south,
while the other two are at 36d slope, 75k east of true south. This
certainly has a detrimental impact on the performance, but it doesn't
seem to me that it could account for all of that energy loss.

Thoughts?

Thanks a lot!

Dana

--
Dana Brandt
Ecotech Energy Systems, LLC 

[5/19/01]
"Brand X" has been taking a lot of arrows lately, some in jest and some
deserved. I can't believe that Xantrex is trying to help Advanced Energy
Systems and SMA gain market share, but it sure looks that way. A little
history and an important question.
First, the ST2500 becomes the hottest thing in PV since the SW.
Next, ST2500 demand exceeds production.
Next, ST2500 has software problems.
Next, Xantrex is "experiencing a shortage of vendor supplied parts" and
shipments stop.
Next, Xantrex tries to get us to switch to the derated ST2000-CB.
Then, Xantrex announces the XR2500 at $2759 with nearly the same specs as
the $2500 ST2500.
Meanwhile, we are told ST2500 inverters are still being produced and to
continue to take customer orders.
However, I am waiting for ST2500 inverters that I ordered since April 4.
(How long are you back-ordered without ship dates?)
And now we are told that the XR2500 "will be available for delivery by July
1."
Joel Davidson 

 > [2/14/01]: 
>The ST normally tracks the solar irradiance fairly accurately, when a cloud
>passes over the output drops proportionally. The LCD meter is powered
solely
>from the array output, no AC backup power. The ST will disconnect from the
>grid if the grid voltage goes out of the window of acceptance. UL 1741
>requires a 5 minute timeout before reconnecting.
>The cooling fan comes on at about 200 watts of output; it is controlled by
>output, not thermally controlled. (This may change with future versions of
>the ST.)
>
>Here is the situation with the dealer's system. There are two 2300-watt
>arrays with an ST2500 for each array. To date, the ST as generated up about
>1,800 watts of output from each array. The LCD indicates that the ST
>intermittently cycles OFF-ON at around 600-700 watt output level. The unit
>does come back on. It appears that the LCD can, under some circumstances,
>"lock-up". During the lock-up the LCD only displays "Rev 3". So far Trace
>has not been able to recreate this "lock-up" even with a unit that suffered
>from intermittent lock-up in the field. Trace is still studying the
problem.
>Perhaps there are some sensitivities to installation environments, like
>inductive coupling to a parallel high voltage line at the site.
>
> >From conversations with the Trace engineers, the occasional, intermittent
>cycling seems to be caused by the ST's MPPT algorithm being a little too
>aggressive in tracking the mpp on the knee of the IV curve. It appears that
>with certain modules, under certain conditions, the algorithm can
over-shoot
>the knee of the curve. Trace is actively studying any occurrences of this
>problem. If and when a new algorithm is released, it will be field
>upgradable with a single replaceable chip.
>
>The Trace engineers have been very helpful and responsive with this
>situation. They are very willing to help with any problem ST installations.
>They both want help get the system running and they are learning about
>unexpected glitches and quirks that can occur with any new product release.
>
>Several dealers have asked my opinion about the ST inverters. I advise them
>the ST (Rev.1) like any other first release product, is very likely to have
>some quirks and problems that occasionally show up. If I were to
>sell/install any newly released, Rev.1 product, I would advise the customer
>that "the product is a first generation product and there may be some
>unexpected quirks. That both I (the dealer) and the factory will stand
>behind the product and will work to resolve any problems that might occur."
>If the customer (or you as the dealer) are not comfortable with that
>arrangement and understanding, then they should either choose another
>produce or wait until the new product has proven itself in the field
>(perhaps with a few up-grades or expanded installation guidelines).
>
>I hope this helps shed some light on the current situation with the ST
>inverters. If any of you dealers are having problems with STs that you've
>installed and your distributor can not help to work with Trace, please
>contact me and I will see what I can do to help.
>
>Sincerely,
>Steve Bell
>SunWize Technologies

[2/9/01] 
According to well-informed sources, there is pressure being put on Trace to 
pull them from the market until they work out the bugs on the MPPTracking.

I don't know about you all, but reading reports of a 2200 watt system under 
full sun putting out all of 800 or so watts is rather disturbing.  With the 
grid-tie market going crazy in CA., it would give the industry and real 
black eye if battery-less ST systems were putting out a fraction of the 
appropriate output. 
Marco Mangelsdorf

[2/7/01]
I just got off the phone with John, our dealer (he is competent) ; here
is what he says.
He has two ST-based systems operating; one is a single ST2500 with 1,000
watts of Arco modules, the other is system has two ST-2500s and about 2,200
watts of UniSolar modules per ST.
Both systems seem to be acting the same way. Multiple times during the day
the ST will power up to about 650 to 700 watts and then cycle off. Many
times the LCD display goes dim or shuts off and the Total Daily Watt-Hour
reading on the LCD re-zeros when it cycles down. The units do come back on
after a short while. This happens many times during the day.
Although he does not have exact monitored data, it seemed that the power
output of the ST is well below expected. On a sunny day with 2,200 watts of
UniSolar the ST was indicating less than 800 watt-hours of output.
The cooling fan comes on whenever the ST output climbs above about 200
watts.
John talked to Dean at Trace about the problems he is having. Dean says that
the ST may cycle off and on several times in the morning and then
occasionally (two-three times) during the day. John reports that the cycling
is much more frequent throughout the day.
Dean says that the ST may be too aggressive in its power tracking and they
(Trace) may need to adjust it's aggressiveness. The fan operating anytime
the ST output is over 200 watts is supposed to be some code or regulatory
requirement. (It seems like it should only operate when the ST is warm.)
Because the ST sometimes losses the daily watt-hour total on the LCD when it
cycles, it sounds like the unit is totally cycling down during it's many
daily cyclings. (The LCD also shuts off and clears the WHr total every
night.) It sounds like Trace may need to supply a replacement chip to fix
this cycling problem. It also sounds like some independent measurements of
ST output v.s. array input may be well advised.
In fairness to Trace, this is their Ver.1 of the ST. Hopefully they will fix
the problems quickly. Remember the Ver.1 SW-series had problems too.
I hope this explaination makes sense. Thanks for all the feed-back so far.
Any other experiences with the ST are welcome.
Steve Bell
SunWize Technologies

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