ST inverters [RE-wrenches]

[Steve Bell]

Hi Wrenches,

    I wanted to share what limited information I have about the "quirks"
with the ST inverters. After conversations with the Trace engineers and tech
support as well as our dealer, here is what we know.

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
815-256-2222
sebpv at stelle.net

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