ST2500 vs. SB 2500 [RE-wrenches]

[Matt Lafferty]

Bob/Wrenches:

> Joel's customers are apparently happy with their Sun Ties. I'd be
> interested to know what the current feeling of the Wrench list is
> regarding mid-size, residential, grid-tied, batteryless inverters.
> Did "XR" fix the ST's power limitations? Is the SB's high-voltage on
> the roof a problem or a benefit?
>
> Bob Galbreath
> Geo-Lite Systems
>

Yes, Joel's recent experience is most encouraging.

To date we have installed approximately 50 each, ST-2500's and SWR-2500
(Sunny-Boys).

Regarding the ST's:  Xantrex has upgraded the software in the problem
ST's...Some several times... After numerous site "upgrades" they finally
began entire unit replacements in lieu of the upgrades.  Through the Winter
months, the units have not been reported to "crash".  I have, however, been
called out to check performance of a number of systems that customers do not
believe to be producing to their capacity.  My testing has shown that there
are some watts being left on the roof, compared to the claimed efficiency
numbers of the ST.  Since we have been in the Winter months, we have not
been able to monitor the performance in the heat of Summer.  (ST Array Mix:
~75% Asi; 25% Crystalline)

Regarding the SB's:  Our experience has been quite positive.  We have had a
few failures (5). These were erroneous "Grid Failure" messages.  SMA has
been very responsive and cooperative.  <Knocking on wood> We have not had
one of these failures in about 20 jobs, now.  I call the SB "Big Red" & "My
Little Pit-Bull" because it "gets on the array, tracks it, stays on it and
drags every watt possible off the roof".  (SB Array Mix: ~90% Asi; 10%
Crystalline)

Regarding High Voltage vs. Low Voltage:  I have been a proponent of High
Voltage for a long time.  The smaller conduits, smaller wires, less wires of
a HV system leads to lower installed cost and a more aesthetic install.

Issues to be addressed with a HV system are:

DC wiring within a dwelling must be disconnectable near the entry point to
the dwelling.  (Same as LV but the building agencies get a little more
nervous with HV)  Any of our installs requiring such a configuration have
continuous conduit with overcurrent protection on the roof.

HV systems may be more prone to ground faults only due to the higher arcing
capacity of the voltage.  If you look at it this way, though, you will see
that it is not a problem:  HV = 2 wires.  LV = 10 or 12 wires.  If you are
installing in a wreckless enough manner that you are creating ground faults
with 2 wires, you have 5-6 times the potential for the same ground faults in
a LV system.  It is only the lower arcing capacity of the LV that makes the
ground fault not show up, even though the condition(s) exist.  My experience
with ground faults has been 100% Installer related!

HV systems require a whole lot of Crystalline modules in series to get into
the voltage window.  Some customers may not have the money or roof area for
that large a system, but who wants to work for them anyway?  lol  (SMA's
SB-1100 will reduce this by lowering the voltage window.  Also, modules such
as the MSX-120 is 24 VDC)

600 Volt DC rated equipment, connections and overcurrent protection devices
are more epensive and require larger enclosures.  With Crystalline arrays,
this is very insignificant.  With Thin-Film arrays, it can be a hair-pulling
experience.  There are developments underway to reduce this hurdle.

If you are installing on an existing structure or Pole-Mounting, running the
DC external to the dwelling, in conduit overcomes most of the issues raised.

NOTE:  My position is different than many of the Wrenches.  I work
exclusively in the Grid-Tie, Battery-less PV arena.  We use multiple Module
technologies, with a lot of Asi, which provides its own challenges.  We just
kicked off another 100 roof project yesterday....100 Roofs, 1 System, 1
Option, Expected to have Installations completed July.  This will allow us
to benchmark efficiency of our process from the front to the back.  Stay
tuned for the results!

-Matt Lafferty
pvpro at attbi.com

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