[RE-wrenches] Sunny Island does not support using a transfer switching grid tie mode

[Peter Parrish]

All:

 

I haven't read the whole email but I want to let everyone know that we have
had terrible problems with the Xantrex XW product. Part of the problem is
that not everyone in tech support there is equally knowledgeable about their
XW line and they give inconsistent advice and in some cases incorrect
advice, Chalk it up to good intentions if you will but in this case they
paved the way to my private hell.

 

We have had problems with the last two XW systems we have installed and in
each case the resolution was slow in coming. To make things worse, Xantrex
kept trying us to upload "new firmware" as a panacea, which requires a piece
of equipment that they charge the installer for, and a laptop. The bottom
line, it takes another week for the stuff to come, another service call to
upload the firmware and shipping the equipment back to Xantrex (if you want
you CC charge reversed).

 

In one case the "new firmware" was suggested for an XW that was manufactured
two months earlier. So either Xantrex has prematurely released the XW line
(by over a year) or they're just guessing at our time and expense).

 

I would like to nominate "I think some new firmware should solve your
problem" as one of the "top ten WAGs" in the inverter tech support
community. Does anyone want to share their favorite?

 

- Peter

Peter T. Parrish, President
California Solar Engineering, Inc.
820 Cynthia Ave., Los Angeles, CA 90065
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885
CA Lic. 854779, NABCEP Cert. 031806-26
peter.parrish at calsolareng.com 

  _____  

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Mark
Drummond
Sent: Friday, April 24, 2009 12:40 PM
To: RE-wrenches at lists.re-wrenches.org
Subject: [RE-wrenches] Sunny Island does not support using a transfer
switching grid tie mode

 

Hello Wrenches,

 

We've installed 2 sunny island systems, and were planning to install three
or four more, until we identified what I consider to be a serious functional
deficiency with the product. In commissioning the first two inverters
(different customers, but around the same time) I found that the Sunnyboy
inverters that were feeding the island would error out for AC frequency
tolerance exceeded when the inverter was in backup mode (no grid signal
present) and the batteries were mostly charged with charge current coming in
from the array. The SI frequency modulates to reduce battery charge current
and control battery voltage to absorption or float voltage - this causes the
SB to error, wait 5 minutes (because frequency returns to normal once
charging stops) then restart and error out again. This is particularly
problematic with a smallish battery bank and largish array as voltage can go
high fast.

 

When I first reported this to SMA tech support it was described as a
communication problem. Apparently if the two inverters are communicating,
the SB is informed by the SI that it needs to operate in off-grid mode and
it should disregard the normal grid frequency tolerance. So after a few
return trips with new RS-485 cards and checking and double checking the com
wires to no avail, I was told that this was a firmware bug and that a fix
could be expected in some months, but with no solid time frame commitment.
An alternative was presented that the SB can be reprogrammed to run in
off-grid mode permanently, but since our systems have an inverter bypass
transfer switch in then we could not do that, because if that switch is
switched then the SB would be connected directly to the grid without the
isolation of the SI, and would take responsibility for anti-islanding.
That's clearly a no-no. 

 

The transfer switch at the time was a requirement of the utility (all loads
must be able to be served directly by the utility if necessary). This
requirement was just removed by the PRC, but there are serious design issues
that are unacceptable in my eyes with removing the bypass. 

 

1)       If the sunny island breaks, there is no option to power the
critical loads directly from the grid. We sell battery backup systems so
that people have reliable power to their critical loads. This would be
clearly a better designed system if the inverter could be bypassed. The
other backup systems, like outback and Xantrex (DC coupled) have easily
integrateable and supported transfer switches for this purpose - as they
should. 

2)       If the inverter was out for repair (say it's out of warranty, and
has to be sent for repair, not just quickly swapped out) the sunny boy would
be down too as there is no alternate path to the grid. With a
bypass/transfer, the customer could still be producing power and net
metering while the backup system is down.

3)       Because the SI is 120Vac, and the SBs are all 240 V, this means
there must be a transformer, or two inverters (and most people don't need
10Kw of backup power). Some customers would choose to forgo the automatic
backup in favor of eliminating the efficiency loss of the transformer in day
to day grid-tie operation by leaving the bypass switch activated except
during a power outage, and manually activate the backup system only when
it's needed. This is a less critical issue, but having the option would be
better.

 

Page 122 of the SI manual warns that if the batteries are full, the
frequency shifts and the inverter shuts down, but this is not quite true. If
the battery is small relative to the array size, the voltage will shoot up
fast, even when it is at a lower state of charge. It appears to be an all or
nothing charge - no tapering. I watched as one system continued to go down
In SOC until it got to the low eighties. I did not stick around to see how
low it would get. I reconnected the grid and promised the customer to try to
get to the bottom of it. 95% of the time during this test the SB was
completely disconnected. Because it waits 5 minutes to reconnect, it doesn't
even work as well as the old series charge controllers (like the Trace
C30A).

 

When we were designing the systems, we sent one-line drawings to SMA to make
sure it would work the way we wanted, and they were given the thumbs up.
This includes a more complex arrangement on a 3-phase service that has not
been installed yet and is on hold. We do not want to install any more of
them until this is resolved. We have customers with battery-less systems
that would like to retrofit. We've told many of our customers that if they
want to add battery backup later they can. I'm anxious to see the fix.

 

Has anyone else seen this problem?

Does anyone have a solution?

Do any of you have systems that might have this problem, but haven't been
put to the test?

Am I missing something in the programming and tech support just hasn't
caught it?

 

Any help would be greatly appreciated

 

Thanks,

 

 

Mark Drummond

Field Manager

Positive Energy, Inc.

NABCEP Certified PV installer

 

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