A real stumper--Grid-tied system no longer grid-ties [RE-wren ches] [RE-wre

Fri Feb 18 18:31:25 PST 2005

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Tom -

Assuming this is an intermittent problem:

Once we found that the bussing was poor in the breaker location of the
panel.  We moved the breaker to another location within the panel and found
the system to operate properly.  It would also be possible that if the
bussing was damaged or very old that small fracture in the bussing would be
"visible" during periods of contraction and expansion (cold & heat).  Does
there appear to be a "pattern" or time of day when err message shows up?  Is
it consistently failing at this point?

With only 3' of wire , I would pull it and check it for abrasions/insulation
knics - although I would have expected a different type of err message.

Good luck with it.  
Kindest regards.

Barbra K. Kerr
President
Kerr Enterprises, Inc
858.503.0137 x 107
858.503.0137 Fax
858.337.5097 cell

-----Original Message-----
From: Tom McCalmont [mailto:tom at regrid.com]
Sent: Friday, February 18, 2005 5:59 PM
To: RE-wrenches at topica.com
Subject: A real stumper--Grid-tied system no longer grid-ties
[RE-wrenches]

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Wrenches,

I have a real stumper and could use your collective wisdom and ideas.
Here's the situation:

-- A residential grid-tied system consisting of 12 Matrix 165's (12V) in a
single string feeding a SMA 1800U.  PV voltage and string parameters are
fully within spec for the inverter.  Typ. PV input voltage (mp) is around
242V, so there appear to be no problems on the PV side of the system.

-- The system operated without problems or errors for 9 months.  Then,
suddenly it quit running with the 1800U display showing either "waiting" or
"Fac-Bfr" errors indicating that it cannot connect to the grid.  It doesn't
attempt to enter the "grid mon" phase.

-- The grid voltage measured at the inverter terminals is stable at around
122V, completely within spec for the inverter.  A Fluke meter with Min/Max
settings shows the grid voltage varying very little (between 122.3V and
122.9V).  The meter shows the frequency locked on at 60.00Hz. and only
occasionally varying up to 60.01Hz. (again, via Min/Max).

-- We swapped out the inverter with a new 1800U, and the new inverter
displays exactly the same errors.  The old inverter that was sent back to
SMA worked just fine on their bench, and they couldn't find anything wrong
with it.

-- We replaced the circuit breaker inside the load center so we could rule
that out as a variable.  The wire length from the inverter to the load
center is 3 ft., and the conductors are #12 solid copper as they should be
for the inverter's output current.  The voltages measured inside the load
center are identical to those measured inside the inverter.  In short, the
grid seems completely stable and within its normal voltage and frequency
parameters.

-- The system is properly grounded via a driven ground rod, and DC and AC
grounds are bonded together.  The neutral and ground bond inside the load
center is in place and solid.  All wire connections have been checked and
are tight.

-- A solar system on a house two doors down from this system is functioning
just fine on the same utility grid power, which would appear to indicate
that the grid is stable and there are no micro-spikes on the line.

-- The same errors occur regardless of whether or not we turn off every
breaker in the load center (except the solar breaker), or the homeowner
turns on every load in the house (in other words, whether or not there is a
load through the meter).

In short, everything about this system seems completely normal and according
to Hoyle, and yet two different 1800 inverters that work fine at another
location still cannot connect to the grid.  We have replaced every variable
in the system except the wiring itself.

Have any of you gurus out there ever run into anything like this, and what
ideas might you have to help us figure this one out?

Many thanks for any suggestions any of you may have.

Tom McCalmont
NABCEP-certified PV Installer
REgrid Power, Inc.
(408) 656-2944 (cell)
tom at regrid.com 

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