A real stumper--Grid-tied system no longer grid-ties [RE-wrenches]

Sun Feb 20 10:54:42 PST 2005

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Tom,

I think the other answers have been good suggestions, but one other
thing to remember is that just because a system works two doors down
does not mean it's not a utility issue. If this house is served by  a
different transformer, that could be an issue, or there could be an
issue with the connection at the meter or the main lugs in the house.
(Pull the meter and check for both). House loads may not react to it
badly (house loads are often pretty tolerant of crud. They need to be to
work on the US electric grid.)

Also, are there any X10 applications or other high harmonic generators
in the house? I've never heard of that being a problem, but it seems the
inverter thinks it's having a frequency problem. If there is X10, try
disconnecting and seeing what happens.

But I would definitely pull the AC wire first and replace with stranded.

Jeff

Jeffery D. Wolfe, P.E.
NABCEP Certified Solar PV Installer(tm)
Global Resource Options, LLP, Solar  Wind  Energy Solutions

-----Original Message-----
From: Tom McCalmont [mailto:tom at regrid.com] 
Sent: Friday, February 18, 2005 8:59 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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