Grid-Tied SW output meter [RE-wrenches]

[Bill Brooks]

Todd and Christopher,

The trick is getting the right voltage on the coil in the meter. I'm not
sure Todd's idea will work correctly. I gave a very confusing explanation of
the correct way to wire a 240-Volt meter for 120 volts, but I am unaware of
any other method that works properly. The 120 Volt method requires running
the current through both side of the meter, so I don't think you can only do
on one side of the meter without running the meter at 240-volts. A utility
meter person could probably answer the question for us. I have 3 pages of
diagrams of how to wire a meter properly and they don't show Todd's idea on
the diagrams.

If you have 240-Volts available and you are only measuring power flow on one
leg, you can bring 240-Volts to the meter on either side and have the
current only go through one leg. This is the simplest and most straight
forward method, but does not work on the ACout of a single 120-Volt inverter
(unless the output goes to a 240-Volt transformer)--that requires the meter
to be wired for 120-volts.

Bill.


-----Original Message-----
From: Christopher Freitas - OutBack Power
[mailto:cfreitas at outbackpower.com]
Sent: Wednesday, March 19, 2003 10:54 AM
To: RE-wrenches at topica.com
Subject: RE: Grid-Tied SW output meter [RE-wrenches]


Yes - this method does work for single SW installations.  For dual I
think you would have to use two separate meters.  I would first verify
that it does work before the installation to make sure the hookup is
correct - you don't want to come back a month later and find some odd
results...

The idea of this technique is that the pass-thru AC current (power going
directly from the grid to the loads will not be recorded as the AC
current going out cancels the AC current coming in.  Only the AC current
going either out to the loads or out to the grid is added to the meter -
both as positive.  Any current coming in from the grid that is used to
battery charge will also be subtracted from the meter reading - and then
would be added back in correctly as a positive value if it was sold
again later on (with the losses taken in account).

I have done this trick with data acquistion systems and single Current
Transformers (CTs) - just not with a single AC kilowatt meter however. I
have used multiple meters to record input and output current and it gets
really confusing quick when you looking at them on the wall.

Christopher








Todd Cory, Mt. Shasta Energy Services wrote:
> Did any one want to comment on whether this might work? It sounds
> interesting
> to me.
>
> Todd
>
>
> William Korthof wrote:
>
> > I had an idea for this situation... for an installation with one
> > SW inverter (120 Vac only) perhaps a single meter could
> > be used to measure both outputs from the inverter---use
> > the "line 1" side of the meter for the grid side of the meter
> > and "line 2" for the load side. I think it would need to be a
> > mechanical type meter with a neutral coil connection
> > (ie, "single phase" meter for use on 120/208 3-phase).
> > The neutral connection should allow the two lines to be
> > measured properly and independently, whether they are
> > in phase (normal operation), or otherwise (grid off, grid
> > frequency error...).
> >
> > /wk
> >
> > At 10:57 AM 3/12/03 -0800, you wrote:
> > >The new CEC guidelines require a "System Performance Meter" for grid
> > >tied
> > >systems which receive their final after March 31, 2003. We occasionally
> > >use an SW with back-up batteries to serve a critical load sub-panel. I
> > >think this is how we can meter both the output going to the critical
> > >loads
> > >as well as the main panel/grid during daytime energy production and
> > >account for power the inverter will feed through from the grid at
night.
> > >One kWh meter on the grid AC IN 1 side of the inverter and another on
> > >the
> > >AC Out to the critical loads. Total output equals the total of both of
> > >them. The grid power used for the AC Out loads will be subtracted from
> > >the
> > >AC In meter which cancels the amount added to the AC Out meter.
> > >
> > >Does this make sense and/or is there an easier way to do this?
> > >
> > >Thanks,
> > >--
> > >David Henry
> > >Harmony Farm Supply
> > >3244 Hwy 116 N., Sebastopol, CA 95472
> > >707-823-9125 X14 voice
> > >707-823-1734 fax
> > >david at harmonyfarm.com
> > >www.harmonyfarm.com
>
>
>



Christopher Freitas
OutBack Power Systems, Inc.
cfreitas at outbackpower.com  www.outbackpower.com
Tel 360 435 6030  Arlington WA USA

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