Grid-Tied SW output meter [RE-wrenches]

[Bill Brooks]

David,

This is an excellent question. Your suggestion is probably the cheapest way
out although it takes some space to mount the meters. Use the round bases
and "easy-read" cyclometer register meters (like an odometer).

It depends on how big the array is relative to backup subpanel load as to
how to wire the meters. If PV energy is much greater than the energy
consumption of the backup subpanel, I would make the meters turn in the
forward direction for power coming out of the inverter. That way the PV
output would be the sum of the two meters and that is straightforward.

If the PV energy is less than the backup subpanel, then the AC IN meter will
start to go negative with the above setup and make the readings very
confusing. In that case I would suggest making the AC OUT reading run
positive direction coming out of the inverter and the AC IN read negative
coming out of the inverter. In this case AC OUT is subtracted from AC IN to
determine PV performance.

Remember that a 240-Volt meter must be wired differently to run at
120-Volts. If it is not rewired for 120-Volts, it will be way off in the
readings and you will have very unhappy customers. The proper way is to
jumper the bottom two lugs in the meter (load side of the meter), loosen
both screws on the small tab in the back of the meter, without removing
either screw-swing the open side of the tab away from one of the terminals
(only one will have an open side), and attach a small (#12 AWG) wire via a
fork connector to the terminal that still has the tab and connect that small
wire to the neutral reference point. Power comes in the upper left lug and
goes out the upper right lug to make the meter run in the forward direction
(top-to-bottom; left-to-right). (got all that?)

The Brand Electronics meter is a good alternative to all this mess. I'm not
sure they have produced a compliance letter yet--Maybe someone on the list
knows???

Bill.


-----Original Message-----
From: David Henry [mailto:david at harmonyfarm.com]
Sent: Wednesday, March 12, 2003 10:58 AM
To: RE-wrenches at topica.com
Subject: Grid-Tied SW output meter [RE-wrenches]


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

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