Grid-Tied SW output meter [RE-wrenches]

[Bill Brooks]

Matt and David,

Most meters are bi-directional as long as the register does not go below
00000. Some meters have detents so they only go in one direction, but these
are special order meters and are only used by very paranoid utilities. Don't
ever go below 00000 however because very few meters know how to read that
properly. If you have a meter that you think may go negative, start it out
with 01000 or 10000 kWh on the meter so it won't go below zero.

Bill.


-----Original Message-----
From: Matt Lafferty [mailto:pvpro at attbi.com]
Sent: Wednesday, March 12, 2003 11:41 AM
To: RE-wrenches at topica.com
Subject: SPAM: RE: Grid-Tied SW output meter [RE-wrenches]


Wrenches:

David asks:

>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?

Answer:

You're on the right track, David.  Don't forget the Revenue or Net
Meter....If you're connected on the Customer Side of the Revenue Meter.
As long as that is changed out to a Bi-Directional Meter, as usual, we
can drop that one for this conversation.

The CRUCIAL thing is to have a Bi-Directional kWH meter on the AC IN
side.  (You do plan to "export" at least some of the time, don't you?)
A single direction meter on the AC OUT is suitable.  (Don't get caught
firing up the Honda!)

The Total System Output is technically calculated as follows:

AC IN Meter Difference (this month's reading minus last month's) minus
AC OUT Meter Difference (this month's reading minus last month's).

The Utilities bill on "Difference" between readings, not on the meter
reading itself.  I know....we all know this, but it's just good to
remember.

This oughta be a fun time in the Grid-Tied Battery Based PV Systems
World while we wait for the Utilities to "catch-up"!  I would warn your
customers that they will most likely encounter problems, at least
initially, with Utility Billing / Meter Readers......Sigh!  Been there!
More than a few times....

Best to all,

Matt Lafferty
Still the pvpro....just moving e-mails over to
mlafferty at universalenergies.com .... make a note of it if you care.

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