cyclometers [RE-wrenches]

[RE wrenches]

OK, just to clarify ('cause I am going to try this on two jobs I have going)

I have a typical single SW in grid tie with some actively used loads split
off onto a sub panel.  My goal is to measure "RE produced" for that site
(and if I can avoid counting the SW's battery float charge from the grid
inefficiency so much the better as, IMHO, this is not a reflection of RE
produced but rather a reflection of SW and battery back up inefficiencies.
The sooner the FX is cleared for grid tie the better!)

So - I can use a ratcheting Kwh meter , with the SW utility leg (AC in)
going through it to the main panel and the SW AC out going through it on the
other leg to the sub panel.

This way the meter picks up power sent to the sub panel and to the grid.  If
sub panel loads exceed RE capacity and the power comes from the grid they
cancel each other out and the meter doesn't move (or moves a little
proportionate to how much help the grid is giving the RE).

So far so good.  Page 88 of the SW manual diagrams this and shows the use of
2 meters for "production".  It makes sense to use a single meter if current
flow in opposite direction on each phase does cancel out or reduce
proportionately.

Have I missed something?

Sincerely,

Geoff Greenfield
NABCEP Certified Solar PV Installer TM
GLREA Certified Photovoltaic Systems Integrator/Installer License Number
0211-01

THIRD SUN SOLAR AND WIND POWER Ltd.
340 West State Street, Unit 25
Athens, OH 45701

Phone (740) 597-3111
Fax   (740) 597-1548

www.third-sun.com


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------------------------------

Date: Thu, 11 Dec 2003 21:49:19 -0800
From: "Doug Pratt" <dmpratt at sbcglobal.net>
Subject: RE: ratcheting cyclometers [RE-wrenches]



-----Original Message-----
From: Kelly Keilwitz [mailto:kelly at whidbeysunwind.com]

<snip>
But, is it possible to distinguish between grid feed and PV feed to the
subpanel? <snip>


Simple. Using a standard 240v utility meter, wire the 120v leg from the
SW output to the subpanel so that power passing to the subpanel spins
the meter forward. Wire the other 120v leg so that power passing from
the main panel to the SW input spins the meter backwards.

If the SW is simply passing utility power straight thru to the subpanel,
you'll have no meter action. The two currents cancel each other out. If
the SW is pushing solar power to the subpanel, the meter spins forward.
If the SW is pushing solar power to the subpanel *and* the utility, the
meter spins forward faster.

This ought to still work just fine with a ratcheted meter so that night
time battery charging isn't deducted.

*Caution*, I must admit I haven't DONE this, but I can't see any problem
with it. We run meters forward and backward like this all the time. If
I'm missing something obvious, I'm sure we'll all hear about it. :-)

Cheers,
Doug Pratt

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