kwh meter workaround [RE-wrenches]

Robert Nuese r.nuese at comcast.net
Wed Feb 4 21:38:20 PST 2004


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Hello Wrenches, Hello Kirk

Why 3 meters?
I can see that 3 will give a bit more info, but for most applications 
won't 2 be good enough, as well as cheaper and easier to fit in the 
equipment room?
In most cases I think it will be preferable if your meters A & B are 
replaced with a single meter that is not detented, and which works 
forwards and backwards with good accuracy. It would be wired to give a 
positive reading when the system is selling to the grid, and a negative 
reading when grid power is being used to supply the dedicated subpanel. 
Then it will automatically make the subtraction of the energy metered 
by your meter A, which means a simpler calculation for the user. The 
only drawback in using 2 meters that I can see is that it would be 
impossible to determine how much power went to the dedicated panel, and 
how much to the grid, but I think that in 90+% of the jobs I do, the 
customer will not care much about that info, and will not want to pay 
for yet another meter to get it.
So, why not 2?

And Hello to Geoff

Regarding 'option B', the 5 jaw meter:
I've learned this much:
A reconditioned GE KV 12s 5 jaw meter is available from Austin 
International for $100.
(I didn't find out about the cost of the base!)
It is non-detented and, according to Austin Int., works with good 
accuracy forwards and backwards.
For those of us in California, it's on the CEC approved equipment list.
I intend to try this method on at least one of the systems that I'm 
currently installing.

Regarding 'option C',
I'm pretty sure that the metering could also be done with a combination 
of current sensing transformer meters from Integrated Metering Systems 
(IMS) in Florida. So far as I can tell, a single inverter, 120v 
photovoltaic system would require 2 meters with 3 counters, would not 
automatically add/subtract the inputs and outputs to get total output, 
and would cost about $400, so I think that particular route is pretty 
well ruled out.

Finally, in the case of double inverter, 240v systems, I think the 
simplest solution so far is to use (2) Form 2S, 240v meters. One on the 
wires to the dedicated panel, and one on the wires to/from the grid. In 
this case there seems to be no advantage to using the 5-jaw meter, I 
gather you'd still have to use two of them, and would still need to do 
an addition to get total output.
I installed such a metering system yesterday, but still don't know with 
certainty that it works, because It's on a new house, and the grid 
isn't connected yet. Wish me luck

And Good Luck to all of you, with this and all your other vexing 
problems,
Robert Nuese
707-431-1129

On 2/2/04 Kirk Herander, VSE wrote
>
> One 2S meter will not work. Two 2S meters will not work either. You 
> need 3
> 2S meters. Meters A and B are detented and wired in series wilh the AC1
> input, they are wired such that meter A measures utility power only, B
> measures solar ac sent back to the grid only. Meter C is non-detent 
> and is
> wired between inverter output and critical loads. (Meter C - meter A) +
> meter B = total solar AC generated.
>
> This should work fine, if the 5 jaw, form 12S meter won't.
>
> Kirk
> Vermont Solar Engineering
> North American Board of Certified Energy Practitioners Certified Solar 
> PV
> InstallerT
> Xantrex Certified Dealer Charter Member
> Kirk Herander
> PO Box 697
> Burlington, VT. 05402
> www.vermontsolar.com
> www.backeastsolar.com
> 800.286.1252 - 802.863.1202
> fax 802.863.7908
>

On 2/2/04, Geoff Greenfield wrote

Damn-

Now I am completely confused!  And I am wrapping up the AC portion of 
this
install TOMORROW! Arrrrgggg...
My situation is similar to Doug's:  SW in grid tie with subpanel too.
I have a non-ratheting "form 2-s" meter (rebuilt, cheap, from AEE).  I 
was
planning on wiring it as per the original instruction, 120 to subpanel 
on
one leg, 120 from inverter to main panel on the other leg - assuming the
production would be measured in power to sub panel, power to backfeed 
the
main, and any grid supported or charging losses subtracted or cancelled 
out
against output (this is a non-ratcheting)...
Now, assuming this won't work  I need to change my plans fast!

Option A: install the unit as simple 120 Volt Kwh meter on AC output to 
main
only.  (flaw - we don't measure/record the power sent to the sub panel) 
-
Workaround - a second Kwh meter for this sub panel only- and "addition" 
by
the customer.
Option B - go with the unknown 5 tab approach and buy a new meter
Option c:?

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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