kwh meter workaround [RE-wrenches]

[Kirk Herander, VSE]

Robert,

I do like to have as much info as possible. The three meter option will give
you a gross solar AC into the main panel and gross grid power to the
inverter/sub-panel. If you just use one meter between main & inverter,
you'll only measure the net power to/from the main panel. In addition, the
single meter between main and inverter will sometimes measure less than its
previous reading. Some of my customers get totally confused when they have
to deal with the math of negative numbers. I'd rather have each meter count
forward as in the three meter scenario.

BTW, I just ordered a single 12S, 5 jaw meter for this application. I will
keep the list posted as to how well it works. Hopefully the 12S will make
the multiple-meter solution irrelevant. If anyone is thinking of doing the
same, a standard 4 jaw meter socket can be converted to to 5 jaw with the
proper adapter kit.

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

----- Original Message -----
From: "Robert Nuese" <r.nuese at comcast.net>
To: <RE-wrenches at topica.com>
Sent: Thursday, February 05, 2004 12:38 AM
Subject: Re: kwh meter workaround [RE-wrenches]


> 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
>

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