Meters vs. Displays - Was: Batteryless inverter recommendation [RE-wrenches]

Tue Mar 4 13:28:25 PST 2008

Hi all
I have heard the cyclometers (thoes that display the
readout in numbers)   do not reverse as well as clock
type meters.  Also the cyclometers do not last as
long, only what I have heard.
Darryl

--- Joel Davidson <joel.davidson at sbcglobal.net> wrote:

> 
> Hello Matt,
> 
> I don't know what you mean by cyclometer style.
> 
> The GE meter is model number 1-70-S 2.
> Cat No 721X070088
> 91 530 279
> Parker Metering Specialists
> Lodi, CA
> Tested 6-07
> 
> Why is it unbelievable that the inverter display
> matches the generation 
> meter and PV Watts being so close?
> 
> PVWATTS uses algorithms PV engineers have been using
> for decades. If you put 
> in the right derating, azimuth, and tilt, you get
> pretty accurate monthly 
> and annual results. Here are the actual meter
> readings:
> Date, SunnyBoy, GE
> 7/23/07, 48.4, -
> 8/21/07, 270.7, 80
> 9/20/07, 496.8, 304
> 10/22/07, 698.2, 504
> 11/20/07, 820.6, 626
> 12/21/07, 949.1, 755
> 1/23/08, 1095, 898
> 2/22/08, 1237, 1040
> 
> Best regards,
> Joel Davidson
> 
> ----- Original Message ----- 
> From: "Matt Lafferty"
> To: <RE-wrenches at topica.com>
> Sent: Friday, February 29, 2008 7:45 PM
> Subject: RE: Meters vs. Displays - Was: Batteryless
> inverter recommendation 
> [RE-wrenches]
> 
> 
> >
> > Wrenches,
> >
> > Great thread. There have been quite a few really
> good threads lately. Love
> > to see the participation and sharing of knowledge.
> I'll keep my post 
> > limited
> > to the topic of "inverter display" data vs.
> "generation meter" data.
> >
> > The short answer to Jeff C's question about "any
> new info since May
> > '06?".... Yes. I've learned a &@!* load about
> different metering
> > methodologies and, perhaps more important than
> anything... Just how screwy
> > it is that, in this day and age, there are still
> huge gaping holes in the
> > standards for solid-state meters. Yes, this
> includes "Utility Revenue 
> > Grade"
> > models. I'll leave the muddy details out of this
> conversation. There is
> > ongoing work on that front by utility and related
> folks. (This affects
> > waaaaaay more than RE. In fact, RE is not even a
> flea on the back of this
> > issue...)
> >
> > There is also an in-progress development of
> testing requirements for
> > inverter integrated +/- 5% Class meters. For the
> foreseeable future, I
> > recommend installing at least a meter socket
> capable of accepting a
> > "standard" socket-type meter in the output circuit
> of all grid-connected 
> > PV
> > systems. Whether or not a generation meter is
> required by the utility or
> > incentive program. Whether or not you actually
> install a meter. At least 
> > put
> > the meter socket in there. It's cheap. I care less
> and less about whether 
> > or
> > not people take my advice with each passing day,
> so... Take that advice or
> > leave it.
> >
> > Another thing I have learned is how many brand new
> meters flunk utility
> > meter shop testing and are returned to the
> manufacturer for replacement
> > instead of being deployed. And those are
> self-certified and calibrated by
> > the mfrs. Some utilities physically test every
> single meter and some only
> > test sample quanitities. If the sample fails, then
> the batch fails. Along
> > the same line is something else I've learned,
> which explains a lot of
> > "unanswered questions"... The meters you get from
> Austin or Hialeah or 
> > other
> > such supplier, may or may not be fully tested and
> calibrated to the same
> > accuracy standard. In a nutshell, this means that
> apparently identical
> > meters installed in paralell on the same circuit,
> may or may not record 
> > the
> > same kWH readings over time. The differences might
> or might not be
> > significant, which in and of itself is subject to
> ones definition of
> > significant. The important thing to insist on is a
> certificate stating 
> > what
> > standard the meter you get is tested to. For
> "standard" socket type 
> > meters,
> > you're looking for ANSI C12.20 and an accuracy
> class.
> >
> > And, oh by the way, if you are installing one of
> the 3rd Party monitoring
> > systems that has an independent meter and they
> "calibrate" the meter data
> > feed to match the inverter display... Now you
> really don't know what the
> > truth is... But hey, this is solar after all, so
> maybe some don't care to
> > know the truth. Or maybe it doesn't matter in the
> big picture that I can't
> > see because, well, I care too much about the
> truth. Speaking of truth, I
> > don't think I've seen any module mfr reps on the
> list in like forever... 
> > But
> > back to metering.
> >
> > Joel D's SB2100 had approximately a 0.57%
> difference in kWH between the
> > inverter and the generation meter. (740.2 vs. 736
> respectively.) This is
> > over a 5 month period. Assuming Joel's generation
> meter is fully certified
> > and calibrated, this is a reasonable discrepancy
> in my opinion.  Nightime
> > and standby losses being accounted for on the
> generation meter but not on
> > the inverter display could account for the entire
> difference. In a 
> > nutshell,
> > they may not actually be measuring exactly the
> same things.... Either way,
> > at least for that 5-month period, at Joel's place,
> the SB2100 kWH display
> > was nearly identical to his GE I70. (Joel, do you
> happen to have the
> > "cyclometer" style? According to the Maryland
> Public Service Commission, 
> > the
> > cyclometer style I70 is not recommended for some
> unstated reason... Maybe
> > they found out that is is calibrated to SMA SB2100
> inverters!  LOL) Joel, 
> > I
> > hope you feel special. Nobody else's inverter
> displays match a 
> > socket-based
> > meter that closely over a 5-month period... I
> don't know which part of the
> > story I find more unbelievable... The part about
> the inverter display
> > matching the generation meter or the part about PV
> Watts being so close!
> > LOL
> >
> > Brad B & Ian W report "wildly" different and
> greater inverter display
> > readings than the utility generation meters.  Both
> of these inverters are
> > reported to be SMA SB700's. (120 VAC inverters
> with three output power 
> > level
> > ratings... 460, 600 & 700 Watts).  I suspect a
> couple of things here.
> >
> > Brad & Ian: Are you comparing readings for the
> same time periods? You 
> > didn't
> > happen to turn the system on before the utility
> got there with a 
> > generation
> 
=== message truncated ===

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