KWH meter discrepancy [RE-wrenches]

[Bill Brooks]

Jeff, Bob, and All,

Bob and I have briefly discussed this in the past. They have seen
discrepencies, and I believe they were due to improper programming or damage
in shipment. The idea that a utility meter is inaccurate at low power just
can't be true. A residence lives at 200-800 watts for over 12 hours a day
considering night and midday. They are tested at several points including
low power. All utilities retest their meters and occasionally they reject a
meter for being out of calibration. Net meter meters require testing several
meters to find one that is in calibration in both directions. However, the
specs are so tight (I believe they have to be within 1.5% in both
directions), that it is tough for a meter that has been calibrated only in
the forward direction.

Utility meters calibrated by Austin Intl. should be extremely accurate
unless it was damaged in shipping. The specs are more stringent than
inverter manufacturers. However, I have seen several inverter meters in very
good agreement with well-calibrated utility meters, so not all manufacturers
push the truth.

Bill.


-----Original Message-----
From: Jeff Clearwater [mailto:clrwater at earthlink.net] 
Sent: Friday, May 19, 2006 8:05 PM
To: RE-wrenches at topica.com
Subject: Re: KWH meter discrepancy [RE-wrenches]



Hi Bob and all,

Yes that has been my theory as well - mostly because I trust digital 
internal inverter metering - and because the effect does seem to be 
pronounced on systems that spend alot of time in the lower wattage 
realm (like a Whisper wind Link that's always just over startup 
speeds).

But I must say my trust of the inverter companies internal metering 
here is in question - does seem funny that utility grade meters would 
be that far off.

Either way we really need to solve it as more and more state rebate 
programs (MA, WA) now require a "utility grade" meter and are based 
on performance - and the customers love EZ read meters over something 
complicated or digital or menu driven.

How about a call to Austin and research it with them - maybe they 
have an idea or a higher grade meter or ???

Any other simple approved meters out there?

Thanks!

Jeff





>Jeff and all,
>
>We've seen exactly the same results with most meters we've tested.  
>It's just a thought in the back of my mind and have not proven this, 
>but I suspect residential utility grade meters in general may have a 
>"sweet spot" in accuracy based on the average residential loads.  
>Perhaps they just aren't accurate at the low power levels we see from 
>pv early morning, late afternoon, and cloudy weather?
>
>Best Regards,
>Bob Maynard
>Energy Outfitters
>
>


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